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Solar drying of henna (Lawsonia inermis) using different models of solar flat plate collectors: an experimental investigation in the region of Biskra (Algeria)
Accepted Manuscript Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria) Adnane Labed, Noureddine Moummi, Kamel Aoues, Adel Benchabane PII:
S0959-6526(15)01525-5
DOI:
10.1016/j.jclepro.2015.10.058
Reference:
JCLP 6289
To appear in:
Journal of Cleaner Production
Received Date: 24 July 2014 Revised Date:
14 October 2015
Accepted Date: 14 October 2015
Please cite this article as: Labed A, Moummi N, Aoues K, Benchabane A, Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria), Journal of Cleaner Production (2015), doi: 10.1016/j.jclepro.2015.10.058. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria). Adnane Labed 1, Noureddine Moummi 1, Kamel Aoues 2, Adel Benchabane2 1 Laboratoire de Génie Mécanique (LGM), Université de Biskra B.P. 145 R.P. 07000, Biskra, Algeria
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2 Laboratoire de Génie Energétique et Matériaux (LGEM), Université de Biskra B.P. 145 R.P. 07000, Biskra, Algeria
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e-mails: [email protected] / [email protected]
Submitted to:
Journal of Cleaner Production
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(July 2014)
Author to whom all correspondence should be addressed: E-mails: [email protected] / [email protected] Tel.: +213 (0) 33543148 / +213 (0) 670 439 303 Fax.:+213 (0) 33543148
ACCEPTED MANUSCRIPT ABSTRACT
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In this article, an experimental study is presented in two parts: First, the best performing solar dryer is selected between two models of flat plate solar collectors (FPCs). The second part investigates the drying behavior of henna (Lawsonia alba, syn. Lawsonia inermis Linn.) using the best selected FPC. The aim of this study is to get a clean product in a reduced time by using solar FPCs. Therefore, we first present the results of an experimental investigation on the thermal performances and pressure drops of two models of FPCs for indirect drying applications: i) simple-pass collector with trapezoidal obstacles (model I) and ii) double pass collector with trapezoidal obstacles in the air flow duct (model II). In the second part, we compare different methods of henna drying; we have proceeded to the application of the best indirect dryer (model II) for drying of henna under climatic conditions of Biskra, Algeria. As a result, some conclusions are made on the drying behavior of henna by the study of the influence of: drying process, air flow rate and masse of the product on the drying kinetic of the product for the forced convection hot air drying and their temperature dependence. Keywords
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Solar drying, flat plate collector, thermal efficiency, pressure drop, henna, Lawsonia inermis.
ACCEPTED MANUSCRIPT 1. Introduction Henna is an odoriferous plant very widespread in Algeria because it is used for the tattooing (hand, feet, hair, etc.). However, this plant can also be used for various reasons all the time: treatment, drug, dye, etc.
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The production of henna in the region of Biskra presents two third of the national harvest (more than 1000 tones). Nevertheless, these quantities remain unable to meet national and local needs of this important product in view of our customs and traditions. The largest crop production of henna is in the prefecture of Zribet Eloued (henna Zribya) then Loutaya and a lesser extent in the commune of Seriana. Despite the large consumption of henna in Algeria, however, its production is down since 1998. This withdrawal is due to the lack of development of agricultural, harvesting and drying processes of this plant, as well as the interests of farmers with other products such as wheat and watermelon (Fig. 1).
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Fig.1
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According to the agricultural state services (DSA), more than 1500 ha are cultivated of henna in a regular manner in the national territory. However, the actual area of lands that have not been counted by agricultural state services is much higher than previously reported. Henna gives their best yields during the first 10 years; under intensive cultivation the plants are usually harvested twice a year from the second year onwards, while it has exceeded four times a year in some areas (clan of Ouled Bouhdaidja). In Zribet Eloued, crops of the first year are called “Henna of the bride” (Hennet Laarous), it represents the finest crop and usually devoted to medicinal uses and to get rid from stress and dread's effects.
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All fresh and dry leaves and seeds of the henna demonstrated antibacterial activity. Henna dry leaves demonstrated the best in-vitro antimicrobial activity and in particular against Shigella sonnei… (Habbal et al., 2000; Hassanain, 2010).
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Traditional drying of henna can take two (02) days under a direct sunning with the free air and three (03) days under shadow. Leaves are dried in the shade to retain the green color with two drying periods a year to facilitate postharvest leaf drying. This form of drying has many drawbacks, such as degradation by wind-blown, debris, rain, insect infestation, human and animal interference that will result in contamination of the product. Drying rate will decrease due to intermittent sunshine, interruption and wetting by rain (Mohanraj and Chandrasekar, 2009).
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More than 20% of the production is wasted during traditional harvesting and drying operations due to the lack of development of new agricultural, harvesting and drying processes of this plant. Since the last decades, the energy researches have rapidly been oriented towards a clean, sustainable and renewable-based energy systems, such as wind, geothermal and solar energy technologies , this has been made for many applications, such as drying and heating (Chang and Kim, 2001; Moummi et al., 2004; Battisti and Corrado, 2005). Further, other renewable energy technologies are investigated for space heating, cooling and hot domestic water production (Koroneos and Tsarouhis, 2012; Koroneos and Nanaki, 2012; Labed et al., 2015). These techniques are gaining popularity in sustainable energy management for their economic, environmental health and safety benefits. Solar drying technology offers an alternative that can process the plants, vegetables and fruits in clean, hygienic, and sanitary conditions to national and international standard.
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Many types of solar air heaters and dryers have been developed in the past for the efficient utilization of solar energy (Sami et al., 2011). Among stationary solar heaters, air flat-plate collectors, FPCs, have been widely used for energy management in an increasing number of installations. They are quite attractive for low-temperature solar energy technology which requires air temperatures below 100°C. In fact, solar air FPCs are extensively used over years because they are relatively simple with a minimal use of materials, easy to operate and have low capital costs (Duffie et al., 2013; Kalogirou 2004). Furthermore, it is established that the introduction of different geometries of artificial roughness, in the dynamic air vein of the FPC, increases the transfer rate and favors the creation of turbulences near the absorber plate (Karim and Hawlader, 2006). Many studies on the drying of agricultural products have also shown that the use of the obstacles in the collector duct improves the performance of the drying unit (Ahmed‐Zaid et al. 1999; Abene et al,. 2004). They reported that, for the same rack, the increase in air flow permits a relative reduction of 13.8% of drying time. Nevertheless, another experimental study of an indirect dryer in forced-mode has been conducted for drying fruit and vegetable in Iraq (Al-Juamily et al., 2007). The authors concluded that, the air temperature is the most effective factor on drying rate. The effect of the air speed variation inside the drying cabinet is small and can be neglected.
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The effects of bed height and initial moisture concentration of the coal on the drying kinetic were studied (Çalban, 2006). It has been found that, time taken to reach the equilibrium moisture content, is fixed when decreasing bed height, while the critical moisture content increased.
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Furthermore, new drying techniques have been studied to reduce the drying time for convective drying processes by using airborne ultrasound (Bantle and Eilevik, 2014). The drying kinetics of the convective drying of clipfish with and without the assistance of ultrasound are presented. It has been found that the energy consumption for ultrasonic drying increases multiple times despite its faster dehydration. In order to be efficient, ultrasonic intensities in the convective drying of clipfish should not exceed 2 W/kg, while resulting in a drying time reduction of clipfish of at least 50%.
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In our laboratories, there have been many contributions on the enhancement and testing of thermal performances of solar FPCs designed for drying, heating and cooling applications (Moummi et al., 2010; Aoues et al., 2011; Labed et al., 2009, 2011, 2012(a, b and c), 2013, 2014). In all these studies, the authors use different forms of obstacles mounted under the absorber plate on the air channel duct.
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Most researches on henna are oriented towards its chemical composition, its anti-bacterial, antiinflammatory, antipyretic and analgesic effects, but they neglect the process of obtaining a clean product with a good quality and at a reduced time. In the present paper, we have focused on the effects of the use of solar dryers to improve drying time. Thus, we have conducted a comparative study between two types of solar air FPCs with artificial roughness in the air channel duct; model I): is a simple-pass solar FPC having trapezoidal obstacles, and model II): is a double-pass FPC having trapezoidal obstacles and the end of the flow channel is brought together by a metal transition, which turns the airflow 180 degrees over the back plate, and the gap under the back plate is reserved to the crop drying. Consequently, the comparison of these two models intends to determine the best performing model for the drying uses. As application, we have used these two FPC models in the drying of henna and compare them to the traditional open sun drying of this product. We have also used the best FPC (model II) to dry the henna with different air flow rates.
ACCEPTED MANUSCRIPT 2. Experimental 2.1 Experimental setup
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Both solar air FPCs are tested in the University of Biskra under similar environmental conditions in the spring of 2010. The used collectors are designed, constructed and tested in the same context in a stand facing south at an inclination angle equal to the local latitude. Biskra is located in the East of Algeria with latitude of 34°48' N, longitude of 5°44’E and Altitude of 85 m.
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The two collectors have the same component sizes: thickness of the single cover glass (5 mm), height of the air gap between the cover and the absorber plat (25 mm), height of the air duct (25 mm), dimensions of the absorber (1.96 m×0.9 m with the thickness of 0.4 mm) and thickness of the rear insulation (40 mm). The materials used in the fabrication of all FPCs components are also the same. The absorbers are made of galvanized steel with non selective black coating. The heated air flows between the inner surface of the absorber plate and the back plate with, or without, obstacles. The rear insulation is made of polystyrene sheet (30 mm of thickness), which is sandwiched between two plywood sheets of 5 mm each.
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The first experimental device (model I) is a FPC connected to a drying chamber by a flexible duct (Fig. 2(a)). The absorber plate is placed behind the transparent glass cover, with a layer of static air separating it from the cover of the collector. The drying chamber is a hard plastic drum of 8 mm thickness, 50 cm in diameter and 80 cm height, positioned meadows of the collectors and supported by a metal frame.
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The second system (model II) is a single frame dryer, where the end of the air flow channel of the FPC is brought together by a metal transition, which turns the air flow 180 degrees. The materials used in the fabrication of these FPC components are the same as in the first FPC employed in the previous Section. An exception is that the height of the gap under the back plate is different (H = 12 cm). It is equipped with wire mesh trays for the crop depositing (Fig. 2(b)). This is made so as to conduct tests of the FPC in the double-pass mode in the previous part of this study and to dispose the drying product in the second part of the manuscript (Labed et al., 2012(a)).
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Figs. 2 and 3
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Both FPC models are equipped with trapezoidal fin obstacles in the dynamic air vein. The fin obstacles are oriented parallel to the fluid flow and are soldered to the upper side of the back plate (Fig. 3). In both studied collectors, the air outlet and inlet cross-sections are equipped by divergent channel duct. The test facility permits to vary the mass flow rate of the air. In summary, the above experimental setup is instrumented for the measurement of the solar radiation, wind velocity, pressure drop, temperature of the atmosphere air, inlet and outlet air temperatures, surface temperature of absorber plate and the air mass flow rate. The test data of FPCs are measured at an interval of 10 min. The parameters measured in the experiments are: collector inlet temperature, collector outlet temperature, ambient temperature, air velocity and pressure in the duct, solar radiation intensity, pressure drop, air flow rate, wind velocity, relative humidity and mass of drying product. To carry out these experiments, K-type thermocouples with an accuracy 0.1°C, Kimo type anemometer with hot wire (VT300) with an accuracy ±3% of reading and ±0.1 m/s for velocity, pressure transducer (Kimo CP301) with an accuracy ±1 Pa and 0.5% of reading, Kipp and Zonen pyranometer CM 11 with 1% accuracy, Q.C.58 hygrometer with error ranges of 3% and laboratory balance with ±1 g accuracy are used.
ACCEPTED MANUSCRIPT 2.2 Experimental Analysis Before the presentation of these two configurations in the previous Section, we present the expressions used for the calculation of global heat loss, useful energy, and efficiency of the solar collectors: The useful energy gain is given by Duffie et al. (2013) as below : Qu = m& c P (T fo − T fi )
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η = QU ( I G AC ) Solving Eqs. (1) and (2), the efficiency can be written as:
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η = m& cP (T fo − T fi ) ( I G . AC )
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A measure of collector performance is the thermal efficiency, defined as the ratio of useful heat gain over any time period to the incident solar radiation over the same period; thus, we can define efficiency as,
(3)
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The drying characteristics of the henna such as moisture content and drying rate are determined by using Eqs. (4) and (5), respectively. The moisture content, Mdb on dry basis is calculated by using Eq. (4). M db = 100% × (M t − M d ) M d
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The drying rate, DR, should be proportional to the difference in moisture content between material to be dried and the equilibrium moisture content (Ekechukwu, 1999). The concept of thin layer drying is assumed for the experiments as reported by Eq. (5). (5)
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DR = dM dt = − k ( M t − M e )
Based on the analysis of the errors in the experimental measurements through the used instruments, the uncertainties in experimental measurement and results are often used to refer to possible values that may include errors. According to (Esen, 2008), the result R of an experiment is assumed to be calculated from a set of measurements. It is given as a function of the independent variables X1, X2,..., Xn (6)
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R = R ( X 1 , X 2 , X 3 ,..., X n )
Where in, X1 , X2 , .. Xn are measured variables.
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Let δR be the uncertainty in the result and δX 1 , δX 2 ,…, δX n be the uncertainties in the independent variables. If the uncertainties in the independent variables are all given with same odds, then uncertainty in the result having these odds is calculated by Duffie et al. (2013). 2 2 2 ∂R ∂R ∂R δR = δX 1 + δX 2 + .... + δX n ∂X 1 ∂X 2 ∂X n
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The independent parameters measured in the experiments reported here are: collector inlet temperature Tfi, collector outlet temperature Tfo, ambient temperature Ta, mass flow rate and solar irradiation. If Ac and Cp are considered constants in the Eq. (4), it can be written:
η = f (T fo , T fi , I G , m& )
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ACCEPTED MANUSCRIPT The total uncertainty equation for collector thermal efficiencyη , moisture content Mdb, and drying rate DR can be written as: 2 2 2 2 ∂η ∂η ∂η ∂η δη = δm& + δT fo + δT fi + δI G ∂T fi ∂I G ∂m& ∂T fo 1
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2 2 2 ∂DR ∂DR ∂DR δDR = δM t + δM d + δt ∂M t ∂M d ∂t
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2 2 ∂M ∂M δM db = db δM t + db δM d ∂M t ∂M d
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Calculations show that the total uncertainty in calculating efficiency, η , moisture content Mdb and drying rate DR are almost in the order of 1, 2.8 and 3%, respectively.
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3. Results and Discussions 3.1 FPCs Performances
Fig. 4
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The basic method of measuring collector performance is to expose operating collector to solar radiation and measure. The fluid inlet and outlet temperature and the fluid flow rate addition, radiation on the collector, ambient temperature, and wind speed are also recorded. ASHRAE standard requires that, for the collector efficiency test, the solar insulation must be above 630 W/m2 (Karim and Hawlader, 2006). The variation of the efficiency (η) is studied as a function of variation in the mass flow rate (Fig. 4), and the improvements of thermal performances are important in relation to the FPC. It can be seen that the collector efficiency increases considerably with increasing air mass flow rate. This means, at higher air flow rate, the overall loss is lower. Furthermore, it is found that model II has the highest efficiency. The maximum efficiencies for these two FPCs (model I and model II) are determined as 76.2% and 79.9%, respectively at m& = 0.044 kg / s .
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A series of experiments are conducted to establish the variation of the pressure drop as a function of the air flow rate for both models of solar FPCs (Fig.5). The air in the double pass FPC (model II) has a long trajectory. Substantial heat transfer enhancement is obtained. There is, of course, an associated increase in pressure drop due to increased friction with the inferior air flow channel duct. It attaints the values 8, 20 and 31.5 Pa for air flow rates of 0.011, 0.022 and 0.028 kg/s, respectively. The simple pass FPC (model I) presents the lower pressure drops. They attain the value 7, 17.5 and 25 Pa for air flow rates of 0.011, 0.022 and 0.028 kg/s, respectively. Fig. 5 3.2 Effect of the FPC performances on the drying time improvement Field tests of the dryer for henna drying also are carried out in the spring 2010; the typical results are shown in (Figs. 6-10). In all experiments, the initial moisture content (d.b.) of the product is 4.6 kgwater/kg, and the final moisture content must reach to 0.05 kgwater/kg (d.b.).
ACCEPTED MANUSCRIPT A typical experimental evolution of the henna moisture content (d.b.) is presented as a function of the drying time, in the cases of models I and II with m& =0.024 kg/s compared to the drying in the open air under direct sun rays (Fig. 6). Drying is started at 09:00 with an initial moisture content of 4.6 kgwater/kg (d.b.) and continued until 18:00 (9h 00min of drying time/day). The final moisture content of the samples is obtained after 7h 45min and 4h 15min in the cases of model I and II, respectively, and it took 15h 00min under direct sun.
3.3 Effect of the air flow rate on the drying time
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Fig.6
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To show the influence of the air flow rate on the improvement of the drying time, this study is conducted under different outdoor conditions by using of the best performing FPC (model II). Since the drying time with the double pass FPC (model II) can take less than seven hours, the drying is started at 09:00 and continued until 16:00 (7h 00min of drying time). Environmental conditions are presented in the form of graphs that describe the relative humidity and the global hourly insulation of the characteristic day, which we have determined by using the collector inclination angle value (34.8◦). The recorded values of these two important parameters can be seen in (Fig. 7). The variations of the temperatures of air at the solar FPC outlet and in the drying chamber and the ambient temperature for a typical day during the drying of henna are shown in (Fig. 8).
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Figs. 7 and 8 The drying kinetic of the product can be represented on the quantity of moisture present in the sample, its loss of mass or expressed on drying rate. To study the influence of the air flow rate on the drying time, we have used model II with three air flow rate 0.036, 0.024 and 0.012 kg/s. Afterwards, we have illustrated how the loss of mass variation is affected during the drying time. Drying is started with initial moisture content of 0.82 kgwater/kg (w.b.) and continued, until a final moisture content of the samples ranged from 0.00 to 0.083 kgwater/kg (w.b.) attained after 7h 00min, which correspond to a loss of mass ranged from 80.33% to 82%.
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According to the literature, the drying air temperature is much more influential than the air flow velocity (Al-Juamily et al., 2007). We note that, the air temperature in the drying chamber is closely dependent on the air velocity inside the dryer. The air temperature decreases with the increase in air velocity, these two parameters affect the loss of the moisture content; increasing one of these two parameters improves the drying time. However, the increase in one of these two parameters leads to decreasing the second. It is significant to have the right drying temperature and the optimum air flow. In this case, we can observe that it is more interesting to operate with an air flow rate of about 0.024 kg/s and an average drying temperature around 45°C. Time taken to reach particular moisture content corresponds to a value of loss of mass of 82% is shorter (4h 15min) with the second air flow rate (0.024 kg/s), but is equal to 7h 00min and 5h 15min with the first and the third flow rate (0.036 and 0.012 kg/s), which corresponds to a relative reductions in drying time of 39.29% and 25%, respectively (Fig. 9). Fig.9 3.4 Effect of the product quantity on the drying time The influence of the henna quantity existing in the drying chamber on its moisture content (d.b.) evolution is presented as a function of the drying time (Fig. 10). There is a relationship
ACCEPTED MANUSCRIPT between the initial product weight and its moisture content during drying. After 6 h 45min of drying of 1 kg of henna, the resulting moisture content in product is equal to 0.05 [kgwater/kg] (d.b.), while it takes 5h 45min and 4h 30min to get a similar value of moisture content when the weight of the henna is 0.5 and 0.2 kg, corresponding to a relative reduction of 15 and 33%, respectively.
4. Conclusion and future perspectives
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Fig. 10
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In this study, we have first conducted a comparative study between two types of solar air FPCs - i) simple-pass collector with trapezoidal obstacles (model I) and ii) double-pass collector with trapezoidal obstacles in the air flow duct (model II)- in order to determine the best performing model for the drying uses. Thereafter, the best FPC is experimentally tested for the drying of the henna in Biskra, Algeria.
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The first study has allowed us to show that, at different air mass flow, the highest efficiencies are obtained from the double pass solar air FPC with trapezoidal obstacles. In addition, the use of the best performing FPC (model II) reduces 20% of henna drying time in comparison with model I and 75% comparing to the traditional drying. The effect of the air mass flow rate is also studied to find the optimum drying air rate. It is clear that drying time with 0.024 kg/s is shorter than those with 0.012 and 0.036 kg/s. However, the influence of some parameters specific to the product, such as the quantity of the product on the drying time is investigated in outdoor conditions. It was found that, the increase in the initial product quantity increases the total drying time.
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It could be concluded that, the use of solar dryers allows us to avoid the mixture of henna leaves with the ground during drying and also prevents the penetration of insects and scorpions in the dried samples.
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Acknowledgment
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Finally, we hope that this contribution can give a look at the causes of the decline in the production of this important plant and how to improve the quality of the product through a fast and clean drying. It is expected that this study will be followed by a second one which will attempt to compare the qualities, and the chemical compositions of the samples derived from different drying methods cited in this paper.
The authors acknowledge the assistance of Drs. Ahmed-Chouaki Houadjli and Lamri Segni (English Department, Univ. of Biskra) for their contributions in the improvement of the quality of this paper. We also acknowledge the direction of agricultural services (DSA) of Biskra.
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ACCEPTED MANUSCRIPT Al-Juamily, K. E., Khalifa, A. J. N., & Yassen, T. A., 2007. Testing of the performance of a fruit and vegetable solar drying system in Iraq. Desalination, 209(1), 163-170. Aoues, K., Moummi, N., Zellouf, M., Benchabane, A., 2011. Thermal performance improvement of solar air flat plate collector: a theoretical analysis and an experimental study in Biskra, Algeria. International Journal of Ambient Energy, 32, 95-102. Bantle, M., Eikevik, T. M., 2014. A study of the energy efficiency of convective drying systems assisted by ultrasound in the production of clipfish. Journal of Cleaner Production, 65, 217-223.
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Battisti, R., Corrado, A., 2005. Environmental assessment of solar thermal collectors with integrated water storage. Journal of Cleaner Production, 13, 1295-1300. Çalban, T., 2006. The effects of bed height and initial moisture concentration on drying lignite in a batch fluidized bed. Energy Sources, Part A, 28, 479-485.
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Chang, I. S., Kim, J. H., 2001. Development of clean technology in wafer drying processes. Journal of Cleaner Production, 9, 227-232. Duffie, J. A., Beckman, W. A., 2013. Solar engineering of thermal processes. John Wiley & Sons.
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Karsli, S., 2007. Performance analysis of new-design solar air collectors for drying applications. Renewable Energy, 32, 1645–1660.
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Labed, A., Rouag, A., Benchabane, A., Moummi, N., & Zerouali, M., 2015. Applicability of solar desiccant cooling systems in Algerian Sahara: Experimental investigation of flat plate collectors. Journal of Applied Engineering Science & Technology, 1(2), 61-69.
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Mohanraj, M., Chandrasekar, P., 2009. Performance of a forced convection solar drier integrated with gravel as heat storage material for chili drying. Journal of Engineering Science and Technology, 4, 305-314. Moummi, N., Moummi, A., Aoues, K., Mahboub, C., Youcef Ali, S., 2010. Systematic forecasts of solar collector's performance in various sites of different climates in Algeria. International journal of sustainable energy, 29, 142-150. Moummi, N., Youcef-Ali, S., Moummi, A., Desmons, J. Y., 2004. Energy analysis of a solar air collector with rows of fins. Renewable Energy, 29(13), 2053-2064.
NOMENCLATURE
Lc lc Mdb m& QU RH Ta T fi
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Collector surface area (m2) Specific heat of air at constant pressure (kJ/kg K) Dry basis. Drying rate (kg kg-1h-1) Collector heat removal factor depending air inlet temperature (dimensionless) Global irradiance incident on solar air heater collector (Wm-2)
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AC cp d.b. DR FR IG
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Sami, S., Rahimi, A., Etesami, N., 2011. Dynamic modeling and a parametric study of an indirect solar cabinet dryer. Drying Technology, 29, 825-835.
Length of the flat plate collector (m)
Width of the flat plate collector (m) Moisture content (d.b.) (kg kg-1) Air mass flow rate (kg s-1) Useful energy gain of the collector (W) Relative humidity of ambient air (%) Ambient temperature (°C)
Inlet air temperature of the collector (°C)
T fo
Outlet fluid temperature of the collector (°C)
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Collector overall heat loss coefficient (W/m2 °C)
ACCEPTED MANUSCRIPT wet basis Loss of mass of the drying product (%) Pressure loss [Pa]
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Greek Letters Absorptance (dimensionless) α abs Collector tilt (degrees) (dimensionless) β τv Transparent cover transmittance (dimensionless) Thermal efficiency (dimensionless) η
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w.b. ∆M ∆P
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Journal of Cleaner Production Date: 14/10/2015 Revised manuscript entitled “Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria)” Corresponding author: Co-authors:
Dr. Adnane Labed Pr. Noureddine Moummi
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Dr. Kamel Aoues Pr. Adel Benchabane
Figures captions: Fig. 1: National production of henna during the last 20 years.
Fig. 3: Schematic view of fin obstacles in dynamic air vein.
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Fig. 2: Experimental devices for henna drying; a) model I, b) model II.
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Fig. 4. Efficiencies versus air flow rate for different both FPC models.
Fig. 5: Pressure drop (Pa) vs. the air mass flow rate (Kg/s) for different studied FPCs. Fig. 6: Evolution of the henna moisture content (d.b.) vs. the drying time for different dryer models ( m& =0.024Kg/s), compared to the traditional drying. Fig.7: Recorded values of the relative humidity and solar radiation during the testing days (17/04/2011, 18/04/2011 and 25/04/2011).
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Fig. 8: Recorded values of the FPC, drying chamber and ambient temperatures during drying the testing days. Fig. 9: Evolution of the henna loss of mass vs. drying time, for different air flow rates: 0.012, 0.024 and 0.036Kg/s respectively, in the case of model II.
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Fig. 10: Evolution of the henna moisture content (d.b.) vs. drying time, for different product weights: 0.2, 0.5 and 1 Kg respectively, in the case of model II ( m& =0.024 kg/s).
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Fig. 1. National production of henna during the last 20 years.
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Air exhaust
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Drying chamber Fan
Wire mesh trays for crop drying
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Cover Absorber Fin obstacles
200g
Air
Insulator
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Plywood sheets
(a)
Fig. 2. Experimental devices for henna drying; a) model I, b) model II.
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Back plate
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6 cm
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2,5 cm
6 cm
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Fig. 3. Schematic view of fin obstacles in dynamic air vein.
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Fig. 4. Efficiencies versus air flow rate for different both FPC models.
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Fig. 5. Pressure drop (Pa) vs. the air mass flow rate (Kg/s) for different studied FPCs..
Fig. 6. Evolution of the henna moisture content (dry basis) vs. the drying time for different dryer models ( m& =0.024Kg/s), compared to the traditional drying.
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Fig. 7. Recorded values of the relative humidity and solar radiation during the testing days (17/04/2011, 18/04/2011 and 25/04/2011)
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Fig. 8. Recorded values of the FPC, drying chamber and ambient temperatures during drying the testing days.
Fig. 9. Evolution of the henna loss of mass vs. drying time, for different air flow rates: 0.012, 0.024 and 0.036Kg/s respectively, in the case of model II.
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Fig. 10. Evolution of the henna moisture content (d.b.) vs. drying time, for different product weights: 0.2, 0.5 and 1 kg respectively, in the case of model II.
S0959-6526(15)01525-5
DOI:
10.1016/j.jclepro.2015.10.058
Reference:
JCLP 6289
To appear in:
Journal of Cleaner Production
Received Date: 24 July 2014 Revised Date:
14 October 2015
Accepted Date: 14 October 2015
Please cite this article as: Labed A, Moummi N, Aoues K, Benchabane A, Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria), Journal of Cleaner Production (2015), doi: 10.1016/j.jclepro.2015.10.058. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria). Adnane Labed 1, Noureddine Moummi 1, Kamel Aoues 2, Adel Benchabane2 1 Laboratoire de Génie Mécanique (LGM), Université de Biskra B.P. 145 R.P. 07000, Biskra, Algeria
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2 Laboratoire de Génie Energétique et Matériaux (LGEM), Université de Biskra B.P. 145 R.P. 07000, Biskra, Algeria
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e-mails: [email protected] / [email protected]
Submitted to:
Journal of Cleaner Production
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(July 2014)
Author to whom all correspondence should be addressed: E-mails: [email protected] / [email protected] Tel.: +213 (0) 33543148 / +213 (0) 670 439 303 Fax.:+213 (0) 33543148
ACCEPTED MANUSCRIPT ABSTRACT
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In this article, an experimental study is presented in two parts: First, the best performing solar dryer is selected between two models of flat plate solar collectors (FPCs). The second part investigates the drying behavior of henna (Lawsonia alba, syn. Lawsonia inermis Linn.) using the best selected FPC. The aim of this study is to get a clean product in a reduced time by using solar FPCs. Therefore, we first present the results of an experimental investigation on the thermal performances and pressure drops of two models of FPCs for indirect drying applications: i) simple-pass collector with trapezoidal obstacles (model I) and ii) double pass collector with trapezoidal obstacles in the air flow duct (model II). In the second part, we compare different methods of henna drying; we have proceeded to the application of the best indirect dryer (model II) for drying of henna under climatic conditions of Biskra, Algeria. As a result, some conclusions are made on the drying behavior of henna by the study of the influence of: drying process, air flow rate and masse of the product on the drying kinetic of the product for the forced convection hot air drying and their temperature dependence. Keywords
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Solar drying, flat plate collector, thermal efficiency, pressure drop, henna, Lawsonia inermis.
ACCEPTED MANUSCRIPT 1. Introduction Henna is an odoriferous plant very widespread in Algeria because it is used for the tattooing (hand, feet, hair, etc.). However, this plant can also be used for various reasons all the time: treatment, drug, dye, etc.
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The production of henna in the region of Biskra presents two third of the national harvest (more than 1000 tones). Nevertheless, these quantities remain unable to meet national and local needs of this important product in view of our customs and traditions. The largest crop production of henna is in the prefecture of Zribet Eloued (henna Zribya) then Loutaya and a lesser extent in the commune of Seriana. Despite the large consumption of henna in Algeria, however, its production is down since 1998. This withdrawal is due to the lack of development of agricultural, harvesting and drying processes of this plant, as well as the interests of farmers with other products such as wheat and watermelon (Fig. 1).
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Fig.1
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According to the agricultural state services (DSA), more than 1500 ha are cultivated of henna in a regular manner in the national territory. However, the actual area of lands that have not been counted by agricultural state services is much higher than previously reported. Henna gives their best yields during the first 10 years; under intensive cultivation the plants are usually harvested twice a year from the second year onwards, while it has exceeded four times a year in some areas (clan of Ouled Bouhdaidja). In Zribet Eloued, crops of the first year are called “Henna of the bride” (Hennet Laarous), it represents the finest crop and usually devoted to medicinal uses and to get rid from stress and dread's effects.
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All fresh and dry leaves and seeds of the henna demonstrated antibacterial activity. Henna dry leaves demonstrated the best in-vitro antimicrobial activity and in particular against Shigella sonnei… (Habbal et al., 2000; Hassanain, 2010).
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Traditional drying of henna can take two (02) days under a direct sunning with the free air and three (03) days under shadow. Leaves are dried in the shade to retain the green color with two drying periods a year to facilitate postharvest leaf drying. This form of drying has many drawbacks, such as degradation by wind-blown, debris, rain, insect infestation, human and animal interference that will result in contamination of the product. Drying rate will decrease due to intermittent sunshine, interruption and wetting by rain (Mohanraj and Chandrasekar, 2009).
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More than 20% of the production is wasted during traditional harvesting and drying operations due to the lack of development of new agricultural, harvesting and drying processes of this plant. Since the last decades, the energy researches have rapidly been oriented towards a clean, sustainable and renewable-based energy systems, such as wind, geothermal and solar energy technologies , this has been made for many applications, such as drying and heating (Chang and Kim, 2001; Moummi et al., 2004; Battisti and Corrado, 2005). Further, other renewable energy technologies are investigated for space heating, cooling and hot domestic water production (Koroneos and Tsarouhis, 2012; Koroneos and Nanaki, 2012; Labed et al., 2015). These techniques are gaining popularity in sustainable energy management for their economic, environmental health and safety benefits. Solar drying technology offers an alternative that can process the plants, vegetables and fruits in clean, hygienic, and sanitary conditions to national and international standard.
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Many types of solar air heaters and dryers have been developed in the past for the efficient utilization of solar energy (Sami et al., 2011). Among stationary solar heaters, air flat-plate collectors, FPCs, have been widely used for energy management in an increasing number of installations. They are quite attractive for low-temperature solar energy technology which requires air temperatures below 100°C. In fact, solar air FPCs are extensively used over years because they are relatively simple with a minimal use of materials, easy to operate and have low capital costs (Duffie et al., 2013; Kalogirou 2004). Furthermore, it is established that the introduction of different geometries of artificial roughness, in the dynamic air vein of the FPC, increases the transfer rate and favors the creation of turbulences near the absorber plate (Karim and Hawlader, 2006). Many studies on the drying of agricultural products have also shown that the use of the obstacles in the collector duct improves the performance of the drying unit (Ahmed‐Zaid et al. 1999; Abene et al,. 2004). They reported that, for the same rack, the increase in air flow permits a relative reduction of 13.8% of drying time. Nevertheless, another experimental study of an indirect dryer in forced-mode has been conducted for drying fruit and vegetable in Iraq (Al-Juamily et al., 2007). The authors concluded that, the air temperature is the most effective factor on drying rate. The effect of the air speed variation inside the drying cabinet is small and can be neglected.
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The effects of bed height and initial moisture concentration of the coal on the drying kinetic were studied (Çalban, 2006). It has been found that, time taken to reach the equilibrium moisture content, is fixed when decreasing bed height, while the critical moisture content increased.
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Furthermore, new drying techniques have been studied to reduce the drying time for convective drying processes by using airborne ultrasound (Bantle and Eilevik, 2014). The drying kinetics of the convective drying of clipfish with and without the assistance of ultrasound are presented. It has been found that the energy consumption for ultrasonic drying increases multiple times despite its faster dehydration. In order to be efficient, ultrasonic intensities in the convective drying of clipfish should not exceed 2 W/kg, while resulting in a drying time reduction of clipfish of at least 50%.
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In our laboratories, there have been many contributions on the enhancement and testing of thermal performances of solar FPCs designed for drying, heating and cooling applications (Moummi et al., 2010; Aoues et al., 2011; Labed et al., 2009, 2011, 2012(a, b and c), 2013, 2014). In all these studies, the authors use different forms of obstacles mounted under the absorber plate on the air channel duct.
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Most researches on henna are oriented towards its chemical composition, its anti-bacterial, antiinflammatory, antipyretic and analgesic effects, but they neglect the process of obtaining a clean product with a good quality and at a reduced time. In the present paper, we have focused on the effects of the use of solar dryers to improve drying time. Thus, we have conducted a comparative study between two types of solar air FPCs with artificial roughness in the air channel duct; model I): is a simple-pass solar FPC having trapezoidal obstacles, and model II): is a double-pass FPC having trapezoidal obstacles and the end of the flow channel is brought together by a metal transition, which turns the airflow 180 degrees over the back plate, and the gap under the back plate is reserved to the crop drying. Consequently, the comparison of these two models intends to determine the best performing model for the drying uses. As application, we have used these two FPC models in the drying of henna and compare them to the traditional open sun drying of this product. We have also used the best FPC (model II) to dry the henna with different air flow rates.
ACCEPTED MANUSCRIPT 2. Experimental 2.1 Experimental setup
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Both solar air FPCs are tested in the University of Biskra under similar environmental conditions in the spring of 2010. The used collectors are designed, constructed and tested in the same context in a stand facing south at an inclination angle equal to the local latitude. Biskra is located in the East of Algeria with latitude of 34°48' N, longitude of 5°44’E and Altitude of 85 m.
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The two collectors have the same component sizes: thickness of the single cover glass (5 mm), height of the air gap between the cover and the absorber plat (25 mm), height of the air duct (25 mm), dimensions of the absorber (1.96 m×0.9 m with the thickness of 0.4 mm) and thickness of the rear insulation (40 mm). The materials used in the fabrication of all FPCs components are also the same. The absorbers are made of galvanized steel with non selective black coating. The heated air flows between the inner surface of the absorber plate and the back plate with, or without, obstacles. The rear insulation is made of polystyrene sheet (30 mm of thickness), which is sandwiched between two plywood sheets of 5 mm each.
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The first experimental device (model I) is a FPC connected to a drying chamber by a flexible duct (Fig. 2(a)). The absorber plate is placed behind the transparent glass cover, with a layer of static air separating it from the cover of the collector. The drying chamber is a hard plastic drum of 8 mm thickness, 50 cm in diameter and 80 cm height, positioned meadows of the collectors and supported by a metal frame.
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The second system (model II) is a single frame dryer, where the end of the air flow channel of the FPC is brought together by a metal transition, which turns the air flow 180 degrees. The materials used in the fabrication of these FPC components are the same as in the first FPC employed in the previous Section. An exception is that the height of the gap under the back plate is different (H = 12 cm). It is equipped with wire mesh trays for the crop depositing (Fig. 2(b)). This is made so as to conduct tests of the FPC in the double-pass mode in the previous part of this study and to dispose the drying product in the second part of the manuscript (Labed et al., 2012(a)).
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Figs. 2 and 3
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Both FPC models are equipped with trapezoidal fin obstacles in the dynamic air vein. The fin obstacles are oriented parallel to the fluid flow and are soldered to the upper side of the back plate (Fig. 3). In both studied collectors, the air outlet and inlet cross-sections are equipped by divergent channel duct. The test facility permits to vary the mass flow rate of the air. In summary, the above experimental setup is instrumented for the measurement of the solar radiation, wind velocity, pressure drop, temperature of the atmosphere air, inlet and outlet air temperatures, surface temperature of absorber plate and the air mass flow rate. The test data of FPCs are measured at an interval of 10 min. The parameters measured in the experiments are: collector inlet temperature, collector outlet temperature, ambient temperature, air velocity and pressure in the duct, solar radiation intensity, pressure drop, air flow rate, wind velocity, relative humidity and mass of drying product. To carry out these experiments, K-type thermocouples with an accuracy 0.1°C, Kimo type anemometer with hot wire (VT300) with an accuracy ±3% of reading and ±0.1 m/s for velocity, pressure transducer (Kimo CP301) with an accuracy ±1 Pa and 0.5% of reading, Kipp and Zonen pyranometer CM 11 with 1% accuracy, Q.C.58 hygrometer with error ranges of 3% and laboratory balance with ±1 g accuracy are used.
ACCEPTED MANUSCRIPT 2.2 Experimental Analysis Before the presentation of these two configurations in the previous Section, we present the expressions used for the calculation of global heat loss, useful energy, and efficiency of the solar collectors: The useful energy gain is given by Duffie et al. (2013) as below : Qu = m& c P (T fo − T fi )
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η = QU ( I G AC ) Solving Eqs. (1) and (2), the efficiency can be written as:
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η = m& cP (T fo − T fi ) ( I G . AC )
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A measure of collector performance is the thermal efficiency, defined as the ratio of useful heat gain over any time period to the incident solar radiation over the same period; thus, we can define efficiency as,
(3)
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The drying characteristics of the henna such as moisture content and drying rate are determined by using Eqs. (4) and (5), respectively. The moisture content, Mdb on dry basis is calculated by using Eq. (4). M db = 100% × (M t − M d ) M d
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The drying rate, DR, should be proportional to the difference in moisture content between material to be dried and the equilibrium moisture content (Ekechukwu, 1999). The concept of thin layer drying is assumed for the experiments as reported by Eq. (5). (5)
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DR = dM dt = − k ( M t − M e )
Based on the analysis of the errors in the experimental measurements through the used instruments, the uncertainties in experimental measurement and results are often used to refer to possible values that may include errors. According to (Esen, 2008), the result R of an experiment is assumed to be calculated from a set of measurements. It is given as a function of the independent variables X1, X2,..., Xn (6)
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R = R ( X 1 , X 2 , X 3 ,..., X n )
Where in, X1 , X2 , .. Xn are measured variables.
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The independent parameters measured in the experiments reported here are: collector inlet temperature Tfi, collector outlet temperature Tfo, ambient temperature Ta, mass flow rate and solar irradiation. If Ac and Cp are considered constants in the Eq. (4), it can be written:
η = f (T fo , T fi , I G , m& )
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ACCEPTED MANUSCRIPT The total uncertainty equation for collector thermal efficiencyη , moisture content Mdb, and drying rate DR can be written as: 2 2 2 2 ∂η ∂η ∂η ∂η δη = δm& + δT fo + δT fi + δI G ∂T fi ∂I G ∂m& ∂T fo 1
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2 2 2 ∂DR ∂DR ∂DR δDR = δM t + δM d + δt ∂M t ∂M d ∂t
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2 2 ∂M ∂M δM db = db δM t + db δM d ∂M t ∂M d
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Calculations show that the total uncertainty in calculating efficiency, η , moisture content Mdb and drying rate DR are almost in the order of 1, 2.8 and 3%, respectively.
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3. Results and Discussions 3.1 FPCs Performances
Fig. 4
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The basic method of measuring collector performance is to expose operating collector to solar radiation and measure. The fluid inlet and outlet temperature and the fluid flow rate addition, radiation on the collector, ambient temperature, and wind speed are also recorded. ASHRAE standard requires that, for the collector efficiency test, the solar insulation must be above 630 W/m2 (Karim and Hawlader, 2006). The variation of the efficiency (η) is studied as a function of variation in the mass flow rate (Fig. 4), and the improvements of thermal performances are important in relation to the FPC. It can be seen that the collector efficiency increases considerably with increasing air mass flow rate. This means, at higher air flow rate, the overall loss is lower. Furthermore, it is found that model II has the highest efficiency. The maximum efficiencies for these two FPCs (model I and model II) are determined as 76.2% and 79.9%, respectively at m& = 0.044 kg / s .
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A series of experiments are conducted to establish the variation of the pressure drop as a function of the air flow rate for both models of solar FPCs (Fig.5). The air in the double pass FPC (model II) has a long trajectory. Substantial heat transfer enhancement is obtained. There is, of course, an associated increase in pressure drop due to increased friction with the inferior air flow channel duct. It attaints the values 8, 20 and 31.5 Pa for air flow rates of 0.011, 0.022 and 0.028 kg/s, respectively. The simple pass FPC (model I) presents the lower pressure drops. They attain the value 7, 17.5 and 25 Pa for air flow rates of 0.011, 0.022 and 0.028 kg/s, respectively. Fig. 5 3.2 Effect of the FPC performances on the drying time improvement Field tests of the dryer for henna drying also are carried out in the spring 2010; the typical results are shown in (Figs. 6-10). In all experiments, the initial moisture content (d.b.) of the product is 4.6 kgwater/kg, and the final moisture content must reach to 0.05 kgwater/kg (d.b.).
ACCEPTED MANUSCRIPT A typical experimental evolution of the henna moisture content (d.b.) is presented as a function of the drying time, in the cases of models I and II with m& =0.024 kg/s compared to the drying in the open air under direct sun rays (Fig. 6). Drying is started at 09:00 with an initial moisture content of 4.6 kgwater/kg (d.b.) and continued until 18:00 (9h 00min of drying time/day). The final moisture content of the samples is obtained after 7h 45min and 4h 15min in the cases of model I and II, respectively, and it took 15h 00min under direct sun.
3.3 Effect of the air flow rate on the drying time
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Fig.6
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To show the influence of the air flow rate on the improvement of the drying time, this study is conducted under different outdoor conditions by using of the best performing FPC (model II). Since the drying time with the double pass FPC (model II) can take less than seven hours, the drying is started at 09:00 and continued until 16:00 (7h 00min of drying time). Environmental conditions are presented in the form of graphs that describe the relative humidity and the global hourly insulation of the characteristic day, which we have determined by using the collector inclination angle value (34.8◦). The recorded values of these two important parameters can be seen in (Fig. 7). The variations of the temperatures of air at the solar FPC outlet and in the drying chamber and the ambient temperature for a typical day during the drying of henna are shown in (Fig. 8).
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Figs. 7 and 8 The drying kinetic of the product can be represented on the quantity of moisture present in the sample, its loss of mass or expressed on drying rate. To study the influence of the air flow rate on the drying time, we have used model II with three air flow rate 0.036, 0.024 and 0.012 kg/s. Afterwards, we have illustrated how the loss of mass variation is affected during the drying time. Drying is started with initial moisture content of 0.82 kgwater/kg (w.b.) and continued, until a final moisture content of the samples ranged from 0.00 to 0.083 kgwater/kg (w.b.) attained after 7h 00min, which correspond to a loss of mass ranged from 80.33% to 82%.
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According to the literature, the drying air temperature is much more influential than the air flow velocity (Al-Juamily et al., 2007). We note that, the air temperature in the drying chamber is closely dependent on the air velocity inside the dryer. The air temperature decreases with the increase in air velocity, these two parameters affect the loss of the moisture content; increasing one of these two parameters improves the drying time. However, the increase in one of these two parameters leads to decreasing the second. It is significant to have the right drying temperature and the optimum air flow. In this case, we can observe that it is more interesting to operate with an air flow rate of about 0.024 kg/s and an average drying temperature around 45°C. Time taken to reach particular moisture content corresponds to a value of loss of mass of 82% is shorter (4h 15min) with the second air flow rate (0.024 kg/s), but is equal to 7h 00min and 5h 15min with the first and the third flow rate (0.036 and 0.012 kg/s), which corresponds to a relative reductions in drying time of 39.29% and 25%, respectively (Fig. 9). Fig.9 3.4 Effect of the product quantity on the drying time The influence of the henna quantity existing in the drying chamber on its moisture content (d.b.) evolution is presented as a function of the drying time (Fig. 10). There is a relationship
ACCEPTED MANUSCRIPT between the initial product weight and its moisture content during drying. After 6 h 45min of drying of 1 kg of henna, the resulting moisture content in product is equal to 0.05 [kgwater/kg] (d.b.), while it takes 5h 45min and 4h 30min to get a similar value of moisture content when the weight of the henna is 0.5 and 0.2 kg, corresponding to a relative reduction of 15 and 33%, respectively.
4. Conclusion and future perspectives
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Fig. 10
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In this study, we have first conducted a comparative study between two types of solar air FPCs - i) simple-pass collector with trapezoidal obstacles (model I) and ii) double-pass collector with trapezoidal obstacles in the air flow duct (model II)- in order to determine the best performing model for the drying uses. Thereafter, the best FPC is experimentally tested for the drying of the henna in Biskra, Algeria.
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The first study has allowed us to show that, at different air mass flow, the highest efficiencies are obtained from the double pass solar air FPC with trapezoidal obstacles. In addition, the use of the best performing FPC (model II) reduces 20% of henna drying time in comparison with model I and 75% comparing to the traditional drying. The effect of the air mass flow rate is also studied to find the optimum drying air rate. It is clear that drying time with 0.024 kg/s is shorter than those with 0.012 and 0.036 kg/s. However, the influence of some parameters specific to the product, such as the quantity of the product on the drying time is investigated in outdoor conditions. It was found that, the increase in the initial product quantity increases the total drying time.
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It could be concluded that, the use of solar dryers allows us to avoid the mixture of henna leaves with the ground during drying and also prevents the penetration of insects and scorpions in the dried samples.
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Acknowledgment
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Finally, we hope that this contribution can give a look at the causes of the decline in the production of this important plant and how to improve the quality of the product through a fast and clean drying. It is expected that this study will be followed by a second one which will attempt to compare the qualities, and the chemical compositions of the samples derived from different drying methods cited in this paper.
The authors acknowledge the assistance of Drs. Ahmed-Chouaki Houadjli and Lamri Segni (English Department, Univ. of Biskra) for their contributions in the improvement of the quality of this paper. We also acknowledge the direction of agricultural services (DSA) of Biskra.
References Abene, A., Dubois, V., Le Ray, M., and Ouagued, A., 2004. Study of a solar air flat plate collector: use of obstacles and application for the drying of grape. Journal of food engineering, 65, 15-22. Ahmed‐Zaid, A., Messaoudi, H., Abenne, A., Le Ray, M., Desmons, J. Y., Abed, B., 1999. Experimental study of thermal performance improvement of a solar air flat plate collector through the use of obstacles: application for the drying of ‘Yellow Onion’. International journal of energy research, 23, 1083-1099.
ACCEPTED MANUSCRIPT Al-Juamily, K. E., Khalifa, A. J. N., & Yassen, T. A., 2007. Testing of the performance of a fruit and vegetable solar drying system in Iraq. Desalination, 209(1), 163-170. Aoues, K., Moummi, N., Zellouf, M., Benchabane, A., 2011. Thermal performance improvement of solar air flat plate collector: a theoretical analysis and an experimental study in Biskra, Algeria. International Journal of Ambient Energy, 32, 95-102. Bantle, M., Eikevik, T. M., 2014. A study of the energy efficiency of convective drying systems assisted by ultrasound in the production of clipfish. Journal of Cleaner Production, 65, 217-223.
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Battisti, R., Corrado, A., 2005. Environmental assessment of solar thermal collectors with integrated water storage. Journal of Cleaner Production, 13, 1295-1300. Çalban, T., 2006. The effects of bed height and initial moisture concentration on drying lignite in a batch fluidized bed. Energy Sources, Part A, 28, 479-485.
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Chang, I. S., Kim, J. H., 2001. Development of clean technology in wafer drying processes. Journal of Cleaner Production, 9, 227-232. Duffie, J. A., Beckman, W. A., 2013. Solar engineering of thermal processes. John Wiley & Sons.
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Ekechukwu, O. V., 1999. Review of solar-energy drying systems I: an overview of drying principles and theory. Energy Conversion and Management, 40, 593-613. Esen, H., 2008. Experimental energy and exergy analysis of a double-flow solar air heater having different obstacles on absorber plates. Building and Environment, 43, 1046-1054. Habbal, O. A., Al-Jabri A. A., El-hag A. H., Al-Mahrooqi Z. H., Al-Hashmi N. A., 2005. Invitro antimicrobial activity of Lawsonia Ineermis Linn (henna). A pilot study on the Omani henna, Saudi medical journal, 26(1), 69-72. Hassanain, A. A., 2010. Unglazed Transpired Solar Dryers for Medicinal Plants. Drying Technology, 28(2), 240-248.
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Kalogirou, S. A., 2004. Solar thermal collectors and applications. Progress in energy and combustion science, 30, 231-295. Karim, M. A., Hawlader, M. N. A., 2006. Performance investigation of flat plate, v-corrugated and finned air collectors. Energy, 31, 452-470.
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Karsli, S., 2007. Performance analysis of new-design solar air collectors for drying applications. Renewable Energy, 32, 1645–1660.
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Koroneos, C. J., Nanaki, E. A., 2012. Life cycle environmental impact assessment of a solar water heater. Journal of Cleaner Production, 37, 154-161. Koroneos, C., Tsarouhis, M., 2012. Exergy analysis and life cycle assessment of solar heating and cooling systems in the building environment. Journal of Cleaner Production, 32, 52-60. Labed, A., Moummi, N., Aouès, K., Zellouf, M., Moummi, A., 2009. Etude théorique et expérimentale des performances d’un capteur solaire plan à air muni d’une nouvelle forme de rugosité artificielle. Revue des Energies Renouvelables, 12, 551-561. Labed, A., Moummi, N., Benchabane, A., 2011. Etude expérimentale de l’efficacité d’une nouvelle forme de rugosité artificielle sur les performances d’un capteur solaire plan à air ; application au séchage du Henné, Premier Séminaire Nationale de Génie Mécanique, 7- 8 December, Biskra, Algeria. Labed, A., Moummi, N., Benchabane, A., Aoues, K., Moummi, A., 2012(a). Performance investigation of single-and double-pass solar air heaters through the use of various fin geometries. International Journal of Sustainable Energy, 31, 423-434.
ACCEPTED MANUSCRIPT Labed, A., Moummi, N., Benchabane, A., 2012(b). Experimental investigation of various designs of solar flat plate collectors: Application for the drying of green chili. Journal of Renewable and Sustainable Energy, 4, 043116 (doi: 10.1063/1.4742337). Labed, A., Moummi, N., Benchabane, A., 2012(c). Experimental investigation of various designs of solar dryer: Application for the drying of hot chili, Sixth International Conference on Thermal Engineering: Theory and Applications,29- 1st jun 2012, Istanbul, Turky.
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Labed, A., Moummi, N., Aoues, K., Zellouf, M., 2013.Etude expérimentale des performances thermiques et des pertes de charges de différentes configurations de capteurs solaires plans à air, 16ème Edition des Journées Internationales de Thermique (JITH2013), 13-15 Novembre, Marrakech, Maroc. Labed, A., Moummi, N., Zellouf, M., Aoues, K., Rouag, A., 2014. Effect of different parameters on the solar drying of henna ; experimental investigation in the region of Biskra (Algeria). 13th International conference on clean energy (ICCE 2014), Istanbul, Turkey.
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Labed, A., Rouag, A., Benchabane, A., Moummi, N., & Zerouali, M., 2015. Applicability of solar desiccant cooling systems in Algerian Sahara: Experimental investigation of flat plate collectors. Journal of Applied Engineering Science & Technology, 1(2), 61-69.
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Mohanraj, M., Chandrasekar, P., 2009. Performance of a forced convection solar drier integrated with gravel as heat storage material for chili drying. Journal of Engineering Science and Technology, 4, 305-314. Moummi, N., Moummi, A., Aoues, K., Mahboub, C., Youcef Ali, S., 2010. Systematic forecasts of solar collector's performance in various sites of different climates in Algeria. International journal of sustainable energy, 29, 142-150. Moummi, N., Youcef-Ali, S., Moummi, A., Desmons, J. Y., 2004. Energy analysis of a solar air collector with rows of fins. Renewable Energy, 29(13), 2053-2064.
NOMENCLATURE
Lc lc Mdb m& QU RH Ta T fi
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Collector surface area (m2) Specific heat of air at constant pressure (kJ/kg K) Dry basis. Drying rate (kg kg-1h-1) Collector heat removal factor depending air inlet temperature (dimensionless) Global irradiance incident on solar air heater collector (Wm-2)
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AC cp d.b. DR FR IG
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Sami, S., Rahimi, A., Etesami, N., 2011. Dynamic modeling and a parametric study of an indirect solar cabinet dryer. Drying Technology, 29, 825-835.
Length of the flat plate collector (m)
Width of the flat plate collector (m) Moisture content (d.b.) (kg kg-1) Air mass flow rate (kg s-1) Useful energy gain of the collector (W) Relative humidity of ambient air (%) Ambient temperature (°C)
Inlet air temperature of the collector (°C)
T fo
Outlet fluid temperature of the collector (°C)
UL
Collector overall heat loss coefficient (W/m2 °C)
ACCEPTED MANUSCRIPT wet basis Loss of mass of the drying product (%) Pressure loss [Pa]
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Greek Letters Absorptance (dimensionless) α abs Collector tilt (degrees) (dimensionless) β τv Transparent cover transmittance (dimensionless) Thermal efficiency (dimensionless) η
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w.b. ∆M ∆P
ACCEPTED MANUSCRIPT Figures captions
Journal of Cleaner Production Date: 14/10/2015 Revised manuscript entitled “Solar drying of henna (Lawsonia Inermis) using different models of solar flat plate collectors: An experimental investigation in the region of Biskra (Algeria)” Corresponding author: Co-authors:
Dr. Adnane Labed Pr. Noureddine Moummi
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Dr. Kamel Aoues Pr. Adel Benchabane
Figures captions: Fig. 1: National production of henna during the last 20 years.
Fig. 3: Schematic view of fin obstacles in dynamic air vein.
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Fig. 2: Experimental devices for henna drying; a) model I, b) model II.
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Fig. 4. Efficiencies versus air flow rate for different both FPC models.
Fig. 5: Pressure drop (Pa) vs. the air mass flow rate (Kg/s) for different studied FPCs. Fig. 6: Evolution of the henna moisture content (d.b.) vs. the drying time for different dryer models ( m& =0.024Kg/s), compared to the traditional drying. Fig.7: Recorded values of the relative humidity and solar radiation during the testing days (17/04/2011, 18/04/2011 and 25/04/2011).
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Fig. 8: Recorded values of the FPC, drying chamber and ambient temperatures during drying the testing days. Fig. 9: Evolution of the henna loss of mass vs. drying time, for different air flow rates: 0.012, 0.024 and 0.036Kg/s respectively, in the case of model II.
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Fig. 10: Evolution of the henna moisture content (d.b.) vs. drying time, for different product weights: 0.2, 0.5 and 1 Kg respectively, in the case of model II ( m& =0.024 kg/s).
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Fig. 1. National production of henna during the last 20 years.
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Air exhaust
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Drying chamber Fan
Wire mesh trays for crop drying
35°
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Cover Absorber Fin obstacles
200g
Air
Insulator
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Plywood sheets
(a)
Fig. 2. Experimental devices for henna drying; a) model I, b) model II.
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Back plate
5 cm
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6 cm
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2,5 cm
6 cm
4 cm
Air in
Fig. 3. Schematic view of fin obstacles in dynamic air vein.
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Fig. 4. Efficiencies versus air flow rate for different both FPC models.
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Fig. 5. Pressure drop (Pa) vs. the air mass flow rate (Kg/s) for different studied FPCs..
Fig. 6. Evolution of the henna moisture content (dry basis) vs. the drying time for different dryer models ( m& =0.024Kg/s), compared to the traditional drying.
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ACCEPTED MANUSCRIPT
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Fig. 7. Recorded values of the relative humidity and solar radiation during the testing days (17/04/2011, 18/04/2011 and 25/04/2011)
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ACCEPTED MANUSCRIPT
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Fig. 8. Recorded values of the FPC, drying chamber and ambient temperatures during drying the testing days.
Fig. 9. Evolution of the henna loss of mass vs. drying time, for different air flow rates: 0.012, 0.024 and 0.036Kg/s respectively, in the case of model II.
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ACCEPTED MANUSCRIPT
AC C
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Fig. 10. Evolution of the henna moisture content (d.b.) vs. drying time, for different product weights: 0.2, 0.5 and 1 kg respectively, in the case of model II.