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Measurement of properties of a lithium bromide aqueous solution for the determination of the concentration for a prototype absorption machine
Accepted Manuscript Research Paper Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine L. Labra, D. Juárez-Romero, J. Siqueiros, A. Coronas, D. Salavera PII: DOI: Reference:
S1359-4311(16)32758-2 http://dx.doi.org/10.1016/j.applthermaleng.2016.10.162 ATE 9364
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
7 January 2016 25 October 2016 25 October 2016
Please cite this article as: L. Labra, D. Juárez-Romero, J. Siqueiros, A. Coronas, D. Salavera, Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine, Applied Thermal Engineering (2016), doi: http://dx.doi.org/10.1016/j.applthermaleng. 2016.10.162
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Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2 *
Centro de Investigación en Ingenierías y Ciencias Aplicadas (CIICAp), Universidad Autónoma del Estado de Morelos (UAEM), México. Av. Universidad 1001, Chamilpa, Cuernavaca 62209, Morelos, México. e-mail; [email protected]. 1 Consejo de Ciencia y Tecnologia del Estado de Morelos Av. Atlacomulco No. 13. Esq. Calle de la Ronda Col. Acapantzingo,Mor. C.P. 62440 Tel.: [52] 777-3121222, México.e-mail:[email protected] 2 Departamento de Mecánica, Centro de Innovación en Recuperación de Energía y Refrigeración (CREVER), Universidad Rovira i Virgili, Tarragona, España.e:mail:{[email protected] , [email protected]}
_________________________________________________________________________ ABSTRACT An electrolyte solution of Lithium Bromide (LiBr) water was chosen for study because of its wide use in prototype absorption machines. The LiBr must be operated close to the temperature and mass fraction at which lithium bromide achieves the highest efficiency. For the purpose of establishing the concentration in a prototype absorption machines, measurements were made of the properties that vary with temperature and concentration. The selected properties are electrical conductivity, density, refractive indexes and sound velocity. The resulting measured properties values were compared with some values found in previous works. The properties of aqueous lithium bromide solutions were measured at the concentration range of 45 to 65 % of LiBr and temperatures range of 20 to 80 °C. Semi-empirical correlations that determine the properties of lithium bromide are also proposed. The methods for measuring the properties of aqueous solutions were considered taking into account their reliability, simplicity and sampling time. Keywords: LiBr solution, measurement, properties, prototype absorption machines. ________________________________________________________________________________________
1. Introduction Aqueous lithium bromide is one of the best choices as working fluid in absorption heat transformers, and absorption refrigerating machines [1, 2 and 3]. The prototype absorption machine consists of, a generator, a condenser, an evaporator and an absorber. A key component of these machines is the absorber. In this component, the concentration of lithium bromide (LiBr) changes inside the absorber by absorbing vapor from the evaporator. The concentration of the aqueous lithium bromide solution plays a significant role in the performance of such system. Therefore, it is necessary to obtain the concentration of the aqueous solution of lithium bromide in the absorber and in the generator, in both components circulate the LiBr solution [4, 5, 6 and 7]. Table 1 shows a list
1
of reported experimental data properties of the LiBr solution at different intervals of concentrations and temperatures, employing different measurement techniques. 1
-
- Table 1 around here - -
The LiBr solution must be operated close to the temperature and mass fraction at which lithium bromide crystallizes in order to achieve the highest efficiency in a prototype absorption machine. The objective of the present study is to measure the properties of the LiBr solution as a function of temperature and concentration; to evaluate their reliability and feasibility as a real-time monitoring method for determination of the concentration of LiBr. Variables such as the reflow ratio
FR
WRfr WAB
X GE X AB are useful performance indices, since the higher the ratio, the higher the X GE
heat released in the absorber We report measurements of the properties of density, electrical conductivity, refractive index and the sound velocity of the LiBr solution to a temperature range from 20 to 80 ° C and a concentration range from 45 to 65%. This interval is considered for study because prototype absorption machine operates under these conditions.
Heinonen and Tapscott [15] analyzed property-sensor for LiBr. The evaluated criteria were: estimated cost of the sensor, precision to determine the mass fraction, availability of instrument, reliability of the measurement and experimental data reported in the literature. They concluded that the sensors that measure the properties of refractive index, electrical conductivity, density and sound velocity are sensors that can be considered with optimal performance in the measurement of the properties.
2. Experimental process 2.1 Sample Preparation As the lithium bromide is extremely hygroscopic, it is important to follow a procedure to ensure that no moisture from the atmosphere is absorbed unintentionally when the measuring samples are being prepared. The LiBr was obtained from Sigma-Aldrich Company with a mass fraction purity ≥ 99 %. It was used after heating the salt to T= 383 K in an electrical oven for about 24 h and cooling it to the room temperature in a desiccator containing silica gel to remove traces of water. A digital mass balance was used to measure the masses of LiBr and a milliq water. All solutions were prepared as percent by weight (% wt) of LiBr, with uncertainty in the preparation of the solutions within ± 0.0002 %wt LiBr.
* Corresponding author. Tel: +52 777 3297084; e-mail address: [email protected] (D. Juarez-Romero)
2
2.2 Principle of Measurement of Electrical Conductivity The electrical conductivity of liquids is the measure the ions present in a solution for to transport electrical current. The electrical conductivity, k (S cm-1) is expressed in terms of the geometry of the cell conductivity (area of the electrodes and distance between them) and electrical resistivity. The principle of measurement is based on applying a potential difference between two inert electrodes of a specific surface, placed at a distance, L, introduced in the electrolytic solution. A potential gradient is generated, whereby each ion moves toward the electrode with opposite direction. Due to the charge associated with the ions, this displacement will produce an electric current.
2.2.1 Apparatus and Procedure The electrical conductivity of LiBr solution was continuously measured with a Basic 30 Crison conductivity meter, coupled to a glass conductivity cell model 5298 with constant (k=10). The conductivity meter has an electrical conductivity measurement range from 0.01 µS cm-1 to 1000 mS cm-1 with resolution 0.01 S and accuracy ± 0.1 %. The solution temperature was measured using an Anton Paar MKT 100 precision thermometer, with resolution 0.001 °C. The coupling cell conductivity and conductivity meter were calibrated with a standard solution of 0.1 M potassium chloride at room temperature. The precision thermometer was previously calibrated. The estimated uncertainty in the measurement of electrical conductivity of LiBr solutions is within ± 3.68 mS cm1 . The procedure was to place a volume approximately 12 ml of LiBr solution in an Erlenmeyer glass flask, with a magnetic stirrer, a precision temperature sensor and a cell with three electrodes. The system was insulated to prevent heat losses. A thermal bath was used to heat the LiBr solution contained in an Erlenmeyer glass flask. The measurement LiBr solution was carried out at a temperature of 30 °C and heated up to 80 °C. Electrical conductivity measurements were taken after to reach steady state. The sampling time was approximately 30 minutes for each temperature. The measurements were performed in a laboratory at ambient conditions.
2.3 Principle of Measurement of Refractive Index The refractive index is the measure of the change of the speed of light when passing from one medium to another. The refractive indexes, nD is dimensionless. The principle of measurement is based on the velocity change experienced by the electromagnetic radiation passing from one medium to another, as a result of its interaction with atoms and molecules the other means. Said velocity change is manifested in a variation in the propagation direction, using two prisms: one fixed light on which the sample is deposited and one mobile refractive.
2.3.1 Apparatus and Procedure
3
Index refractive of LiBr solution was continuously measured with a RXA170 Anton Paar Abbemat refractometer. The Abbemat refractometer has a refractive index measurement range from 1.3 to 1.7 with resolution 1*10-6 nD and accuracy ± 4*10 -5 nD. The solution temperature was measured using a cell with a built-in temperature meter, with resolution 0.03 °C. The Abbemat refractometer was previously calibrated. The estimated uncertainty in the measurement of refractive indexes of LiBr solutions is within ± 0.00005 nD. The procedure was to place a volume of LiBr solution of approximately 4 ml in the refractometer, through a fill tube via a syringe. The measurement LiBr solution was carried out at a temperature of 20 °C and heated up to 70 °C. The refractive indexes measurements were taken after reaching steady state. The sampling time was approximately 6 minutes. The measurements were performed in a laboratory at ambient conditions.
2.4 Principle of Measurement Density and Sound Velocity The density is the measure of the amount of matter that has a substance in a given volume. The density ρ (g cm-3), is expressed in terms mass of the substance per unit volume. The sound velocity is the dynamics of propagation of sound waves. The sound velocity ν (m s-1), is expressed in terms of length per unit of time. The sound velocity and density of the solution were determined by sound velocity and density meter U-shaped tube. The principle of measurement is based on a U-shaped tube of metal or glass containing the measurement sample that is electromagnetically activated to vibrate at its resonant frequency in a U-shaped tube. This resonant frequency is a function of material construction, geometry of the tube and the mass of the tube assembly (consisting of the tube itself and the fluid in the tube). As the volume is kept constant, the density is determined. The sound velocity is determined as a function of the density and the compressibility factor of the molecules present in the sample.
2.4.1 Apparatus and Procedure Density and sound velocity of LiBr solution were continuously measured with an Anton Paar DSA 5000 sound velocity and density meter. The density and sound velocity meter have a density and sound velocity measurement ranges from 0 to 3 g cm-3 and 1000 to 2000 ms -1, with resolutions 1*10-7 g cm-3 and 0.1 ms-1 respectively. The solution temperature was measured using a cell with a built-in temperature meter, with resolution 1*10-3 °C. The density and sound velocity meter was previously calibrated. The estimated uncertainty in the measurement density of LiBr solutions is within ± 0.00007 g cm-3 and ± 0.5 m s-1 for measurements of the sound velocity. The procedure was to place a volume of LiBr solution of approximately 4 ml in the density and sound velocity meter, through a fill tube via a syringe. The measurement LiBr solution was carried out at a temperature of 20 °C and heated up to 70 °C. The density and sound velocity measurement were taken after to reach steady state. The sampling time was approximately 12 minutes for sound velocity and 15 minutes for density. The measurements were performed in a laboratory at ambient conditions.
4
3. Results and discussion 3.1 Electrical Conductivity The electrical conductivity of the LiBr solution was measured in a temperature range and concentration from 35 to 80 ° C and 45 to 65 % wt LiBr respectively. The experimental electrical conductivity data of LiBr solutions at different temperatures and concentrations are summarized in Tables 2, while the trend presented with respect to temperature and concentration are plotted in Figure 1. --- Table 2 around here---- Figure 1. around here-The increase in electrical conductivity occurs when the temperature increases, this is because the viscosity of the LiBr solution decreases, favoring ions mobility and therefore the electric charge transport [16]. For this range of measurement, the electrical conductivity presents a linear behavior with respect to temperature. It graphically shows that at concentrations up to 55 wt% LiBr, increased electrical conductivity with respect to variation in temperature is greater than at concentrations above 55 wt% LiBr. This is due to the excess of dissolved ions from that concentration, producing saturation of the LiBr solution, therefore a decrease in the electrical conductivity. Some aspects that we consider in electrical conductivity measurements was to use a toroid cell with two electrodes to avoid the effect of polarization. The LiBr solution remained homogeneous during the measurement using a magnetic stirrer. Heat loss is prevented with an insulator. In Figure 2 is shown the comparison of experimental electrical conductivity data obtained in this study and presented by Fried & Segal [5]. Only was considered experimental values of electrical conductivity for two particular concentrations from 45 wt% LiBr and 55 wt% LiBr, these measurements were considered for similar conditions of measurement. Our experimental electrical conductivity data obtained in this work shows a good agreement with those presented by Fried & Segal. There is a difference of up to 13.2 % with the data obtained experimentally. --- Figure 2 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is presented in equation (1). (1) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the electrical conductivity. The coefficients obtained through the method of least squares, these coefficients are presented in Table 3, which are used in the correlation of the electrical conductivity, to determine the LiBr concentration. --Table 3 around here-5
3.2 Refractive Index The refractive index of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 % wt LiBr respectively. The experimental refractive indexes data of LiBr solutions at different temperatures and concentrations are summarized in Tables 4, while the trend presented with respect to temperature and concentration are plotted in Figure 3.
---Table 4 around here— --- Figure 3 around here -The refractive index decreases with increasing temperature, this is because the temperature has a great influence on the density of the medium causing a change in propagation velocity in the vacuum and in the sample, but tends to increase when the concentration increases. For this measurement range the refractive index has a linear behavior with respect to temperature. Zaltash & Ally [11] performed measurements refractive indexes with a refractometer for the temperature range of 5 to 80 ° C and concentration range of 0 to 59 wt% LiBr. They performed measurements of refractive index by coupling the thermal bath to a refractometer. While our experimental refractive index measurements were made only in the refractometer, which had the option of heating to the desired temperature, without the need for a thermal bath. In Figure 4 is shown the comparison of experimental refractive indexes data obtained in this study and presented by Zaltash & Ally[11]. Only were considered experimental values of refractive indexes for concentrations from 45 wt% LiBr, 50 wt% LiBr, and 55 wt% LiBr, these measurements were considered for similar conditions of measurement. Our experimental refractive indexes data obtained in this work shows a good agreement with those presented by Zaltash & Ally [11]. There is a difference of up to 0.2 % with the data obtained experimentally. --- Figure 4 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is presented in equation (2).
% LiBr A(T )nD 2 B(T )nD C (T ) (2) A(T ) ai ,1 ai ,2 x ai ,3 x 2 B(T ) bi ,1 bi ,2 x bi ,3 x 2 C (T ) ci ,1 ci ,2 x ci ,3 x 2 Where is the concentration of the solution of LiBr. T is temperature, x, is composition, and nD is the refractive index. The coefficients obtained through the method of least squares; these are presented in Table 5, which are used in the correlation of the refractive index, to determine the LiBr concentration.
----Table 5 around here-3.3 Density 6
The density of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 wt% LiBr respectively. The experimental density data of LiBr solutions at different temperatures and concentrations are summarized in Tables 6, while the trend presented with respect to temperature and concentration are plotted in Figure 5. --- Table 6 around here-----Figure 5 around here-The density decreases with increasing temperature, this is because that with the rise in temperature in the solution of LiBr atoms begin to vibrate and expand, taking more volume, but tends to increase with increasing concentration, because the mass is greater in the same sample volume. In Figure 6 is shown the comparison of experimental density data obtained in this study and presented by Fried & Segal [5], Wimby & Berntsson [12] and Lee et al [7]. Only was considered experimental values of density for concentrations from 45 wt% LiBr and 55 wt% LiBr These measurements were considered for similar conditions of measurement. Our experimental density data obtained in this work shows a good agreement with those presented by Fried & Segal [5], and Lee et al. [7] There is a difference of up to 3.4 % with the data obtained experimentally. ---Figure 6 --An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This relationship is presented in equation (3). (3) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the density. The coefficients obtained through the method of least squares; these are presented in Table 7, which are used in the correlation of the density, to determine the LiBr concentration. ---Table 7---
3.4
Sound Velocity
The sound velocity of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 wt% LiBr respectively. The experimental sound velocity data of LiBr solutions at different temperatures and concentrations are summarized in Tables 8, while the trend presented with respect to temperature and concentration are plotted in Figure 7. --- Table 8 around here— --- Figure 7 around here-The sound velocity presents a maximum with respect to the variation of temperature; that depends on concentration. For this measurement interval, the sound velocity has a parabolic comportment with respect to temperature. In the literature there is little information on the measurement sound velocity, there is experimental data reported by Rohman et al [13] on the sound velocity for range temperature and concentration 7
from 0 to 50 ° C and 0 to 55 % wt LiBr respectively. In Figure 8 is shown the comparison of experimental sound velocity data obtained in this study and presented by Rohman et al. [13]. Since the graph shows that the trends presented by our measurements the sound velocity according to the behavior are presented by Rohman et al. [13] --- Figure 8 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is relationship is presented in equation (4). (4) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the sound velocity. The coefficients obtained through the method of least squares, these are presented in Table 9, which are used in the correlation of the sound velocity, to determine the LiBr concentration. ---Table 9 around here---
3.5
Normalized Comparison of Density, Electrical Conductivity and Refractive index.
Figure 9 shows the comparison of temperature with respect to electrical conductivity, density and refractive index with shifted scales x ( x xmin ) for dependent and normalized scales for dependent variables, ie. y ( y ymin ) / ( ymax ymin ) For these properties, a linear trend occurs with respect to temperature and composition. From this figure it is appreciated that the electrical conductivity is more sensible to temperature variations, compared with the density and refractive index. Changes of density and refractive index with respect to temperature variation are very similar. ---Figure 9 around here--
4. Conclusions Experimental data of the properties of electrical conductivity, refractive indexes, density and sound velocity of LiBr solution at different temperatures and concentration were obtained. They show a good agreement with previously published data found in the literature. The proposed equations to determine the LiBr concentration, apply mainly in the next measurement interval: 45 to 60% for the concentration and from 50 to 70 ° C for the temperature. It is noteworthy that the only property that is not considered appropriate to determine the concentration was the sound velocity because it has a parabolic behavior. Propose to take into account the criteria of sampling time, sample volume, cost and repeatability of the instrument, in choosing the method of measurement of properties of working fluids used in the prototypes of absorption. It was selected the technique of electrical conductivity as a viable and reliable method to determine concentration of the solution of LiBr, because low-cost instrument, requires a small sample volume, the sensor can be installed inside the prototype machines absorption and simple measurement.
8
Acknowledgment We thank the CONACYT for their support in the realization of this work. We thank the working group CREVER for their support in carrying out experimentation measuring the properties of the lithium bromide solution
References [1] Deng S. M., and Ma W. B. (1999). Experimental studies on the characteristics of an absorber using LiBr/H2O solution as working fluid. International journal of refrigeration 22, 293-301. [2] Nabil Hafsia Ben, Bechir Chaouachi, Gabsi Slimane (2014). Global modeling of heat and mass transfer in spiral tubular absorber of water lithium bromide absorption chiller. International journal of refrigeration 38, 323-332. [3] Nomura T., Nishimura N., Wei S., and Yamaguchi S. (1993). International absorption heat pump conference, ASME 31, 203-208. [4] Conde M. R. (2004). Properties of aqueous solutions of lithium bromide and calcium chlorides: formulations for use in air conditioning equipment design. International journal of thermal sciences 43, 367-382. [5] Fried I. and Segal M. (1983). Electrical conductivity of concentrated lithium bromide aqueous solutions. J. Chem. Eng. Data 28, 127-130. [6] Herold K. E. and Yuan Z. (2005). Thermodynamic properties of aqueous lithium bromide using a multiproperty free energy correlation. American society of heating refrigerating and air conditioning engineers, Inc. [7] Lee R. J., DiGuilio R. M., Jeter S. M. and Teja A.S. (1990). Properties of lithium bromide wáter solutions at high temperatures and concentration II Density and Viscosity. J. Chem. Eng. Data [8] Boryta D. A. (1970). Solubility of lithium bromide in water between -50 °F and + 100°F (45 to 70 % lithium bromide). J. Chem. Eng. Data 1, 142-144. [9]Patil K. R., Tripathi A. D., Pathak g. and Katti S. S. (1990). Thermodynamic properties of aqueous electrolyte solutions. Vapor pressure of aqueous solutions of LiCl, LiBr and LiI. J. Chem. Eng. Data 35, 166-168. [10] DiGuilio R. M. and Teja A. S. (1992). Thermal conductivity of aqueous salt solutions at high temperatures and high concentration. Ind. Eng. Chem. Res. 31, 1081-1085. [11] Zaltash A. and Ally R. M. (1992). Refractive indexes of aqueous LiBr solutions. J. Chem. Eng. 37, 110-113. [12] Wimby J. M. and Berntsson T. S. (1994). Viscosity and density of aqueous solutions of LiBr, LiCl, ZnBr2, CaCl2 and LiNO3. 1. Single salt solutions. J. Chem. Eng. 39, 68-72. [13]Rohman N., Dass N. N. and Mahiuddin S. (2002). Isentropic compressibility, effective pressure, classical sound absorption and shear relaxation time of aqueous lithium bromide, sodium bromide and potassium bromide solutions. Journal of Molecular Liquids 100/3, 265-290. 9
[14] Shishkin A. V. (2005). Surface tension of H2O-LiBr solutions data processing. KORUS. [15] Heinonen.E. W. and R. E. Tapscott (1997). Secondary properties of aqueous lithium bromide solutions. [16] De Diego A., Usobiaga A., Fernández L. A. and Madariaga J. M. (2001). Application of the electrical conductivity of concentrated electrolyte solutions to industrial process control and design: from experimental measurement towards prediction through modelling. Trends in Analytical Chemistry. Vol 20, No 2, 65-77.
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Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2
Electrical conductivity (mS cm-1)
450.0 44.96 % 50.05 % 55.02 %
400.0 350.0 300.0
60.03 %
250.0
64.95 %
200.0 150.0 100.0 50.0 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 1. Behavior electrical conductivity LiBr solutions at different temperatures and concentrations.
11
Electrical conductivity (mS cm-1)
450
This work Fried & Segal
400
45 %
350
55 %
300 250 200 150 100 50 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 2. Comparison of the experimental data obtained (-) and presented by Fried & Segal (o).
12
1.490
Refractive Indexes
1.480 64.8 %
1.470 1.460
59.9 %
1.450 55.3 %
1.440 1.430
50.1 %
1.420
45.0 %
1.410 10
20
30
40 50 Temperature (°C)
60
70
80
Figure 3. Behavior refractive indexes LiBr solutions at different temperatures and concentrations.
13
1.480
This work Zaltash & Ally
Refractive Indexes
1.470 1.460 1.450
55 %
1.440 1.430
50%
1.420
45%
1.410 1.400 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 4. Comparison of the experimental Refractive Index obtained (-) and presented by Zaltash & Ally (o).
14
1.800 1.750
64.85 %
Density (g ml-1)
1.700 1.650
59.95 %
1.600
55.30 %
1.550 1.500
50.15 %
1.450
45.0 0%
1.400 1.350 10
20
30
40
50
60
70
80
Temperature (°C) Figure 5. Behavior density LiBr solutions at different temperatures and concentrations.
15
This work Fried & Segal Lee et al Wimby & Berntsson
2.00 1.90
Density (g ml-1)
1.80 1.70 1.60
55 %
1.50 45 %
1.40 1.30 1.20 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 6. Comparison of the experimental data obtained (-) and presented by Fried & Segal (□), Lee et al (∆) and Wimby & Berntsson (○).
16
1670 Sound Velocity (m s-1)
1660
1650 1640
64.85 %
1630 1620
59.95 %
1610
55.30 %
1600
50.15 % 45.00 %
1590 1580 1570 10
20
30
40
50
60
70
80
Temperature (°C) Figure 7. Behavior sound velocity LiBr solutions at different temperatures and concentrations.
17
1600
This work
Speed Sound (m s-1)
1599
Rohman et al
1598 1597 1596
45.0 %
1595 1594 1593 1592 46.4 %
1591 1590 0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Temperature (°C) Figure 8. Comparison of the experimental data obtained (-) and presented by Rohman et al. (o).
18
Figure 9
Normalized Electric Conductivity(- -)
density (.-) and refractive index(-).
19
Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2
Table 1 Statistical Analog of Properties of LiBr Solutions in Previous Works. Year First autor Property T LiBr Method °C % mass 1970 Boryta[8] Solubility -50–100 45-70 Several Technical Fried & Electrical 1983 15–80 40-63 Conductometer Segal [5] conductivity Density & Pycnometer & 1990 25–200 45-65 Lee et al. [7] viscosity Viscosimeter 1990 Patil et al. [9] Vapor pressure 30–70 15-60 Manometer DiGuilio, et Thermal Transient Hot1992 20–185 30-65 al. [10] conductivity Water Zaltash & Refractive 1992 5–80 0-58 Refractometer Ally [11] indexes Wimby & Densitometer & Viscosity & 1994 Berntsson 20–70 15-60 Ubbelohde density [12] Capillaries Rohman et 2002 Sound Velocity 0–50 0-55 Interferometer al. [13] 2005 Shishkin [14] Surface tensión 0–100 0-60 Simulation
Accuracy ± 0.70 % ± 0.25 % ± 1.00 % ± 2.00 % ± 0.30 % ± 0.70 % ± 0.05 % ± 0.01 % ± 0.10 %
20
Table 2 Experimental Data Electrical Conductivity (κ, mS cm-1) of LiBr Solutions.
°C 35.00 40.00 50.00 60.00 70.00 80.00
44.96% 235.1 253.5 291.3 329.9 368.6 405.7
50.05% 217.7 235.4 272.0 309.3 347.0 383.9
55.02% 197.0 213.7 248.2 283.9 320.6 357.7
60.03% 153.1 167.5 198.1 230.5 264.5 299.6
64.95% 118.1 130.3 157.2 186.7 218.2 251.5
21
Table 3. Coefficients obtained for use in the correlation of electrical conductivity
1 2 3
1 1.3348E-5 -8.9372E-4 1.3222E-2
2 -3.0879E-3 2.3159E-1 -3.6024E-1
3 -7.6133E-2 5.4926 8.9221
A B C
22
Table 4. Experimental Data Refractive Index of LiBr Solutions
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1.423746 1.422463 1.420980 1.419481 1.417915 1.416320
50.15% 1.437114 1.435534 1.433910 1.432277 1.430632 1.428969
55.30% 1.453971 1.452544 1.450944 1.449335 1.447748 1.446089
59.95% 1.463704 1.462009 1.460245 1.458504 1.456773 1.455044
64.85%
1.478116 1.476188 1.474466
23
Table 5. Coefficients obtained for use in the correlation of refractive index
1 2 3
1 -5.767E-10 7.8251E-8 -2.6583E-6
2 3.6167E-8 -6.7480E-6 1.0659E-4
3 -3.6763E-5 6.6462E-3 1.2011
A B C
24
Table 6 Experimental Data Density ρ, (g cm-3) of LiBr Solutions.
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1.447655 1.442662 1.437452 1.432106 1.426623 1.421015
50.15% 1.514361 1.508916 1.503401 1.497800 1.492104 1.486314
55.30% 1.586826 1.580058 1.574177 1.568165 1.562083 1.555934
59.95% 1.655064 1.648673 1.642309 1.635948 1.629575 1.623178
64.85%
1.745914 1.738809 1.731743
25
Table 7. Coefficients obtained for use in the correlation of density
1 2 3
1 -7.2767E-9 8.2493E-7 -2.3220E-5
2 6.8122E-7 -8.4286E-5 1.9577E-3
3 6.4044E-6 1.3447E-2 8.3853E-1
A B C
26
Table 8 Experimental Data Speed of Sound, ν (m s-1] of LiBr Solutions.
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1593.70 1596.67 1598.34 1598.69 1597.74 1595.56
50.15% 1601.94 1603.64 1604.29 1603.90 1602.42 1599.92
55.30% 1615.12 1616.24 1616.08 1615.01 1613.00 1610.27
59.95% 1625.67 1626.34 1625.90 1624.98 1622.89 1619.96
64.85%
1645.49 1642.89 1639.42
27
Table 9. Coefficients obtained for use in the correlation of sound velocity
1 2 3
1 -8.3214E-6 1.0086E-3 -3.4979E-2
2 1.3840E-3 -1.6768E-1 5.3612
3 -1.9885E-3 2.7850 1.4622E3
A B C
28
Highlights * Determination of concentration of absorption mixture for absorption heat transformers. * Measurement of physical properties for heat transformer assessment. * Comparative behavior of Electric conductivity, Refractive index, and density of LiBr-H2O.
29
S1359-4311(16)32758-2 http://dx.doi.org/10.1016/j.applthermaleng.2016.10.162 ATE 9364
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
7 January 2016 25 October 2016 25 October 2016
Please cite this article as: L. Labra, D. Juárez-Romero, J. Siqueiros, A. Coronas, D. Salavera, Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine, Applied Thermal Engineering (2016), doi: http://dx.doi.org/10.1016/j.applthermaleng. 2016.10.162
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Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2 *
Centro de Investigación en Ingenierías y Ciencias Aplicadas (CIICAp), Universidad Autónoma del Estado de Morelos (UAEM), México. Av. Universidad 1001, Chamilpa, Cuernavaca 62209, Morelos, México. e-mail; [email protected]. 1 Consejo de Ciencia y Tecnologia del Estado de Morelos Av. Atlacomulco No. 13. Esq. Calle de la Ronda Col. Acapantzingo,Mor. C.P. 62440 Tel.: [52] 777-3121222, México.e-mail:[email protected] 2 Departamento de Mecánica, Centro de Innovación en Recuperación de Energía y Refrigeración (CREVER), Universidad Rovira i Virgili, Tarragona, España.e:mail:{[email protected] , [email protected]}
_________________________________________________________________________ ABSTRACT An electrolyte solution of Lithium Bromide (LiBr) water was chosen for study because of its wide use in prototype absorption machines. The LiBr must be operated close to the temperature and mass fraction at which lithium bromide achieves the highest efficiency. For the purpose of establishing the concentration in a prototype absorption machines, measurements were made of the properties that vary with temperature and concentration. The selected properties are electrical conductivity, density, refractive indexes and sound velocity. The resulting measured properties values were compared with some values found in previous works. The properties of aqueous lithium bromide solutions were measured at the concentration range of 45 to 65 % of LiBr and temperatures range of 20 to 80 °C. Semi-empirical correlations that determine the properties of lithium bromide are also proposed. The methods for measuring the properties of aqueous solutions were considered taking into account their reliability, simplicity and sampling time. Keywords: LiBr solution, measurement, properties, prototype absorption machines. ________________________________________________________________________________________
1. Introduction Aqueous lithium bromide is one of the best choices as working fluid in absorption heat transformers, and absorption refrigerating machines [1, 2 and 3]. The prototype absorption machine consists of, a generator, a condenser, an evaporator and an absorber. A key component of these machines is the absorber. In this component, the concentration of lithium bromide (LiBr) changes inside the absorber by absorbing vapor from the evaporator. The concentration of the aqueous lithium bromide solution plays a significant role in the performance of such system. Therefore, it is necessary to obtain the concentration of the aqueous solution of lithium bromide in the absorber and in the generator, in both components circulate the LiBr solution [4, 5, 6 and 7]. Table 1 shows a list
1
of reported experimental data properties of the LiBr solution at different intervals of concentrations and temperatures, employing different measurement techniques. 1
-
- Table 1 around here - -
The LiBr solution must be operated close to the temperature and mass fraction at which lithium bromide crystallizes in order to achieve the highest efficiency in a prototype absorption machine. The objective of the present study is to measure the properties of the LiBr solution as a function of temperature and concentration; to evaluate their reliability and feasibility as a real-time monitoring method for determination of the concentration of LiBr. Variables such as the reflow ratio
FR
WRfr WAB
X GE X AB are useful performance indices, since the higher the ratio, the higher the X GE
heat released in the absorber We report measurements of the properties of density, electrical conductivity, refractive index and the sound velocity of the LiBr solution to a temperature range from 20 to 80 ° C and a concentration range from 45 to 65%. This interval is considered for study because prototype absorption machine operates under these conditions.
Heinonen and Tapscott [15] analyzed property-sensor for LiBr. The evaluated criteria were: estimated cost of the sensor, precision to determine the mass fraction, availability of instrument, reliability of the measurement and experimental data reported in the literature. They concluded that the sensors that measure the properties of refractive index, electrical conductivity, density and sound velocity are sensors that can be considered with optimal performance in the measurement of the properties.
2. Experimental process 2.1 Sample Preparation As the lithium bromide is extremely hygroscopic, it is important to follow a procedure to ensure that no moisture from the atmosphere is absorbed unintentionally when the measuring samples are being prepared. The LiBr was obtained from Sigma-Aldrich Company with a mass fraction purity ≥ 99 %. It was used after heating the salt to T= 383 K in an electrical oven for about 24 h and cooling it to the room temperature in a desiccator containing silica gel to remove traces of water. A digital mass balance was used to measure the masses of LiBr and a milliq water. All solutions were prepared as percent by weight (% wt) of LiBr, with uncertainty in the preparation of the solutions within ± 0.0002 %wt LiBr.
* Corresponding author. Tel: +52 777 3297084; e-mail address: [email protected] (D. Juarez-Romero)
2
2.2 Principle of Measurement of Electrical Conductivity The electrical conductivity of liquids is the measure the ions present in a solution for to transport electrical current. The electrical conductivity, k (S cm-1) is expressed in terms of the geometry of the cell conductivity (area of the electrodes and distance between them) and electrical resistivity. The principle of measurement is based on applying a potential difference between two inert electrodes of a specific surface, placed at a distance, L, introduced in the electrolytic solution. A potential gradient is generated, whereby each ion moves toward the electrode with opposite direction. Due to the charge associated with the ions, this displacement will produce an electric current.
2.2.1 Apparatus and Procedure The electrical conductivity of LiBr solution was continuously measured with a Basic 30 Crison conductivity meter, coupled to a glass conductivity cell model 5298 with constant (k=10). The conductivity meter has an electrical conductivity measurement range from 0.01 µS cm-1 to 1000 mS cm-1 with resolution 0.01 S and accuracy ± 0.1 %. The solution temperature was measured using an Anton Paar MKT 100 precision thermometer, with resolution 0.001 °C. The coupling cell conductivity and conductivity meter were calibrated with a standard solution of 0.1 M potassium chloride at room temperature. The precision thermometer was previously calibrated. The estimated uncertainty in the measurement of electrical conductivity of LiBr solutions is within ± 3.68 mS cm1 . The procedure was to place a volume approximately 12 ml of LiBr solution in an Erlenmeyer glass flask, with a magnetic stirrer, a precision temperature sensor and a cell with three electrodes. The system was insulated to prevent heat losses. A thermal bath was used to heat the LiBr solution contained in an Erlenmeyer glass flask. The measurement LiBr solution was carried out at a temperature of 30 °C and heated up to 80 °C. Electrical conductivity measurements were taken after to reach steady state. The sampling time was approximately 30 minutes for each temperature. The measurements were performed in a laboratory at ambient conditions.
2.3 Principle of Measurement of Refractive Index The refractive index is the measure of the change of the speed of light when passing from one medium to another. The refractive indexes, nD is dimensionless. The principle of measurement is based on the velocity change experienced by the electromagnetic radiation passing from one medium to another, as a result of its interaction with atoms and molecules the other means. Said velocity change is manifested in a variation in the propagation direction, using two prisms: one fixed light on which the sample is deposited and one mobile refractive.
2.3.1 Apparatus and Procedure
3
Index refractive of LiBr solution was continuously measured with a RXA170 Anton Paar Abbemat refractometer. The Abbemat refractometer has a refractive index measurement range from 1.3 to 1.7 with resolution 1*10-6 nD and accuracy ± 4*10 -5 nD. The solution temperature was measured using a cell with a built-in temperature meter, with resolution 0.03 °C. The Abbemat refractometer was previously calibrated. The estimated uncertainty in the measurement of refractive indexes of LiBr solutions is within ± 0.00005 nD. The procedure was to place a volume of LiBr solution of approximately 4 ml in the refractometer, through a fill tube via a syringe. The measurement LiBr solution was carried out at a temperature of 20 °C and heated up to 70 °C. The refractive indexes measurements were taken after reaching steady state. The sampling time was approximately 6 minutes. The measurements were performed in a laboratory at ambient conditions.
2.4 Principle of Measurement Density and Sound Velocity The density is the measure of the amount of matter that has a substance in a given volume. The density ρ (g cm-3), is expressed in terms mass of the substance per unit volume. The sound velocity is the dynamics of propagation of sound waves. The sound velocity ν (m s-1), is expressed in terms of length per unit of time. The sound velocity and density of the solution were determined by sound velocity and density meter U-shaped tube. The principle of measurement is based on a U-shaped tube of metal or glass containing the measurement sample that is electromagnetically activated to vibrate at its resonant frequency in a U-shaped tube. This resonant frequency is a function of material construction, geometry of the tube and the mass of the tube assembly (consisting of the tube itself and the fluid in the tube). As the volume is kept constant, the density is determined. The sound velocity is determined as a function of the density and the compressibility factor of the molecules present in the sample.
2.4.1 Apparatus and Procedure Density and sound velocity of LiBr solution were continuously measured with an Anton Paar DSA 5000 sound velocity and density meter. The density and sound velocity meter have a density and sound velocity measurement ranges from 0 to 3 g cm-3 and 1000 to 2000 ms -1, with resolutions 1*10-7 g cm-3 and 0.1 ms-1 respectively. The solution temperature was measured using a cell with a built-in temperature meter, with resolution 1*10-3 °C. The density and sound velocity meter was previously calibrated. The estimated uncertainty in the measurement density of LiBr solutions is within ± 0.00007 g cm-3 and ± 0.5 m s-1 for measurements of the sound velocity. The procedure was to place a volume of LiBr solution of approximately 4 ml in the density and sound velocity meter, through a fill tube via a syringe. The measurement LiBr solution was carried out at a temperature of 20 °C and heated up to 70 °C. The density and sound velocity measurement were taken after to reach steady state. The sampling time was approximately 12 minutes for sound velocity and 15 minutes for density. The measurements were performed in a laboratory at ambient conditions.
4
3. Results and discussion 3.1 Electrical Conductivity The electrical conductivity of the LiBr solution was measured in a temperature range and concentration from 35 to 80 ° C and 45 to 65 % wt LiBr respectively. The experimental electrical conductivity data of LiBr solutions at different temperatures and concentrations are summarized in Tables 2, while the trend presented with respect to temperature and concentration are plotted in Figure 1. --- Table 2 around here---- Figure 1. around here-The increase in electrical conductivity occurs when the temperature increases, this is because the viscosity of the LiBr solution decreases, favoring ions mobility and therefore the electric charge transport [16]. For this range of measurement, the electrical conductivity presents a linear behavior with respect to temperature. It graphically shows that at concentrations up to 55 wt% LiBr, increased electrical conductivity with respect to variation in temperature is greater than at concentrations above 55 wt% LiBr. This is due to the excess of dissolved ions from that concentration, producing saturation of the LiBr solution, therefore a decrease in the electrical conductivity. Some aspects that we consider in electrical conductivity measurements was to use a toroid cell with two electrodes to avoid the effect of polarization. The LiBr solution remained homogeneous during the measurement using a magnetic stirrer. Heat loss is prevented with an insulator. In Figure 2 is shown the comparison of experimental electrical conductivity data obtained in this study and presented by Fried & Segal [5]. Only was considered experimental values of electrical conductivity for two particular concentrations from 45 wt% LiBr and 55 wt% LiBr, these measurements were considered for similar conditions of measurement. Our experimental electrical conductivity data obtained in this work shows a good agreement with those presented by Fried & Segal. There is a difference of up to 13.2 % with the data obtained experimentally. --- Figure 2 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is presented in equation (1). (1) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the electrical conductivity. The coefficients obtained through the method of least squares, these coefficients are presented in Table 3, which are used in the correlation of the electrical conductivity, to determine the LiBr concentration. --Table 3 around here-5
3.2 Refractive Index The refractive index of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 % wt LiBr respectively. The experimental refractive indexes data of LiBr solutions at different temperatures and concentrations are summarized in Tables 4, while the trend presented with respect to temperature and concentration are plotted in Figure 3.
---Table 4 around here— --- Figure 3 around here -The refractive index decreases with increasing temperature, this is because the temperature has a great influence on the density of the medium causing a change in propagation velocity in the vacuum and in the sample, but tends to increase when the concentration increases. For this measurement range the refractive index has a linear behavior with respect to temperature. Zaltash & Ally [11] performed measurements refractive indexes with a refractometer for the temperature range of 5 to 80 ° C and concentration range of 0 to 59 wt% LiBr. They performed measurements of refractive index by coupling the thermal bath to a refractometer. While our experimental refractive index measurements were made only in the refractometer, which had the option of heating to the desired temperature, without the need for a thermal bath. In Figure 4 is shown the comparison of experimental refractive indexes data obtained in this study and presented by Zaltash & Ally[11]. Only were considered experimental values of refractive indexes for concentrations from 45 wt% LiBr, 50 wt% LiBr, and 55 wt% LiBr, these measurements were considered for similar conditions of measurement. Our experimental refractive indexes data obtained in this work shows a good agreement with those presented by Zaltash & Ally [11]. There is a difference of up to 0.2 % with the data obtained experimentally. --- Figure 4 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is presented in equation (2).
% LiBr A(T )nD 2 B(T )nD C (T ) (2) A(T ) ai ,1 ai ,2 x ai ,3 x 2 B(T ) bi ,1 bi ,2 x bi ,3 x 2 C (T ) ci ,1 ci ,2 x ci ,3 x 2 Where is the concentration of the solution of LiBr. T is temperature, x, is composition, and nD is the refractive index. The coefficients obtained through the method of least squares; these are presented in Table 5, which are used in the correlation of the refractive index, to determine the LiBr concentration.
----Table 5 around here-3.3 Density 6
The density of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 wt% LiBr respectively. The experimental density data of LiBr solutions at different temperatures and concentrations are summarized in Tables 6, while the trend presented with respect to temperature and concentration are plotted in Figure 5. --- Table 6 around here-----Figure 5 around here-The density decreases with increasing temperature, this is because that with the rise in temperature in the solution of LiBr atoms begin to vibrate and expand, taking more volume, but tends to increase with increasing concentration, because the mass is greater in the same sample volume. In Figure 6 is shown the comparison of experimental density data obtained in this study and presented by Fried & Segal [5], Wimby & Berntsson [12] and Lee et al [7]. Only was considered experimental values of density for concentrations from 45 wt% LiBr and 55 wt% LiBr These measurements were considered for similar conditions of measurement. Our experimental density data obtained in this work shows a good agreement with those presented by Fried & Segal [5], and Lee et al. [7] There is a difference of up to 3.4 % with the data obtained experimentally. ---Figure 6 --An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This relationship is presented in equation (3). (3) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the density. The coefficients obtained through the method of least squares; these are presented in Table 7, which are used in the correlation of the density, to determine the LiBr concentration. ---Table 7---
3.4
Sound Velocity
The sound velocity of the LiBr solution was measured in a temperature range and concentration from 20 to 70 ° C and 45 to 65 wt% LiBr respectively. The experimental sound velocity data of LiBr solutions at different temperatures and concentrations are summarized in Tables 8, while the trend presented with respect to temperature and concentration are plotted in Figure 7. --- Table 8 around here— --- Figure 7 around here-The sound velocity presents a maximum with respect to the variation of temperature; that depends on concentration. For this measurement interval, the sound velocity has a parabolic comportment with respect to temperature. In the literature there is little information on the measurement sound velocity, there is experimental data reported by Rohman et al [13] on the sound velocity for range temperature and concentration 7
from 0 to 50 ° C and 0 to 55 % wt LiBr respectively. In Figure 8 is shown the comparison of experimental sound velocity data obtained in this study and presented by Rohman et al. [13]. Since the graph shows that the trends presented by our measurements the sound velocity according to the behavior are presented by Rohman et al. [13] --- Figure 8 around here-An equation is then constructed by least squares fit to produce a relationship giving the concentration of LiBr solution as a function of temperature and electrical conductivity. This is relationship is presented in equation (4). (4) Where is the concentration of the solution of LiBr, A, B and C are coefficients depending on the temperature and is the sound velocity. The coefficients obtained through the method of least squares, these are presented in Table 9, which are used in the correlation of the sound velocity, to determine the LiBr concentration. ---Table 9 around here---
3.5
Normalized Comparison of Density, Electrical Conductivity and Refractive index.
Figure 9 shows the comparison of temperature with respect to electrical conductivity, density and refractive index with shifted scales x ( x xmin ) for dependent and normalized scales for dependent variables, ie. y ( y ymin ) / ( ymax ymin ) For these properties, a linear trend occurs with respect to temperature and composition. From this figure it is appreciated that the electrical conductivity is more sensible to temperature variations, compared with the density and refractive index. Changes of density and refractive index with respect to temperature variation are very similar. ---Figure 9 around here--
4. Conclusions Experimental data of the properties of electrical conductivity, refractive indexes, density and sound velocity of LiBr solution at different temperatures and concentration were obtained. They show a good agreement with previously published data found in the literature. The proposed equations to determine the LiBr concentration, apply mainly in the next measurement interval: 45 to 60% for the concentration and from 50 to 70 ° C for the temperature. It is noteworthy that the only property that is not considered appropriate to determine the concentration was the sound velocity because it has a parabolic behavior. Propose to take into account the criteria of sampling time, sample volume, cost and repeatability of the instrument, in choosing the method of measurement of properties of working fluids used in the prototypes of absorption. It was selected the technique of electrical conductivity as a viable and reliable method to determine concentration of the solution of LiBr, because low-cost instrument, requires a small sample volume, the sensor can be installed inside the prototype machines absorption and simple measurement.
8
Acknowledgment We thank the CONACYT for their support in the realization of this work. We thank the working group CREVER for their support in carrying out experimentation measuring the properties of the lithium bromide solution
References [1] Deng S. M., and Ma W. B. (1999). Experimental studies on the characteristics of an absorber using LiBr/H2O solution as working fluid. International journal of refrigeration 22, 293-301. [2] Nabil Hafsia Ben, Bechir Chaouachi, Gabsi Slimane (2014). Global modeling of heat and mass transfer in spiral tubular absorber of water lithium bromide absorption chiller. International journal of refrigeration 38, 323-332. [3] Nomura T., Nishimura N., Wei S., and Yamaguchi S. (1993). International absorption heat pump conference, ASME 31, 203-208. [4] Conde M. R. (2004). Properties of aqueous solutions of lithium bromide and calcium chlorides: formulations for use in air conditioning equipment design. International journal of thermal sciences 43, 367-382. [5] Fried I. and Segal M. (1983). Electrical conductivity of concentrated lithium bromide aqueous solutions. J. Chem. Eng. Data 28, 127-130. [6] Herold K. E. and Yuan Z. (2005). Thermodynamic properties of aqueous lithium bromide using a multiproperty free energy correlation. American society of heating refrigerating and air conditioning engineers, Inc. [7] Lee R. J., DiGuilio R. M., Jeter S. M. and Teja A.S. (1990). Properties of lithium bromide wáter solutions at high temperatures and concentration II Density and Viscosity. J. Chem. Eng. Data [8] Boryta D. A. (1970). Solubility of lithium bromide in water between -50 °F and + 100°F (45 to 70 % lithium bromide). J. Chem. Eng. Data 1, 142-144. [9]Patil K. R., Tripathi A. D., Pathak g. and Katti S. S. (1990). Thermodynamic properties of aqueous electrolyte solutions. Vapor pressure of aqueous solutions of LiCl, LiBr and LiI. J. Chem. Eng. Data 35, 166-168. [10] DiGuilio R. M. and Teja A. S. (1992). Thermal conductivity of aqueous salt solutions at high temperatures and high concentration. Ind. Eng. Chem. Res. 31, 1081-1085. [11] Zaltash A. and Ally R. M. (1992). Refractive indexes of aqueous LiBr solutions. J. Chem. Eng. 37, 110-113. [12] Wimby J. M. and Berntsson T. S. (1994). Viscosity and density of aqueous solutions of LiBr, LiCl, ZnBr2, CaCl2 and LiNO3. 1. Single salt solutions. J. Chem. Eng. 39, 68-72. [13]Rohman N., Dass N. N. and Mahiuddin S. (2002). Isentropic compressibility, effective pressure, classical sound absorption and shear relaxation time of aqueous lithium bromide, sodium bromide and potassium bromide solutions. Journal of Molecular Liquids 100/3, 265-290. 9
[14] Shishkin A. V. (2005). Surface tension of H2O-LiBr solutions data processing. KORUS. [15] Heinonen.E. W. and R. E. Tapscott (1997). Secondary properties of aqueous lithium bromide solutions. [16] De Diego A., Usobiaga A., Fernández L. A. and Madariaga J. M. (2001). Application of the electrical conductivity of concentrated electrolyte solutions to industrial process control and design: from experimental measurement towards prediction through modelling. Trends in Analytical Chemistry. Vol 20, No 2, 65-77.
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Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2
Electrical conductivity (mS cm-1)
450.0 44.96 % 50.05 % 55.02 %
400.0 350.0 300.0
60.03 %
250.0
64.95 %
200.0 150.0 100.0 50.0 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 1. Behavior electrical conductivity LiBr solutions at different temperatures and concentrations.
11
Electrical conductivity (mS cm-1)
450
This work Fried & Segal
400
45 %
350
55 %
300 250 200 150 100 50 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 2. Comparison of the experimental data obtained (-) and presented by Fried & Segal (o).
12
1.490
Refractive Indexes
1.480 64.8 %
1.470 1.460
59.9 %
1.450 55.3 %
1.440 1.430
50.1 %
1.420
45.0 %
1.410 10
20
30
40 50 Temperature (°C)
60
70
80
Figure 3. Behavior refractive indexes LiBr solutions at different temperatures and concentrations.
13
1.480
This work Zaltash & Ally
Refractive Indexes
1.470 1.460 1.450
55 %
1.440 1.430
50%
1.420
45%
1.410 1.400 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 4. Comparison of the experimental Refractive Index obtained (-) and presented by Zaltash & Ally (o).
14
1.800 1.750
64.85 %
Density (g ml-1)
1.700 1.650
59.95 %
1.600
55.30 %
1.550 1.500
50.15 %
1.450
45.0 0%
1.400 1.350 10
20
30
40
50
60
70
80
Temperature (°C) Figure 5. Behavior density LiBr solutions at different temperatures and concentrations.
15
This work Fried & Segal Lee et al Wimby & Berntsson
2.00 1.90
Density (g ml-1)
1.80 1.70 1.60
55 %
1.50 45 %
1.40 1.30 1.20 30
35
40
45
50
55
60
65
70
75
80
85
Temperature (°C) Figure 6. Comparison of the experimental data obtained (-) and presented by Fried & Segal (□), Lee et al (∆) and Wimby & Berntsson (○).
16
1670 Sound Velocity (m s-1)
1660
1650 1640
64.85 %
1630 1620
59.95 %
1610
55.30 %
1600
50.15 % 45.00 %
1590 1580 1570 10
20
30
40
50
60
70
80
Temperature (°C) Figure 7. Behavior sound velocity LiBr solutions at different temperatures and concentrations.
17
1600
This work
Speed Sound (m s-1)
1599
Rohman et al
1598 1597 1596
45.0 %
1595 1594 1593 1592 46.4 %
1591 1590 0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Temperature (°C) Figure 8. Comparison of the experimental data obtained (-) and presented by Rohman et al. (o).
18
Figure 9
Normalized Electric Conductivity(- -)
density (.-) and refractive index(-).
19
Measurement of Properties of a Lithium Bromide Aqueous Solution for the Determination of the Concentration for a Prototype Absorption Machine Labra L., Juárez-Romero D. *, J. Siqueiros1, A.Coronas2. and D.Salavera2
Table 1 Statistical Analog of Properties of LiBr Solutions in Previous Works. Year First autor Property T LiBr Method °C % mass 1970 Boryta[8] Solubility -50–100 45-70 Several Technical Fried & Electrical 1983 15–80 40-63 Conductometer Segal [5] conductivity Density & Pycnometer & 1990 25–200 45-65 Lee et al. [7] viscosity Viscosimeter 1990 Patil et al. [9] Vapor pressure 30–70 15-60 Manometer DiGuilio, et Thermal Transient Hot1992 20–185 30-65 al. [10] conductivity Water Zaltash & Refractive 1992 5–80 0-58 Refractometer Ally [11] indexes Wimby & Densitometer & Viscosity & 1994 Berntsson 20–70 15-60 Ubbelohde density [12] Capillaries Rohman et 2002 Sound Velocity 0–50 0-55 Interferometer al. [13] 2005 Shishkin [14] Surface tensión 0–100 0-60 Simulation
Accuracy ± 0.70 % ± 0.25 % ± 1.00 % ± 2.00 % ± 0.30 % ± 0.70 % ± 0.05 % ± 0.01 % ± 0.10 %
20
Table 2 Experimental Data Electrical Conductivity (κ, mS cm-1) of LiBr Solutions.
°C 35.00 40.00 50.00 60.00 70.00 80.00
44.96% 235.1 253.5 291.3 329.9 368.6 405.7
50.05% 217.7 235.4 272.0 309.3 347.0 383.9
55.02% 197.0 213.7 248.2 283.9 320.6 357.7
60.03% 153.1 167.5 198.1 230.5 264.5 299.6
64.95% 118.1 130.3 157.2 186.7 218.2 251.5
21
Table 3. Coefficients obtained for use in the correlation of electrical conductivity
1 2 3
1 1.3348E-5 -8.9372E-4 1.3222E-2
2 -3.0879E-3 2.3159E-1 -3.6024E-1
3 -7.6133E-2 5.4926 8.9221
A B C
22
Table 4. Experimental Data Refractive Index of LiBr Solutions
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1.423746 1.422463 1.420980 1.419481 1.417915 1.416320
50.15% 1.437114 1.435534 1.433910 1.432277 1.430632 1.428969
55.30% 1.453971 1.452544 1.450944 1.449335 1.447748 1.446089
59.95% 1.463704 1.462009 1.460245 1.458504 1.456773 1.455044
64.85%
1.478116 1.476188 1.474466
23
Table 5. Coefficients obtained for use in the correlation of refractive index
1 2 3
1 -5.767E-10 7.8251E-8 -2.6583E-6
2 3.6167E-8 -6.7480E-6 1.0659E-4
3 -3.6763E-5 6.6462E-3 1.2011
A B C
24
Table 6 Experimental Data Density ρ, (g cm-3) of LiBr Solutions.
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1.447655 1.442662 1.437452 1.432106 1.426623 1.421015
50.15% 1.514361 1.508916 1.503401 1.497800 1.492104 1.486314
55.30% 1.586826 1.580058 1.574177 1.568165 1.562083 1.555934
59.95% 1.655064 1.648673 1.642309 1.635948 1.629575 1.623178
64.85%
1.745914 1.738809 1.731743
25
Table 7. Coefficients obtained for use in the correlation of density
1 2 3
1 -7.2767E-9 8.2493E-7 -2.3220E-5
2 6.8122E-7 -8.4286E-5 1.9577E-3
3 6.4044E-6 1.3447E-2 8.3853E-1
A B C
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Table 8 Experimental Data Speed of Sound, ν (m s-1] of LiBr Solutions.
°C 20.00 30.00 40.00 50.00 60.00 70.00
45.00% 1593.70 1596.67 1598.34 1598.69 1597.74 1595.56
50.15% 1601.94 1603.64 1604.29 1603.90 1602.42 1599.92
55.30% 1615.12 1616.24 1616.08 1615.01 1613.00 1610.27
59.95% 1625.67 1626.34 1625.90 1624.98 1622.89 1619.96
64.85%
1645.49 1642.89 1639.42
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Table 9. Coefficients obtained for use in the correlation of sound velocity
1 2 3
1 -8.3214E-6 1.0086E-3 -3.4979E-2
2 1.3840E-3 -1.6768E-1 5.3612
3 -1.9885E-3 2.7850 1.4622E3
A B C
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Highlights * Determination of concentration of absorption mixture for absorption heat transformers. * Measurement of physical properties for heat transformer assessment. * Comparative behavior of Electric conductivity, Refractive index, and density of LiBr-H2O.
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