Diffusion Absorption Refrigeration Research Articles

A Parametric Examination of the Factors Affecting the Performance of a Diffusion Absorption Refrigeration System

Abstract Despite being identified nearly a century ago, the diffusion absorption refrigeration (DAR) cycle has received relatively little attention. One of the strongest attractions of the DAR cycle lies in the fact that it is thermally driven and does not require high value work. This makes it a prime candidate for harnessing low-grade heat from solar collectors, or the waste heat from stationary generators, to produce cooling. However, to realize the benefits of the DAR cycle, there is a need to develop an improved understanding of how design parameters influence its performance. In this vein, this work developed a new, validated, parametric model that can be used by designers and practitioners to examine the performance of the DAR cycle for a range of operating conditions. The results showed that the cycle’s performance was particularly sensitive to several factors: the rate of heat added and the temperature of the generator, the effectiveness of the gas and solution heat exchangers, the mass flowrate of the refrigerant and the type of the working fluid. It was shown that it can deliver good performance at low generator temperatures if the refrigerant mass fraction in the strong solution is made as high as possible. Moreover, it was shown that a H2O–LiBr working pair could be useful for achieving cooling at low generator temperatures.

Steady state numerical simulation and studying performance of a modified diffusion absorption refrigeration cycle

In this paper, numerical simulations of Diffusion Absorption Refrigeration – DAR cycle were conducted in order to study the performance of two configurations in steady state mode and use ammonia, water, hydrogen as working fluids. The two configurations were numerically simulated using models developed with the commercial flow sheet Aspen HYSYS V10 software. The first configuration where the main simple DAR cycle components were simulated and validated the experimental results. The second configuration where the modified DAR cycle was simulated which has an auxiliary heat exchanger added to the main simple DAR cycle as a modification. It was found that for the same input assumptions and heat applied, the modified DAR cycle shows higher cooling load. Therefore, higher COP than the simple DAR cycle. The optimal operation of the modified cycle is 36 W applied to the generator to achieve a COP of 0.235 instead of 0.209 for simple DAR cycle. The Simulation results show that by using the modified cycle, the COP improves by 12.4%.

Conceptual design and evaluation of an innovative hydrogen purification process applying diffusion-absorption refrigeration cycle (Exergoeconomic and exergy analyses)

A novel process for hydrogen purification by a diffusion-absorption refrigeration cycle and auxiliary nitrogen refrigeration stream is proposed and exergoeconomically analyzed. The diffusion-absorption refrigeration cycle provides a refrigeration load of 7.125 kW at a refrigeration temperature of −32.61 °C. The coefficient of performance of this refrigeration cycle is calculated to be 0.424. The thermal energy of 16.81 kW is supplied to drive the refrigeration unit. This refrigeration system utilizes ammonia as the refrigerant, water as the absorbent, and helium as the inert gas. The feed gas stream is divided into high-hydrogen and low-hydrogen streams by passing through cryogenic heat exchangers, expansion valves, and flash drums. The inlet unprocessed stream consists of H2, CH4, C2H6, C3H8, N2, and C6H6. Power of 63.42 kW is consumed by the compressors and air coolers to increase the pressure of the feed stream to 4482 kPa. The Aspen HYSYS V11 simulator and MATLAB software are utilized to develop the integrated process and perform the exergy-economic analysis. It was found that the purity of the separated hydrogen stream is about 88%. Two novel criteria for the overall exergy efficiency are introduced to evaluate the overall exergy efficiency of the process. The first and the second-mentioned criteria are computed as 93.825% and 35.053%, respectively. Also, the overall exergy destruction rate is found to be 45.764 kW that 32% of the irreversibility occurred in the air cooler as the main component of exergy wasting. Exergy-economic analysis of the system shows that air coolers are the most important equipment of the plant and should be precisely designed, manufactured, and arranged. Besides, the highest amount of relative cost difference and exergoeconomic factor are related to HX-104 and HX-107 heat exchangers with values of 750.34% and 60.53%, respectively. Finally, sensitivity analyses are conducted to determine the effective parameters on the system performance.

Inert Gas and Refrigerating Vapor Mass Flow Rates Ratio: A Much Promising Parameter for Diffusion-Absorption-Refrigeration Systems Performances Evaluation

This paper is consecrated to the thermodynamic study and analysis of diffusion-absorption-refrigeration (DAR) plants. The mass and energy balances analysis at the evaporator has allowed to highlight a new and original parameter, which can be used to analyze DAR system performances. It is the ratio of inert gas to refrigerant vapor mass flow rates at the evaporator inlets. This coefficient, which expression has been for the first time deduced mathematically, informs about the quality of the cycle and its performance, which are deeply affected by the growth of the inert gas flow energy expended to drive the refrigerant through the evaporator. The study shows that the coefficient of performance is decreasing with the increase of the mass flow rates ratio. The latter can be also used to find the optimal operating mode for the DAR machine with a specified working fluid.

Enhancing the thermal performance of diffusion absorption refrigeration system by using magnesium aluminate spinel oxide compound nanoparticles: an experimental investigation

This article aims to enhance the efficiency of Diffusion Absorption Refrigeration (DAR) systems which operate at low efficiency. This study experimentally investigates the effect of passive heat transfer enhancement by using various nanofluids as working fluids including ammonia/water couple with different rates of magnesium oxide aluminate spinel (MgOAl2O3) particles. The tests have been carried at the same ambient conditions to obtain reliable results. Additionally, nanofluid has been prepared and tested in two different particle concentration (1% and 2%). Adding nanoparticles to the base fluid (25% ammonia/water) can make an important positive effect in increasing heat transfer by extending surface area and heat capacity of the fluid. Experimental results showed that using nanofluid as working fluid in DAR system results in faster evaporation which decreases operation time and increases heat transfer in generator. Moreover, the DAR system containing 2% concentration of nanofluid solution led to a 37.4% increase in performance coefficient (COP) and a 44.2% increase in exergetic performance coefficient (ECOP) compared to the DAR system without nano particles.

A Comparison between Exhaust Gas and Electrical Grid Heating of a Diffusion Absorption Refrigerator

A considerable quantity of waste energy in the exhaust system could be reutilized and added in a vehicle to run auxiliary systems, and contribute to improving the overall efficiency of the system. In the current work, a comparison between the conventional electrical grid and exhaust gas heating of an absorption refrigeration system was performed experimentally. A heat exchanger was fabricated to recover the wasted exhaust gas energy of internal combustion engine and operate the generator portion of a diffusion type refrigeration absorption system. The components performance of the absorption refrigerator was analyzed and estimated thermodynamically as a function of type energy source. The results revealed that the components temperatures were rapidly responded in case of the exhaust gas energy with the maximum and minimum steady state temperatures of the generator and evaporator of 140 °C and -1.1 °C, respectively. The steady state values of the COP can be reached from electrical grid, and the exhaust gas energy sources of the refrigerated system were 0.083 and 0.072, respectively. The key conclusion to be drawn is that the proposed system can be used to recycle the waste heat for refrigeration purpose; yet, with low COP values.

Experimental analysis on diffusion absorption refrigeration cycle with the magnetic field

ABSTRACT The main objective of this paper is to understand the impact of Diffusion Absorption Refrigeration (DAR) system coupled with a magnetic field through experimental investigation. DAR is an emerging technology which converts waste heat into useful work. The addition of the magnetic field increases the coefficient of performance of the DAR system. The waste heat from automobile exhaust was introduced as heat input and the performance and feasibility were studied for a different arrangement of the magnets. The absorption enhancement was compared with and without magnetic effect. The influence of magnetic field reduces the viscosity of the working fluid which causes the free flow and impacts the heat transfer rate due to its higher mass flow rate. The result indicates that the performance of the system increased with the application of magnets.

ENERGY AND EXERGY ANALYSIS OF USING FeOTiO2 NANOFLUID IN DIFFUSION ABSORPTION REFRIGERATION SYSTEMS

ENERGY AND EXERGY ANALYSIS OF USING FeOTiO2 NANOFLUID IN DIFFUSION ABSORPTION REFRIGERATION SYSTEMS

Cycle performance analysis and experimental validation of a novel diffusion absorption refrigeration system using R600a/n-octane

Diffusion absorption refrigeration (DAR) is a promising cycle with regard to renewable energy utilization, as the cycle can operate using only a thermal energy input. This study focuses on the application of a low-global warming potential (GWP) refrigerant as a substitution for conventional ammonia refrigerant. In this study, R600a/n-octane is chosen as a novel refrigerant/absorbent pair for DAR. The cycle operation characteristics are investigated through numerical analysis, in terms of the coefficient of performance (COP) and minimum temperature. The influences of five key parameters (driving temperature, total pressure, evaporator temperature, absorber effectiveness, and solution heat exchanger effectiveness) on the COP are also analyzed. Furthermore, additional experiments are performed to validate the simulation results through comparisons with the experimental data. The variation trend of the COP shows good agreement between the simulations and experiments, and the mathematical model provides a reasonable estimation of the maximum COP. It is concluded that R600a/n-octane has significant potential for DAR application, as a maximum COP of 0.162 is achieved at a driving temperature of approximately 100 °C, making it more favorable than other low-GWP refrigerant working fluids pairs and applicable for solar cooling.

Experimental and numerical investigation of diffusion absorption refrigeration system working with ZnOAl2O3 and TiO2 nanoparticles added ammonia/water nanofluid

ABSTRACT In this paper, the effect of various zinc oxide aluminate spinel (ZnOAl2O3) and titanium oxide (TiO2) nanoparticle concentrations on the thermal performance of the Diffusion Absorption Refrigeration (DAR) system is investigated. The main aim of the study is to increase the efficiency of DAR systems operating with low thermal performance. The first part of the study is experimentally tested on the system under the same ambient conditions in order to develop passive heat transfer using different nanofluids as working liquids, including ammonia/water solution containing different amounts (1 wt.% and 2 wt.%) of ZnOAl2O3 and TiO2 particles. In the next part of the study, the tested system is designed in MATLAB/Simulink toolbox environment to compare experimental and numerical results. The use of nanofluids can increase the surface area expansion and the heat capacity of the fluid, resulting in a significant positive increase in heat transfer. The results clarify that the use of nanofluid as working fluid in the DAR system helps quicker evaporation, which reduces operating time and increases heat transfer in the generator. Compared to a base DAR system, the nanofluid solution with a 2 wt.% ZnOAl2O3 nanoparticle concentration among other nanofluid and proportions causes a 57% increase in the coefficient of performance (COP) of DAR system.

Experiments on the performance of bubble pumps with R134a/R23-DMF solutions for diffusion absorption refrigerator

Experiments on the performance of a bubble pump for diffusion absorption refrigerator with different lifting tubes (diameter of 8 mm and 10 mm), different filling compositions of R134a/R23 (35%/0%, 33.5%/4%, 32.2%/8%, and 30.8%/12%) and different heads (0.51 m, 0.54 m, 0.57 m, 0.6 m and 0.63 m) were conducted. The range of heat input was 233–1080 W. The experimental results revealed that: (1) larger heat input and lower head resulted in not only larger gas mass flow rate, but also higher generating temperature; (2) larger gas mass flow rate and lower head led to smaller pumping ratio; (3) the system pressure increased with mass fraction of R23; (4) at the same R134a/R23 mass fraction and head, the operation ranges of the 10 mm lifting tube were wider than those for the 8 mm lifting tube considering of pumping ratio, poor solution mass flow rate and gas mass flow rate. These results will be helpful to the design of bubble pumps for diffusion absorption refrigerators working with binary refrigerants.

Performance analysis on a novel micro-scale combined cooling, heating and power (CCHP) system for domestic utilization driven by biomass energy

The CCHP system driven by biomass energy is essential for mitigating the fossil energy crisis and reducing CO2 emission. But few research work focuses on the micro-scale system due to the limited efficiency. In this paper an efficient household CCHP system is designed, which is driven by the water steam (100 °C-120 °C) from the biomass boiler and is consisted of an R245fa power cycle with a gravity assisted thermal driven “pump”, a single-pressure R134a/DMF/He diffusion absorption refrigeration cycle, and several heat exchangers for heating supply. The models of the system are constructed, and the energy, economic and environmental indexes are evaluated. The results reveal that the higher temperature of heat source and the lower temperature of ambient could improve the thermal efficiency of the CCHP system, and realize the lower cost and CO2 emission. The highest thermal efficiency of the CCHP system can reach to 55.26%. The quarterly energy saving for summer of a 100 m2 isolated house of a rural family can reach to 5059 kW⋅h (497 kW⋅h for cooling, 3154 kW⋅h for heating and 1408 kW⋅h for power generation), which can save about 3121.40 RMB electricity bill and reduce 0.15 t CO2 emissions.

Experimental study on diffusion absorption refrigeration systems with low GWP refrigerants

The diffusion absorption refrigeration (DAR) cycle is driven by heat input. The DAR systems do not employ pumps or compressors; they use refrigerants, absorbents, and auxiliary gases as working fluids. In this study, experiments were conducted on refrigerants with low GWP. The refrigerants R1234ze(E) and R600a (a natural refrigerant) were used in the DAR cycles with dimethylacetamide (DMAC) and isooctane as the absorbents, respectively. To investigate the operating characteristics of refrigerants with low GWP in the DAR cycle, the evaporation temperature and generator outlet temperature of the cycle were analyzed against the concentration of the working fluid and its charge pressure. In addition, the performance of the cycle was evaluated by the bubble pump shape. Using the results, the relationship between the shape of the bubble pump and the performance of the DAR cycle was analyzed. The maximum coefficient of performance of DAR achieved using R600a/isooctane was estimated as 0.157with the tube diameter of 3.17 mm and that of R1234ze(E)/DMAC DAR was estimated as 0.134 with the tube diameter of 4.76 mm.

Experimental study of a diffusion absorption refrigeration cycle supplied by the exhaust waste heat of a sedan car at low engine speeds

The wasted energy from a car exhaust can be considered as the heat supply for an absorption refrigeration cycle. In practice however, application of such cooling systems in automobiles has been facing a number of technical restrictions one of which is once the car engine runs idle or at low speed. To tackle this matter, the present experimental study has been carried out. A commercial diffusion absorption refrigerator with internal volume of 0.04 cubic meters (Electrolux 27A1) and the exhaust flow from a compact car engine (X100 KIA) are applied. Various engine speeds (1000–2500 rpm) have been tested. First, it was confirmed that the amount of heat transferred to the generator at low engine speeds was not adequate to obtain the low temperature required for the refrigerator compartment. A new generator was therefore designed and built. The experimental results show that by using the modified generator, the heat transfer to the generator improves by more than 19%. The evaporator and refrigerator compartment reached the desirable temperatures of −5.7 °C and 4.2 °C respectively at the engine speed of 2000 rpm. Further improvement of the results was observed at the engine speed of 1000 rpm where the temperatures at the evaporator and the refrigerator compartment were reduced by about 4 °C once the modified generator was applied.

Experimental investigation of an ammonia-water-hydrogen diffusion absorption refrigerator

Diffusion absorption refrigeration (DAR) is a small-scale cooling technology that can be driven purely by thermal energy without the need for electrical or mechanical inputs. In this work, a detailed experimental evaluation was undertaken of a newly-proposed DAR unit with a nominal cooling capacity of 100 W, aimed at solar-driven cooling applications in warm climates. Electrical cartridge heaters were used to provide the thermal input which was varied in the range 150–700 W, resulting in heat source temperatures of 175–215 °C measured at the generator. The cooling output during steady-state operation was determined from the power consumed by an electric heater used to maintain constant air temperature in an insulated box constructed around the evaporator. Tests were performed with the DAR system configured with the default manufacturer’s settings (22 bar charge pressure and 30% ammonia concentration). The measured cooling output (to air) across the range of generator heat inputs was 24–108 W, while the coefficient of performance (COP) range was 0.11–0.26. The maximum COP was obtained at a generator heat input of 300 W. Results were compared to performance predictions from a steady-state thermodynamic model of the DAR cycle, showing a reasonable level of agreement at the nominal design point of the system, but noteworthy deviations at part-load/off-design conditions. Temperature measurements from the experimental apparatus were used to evaluate assumptions used in the estimation of the model state point parameters and examine their influence on the predicted system performance.

RESPONSE THE COEFFICIENT OF PERFORMANCE MODELS FOR EVALUATION OF DIFFUSION ABSORPTION REFRIGERATION SYSTEM

Three mathematical models were used to determine the coefficient of performance COP of the diffusion absorption refrigeration system DAR. These models give different results of COP because it depends upon various scientific bases. Therefore, in this study used the three models to compare between the values of COP. The first model from viewpoint of temperature thermodynamic ideal cycle, the second model using mass flow rate thermodynamic and the last model employing the cooling capacity of refrigerator. The highest value of COP by (model 1) was 1.26 while the lowest value was 0.77. Model 2 gave 0.671 as highest value and the lowest value was 0.475, respectively. The highest value of COP by (model 3) was 0.155 while the lowest value was 0106. The exponential function behavior showed the relation between the generator temperature (Tg) and the circulation ratio(f) which can be described by the equation f = 629.52e-0.0193Tg, R2 =1.The statistical indicators to select the actual COP indicated to the majority of values for three models by harmonic mean (HM) were 1.118, 0.567 and 0.124, respectively. The study concluded that using second model is the best way to use for judgment of cycle performance because it depend upon the temperatures of refrigeration cycle parts and mass flow rate of working fluids in each part of this cycle.

Theoretical modeling and experimental validation of a small capacity diffusion-absorption refrigerator

In this paper, an alternative global model of a small commercial diffusion-absorption refrigerator to predict the outlet temperatures of each component, the liquid and vapor mass flow for the bubble pump and COP of the system is presented and compared with the experimental results. The model requires as input parameters: the thermal conditions (based on thermostat positions), the geometrical parameters and the ambient temperature. The results are displayed for seven different thermostat positions, where the temperature predictions indicate that the main components of the system have a deviation lesser than ±4 K. In the case of COP, the maximum relative error is 8% compared with experimental results.

Upgrading of Performance of Diffusion Absorption Refrigeration System

This paper deals with the effects of absorbent used on the thermal performance of commercial diffusion absorption refrigeration systems (DARSs). For this purpose, an ammonia solution with added lithium bromide was used in the DARS system instead of a commercial ammonia solution of NH3-H2O (NH4OH) (25% ammonia and 75% water), and all comparison experiments used a fixed amount of refrigerant to experimentally investigate the effects on performance. The system cooling performance was calculated by means of experimental data. The performance of all the solutions prepared was compared to each other. The added lithium bromide increased the amount of water absorbed by the coolant, increasing the amount of refrigerant carried to the generator and condenser. Consequently, the thermal efficiency of the system was increased. By using a 5% solution of lithium bromide with the ammonia solution, the thermal performance increased by up to 12%. It was concluded that lithium bromide has a higher refrigerant absorption capability than water in diffusion absorption refrigeration systems.

Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-γ Mie

Diffusion-absorption refrigeration (DAR) is a clean thermally-powered refrigeration technology that can readily be activated by low- to medium-grade renewable heat. There is an ongoing interest in identifying or designing new working fluids for performance improvement, particularly in solar applications with non-concentrating solar collectors providing heat at temperatures < 150 °C. In this work, the state-of-the-art statistical associating fluid theory (SAFT) is adopted for predicting the thermodynamic properties of suitable DAR working fluids. A first-law thermodynamic analysis is performed in the software environment gPROMS for a DAR cycle using ammonia as the refrigerant, water as the absorbent and hydrogen as the auxiliary gas. The simulation results show good agreement with experimental data generated in a prototype DAR system with a nominal cooling capacity of 100 W. In particular, at a charge pressure of 17 bar and when delivering cooling at 5 °C, the model results agree with experimental COP data to within ± 7 % over a range of heat inputs from 150 to 500 W. The maximum coefficient of performance (COP) is estimated to be 0.24 at a heat input of 250 W. The group-contribution SAFT-γ Mie equation of state is of particular interest as it offers good agreement with experimental data and provides flexibility in extending the model to test different working fluids with a high degree of fidelity. A methodology is also presented that allows the DAR thermodynamic analysis and working-fluid modelling to be integrated into a more general technology optimisation framework.

Experimental study and modeling within validation of a diffusion absorption refrigerator

This article presents a mathematical model of a diffusion absorption refrigerator (DAR) equipped with a shell-tube vapor generator. The DAR is charged with 3 fluids: ammonia, water and hydrogen. The modeling was based on using mass and energy balances in control volumes to simulate operations DAR. The model is composed of 14 interconnected distinct parts that allow to calculate: poor and rich concentrations of the solutions, the heating in the generator and the heating transfer in the other components, the mass flow rate of solution in several part of the system, as well as the temperature and pressure. The model also allows to simulate the homogenization of vapors, to predict the rectification process final location, the condensed ammonia fraction, the heat losses in the condenser and in the other components. These phenomena haven't been quantified in other diffusion absorption refrigerator models. The present model's validation was achieved by comparing the model results with results obtained experimentally in a commercial refrigerator with 80 W of nominal electric power. The model designing allows new DARs.