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In this study, the characteristics of the hybrid type absorption chiller, combined with the single effect absorption chiller and the double effect absorption chiller, are numerically studied to use waste hot water effectively. In the case of the full load for hybrid type absorption system, the concentration and temperature of LiBr solution increase about 2.2°C and 0.7%, respectively, at the single effect generator by the hot water. As the partial load decreases, the COP decreasing ratio of the hybrid type absorption chiller is higher than that of the double effect absorption chiller. On the other hand, COP_f shows the opposite result of COP. The cycle COP of the hybrid type is about 1.07 on the full load which is 0.11 lower than that of the conventional double effect type. But COP_f of the hybrid type is 1.28 which is 0.22 larger than that of double effect type. In the case of 50% partial load, COP_f of the hybrid type is 2.66 and at below 50% partial load, system can be operated without any fuels. As the temperature of hot water and the mass flow ratio of hot water increase, the fuel saving ratio increases. The effect of the inlet temperature on the COP and COP_f is much more significant than that of the mass flow rate of the hot water.

The cooling load in winter is significant in buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. Hence, the development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a simultaneous heating and cooling heat pump was investigated in the heat recovery mode (HR mode). The system adopted a variable speed compressor using R-410A with four indoor units and one outdoor unit. In the HR mode, the capacity and COP were improved as compared with those in the cooling or heating mode because the waste heat in the outdoor unit was utilized as useful heat in the indoor units. However, energy imbalance between heating and cooling capacities of each indoor unit was observed in the 2H–1C HR mode. Therefore, the performance of the system in the 2H–1C HR mode was enhanced by controlling refrigerant flow rate through the outdoor unit.

The use of two-phase ejector in improving the performance of transcritical CO₂ refrigeration system needs further experimental verification particularly the effects of its geometrical design. In this study, experimental data were gathered for ejectors with different mixing cross-sectional areas at different operating temperature and pressure. The results have shown that a smaller mixing area yields higher efficiency due to its higher pressure recovery and entrainment ratio, but its advantages are limited to lower ejector inlet pressure P_c. A larger mixing area is required for higher cooling capacity which can be achieved at higher ejector inlet pressure or lower ejector inlet temperature but excessive increase in this area considerably decreases the efficiency of the system. In this study, the ejector with the largest mixing area was the most inefficient and reduced the COP up to 10% compared to most efficient type. It demonstrates the significant effect of ejector's geometrical features, particularly the mixing cross-sectional area and its related geometrical ratio, in the performance of CO₂ ejector system. The effect of motive nozzle inlet condition on pressure recovery profile has been more evident for ejector with smaller mixing area while the evaporator temperature has the least effect in the performance of the system. In the conditions used in this study, using ejector yielded a COP improvement of up to 35% compared to the conventional system.

This article presents the experimental results of a three-bed advanced adsorption chiller using silica gel–water as the adsorbent–refrigerant pair. The three-bed adsorption chiller comprises three sorption elements (Hexs), one evaporator and one condenser. In the present study, the heat source temperature varies from 55°C to 80°C along with coolant inlet temperature at 30°C and the chilled water inlet temperature at 14°C. Mass recovery process occurs between Hex1 and Hex2 and no mass recovery with Hex3. The performances in terms of cooling capacity (CC) and coefficient of performance (COP) are compared with those of conventional three-bed without mass recovery scheme. Results show that three-bed with mass recovery scheme provides more CC values than those provided by the three-bed system without mass recovery scheme while it provides better COP values for 65–75°C heat source temperature.

This work presents the experimental evaluation of the energy performance of transcritical CO₂ refrigeration and heat pump systems. The optimal gas cooler pressures and the optimal COP have been analyzed from a thermodynamic point of view. The systems used a new dual expansion valve and a balance CO₂ liquid receiver adjustment device, which can control high and low side pressure effectively. Moreover, we demonstrate the influence of the internal heat exchanger (IHX) on the systems' performances, on the basis of the analysis of the relative COP index RCOPI, the compressor power index RP_CI and other parameters which can confirm the truth of. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler pressures (75 to 120 bar). It is concluded that with the IHX system, compressor power is relatively low when the high side pressure is over 100 bar, and the evaporation temperature is below 0°C. The COP of the system without the IHX is slightly higher than the system with the IHX; it is increasing about 3% to 5%, when the evaporation temperature is over 5°C. Relative to the single expansion process, the dual expansion cycle can decrease the influence of pressure fluctuations of CO₂ supercritical fluid and liquid mixture on the systems.

A variable speed refrigeration system was designed to supply chilled liquid for cooling high-power electronic devices to maintain the temperature at an acceptable level. Fin-plate heat exchangers were adopted to save space. The paper presents the simulation of the refrigeration system to study its steady performance. The simulation model was developed by using a detailed thermodynamic model and containing a series of heat transfer correlations for specific parameters. The cooling capacity of the refrigeration system under different working conditions is investigated. The simulation results keep in agreement with experimental data. The cooling capacity increases with the rise of cooled oil inlet temperature. Besides, condenser cooling liquid inlet temperature affects the cooling capacity greatly. The cooling capacity and the coefficient of performance (COP) of the system under different motor speeds are studied subsequently. The simulation results have been validated by experiments. The mean relative error of the cooling capacity and the COP between simulation results and experimental data is 12.6% and 4.8%, respectively. The results can be used to develop control strategy for regulating refrigeration flow rate to offer adequate cooling capacity and supply cooled oil of constant temperature.

An experimental investigation has been carried out to know about the performance improvement of a household refrigerator using phase change material (PCM). PCMs are used as latent heat thermal storage system to enhance the heat transfer of the evaporator. PCM is located behind the five sides of the evaporator cabinet in which the evaporator coil is immersed. Water (melting point 0°C) and Eutectic solutions (melting point −5°C) are used as PCMs for this experiment at different thermal loads. Depending on the types of PCM and thermal load, around 20–27% COP improvement of the refrigeration cycle has been observed with PCM with respect to without PCM. With the increase of the quantity of PCM (0.003 to 0.00425 m³) COP increases about 6%. Between two different PCMs the COP improvement for Eutectic solution is higher than Water. The experimental results with PCM confirm that, depending on the thermal load and the types of PCM average compressor running time per cycle is reduced significantly and it is found about 2–36% as compared to without PCM.

In this paper, comparative thermodynamic analysis of system-1 (multiple evaporators and compressors with individual expansion valves) and system-2 (multiple evaporators and compressors with multiple expansion valves) has been presented which is based on energy and exergy principles. The comparison of systems-1 and -2 using ecofriendly R410A, R290, R1234YF, R502, R404A, R152A and R134A refrigerants was done in terms of COP (energetic efficiency), exergetic efficiency and system defect. Numerical model has been developed for systems-1 and -2 for finding out irreversibility and it was observed that system-2 is better system in comparison with system-1 for selected refrigerants. It was also found that R152a shows better performances than other considered refrigerants for both systems.

This communication presents the energy and exergy analysis of an actual double effect steam powered LiBr–H₂O vapor absorption refrigeration plant. Exergy loss, COP, exergy efficiency and heat rate for each component of the system are calculated. The effect of generator as well as evaporator temperature on the COP and exergy efficiency is evaluated and it is found that the irreversibility rate is highest in the generator while it is found to be the lowest in the case of absorber and condenser. It is also found that the COP of the system increases with the increase in the evaporator temperature while it is found to be reverse in case of exergy efficiency. Results revealed that average exergy loss is highest in the generator as compared to other components. The results obtained are helpful for designers to bring changes in the actual system for performance optimization and less wastage of energy. The study clearly explain the operational and maintenance problems in the machine and point out the areas of energy wastage which the operational engineer should look into for the optimum operation of the plant.

The application of biogas powered refrigeration system is being studied because of many folds increase in the cost of conventional fuels. This paper presents a numerical study of biogas operated ammonia–water hybrid vapor compression absorption refrigeration system for onsite dairy cooling applications. This system involves the compressor between the generator and condenser and use biogas (generated from the cattle dung) fired boiler to heat water which acts as an energy source for generator in the hybrid system. The variation of performance parameters such as heat load of different components, exergy loss, COP_cooling, COP_heating and exergy efficiency are studied with varying generator temperature. The results indicate that COP_cooling as well COP_heating values are in the range of 0.1125–0.2159 and 1.112–1.169, respectively, for the same variation in the generator temperature from 65°C to 130°C. The work done by the compressor is also calculated and found to be decreasing with an increase in the condenser, evaporator and generator temperature. The effect of the ambient temperature on the exergy loss in different components is also studied in the analysis and the results revealed that the maximum exergy loss is found in the generator and it is found to be the lowest in compressor.

Steam power plants are the largest industrial users for water. New restrictions for using water in cooling systems have led to a search for alternative cooling methods. This paper presents an experimental study of using a vapor compression refrigeration system (VCRS) for cooling a steam power plant condenser. The refrigeration system uses commercially available and environmental friendly R-410A to cool an intermediate chilled water loop which is used as a coolant for the steam condenser. Working under lower condenser pressure with higher coolant flow rates reduces the power required for the refrigeration system and rises the coefficient of performance (COP) and condensation rate. Based on the present experimental data an adjustment to a known empirical correlation for the Nusselt number in a shell and tube steam condenser is presented. The results show that decreasing the inlet coolant temperature increases condensation rate, heat rejection, COP, overall heat transfer coefficient, and R-410A to condensate mass flow ratio. Moreover, the increase in the rate of condensation and COP is most pronounced at lower steam condenser operating pressure and higher water coolant mass flow rate. The results reveal that using a VCRS is capable of providing a steam condenser with a more constant and lower coolant temperature than traditional wet and dry cooling technologies.

This paper presents reports on simulation and comparative analysis of single stage vapor compression refrigeration system and cascade systems using carbon dioxide, hydrocarbons (HCs) and CO₂/HCs mixture. Thermodynamic parameters of fluids are given using the software REFPROP 9.0. To select the most suitable HCs, three criteria have been fixed: T_c, T_t and T_b. It is found that the HCs chosen in low-stage are propane, propylene and ethane and those for the high-stage are propane, propylene and isobutane. The fraction mixture in the two loops has been varied and results are compared with single stage and cascade systems using CO₂ and R22. The fraction x${}_{\mathrm{\text{CO2}}}$ is varied in the two loops. Results are compared for single and cascade systems using CO₂ and R22. For the single stage system, we find for x_CO2 = 0.5, an improvement of COP of 14% for CO₂/propane mixture and 36% for the CO₂/propylene mixture. It is found that for x_CO2 = 0.3, cascade system using propane/CO₂ mixtures presents a COP lower than that of cascade system using pure CO₂. About of 70% of unfriendly fluids like CFCs and HCFCs can be replaced with CO₂, without affecting the performance of cascade refrigeration systems.

According to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number ($500\le \mathrm{\text{Re}}{}_j\le 1150$), jet-to-surface spacing ($H∕D=2$ and $H∕D=4$) and the stroke length ($1.75\le L{}_0∕D\le 4.75$ and $L{}_0∕H<2.5$). It is found that correlation can provide predictions with an $R{}^2$ value of over 98%.

A new refrigerant is needed because the GWP of the R404A and R134a that are used in existing refrigerated trucks and automotive air conditioners is so high. This study predicts cooling performance by using an analytical model, for refrigeration systems using R404A and R134a. Furthermore, the performances of those systems were compared with those of alternative refrigeration systems using R1234yf and R744. The performance data of the analytical model had a trend similar to that of the experimental data: the average error between the analytical and experimental results was within 5.4%. The frost thickness of the R404A system for all operating conditions was about 2.4–3.7% larger than that of other systems because the evaporating temperature of the R404A system was lower than that for other refrigerants. For various operating conditions, the coefficient of performance (COP) of the R134a system was higher than that of other systems, while the R744 system showed the lowest performance. However, the COP reduction of the R744 system with operating time was the smallest because the thermodynamic properties of R744 were very superior. In addition, the frost thickness was seriously affected by the variations of indoor air temperature and compressor rotation speeds, and the system performance decreased significantly for severe operating conditions.

The objective of the present work is to assess experimentally the performance characteristics of a R410A domestic air conditioner under different in-door operating conditions. In order to achieve this objective, a test facility of the investigated system is developed and experiments are conducted. Experimental results on R410A air conditioning system are obtained over a wide range of in-door operating conditions. Experimental results confirmed that the cooling capacity, compressor power and COP increase by 90.9%, 5.2% and 81.5%, respectively, as air humidity ratio increases from 8 to 25.5g_w kg${}_{\mathrm{\text{a}}}^{-1}$. The cooling capacity, condenser heat load, compressor power and COP increase by 7.2%, 6.1%, 2.8% and 4.1%, respectively, when the evaporator air inlet temperature increases from 28${}^{\circ }$C to 34${}^{\circ }$C for a given humidity ratio. COP increases by 25.6% while pressure ratio decreases by 2.5% as the air volume flow rate increases from 400 to 550m³ h${}^{-1}$.

Ozone depletion and global warming phenomenon necessitates the replacement of widely used refrigerants which consist of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) in refrigeration and air-conditioning systems. In this paper, experimental analysis on the performance of hydrofluorocarbon/hydrocarbon (HFC/HC) mixture as a possible drop-in replacement for R134a refrigerant is presented. The influence of capillary length, composition of the mixture and refrigerant charge at various evaporator temperatures on coefficient of performance (COP) are investigated. The optimum operating conditions are obtained by applying Taguchi technique for the acquired experimental results. The results of analysis of variance indicated that for a given evaporator temperature, HFC/HC mixture charge amount is the most influencing parameter. At the optimum condition, the simulation showed that the amount of charge required for HFC/HC mixture in visi-cooler is 120g which is 50% lower than required quantity of R134a for the same system. The HC mixture quantity amounted to 90g in the HFC/HC mixture which is lower than the safe limit of 150g. This eliminates the risk of flammability of HC in the proposed mixture while reducing the quantity of R134a by 87.5%.

It is effective to recover waste heat to reduce primary energy consumption. From this point of view, we proposed and examined a new idea of heat transportation using ammonia–water as the working fluid in the system named the Solution Transportation Absorption chiller (STA). As waste heat sources are not necessarily located close to areas of heat demand, conventionally, absorption chillers are located on heat source side and produce chilled water that is transported to heat demand side through pipelines with an insulation. In contrast, the proposed system STA divides an absorption chiller into two parts. The generator and the condenser are located on heat source side while the evaporator and the absorber are on heat demand side. Both the conventional system and STA system satisfy the same boundary condition of heat recovery and heat supply to the demand side, STA can work for transferring thermal energy as the conventional system does even though the temperature of the media is ambient without an insulation. Our previous studies of the STA were based on the experimental investigation with the STA facility where the cooling power was 90kW (25.6 refrigeration ton) at the generator temperature 120${}^{\circ }$C from 0m (normal absorption chiller) to 1000m. Thus, the Coefficient of Performance (COP) of STA was found to have almost the same value of 0.65 with conventional absorption chillers without depending on the transportation distances. The objective of this study is to examine the effect of generator temperature from 100${}^{\circ }$C to 120${}^{\circ }$C on the performance of solution transportation of ammonia–water solution, because the generator temperature is directly linked to the waste heat temperature, so its effect needs to be investigated. The experimental facility tested the performance with 0m (normal absorption chiller), 200m and 500m distance. The results indicate that the effect of the generator temperature and solution transportation distances showed no significant on the COP.

In this study, a two-dimensional numerical model of finned-tube type adsorbers was developed and used to examine heat recovery time to improve the performance of an adsorption cooling system. The optimal heat recovery time, which resulted in the highest COP, was determined for a range of heat source temperatures (60–90${}^{\circ }$C) and cycle times (600–1200s). The introduced heat recovery process enhanced COP, but also reduced SCP. This penalty became more serious when the hot water temperature was low and cycle time was short, which serves as a guideline for when heat recovery should be adopted in a given operating condition.

This paper presents a review on energy and exergy analysis of two-stage vapour compression refrigeration (VCR) system. The use of alternative refrigerants instead of conventional refrigerants has also been addressed. The governing equations for the energetic and exergetic analysis of two-stage VCR system have been identified and presented. Several experimental and numerical investigations and their findings on the performance of the two-stage VCR system available in the literature have been discussed in brief. Some of the results have also been reproduced as case studies.

In this paper, a model of a water-cooled centrifugal chiller system is developed and its control performance is studied. The overall system consists of three control loops: (i) a compressor speed control; (ii) an inlet guide vane control and (iii) a condenser liquid-level control. The model is validated by comparing the simulation results with the experimental data under steady state conditions. The results match to within 10% accuracy. A multi-mode control strategy was designed to simulate the operation of the centrifugal chiller as it transitions between start-up, speed control mode, IGV control mode and shutdown mode during a typical day operation. COP of the chiller was studied by conducting simulation runs under a wide range of operating conditions. The results showing the coefficient of performance of the system at different cooling loads as a function of cooling water temperature under IGV control mode and compressor speed control mode are presented.