Designing of system for high grade heat recovery in thermal coolingsystem for process heat applicati
Journal of Thermal Engineering 2023, Vol. 9, Issue 3, pp. 679-701; doi.org/10.18186/thermal.1299161
Abstract
Keywords: Single Effect Absorption System; Water-Lithium Bromide; Process Heat; Dairy Industry
Introduction
The dairy industry has been growing at a good pace worldwide. The demand for dairy products has been increasing steadily with the improvement in living standards of people all around [1]. The energy in the processing of dairy products in any dairyindustry plays a significant role. Most of the dairy industries of developing countriesmainly rely on low-grade energy sources such as wood, kerosene oil and diesel etc. for steam generation and other applications. The rest of the dairy sectors rely on high-grade energy, i.e. electricity. The dairy industry useaadequate
quantity ofpower in process heat applications [2] which shows a strong evidence of increase in level of CO2 emission [3]. The continuous usage of fossil fuels outcomes in ozone depletion and global warming [4]. Thus, there is a great need to improve the efficiency of dairy industries and reducling the level of CO2 emission for contributing to sustainable development. Hence, there is a need for the slection of a new renewable energy technologies [5]. Tremendous growth has been observed in the renewable energy sector worldwide. Solar energy is the most popular choice for absorption cooling system [6]. Several innovative and efficient technologies are available that can be used for
*Corresponding author. *E-mail address: alkasolanki10@gmail.com This paper was recommended for publication in revised form by Regional Editor Ahmet Selim Dalkılıç Published by Yıldız Technical University Press, İstanbul, Turkey Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
process heat applications in dairy industries. In particular, renewable energy can aid in cost-cutting in plus to reducing carbon footprints. Further, dairy industries are acquiring green energy technologies to meet their needs. For instance, Mahanand Dairy situated in Latur, India has been usinghuge solar dish ollector to meet their thermal needs [7]. The global dairy industry is sincerely exploring renewable energy for dairy processing plants of the future as it improves efficiency, reduces cost and complies with environmental responsibilities [8]. The Integrationofa vapor absorption system in process heat applications in the dairy industry can provide energy-efficient opportunities. Using such technology towards savings in electricity can replace the existing system in process heat applications. The collective savings of energy in the chilling process and hot water generation can have a significant effect on whole dairy powercharges. Zhang et al. [9] analyzed electricity usage and production cost of milk in eleven dairy farms in China and evaluated the potential of solar energy generated by PV water pumping system. Desai et al. [1] discussed the implementationof solar energy for reliable dairy advancement. Panchal et al. [10] discussed the various research works on milk pasteurization using solar energy, which is theright solution in terms of energy-saving and efficiency. Yildirim et al. [11] analyzed thermodynamically the milk pasteurization system that is assisted by geothermal energy. The results indicatedtheincrease in pasteurization capacity with the raise in geothermal resource flow rate. Cocco et al. [12] manifested the use of solar technology as an excellent option if both the power and heat are required at a common point of application. Further, solar technology has flexibility features likeusing different control variables; thelocalelectricity demand may also be fulfilled. Praveen et al. [13] studied the classification, working principle, applications, benefits and limitations of solar thermal power in the milk and their productindustry. Sandeyet al. [14] concluded that the solar energy could be used in the dairy industry for solar drying, for pumping dairy fluid, for room conditioning, for cold storage of milk & milk products, for lighting and electric fencing. Anderson et al. [15] simulated the performance of four types of solar representativeconcerning their adaptability for heating and cooling in themilk and other industry. Finally, it is concluded that both flat plate and evacuated tube-based solar collector systems have better performance and make it sincere contribution to energy saving in the dairy industry. Modi et al. [16] utilized the waste heat in milk process plants that resulted in low investment withhighenergy saving. Ketfi et al. [17] had done a simulation study on the single-effect absorption system by varying evaporator, condenser, absorber and generator temperature. Manu et al. [18] conducted a simulation research of a sole-phase absorption heat pump mechanism for chip cooling using Matlab (2008b). Lamineet al. [19] studied an absorption refrigeration mechanismfunctioning in the industrial manufacturing of detergent (Henkel Algeria). Pandya et al. [20] had done a simulation study of
1. TR capacity using EES software. The result revealed that
the temperature of generator decline with rise in evaporator temperature and further raises with the temperature of condenser. Patel et al. [21] investigated a LiBr-H2O vapourabsorptionmechanism designed forthecooling capacity of 140 kW. The various parameters viz. heat load, circulation ratio, pump work, COP, COPrev and ηex are analyzed at different operating conditions. The results have showna rise in the heat load on the generator and absorber increases with the the exit temepratures of generator and condenser. Uckan and Yousif [22] sinulated the single effect vapour absorption system under the climate of Duhok City situated in the North of Iraq via utilizing TRNSYS 17 programs and the COP of the mechanism was found as 0.63. Iyer and Mastorakis [23] discussed the energy conservation measures in dairy industries. Further, this study provides the energy conservation techniques for dairy industries. Singh et al. [24] stated that requirements of energy and temperature range in milk processing plants are amenable for the adoption of solar energy. Zhu and Gu [25] analyzed the performance of a novel absorption system for cooling and heating applications. The active component of the sorbent used in this study is sodium thiocyanate (NaSCN). Ammonia (NH3) is chosen as sorptive. The results show that the COP of cooling and heating increases with the heat source temperature and decreases with the cooling water inlet temperature, but the system exergetic efficiency does not show the same trends for both cooling and heating applications. Farshi et al. [26] presented systematic procedure for estimating thermodynamic properties of working fluids (Ammonia/LiNO3 and Ammonia/NaSCN) formulated. Mathematical expressions also formulated for estimating thermodynamic properties (Specific enthalpy & Specific entropy) of Ammonia/LiNO3 and Ammonia/NaSCN. Singh and verma [27] exploited artificial intelligence for performing energy analysis of absorption refrigeration system (ARS) with water-lithium chloride as working fluid. The maximum difference between the predicted results and experimental data of thermodynamic properties are less than 1%. Value of the coefficient of multiple determinations is 1 for test data set and can be considered satisfactorily for using ANN in vapour absorption refrigeration system. Singh and verma [28] have done a simulation for estimating thermodynamic properties (specific enthalpy and specific entropy) of water–lithiumbromide solution using artificial neural network under MATLAB Simulink environment. AI-Simulink simulator is developed by deploying extracted weights and bias from modeled artificial neural networks. Optimized performance is achieved with 2-10-2 ANN architecture which is validated on the basis of mean square error, coefficient of multiple determination (R2), and absolute relative error. Oudina [29] investigation of natural convection heat transfer stability in cylindrical annular with discrete isoflux heat source of different lengths. The results show that the increase of heat source length ratio decreases the critical Rayleigh number.
Previous literature have done simulation as well as experimental results on vapour absorption system or change the working fluids but present research is focused on utilizing of vapour absorption system in process heat application in dairy industry. However, a minimal study on the application of an absorption system in process heat applications in the dairy industry has been observed. Accordingly, in the current work, an experimental study on the feasibility of vapor absorption system in process heat applications in the dairy industry has been carried out. An absorption system has been designed at National Institute of Solar Energy (NISE), Gurugram, India. The experiments have been conducted on the experimental set-up using LiBr–H2O. Further, a mathematical model has been developed using Engineering Equation Solver (EES) Academic Professional Version: V10.644 [2019-06-10]software to validate the experimental results. The influence of generator, absorber, condenser and evaporator temperature on coefficient of performance and circulation ratio have been investigated. Finally, the feasibility of a single-effect vapor absorption system in process heat applications in the dairy industry has been discussed.
Thermodynamic Modelling The first law of thermodynamics has been used to perform the analysis. Conservation of mass and energy balance has been applied to each component of the absorption system. In this way, steady-state equations have been formulated. System Description A model of single-effect vapor absorption system has been developed, as shown in Figure 1. The system consists of an absorber, a generator, a condenser, an evaporator, a solution heat exchanger (SHE), a refrigerant heat exchanger (RHE), a solution expansion valve, a pump and a refrigerant expansion valve. The cycle has two circuits: the refrigerant circuit (7-11) and LiBr–H2O solution circuit (1-6). Heat is supplied to the generator (Qg) which evaporates the refrigerant H2O at high pressure (Pc), the evaporated H2O is thenconvected to the condenser (7). The condenser dissipates heat (Qc) and then H2O changes phase from vapour to liquid (8). Then, the refrigerant H2O is flowed to refrigerant expansion valve (RTV) viarefrigerant heat exchanger to reach evaporation pressure (Pc); consequently, it led to the
Figure 1. Model of the sole-impact vapor absorption mechanism.
evaporator (10). The cooling process is conducted in the evaporator once the refrigerant soak up heat (Qe) from the environment, this causes that refrigerant evaporates once again (11) and then led to the absorber, where it mixes with the weak solution coming from the generator. Once they mix-up, a LiBr–H2O solution with low concentration is formed and release heat (Qa). After that, the solution is pumped to the generator (3) until it reaches condenser pressure (Pc) via a solution heat exchanger which increases solution temperature. The cycle initiatesafter getting sufficient temperature in the generator. Apart of the refrigerant evaporates and goes to the condenser (7). The rest of the solution with high concentration is led to the heat exchanger (4) where its temperature is lowered. Then it is passed byathrottle valve (TV) where its pressure is decreasedto the evaporation pressure (Pe). Finally, it comes to the absorber, and the cycle continues.Further, the following assumptions were made for thermodynamic modelling. i. The analysis has beendone for steady flow conditions. ii. The refrigerant at the exit of condenser has been assumed to be a saturated liquid. iii. The refrigerant at the exit of the evaporator has been assumed to be saturated vapour. iv. A strong solution has been assumed to leave of the absorber at absorber temperature. v. The isenthalpic process of throttling in the expansion valve and solution valve has been assumed. vi. No heat exchange between the system and surroundings has been assumed. vii. The refrigerant vapour leaving the generator has been assumed to be superheated. viii. Heat exchanger effectiveness (εSHE1, εSHE2 andεSHE3) has been taken as 0.7. Mass conservation It involvesa mass equilibrium of total mass and everymaterial of the solution. For steadystate-flow, the governing equations ofmass and type of material conservations are: [30]
where, m is the mass flow rate and X is the mass fraction of LiBr in the solution. Using Eq. (1) and (2), the mass balancing of each components of the absorption system has been formulated as: Generator: m3 = m4 + m7
STV: Where suffix, i = 1,2,---11 shows mass flow rate at different state points
2.3. First law analysis
The first law of thermodynamics for each component of the absorption system is expressed as follows: (14) Energy balance equations of each component of the absorptionsystem are as: Condenser: Qc = m7(h7-h8) = mc(hcb-hca)
The overall performance of the absorption system has been determined by evaluating its coefficient of performance (COP) as:
respectively. The variation in results is due to irreversibility distribution among everycomponentofthe absorption system. Also, the current single-impactvapor absorption system is satisfactory for the simulation.
where, Qe is the refrigerant effect, QHTG is the heat rate in the generator, and Wp is the pump work. Model validation The EES code validation has been carried out through comparing the current simulation results with that of Ketfi et al. [12], Kaushik et al. [18] and Modi et al. [31]. A comparison of simulation results has been shown in Table 1. The deviation in COP is -2.83% when compared with Ketfi et al. [12]. Similarly, the deviation in COP is +6.63% and +6.71% of present simulation results when compared with the results of Modi et al. [31] and Kaushik et al. [32],
Experimental Test Facility Experimental set-up with cooling capacity of 1.5 kW has been developedfor the feasibility assessment of its applicability in the dairy industry. The test facilityhas been shown schematically and photographicallyas Figure 2 and 3, respectively.
Table 1. Comparison of simulation results with the published results Sr. No.
Figure 2. Representative diagram of the practical test facility.
Figure 3. Practicaltest facility of the vapor absorption system.
All the four seamless vessels used as evaporator, condenser, generator and absorber have been made of copper. In the generator, baffle plates have been provided at the upper end to get pool boiling and to avoid liquid solution droplets going out with water vapours. The evaporator has been designed like a spray column to ensure maximum heat transfer in the present case. The absorber used in the experimentalfacilityact as a falling film column. The solution has been made to spray over a cooling coil in the absorber to form a liquid film over the coil to get maximum heat transfer in the present case. The solution heated up with the help of ETC in the generator and the cold solution from the absorber has been made to in counter currentdirectionsvia the annular duct and the inner tube, respectively. A bypass flow control valve has been employed at the inlet of the heat exchanger to measure the heat exchanger effectiveness. Voltage and current transducers havebeenused for measuring supply power. The cooling water flow ratesacross the condenser and the absorber have been
controlled with the help of solenoid control valves. All of the vessels used as the main components of vapourabsoption system were provided with sight-glasses to observeinsideliquid levels. Infra-red switches have been employed on the sight glasses to measure the fluid levels. In the steadystate condition, the liquid volume has been measured using sight-glass over a finite time interval. A rotameter has beenutilize to distance the flow rate of solution flowing through the absorber. The performance of the practicalmechanism has been analyzed using experimental observationstakenabove a linear-state processing time of 60 minutes. The experimental outcomes have been recorded by varying the temperatures ofthe absorber, generator, condenser and evaporator. Further, the detailsof the measuring instruments have been given in Table 2. The heat required to regenerate the solution has been produced using an evacuated tube collector, as shown in Figure 4. The internal coils used in the various sub-systems of the experimental facility have been shown
photographically as Figure 5. The detailed specifications of the collector have been given in Table 3. Experimental Procedure Initially, the experimental unit was evacuated using a vacuum pump to remove the condensable gases from the system. The deionized water wasused to charge the receiver tank and the evaporator, while the absorber and the generator were arraigned with lithium–bromide solution (55% v/v). Thethermal input was given to the generator through the evacuated tube collector,andconsequently,the solution in the generator vessel started to gain the temperature and pressure. The temperature in the generator was raised to 140oC using the ETC collector and a storage tank. The pressure was measured using pressure gauges, as shown in the photographic view of the system. Subsequently, the water got evaporated asvapoursfrom the LiBr–H2O
solution and moved from the generator to the condenser. Thevapours at huge temperature and pressure entered into the condenser. The condenser has been designed specially to extract waste heat recovery. The main aim was to extract heat for its conversionintoa useful form. The condenser has been employed with helical coils to get maximum heat transfer as shown in Figure 5. The vapours got condensed in the condenser by virtue of the temperature gradientdue to circulation cold water at ambient conditions through the helical coils. The condensed water was collected at the bottom of the condenser tank. The condensed was made to flow throughanexpansion valve and a heat exchanger. Further the low temperature condensed water entered intotheevaporator through a helical coil. The flow of the condensed water was controlledby a valve employed just after a heat
Figure 4. A photographic view of the Evacuated Tube Collectorused in the experiments.
Figure 5. Photographic views of internal coils used in (a) generator, (b) condenser, (c) evaporator and (d) absorber.
Table 3. The detailed specifications of the ETC collector Material of Glass
0.2. kg/cm2
exchanger. The heat exchangers having counterflow current were used between the condenser and the evaporator & between the generator and the absorber, respectively to utilize the waste heat throughout the cycle. Uncertainty Analyses Generally, the accuracy of the experimental results hinges on the accuracy of the individual measuring
instruments and techniques. The uncertainty of the parameters was calculated based upon the root sum square combination of the effects of each of the individual inputs as presented by Kline and McClintock [33]. For all experimental runs, the maximum uncertainties in the main parameters are shown in Table 4. For the estimated uncertainties in the other variables and parameters used in the current research, additional information is given in Appendix A.
The association for uncertainty examination has been described below: (23) Where x is the reliant variable and Δ x is its total uncertainty and m is a function of the independent variable z1, Δz1 is the absolute uncertainty. The relative uncertainty is given by: (24) Based on the above interactions, a comprehensive error calculation has been made through uncertainty analysis. The mean of the error and standard deviation for all the observations used to calculate the COP of the system are 0.03and 13.44 respectivley.
Results And Discussion
An Engineering Equation Solver software is utilized to simulate the vapour absorption systemto validate the experimental results and found in good agreement with each other. The experimental set-up was examined with a broadvariation of regulating temperatures. The operating parameters for present experimental and simulation work are presented in Table 5. The Comparison of the experimental and simulation results has been carried out by varying the influence of generator, condenser, evaporator and
absorber temperatures on COP and circulation ratio have been discussed in subsequent sub-section 4.1, 4.2, 4.3 and 4.4, respectively. Impact of generator temperature The LiBr-Water system has been analyzedby conductiong experiments and simulation by varyingtemperature ofthe generator, absorber (Qa), condenser (Qc), and evaporator (Qe).The effects of high generator temperature (Tg) on heat flow rates in the generator (Qg), absorber (Qa), condenser (Qc), and evaporator (Qe) have been shown in Table 6 and Figure 7. Table 6 shows the experimental and simulation results of effect of generator temperature (Tg) on heat flow rate in generator, absorber, condenser and evaporator at Tc= 50°C, Ta= 40°C, Te= 5°C, and eHX= 0.7. Figure 6 depicts that with an increase of generator temperature heat transfer in
Table 6. Computed heat flow rate in generator, absorber, condenser and evaporator at different generator temperature at (Tc= 50°C Ta = 40°C, Te= 5°C, eHX= 0.7) 95 Generator temperature, Tg (oC)
Figure 6. Effect of generator temperature on heat flow rate in generators, absorber, condenser and evaporator (Tc= 50°C, Ta= 40°C, Te= 5°C, eHX= 0.7).
absorber and condenser increases but heat transfer in generator decreases gradually. Moreover, the effect of increase in the generator temperature on heat transfer in evaporator remains constant. It is because with increase in generator temperatures causes circulation ratio to decrease and consequently produce the same effect as mentioned above. Further, experimental and simulation results are in good agreement.
Table 7 shows the experimental and simulation results on effect of generator temperature and on circulation ratio at Te= 5°C and eHX= 0.7). Figure 7 presents the variation of circulation ratio with generator temperature at different absorber and condenser temperatures. Figure 6 demonstrates that with a raise in generator temperature, circulation ratio decreases with varrying absorber temperature. The lowest value of circulation is achieved at low values
Table 7. Computed circulation ratio at different generator temperature (Te= 5°C, eHX= 0.7) 95 Generator temperature, Tg (oC)
Ta=Tc=30°C Simulation data Circulation ratio (CR) Ta=Tc=30°C
Figure 7. Effect of generator temperature on circulation ratio (Te= 5°C, eHX= 0.7).
of absorber and condenser temperatures. Similarly, highest value of circulation is attained at low temperatures of absorber and condenser. It is due to fact that with increase in generator temperature, the flow rate of strong solution decreases. Further, experimental and simulation results are in good agreement.
Table 8 shows the experimental and simulation results on coefficient of performance at different generator temperature with Tc= 50°C, Te= 5°C, and eHX= 0.7. Figure 8 depicts that when the condenser and evaporator temperature is maintained at 50°C, and 5°C with heat exchanger effectiveness of 70%, COP of absorption system increases with the rise in generator temperature. Further, maximum
Table 8. Computed Coefficient of performance at different generator temperature (Tc= 50°C, Te= 5°C, eHX= 0.7) Generator temperature, Tg (oC)
Figure 8. Impact of generator temperature (Tg) on COP (Tc= 50°C, Te= 5°C, eHX= 0.7).
COP is achieved at low absorber temperature, i.e. 20°C. Similarly, minimum COP is obtained at high absorber temperature, i.e. 50°C. It is due to fact that concentration of the weak solution increases with a rise in generator temperature that alsoenhance the circulation ratio; hence COP of
absorption system rises. Moreover, simulation and experimental results are in good agreement. Table 9 shows the experimental and simulation results oncoeffienct of performance at different generator temperature with Ta= 40°C, Te= 5°C, and eHX= 0.7. Figure 9
Table 9. Computed coeffienct of performance at different generator temperature (Ta= 40°C, Te= 5°C, eHX= 0.7) Generator temperature, Tg (oC)
Figure 9. Impact of generator temperature on COP (Ta= 40°C, Te= 5°C, eHX= 0.7).
depicts that when the absorber and evaporator temperature is mainted at 40°C, and 5°C with heat exchanger effectiveness of 70%, COP of absorption system increases with the increase in generator temperature. Further, at the condenser temperature of 20°C and 30°C, the COP of the system decreases gradually. This is due to fact that circulation ratio decreases.
Table 10 shows the experimental and simulation results oncoeffienct of performance at different generator temperature with Tc= 50°C, Ta= 40°C, and eHX= 0.7. Figure 10 depicts that when the absorber and condenser temperature is maintained at 40°C and 50°C with heat exchanger effectiveness of 70%, COP of absorption system increases with the rise in generator temperature, at different temperatures of theevaporator. Further, maximum COP is
Table 10. Computed coeffienct of performance at different generator temperature (Tc= 50°C, Ta= 40°C, eHX= 0.7) Generator temperature, Tg (oC)
Figure 10. Effect of generator temperature on COP (Tc= 50°C, Ta= 40°C, eHX= 0.7).
achieved at high evaporator temperature. Similarly, minimum COP is obtained at low evaporator temperature. This is because ofthefacts with an increase in generator temperature, the concentration of the strong solution raises which increase the circulation ratio; hence COP of absorption system rises. Table 11 shows the experimental and simulation results on coeffienct of performance at different generator
temperature with eHX= 0.7. Figure 11 depicts the variation of condenser, absorber and evaporator temperature with heat exchanger effectiveness of 70%, COP of absorption system increases with increase in generator temperature, at higher values of condenser, absorber and evaporator temperature. Further, at low values of condenser, absorber and evaporator temperature, the COP of the system decreases gradually. This is due to fact that circulation ratio decreases.
Table 11. Computed coeffienct of performance at different generator temperature (eHX= 0.7) Generator temperature, Tg (oC)
Figure 11. Effect of generator temperature (Tg) on COP (eHX= 0.7).
Effect of absorber temperature In this context, the impact of absorber temperature on heat flow rate in the generator, absorber, condenser, and evaporator, COP of absorption system has been discussed. Table 12 shows the experimental and simulation results on heat flow rate in generators, absorber, condenser and evaporator at different absorber temperature at Tg= 110°C,
Tc= 50°C, Te= 5°C, with eSHE= 0.7. Figure 12 presents the effect of high absorber temperature (Ta) on the heat flow rate in the generator, absorber, condenser, and evaporator. With increase in absorber temperature, heat flow rate in theabsorber andgenerator increases and its effect on heat flow rate in the condenser, and evaporator is independent, i.e. it remains constant. It is due to fact that withincrease of absorber temperature, circulation ratio increases and
Table 12. Computed heat flow rate in generator, absorber, condenser, and evaporatorat different absorber temperature (Tg= 110°C, Tc= 50°C, Te= 5°C, eSHE= 0.7) Absorber temperature, Ta (oC) 20
Figure 12. Effect of absorber temperature on heat flow rate in generator, absorber, condenser, and evaporator (Tg= 110°C, Tc= 50°C, Te= 5°C, eSHE= 0.7).
subsequently increase the heat transfer rate in absorber and generator. Table 13 shows the experimental and simulation results on the effect of COP in absorber at different condenser temperature with Tg= 110°C, Te= 5°C, and eSHE=
0.7. Figure 13 depicts that with increase in absorber
temperature, the COP of the absorption system decreases. Further, the values of COP is highest at low temperaturesof condenser and vice-versa. This is because, with a raise in temperature of absorber, the heat exchange rate in generator increases.
Table 13. Computed the effect of COP in absorber at different condenser temperature (Tg= 110°C, Te= 5°C, eSHE= 0.7) Absorber temperature, Ta(oC)
Figure 13. Effect of absorber temperature on COP at different condenser temperature (Tg= 110°C, Te= 5°C, eSHE= 0.7).
Table 14 shows the experimental and simulation results on COP at different absorber temperature at Tg= 110°C, Te= 5°C, and eSHE= 0.7. Figure 14 depicts that the COP of the absorption system decreases with increase in absorber temperature. Further, the values of COP is highest at high temperatures of generator and vice-versa. It is due to fact
that concentration of the strong solution increases with an increase in absorber temperature. Effect of condenser temperature In this context, the impact of condenser temperature on heat flow rate in the generator, absorber, condenser, and
Table 14. Computed COP at different absorbertemperature (Tg= 110°C, Te= 5°C, eSHE= 0.7) Absorber temperature, Ta (oC)
Figure 14. Effect of absorber temperature on COP at different generator temperature (Tg= 110°C, Te= 5°C, eSHE= 0.7).
evaporator and COP of absorption mechanism have been presented. Table 15 shows the experimental and simulation results on heat flow rate in generators, absorber, condenser and evaporator at differnet condenser temperature at Tg= 110°C, Ta= 40°C, Te= 5°C, and eSHE= 0.7. Figure 15 presents the effect of condenser temperature (Tc) on heat flow rates in the generator, absorber, condenser, and evaporator. Figure 15 depicts that with the increase in condenser
temperature, heat flow rates in absorber, condenser, and evaporator decreases but increases in the generator. This is due to fact that with increase of condenser temperature, circulation ratio increases and consequently increase the heat transfer rate. Table 16 shows the experimental and simulation results on COP at different evaporator temperature, condenser temperature at Tg= 110°C, Ta= 40°C, and eSHE=
0.7. Figure 16 depicts that with an increase in condenser
Table 15. Computed heat flow rate in generator, absorber, condenser, and evaporator at differnet condenser temperature at (Tg= 110°C, Ta= 40°C, Te= 5°C, eSHE= 0.7) Condenser temperature, Tc (oC)
Figure 15. Effect of condenser temperature on heat flow rate in generator, absorber, condenser, and evaporator (Tg= 110°C, Ta= 40°C, Te= 5°C, eSHE= 0.7).
temperature, the COP of the absorption system decreases at different values of evaporator temperature. Further, the values of COP is highest at high evaporator temperature and vice-versa. This is due to fact that with increase in evaporator temperature, the heat transfer rate in evaporator increases.
Effect of evaporator temperature In this section, the effect of evaporator temperature on heat flow rate in the generator, absorber, condenser, and evaporator and COP of absorption mechanism have been presented.
Table 16. Computed COP at different evaporator temperature, condenser temperature (Tg= 110°C, Ta= 40°C, eSHE= 0.7) Condenser temperature, Tc (oC)
Figure 16. Impact of condenser temperature on COP at variant evaporator temperature (Tg= 110°C, Ta= 40°C, eSHE= 0.7).
Table 17 shows the experimental and simulation results on COP at different evaporator temperature at Tg= 110°C, Ta= 40°C, Tc= 50°C, and eSHE= 0.7. Figure 17 depicts that the COP of the absorption system increases with increase in evaporator temperature at different values of generator temperature. This is due to fact that at low pressure,
the enthalpy at evaporator exit increases. Further, with an increament in generator temperature, the concentration of the weak solution increases too which increases the COP of the absorption system.In other words, refrigeration capacity increases and heat transfer in HTG decreases. Thus, COP of system increases at different generator temperature.
Table 17. Computed COP at different evaporator temperature (Tg= 110°C, Ta= 40°C, Tc= 50°C, eSHE= 0.7) Evaporator temperature, Te (oC)
Figure 17. Impact of evaporator temperature on COP of absorption system (Tg= 110°C, Ta= 40°C, Tc= 50°C, eSHE= 0.7).
Conclusion
The experimental and numerical research on a LiBrwater vapor absorption system has been conducted. The experimental values of COP and circulation ratio of the vapor absorption system have been compared with the values predicted using EES. The effect of operating variables onLiBr-Waterabsorption system has been doneovera broad range of operating conditionsfor the feasibility assessment in the dairy industry. The conclusions drawn from the analysis have been summarized as: • A simulation model has been developed, and the results have been compared with the experimental outcome. The results of both the simulation and the experiments have been observed to be in good agreement of 5.3%. • The COP of the system increased with raise in the generator temperature at different temperatures of absorber and evaporator. However, the COP decreased by varyingthe temperature of the condenser due to a decrease in circulation ratio. Further, under the simultaneous variations in temperature of absorber, condenser and evaporator, the COP of the system decreased. • The rate of heat exchanger in absorber and condenser has been observed to be increased with a rise in generator temperature. Although, the rate of heat exchange in the generator decreased gradually as the circulation ratio tend to fall. Moreover, the impact of the rise of generator temperature on heat transfer in evaporator
remains constant. It is since the increase in generator temperature cause the circulation ratio to decrease. The heat flow rates in the generatorand absorber increased with the increase in absorber temperature while remained constant in the condenser and evaporator due to the rise in circulation proportion. The heat flow rates in absorber, condenser and evaporator decreased with the increase in condenser temperature while increased in the generator. It has been observed that with the increase in evaporator temperature the heat transfer rate in the absorber and the generator decreased while increased in the evaporator. Moreover, heat transfer in the condenser remained constant. The main reason for the drop of heat transfer in the absorber was that the circulation proportiontends to decline, and the concentration of less stable solution leaving from the generator increased. The decline of heat transfer in the generator was because of the gradual drop of enthalpy of refrigerant entering the condenser. According to study conducted by Yildrem and Genc [11] the heat required in dairy industry for process heat application is 2375kW. In this research work heat rejected from the condenser of the experimental facility has been observed to be in same range approx. (2100 – 2400 kW) that is quite sufficient to fulfil the requirement of a dairy industry.
Ethics
Symbols and abbreviations COP Coefficient of performance CR Circulation ratio EES Engineering equation solver LiBr Lithium bromide Mass flow rate (kg/s) Mass flow rate of refrigerant (kg/s) P Pressure (kPa) Qe Refrigerating effect (kW) QG Heat input of generator (kW) T Temperature (°C) Ta Absorber temperature (°C) Tb Boundary temperature (K) Tc Condenser temperature (°C) Te Evaporator temperature (°C) Tg Generator temperature (°C) X Concentration of Lithium bromide in solution (%)
There are no ethical issues with the publication of this manuscript.
Subscripts a, Abs Absorber c Condenser D Destruction e Evaporator g Generator Ex. Expansion i Represents, corresponding state points o Outlet condition p Pump r Refrigerant RTV Expansion valve S Strong SHE Solution heat exchanger STV Solution throttle valve W Weak
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SOLANKI, A.; PAL, Y. Designing of system for high grade heat recovery in thermal coolingsystem for process heat applicati. Journal of Thermal Engineering 2023, Vol. 9, pp. 679-701. https://doi.org/10.18186/thermal.1299161