Determination of a Vapor Compression Refrigeration System Refrigerant Charge

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Thermoeconomic optimization of subcooled and superheated vapor compression refrigeration cycle

An exergy-based thermoeconomic optimization application is applied to a subcooled and superheated vapor compression refrigeration system. The advantage of using the exergy method of thermoeconomic optimization is that various elements of the system—i.e., condenser, evaporator, subcooling and superheating heat exchangers—can be optimized on their own. The application consists of determining the optimum heat exchanger areas with the corresponding optimum subcooling and superheating temperatures. A cost function is specified for the optimum conditions. All calculations are made for three refrigerants: R22, R134a, and R407c. Thermodynamic properties of refrigerants are formulated using the Artificial Neural Network methodology.     

A review on two-phase ejector as an expansion device in vapor compression refrigeration cycle

This paper presents a comprehensive review of two-phase ejector as an expansion device in vapor compression refrigeration cycle over the past two decades. It also covers research opportunities that are still open in the field of two-phase ejectors as an expansion valve. The studies of the application of ejector as an expansion device are relatively scarce compared to the application of ejector as heat-driven refrigeration system. A better understanding of two-phase flow in the ejector is necessary to optimize energy saving of the system. This paper also presents effects of geometric parameters of the ejector as an expansion valve on the performance of vapor compression refrigeration cycle. In addition, the effect of working fluid on the two-phase expansion refrigeration system is covered. The authors predict that the challenge of future research on design of two-phase ejector is how to generate a pressure rise in diffuser for minimum compressor work and optimum COP improvement.     

An experimental investigation of a different type vapor compression cascade refrigeration system

Experimental investigation and theoretical study of a different type of two-stage vapor compression cascade refrigeration system using R-134 as the refrigerant are presented. Performance evaluations of two single stage vapor compression systems and two-stage vapor compression refrigeration cascade system are performed with respect to theoretical model developed. In the first section of the experiments, one refrigeration system, namely RU2, is operated. During the experiments, rate of the water flow connecting both systems is kept constant at various values and the voltage across evaporator heaters is increased from 100 to 200 V with intervals of 20 V. In the second part of the first category, experiments are repeated by using different mass flow rates of water. In the second section, two separate refrigeration systems, namely RU1 and RU2 are connected to each other by using the water loop. This system is also called cascade refrigeration system. It is observed that the change in water mass flow rate has little effect on the coefficient of performance for single stage and cascade stage refrigeration systems. It is also observed that the coefficient of performance is mainly a function of evaporator temperature and pressure. When RU2 operating in the single stage refrigeration system is compared with RU2 operating in the two-stage cascade refrigeration system at the same refrigeration load interval (360–460 W), the average percentage values of the decrease in the condensing pressure, the decrease in the compressor power and the increase in the COP are 21.9, 31.7 and 32.7, respectively.     

Suggested solution concentration for an energy-efficient refrigeration system combined with condensation heat-driven liquid desiccant cycle

This paper presents a hybrid energy-efficient refrigeration system enhanced by liquid desiccant evaporative cooling technology for subcooling the refrigerant, where the liquid desiccant cycle is driven by the exhausted heat from the condenser and three commonly used liquid desiccants: LiCl, LiBr and CaCl₂ aqueous solutions are considered here. The solution concentration for the proposed hybrid energy-efficient refrigeration system should be determined and optimized carefully for better performance. Sensitive study of solution concentration involved in the hybrid system is conducted at different condensation temperature. The results indicates that under standard working condition (i.e., condensing temperature is 50 °C), the optimum solution concentration is 0.31 for LiCl aqueous solution, 0.45 for LiBr aqueous solution and 0.42 for CaCl₂ aqueous solution, while the maximum COPs are nearly same. When the condensing temperature is 45 °C, the optimum solution concentration should be set at 0.27 for LiCl aqueous solution, and 0.41 for LiBr aqueous solution and 0.37 for CaCl₂ aqueous solution, while condensing temperature is 55 °C, it is 0.35 for LiCl aqueous solution, 0.49 for LiBr aqueous solution and 0.45 for CaCl₂ aqueous solution. The simple fitting formulas are obtained, and performance improvement potential is discussed.     

Energy and exergy analysis of vapor compression refrigeration system using pure hydrocarbon refrigerants

This study presents a comparison of energetic and exergetic performance of a vapor compression refrigeration system using pure hydrocarbon (HC) refrigerants. In this study, four different pure HCs propane (R290), butane (R600), isobutane (R600a) and isopentane (R1270) are used in theoretical analysis. R22 and R134a are also used in the analysis. For the analysis, EES package program was used for solving thermodynamic equations of the refrigerants. Results have been presented graphically. According to results, differences of coefficient of cooling performance values of these refrigerants are quite small. Energetic and exergetic efficiency values obtained with R1270 and R600 are higher than R600a and R290. Copyright © 2009 John Wiley & Sons, Ltd.     

溶液蓄能制冷与压缩制冷复合循环工作特性分析

以长江中下游地区一办公建筑为例,通过对采用氨水溶液的蓄能制冷与压缩制冷复合循环系统在分量蓄能策略下的工作过程进行数值模拟,得到复合循环系统工作参数和特性的变化规律。研究结果表明在分量蓄能策略下采用复合系统可以获得更佳的效果。     

Performance of a combined organic Rankine cycle and vapor compression cycle for heat activated cooling

Heat activated cooling has the potential of utilizing thermal sources that currently go unused such as engine exhaust heat or industrial waste heat. Using these heat sources can provide enhanced energy utilization and reduced fuel usage in applications where cooling is needed. The concept developed here uses waste heat from stationary and mobile engine cycles to generate cooling for structures and vehicles. It combines an organic Rankine cycle (ORC) with a conventional vapor compression cycle. A nominal 5 kW cooling capacity prototype system was developed based on this concept and tested under laboratory conditions. In order to maintain high system performance while reducing size and weight for portable applications, microchannel based heat transfer components and scroll based expansion and compression were used. Although the system was tested off of its design point, it performed well achieving 4.4 kW of cooling at a measured heat activated COP of 0.48. Both the conversion and 2nd law efficiencies were close to the model results, proving it to be an attractive technology. The measured isentropic efficiency of the scroll expander reached 84%, when the pressure ratio was close to the scroll intrinsic expansion ratio. The reduced cooling capacity was attributed to off design operation.     

Development of a hybrid refrigerator combining thermoelectric and vapor compression technologies

A domestic refrigerator with three compartments has been developed: refrigerator compartment, at 4 °C (vapor compression cooling system); freezer compartment, at −22 °C (vapor compression cooling system); and a new super-conservation compartment, at 0 °C (thermoelectric cooling system). The thermoelectric system designed for the super-conservation compartment eliminates the oscillation of its temperature due to the start and stop compressor cycles, obtaining a constant temperature and thus, a better preservation of the food.For the design and optimization of this application, a computational model, based in the numerical method of finite differences, has been developed. This model allows to simulate the complete hybrid refrigerator (vapor compression–thermoelectricity). The accuracy of the model has been experimentally checked, with a maximum error of 1.2 °C for temperature values, and 8% for electric power consumption.By simulations with the computational model, the design of the refrigerator has been optimized, obtaining a final prototype highly competitive, by the features on food preservation and power consumption: 1.15 kW h per day (48.1 W) for an ambient temperature of 25 °C. According to European rules, this power consumption value means that this new refrigerator could be included on energy efficiency class B.     

A review of emerging technologies for food refrigeration applications

Refrigeration has become an essential part of the food chain. It is used in all stages of the chain, from food processing, to distribution, retail and final consumption in the home. The food industry employs both chilling and freezing processes where the food is cooled from ambient to temperatures above 0 °C in the former and between ?18 °C and ?35 °C in the latter to slow the physical, microbiological and chemical activities that cause deterioration in foods. In these processes mechanical refrigeration technologies are invariably employed that contribute significantly to the environmental impacts of the food sector both through direct and indirect greenhouse gas emissions. To reduce these emissions, research and development worldwide is aimed at both improving the performance of conventional systems and the development of new refrigeration technologies of potentially much lower environmental impacts. This paper provides a brief review of both current state of the art technologies and emerging refrigeration technologies that have the potential to reduce the environmental impacts of refrigeration in the food industry. The paper also highlights research and development needs to accelerate the development and adoption of these technologies by the food sector.     

Assessment of the controlling envelope of a model-based multivariable controller for vapor compression refrigeration systems

This paper explores the controlling characteristics of a first-principles model-based controller specially developed for vapor compression refrigeration systems. Mathematical sub-models were put forward for each of the system components: heat exchangers (condenser and evaporator), variable-speed compressor and variable-orifice electric expansion device. The dynamic simulation model was then used to design a multivariable controller based on the linear-quadratic-Gaussian technique using a Kalman filter for the estimator design. A purpose-built testing apparatus comprised of a variable-speed compressor and a pulse-width modulated expansion valve was used to collect data for the system identification, and model and controller validation exercises. It was found that the model reproduces the experimental trends of the working pressures and power consumption in conditions far from the nominal point of operation (±30%) with a maximum deviation of ±5%. Additional experiments were also performed to verify the ability of the controller of tracking reference changes and rejecting thermal load disturbances. It was found that the controller is able to keep the refrigeration system running properly when the thermal load was changed from 340 to 580 W (460 W nominal), and the evaporator superheating degree was varied from 9.5 °C to 22 °C (16.6 °C nominal).     

Case study and theoretical analysis of a solar driven two-stage rotary desiccant cooling system assisted by vapor compression air-conditioning

In this paper, a solar hybrid desiccant air conditioning system, which combines the technologies of two-stage desiccant cooling (TSDC) and air-source vapor compression air-conditioning (VAC) together, has been configured, experimentally investigated and theoretically analyzed. The system mainly includes a TSDC unit with design cooling capacity for 10 kW, an air-source VAC unit with 20 kW in nominal cooling capacity, a flat plate solar collector array for 90 m², a hot water storage tank and a cooling tower. Performance model of the system has been created in TRNSYS simulation studio. The objective of this paper is to report the test result of the solar hybrid air conditioning system and evaluate the energy saving potential, thereby providing useful data for practical application. Experimental results show that, under typical weather condition, the solar driven desiccant cooling unit can achieve an average cooling capacity of 10.9 kW, which contributes 35.7% of the cooling capacity provided by the hybrid system. Corresponding average thermal COP is over 1.0, electric COP is up to 11.48. Under Beijing (temperate), Shanghai (humid) and Hong Kong (extreme humid) weather conditions, the solar TSDC unit can remove about 57%, 69% and 55% of the seasonal moisture load, thereby reducing electric power consumption by about 31%, 34% and 22%, respectively. These suggest that the solar hybrid system is feasible for a wide range of operating conditions.     

基于单级蒸汽压缩制冷系统冷凝废热回收的制冷剂数值优选研究

在大型制冷工程中,若能合理回收制冷系统的冷凝热并应用于牛奶厂、屠宰场、水果烘干、生活热水供应等场合,具有十分积极的节能减排意义。为保证冷凝热回收的同时制冷系统高效运行,制冷剂的选择至关重要。通过流程模拟软件模拟单级蒸汽压缩制冷过程,在制冷量80 kW,蒸发温度-25℃的设定条件下,从热力学性能、系统运行参数以及其对环境的影响大小等方面比较了12种不同的制冷剂。结果表明R21既能获得很高的系统性能系数,又对环境负面影响小,是优选的冷凝废热回收单级蒸汽压缩制冷系统制冷剂。     

Design study of configurations on system COP for a combined ORC (organic Rankine cycle) and VCC (vapor compression cycle)

The study introduced a novel thermally activated cooling concept - a combined cycle couples an ORC (organic Rankine cycle) and a VCC (vapor compression cycle). A brief comparison with other thermally activated cooling technologies was conducted. The cycle can use renewable energy sources such as solar, geothermal and waste heat, to generate cooling and power if needed. A systematic design study was conducted to investigate effects of various cycle configurations on overall cycle COP. With both subcooling and cooling recuperation in the vapor compression cycle, the overall cycle COP reaches 0.66 at extreme military conditions with outdoor temperature of 48.9 °C. A parametric trade-off study was conducted afterwards in terms of performance and weight, in order to find the most critical design parameters for the cycle configuration with both subcooling and cooling recuperation. Five most important design parameters were selected, including expander isentropic efficiency, condensing and evaporating temperatures, pump/boiling pressure and recuperator effectiveness. At the end, two additional cycle concepts with either potentially higher COP or practical advantages were proposed. It includes adding a secondary heat recuperator in the ORC side and using different working fluids in the power and cooling cycles, or so-called dual-fluid system.     

Experimental investigation of an automotive air-conditioning system driven by a small biogas engine

A compact air conditioning module run on biogas for rural use is proposed. The research study is to investigate the use of small biogas engine to drive the automotive vapour-compression air-conditioning system. The engine used is single-cylinder, four-stroke gasoline engine with capacity of 125 cm³ and compression ratio of 11:1. The biogas engine can be used to run the air-conditioning system with acceptable operation over a range of speeds and loads. The modular system can operate at a range of cooling loads above 3.5 kW at high coefficient of performance, with the proper speed ratio between the engine and the compressor. Overall primary energy ratio of the modular refrigeration system driven by the biogas engine was found to be maximum at about 1.0–1.2. The performance of the modular system tends to decrease with an increase in engine speed.     

Applications of nanorefrigerant and nanolubricants in refrigeration,air-conditioning and heat pump systems: A review

Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration, air conditioning systems, and heat pumps. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oils of refrigerating systems were reviewed. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO₂ nanoparticles work normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO₂ nanoparticles compared to the HFC134a and POE oil system.     

Applications of artificial neural networks for refrigeration, air-conditioning and heat pump systems—A review

In this paper, an attempt has been made to review the applications of artificial neural networks (ANN) for energy and exergy analysis of refrigeration, air conditioning and heat pump (RACHP) systems. The studies reported are categorized into eight groups as follows: (i) vapour compression systems (ii) RACHP systems components, (iii) vapour absorption systems, (iv) prediction of refrigerant properties (v) control of RACHP systems, (vi) phase change characteristics of refrigerants, (vii) heat ventilation air conditioning (HVAC) systems and (viii) other special purpose heating and cooling applications. More than 90 published articles in this area are reviewed. Additionally, the limitations with ANN models are highlighted. This paper concludes that ANN can be successfully applied in the field of RACHP systems with acceptable accuracy.     

The performance assessment of a combined organic Rankine-vapor compression refrigeration cycle aided hydrogen liquefaction

In this study, the performance of the combined cooling cycle with the Organic Rankine power cycle, which provides cooling of the hydrogen at the compressor inlet which compresses the constant temperature in the Claude cycle used for hydrogen liquefaction, on the system is examined. The Organic Rankine combined cooling cycle was considered to be using a geothermal source with a flow rate of 120 kg/s at a temperature of 200 °C. The first and second law performance evaluations of the whole system were made depending on the heat energy at different levels taken from the geothermal source. The thermodynamic analysis of the equipment making up the system has been done in detail. The temperature values at which the hydrogen can be effectively cooled were determined in the presented combined system. The efficiency coefficient of the total system was calculated based on varying pre-cooling values. As a result of the study, it was determined that cold entry of hydrogen into the Claude cycle reduced the energy consumption required for liquefaction. Amount of hydrogen cooled to specified temperature increase by increase in mass flow of geothermal water and its temperature. Liquefaction cost is calculated to be 0.995 $/kg H₂ and electricity produced by itself is calculated to be 0.025 $/kWh by the new model of liquefaction system. Cost of the liquefaction in the proposed system is about 39.7% lower than direct value of hydrogen liquefaction of 1.650 $/kg given in the literature.     

Performance and exergetic analysis of vapor compression refrigeration system with an internal heat exchanger using a hydrocarbon,isobutane (R600a)

Hydrocarbons (HCs) are excellent refrigerants in many ways such as energy efficiency, critical point, solubility, transport and heat transfer properties, but they are also flammable, which causes the need for changes in standards, production and product. There are increasing number of scientists and engineers who believe that an alternative solution, which has been overlooked, may be provided by using HCs. The main objective of this study is to perform energy and exergy analyses for a vapor compression refrigeration system with an internal heat exchanger using a HC, isobutene (R600a). For a refrigeration capacity of 1 kW and cold chamber temperature of 0°C, energy and exergy balances are taken into account to determine the performance of the refrigeration system. Energy and exergy fluxes are determined, and irreversibility rates are calculated for every component of the system. It is seen that the compressor has the highest irreversibility rate, and the heat exchanger has the lowest. Also from the result of the analysis, it is found that condenser and evaporator temperatures have strong effects on energetic and exergetic performances of the system such as coefficient of performance (COP), efficiency ratio (τ), exergetic efficiency (ξ) and irreversibility rate. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance of hybrid vaccine freezer that combined thermoelectric coolers with vapor compression refrigeration: Experimental assessment

In the medical field, refrigeration systems are used to store and transport vaccines, blood, and other medical supplies that require specific temperature ranges to remain effective. As technology continues to advance, the demand for more efficient and sustainable refrigeration systems is also increasing. The freezer compartment is typically designed to maintain a temperature of −18°C to −23°C for storing frozen items. Consequently, this work aims to develop a hybrid refrigeration system that combines a thermoelectric cooler system (TEC) and a vapor compression refrigeration cycle (VCC) system to achieve lower temperatures than conventional refrigerators. Also, the performance of the proposed hybrid refrigeration system is experimentally assessed with various operating conditions, including varying the voltage delivered to the system. The experimental results exhibited that the temperature inside the freezer room reached −33°C, while the cold side temperature is −47°C. Also, the maximum coefficient of performance of the VCC system, TEC, and hybrid system is 2.07, 1.06, and 0.37, respectively, at a DC voltage applied of 6 V. Moreover, the results revealed that the hybrid system combining a TEC and a VCC system can be a valuable technology for specific applications with low temperatures and limited capacity requirements.