Papers by Keyword: COP

Abstract: Diffusion Absorption Refrigeration (DAR) systems offer a sustainable alternative to vapor compression refrigeration by utilizing thermal energy instead of mechanical work, making them well-suited for renewable energy applications and waste heat recovery. This review presents a comprehensive analysis of DAR systems, incorporating a statistical evaluation of various research aspects. It focuses on energy sources, alternative working fluids, system configurations, and their impact on the coefficient of performance (COP) and operating temperature. The evolution of DAR technology is traced from early theoretical models to recent experimental developments, supported by a bibliometric study that highlights key research trends, contributing countries, and periods of increased academic activity. The review assesses DAR performance in terms of efficiency improvements, integration of renewable energy, and the use of alternative working fluids. Bibliometric data indicate a growing research interest since 1990, with a notable peak in 2019, and significant contributions from China, India, Germany, and the United States. The study concludes by emphasizing the need for further research into advanced working fluids, the integration of thermal energy storage to enhance stability, and the development of computational models for optimized design and performance. Addressing these challenges will help advance DAR technology as a viable, sustainable cooling solution, supporting innovation and contributing to global energy sustainability.

Abstract: This study examines the thermodynamic performance of a ternary refrigerant mixture composed of R32, R1234ze (E), and R152a (20/20/60 % by mass fraction) as a low-global warming potential (GWP) alternative to R410A in vapour compression refrigeration systems. The simulation was performed using REFPROP under standard operating conditions linked with an engineering equation solver, including 5 K of superheating and 5 K of subcooling. Under different operating conditions of constant evaporation temperature (T_e = 5 °C) with varying condensation temperatures (T_C) (40 to 55 °C by step 2.5°C). Key parameters, including cooling capacity (Qₑ), compressor work (W_c), pressure ratio (P_r), discharge temperature (T_D), mass flow rate (ṁ), and volumetric efficiency (ηᵥ), were evaluated to assess performance. The mixture’s discharge temperature was slightly lower than that of R410A; this will reduce compressor thermal stress and increase compressor life span. Charts illustrating the effect of Tc on all performance indicators were created. In addition to thermodynamic analysis, safety considerations were reviewed. Despite its mild flammability (A2L), the adopted mixture demonstrated stable operation across various conditions and offers potential for applications where safety measures can be effectively implemented. The results indicate that the new mixture presents an energy-efficient and environmentally sustainable replacement for R410A. Further experimental validation is recommended to confirm these findings in real-world scenarios.

Abstract: Vapour compression refrigeration system (VCRS) is being used in various applications, but their high power consumption poses challenges when it comes to energy efficiency and impact on the environment. One approach to improve performance of VCRS is through sub-cooling, which involves cooling the refrigerant coming out of the condenser coil. Dedicated mechanical sub-cooling system, which utilize a separate sub-cooling cycle attached to the main cycle, have shown the potential for enhancing system performance. This paper focuses on the study of the effect of alternative refrigerants, evaporator temperature, condenser temperature, degree of overlap, and the degree of sub-cooling on VCRS with dedicated mechanical sub-cooling system. The findings suggest that using R134a in both cycles leads to maximum COP of system and second-law efficiency. Optimizing certain variables such as evaporator temperature, condenser temperature, degree of overlap, and degree of sub-cooling can also enhance net COP and second-law efficiency of system. This paper investigates the optimum degree of sub-cooling under ideal dedicated mechanical sub-cooling cycles, and it is observed that the system have maximum net COP when degree of sub-cooling is 17 °C. Keywords: VCRS, Dedicated mechanical sub-cooling, COP, R134a, Energy analysis

Abstract: This study compares the performance of a vapor compression refrigeration system (VCRS) with an integrated mechanical subcooled vapor compression refrigeration system (IMS-VCRS) in water-cooled centrifugal chillers. Specifically, this study uses four different refrigerants R134a, R450a, R513a, and R515a. A mathematical model of IMS-VCRS is developed to determine the performance parameters at a fixed cooling capacity of 1750 kW. This study investigates that the energy consumption of an IMS-VCRS is reduced by 11.36% for R134a, 11.98% for R450a, 13.36% for R513a, and 11.89% for R515a. The mechanical subcooled system's COP is increased by 12.84% for R134a, 13.59% for R450a, 15.40% for R513a, and 13.48% for R515a due to the low power requirement. In addition, exergetic analysis is also used to determine the system's second law efficiencies, which in this study improved by 11.25%, 11.84%, 13.41%, and 11.77% for R134a, R450a, R513a, and R515a respectively. Furthermore, parametric analyses were performed to investigate the effects of various system parameters such as evaporator and condenser temperatures.

Abstract: Vapour compression heat pump will have good prospects in future large-scale spacecraft thermal control technology. Its environmental reliability and safety needs to be tested on the ground before being carried with the spacecraft launch. Vibration test is used to assess the anti-vibration capability in its transport and use. It is essential to build a performance test system of vapour compression heat pump to explore its operating characteristics at a given random vibration conditions. The results shows that the vapour compression heat pump is normal operation after the vibration and the cooling performance (COP) of 3.09 is achieved. Vibration test is equipped to provide a guarantee for future success carrying. The performance of vapour compression heat pump at high and low temperature and vacuum environment will be carried out.

Abstract: In this research, solar desiccant cooling cycles in ventilation and hybrid mode are simulated. To simulate cycles, at first a model for desiccant wheel simulation is presented and a computer code based on experimental correlations is used to solve equations. Then by TRNSYS software a model for solar hot water system is simulated, and eventually by representing a suitable algorithm, computer program for simulating solar desiccant cooling cycles by EES software is developed. For all components of desiccant cycle, the dynamic optimum were based on regeneration temperature and solar fraction, and after optimum, dynamic cycle performance in an office building with an area of 115 m² located in Bushehr city, capacity of cooling 3 ton refrigeration were analyzed. The results show that solar desiccant cooling cycles in comparison with compression refrigeration cycles with 40% saving in energy consumption and also during the day and in office buildings have a better performance.

Abstract: Propane (HC-290) is one of hydrocarbons often called as a green refrigerant. As a result, in the long term, this refrigerant is able to be used as a substitute refrigerant to HCFC-22. Generally, the amount of charging HC-290 to replace HCFC-22 based on the density ratio of the refrigerants, for instance, the ratio of liquid density at-10°C between HCFC-22 and HC-290 is 40.59%. Also, most investigations reported that the refrigeration system performances of HC-290 were better compared to HCFC-22 without varying the refrigerant charging of HC-290. By varying the refrigerant charging of HC-290 in a freezer, the performances can be optimized. This study presents an experimental investigation of the impacts on the performances of a freezer when the refrigerant charging of HC-290 is varied replacing HCFC-22. Three performances are reported in the present study, namely: cooling capacity, input power and COP. The first experiment was performed on a freezer using HCFC-22 as working fluid and the amount of refrigerant charging was 450 gram. Furthermore, the tests were carried out using HC-290 with six charging conditions: viz.: 30, 35, 40, 45, 50 and 55% of the mass of HCFC-22. The results showed that when refrigerant of HC-290 was charged 45% (mass) of HCFC-22, the freezer yielded the biggest increase in the cooling capacity and COP.

Abstract: This paper investigates the reliability and performance of a refrigeration system using nanolubricant with 1, 1, 1, 2-Tetrafluoroethane (HFC-134a) refrigerant. Mineral Oil (MO) is mixed with nanoparticles such as Titanium Dioxide (TiO₂) and Aluminium Oxide (Al₂O₃). These mixtures were used as the lubricant instead of Polyolester (POE) oil in the HFC-134a refrigeration system as HFC-134a does not compatible with raw mineral oil. An investigation was done on compatibility of mineral oil and nanoparticles mixture at 0.1 and 0.2 grams / litre with HFC-134a refrigerant. To carry out this investigation, an experimental setup was designed and fabricated in the lab. The refrigeration system performance with the nanolubricant was investigated by using energy consumption test. The results indicate that HFC-134a and mineral oil with above mentioned nanoparticles works normally and safely in the refrigeration system. The refrigeration system performance was better than the HFC-134a and POE oil system. Thus nanolubricant (Mixture of Mineral Oil (MO) and nanoParticles) can be used in refrigeration system to considerably reduce energy consumption and better Coefficient of Performance (COP).

Abstract: Working fluid of R134a is widely used as a refrigerant in automotive air conditioner. This refrigerant has a good performance on the automotive air conditioner. However, because R134a still has a high global warming potential, this refrigerant must be reduced and replaced by environmentally friendly refrigerants. Hydrocarbons of R600a, R290 and their mixtures are widely used as substitute refrigerant. These refrigerants are natural fluids, no effect on the climate, inexpensive and readily available. There are three performances will be discussed in the present study, namely COP, mass flow rate and compression ratio. The present study investigates the effect of three refrigerants, i.e. R134a, R600a and R290 on the performance of automotive air conditioner. The results show that the COP of R600a is higher than those R134a and R290. For the same cooling capacity, the mass flow rate of R600a is approximately 50% of R134a for all ambient temperatures. In addition, the compression ratio of R600a is lower than that of R134a.

Abstract: Most air conditioners utilize vapor compression refrigeration cycle in their operation. In this cycle, the compressor is deployed to circulate the refrigerant from low to high pressures. Lubrication is an important aspect in the compressor to lubricate internal parts. Due to their remarkable properties in the thermo-physical and heat transfer capabilities, nanoparticles have prospect to be applied in the refrigeration and air conditioning system. The reliability and solubility nanoparticle of TiO₂ in refrigeration systems have been investigated by several by several researchers. By introducing TiO₂ nanoparticle in the lubricant, the friction coefficient and input power of the compressor can be decreased. An air conditioner with cooling capacity of 2.5 kW is utilized in the experiment. Five different concentrations of nanoparticle in the lubricant, viz.: 0.1, 0.2, 0.4, 0.5 and 0.6 gram of TiO₂ in one liter of lubricant were mixed using a magnetic stirrer. After 10 days, TiO₂ nanoparticles in the lubricant were observed its solubility. Furthermore, based on their solubility, TiO₂ nanoparticle with concentration of 0.2 g/L was selected in the experiments. The results show that the air conditioner using R290 with TiO₂ nanoparticle in the lubricants works normally and the input power of the air conditioner decreases about 3.1% and the cooling capacity and the COP increase about 5.1% and 8.4%, respectively, compared to the system without nanoparticle in the lubricant.