Energy and exergy analyses of the spray drying process of fish oil microencapsulation

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Available online at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/issn/15375110

Research Paper

Energy and exergy analyses of the spray drying process of fish oil microencapsulation Mortaza Aghbashlo a,*, Hossien Mobli a, Shahin Rafiee a, Ashkan Madadlou b a

Faculty of Agricultural Engineering and Technology, University of Tehran, Karaj, Iran Department of Food Technology, Institute of Chemical Technologies, Iranian Research Organization for Science & Technology (IROST), Tehran, Iran b

article info Article history:

An energy and exergy analysis was carried out on the process of fish oil microencapsulation using spray drying. The process was carried out on a mini-spray dryer conducted at

Received 2 October 2011

three drying air temperatures of 140, 160, and 180
C. Various milk-originated single, and

Received in revised form

composite wall materials including skim milk powder (SMP), whey protein concentrate

23 November 2011

(WPC), whey protein isolate (WPI), 80% WPI þ 20% milk protein concentrate (MPC), and 80%

Accepted 1 December 2011

WPI þ 20% sodium caseinate (NaCas) were used in the formulation of emulsions. The

Published online 23 December 2011

effects of drying air temperature and wall material on the energy efficiency, energy loss from drying chamber, exergy efficiency, exergy destruction, entropy generation and improvement potential were investigated. The energy and exergy efficiency values for spray drying process of fish oil microencapsulation at the drying air temperature between 140 and 180
C were found to be in the ranges of 7.48e8.54% and 5.25e7.42%, respectively. The results of this study also confirmed that the exergy analysis using second law of thermodynamics is a potential tool for optimising dryer operation and design. ª 2011 IAgrE. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

Functional foods supplemented with omega-3 and long-chain polyunsaturated fatty acids, namely docosahexanoic acid, and eicosapentanoic acid coming from marine sources, have attracted much of interest in the world food market (Drusch, Serfert, Scampicchio, Schmidt-Hansberg, & Schwarz, 2007; Klaypradit & Huang, 2008). Incorporation of long-chain polyunsaturated fatty acids into foods is, however, limited due to their low solubility in most food systems and their extreme sensitivity to oxidation. Encapsulation of bioactive substances within microcarriers provides a new approach to protecting their functionality. Microencapsulation is the technology of packing solid, liquid or gaseous materials into miniature sealed

capsules that can release their contents at controlled rates under specific conditions (Fang & Bhandari, 2010; Klaypradit & Huang, 2008). The main reasons of encapsulation is to reduce the core reactivity with environmental factors; to decrease the transfer rate of the core material to the outside environment; to promote easier handling; to control the release of the core material; to mask the core taste and odour; and to dilute the core material when it should be used in only very small amounts (Gharsallaoui, Roudaut, Chambin, Voilley, & Saurel, 2007; Shahidi & Han, 1993). Amongst the various techniques developed to encapsulate food ingredients such as spray drying, spray cooling/chilling, extrusion, fluidised bed coating, coacervation, liposome entrapment and etc. (Desai & Park, 2005; Fang & Bhandari, 2010), spray drying is the most

* Corresponding author. Tel.: þ98 2612801011; fax: þ98 261 2808138. E-mail address: [email protected] (M. Aghbashlo). 1537-5110/$ e see front matter ª 2011 IAgrE. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biosystemseng.2011.12.001

230

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Nomenclatures A Cp e ex E_ _ Ex F h hfg IP_ _ m P Q Q_ R s S_ T u U v x X z

2

Surface area (m ) Specific heat (kJ kg1 K1) Specific energy (kJ kg1) Specific exergy (kJ kg1) Rate of energy (kJ s1) Rate of exergy (kJ s1) Function of the independent variables Specific enthalpy (kJ kg1) Latent heat of water (kJ kg1) Improvement potential rate (kJ s1) Mass flow rate (kg s1) Pressure (kPa) Volume flow rate (m3 s1) Rate of heat transfer (kJ s1) Specific gas constant (kJ kg1 K1) Specific entropy (kJ kg1 K1) Rate of entropy (kJ s1 K1) Temperature (K or
C) Uncertainty in the independent variables Uncertainty in the result Velocity (m s1) Mole fraction Fraction of component (%) Independent variable

Greek symbols r Density (kg m3) u Humidity ratio of air (kg [Water] kg1 [Dry Air])

common technology due to its low cost and availability of equipments (Gharsallaoui et al., 2007). Microencapsulation of fish oil via spray drying with different wall materials has been extensively studied by many authors (Anwar & Kunz, 2011; Hogan, O’Riordan, & O’Sullivan, 2003; Kagami et al., 2003; Keogh et al., 2001; Kolanowski, Ziolkowski, Weißbrodt, Kunz, & Laufenberg, 2006). The critical aspect of drying technology is the low thermal efficiency of drying equipment. Therefore, it is vital for researchers and engineers to increase the thermal efficiency of drying systems using engineering analyses. Traditionally, energy analysis was used as the basic approach to estimating various energy conversion processes. However, the energy analysis is unable to distinguish different qualities of energy such as heat quality which is dependent on the temperature of the heat source. Exergy analysis using second law of thermodynamics is a powerful tool, which has been extensively applied for the design, operation and performance evaluation of energy systems such as drying facilities. Exergy can be viewed as a quantitative measure of the “quality” or “usefulness” of an amount of energy (Erek & Dincer, 2009) and has been widely used for assessing energy status of a thermal process from thermodynamic point of view (Tambunan, Manalu, & Abdullah, 2010) Exergy gives more meaningful and useful information than energy analysis regarding the efficiency, losses and performance for drying systems and processes (Dincer & Sahin, 2004). Recently, several studies have been undertaken on exergy analyses of different drying facilities (Aghbashlo, Kianmehr, &

j h n

Exergy efficiency (%) Energy efficiency (%) Specific volume (m3 kg1)

Subscripts a Air at Atmosphere d/p Droplet/particle dc Drying chamber des Destruction e Emulsion ev Evaporated f Saturated liquid state g Saturated vapour state gen Generation i Numerator in Inlet l Loss n Nozzle out Outlet p Product v Water vapour w Water 0 Dead state 1 Inlet drying air Spraying air 10 2 Inlet wet product 3 Outlet moist air 4 Dry product Stuck product 40

Arabhosseini, 2008; Aghbashlo, Kianmehr, & Arabhosseini, 2009; Akpinar & Sarsilmaz, 2004; Cay, Tarakcioglu, & Hepbasli, 2009; Cay, Tarakcioglu, & Hepbasli, 2010; Chowdhury, Bala, & Haque, 2011; Gungor, Erbay, & Hepbasli, 2011; Hancioglu, Hepbasli, Icier, Erbay, & Colak, 2010; Hepbasli, Erbay, Colak, Hancioglu, & Icier, 2010; Icier, Colak, Erbay, Kuzgunkaya, & Hepbasli, 2010; Ozgener & Ozgener, 2006, 2009a, 2009b; Syahrul, Hamdullahpur, & Dincer, 2002; Tiwari, Das, Chen, & Barnwal, 2009). Results of those studies have indicated that the exergy approach presented based on the experimental drying data, has provided a quantitative grasp of process inefficiencies, a more comprehensive and deeper insight into the process and new unforeseen ideas for improvements. Also, the results of exergy analysis have elucidated that this approach is an efficient technique in identifying locations, kinds and true magnitudes of wastes and losses, furthering the objective of more efficient energy use, and revealing whether or not and how much it is possible to design and select more efficient drying systems and processes by diminishing the inefficiencies in the system and its major components e.g. air, water and product (Ozgener & Ozgener, 2006). Based on authors’ best knowledge, very little information is available on exergy analysis of the spray drying processes. The main objective of the present study is to analyse the exergy of a spray drying process applied for microencapsulating fish oil using different wall materials and drying air temperatures.

231

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

2.

Materials and methods

2.1.

Materials

Fish oil was purchased from Qeshm Fish Oil Co. (QFOC, Qeshm, Iran). Whey protein concentrate (WPC) and whey protein isolate (WPI) were kindly donated by Alra Foods, Viby, Denmark. Milk protein concentrate (MPC), sodium caseinate (NaCas) and skim milk powder (SMP) were obtained from Sundiet SA, Corminboeuf, Switzerland, Iran Caseinate Co., Tehran, Iran, and Pegah Dairy Co., Tehran, Iran, respectively. Phosphate buffer (pH ¼ 7.0) and sodium azide were purchased from Merck, Darmstadt, Germany.

2.2.

Preparation of emulsions

Wall material solution was prepared by dissolving 20 g powder in 70 g phosphate buffer (5 mM, pH 7.0) and stirring at 500 rpm for 30 min at room temperature; sodium azide (100 mg l1) was added to prevent microbial growth. The wall material solution was stored at 4
C for 10 h to allow complete hydration (Madadlou, Mousavi, Emam-Djomeh, Ehsani, & Sheehan, 2009). Ten gram of fish oil was progressively added to the wall material solution while stirring at 3500 rpm for 2 min using a rotor-stator blender (Ultra-turrax IKA T18 Basic, Wilmington, NC, USA), after which the emulsion was homogenised at 24,000 rpm for 5 min.

2.3.

Treatments

Five single and composite wall materials including WPC, WPI, SMP, 80% WPI þ 20% MPC, and 80% WPI þ 20% NaCas were used in preparation of aqueous solutions. The composition of emulsions used in calculations is represented in Table 1. The chemical composition of wall materials were considered according to the manufacture’s report.

2.4.

Spray dryer

¨ CHI MiniThe drying of emulsions was accomplished in a BU Spray B-191, Flawil, Switzerland located in Iranian Research Organisation for Science & Technology (IROST), Tehran, Iran (Fig. 1). The dryer was equipped with a twin-fluid internal mixing nozzle (0.7 mm diameter). The drying air was either sucked or blown through the chamber by the aspirating fan. The amount of heated drying air available was regulated by the speed of

the aspirator and was up to 35 m3 h1. The heated air temperature was monitored prior to flow into the drying chamber using Pt 100 thermocouple with precision of 1
C. It could be controlled up to 220
C. The outlet drying air temperature was monitored on the control panel using Pt 100 thermocouple. The inlet and outlet temperatures of drying air and dryer chamber temperature were also recorded using Testo-465 thermocouple (Testo, Lenzkirch, Germany) with precision of 0.1
C. Temperature of the air carrying the generated capsules before it enters the cyclone was designated as the outlet temperature. The feeding pump regulated the inlet mass of emulsion into chamber. The spraying air flow rate was the amount of compressed air needed to disperse the solution, emulsion or suspension and it could set on the device up to 800 l h1 and corresponded to an air pressure of 8 kPa. During the experiments, the temperature and relative humidity of ambient air were recorded. Figure 2 shows a schematic diagram of the spray dryer during its working state.

2.5.

Experimental procedure

Before each experiment, the dryer was run using distilled water for 15 min in order to achieve desirable steady-state conditions. The emulsion was fed into the drying chamber through a peristaltic pump at the nominal rate of 10%. The initial and final weight of emulsion container was recorded using a digital balance. Three drying air temperatures of 140, 160 and 180
C were used in drying experiments and the flow rate of drying air was adjusted by aspirator to 65%. The spraying air flow rate was 700 l h1. The microcapsules collected in the product vessel were weighted and 2 g was dried in an oven (Memmert, Frankfurt, Germany) at 70
C for 24 h. Weight measurement were performed using AAA 250L balance (Adam Co., Milton Keynes, UK) with precision of 0.0001 g. The particle size of microcapsules was determined using a laser diffraction based particle counter (PC-2000, Spectrex Inc, Cedar Grove, NJ, USA). For this purpose, 0.3 g of microcapsule was suspended in 60 ml ethanol under agitation and the particle size distribution was recorded. All experiments were replicated twice.

2.6.

Experimental uncertainty

The precision of all measurement devices explained in pervious sections. In this study, an uncertainty analysis using the method described by Holman (2001) was performed to prove the accuracy of the experiments:

Table 1 e The composition of emulsion obtained from different wall material. Wall material WPC WPI SMP 80% WPI þ 20% MPC 80% WPI þ 20% NaCas

Water (%)

Protein (%)

Fat (%)

Carbohydrate (%)

Fibre (%)

Ash (%)

70 70 70 70 70

17 18 7 16 16.6

11 10.4 10.4 10.8 10.8

0.4 0.4 10.4 0.8 0.4

0.8 0.4 1 1.2 1

0.8 0.8 1.2 1.2 1.2

232

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

_ p Þ40 is the mass flow rate of suck product (kg s1); (kg s1); ðm _ a Þ10 is the _ a Þ1 is the mass flow rate of drying air (kg s1); ðm ðm _ a Þ3 is the mass flow mass flow rate of spraying air (kg s1); ðm _ w Þ2 is the mass flow rate of inlet rate of outlet air (kg s1); ðm _ w Þ4 is the mass flow rate of water inside dry water (kg s1); ðm _ w Þ40 is the mass flow rate of water inside product (kg s1); ðm stuck product (kg s1); u1 is the humidity ratio of drying air (kg [Water] kg1 [Dry Air]); u10 is the humidity ratio of spraying air (kg [Water] kg1 [Dry Air]); u3 is the humidity ratio of outlet air (kg [Water] kg1 [Dry Air]).

3.2.

Energy balance equations

The first law of thermodynamics can be applied for dryer system, by equating input and output energy terms: 

         _ a 10 ðea Þ10 þ m _ p 2 ep 2 þ m _ w 2 ðew Þ2 _ a 1 ðea Þ1 þ m m             _ a 3 ðea Þ3 þ m _ p 4 ep 4 þ m _ p 40 ep 40 þ m _ w 4 ðew Þ4 ¼ m   _ _ w 40 ðew Þ40 þ Q l þ m

ð5Þ

1

¨ CHI Mini-Spray B-191 spray dryer. Fig. 1 e The image of BU

2  2 2 #1=2  vF vF vF u1 þ u2 þ. þ un vz1 vz2 vzn



" UF ¼

where (ea)1 is the specific energy of drying air (kJ kg ); ðea Þ10 is the specific energy of spraying air (kJ kg1); (ep)2 is the specific energy of inlet wet product (kJ kg1); (ew)2 is the specific energy of inlet water (kJ kg1); (ea)3 is the specific energy of outlet air (kJ kg1); (ep)4 is the specific energy of dry product (kJ kg1); ðep Þ40 is the specific energy of stuck product (kJ kg1); (ew)4 is the specific energy of water inside outlet product (kJ kg1); ðew Þ40 is the specific energy of water inside stuck product (kJ kg1); Q_ l is the heat transfer rate to environment from drying chamber (kJ s1). _a m

 1

¼ ðra Þ1 ðQa Þ1

(1)

where UF is the uncertainty in the result; u1, u2, ., un are the uncertainty in the independent variables; z1, z2, ., zn are the independent variables; F is the function of the independent variables.

3.

Theoretical principle

3.1.

Mass balance equations

The proposed thermodynamic model by Dincer and Sahin (2004) was modified according to the spray dryer characteristics. The schematic view of drying process with input and output terms is shown in Fig. 3. In order to write the mass balance equations, three components are considered; namely the product and the air and water in the dryer. Product Air



_p m

 2

    _p 4þ m _ p 40 ¼ m _p ¼ m

      _ a 10 ¼ m _a 3 _a 1þ m m

      _w 2 _ a 1 þ u10 m _ a 10 þ m Water u1 m       _w 4þ m _ w 40 _a 3þ m ¼ u3 m

(2) (3)

(4)

_ p Þ2 and m _ p are the mass flow rate of inlet wet product where ðm _ p Þ4 is the mass flow rate of outlet dry product (kg s1); ðm

Fig. 2 e Schematic view of mini-spray dryer during working state.

(6)

233

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Fig. 3 e Schematic illustration of drying process with input and output terms.

ðea Þ1 ¼

     ðva Þ21 Cp a 1 ðT1  T0 Þ þ u1 hfg 1 þ 2  1000

(7)

ðva Þ1 ¼

ðQa Þ1 ðAa Þ1

(8)

where (ra)1 is the density of drying air (kg m3); Qa is the volume flow rate of drying air (m3 s1) which can be determined from dryer operating manual; ((Cp)a)1 is the specific heat of drying air (kJ kg1 K1); T1 is the temperature of drying air (K); T0 is the reference-dead state temperature (K); (hfg)1 is the latent heat of water at drying air temperature (kJ kg1); (va)1 is the velocity of drying air (m s1); (Qa)1 is the volume flow rate of drying air (m3 s1); (Aa)1 is the surface area of drying air entrance (m2). The term of 1000 is Eq. (7) was used to transform the dimensions J kg1to kJ kg1 for kinetic energy. The specific heat capacity of air is a function of temperature (Moran & Shapiro, 1995) and can be described by: 

Cp

 a

¼1:04841  0:000383719T þ

9:45378T2 5:49031T3  107 1010

4

7:92981T þ 1014

(9)

where (Cp)a is the specific heat of dry air at known temperature (kJ kg1 K1); T is the temperature of air (K). The latent heat of vaporisation (hfg) can be calculated at the saturation condition by an equation developed by Brooker (1967). Two equations are used for hfg (J kg1) as the function of absolute temperature: hfg ¼ 2:503  106  2:386  103 ðT  273:16Þ 273:16  TðKÞ  338:72 0:5 hfg ¼ ð7:33  1012  1:60  107 T2 Þ 338:72  TðKÞ  533:16

where ððCp Þa Þ10 is the specific heat of spraying air (kJ kg1 K1); T10 is the temperature of spraying air (K); ðhfg Þ10 is the latent heat of water at spraying air temperature (kJ kg1); ðva Þ10 is the velocity of spraying air (m s1). Due to internal mixing of the emulsion and air inside the spray nozzle, the air velocity is assumed to be approximately equal to the velocity of spray and can be approximated as follows: ðQa Þ10 þ ðQe Þ2 ðva Þ10 yvd=p y An

vd=p is the velocity of droplet or particle (m s1); ðQa Þ10 is the volume flow rate of spraying air (l h1) or (m3 s1) and was set to 700 (l h1) during this study; (Qe)2 is the volume flow rate of emulsion (l h1) or (m3 s1); An is the surface area of nozzle (m2). The volume flow rate of emulsion into the atomising nozzle was estimated using: ðQe Þ2 ¼

ðea Þ10 ¼



Cp

  a 10

  ðT10  T0 Þ þ u10 hfg 10 þ

ðva Þ210 2  1000

(11)

_ e Þ2 ðm ðre Þ2

(13)

_ e Þ2 is the mass flow rate of emulsion (kg s1); (re)2 is where ðm density of emulsion (kg m3). The mass flow rate of emulsion _ e Þ2 Þ into the atomising nozzle was computed by recording ððm the initial and final weight of emulsion container. The mass flow rate of spraying air was identified as follows: 

_a m

 10

¼ ðra Þ10 ðQa Þ10

(14) 3

where ðra Þ10 is the density of spraying air (kg m ). The density of spraying air was computed using following equation:

(10) The enthalpy of an ideal gas depends only on temperature and is independent of pressure. By assuming that the air is an ideal gas, the specific energy of the spraying air at the specified temperatures is determined using Eq. (11).

(12)

ðra Þ10 ¼

P10 Ra T10

(15)

where P10 is the pressure of spraying air (kPa); Ra is the specific gas constant (kJ kg1 K1). The specific energy of sprayed wet product was calculated using Eq. (16) below. It is postulated that the temperature and velocity of spraying droplet is equal to the temperature and velocity of spraying air.

234

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

 2          vd=p ðva Þ210 y Cp p ðT10  T0 Þ þ ep 2 ¼ Cp p ðT2  T0 Þ þ 2 2 2  1000 2  1000 (16)

Table 2 e Specific heat of different product components and water as the function of temperature (
C) (Singh & Heldman, 2001).

X     Cp p ¼ Xi Cp i

Equation, T (
C)

Component

where ((Cp)p)2 is the specific heat of inlet wet product (kJ kg1 K1); T2 is the temperature of wet inlet product (K). The specific heat of the fresh and dried products was determined as follows (Choi & Okos, 1986):

(Cp)Protein ¼ 2.0082 þ 1.2089  103T  1.3129  106T2 (Cp)Fat ¼ 1.9842 þ 1.4733  103T  4.8008  106T2 (Cp)Carbohydrate ¼ 1.5488 þ 1.9625  103T  5.9399  106T2 (Cp)Fibre ¼ 1.8459 þ 1.8306  103T  4.6509  106T2 (Cp)Ash ¼ 1.0926 þ 1.8896  103T  3.6817  106T2 (Cp)Water ¼ 4.0817e5.3062  103T þ 9.9516  104T2 0  T (
C)  150

Protein Fat Carbohydrate

(17)

i

where (Cp)p is the specific heat of product (kJ kg1 K1); Xi is the fraction of component (%); (Cp)i is the specific heat of each component (kJ kg1 K1). The specific heat of product component is function of temperature. The equations which used in the calculation of specific heat of product are presented in Table 2. The specific energy of sprayed water inside the droplets was calculated as follows: ðew Þ2 ¼

ðva Þ2d=p       ðva Þ210 y Cp w 2 ðT10  T0 Þ þ Cp w 2 ðT10  T0 Þ þ 2  1000 2  1000 (18)

where ((Cp)w)2 is the specific heat of inlet water (kJ kg1 K1).The specific heat of water can be obtained using last equation in Table 2. The specific energy of outlet air was identified as follows: ðea Þ3 ¼



Cp

  a 3

  ðT3  T0 Þ þ u3 hfg 3 þ

ðva Þ23

(19)

2  1000

_ a Þ3 ðm ðva Þ3 ¼ ðra Þ3 ðAa Þ3

(20)

where ((Cp)a)3 is the specific heat air at outlet air temperature (kJ kg1 K1); T3 is the temperature of outlet air (K); (hfg)3 is the latent heat of water at outlet air temperature (kJ kg1); (va)3 is the velocity of outlet air (m s1); (ra)3 is the density of outlet air (kg m3); (Aa)3 is the surface area of outlet air exhaust (m2).

h¼

Fibre Ash Water

For the stuck products (i.e. wall deposited products), it is assumed that the product heated up to the temperature of inlet drying air and the products lost its moisture completely. The possible errors raised from these assumptions were negligible.         ep 40 ¼ Cp p 0 ðT40  T0 Þ ¼ Cp p 0 ðT1  T0 Þ 4

 



_w m

 40

(24)

ðew Þ40 ¼ 0

(25)

where ððCp Þp Þ40 is the specific heat of stuck product (kJ kg1 K1); T40 is the temperature of stuck product (K). The mass flow rate of stuck product was obtained by deduction of mass flow rate inlet and finished product. Thus, the heat loss from dryer chamber can be identified using Eq. (5). Energy efficiency of the spray drying process is the ratio of energy use (investment) in the drying of the product to energy of the drying air supplied (including the energy of spraying air) to the system:

ðEnergy investment in the evaporation of moisture in the productÞ  100 ðEnergy of drying air supplied þ Energy of spraying airÞ

The specific energy of outlet dried product and water inside particle can be calculated using Eqs. (21) and (22) below. The temperature and velocity of outlet dried particles was assumed to be equal as outlet air.   ep 4 ¼



Cp

  p

4

ðT4  T0 Þ þ

   ðew Þ4 ¼ Cp w 4 ðT4  T0 Þ þ

ðva Þ24

2  1000

ðva Þ24

¼

2  1000



¼

Cp



 

Cp

p

4

ðT3  T0 Þ þ

  w 4

ðva Þ23

2  1000 (21)

ðT3  T0 Þ þ

ðva Þ23

2  1000 (22)

where ((Cp)p)4 is the specific heat of dry product (kJ kg1 K1); ((Cp)w)4 is the specific heat of water inside dry product (kJ kg1 K1); T4 is the temperature of dry product (K).

(23)

¼0

40

_w m

4

h¼

 _ w Þev ðew Þ3  ðew Þ2 ðm  100 _ a Þ1 ðea Þ1 þ ðm _ a Þ10 ðea Þ10 ðm

(26)

(27)

_ w Þev is the mass flow where h is the energy efficiency (%); ðm rate of evaporated water (kg s1); (ew)3 is the specific energy of water vapour at outlet air (kJ kg1). 

_w m

3.3.

 ev

    _w 2 m _w 4 ¼ m

(28)

Exergy balance equations

The exergy balance equation for the dryer systems was written as:

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1



         _ a 10 ðexa Þ10 þ m _ p exp þ m _ w 2 ðexw Þ2 _ a 1 ðexa Þ1 þ m m        2  2    _ _ _ _ w 4 ðexw Þ4 ¼ ma 3 ðexa Þ3 þ mp 4 exp 4 þ mp 40 exp 40 þ m   _ _ _ w 40 ðexw Þ40 þ Exl þ Exdes þ m

(29)

where (exa)1 is the specific exergy of drying air (kJ kg1); ðexa Þ10 is the specific exergy of spraying air (kJ kg1); (exp)2 is the specific exergy of inlet wet product (kJ kg1); (exw)2 is the specific exergy of inlet water (kJ kg1); (exa)3 is the specific exergy of outlet air (kJ kg1); (exp)4 is the specific exergy of dry product (kJ kg1); ðexp Þ40 is the specific exergy of stuck product (kJ kg1); (exw)4 is the specific exergy of water inside outlet product (kJ kg1); ðexw Þ40 is the specific exergy of water inside _ l is the exergy transfer rate to stuck product (kJ kg1); Ex _ des is the exergy environment from drying chamber (kJ s1); Ex destruction rate (kJ s1). The specific exergy of inlet drying air was obtained as ðexa Þ1 ¼

         Cp a 1 Cp a 1 þ u1 Cp v 1 ðT1  T0 Þ  T0        T1 P1  ðRa þ u1 Rv Þln þ u1 Cp v 1 ln T0 P0

    1 þ 1:607u0 u1 þ T0 ðRa þ u1 Rv Þln þ 1:607u1 Ra ln 1 þ 1:607u1 u0 ðva Þ21 þ 2  1000

(30)

where ((Cp)v)1 is the specific heat of water vapour at drying air temperature (kJ kg1 K1); Rv is the specific gas constant (kJ kg1 K1); P1 is the pressure of drying air (kPa); P0 is the pressure of reference-dead state (kPa); u0 is the humidity ratio of reference-dead state (kg [Water] kg1 [Dry Air]).In this type of spray dryer, the air is sucked by aspirator. Therefore, the pressure of inlet drying air can be determined using Bernoulli’s law.

P1 Pat ðva Þ21 ¼  ðra Þ1 ðra Þat 2

(31)

where ððCp Þv Þ10 is the specific heat of water vapour at spraying air temperature (kJ kg1 K1); P10 is the pressure of spraying air (kPa). The specific exergy of sprayed wet product was determined using the following: 

exp



Cp

 v

¼ 1:6083þ8104 T1107 T2 þ71012 T3 175  TðKÞ  6000

  ¼ hp ðT2 ;P10 Þhp ðT0 ;P0 Þ T0 sp ðT2 ;P10 Þsp ðT0 ;P0 Þ      v2d=p T2 ðva Þ210 ðT2 T0 ÞT0 ln þ y Cp p þ 2 21000 T0 21000

where hp is the specific enthalpy of wet product at known pressure and temperature (kJ kg1); sp is the specific entropy of wet product at known pressure and temperature (kJ kg1 K1). The specific exergy of water inside sprayed droplets was determined as:    ðexw Þ2 ¼ hf ðT2 Þ  hg ðT0 Þ þ nf P10  Pg ðT2 Þ  T0 sf ðT2 Þ  sg ðT0 Þ

v2d=p Pg ðT0 Þ þ T0 Rv ln 0 þ (35) xv P0 2  1000 where hf is the specific enthalpy of water at saturated liquid state (kJ kg1); hg is the specific enthalpy of water at saturated vapour state (kJ kg1); n is the specific volume of water at saturated liquid state (m3 kg1); sf is the specific entropy of water at saturated liquid state (kJ kg1 K1); sg is the specific entropy of water at saturated vapour state (kJ kg1 K1); Pg is the saturation pressure of water (kPa); x0v is the mole fraction of vapour of air at dead state (). The specific exergy of outlet air was obtained as:

h h      i    ðexa Þ3 ¼ Cp a 3 þ u3 Cp v 3 ðT3  T0 Þ  T0 Cp a 3     i    T3 P3  ðRa þ u3 Rv Þln þ u3 Cp v 3 ln T0 P0

    1 þ 1:607u0 u3 þ T0 ðRa þ u3 Rv Þln þ 1:607u3 Ra ln 1 þ 1:607u3 u0 ðva Þ23 2  1000

(36)

P3 Pat ðva Þ23 ¼  ðra Þ3 ðra Þat 2

(37)

þ

(32)

where (Cp)v is the specific heat of water vapour at known temperature (kJ kg1 K1). The specific flow exergy of spraying air was determined from the following equation:

         Cp a 10 ðexa Þ10 ¼ Cp a 10 þ u10 Cp v 10 ðT10  T0 Þ  T0        T10 P10  ðRa þ u10 Rv Þln þ u10 Cp v 10 ln T0 P0

  1 þ 1:607u0 þ 1:607u10 Ra ln þ T0 ðRa þ u10 Rv Þln 1 þ 1:607u10   2 u10 ðva Þ10 þ  u0 2  1000

2

(34)

where Pat is the atmospheric air pressure (kPa); (ra)at is the density of air at atmospheric condition (kPa). The specific heat of water vapour can be obtained using following equation with a correlation coefficient of 0.9949 (R2). 

235

where ((Cp)v)3 is the specific heat of water vapour at outlet drying air temperature (kJ kg1 K1); P3 is the pressure of outlet drying air (kPa); (ra)3 is the density of outlet drying air (kg m3). The temperature and velocity of dried particles should be equal to that of the outlet air and the specific exergy of exhaust particles and water inside them was obtained using following equations: 

(33)

exp



     T4 ðT ¼  T Þ  T ln C p 4 0 0 4 p 4 T0      ðva Þ24 T3 ðT3  T0 Þ  T0 ln y Cp p þ 4 2  1000 T0 þ

ðva Þ23 2  1000

ð38Þ

236

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Table 3 e Uncertainties of the experimental measurements and total uncertainties for predicted values. Parameter

Unit

Experimental measurement Uncertainty in the temperature measurement Uncertainty in the chamber temperature measurement Uncertainty in the weight measurement Uncertainty in the time measurement Predicted measurements Total uncertainty for feeding rate of emulsion Total uncertainty for production rate of microcapsule Total uncertainty for drying air mass flow rate Total uncertainty for spraying air mass flow rate Total uncertainty for specific heat of product Total Uncertainty for moisture content Total uncertainty for E_ in Total uncertainty for E_ out Total uncertainty for Q_ l Total Total Total Total Total Total

uncertainty for uncertainty for uncertainty for uncertainty for uncertainty for uncertainty for




h _ in Ex _ out Ex _ l Ex _ des Ex j

 40

         T40 y Cp p 0 ¼ Cp p 0 ðT40  T0 Þ  T0 ln 4 4 T0   T1  ðT1  T0 Þ  T0 ln T0

  _ w 40 ðexw Þ40 ¼ 0 m

j¼

0.141 0.173 0.00028 0.223

e e e e

kg s1 kg s1 kg s1 kg s1 kg kg1
C1 Dimensionless J s1 J s1 J s1 Dimensionless J s1 J s1 J s1 J s1 Dimensionless

0.166% 0.166% 0.750% 1.346% 1.683% 0.00014% 2.597% 3.115% 2.983% 1.756% 2.075% 3.461% 4.532% 3.045% 1.894%

1.5  105 9.28  106 5.73  103 1.94  104 2.00 1.85 1141.90 761.45 380.44 7.499 227.91 97.02 49.91 80.98 5.267

In addition, exergy flow due to heat loss through the chamber of the dryer was identified as:

(39) The specific exergy of stuck products was computed as: exp

Nominal value

C C g s




   ðexw Þ4 ¼ hf ðT3 Þ  hg ðT0 Þ þ nf P3  Pg ðT3 Þ  T0 sf ðT3 Þ  sg ðT0 Þ

Pg ðT0 Þ ðva Þ23 þ þ T0 Rv ln 0 xv P0 2  1000



Comment

(40)

(41)

_ l¼ Ex

 1

 T0 _ Ql Tdc

(42)

where Tdc is the average temperature of drying chamber (K). Exergy efficiency of the spray drying process is the ratio of exergy use (investment) in the drying of the product to exergy of the drying air supplied (including the exergy of spraying air) to the system:

ðExergy investment in the evaporation of moisture in the productÞ  100 ðExergy of drying air supplied þ Exergy of spraying airÞ

(43)

Table 4 e Data obtained from drying experiments for fish oil microencapsulation by spray drying. Wall material WPC

WPI

SMP

80% WPI þ 20% MPC

80% WPI þ 20% NaCas

Inlet temperature (
C) 140 160 180 140 160 180 140 160 180 140 160 180 140 160 180

Outlet temperature (
C) 79.45 90.60 101.05 80.25 91.05 101.00 77.85 88.20 99.55 80.00 90.00 101.15 82.30 92.10 103.20

              

Average temperature of dryer chamber (
C)

0.65a 0.30b 0.15c 0.15a 0.25bh 0.30c 0.45d 0.70e 0.35f 0.30a 0.20b 0.25c 0.10g 0.30h 0.30i

Different superscripts in the same column indicate significant differences ( p < 0.05).

52.35 63.30 70.35 53.55 63.25 70.40 52.10 61.05 69.00 53.25 63.15 70.20 54.30 63.60 72.15

              

0.45a 0.40b 0.25c 0.15de 0.35b 0.10c 0.20a 0.25f 0.30g 0.25d 0.25b 0.20c 0.50e 0.30b 0.15h

Moisture content of finished product (%) 3.61 2.73 1.82 3.52 2.67 1.48 4.36 3.58 2.50 3.64 2.39 1.41 4.14 3.01 1.9

 0.14a  0.05bf  0.02c  0.00a  0.05bf  0.04c  0.17d  0.02a  0.07bf  0.14a  0.10ef  0.12c  0.03d  0.49b  0.22ce

237

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

j¼

 _ w Þev ðexw Þ3  ðexw Þ2 ðm  100 _ a Þ1 ðexa Þ1 þ ðm _ a Þ10 ðexa Þ10 ðm

(44)

where j is the exergy efficiency (%); (exw)3 is the specific exergy of water vapour at outlet air (kJ kg1).   ðexw Þ3 ¼ hðT3 ; Pv3 Þ  hg ðT0 Þ  T0 sðT3 ; Pv3 Þ  sg ðT0 Þ

Pg ðT0 Þ þ T0 Rv ln 0 xv P0

(45)

where h is the specific enthalpy of water vapour at known temperature and pressure (kJ kg1); s is the specific entropy of water vapour at known temperature and pressure (kJ kg1 K1); Pv3 is the vapour pressure of outlet drying air (kPa). Pv3 ¼ ðxv Þ3 P3

(46)

where (xv)3 is the mole fraction of vapour at outlet drying air (). The mole fraction of vapour was approximated as follows: xv ¼

uð1  0:622uÞ 0:622

_ ¼ IP

   j _ _ out Exin  Ex 1 100

(49)

_ in is the _ is the improvement potential rate (kJ s1); Ex where IP _ out is the total outlet exergy total inlet exergy rate (kJ s1); Ex rate (kJ s1). The reference-dead state conditions were considered as T0 ¼ 25
C, P0 ¼ 101.325 kPa, x0v ¼ 0:003211, and u0 ¼ 0.002 kg [Water] kg1 [Dry Air].

3.4.

Statistical analysis

The energetic and exergetic calculations of fish oil microencapsulation process by spray drying were carried out using Excel Ver.2007 (MS Office, 2007). A one-way analysis of variance (ANOVA) was performed using SPSS Statistics 15.0 (SPSS Inc., Chicago, IL, USA) software to evaluate the effect of the drying temperatures and wall material on the parameters studied. Differences among mean values were examined using the least significant difference (LSD) and Duncan’s multiple range test at p < 0.05 significance level.

(47)

where xv is the mole fraction of vapour at known humidity ratio (); u is the humidity ratio of air at known condition (kg [Water] kg1 [Dry Air]). The exergy destroyed or the irreversibility was expressed as follows: _ des ¼ T0 S_ gen Ex

(48)

where S_ gen is the entropy generation rate (kJ s1 K1). Van Gool (1997) proposed that maximum improvement in the exergy efficiency for a process or system was obviously achieved when the exergy loss or irreversibility was minimised. Consequently, he suggested that it was useful to use the concept of an exergetic “improvement potential” when analysing different processes or sectors of the economy and this improvement potential in the rate form was given by Hammond & Stapleton (2001).

4.

Results and discussion

Uncertainties in the experimental measurements and total uncertainties for the predicted values are listed in Table 3. It was determined that all uncertainties were within an acceptable range. The specific heat of product and water were obtained according to Tables 1 and 2 and were used in calculations. The energy and exergy analysis of the spray drying system was carried out by using the data obtained from the experiments conducted at various drying air temperatures for oil-in-water (O/W) emulsions with different aqueous phases. Exergy analysis of drying systems provides useful insight into many facet of drying systems including destroyed exergy and generated entropy in drying process, the optimum operation condition, and fuel management. In a typical spray drying process, atomisation of the feed into fine spray generates large

Table 5 e Results of inlet, outlet, lost energy, and energy efficiency of fish oil microencapsulation by spray drying. Wall material WPC

WPI

SMP

80% WPI þ 20% MPC

80% WPI þ 20% NaCas

T (
C) 140 160 180 140 160 180 140 160 180 140 160 180 140 160 180

E_ in ðJ s1 Þ a

1002.717 1075.958b 1141.904c 1002.718a 1075.959b 1141.905c 1002.645a 1075.885b 1141.831c 1002.708a 1075.948b 1141.894c 1002.708a 1075.948b 1141.894c

Q_ l ðJ s1 Þ

E_ out ðJ s1 Þ 687.984 726.801 761.264 689.315 731.262 761.165 674.342 708.681 751.285 687.224 724.690 760.793 707.654 737.232 772.615

              

a

3.105 3.100b 0.190c 0.072a 0.094bf 0.034c 3.200d 3.560e 2.714g 3.591a 0.011b 0.419c 3.512e 0.166f 0.153h

Different superscripts in the same column indicate significant differences ( p < 0.05).

314.732 349.156 380.639 313.403 344.695 380.739 328.302 367.203 390.545 315.482 351.257 381.100 295.053 338.714 369.278

              

h (%) a

3.105 3.100b 0.190c 0.072a 0.094bg 0.034c 3.200d 3.560e 2.714f 3.591a 0.011b 0.419c 3.512h 0.166g 0.153e

8.528 7.950 7.501 8.516 7.953 7.509 8.516 7.936 7.505 8.518 7.934 7.499 8.547 7.952 7.486

              

0.003ad 0.000b 0.002c 0.000a 0.006b 0.000c 0.000a 0.011b 0.019c 0.013a 0.011b 0.000c 0.009d 0.002b 0.017c

238

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

surface area to facilitate both heat and mass transfer (Dalamaz, Ozbelge, Eraslan, & Uludag, 2007). It also makes it one of the most exergy-destructive and entropy-generative processes. The outlet temperature, average temperature of drying chamber and moisture content of produced microcapsule obtained from drying experiments for different wall materials at different inlet drying air temperatures are given in Table 4. It is clear that increasing the inlet drying air temperature increased ( p < 0.05) the outlet temperature and the average temperature of the drying chamber but it decreased ( p < 0.05) the moisture content of finished product. The inlet energy, outlet energy, heat loss from drying chamber and energy efficiency of the spray drying process of fish oil microencapsulation are presented in Table 5. Inlet energy values varied between 1002.64 and 1141.90 J s1 and increased ( p < 0.05) as the drying air temperature increased. The type of wall material did not significantly ( p > 0.05) influence the inlet energy due to the negligible value of product energy at the inlet state and smaller difference in specific heat of different wall materials. The inlet drying air temperature significantly increased ( p < 0.05) the outlet energy (Table 5). The results indicated that the outlet energy for emulsion prepared with 80% WPI þ 20% NaCas was the highest ( p < 0.05), followed by emulsions prepared with WPI, WPC, 80% WPI þ 20% NaCas, and SMP, respectively. It is obvious from Table 5 that the energy loss from drying chamber to ambient varied between 295.05 and 390.54 J s1 and increased as the inlet drying air temperature increased, probably due to the increase in overall heat transfer coefficient from drying chamber at higher drying temperatures. Energy loss during drying of emulsion formulated with SMP was the highest ( p < 0.05) and for emulsion formulated with 80% WPI þ 20% NaCas was the lowest ( p < 0.05), since the energy loss to environment was inversely related to the total outlet energy from drying chamber, according to Eq. (5). The energy efficiency for fish oil microencapsulation process by spray drying ranged from a minimum value of

7.48% to a maximum value of 8.54%. Increase in inlet drying air temperature at constant feed rate decreased ( p < 0.05) the energy efficiency because of inverse relation between energy efficiency and energy of inlet drying air, according to Eq. (26). The type of wall material did not influence the energy efficiency. It was attributed to the identical amount of applied solvent during preparation of the aqueous phase and the negligible difference in the final moisture content of finished product. Therefore, according to Eq. (26), the type of wall material did not lead to significant differences in the magnitude of invested energy for water evaporation from atomised droplets and correspondingly energy efficiency. The total inlet exergy of drying systems at different drying air temperatures and emulsions formulated with various wall materials is presented in Table 6. The inlet exergy values varied between 166.46 and 227.91 J s1 and increased ( p < 0.05) as the drying air temperature increased. This could be related to the higher entering energy to drying chamber at higher drying air temperatures. The type of wall material did not significantly ( p > 0.05) influence the inlet exergy, for same reasons previously stated for inlet energy. The outlet exergy values increased ( p < 0.05) as the inlet drying air temperature increased (Table 6). It was observed that the outlet exergy for emulsion formulated with SMP was lower ( p < 0.05) than those for emulsions with WPC, WPI, and 80% WPI þ 20% MPC. The outlet exergy for emulsion formulated with 80% WPI þ 20% NaCas as the wall material was the highest. These results could be attributed to droplet/particle size, emulsion composition, and rheological properties of emulsion. The average particle size of generated microcapsule is reported in Table 7. From this table, it is clear that SMPcoated microcapsules are the largest followed by capsules coated with WPI, WPC, 80% WPI þ 20% MPC and 80% WPI þ 20% NaCas. It could be argued that the lower content of protein component and presence of disaccharide lactose in chemical composition of SMP manifested themselves in the composition of emulsions (Table 1) and had a significant role in generating somewhat larger microcapsules. The

Table 6 e Results of inlet, outlet, destructed and lost exergy, entropy generation and exergy efficiency of fish oil microencapsulation by spray drying. _ in ðJ s1 Þ _ out ðJ s1 Þ _ l ðJ s1 Þ _ des ðJ s1 Þ Ex Ex Ex Ex Sgen ðJ s1 K1 Þ j (%) Wall material T (
C) WPC

WPI

SMP

80% WPI þ 20% MPC

80% WPI þ 20% NaCas

140 160 180 140 160 180 140 160 180 140 160 180 140 160 180

166.461a 196.673b 227.919c 166.461a 196.673b 227.919c 166.461a 196.673b 227.918c 166.461a 196.673b 227.919c 166.461a 196.673b 227.919c

76.125 86.345 96.971 76.540 87.003 97.008 73.935 83.004 95.210 76.039 85.870 97.105 78.811 88.297 99.576

              

0.485a 0.581b 0.053c 0.006a 0.075b 0.009c 0.334d 0.606e 0.532f 0.758a 0.062b 0.017c 0.206g 0.013h 0.069i

26.147 39.029 49.454 26.918 38.983 49.951 27.274 39.578 50.245 27.096 39.260 49.998 26.571 38.752 50.307

              

0.257a 0.808b 0.458c 0.006a 0.010b 0.004c 0.265a 0.383b 0.349c 0.308a 0.463b 0.054c 0.093a 0.426b 0.020c

Different superscripts in the same column indicate significant differences ( p < 0.05).

64.188 71.298 81.493 63.003 70.687 80.959 65.252 74.090 82.463 63.325 71.542 80.814 61.078 69.623 78.035

              

0.227a 0.226b 0.512c 0.000d 0.064b 0.004c 0.068e 0.222f 0.183g 0.449d 0.526b 0.037c 0.112h 0.440i 0.048j

0.215 0.239 0.273 0.211 0.237 0.271 0.218 0.248 0.276 0.212 0.240 0.271 0.204 0.233 0.261

              

0.000a 0.000b 0.001c 0.000d 0.000b 0.000c 0.000e 0.000f 0.000g 0.001d 0.001b 0.000c 0.000h 0.001i 0.000j

7.405 6.168 5.266 7.393 6.170 5.271 7.393 6.157 5.269 7.395 6.156 5.265 7.421 6.169 5.255

 0.002ad  0.000b  0.001c  0.000a  0.004b  0.000c  0.000a  0.008b  0.013c  0.011a  0.009b  0.000c  0.008d  0.002b  0.011c

239

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Table 7 e Particle size of fish oil microcapsules obtained using different wall materials. Drying air temperature (
C)

Particle size (mm) Wall material

140

WPC WPI SMP 80% WPI þ 20% MPC 80% WPI þ 20% NaCas

2.26  2.38  3.09  1.68  1.37 

160 a

0.029 0.005b 0.004e 0.006h 0.007j

2.39 2.76 3.78 2.04 1.41

    

180 b

0.014 0.014d 0.010f 0.024i 0.010j

2.62 3.10 4.59 2.41 1.53

 0.007c  0.004e  0.017g  0.011b  0.012k

Different superscripts indicate significant differences ( p < 0.05).

previously for the outlet exergy. It is noteworthy that in spray drying process, the major part of exergy entering the drying chamber destroyed due to an intensive increase in transport phenomena generated via atomisation of liquid into fine spray. The entropy generating during spray drying process of fish oil microencapsulation is shown in Table 6. Entropy generation in a spray dryer can be due to heat transfer, mass transfer, body force, and vaporisation (Jin & Chen, 2011). The entropy generation varied between 0.2049 and 0.2767 J s1 K1 and higher inlet drying temperatures resulted in higher entropy generation ( p < 0.05), probably because of more rapid droplet/ particle drying and higher heat transfer coefficients. Jin and Chen (2011) indicated that the entropy generation rate due to heat transfer between the two phases is the most important component in the total entropy generation rate. Also, they concluded that the next most significant contributions to total entropy generation rate results from entropy generation rate to mass transfer between the two phases, gas phase viscous dissipation, gas phase heat transfer and gas phase mass transfer. Table 6 reports the exergy efficiency of fish oil microencapsulation process by spray drying using different wall materials. It is obvious from this table that the exergy efficiencies in the temperatures studied ranged from 5.25 to 7.42%. It is also evident that the spray drying process is not exergy efficient process. Comparison between the energy efficiency value (Table 5) with exergy efficiency value (Table 6) at same conditions shows that the exergy efficiency was lower

130 Improvement potential (J s 1)

significantly lower protein content caused a lower amount of bound water in aqueous phase producing a lower viscosity for the emulsion. This accelerated the evaporation rate of water from the droplet and diffusion rate of substances inside the droplet at the early instances of drying. The rapid accumulation of water soluble ingredients near the droplet surface may have progressively caused the early formation of a crust structure preventing further shrinkage of particles during drying. On the other hand, the presence of lactose in chemical composition of SMP hastens the crust formation by changing the drying properties of the wall. This occurs through the formation of a continuous glass phase of lactose at droplet surface in which the protein chains are dispersed (Gharsallaoui et al., 2007). The crust encloses moisture within the bulk of the solid, so that, the interior moisture cannot be easily removed. Therefore, the major portion of the supplied exergy to drying chamber was destroyed by moisture evaporation from the crust-reinforced particle and the outlet exergy decreased, correspondingly. Jin and Chen (2011) numerically computed entropy generation for droplet/ particle drying with different sizes and conclude that the increase in droplet/particle size increased the entropy generation and correspondingly exergy destruction. The composite wall material solution of WPI and NaCas had visually a higher consistency inferring that it was more viscous nature and had high amounts of bound water because of its higher protein content. This was likely to reduce the molecular diffusion rate inside the atomised droplets and reduced the migration of crust-forming materials to the particle surface which in turn postponed the crust formation and thus the shrunk particles with smaller sizes were obtained. The moisture of droplet/particle easily evaporated and exergy destruction was relatively low. The exergy loss to environment from drying chamber for fish oil microencapsulation by spray drying at the conditions studied was in the range of 26.14e50.3 J s1 (Table 6). The exergy loss to environment increased ( p < 0.05) as the inlet drying air temperature increased because of an increase in the energy loss from drying chamber at higher drying temperatures. The effect of wall material type on exergy loss to environment was not statistically significant ( p > 0.05). As reported in Table 6, the exergy destruction varied between 61.07 and 82.46 J s1 for fish oil microencapsulation process by spray drying process, indicating that the process is extremely exergy-destructive. The exergy destruction increased ( p < 0.05) as the inlet drying air temperature increased, due to an increase in heat and mass transfer coefficient between drying media and droplets entered to drying chamber. On the other hand, producing microcapsules with slightly larger size at higher drying air temperatures (Table 7) might play an important role in the destruction of the major part of supplied exergy to drying chamber. Higher evaporation rates at higher drying temperatures rapidly forms a dry crust and prevents more shrinkage of particles during drying. This could produce somewhat larger capsules as the inlet drying air temperature is raised. Thus, the main part of supplied exergy to drying chamber destructed for evaporation of moisture from earlyskinned particle. The wall material type had a significant effect ( p < 0.05) on exergy destruction, as explained

120 110

WPC WPI SMP 80%WPI+20%MPC 80%WPI+20%NaCas

100 90 80 120

140

160

180

200

Temperature (C)

Fig. 4 e The variation of improvement potential rate value with drying temperature and wall material of fish oil microencapsulation process by spray drying.

240

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

( p < 0.05) than the energy efficiency for all inlet drying temperatures and wall materials. The main reason for the low exergy efficiency is the high inlet drying temperature in the spray drying operation and the considerably small amount of water removed in drying chamber compared to supplied exergy. According to Table 6, exergy efficiency was significantly ( p < 0.05) influenced by drying air temperature. At constant feed rate, the higher the drying air temperature, the lower was the exergy efficiency noteworthy due to inverse relation of exergy efficiency with the exergy of drying air, according to Eq. (43). The exergy efficiency was not influenced ( p > 0.05) by wall material type, probably due to same reason given for energy efficiency. One possible solution to avoiding this high irreversibility is to change the dryer operation conditions and to optimise the drying process by considering the final product quality. Using Eq. (49), the improvement potential proposed by Van Gool (1997) was calculated for the temperatures and wall materials studied and results obtained are illustrated in Fig. 4. Improvement potentials were found to range from 81.41 to 125.71 J s1 for the analysed temperatures accounting for 48.62e55.37% of the inlet exergy. The spray drying process therefore offers a big potential for improving the exergy efficiency. It is clear that conscious and planned efforts are required to improve exergy utilisation in the spray drying process. According to the results, it is important to reduce irreversibilities in the drying chamber and exergy loss from dryer frame to improve the system performance. It is worth noting that increasing water removal from generated droplets/ particles at useable lower drying air temperatures can be used to enhance the exergetic efficiency of the spray drying process. Irreversibilities in the drying chamber could occur due to liquid atomisation, heat and mass transfer, and vaporisation. Therefore, the use of other types of atomising nozzle and spray dryer systems, changing the mass flow rate of liquid and drying air, optimising the liquid feed temperature, and selection of the most appropriate drying conditions have all been suggested as ways of increasing spray dryer exergy efficiency. Also, most industrial spray dryers are scaled up from laboratory spray dryers. The scale-up of spray drying processes are mainly based on experimental data obtained from laboratory dryers. The spray drying process is usually scaled up based on thermodynamic, fluid dynamic, drying kinetics considerations, particle formation, and atomisation principles. Therefore, the presented exergetic analysis could be used to determine the appropriate drying conditions to reach the optimal exergy efficiency in industrial spray drying systems.

5.

Conclusion

Spray drying process is a thermal energy consuming operation. The energy and exergy efficiency values during the spray drying process of fish oil microencapsulation were found between 7.48e8.54% and 5.25e7.42%, respectively, for the inlet drying air temperature of 180
C and 140
C. The present study showed that the exergetic efficiency of spray drying process is very poor and lower than the energetic efficiency. This low

exergetic efficiency is mainly due to the higher inlet drying air temperatures prevalent in spray drying operation and the lower amount of invested exergy for moisture removal from atomised spray compared to the supplied exergy introduced into the drying chamber. The lost exergy from drying chamber and destroyed exergy accounted 15.90e22.19% and 34.21e39.24% of total inlet exergy, respectively. Although the results indicated that the spray drying process of fish oil microencapsulation had low exergy efficiency, the improvement potential rate showed a high possibility to improve the exergetic performance of process with the rate of 81.41e125.71 J s1. This suggests that for a more sustainable spray drying process, other methods of liquid atomisation and other drying conditions should be examined. It is necessary to carry out exergetic analyses for other spray drying systems to improve the sustainability of the process.

Acknowledgement The authors thank the University of Tehran for its financial support.

references

Aghbashlo, M., Kianmehr, M. H., & Arabhosseini, A. (2008). Energy and exergy analyses of thin-layer drying of potato slices in a semi-industrial continuous band dryer. Drying Technology, 26(12), 1501e1508. Aghbashlo, M., Kianmehr, M. H., & Arabhosseini, A. (2009). Performance analysis of drying of carrot slices in a semiindustrial continuous band dryer. Journal of Food Engineering, 91(1), 99e108. Akpinar, E. K., & Sarsilmaz, C. (2004). Energy and exergy analyses of drying of apricots in a rotary solar dryer. International Journal of Exergy, 1(4), 457e474. Anwar, S. H., & Kunz, B. (2011). The influence of drying methods on the stabilization of fish oil microcapsules: comparison of spray granulation, spray drying, and freeze drying. Journal of Food Engineering, 105(2), 367e378. Brooker, D. B. (1967). Mathematical model of the psychometric chart. Transactions of ASAE, 10(4), 563. Cay, A., Tarakcioglu, I., & Hepbasli, A. (2009). A study on the exergetic analysis of continuous textile dryer. International Journal of Exergy, 6(3), 422e439. Cay, A., Tarakcioglu, I., & Hepbasli, A. (2010). Exergetic analysis of textile convective drying with stenters by subsystem models: part 1 e exergetic modeling and evaluation. Drying Technology, 28(12), 1359e1367. Choi, Y., & Okos, M. R. (1986). Effects of temperature and composition on the thermal properties of foods. In L. Maguer, & P. Jelen (Eds.), Food engineering and process applications. Transport phenomenon, Vol. 1 (pp. 3e101). New York: Elsevier. Chowdhury, M. M. I., Bala, B. K., & Haque, M. A. (2011). Energy and exergy analysis of the solar drying of jackfruit leather. Biosystems Engineering, 110(2), 222e229. Dalamaz, N., Ozbelge, H. O., Eraslan, A. N., & Uludag, Y. (2007). Heat and mass transfer mechanisms in drying of a suspension droplet: a new computational model. Drying Technology, 25(2), 391e400.

b i o s y s t e m s e n g i n e e r i n g 1 1 1 ( 2 0 1 2 ) 2 2 9 e2 4 1

Desai, K. G. H., & Park, H. J. (2005). Recent developments in microencapsulation of food ingredients. Drying Technology, 23(7), 1361e1394. Dincer, I., & Sahin, A. Z. (2004). A new model for thermodynamic analysis of a drying process. International Journal of Heat and Mass Transfer, 47(4), 645e652. Drusch, S., Serfert, Y., Scampicchio, M., Schmidt-Hansberg, B., & Schwarz, K. (2007). Impact of physicochemical characteristics on the oxidative stability of fish oil microencapsulated by spraydrying. Journal Agriculture and Food Chemistry, 55(26), 11044e11051. Erek, A., & Dincer, I. (2009). A new approach to energy and exergy analyses of latent heat storage unit. Heat Transfer Engineering, 30(6), 506e515. Fang, Z., & Bhandari, B. (2010). Encapsulation of polyphenols e a review. Trends in Food Science & Technology, 21(10), 510e523. Gharsallaoui, A., Roudaut, G., Chambin, O., Voilley, A., & Saurel, R. (2007). Applications of spray-drying in microencapsulation of food ingredients: an overview. Food Research International, 40, 1107e1121. Gungor, A., Erbay, Z., & Hepbasli, A. (2011). Exergetic analysis and evaluation of a new application of gas engine heat pumps (GEHPs) for food drying processes. Applied Energy, 88(3), 882e891. Hammond, G. P., & Stapleton, A. J. (2001). Exergy analysis of the United Kingdom energy system. Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 215(2), 141e162. Hancioglu, E., Hepbasli, A., Icier, F., Erbay, Z., & Colak, N. (2010). Performance investigation of the drying of parsley in a tray dryer system. International Journal of Exergy, 7(2), 193e210. Hepbasli, A., Erbay, Z., Colak, N., Hancioglu, E., & Icier, F. (2010). An exergetic performance assessment of three different food driers. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 224(1), 1e12. Hogan, S. A., O’Riordan, E. D., & O’Sullivan, M. (2003). Microencapsulation and oxidative stability of spray-dried fish oil emulsions. Journal of Microencapsulation, 20(5), 675e688. Holman, J. P. (2001). Analysis of experimental data. In J. P. Holman (Ed.), Experimental methods for engineers (7th ed.). (pp. 48e143) Singapore: McGraw-Hill. Icier, F., Colak, N., Erbay, Z., Kuzgunkaya, E. H., & Hepbasli, A. (2010). A comparative study on exergetic performance assessment for drying of broccoli Florets in three different drying systems. Drying Technology, 28(2), 193e204. Jin, Y., & Chen, X. D. (2011). Entropy production during the drying process of milk droplets in an industrial spray dryer. International Journal of Thermal Sciences, 50(4), 615e625. Kagami, Y., Sungimura, S., Fujishima, N., Matsuda, K., Kometani, T., & Matsumura, Y. (2003). Oxidative stability,

241

structure, and physical characteristics of microcapsules formed by spray drying of fish oil with protein and dextrin wall materials. Journal of Food Science, 68(7), 2248e2255. Keogh, M. K., O’Kennedy, B. T., Kelly, J., Auty, M. A., Kelly, P. M., Fureby, A., et al. (2001). Stability to oxidation of spray-dried fish oil powder microencapsulated using milk ingredients. Journal of Food Science, 66(2), 217e224. Klaypradit, W., & Huang, Y.-W. (2008). Fish oil encapsulation with chitosan using ultrasonic atomizer. LWT-Food Science and Technology, 41(6), 1133e1139. Kolanowski, W., Ziolkowski, M., Weißbrodt, J., Kunz, B., & Laufenberg, G. (2006). Microencapsulation of fish oil by spray drying-impact on oxidative stability. Part 1. European Food Research and Technology, 222(3e4), 336e342. Madadlou, A., Mousavi, M. E., Emam-Djomeh, Z., Ehsani, M., & Sheehan, D. (2009). Sonodisruption of re-assembled casein micelles at different pH values. Ultrasonics Sonochemistry, 16(5), 644e648. Moran, M. J., & Shapiro, H. N. (1995). Fundamentals of engineering thermodynamics. New York: Wiley. Ozgener, L., & Ozgener, O. (2006). Exergy analysis of industrial pasta drying process. International Journal of Energy Research, 30(15), 1323e1335. Ozgener, L., & Ozgener, O. (2009a). Exergy analysis of drying process: an experimental study in solar greenhouse. Drying Technology, 27(4), 580e586. Ozgener, L., & Ozgener, O. (2009b). Parametric study of the effect of reference state on energy and exergy efficiencies of a small industrial pasta drying process. International Journal of Exergy, 6(4), 477e490. Shahidi, F., & Han, X. Q. (1993). Encapsulation of food ingredients. Critical Review in Food Science and Nutrition, 33(6), 501e547. Singh, R. P., & Heldman, D. R. (2001). Introduction to food engineering (3rd ed.). Academic Press. (Food Science and Technology). Syahrul, S., Hamdullahpur, F., & Dincer, I. (2002). Exergy analysis of fluidized bed drying of moist particles. Exergy, an International Journal, 2(2), 87e98. Tambunan, A. H., Manalu, L. P., & Abdullah, K. (2010). Exergy analysis on simultaneous charging and discharging of solar thermal storage for drying application. Drying Technology, 28(9), 1107e1112. Tiwari, G. N., Das, T., Chen, C. R., & Barnwal, P. (2009). Energy and exergy analyses of greenhouse fish drying. International Journal of Exergy, 6(5), 620e636. Van Gool, W. (1997). Energy policy: fairy tales and factualities. In O. D. D. Soares, Martins da Cruz, Coasta Pereira, I. M. R. T. Soares, & A. J. P. S. Reis (Eds.), Innovation and technology-strategies and policies (pp. 93e105). Dordrecht: Kluwer.