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An absorption chiller system using lithium bromide and water as working fluids: exergy analysis.

INTRODUCTION

Absorption refrigeration systems have been adopted for many years. These systems are becoming more and more important nowadays, especially because they are environment friendly. Absorption refrigeration cycles have been studied extensively for the last two decades and because of recent developments in cooling and heating systems there is a growing interest in the applications of these systems. An absorption heat pump is a thermally activated system with natural refrigerants such as water/lithium bromide and ammonia/water pairs. Although the absorption cooling systems have been known for over 100 years, recent environmental concerns on global warming and ozone depletion by chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants have promoted a renewed interest in these refrigerants and systems in which they are employed. In absorption systems, a physiochemical process replaces the mechanical process of the vapor compression system by using energy in the form of heat rather than mechanical work. Absorption cooling represents a practical way of decreasing the electrical energy consumption associated with the peak cooling energy demand in the summer and also for recovering the waste energy from industrial plants or other sources (Kim and Park 2007). In addition to that, it has fewer moving parts, meaning lower noise levels, high reliability, and improved durability. However, the drawbacks of the absorption systems are its heavy weight, relatively high capital cost, etc.

In the present era, there has been a significant interest in energy conservation that has prompted a new methodology, and this has brought a relative change to the critical analysis of almost all thermodynamic processes and installations. There has been a development in the concept of the second law of thermodynamics because the analysis based on the first law of thermodynamics is not adequate due to the fact that the first law is based on material balance, energy balance, and equilibrium relationships. These relationships do not adequately show how effectively a system utilizes the given energy resources. In recent years, there has been a growing interest in the use of the principles of the second law of thermodynamics for analyzing and evaluating the thermodynamic performance of thermal systems as well as their technologies. This is a well established method that is used to study the energy conversion processes (Kotas 1985). The analysis based on exergy provides information for each component of the system and pinpoints the real inefficiencies in a system.

For the last two decades, researchers used second-law analysis based on the theoretical analysis given by Bejan et al. (1995) for thermodynamic optimization of refrigeration plants. The experimental studies were carried on the heat and mass transfer performance of a coiled-tube absorber for R134a-DMAC-based absorption cooling system (Ajib and Karno 2008) and the analysis shows that an absorber is an important component of the absorption system and it greatly affects the overall performance of the system. The analysis also shows that heat and mass transfer in an absorber is greatly influenced by the properties of the fluid, geometry of the absorber, and various operating parameters. An analysis of thermophysical properties of acetone-zinc bromide for a low-temperature-driven absorption refrigeration machine was carried out (Ajib and Karno 2008) by measuring thermal and physical properties; like viscosity, specific enthalpy, and vapor-pressure density; and the required state diagrams like log (p, T) and log (h, T) for solution as well as log (p-h) diagrams for the pure acetone were also calculated, correlated, and presented. The results showed that acetone-zinc bromide solution is a better option to be used as a working solution for low-temperature-driven absorption cycles.

A computer simulation model based on energy and exergy analysis has been developed to carry out detailed thermodynamic analysis of a 10 kW (9.4781 Btu/s) solar-powered absorption system using N[H.sub.3]-[H.sub.2]O as the working fluid (Abu-Ein et al. 2009) and the results obtained indicate that minimum and maximum values of COP and exergetic COP were found to be at the generator temperature of 110[degrees]C and 200[degrees]C (230[degrees]F and 392[degrees]F), respectively, while the maximum exergy losses were found to be in the absorber at the generator temperature of 130[degrees]C (266[degrees]F) for all evaporator temperatures.

A mathematical model based on second-law analysis for water/lithium bromide absorption refrigeration system was developed (Kilic and Kaynakli 2007) to evaluate the system performance, exergy losses of all the components, and the total exergy loss of the system. The results obtained show that performance of the system increases with an increase in the generator and evaporator temperature, but decreases with an increase in absorber and condenser temperature. They also concluded that the highest exergy loss occurs in the generator, irrespective of the operating conditions.

A computational model has been developed for exergy and energy analysis of the single-effect and series flow double-effect water/lithium bromide absorption refrigeration systems (Kaushik and Arora 2009). The analysis includes the determination of the effects of generator, absorber, and evaporator temperature on the energetic and exergetic performance parameters like COP, exergy destruction, exergy efficiency, and exergy defects. The results obtained revealed that the COP of the single effect and series flow double effect lies in the range of 0.6-0.75 and 1-1.28, respectively. An experimental investigation of the performance of a commercially available 10 kW (9.4781 Btu/s) vapor absorption system was carried out (Horuz and Callander 2004) and the response of system to variations in chilled-water inlet temperature, chilled-water level in evaporator drum, chilled-water flow rate, and variable heat input were presented graphically.

An experimental evaluation of a plant aimed at stimulating and verifying performances of a single-stage [H.sub.2]O-LiBr absorption machine was carried out (Asdrubali and Grignaffini 2005). An alternative absorbent (LiBr: CH[O.sub.2]K=2: 1 by mass ratio) and refrigerant (H2O) to replace the absorbent is currently employed (i.e., lithium bromide was studied [De Lucas et al. 2004]).

An exergy analysis of a single-effect absorption refrigeration cycle with lithium bromide/water as the working fluid pair was conducted (Talbi and Agnew 2000). A design procedure was applied to a lithium bromide absorption cycle and an optimization procedure that consists of determining the enthalpy, entropy, temperature, mass flow rate, and heat rate in each component and coefficient of performance was calculated. The performance and temperature formulae for the absorption cycle were also derived (Tozer and James 1997). Performance and temperature relations of double, triple, and multistage cycles were derived, and also the validation of the of absorption cycles was presented by applying the exergy analysis.

The behavior of two-stage compound compression refrigeration cycle with flash intercooling, using refrigerant R-22, by exergy method was investigated (Nikolaidis and Probert 1998). The results obtained show that the greater the temperature difference between either the condenser and the environment, or the evaporator and the cold room, the higher the irreversibility rate.

The present study deals with the analysis of a 5TR (16.66 Btu/s) single-effect lithium bromide/water vapor absorption system using hot water as the heat source and a mixture of LiBr-[H.sub.2]O as the absorbent-refrigerant pair which produces the chilled water for the purpose of air-conditioning applications. The main components involved in the chiller are the generator, condenser, evaporator, absorber, solution heat exchanger, expansion valve, and the hermetically sealed pump. The energy as well as exergy analysis of the system has been carried out and the analysis shows that the operating parameters affect the system performance. The irreversibility rate in the generator is found to be the highest while it is found to be reversing in the case of absorber.

SYSTEM DESCRIPTION

The schematic diagram of a single-effect absorption refrigeration system is shown in Figure 1. The generator uses the heat from the waste hot water, which is at a higher temperature. The ambient temperature considered for the analysis is at 25[degrees]C (77[degrees]F). The strong solution leaving the absorber is pumped to the high-temperature heating source (i.e., generator through the heat exchanger [4-6]). The high-temperature heating source (11) adds heat to the generator to generate the water vapor from the strong solution. These high-temperature refrigerant vapors enter the condenser (7) to form the condensate and the latent heat is released to the cooling water flowing through the condenser (14). Finally, the saturation liquid leaves the condenser. This condensate coming from the condenser is again restricted to flow through the solution-reducing valve where the throttling takes place. The condensate enters the evaporator (9) via throttling process (8) where the chilled water is sprinkled on the evaporator tubes and refrigerant is again converted to vapors by absorbing the latent heat from the chilled water circulated between the evaporator and the space to be cooled (15). The refrigerant vapors produced enter the absorber (10) and are absorbed by a strong solution in the absorber. The solution in the absorber is cooled by the cooling water before it is returned to the generator. The process is continued and refrigeration effect is repeated.

The energy and mass balance equations were written around each component to determine the heat and mass transfer for each component. The thermodynamic analysis of each component indicates the various losses as well as their intensity. The computer program has been developed for energy and mass balance using [C.sup.++] language. The heat and mass transfer equations are also written in terms of interconnected subunits of the system, which are described by the different state points, as shown in Figure 1. The initial conditions that are read in the program include the ambient conditions, capacity, various temperatures of the cooling water, and pump efficiency. The thermodynamic properties of the working fluid have been used (Kothandaraman 2006) and with these conditions, the program calculates various parameters that finally help in the determination of the performance of the absorption system based on energy and exergy analysis. The various operating conditions and fixed parameters for the simulation are given in Table 1.

Thermodynamic Analysis

For the thermodynamic analysis of the absorption system the principles of mass conservation, the first and second laws of thermodynamics are applied to each component of the system. Each component can be treated as a control volume with inlet and outlet streams, heat transfer, and work interactions. The governing equation of mass and type of material balance for steady-state operation of the system are given as follows:

Mass conservation

[summation][[??].sub.i] - [summation][[??].sub.o] = 0 (1)

Species conservation

[summation][([??]x).sub.i] - [summation][([??]x).sub.o] = 0 (2)

where, [??] is mass flow rate and x is concentration of LiBr in the solution. The first law of thermodynamics yields the energy balance of each component of the absorption system as follows:

Energy conservation

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

Energy Analysis

For the thermodynamic analysis of vapor absorption refrigeration system, the energy balance equations of the various components need to be calculated. The refrigeration system can be considered as a perfectly reversible system and the net refrigerating effect is the heat absorbed by the refrigerant in the evaporator. Therefore, the theoretical COP is given as follows:

COP = [[??].sub.e]/[[??].sub.g] (4)

where [[??].sub.e] is the cooling effect and [[??}.sub.g] is the energy supplied to the generator/ heat source. In the case of an absorption refrigeration system, the total energy supplied to the systems is the total of the heat supplied in the generator and work consumed by the pump. The actual COP of an absorption chiller is calculated from the equation as follows:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)

where [[??].sub.p] is the pump work calculated to be very small as compared to the heat supplied to the generator and, hence, neglected in the calculation part for the calculation of COP of the system. The energy balance equations of different components are as follows.

Energy balance in evaporator

[Q.sub.e] = [[??].sub.15] ([h.sub.15] - [h.sub.16]) (6)

Energy balance in condenser

[Q.sub.c] = [[??].sub.13] ([h.sub.14] - [h.sub.13]) (7)

Energy balance in absorber

[Q.sub.a] = [[??].sub.17]([h.sub.18] - [h.sub.17]) (8)

Energy balance in generator

[Q.sub.g] = [[??].sub.11]([h.sub.11] - [h.sub.12]) (9)

Work done by pump

[W.sub.P] = [[??].sub.4][[p.sub.g] - [p.sub.a])/[rho]] (10)

Exergy Analysis

Exergy analysis applied to a system describes all losses in the individual components of the system as well as in the whole system. The principle irreversibilities in a process leading to these losses are due to various factors (ASHRAE 1997) including

* friction

* heat transfer under temperature difference

* unrestricted expansion

With the help of this analysis, the magnitude of losses or irreversibility and their order of importance can be understood. With the use of irreversibility, which is a measure of process imperfection, the optimum operating conditions can be easily determined. The advantage of exergy analysis based on thermoeconomic optimization is that the different elements of the system could be optimized independently. The physical exergy component is associated with the work obtainable in bringing a stream of matter from the initial state to a state that is in thermal and mechanical equilibrium with the environment. Mathematically, physical exergy is expressed as given in Equation 11 (Bejan et al. 1995):

[E.sub.x] = [??][(h - [h.sub.o]) - [T.sub.o](s - [s.sub.o])] (11)

where, [E.sub.x] is the exergy of the fluid at temperature T. The terms h and s are the enthalpy and entropy of the fluid, whereas, [h.sub.o] and [s.sub.o] are the enthalpy and entropy of the fluid at environmental temperature [T.sub.o]. For the thermodynamic analysis of vapor absorption refrigeration systems, the exergy balance equations of the various components are as follows.

Exergy balance in evaporator:

[Ex.sub.e] = [[??].sub.15][([h.sub.15] - [h.sub.16]) - [T.sub.o]([s.sub.15] - [s.sub.16])] (12)

Exergy balance in generator:

[Ex.sub.g] = [[??].sub.11][([h.sub.11] - [h.sub.11]) - [T.sub.0]([s.sub.11] - [s.sub.12])] (13)

Exergy balance in absorber:

[Ex.sub.a] = [[??].sub.17][([h.sub.18] - [h.sub.17]) - [T.sub.o]([s.sub.18] - [s.sub.17])] (14)

Exergy balance in condenser:

[Ex.sub.c] = [[??].sub.13][([h.sub.14] - [h.sub.13]) - [T.sub.o]([s.sub.14] - [s.sub.13])] (15)

The exergy loss in different components is given as: Exergy loss in generator:

[Ex.sub.g] = [[??].sub.11][([h.sub.11] - [h.sub.o]) - [T.sub.o]([s.sub.11] - [s.sub.o])] - [[??].sub.11][([h.sub.12] - [h.sub.o]) - [T.sub.o]([s.sub.12] - [s.sub.o])] (16)

Exergy loss in condenser:

[Ex.sub.c] = [[??].sub.13][([h.sub.13] - [h.sub.o]) - [T.sub.o]([s.sub.13] - [s.sub.o])] - [[??].sub.13][([h.sub.14] - [h.sub.o]) - [T.sub.o]([s.sub.14] - [s.sub.o])] (17)

Exergy loss in absorber:

[Ex.sub.a] = [[??].sub.17][([h.sub.18] - [h.sub.o]) - [T.sub.o]([s.sub.18] - [s.sub.o])] - [[??].sub.17][([h.sub.17] - [h.sub.o]) - [T.sub.o]([s.sub.17] - [s.sub.o])] (18)

Exergy loss in evaporator:

[Ex.sub.e] = [[??].sub.15][([h.sub.15] - [h.sub.o]) - [T.sub.o]([s.sub.15] - [s.sub.o])] - [[??].sub.15][([h.sub.16] - [h.sub.o]) - [T.sub.o]([s.sub.16] - [s.sub.o])] (19)

The second-law performance of the system can be measured in terms of exergetic efficiency, which is given as ratio of exergy loss in evaporator to the generator and is expressed as:

[[eta].sub.ex] = [absolute value of ([([Ex.sub.evap]).sub.in] - [([Ex.sub.evap]).sub.out])]/[absolute value of ([([Ex.sub.gen]).sub.in] - [([Ex.sub.gen]).sub.out])] (20)

Where, [[eta].sub.ex] is the exergy efficiency [([Ex.sub.evap]).sub.in] and [([Ex.sub.evap]).sub.out] are the exergies at the inlet and outlet of evaporator, respectively. Also, [([Ex.sub.gen]).sub.in] and [([Ex.sub.gen]).sub.out] are the exergies at the inlet and outlet of generator, respectively.

ASSUMPTIONS

The analysis presented here is based on the following assumptions:

a. The cooling capacity of the system is taken as 5TR (17.584 kW) (16.66 Btu/s).

b. The cycle is operated in steady-state conditions.

c. Solution and refrigerant are in equilibrium at the given conditions.

d. Refrigerant is totally vaporized in the evaporator and totally absorbed into the solution in the absorber.

e. There is no heat loss to the surroundings.

f. There is no loss in the connecting pipes and pressure drop within the system is negligible.

g. The condition of refrigerant at the exit of evaporator and condenser is saturated.

h. The flow rate at the exit, as well as inlet, remains constant in all components.

RESULTS AND DISCUSSION

A theoretical study of an absorption system using heat from waste hot water to produce chilled water for air-conditioning applications is presented in this paper. A computer program has been developed to analyze the system. The hot-water temperature to the generator is varied from 65[degrees]C to 145[degrees]C (149[degrees]F to 293[degrees]F) and the corresponding effect on the performance of the system being evaluated for a typical set of operating parameters as given in the Table 1. The energy analysis, exergy loss (irreversibility), and other performance parameters were calculated and the results are given in Tables 2 and 3, respectively. The mass flow rate of the different components is also calculated and given in the Table 4. The exergy loss in different components, the exergy efficiency, and other parameter against the generator temperature are shown in Figures 2 through 7.

Table 2 shows the energy analysis of all the components as well as the COP of the system, whereas Table 3 shows the exergy losses in each component as well as exergy efficiency. Imperfect heat and mass transfer in the system components, frictional losses, and mixing and circulating losses are the main factors responsible for the reduction in COP and exergy efficiency. The mixing losses are due to evaporation of refrigerant in the generator because it requires a large amount of heat as compared to refrigerant in the pure state. Due to the huge requirement of heat, there is large exergy loss in the generator. In the present system, the exergy loss for condenser and absorber are almost same, but the exergy loss in the absorber is more as compared to the condenser as in actual practice, and this is due to the fact there is mixing of two streams in different phases (i.e., refrigerant in vapor phase and weak solution in liquid phase), which leads to more entropy generation inside the absorber and hence leads to an increase in the exergy loss. The exergy efficiency can be enhanced by the optimum matching of the heat source with the temperature of the working fluid in the generator.

The variation of exergy loss in the generator with the generator temperature is shown in Figure 2. From the figure it can be seen that with an increase in generator temperature, the exergy loss in generator also increases. This is due to the fact that as the generator temperature increases, the production of refrigerant vapors increases in the generator, indicating more randomness and hence increases the exergy loss. The results also indicate that higher generator temperature produces more refrigerant vapors because of higher energy supply yet generates more exergy losses in the generator, and this might be happening because of the higher rate of heat transfer at higher generator temperature, while in case of absorber the improper heat transfer and mixing of two different phases of streams is responsible for higher exergy loss. The variation of the exergy loss in the evaporator with generator temperature is shown in Figure 3, and it can be seen that exergy loss in evaporator decreases with an increase in generator temperature, indicating that the exergy losses in the evaporator are greatly influenced by the operating parameters in general and the generator temperature in particular. Thus, the exergy loss in the evaporator decreases at higher generator temperature because of the temperature difference between the environment and refrigerant in the evaporator.

Figure 4 shows the variation of the exergy loss in the condenser with respect to generator temperature of the system, and it can be seen from the figure that exergy loss in the condenser decreases with an increase in the generator temperature, which might be due to the lower circulation rate and high quality vapors of the refrigerant in the condenser because of an increase in the generator pressure. As a result, the flow of refrigerant decreases, thereby reducing the exergy losses in the condenser at a higher generator temperature. Figure 5 shows the variation of the exergy loss in the absorber with generator temperature and it also shows the same trend shown in Figure 4. This is due to the fact that circulation ratio varies linearly with the temperature, and, because of this, the exergy loss in the absorber follows the trend which can be seen in Figure 5.

Finally, the variation of exergy efficiency with generator temperature is shown in Figure 6. From the figure, it is found that an increase in generator temperature leads to decrease in exergy efficiency of the system. This may be due to the fact that a higher generator temperature produces more refrigerant vapors, thus leading to higher entropy generation and hence more irreversibility in the system. The increased production of vapors in the generator eventually leads to an increase in the cooling effect. The generator exergy loss also increases with an increase in generator temperature as more exergy input is provided, which leads to increase in entropy of the system and hence exergy efficiency decreases. This is in agreement with the work done by the authors (Kaushik and Arora 2009). The single-effect vapor absorption refrigeration system shows the highest exergy losses at low heat source temperature when compared with the double-effect absorption system.

The variation of COP with the generator temperature is shown in Figure 7, and it can be seen that the COP increases initially up to a small temperature range and then decreases with further increase in the generator temperature. Thus, there is an optimal value of generator temperature at which the COP attains its maximum value for a given set of operating parameters (Figure 7). This is happening because of the fact that with an increase in generator temperature, the boiling-off process of the refrigerant becomes faster, and, hence, the temperature of the refrigerant exiting from the generator also increases, leading to the randomness in the heat source, which leads to more irreversibility in the heat source component. With an increase in generator temperature, the circulation loss increases, and, subsequently, the mixing loss also increases because it requires a large amount of heat, compared to the refrigerant in the pure state.

CONCLUSIONS

A computer program has been developed to predict the performance of single-effect lithium bromide/water vapor absorption system. The thermodynamic analysis of absorption system has been carried out using the concept of energy as well as exergy. The exergy analysis shows that the operating parameters affect the system performance. The irreversibility rate in the generator is found to be the highest, while in the case of absorber, it is found to be the lowest. It is also found that the irreversibility rate in the generator is more because of increased rate of heat transfer in the generator. Also, the exergy losses are found to be more in the generator because of heat of mixing in the solution, which is not the case in pure substances.

Again, it is noticeable that the COP of the system increases minutely as the generator temperature increases and then decreases with further increases in the generator temperature, but the exergy efficiency of the system drops with an increase in generator temperature. The COP of the system shows such a trend because with an increase in the generator temperature the temperature of the refrigerant exiting from the generator also increases, and hence the irreversibility in the component shows an increasing trend. Also, an increase in the generator temperature increases the circulation losses as well as mixing losses which are generated because of the vaporization of the refrigerant in the generator from the strong solution requiring a large amount of heat as compared to the refrigerant in the pure state. This increases the input heat load causing the lower COP of the system. The results with respect to exergy losses in each component and exergy efficiency are very important for the optimization of the absorption system. The results obtained here will be useful to improve the performance of the cycle; attention must be paid to reduce the irreversibilities associated with the components of absorption refrigeration systems.

ACKNOWLEDGMENT

The financial assistance under Project No. 22/541/10-EMR-II from the Council for Scientific and Industrial Research (CSIR), New Delhi, India for this study is highly appreciated.

NOMENCLATURE

COP     = coefficient of performance
TR      = ton of refrigeration (Btu/s)
[??]    = mass flow rate, kg/s (lb/s)
h       = enthalpy, kJ/kg (Btu/lb)
s       = entropy, kJ/kg-K (Btu/lb-[degrees]F)
[??]    = heat flow, kW (Btu/s)
[??]    = power consumption, kW (Btu/s)
p       = pressure, bar (psi)
[rho]   = density, kg/[m.sup.3] (lb/[ft.sup.3])
1-18    = different state points in the system indicating
          flow of water as well as refrigerant
ex      = exergy/exergetic, kW (Btu/s)
T       = temperature, K ([degrees]F)
Ex      = exergy, kW (Btu/s)
[eta]   = efficiency
in      = inlet of the component
out     = outlet of the component

Subscripts

e, evap = evaporator
g, gen  = generator
c       = condenser
a       = absorber
o       = ambient
P       = pump


REFERENCES

Abu-Ein, Suleim Qaseem, Sayel M. Fayyad, Waleed Momani, and Mamdouh Al-Bousoul. 2009. Performance analysis of solar powered absorption refrigeration system. Heat and Mass Transfer 46: 137-45.

Ajib, Salman, and S. Karno. 2008. Thermo-physical properties of acetone-zinc bromide for using in a low temperature driven absorption refrigeration machine. Heat and Mass Transfer 45: 61-70.

Asdrubali, F., and S. Grignaffini. 2005. Experimental Evaluation of the performances of a [H.sub.2]O-LiBr Absorption refrigerator under different service conditions. International Journal of Refrigeration 28: 489-97.

ASHRAE. 1997. ASHRAE Handbook--Fundamentals (SI ed.) Atlanta: ASHRAE.

Bejan, A., G. Tsatsaronis, and M. Moran. 1995. Thermal Design and Optimization. New York: Wiley.

De Lucas, Antonio, Marina Donate, Carolina Molero, Jose Villasenor, Juan F. Rodriguez. 2004. The performance evaluation and simulation of a new absorbent for an absorption refrigeration system. International Journal of Refrigeration 27: 324-30.

Horuz, I., and T.M.S. Callander. 2004. Experimental investigation of a vapor absorption refrigeration system. International Journal of Refrigeration 27: 10-16.

Kaushik, S.C., and A. Arora. 2009. Exergy and energy analysis of the single-effect and series flow double effect water-lithium bromide absorption refrigeration systems. International Journal of Refrigeration 32: 1247-58.

Kilic, M., and O. Kaynakli. 2007. Second law based thermodynamic analysis of water-lithium bromide absorption refrigeration system. International Journal of Energy 32: 1505-12.

Kim, Byongjoo, and Jongil Park. 2007. Dynamic simulation of a single-effect ammonia water absorption chiller. International Journal of Refrigeration 30: 535-45.

Kotas, T.J. 1985. The exergy method of thermal plant analysis. London: Butterworth.

Kothandaraman, C.P. 2006. Steam tables, 2nd ed. New Delhi: New Age International Publishers.

Nikolaidis, C., and D. Probert. 1998. Exergy-method analysis of a two-stage vapor compression refrigeration-plant's performance. Applied Energy 60: 241-56.

Talbi, M.M., and B. Agnew. 2000. Exergy analysis: An absorption refrigerator using lithium bromide and water as the working fluids. Applied Thermal Engineering 20: 619-30.

Tozer, Robert M., and Ron W. James. 1997. Fundamental thermodynamics of ideal absorption cycles. International Journal of Refrigeration 20: 120-35.

Tharves, S. Mohideen, and S. Renganarayan. 2008. Experimental studies on heat and mass transfer performance of a coiled tube absorber for R134a-DMAC based absorption cooling system. Heat and Mass Transfer 25: 47-54.

Table 1. Working Parameters Adopted
for Cycle Simulation

Conditions and Parameters                 Fixed Value

Cooling capacity                 5TR (17.584 kW) (16.66 Btu/s)

Evaporator outlet temperature       281.15 K(46.4[degrees]F)

Absorber outlet temperature          303.15 K(86[degrees]F)

Condenser outlet temperature         303.15 K(86[degrees]F)

Pump efficiency                               0.8

Generator temperature              65[degrees]C-145[degrees]C
                                 (149[degrees]F-293[degrees]F)
                                   (variation of 2[degrees]C
                                     [35.6[degrees]F] each)

High pressure                          20 bar (290.07psi)

Low pressure                             4bar(58.01psi)

Table 2. Energy Analysis of Absorption System

Serial       [Q.sub.e],         [Q.sub.g],         [Q.sub.a],
Number       kW (Btu/s)         kW (Btu/s)         kW (Btu/s)

1         17.433 (16.523)    18.723 (17.745)    16.709 (15.837)
2         17.432 (16.522)    18.700 (17.724)    16.698 (15.826)
3         17.430 (16.520)    18.679 (17.704)    16.685 (15.814)
4         17.428 (16.518)    18.702 (17.726)    16.672 (15.802)
5         17.427 (16.517)    18.746 (17.767)    16.658 (15.788)
6         17.425 (16.515)    18.874 (17.889)    16.645 (15.776)
7         17.423 (16.513)    18.916 (17.928)    16.632 (15.764)
8         17.422 (16.512)    18.942 (17.953)    16.618 (15.750)
9         17.420 (16.510)    18.986 (17.999)    16.605 (15.738)
10        17.418 (16.509)    18.993 (18.001)    16.592 (15.726)
11        17.418 (16.509)    19.054 (18.059)    16.578 (15.712)
12        17.418 (16.509)    19.089 (18.092)    16.567 (15.702)
13        17.416 (16.507)    19.128 (18.129)    16.556 (15.692)
14        17.415 (16.506)    19.152 (18.152)    16.541 (15.677)
15        17.413 (16.504)    19.187 (18.185)    16.525 (15.662)
16        17.411 (16.502)    19.229 (18.225)    16.512 (15.650)
17        17.410 (16.501)    19.272 (18.266)    16.498 (15.637)
18        17.408 (16.499)    19.316 (18.308)    16.485 (15.624)
19        17.406 (16.497)    19.356 (18.345)    16.472 (15.612)
20        17.405 (16.496)    19.406 (18.393)    16.458 (15.599)
21        17.403 (16.494)    19.424 (18.410)    16.445 (15.586)
22        17.401 (16.492)    19.465 (18.449)    16.432 (15.574)
23        17.400 (16.492)    19.507 (18.489)    16.419 (15.562)
24        17.398 (16.490)    19.540 (18.520)    16.406 (15.549)
25        17.396 (16.488)    19.584 (18.562)    16.392 (15.536)
26        17.395 (16.487)    19.624 (18.599)    16.378 (15.523)
27        17.393 (16.485)    19.669 (18.642)    16.365 (15.511)
28        17.391 (16.483)    19.709 (18.680)    16.351 (15.497)
29        17.390 (16.482)    19.748 (18.717)    16.338 (15.485)
30        17.388 (16.480)    19.794 (18.761)    16.327 (15.475)
31        17.386 (16.478)    19.839 (18.803)    16.312 (15.460)
32        17.385 (16.477)    20.019 (18.974)    16.299 (15.448)
33        17.383 (16.475)     20.062 (19.01)    16.285 (15.435)
34        17.381 (16.474)    19.941 (18.900)    16.272 (15.422)
35        17.380 (16.473)    20.011 (18.966)    16.258 (15.409)
36        17.378 (16.471)    20.060 (19.013)    16.245 (15.397)
37        17.376 (16.469)    20.124 (19.073)    16.232 (15.384)
38        17.375 (16.468)    20.164 (19.111)    16.219 (15.372)
39        17.373 (16.466)    20.203 (19.148)    16.206 (15.360)
40        17.371 (16.464)    20.256 (19.198)    16.192 (15.347)
41        17.370 (16.463)    20.310 (19.250)    16.179 (15.334)

Serial       [Q.sub.c],       COP
Number       kW (Btu/s)

1         17.532 (16.617)    0.931
2         17.530 (16.615)    0.932
3         17.528 (16.613)    0.933
4         17.526 (16.611)    0.931
5         17.523 (16.608)    0.929
6         17.521 (16.606)    0.923
7         17.519 (16.604)    0.921
8         17.517 (16.602)    0.919
9         17.515 (16.601)    0.917
10        17.512 (16.598)    0.917
11        17.509 (16.595)    0.914
12        17.506 (16.592)    0.912
13        17.504 (16.590)    0.910
14        17.502 (16.588)    0.909
15        17.499 (16.585)    0.907
16        17.496 (16.583)    0.905
17        17.493 (16.580)    0.903
18        17.491 (16.578)    0.901
19        17.489 (16.576)    0.899
20        17.486 (16.573)    0.896
21        17.483 (16.570)    0.895
22        17.480 (16.567)    0.893
23        17.477 (16.565)    0.891
24        17.474 (16.562)    0.890
25        17.471 (16.559)    0.888
26        17.469 (16.557)    0.886
27        17.466 (16.554)    0.884
28        17.464 (16.552)    0.882
29        17.461 (16.549)    0.880
30        17.458 (16.546)    0.878
31        17.455 (16.544)    0.876
32        17.454 (16.543)    0.868
33        17.453 (16.542)    0.866
34        17.448 (16.537)    0.871
35        17.443 (16.532)    0.868
36        17.440 (16.529)    0.866
37        17.436 (16.526)    0.863
38        17.433 (16.523)    0.861
39        17.430 (16.520)    0.859
40        17.427 (16.517)    0.857
41        17.423 (16.513)    0.855

Table 3. Exergy Losses in Different Components and the
Overall Exergy Efficiency of the System

Serial       Absorber,         Evaporator,         Generator,
Number       kW (Btu/s)         kW (Btu/s)         kW (Btu/s)

1         0.1042 (0.0987)    0.6697 (0.6347)     1.9699 (1.8671)
2          0.1041(0.0986)    0.6696 (0.6346)     2.0266 (1.9208)
3         0.1040 (0.0985)    0.6696 (0.6346)     2.0811 (1.9725)
4         0.1040 (0.0985)    0.6695 (0.6345)     2.1786 (2.0649)
5         0.1039 (0.0984)    0.6695 (0.6345)     2.2876 (2.1682)
6         0.1038 (0.0983)    0.6694 (0.6344)     2.4857 (2.3559)
7         0.1037 (0.0982)    0.6693 (0.6343)     2.5874 (2.4523)
8         0.1036 (0.0981)    0.6693 (0.6343)     2.6779 (2.5381)
9         0.1035 (0.0980)    0.6692 (0.6342)     2.7838 (2.6385)
10        0.1035 (0.0980)    0.6691 (0.6341)     2.8559 (2.7068)
11        0.1034 (0.0980)    0.6691 (0.6341)     2.9816 (2.8260)
12        0.1033 (0.0979)    0.6691 (0.6341)     3.0784 (2.9177)
13        0.1032 (0.0978)    0.6691 (0.6341)     3.1990 (3.0320)
14        0.1031 (0.0977)    0.6690 (0.6340)     3.2676 (3.0970)
15        0.1030 (0.0976)    0.6689 (0.6339)     3.3626 (3.1871)
16        0.1030 (0.0976)    0.6689 (0.6339)    3.4662 (3. 2853)
17        0.1029 (0.0975)    0.6688 (0.6339)     3.5591 (3.3733)
18        0.1028 (0.0974)    0.6687 (0.6338)     3.6502 (3.4597)
19        0.1027 (0.0973)    0.6687 (0.6338)     3.7436 (3.5482)
20        0.1026 (0.0972)    0.6686 (0.6337)     3.8462 (3.6454)
21        0.1025 (0.0971)    0.6686 (0.6337)     3.9207 (3.7161)
22        0.1025 (0.0971)    0.6685 (0.6336)     4.0349 (3.8243)
23        0.1024 (0.0970)    0.6684 (0.6335)     4.1310 (3.9154)
24        0.1023 (0.0969)    0.6684 (0.6335)     4.1989 (3.9797)
25        0.1022 (0.0968)    0.6683 (0.6334)     4.2891 (4.0652)
26        0.1021 (0.0967)    0.6682 (0.6333)     4.3721 (4.1439)
27        0.1020 (0.0966)    0.6682 (0.6333)     4.4830 (4.2490)
28        0.1020 (0.0966)    0.6681 (0.6332)     4.5480 (4.3106)
29        0.1019 (0.0965)    0.6680 (0.6331)     4.6474 (4.4048)
30        0.1018 (0.0964)    0.6680 (0.6331)     4.7405 (4.4931)
31        0.1017 (0.0963)    0.6679 (0.6330)     4.8330 (4.5808)
32        0.1016 (0.0962)    0.6679 (0.6330)     5.0521 (4.7884)
33        0.1016 (0.0962)    0.6678 (0.6329)     5.1367 (4.8686)
34        0.1015 (0.0962)    0.6677 (0.6328)     5.0773 (4.8123)
35        0.1014 (0.0961)    0.6677 (0.6328)     5.1707 (4.9008)
36        0.1013 (0.0960)    0.6676 (0.6327)     5.2624 (4.9877)
37        0.1012 (0.0959)    0.6675 (0.6326)     5.3910 (5.1096)
38        0.1011 (0.0958)    0.6675 (0.6326)     5.4691 (5.1837)
39        0.1011 (0.0958)    0.6674 (0.6325)    5.5146 (5. 2268)
40        0.1010 (0.0957)    0.6673 (0.6324)     5.6018 (5.3094)
41        0.1009 (0.0956)    0.6673 (0.6324)     5.6937 (5.3965)

Serial        Condenser,         Overall
Number        kW (Btu/s)         Exergy,
                               Efficiency

1         0.1093 (0.103596)      0.3399
2         0.1093 (0.103596)      0.3304
3         0.1093 (0.103596)      0.3217
4         0.1093 (0.103596)      0.3073
5         0.1093 (0.103596)      0.2926
6         0.1093 (0.103596)      0.2693
7         0.1092 (0.103502)      0.2587
8         0.1092 (0.103502)      0.2499
9         0.1092 (0.103502)      0.2404
10        0.1092 (0.103502)      0.2343
11        0.1092 (0.103502)      0.2244
12        0.1092 (0.103502)      0.2173
13        0.1092 (0.103502)      0.2091
14        0.1091 (0.103407)      0.2047
15        0.1091 (0.103407)      0.1989
16        0.1091 (0.103407)      0.1929
17        0.1091 (0.103407)      0.1879
18        0.1091 (0.103407)      0.1832
19        0.1091 (0.103407)      0.1786
20        0.1090 (0.103312)      0.1738
21        0.1090 (0.103312)      0.1705
22        0.1090 (0.103312)      0.1656
23        0.1090 (0.103312)      0.1618
24        0.1090 (0.103312)      0.1591
25        0.1089 (0.103217)      0.1558
26        0.1089 (0.103217)      0.1528
27        0.1089 (0.103217)      0.1490
28        0.1089 (0.103217)      0.1469
29        0.1089 (0.103217)      0.1437
30        0.1089 (0.103217)      0.1409
31        0.1088 (0.103122)      0.1382
32        0.1088 (0.103122)      0.1322
33        0.1088 (0.103122)      0.1300
34        0.1088 (0.103122)      0.1315
35        0.1088 (0.103122)      0.1291
36        0.1088 (0.103122)      0.1268
37        0.1087 (0.103028)      0.1238
38        0.1087 (0.103028)      0.1220
39        0.1087 (0.103028)      0.1210
40        0.1087 (0.103028)      0.1191
41        0.1087 (0.103028)      0.1172

Table 4. Calculated Mass Flow Rate of Different
Components of Absorption System

Serial      Mass Flow Rate       Mass Flow Rate
Number       in Generator         in Condenser
           ([[??].sub.11]),     ([[??].sub.13]),
             kg/s (lb/s)          kg/s (lb/s)

1          0.45403 (1.000)      0.42560 (0.9382)
2          0.45467 (1.002)      0.42555 (0.9381)
3          0.45533 (1.003)      0.42550 (0.9380)
4          0.45600 (1.005)      0.42545 (0.9379)
5          0.45663 (1.006)      0.42538 (0.9378)
6          0.45728 (1.008)      0.42503 (0.9370)
7           045795 (1.009)      0.42496 (0.9368)
8          0.45861 (1.011)      0.42521 (0.9374)
9          0.45927 (1.012)      0.42516 (0.9373)
10         0.45991 (1.013)      0.42510 (0.9371)
11         0.46055 (1.015)      0.42503 (0.9370)
12         0.46121 (1.016)      0.42496 (0.9368)
13         0.46195 (1.018)      0.42491 (0.9367)
14         0.46256 (1.019)      0.42485 (0.9366)
15         0.46315 (1.021)      0.42479 (0.9365)
16         0.46379 (1.022)      0.42472 (0.9363)
17         0.46443 (1.023)      0.42465 (0.9361)
18         0.46507 (1.025)      0.42459 (0.9360)
19         0.46573 (1.026)      0.42454 (0.9359)
20         0.46337 (1.021)      0.42447 (0.9357)
21         0.46702 (1.029)      0.42440 (0.9356)
22         0.46766 (1.031)      0.42433 (0.9354)
23         0.46831 (1.032)      0.42426 (0.9353)
24         0.46895 (1.033)      0.42419 (0.9351)
25         0.46958 (1.035)      0.42411 (0.9350)
26         0.47024 (1.036)      0.42407 (0.9349)
27         0.47088 (1.038)      0.42401 (0.9347)
28         0.47150 (1.039)      0.42393 (0.9346)
29         0.47215 (1.040)      0.42386 (0.9344)
30         0.47285 (1.042)      0.42379 (0.9342)
31         0.47345 (1.043)      0.42372 (0.9341)
32         0.47408 (1.045)      0.42369 (0.9340)
33         0.47471 (1.046)      0.42367 (0.9340)
34         0.47534 (1.047)      0.42355 (0.9337)
35         0.47597 (1.049)      0.42343 (0.9335)
36         0.47660 (1.050)      0.42335 (0.9333)
37         0.47723 (1.052)      0.42327 (0.9331)
38         0.47787 (1.053)      0.42319 (0.9329)
39         0.47851 (1.054)      0.42311 (0.9327)
40         0.47914 (1.056)      0.42304 (0.9326)
41         0.47978 (1.057)      0.42296 (0.9324)

Serial      Mass Flow Rate      Mass Flow Rate
Number      in Evaporator         in Absorber
           ([[??].sub.15]),    ([[??].sub.17]),
             kg/s (lb/s)          kg/s (lb/s)

1          0.94087 (2.0742)    0.40567 (0.8943)
2          0.94078 (2.0740)    0.40535 (0.8936)
3          0.94069 (2.0738)    0.40502 (0.8929)
4          0.94060 (2.0736)    0.40471 (0.8922)
5          0.94051 (2.0734)    0.40437 (0.8914)
6          0.94042 (2.0732)    0.40406 (0.8908)
7          0.94033 (2.0730)    0.40374 (0.8900)
8          0.94024 (2.0728)    0.40341 (0.8893)
9          0.94016 (2.0726)    0.40309 (0.8886)
10         0.94007 (2.0724)    0.40276 (0.8879)
11         0.94014 (2.0726)    0.40244 (0.8872)
12         0.94005 (2.0724)    0.40216 (0.8866)
13         0.93996 (2.0722)    0.40189 (0.8860)
14         0.93987 (2.0720)    0.40153 (0.8852)
15         0.93978 (2.0718)    0.40115 (0.8843)
16         0.93969 (2.0716)    0.40083 (0.8836)
17         0.93960 (2.0714)    0.40050 (0.8829)
18         0.93951 (2.0712)    0.40018 (0.8822)
19         0.93942 (2.0710)    0.39985 (0.8815)
20         0.93933 (2.0708)    0.39953 (0.8808)
21         0.93924 (2.0706)    0.39920 (0.8800)
22         0.93915 (2.0704)    0.39889 (0.8794)
23         0.93906 (2.0702)    0.39857 (0.8786)
24         0.93897 (2.0700)    0.39824 (0.8779)
25         0.93888 (2.0698)    0.39792 (0.8772)
26         0.93879 (2.0696)    0.39759 (0.8765)
27         0.93870 (2.0694)    0.39727 (0.8758)
28         0.93861 (2.0692)    0.39693 (0.8750)
29         0.93852 (2.0690)    0.39662 (0.8743)
30         0.93843 (2.0688)    0.39635 (0.8738)
31         0.93834 (2.0686)    0.39598 (0.8729)
32         0.93825 (2.0684)    0.39566 (0.8722)
33         0.93816 (2.0682)    0.39533 (0.8715)
34         0.93804 (2.0680)    0.39501 (0.8708)
35         0.93798 (2.0678)    0.39468 (0.8701)
36         0.93789 (2.0676)    0.39436 (0.8694)
37         0.93780 (2.0674)    0.39403 (0.8686)
38         0.93771 (2.0672)    0.39371 (0.8679)
39         0.93762 (2.0670)    0.39340 (0.8672)
40         0.93753 (2.0668)    0.39307 (0.8665)
41         0.93744 (2.0667)    0.39275 (0.8658)
COPYRIGHT 2014 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE)
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Author:Anand, S.; Gupta, A.; Tyagi, S.K.; Anand, Y.
Publication:ASHRAE Transactions
Article Type:Report
Date:Jul 1, 2014
Words:7250
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