Comparative analysis of a solar‐driven novel salt‐based absorption chiller with the implementation of nanoparticles

The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH₃‐LiNO₃) and ammonia‐sodiumthiocynate (NH₃‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H₂O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at ?5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH₃‐NaSCN chiller is 0.12% higher than that for the NH₃‐LiNO₃ chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH₃‐LiNO₃ absorption system has been found 5.51% higher than that of the NH₃‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH₃‐NaSCN and NH₃‐LiNO₃ systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH₃‐LiNO₃ absorption system be integrated with a nanofluid.     

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100°C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH₃–LiNO₃) are selected as the working fluids and the calculation results for the two‐staged cycle and the three‐staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low‐grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.     

Advances in Solar Energy: K. W. Boer and J. Duffie (Editors), American Solar Energy Society,Inc., 110 W. 34th St. New York,N.Y. 10001, 1982. Cost $95.00

Thermodynamic and physical property data equations are presented for the NH₃?LiNO₃ and NH₃?NaSCN absorption refrigeration systems. These equations are presented in a form readily adaptable to a computer program for use by other investigators when thermodynamic and economic cycle calculations for NH₃?LiNO₃ and NH₃?NaSCN absorption systems are to be performed.     

Modeling and performance analysis of an absorption chiller with a microchannel membrane‐based absorber using LiBr‐H2O,LiCl‐H2O,and LiNO3‐NH3

In order to develop compact absorption refrigeration cycles driven by low heat sources, the simulated performance of a microchannel absorber of 5‐cm length and 9.5 cm³ in volume provided with a porous membrane is presented for 3 different solution‐refrigerant pairs: LiBr‐H₂O, LiCl‐H₂O, and LiNO₃‐NH₃. The high absorption rates calculated for the 3 solutions lead to large cooling effect to absorber volume ratios: 625 kW/m³ for the LiNO₃‐NH₃, 552 kW/m³ for the LiBr‐H₂O, and 318 kW/m³ for the LiCl‐H₂O solutions given the studied geometry. The performance of a complete absorption system is also analyzed varying the solution concentration, condensation temperature, and desorption temperature. The LiNO₃‐NH₃ and the LiBr‐H₂O solutions provide the largest cooling effects. The LiNO₃‐NH₃ can work at a lower temperature of the heating source, in comparison with the one needed in a LiBr‐H₂O system. The lowest cooling effect and coefficient of performance are found for the LiCl‐H₂O solution, but this mixture allows the use of lower temperature heating sources (below 70°C). These results can be used for the selection of the most suitable solution for a given cooling duty, depending on the available heat source and condensation temperature.     

Thermodynamic and physical property data equations for ammonia-lithium nitrate and ammonia-sodium thiocyanate solutions

Thermodynamic and physical property data equations are presented for the NH₃−LiNO₃ and NH₃−NaSCN absorption refrigeration systems. These equations are presented in a form readily adaptable to a computer program for use by other investigators when thermodynamic and economic cycle calculations for NH₃−LiNO₃ and NH₃−NaSCN absorption systems are to be performed.     

Study on a solar-driven ejection absorption refrigeration cycle

This paper deals with a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution. The physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH₃–LiNO₃. It is demonstrated that the EAR cycle has obvious advantages as compared with the conventional absorption refrigeration cycle: (1) the controllable high absorption pressure allows for substantially high coefficients of performance by the action of a liquid–gas ejector in which the low-pressure refrigerant vapour is injected and pressurized as a result of the ejection of high-pressure solution; (2) internal steady operation can be realized for refrigeration cycles driven by unsteady heat sources, especially for solar energy, by adjusting the power input consumed by solution pumps under the condition of economical and reasonable utilization of electric energy. © 1998 John Wiley & Sons, Ltd.     

Thermodynamic evaluations of solar cooling cogeneration cycle using NaSCN–NH<Subscript>3</Subscript> mixture

The commercial refrigeration and air conditioning consumes more electric power for its operation. The solar vapor absorption refrigeration helps to minimize the electric power usage and it is renewable. Large size of solar collector area is required for producing the standalone power as well as cooling cycle. The integration of power and cooling cycle minimizes the number of components such as heat exchanger, separator and collector area. The main objective of the work is to integrate power and cooling for two outputs with single cycle using NaSCN–NH₃ as working fluid. The advantages of NaSCN–NH₃ are having high pressure and pure ammonia vapor at the exit of the generator. The integrated cycle is made by providing the turbine at the exit of the generator along with superheater. It has three pressures of generator, condensing and sink pressure, which is depending on separator and ambient temperature. At the separator temperature of 150°C with weak solution concentration of 0.30, it produces the cogeneration output of 284.80 kW with cycle and plant thermal efficiency of 0.49 and 0.20 respectively.     

Experimental and theoretical study of waste heat recovery from a refrigeration system using a finned helical coil heat exchanger

This paper is an experimental and theoretical study that aimed at conserving energy by utilizing the waste heat generated from a refrigeration system by calculating the range of condensation after the compression stage for the refrigerant (R410A). A helical coil tube‐shell heat exchanger was designed as a heat recovery unit to use the waste heat from an air conditioner 1TR (split type) in the outdoor unit between the compressor and the condenser to produce hot water and increase the coefficient of performance (COP) of the refrigeration cycle. Two experimental types of the helical coil heat exchanger (conventional and finned) were used in attempts to induce absorption of the rejected heat into tap water. The increase in the COP ranges from 12.5% to 40%, an increase in the water outlet temperatures difference reaches 12°C. A cost–benefit analysis in terms of the net present value and the payback period (PP) has been performed. From the analysis, it has been observed that the use of the designed heat recovery unit will save electrical consumption to produce the required hot water with a PP of about 11.7 months for the conventional heat exchanger and 17.5 months for the finned helical coil heat exchanger.     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

New refrigeration system using CO vapor-solid as refrigerant

A refrigerant must be in the vapor-liquid phase in a vapor-compression refrigeration system, therefore, CO₂ cannot be used as a refrigerant for temperatures lower than -56°C because solid CO₂ will form under the triple point temperature of -56°C. A refrigeration system with CO₂ vapor-solid particles as refrigerant is put forward, by which a temperature lower than the triple point is achieved. An adjustable nozzle, a sublimator, a high-pressure regulating valve and a low-pressure regulating valve are used to replace the conventional evaporator. Theoretical cycle analysis of the refrigeration system shows that its COP can be 50% higher than that of the conventional one.     

Performance of hybrid refrigeration system using ammonia

This paper investigates the performance of a hybrid refrigeration system that combines sorption–conventional vapour compression refrigeration machine driven by dual source (heat and/or electricity). The dual source makes the system highly flexible and energy efficient. The ammonia refrigerant (R717) is used in both adsorption and associated conventional refrigeration cycles. The model of thermal compressor corresponds to a multiple pair of compact adsorption generators operating out of phase with both heat and mass recovery for continuous cooling production and better efficiency. Each generator is based on a plate heat exchanger concept using the activated carbon–ammonia pair. The model of conventional vapour compressor is a reciprocating compressor from Frigopol. The hybrid refrigeration performances are presented mainly for ice making and air conditioning applications (T_C = 40 °C, −5 °C < T_E < 20 °C). The exhaust temperature of the compressor (driving temperature for thermal compressor) varies from 90 °C to 250 °C. The results show a cooling production ranging from 4 kW to 12 kW with back-up mode (both cycles not operating simultaneously) and from 8 kW to 24 kW with complementary mode (both cycles operating simultaneously). The effective overall COP based on the total equivalent heat rate input varies from 0.24 to 0.76.     

Temperature–enthalpy/entropy charts of combined ejector–absorption cycle using NH3–H2O

This paper describes the performance of an ammonia–water combine ejector–absorption cycle as refrigerator and heat pump. This combination brings together the advantages of absorption and ejector systems. Also, thermodynamic cycles on the temperature–enthalpy and temperature–entropy charts are shown. The thermodynamics of the combined ejector–absorption cycles are simulated by a suitable method and a corresponding computer code, based on analytic functions describing the behaviour of the binary mixture NH₃–H₂O. It is found that in the case of the refrigerator and heat pump, the theoretical coefficient of performance (COP) or the theoretical heat gain factor (HGF) vary from 1.6 to 90.4 per cent and 0.7 to 37.6 per cent, greater than those of the conventional absorption system, respectively. The operation conditions were: generator temperature (205.5 to 237.1°C), condenser temperature (25.9 to 37.4°C) and evaporator temperature (−8.4 to 5°C). Copyright © 2000 John Wiley & Sons, Ltd.     

Performance investigation of a thermal‐driven refrigeration system

Thermal‐driven refrigeration systems have attracted increasing research and development interest in recent years. These systems do not cause ozone depletion and can reduce demand on electricity. The main objective of this work is to perform tests and theoretical analyses of a thermal‐driven refrigeration system using a new sorbent–sorptive pair as the working pair. The active component of the sorbent used in this study is sodium thiocyanate (NaSCN). Ammonia (NH₃) is chosen as sorptive. Based on the thermodynamic properties of the working solution, a mathematical model is introduced to analyze the system characteristics and performance. A series of experimental data is collected to establish the relationships among different system parameters. The results are compared with those of other thermal‐driven refrigeration systems. It is shown that the advantages provided by this system over others include lower generator and evaporator temperatures and a higher coefficient of performance (COP). Copyright © 2008 John Wiley & Sons, Ltd.     

An experimental study of a direct expansion ground‐coupled heat pump system in heating mode

In this paper, an experimental performance evaluation of a direct expansion ground‐coupled heat pump (DX‐GCHP) system in heating mode is presented. The DX‐GCHP uses R134a as the refrigerant, and consists of three single U‐tube copper ground heat exchangers (GHEs) placed in three 30 m vertical boreholes. During the on–off operations from December 25, 2007, to February 6, 2008, the heat pump supplied hot water to fan‐coil at around 50.4°C, and its heating capacity was about 6.43 kW. The energy‐based heating coefficient of performance (COP) values of the heat pump and the whole system were found to be on average 3.55 and 3.28 at an evaporating temperature of 3.14°C and a condensing temperature of 53.4°C, respectively. The second law efficiency on the DX‐GCHP unit basis was around 0.36. The exergetic COP values of the heat pump and the whole system were obtained to be 0.599 and 0.553 (the reference state temperature was set equal to the average outdoor temperature of ?1.66°C during the tests), respectively. The authors also discussed some practical points such as the heat extraction rate from the ground, refrigerant charge and two possible new configurations to simultaneously deal with maldistribution and instability of parallel GHE evaporators. This paper may reveal insights that will aid more efficient design and improvement for potential investigators, designers and operators of such DX‐GCHP systems. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparative study of an absorber heat recovery cycle for solar refrigeration using NH3-refrigerant with liquid/solid absorbents

This paper presents an investigation on using an ammonia refrigerant with liquid/solid absorbents in an absorber heat recovery cycle where heat released during the absorption process is used to heat up the strong solution coming out of the absorber, thereby reducing the generator heat input and hence improving the coefficient of performance. A comparative thermodynamic study is made with NH₃-H₂O and NH₃-LiNO₃ pairs as working fluids for both conventional absorption and absorber heat recovery systems. It is found that an improvement of about 10 per cent in COP for the absorber heat recovery cycle is achieved over the conventional absorption cycle and the NH₃-LiNO₃ system yields a higher COP than for NH₃-H₂O over a wide range of generator temperatures and condenser/absorber temperatures. A detailed parametric study is also presented in this paper.     

Study on a twin‐bed adsorption refrigeration system using R134a‐activated carbon pair

A low capacity twin‐bed adsorption refrigeration system has been built with R134a as a refrigerant and activated carbon as the adsorbent. Simple tube‐in‐tube heat exchangers have been fabricated and have been used as the adsorber beds. Activated carbon (granular type) has been filled in the annular space of the inner tube and outer tube. A plate heat exchanger has been used as the condenser and the temperature of cooling water has been maintained between 25°C and 30°C, also the evaporator has been custom designed as per requirements. A mathematical model has also been developed and the results obtained have been found to be comparable. While operating the system in the single‐bed mode a cooling power of 250.4 W has been obtained with a coefficient of performance (COP) of 0.38 with an average evaporator temperature of 18.4°C against a predicted value of 263.7 W with a COP of 0.41. While operating in the twin‐bed mode a cooling power of 281.3 W with a COP of 0.47 with an average evaporator temperature of 17.6°C has been obtained against a predicted value of 294.5 W with a COP of 0.52.     

Exergetic performance evaluation of heat pump systems having various heat sources

In this study heat pump systems having different heat sources were investigated experimentally. Solar‐assisted heat pump (SAHP), ground source heat pump (GSHP) and air source heat pump (ASHP) systems for domestic heating were tested. Additionally, their combination systems, such as solar‐assisted‐ground source heat pump (SAGSHP), solar‐assisted‐air source heat pump (SAASHP) and ground–air source heat pump (GSASHP) were tested. All the heat pump systems were designed and constructed in a test room with 60 m² floor area in Firat University, Elazig (38.41°N, 39.14°E), Turkey. In evaluating the efficiency of heat pump systems, the most commonly used measure is the energy or the first law efficiency, which is modified to a coefficient of performance for heat pump systems. However, for indicating the possibilities for thermodynamic improvement, inadequate energy analysis and exergy analysis are needed. This study presents an exergetic evaluation of SAHP, GSHP and ASHP and their combination systems. The exergy losses in each of the components of the heat pump systems are determined for average values of experimentally measured parameters. Exergy efficiency in each of the components of the heat pump systems is also determined to assess their performances. The coefficient of performance (COP) of the SAHP, GSHP and ASHP were obtained as 2.95, 2.44 and 2.33, whereas the exergy losses of the refrigerant subsystems were found to be 1.342, 1.705 and 1.942 kW, respectively. The COP of SAGSHP, SAASHP and GSASHP as multiple source heat pump systems were also determined to be 3.36, 2.90 and 2.14, whereas the exergy losses of the refrigerant subsystems were approximately 2.13, 2.996 and 3.113 kW, respectively. In addition, multiple source heat pump systems were compared with single source heat pump systems on the basis of the COP. Exergetic performance coefficient (EPC) is introduced and is applied to the heat pump systems having various heat sources. The results imply that the functional forms of the EPC and first law efficiency are different. Results show that Ex_loss,total becomes a minimum value when EPC has a maximum value. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental performance of a silica gel–water adsorption chiller

A newly developed adsorption water chiller is described and tested. In this adsorption refrigeration cycle system, there is no refrigerant valve. Thus, the problem of mass transfer resistance occurring in the conventional systems when methanol or water is used as refrigerant and resulting in pressure drop during the flow of refrigerant inside the tubing is eliminated. To make the utilization of low heat source with temperature ranging from 70 to 95 °C possible, silica gel–water was selected as working pair. The experimental results proved that it is able to produce a cooling power of 6.3 kW with a COP of about 0.4. The test results demonstrate that, through the heat recovery, the COP can be increased by 34.4% while mass recovery has the effect of increasing the cooling power by 13.7% and the COP by 18.3%. The performances of the system were analyzed for varied condensation temperature and for varied evaporation temperature. Based on the first prototype, the second prototype is designed and manufactured to improve the performance. Primary test results demonstrate that the performance is highly improved. It has a COP of about 0.5 and cooling power 9 kW for 13 °C evaporation temperature.     

Dynamic characteristics of a novel adsorption refrigerator with compound mass‐heat recovery

A three‐effect heat pipe (heat pipe heating, heat pipe cooling and heat pipe heat recovery) adsorption refrigeration system using compound adsorbent (calcium chloride and activated carbon) was designed. The dynamic characteristics of mass and heat pipe heat recovery were studied. The results show that mass recovery and heat pipe heat recovery can improve (specific cooling power) SCP and (coefficient of performance) COP greatly. The averaged SCP of the cycle with mass recovery and the cycle without mass recovery is 502.9 W/kg and 436.7 W/kg at about 30 °C of cooling water temperature and ?15 °C of evaporating temperature. The corresponding COP is 0.27 and 0.24 respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Modelling non-isothermal absorption of vapour into expanding liquid sheets

The problem of non-isothermal absorption of vapour into freely expanding liquid sheets is addressed in this study. This is done in the context of four models that characterise the coupled heat and mass transfer in the liquid phase: a nonlinear model retaining the effect of sheet growth, an approximate model for slowly increasing mass flow rate in the sheet, a large Lewis number model and finally, a boundary layer model. These models have been numerically or analytically solved and applied to the comparative analysis of two different working pairs, LiBr–H₂O and LiNO₃–NH₃, under conditions representative of adiabatic absorption in refrigeration systems. The limits of applicability of each model have been assessed and the sensitivity of the results to the sheet aperture angle, heat of absorption and initial subcooling has also been tested. For equal initial mass fraction and subcooling, the models indicate that Sherwood number and the rate of absorption in laminar expanding sheets for the LiNO₃–NH₃ solution are always superior to those for the LiBr–H₂O solution.