Conventional Refrigeration System Research Articles

COP Optimization of a R134a Cross Vane Expander Compressor Refrigeration System

Cross Vane Expander Compressor (CVEC) is a newly invented expander-compressor combined unit, where it is introduced to replace the compressor and the expansion valve in traditional refrigeration system. The mathematical model of CVEC has been developed to examine its performance and it was found that the energy consumption of a conventional refrigeration system was reduced by as much as 18%. It is believed that this result can be further improved by optimizing the device. In this paper, the coefficient of performance (COP) of CVEC has been optimized under predetermined operational conditions. Several main design parameters of CVEC were selected to be the variables and the optimization was done with theoretical model in a simulation program. The theoretical model consists of geometrical model, dynamic model, heat transfer model and valve dynamics model. Complex optimization method, which is a constrained, direct search and multi-variables method, was used in the study. As a result, the optimization study suggested that with an appropriate combination of design parameters, a large COP improvement in CVEC R134a refrigeration system is possible. With a reduction of 20% in the shaft radius and 17% in inner cylinder radius, and the increase of around 16% in ports diameter, an improvement of 58% in COP can be achieved.

English

Cross vane expander compressor (CVEC) is a newly invented expander-compressor combined unit, where it is introduced to replace the compressor and the expansion valve in traditional refrigeration system. The mathematical model of CVEC has been developed to examine its performance and it was found that the energy consumption of a conventional refrigeration system was reduced by as much as 18%. It is believed that this result can be further improved by optimizing the device. In this paper, the coefficient of performance (COP) of CVEC has been optimized under predetermined operational conditions. Several main design parameters of CVEC were selected to be the variables and the optimization was done with theoretical model in a simulation program. The theoretical model consists of geometrical model, dynamic model, heat transfer model and valve dynamics model. Complex optimization method, which is a constrained, direct search and multi-variables method, was used in the study. As a result, the optimization study suggested that with an appropriate combination of design parameters, a large COP improvement in CVEC R134a refrigeration system is possible. With a reduction of 20% in the shaft radius and 17% in inner cylinder radius, and the increase of around 16% in ports diameter, an improvement of 58% in COP can be achieved. Key words: Coefficient of performance (COP), cross vane expander-compressor, simulation, optimization.

Thermo-economic analysis of a novel organic Rankine cycle integrated cascaded vapor compression–absorption system

Integration of thermal systems improves the energy efficiency and reduces the carbon emissions. In this paper, a novel trigeneration system, which integrates the organic Rankine cycle and vapor compression–absorption cascade refrigeration cycle is proposed. The cascade refrigeration system combines the advantages of the conventional stand-alone vapor compression system and vapor absorption refrigeration system. The energetic and rational efficiencies of the proposed system, with n-pentane as an ORC working fluid, are calculated as 79.02% and 46.7%, respectively. Effects of variation in different operating parameters as well as organic working fluid on energetic and exergetic efficiencies have been studied. The coefficient of structural bond analysis demonstrates that the evaporator and cascade condenser operating temperature significantly affects the system performance. The proposed trigeneration system powered by waste heat is independent of the grid supply; however, a stand-alone vapor compression refrigeration system requires about 19.15 kWe to meet the equivalent cooling demand. The decision of selection between the stand-alone system and the proposed trigeneration system is influenced by the compressor capacity of stand-alone vapor compression refrigeration system, cost of unit electricity, compressor runtime, cost of organic Rankine cycle power block, and cost of vapor absorption system. Based on the condition of equality of the annualized cost of the stand-alone system and proposed trigeneration system, a methodology for selection between these two configurations, called selection diagram, is also presented in this paper. The selection diagram gives quick suggestion about the optimal configuration at the initial design stage. The economic analysis reveals that the simple payback period and breakeven point for the proposed hybrid system are 6.2 years and 4.9 years, respectively.

Simulation of a Cold Store Driven by Solar Absorption Cooling System under Different Egyptian Climatic Conditions

Storing of products at their recommended storage temperatures in a cold store is expensive due to their cost of electricity consumption. In order to avoid the drawbacks of both fossil fuels shortage and chlorofluorocarbon refrigerants, the substitution of a conventional vapor compression refrigeration system by a solar absorption cooling system is a promising alternative to operate the cold stores. Therefore, the main objective of the present work is to simulate and evaluate the performance of solar powered absorption refrigeration system to operate the cold store under Egyptian climatic conditions. To achieve this objective, a simulation model based on the mass and energy conservation equations is developed using TRNSYS software. The results showed that this model predicts data that are very close to the available data in the literature with an average error of 6.21%. The results indicated that the maximum load is 7.12kW in 21- July. Reported results revealed that solar collector area of 100 m2 and storage tank volume of 1.8m3 are required for a maximum cold store load with solar fraction of 0.75.

Energy analysis of alternative CO2 refrigeration system configurations for retail food applications in moderate and warm climates

Refrigeration systems are crucial in retail food stores to ensure appropriate merchandising of food products. This paper compares four different CO2 refrigeration system configurations in terms of cooling performance, environmental impact, power consumption and annual running costs. The systems studied were the conventional booster refrigeration system with gas bypass (reference system), the all CO2 cascade system with gas bypass, a booster system with a gas bypass compressor, and integrated cascade all CO2 system with gas bypass compressor. The weather conditions of London, UK, and Athens, Greece, were used for the modelling of energy consumption and environmental impacts to represent moderate and warm climatic conditions respectively. The control strategies for the refrigeration systems were derived from experimental tests in the laboratory on a conventional booster refrigeration system. The results from the analysis showed that the CO2 booster system with gas bypass compressor can provide best performance with 5.0% energy savings for the warm climate and 3.65% for the moderate climate, followed by the integrated cascade all CO2 system with gas bypass compressor, with 3.6% and 2.1% savings over the reference system for the warm and moderate climates respectively.

Evaluating Applicability of a Scroll Expander for CO2 Refrigeration System at Warm Climate

Performance of a trans-critical CO2 refrigeration cycle equipped with a scroll work recovery expander is investigated using a semi-empirical model of the scroll, for high ambient temperature application. Maximum isentropic efficiency of 61% is obtained, for a pressure ratio of about 3.7 for the scroll expander. Simulation results obtained are further validated against the reported experimental results. It is also observed that, about 20% of the total energy consumed can be recovered with the help of scroll expander during trans-critical operation. Based on year-round ambient temperature data, at New Delhi (India), an economic analysis is carried out for installation of work recovery scroll system. Total payback period (PBP) for scroll expanders of various capacities are also determined. It is noted that the PBP of scroll expander is about 1 to 2 years or less, which is encouraging. Total Equivalent Warming Impact (TEWI) of the system is compared with that of a conventional trans-critical CO2 refrigeration system and system running on low global warming potential (GWP) hydrofluoroolefin (R1234yf) refrigerant. Trans-critical CO2 system along with work recovery scroll expander appears justified as the same has about 15% lower TEWI compared to conventional trans-critical CO2 system but is 50% more than R1234yf system.

Energy and exergy investigation of ejector refrigeration systems using retrograde refrigerants

Conventional and compression-enhanced ejector refrigeration systems were investigated numerically using regular and retrograde refrigerants. The nature of retrograde fluids was explained, including their main advantages and disadvantages. The numerical model was developed and validated with previous experimental data of both types of working fluids. Energy and exergy analysis were performed to examine system performance and compare between the selected refrigerant candidates. Retrograde refrigerants were found promising with both versions of ejector cycles, when two case studies of an air conditioning application and an indoor ice rink were considered. The butene series showed superior coefficient of performance and exergy efficiency, especially the isomers cis-2-butene and 1-butene.

Influence of Silicon Carbide Nanopowder in R134a Refrigerant Used in Vapor Compression Refrigeration System

This paper deals with the influence of silicon carbide (SiC) nanopowder in R134 a refrigerant used in a vapor compression refrigeration system. The performance study was done by mixing a SiC nanopowder in R134a refrigerant. The energy consumption of the R134a refrigerant with SiC nanoparticles mixture saves 20% energy with 0.25% mass fraction of SiC nanoparticles when compared to the R134a system. The COP of the refrigerant R134a system is 1.24 whereas COP for R134a-SiC nanopowder is 1.81. The SiC nanopowder is cryogenically treated at [Formula: see text]C for 24 h and the COP is found out. The results show that the COP of R134a-SiC nanopowder and R134a-cryo SiC (cryogenically treated silicon carbide nanopowder) is increased when compared to the R134a conventional refrigeration system.

Mathematical Modelling for Thermal and Mechanical Design of Shell and Tube Type Gas Cooler Used in Transcritical CO<sub>2</sub> Refrigeration System

This paper is about Mathematical Modelling for Thermal and Mechanical Design of Shell and Tube type Gas Cooler used in Transcritical CO2 Refrigeration system. Transcritical refrigeration system refers to system whose condenser temperature is above critical temperature of refrigerant. To achieve it, the condenser in conventional refrigeration system is replaced by Gas Cooler where Refrigerant vapour is cooled sensibly without condensation. The gas cooler is used for cooling of refrigerant by using water as coolant. The temperature of refrigerant vapour coming out of compressor in transcritical system is more as compared to conventional refrigerant system. So gas cooler can be effectively used for heating of water. This paper describes a mathematical model that can be used in predicting the heat transfer performance of a shell and tube type Gas Cooler used in transcritical CO2 refrigeration system. The model uses Kern Method of Heat exchanger design. Given the fluid inlet and outlet temperatures flow rates of fluid & fluid properties the model determines (a) the necessary heat transfer surface area, (b) Outside and inside heat transfer coefficient, (c) overall heat transfer coefficient, (d) Pressure drop on shell and tube side, (e) It also determines mechanical design parameters such as shell O. D, Shell thickness, Tube sheet thickness, Flange thickness.

Adsorption Refrigeration System: Design and Analysis

Cooling systems like vapour absorption or vapour adsorption refrigeration system, which runs on low grade energy sources provide favourable alternatives to the conventional vapour compression refrigeration system .These system do not contribute to global warming,depletion of fossil fuel or ozone layer depletion as there is absence of conventional mechanical compressor and use of Eco-friendly refrigerant. This cycle can utilize low grade heat sources like,waste heat of flue gases,Automobile vehicle exhaust,or even solar energy and hence has much scope of development in the near future .The work include design,development and analysis of Adsorption Refrigeration System which is capable of producing 10-15 kg of ice in each cycle,and does not contain any moving part and maintenance free.

Energy and exergy analysis of bus refrigeration system using two-phase ejector with natural refrigerant R744

In conventional bus refrigeration systems, R134a is used extensively as working fluid. According to the international agreements and European parliament directive, studies of mobile refrigeration systems have focused on the alternative refrigerants which have lower global warming potential (GWP). Natural refrigerant R744 (CO2) is one of the best alternative refrigerants with low GWP value, but R744 transcritical refrigeration systems have very low coefficient of performance (COP) value with respect to artificial refrigerant systems. In this study, a two-phase ejector was added as an expansion valve in the transcritical refrigeration system in order to overcome low COP. Transcritical ejector refrigeration system is compared with a standard transcritical refrigeration system for different parameters based on energy and exergy analysis. Results show that COP improvement can be achieved by about 26% and exergy destruction decreased by about 22% for proper design in a Mediterranean climate zone.

Performance Comparison between an Absorption-compression Hybrid Refrigeration System and a Double-effect Absorption Refrigeration Sys-tem

Conventional absorption refrigeration systems (ARSs), which are mainly driven by heat, have a competitive primary energy efficiency (PEE) compared with chillers driven by electricity. In the typical ARS, a large quantity of high-temperature heat is supplied into the generator, while a substantial amount of low-temperature heat is rejected to the environment from the condenser, it’s a huge waste. In order to decrease the input heat for generator and enhance the performance of conventional ARS, a kind of absorption-compression hybrid refrigeration system recovering condensation heat for generation (RCHG-ARS) was ever proposed. In the present study, the models of both RCHG-ARS and double-effect absorption refrigeration system (DEARS) are established, and the effects of different parameters on them are simulated and compared with each other. As a conclusion, the PEE of RCHG-ARS can be 29.0% higher than that of DEARS, and RCHG-ARS has a wider working conditions than DEARS due to the existence of the compressor.

Review of investigations in eco-friendly thermoacoustic refrigeration system

To reduce greenhouse gas emissions, internationally research and development is intended to improve the performance of conventional refrigeration system also growth of new-fangled refrigeration technology of potentially much lesser ecological impact. This paper gives brief review of research and development in thermoacoustic refrigeration also the existing situation of thermoacoustic refrigeration system. Thermoacoustic refrigerator is a novel sort of energy conversion equipment which converts acoustic power into heat energy by thermoacoustic effect. Thermoacoustic refrigeration is an emergent refrigeration technology in which there are no moving elements or any environmentally injurious refrigerants during its working. The concept of thermoacoustic refrigeration system is explained, the growth of thermoacoustic refrigeration, various investigations into thermoacoustic refrigeration system, various optimization techniques to improve coefficient of performance, different stacks and resonator tube designs to improve heat transfer rate, various gases, and other parameters like sound generation have been reviewed.

Coupled Heat and Mass Transfer Analysis of an Adiabatic Dehumidifier – Unique Approach

Abstract Liquid desiccant dehumidifier is one of the most desirable systems for dehumidification of air when compared to conventional refrigeration system and solid desiccant based dehumidifier. In the present study, a finite difference model is developed to simulate the coupled heat and mass transfer processes occur in a counter flow adiabatic dehumidifier employing lithium chloride (LiCl) as a desiccant solution. Mat-lab R13 is used as a simulation package for solving the aforementioned model. This model has taken into the consideration of thermal effectiveness, effective height and moisture effectiveness as variable parameters for obtaining the correlation of the desired operating parameters. The predicted numerical parameters for absorption process have good agreement with the experimental data reported in the literature. This model is unique and can be extended to any type of liquid desiccant solution by changing the solution properties. The performance analysis of adiabatic counter flow dehumidifier is also carried out by varying the operating parameters and the detailed results are presented in the full manuscript.

Experimental study on two-stage ejector refrigeration system driven by two heat sources

In this paper, an experimental study on a two-stage ejector refrigeration system driven by two heat sources is carried out involving system design, setup, operation and experimental evaluation. It is looked at by means of changing temperatures of evaporation, condensation, low and high temperature generation independently for the variation tendency of system performance (including total entrainment ratio and COP) and comparison to the conventional single-stage ejector refrigeration system at variable condensation temperatures that is achieved by the valve switching in this system. In terms of refrigerants, R236fa is selected for stability of the system operation. Total entrainment ratio and COP are increasing as the temperatures of evaporation, high and low temperature generation go up. Different from the conventional single-stage ejector refrigeration system, this two-stage system is finally found to be capable of supplying more refrigerating effect in situations where the condensation temperature is lower than 21.7 °C.

Thermodynamic performance optimization of the absorption-generation process in an absorption refrigeration cycle

The absorption refrigeration cycle is a basic cycle that establishes the systems for utilizing mid-low temperature heat sources. A new thermal compressor model with a key parameter of boost pressure ratio is proposed to optimize the absorption-generation process. The ultimate generation pressure and boost pressure ratio are used to represent the potential and operating conditions of the thermal compressor, respectively. Using the proposed thermal compressor model, the operation mechanism and requirements of the absorption refrigeration system and absorption-compression refrigeration system are elucidated. Furthermore, the two typical heat conversion systems are optimized based on the thermal compressor model. The optimum boost pressure ratios of the absorption refrigeration system and the absorption-compression refrigeration system are 0.5 and 0.75, respectively. For the absorption refrigeration system, the optimum generation temperature is 125.31°C at the cooling water temperature of 30°C, which is obtained by simple thermodynamic calculation. The optimized thermodynamic performance of the absorption-compression refrigeration system is 16.7% higher than that of the conventional absorption refrigeration system when the generation temperature is 100°C. The thermal compressor model proposed in this paper is an effective method for simplifying the optimization of the thermodynamic systems involving an absorption-generation process.

Thermodynamic investigation of a booster-assisted ejector refrigeration system

In order to improve performance of ejector refrigeration system, a booster is added before an ejector to enhance secondary flow pressure, which is called a booster assisted refrigeration system. Based on mass, momentum and energy conservation, a 1D model of ejector for optimal performance prediction was presented and validated with experimental data. A detailed study of working characteristics of the booster assisted ejector refrigeration system was carried out and compared against conventional ejector refrigeration system and compressor based refrigeration system, on the basis of first and second laws of thermodynamics. Effects of booster outlet pressure on COPth based on thermal energy and COPw based on work input, and also on entrainment ratio and area ratio of ejector were studied. The exergy destruction rates were also computed and analyzed for components of the booster-assisted ejector refrigeration system. Ways to reduce exergy destruction were discussed.

Giant rotating magnetocaloric effect at low magnetic fields in multiferroic TbMn2O5 single crystals

In conventional magnetocaloric refrigeration systems, the magnetocaloric effect is exploited by moving the active material in and out of the magnetic field source. Here, we demonstrate that a large and reversible magnetocaloric effect (−ΔSR, max = 6.4 J/kg K and ΔTR, max = 8 K under 2 T) can be generated simply by rotating the multiferroic TbMn2O5 single crystal around its b axis in a relatively low constant magnetic field applied in the ac plane. Our results should inspire and open ways toward the implementation of compact, efficient and embedded magnetocaloric devices for low temperature and space applications.

Estimation of Refrigeration Load Saving for the Cooled Logistic Storage by High Volume Low Speed Fan

층고가 높은 건물 내부의 온도 성층화 현상을 해소하는 설비인 저속순환팬의 적용 효과를 분석하고자 기존 냉동냉장설비가 적용된 물류창고에 저속순환팬을 적용한 수치해석모델을 작성하여 저속순환팬 적용에 따른 순환효과를 분석하고 그에 따른 에너지 절감효과를 검토해 보았다. 열전달 및 기류분석 결과 저속순환팬은 냉동냉장설비로 부터의 냉기를 창고 내에 고르게 전달될 수 있도록 하여 창고 내 평균 온도를 균일하게 형성하였다. 이를 통해 일반적인 냉동냉장설비를 통한 냉각방식을 갖추고 있는 창고에 서는 불가피한 국부적인 고온부 형성을 억제하여 적용 시 냉각의 품질을 개선할 수 있을 것으로 예상되었다. 그리고 이러한 균일 한 온도분포는 동일한 냉동냉장설비의 급기온도에서 창고의 실내 평균온도를 하강시켜 냉동기의 예상 출력이 감소하였다. 또한 저속순환팬 적용 시 보다 높은 냉각 토출온도에서도 창고 내부 평균온도를 기존 냉각방식보다 낮게 유지할 수 있는 것으로 나타나 냉동⋅창고에서 소비되는 냉동기의 소비전력을 절감할 수 있을 것으로 예상되었다.High Volume Low Speed Fan (HVLS Fan) is type of ceiling fan and effective solution for large indoor facility ventilations that conventional fans are inefficient. In HVAC applications, HVLS Fan has de-stratification effect that suppresses temperature stratification when heating or cooling at high ceiling room. In this study, we focused on HVLS Fan ’ s energy saving effect from its high volumetric flow rate with low power consumption and de-stratification effect to the logistic storages that operated on chilled and frozen conditions. In order to estimate effectiveness of HVLS application, we adopt Computational Fluid Dynamics (CFD) approach and those computational domains were referenced from existing commercial refrigeration facilities. Incorporate with our own HVLS Fan design, conjugated heat transfer and fluid flow simulation predicts HVLS Fan ’ s energy saving capability. Compared by conventional refrigeration system, HVLS Fan installation made mixing flow within entire room and uniform distribution of air temperature. Also the certain rage of refrigerator output reduction was discovered with the HVLS Fan application since the HVLS Fan application has decreased average room temperature with lesser capacity of refrigerator.

Cooling performance of a pump-driven two phase cooling system for free cooling in data centers

The energy consumption of data centers is increasing rapidly with the development of technology. In order to reduce the energy consumption, free cooling technology instead of the conventional refrigeration system is feasible in the cold season. In the present work, a pump-driven two phase cooling system which is an excellent free cooling technology was developed and the prototype was investigated experimentally. The experimental results show that the efficiency of the magnetic pump was 7.7% at the motor frequency of 22 Hz, the cooling capacity of the system was able to reach 3.429 kW and 9.241 kW when the temperature differences between indoor and outdoor were 10 °C and 25 °C, respectively, and the EER were 12.9 and 29.7, which are extremely higher than the conventional refrigeration system.