Experimental Investigation and Heat Transfer Analysis of Innovative Thermal Mechanical Refrigeration System Compared to Electric Compressor

Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system

Experimental investigation of a two-phase ejector installed into the refrigeration system for performance enhancement

Natural refrigerants are presented as the perfect, ecologically benign refrigerants and the final answer to ozone loss and global warming in this article. In refrigerated and air-conditioning systems, HFC refrigerants are presently the most common alternative for CFC and HCFC refrigerants. However, they are just as alien to nature as CFCs and HCFCs, providing a solid foundation about the need to embrace natural refrigerants as a substitute for halocarbon refrigerants. This study also looks at the possibilities of refrigerants and their uses in refrigerated and air-conditioning systems. Both oil used in R12 or poly-ol-ester oils in use in R134asystems are miscible with natural refrigerants, particularly hydrocarbons, and their combinations. They are also fully compatible with in all materials typically used in refrigeration systems, with the exception of ammonia. Finally, the results of this study show that natural refrigerants are the best long-term options in refrigerated and air-conditioning systems.

To reduce the expected increase in global mean temperature, the substitution of R134a as working fluid of refrigeration and air conditioning systems using refrigerants with the lowest carbon footprint possible is a priority. In this paper, the use of R1234ze(E) as pure fluid and mixed with R134a (resulting R450A) is assessed from a thermodynamic point of view. Then, these results are used to support experimental data obtained from a vapor compression system at three evaporating temperatures combined with other condensing temperatures. Regarding refrigerant main thermodynamic properties, R450A is very similar to R134a, even though the HFO R1234ze(E) is the main component of the mixture (58% compared to 42%). For both alternatives, the major differences with R134a are observed in relative molar mass, vapor density and liquid thermal conductivity. Compared with R134a, average cooling capacity obtained is lower for both alternatives (until 34% for R1234ze(E)) due to a reduction in suction density and refrigerating effect. Resulting COP of R1234ze(E) is also slightly lower even though specific compression work is significantly lower. Average R450A COP can match that of R134a at the same compression pressure ratios. Attending to the results of the drop-in tests, the main conclusion of the paper is that only R450A can be used as drop-in replacement if light reduction in system cooling capacity can be accepted.

Challenges and opportunities in the management of refrigeration and air conditioning systems to reduce environmental impacts in the Colombian health sector

Applications of refrigerant R1234yf in heating, air conditioning and refrigeration systems: A decade of researches

Nowadays, the use of refrigerants has low GWP and zero ODP applying refrigeration and air conditioning systems is an important concern. There has been a lot of research taking about refrigeration systems using R744. In this study, we focus on the use of the mix of water and air for an evaporative condenser through an experiment to study the heat transfer efficiency between water and the R744. The results of this study show that it is feasible to use water to cool down R744 to a subcritical state. The data obtained show that the R744 temperature at the outlet condenser gradually decreases with each change in the number of tube layers, the condensing pressure is stable at 73 bar with a pressure drop of 0.4 bar. The water temperature is stable between 26oC and 28oC, and the air outlet temperature from the indoor unit gradually decreases from 28oC to 16.8oC. With the 3 configurations of the condenser, the coefficient of performance gradually increases from 3.6 to 4.5 respectively.

Lower GWP refrigerants are essential to mitigate the impact of refrigeration systems on climate change. HFO/HFC mixtures are currently considered to replace HFCs in refrigeration and air conditioning systems. The aim of this paper is to present the main operating and performance differences between R513A (GWP of 573) and R134a (GWP of 1300), the most used refrigerants for medium evaporation temperature refrigeration systems and mobile air conditioners. To perform the experimental comparison, 36 tests are carried out with each refrigerant at evaporating temperatures between −15 and 12.5°C and condensing temperatures between 25 and 35°C. The conclusion of the experimental comparison is that R513A can substitute R134a with only a thermostatic expansion valve adjustment, achieving better performance and higher cooling capacity. The discharge temperature of R513A is always lower than that of R134a.

Nano-enhanced refrigerant is one of the promising heat transfer fluids in refrigeration systems. It has the capability to boost the efficiency of vapour compression refrigeration and air conditioning systems. In heat transfer application, the density of the fluid plays a crucial role in identifying various heat transfer characteristics such as the Reynolds number, Nusselt number, the friction factor and the pressure loss. Compared to thermal conductivity and viscosity, determining the density of nanofluids has received very less attention in research. The liquid and vapour densities of alumina (Al2O3), titanium dioxide (TiO2) and cupric oxide (CuO) nanoparticles suspended in 2,3,3,3-tetrafluoropropene (R1234yf) are investigated in this study. The Pak and Cho model was adopted to examine the densities of nano-refrigerants as the volume concentration of particles in the base refrigerant and temperature varies from 1% to 5% and 273 to 323 K respectively. The models are validated using the experimental studies conducted by various researchers on different nano-refrigerants. The analysis results indicated that the liquid and vapour densities of CuO/R1234yf nano-refrigerant are 10.3% and 62.93% greater than that of Al2O3/R1234yf at 5% particle concentration. From the liquid and vapour density point of view, the CuO/R1234yf nano-refrigerant is superior over Al2O3/R1234yf and TiO2/R1234yf. Results also indicated that at 308 K the liquid phase density of CuO added with R1234yf nano-refrigerant is higher by 12.99% and 8.65% than R134a and R141b respectively. Hence CuO/R1234yf significantly enhances the performance of refrigeration systems.

Performance evaluation of hot-gas by-pass capacity control schemes for refrigeration and air-conditioning systems

Due to increasing concerns about global warming, various environmental regulations will eventually phase out refrigerants used in air conditioning and refrigeration systems (e.g., R-410A, R-404A). Several refrigerants have been proposed as replacements, offering a variety of global warming potential (GWP), levels of energy efficiency and flammability. Some of these options are synthetic HFC/HFO mixtures such as R-454C and R-455A while other are commonly called naturals such as R-290 (Propane) and R-744 (Carbon Dioxide). This study discusses the merits of the leading options for air Conditioning and refrigeration systems. The fundamental requirements (environmental, performance, safety) are employed to fairly evaluate these options. Performance data and Life Cycle analysis results for these options are presented. Overall, this study provides information needed to judge the prospects of getting adequate replacement for R-410A and R-404A in a long-term sustainable basis.

Air-conditioning and refrigeration systems are electrical appliances that use a huge amount of energy and contribute indirectly to global warming. Also, R410A which was initially developed as a substitute for ozone-depleting refrigerants in the air-conditioning systems has been phase-out due to its high global warming potential (GWP) and the resulting harmful effect on the climate. In addition to the issue of refrigerant high GWP, energy consumption is a significant issue. The energy efficiency of new refrigerants must then be considered in the search for alternative refrigerants to ensure that they do not lead to an increase in greenhouse gas generation at the power source. Therefore, this paper investigates the energy and cooling performance of four new multi-components and ecologically friendly refrigerant blends that contained carbon dioxide and hydrofluoroolefins in their compositions as substitutes for R410A in air-conditioning systems. Relevant thermodynamic equations and REFPROP software were employed for the computational analysis. The results indicated that the new blends (R445A, R455A, R470B and R470A) exhibited a desirable low compression ratio and high heat transfer for cooling applications. The blends also exhibited low compressor energy input and low specific cooling energy. R455A has an average coefficient of performance (COP) of 24.6% above that of the reference refrigerant (R410A). The cooling capacity per unit volume for R470B, R455A and R470A across a temperature range of 253 to 293 K are higher by 1.3, 6.0, and 12.6%, respectively than that of R410A. Generally, among all the four new substitute blends, the overall assessment revealed R455A as the best replacement for R410A in air-conditioning systems due to its superior performance in terms of its low compression ratio, compressor energy and specific cooling energy. R455A also has the highest COP and relatively high cooling capacity per unit volume.

An economic evaluation of refrigeration and air-conditioning system retrofit in large-scale public buildings: A case study of Beijing Capital International Airport Terminals

Thermal systems of buildings in the tropics are highly energy intensive. In this study, a novel integrated solar photovoltaic–thermal–refrigeration (PVTR) system used to produce hot water and air-conditioning in the tropical climate conditions of Singapore was analyzed. A dynamic simulation model was formulated for the analysis. Mathematical models were developed for the PV sandwich attached with a solar flat plate collector and for the main components of the refrigeration system. Thorough investigation of the electrical and thermal performances of the system were conducted through the analysis of coefficient of performance (COP), cooling capacity, water temperature and heat capacity in water heater, photovoltaic (PV) module temperature and PV efficiency. The results show that attractive electrical and thermal performance can be achieved with a maximum annual cooling COP of 9.8 and a heating COP of 11.3. The PV efficiency and power saving were 14% and 53%, respectively. The annual cooling, heating and PV energy produced were 9.7, 15.6 and 1.6[Formula: see text]MWh, respectively. The financial payback period of the system was 3.2 years and greenhouse gas (GHG) emission reduction annually was 12.6 tons of CO2 equivalents (tCO2e).

Experimental investigation of effect of different tube row-numbers, fin pitches and operating conditions on thermal and hydraulic performances of louvered and wavy finned heat exchangers