Conventional Refrigeration System Research Articles

Thermodynamic analysis of a novel energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation

A new energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation was proposed in this paper. In the system, liquid desiccant system could produce very dry air for an indirect evaporative cooler, which would subcool the vapor compression refrigeration system to get higher COP than conventional refrigeration system. The desiccant cooling system can use the condensation heat for the desiccant regeneration. Thermodynamic analysis is made to discuss the effects of operation parameters (condensing temperature, liquid desiccant concentration, ambient air temperature and relative humidity) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves significantly higher COP than conventional vapor compression refrigeration system, and even higher than the reverse Carnot cycle at the same operation conditions. The maximum COPs of the hybrid systems using hot air and ambient air are 18.8% and 16.3% higher than that of the conventional vapor compression refrigeration system under varied conditions, respectively.

Performance of Thermoelectrics and Heat Pipes Refrigerator

Most of refrigerators commonly use the conventional refrigeration system known as Vapor Compression Refrigeration System becoming a big issue lately due to ozone depleting substance it uses as the refrigerant. This paper will shows step by step of an experiment with the objective of constructing a refrigeration system based on thermoelectric which is reliable and compete able with the Vapor Compression Refrigeration System. The designing of this refrigeration system shows attention to the environment that is combined with the knowledge so the environmental friendly technology can be applied. The performance of thermoelectric refrigerator was conducted under variation of input power (40W, 72W, and 120W) and operated in ambient temperature and cooling load of water 1000mL to investigate the characteristic of system, the performance, and also the COP. The COP is decrease by increasing of cooling load, QL. The best actual COP is 0.182 reached when the refrigerator operated at input power 40W. The result, it shows that decreasing of ambient temperature affects the decreasing of cabin temperature. Thermoelectric and heat pipe refrigerator cooling system can reach cabin temperature with power 120Watt (8.73A, 14V) produces temperature of compartment is 10.63°C indicates effective performance work-based thermoelectric applications.

Simulation study of the combination of absorption refrigeration and ejector-expansion systems

Recently, in refrigeration industry the use of efficient dual-evaporator refrigeration systems has been paid a lot of attention. These systems sound even more interesting when they are a combination of different kinds of conventional refrigeration systems. In this paper three thermally driven chillers consisting of absorption refrigeration and ejector-expansion transcritical cascade CO2 cycles are proposed and investigated thermodynamically. The systems are called “hybrid dual-evaporator” cycles. The absorption cycle in the systems is either the single-effect or double-effect series-flow or double-effect parallel-flow cycle for each of which a solar collector is considered to supply the required heat in their generator. The performances of hybrid dual-evaporator systems are analyzed and optimized, using the Engineering Equation Solver and applying the principles of conservation of mass and energy as well as the exergy balance to each component of each system. Results indicate that combing the double-effect parallel absorption refrigeration system with ejector-expansion system gives the highest coefficient of performance among the other configurations. However, a combination of single-effect absorption refrigeration system with ejector-expansion cycle may be preferred due to its less complexity and reasonable exergy efficiency. Results also reveal that at optimum generator temperature of 72.92 °C the coefficient of performance and exergy efficiency of hybrid dual-evaporator with single-effect absorption are 1.182 and 0.2564, respectively. In addition, it is observed that increasing the cooling capacity ratio from 1 to 6 results in increases of the coefficient of performance and exergy efficiency of configurations by up to 36.32% and 11.5% respectively.

Experimental study on a sliding vane expander in the HFC410A refrigeration system for energy recovery

Studies on expanders in small-scale refrigeration systems using HFCs as working fluids are rarely found. In this paper, a new sliding vane expander prototype is developed to replace throttling valve for energy recovery in a domestic HFC410A refrigeration system. The experimental results showed that the volumetric ratio of this new prototype can reach 7.48 in the expansion process under the test conditions. Compared with that of the original prototype, the volumetric efficiency and the isentropic efficiency of the new prototype were improved by 57.8% and 61.1% respectively at the rotational speed of 1200 r/min. The maximum COP (coefficient of performance) of the HFC410A refrigeration system with the new prototype was 3.41, improved by 8.97% compared with that of the conventional refrigeration system using a throttling valve. It was expected that the COP of a large-scale HFC410A refrigeration system might be improved greatly by using a similar prototype developed in this paper.

Energy consumption optimization of a continuous ice cream process

This work investigates potential energy saves in an ice cream freezer by using a variable speed compressor and optimization’s methodology for operating conditions during the process. Two configurations to control the refrigeration capacity were analyzed, the first one, modifies the pressure through the pilot control valve (conventional refrigeration system) and the second one with a variable speed compressor, both with a float expansion valve. Variable speed compressor configuration has showed the highest coefficient of performance and around of 30% less of energy consumption than the conventional one. The optimization of operating conditions in order to minimize the energy consumption is also presented. It was calculated only in France, for all ice cream and sorbet production, it is possible to save energy between 11 and 14MWh per year by optimizing the operation of the refrigeration system through a variable speed compressor configuration.

Performance Improvement of a Domestic Refrigerator Using Phase change Material (PCM)

The paper investigates the performance improvement provided by a phase change material (PCM) associated with the evaporator in a domestic refrigerator. The heat release and storage rate of a refrigerator is depends upon the characteristics of refrigerant and its properties. The usage of phase change material (PCM) enhances the heat transfer rate thus improve the COP (Coefficient of performance) of refrigeration . The analysis of the experiment exemplifies the improvement of a conventional refrigeration system's COP (Coefficient of performance) considerably. Using water as PCM and for a certain thermal load it is found that the COP (Coefficient of performance) of the conventional refrigerator increased by 18-26% on average. Here the phase change material (PCM) used in a chamber built manually and which surrounds the Evaporator chamber of a conventional refrigerator. The whole heat transfer from load given to refrigerator cabinet to evaporator, evaporator to phase change material (PCM) by conduction. So the heat transfer rate of evaporator refrigerant increases remarkably which improves the COP (Coefficient of performance) the refrigeration system.

Investigation of heat recovery in CO2 trans-critical solution for supermarket refrigeration

Using computer simulation modeling this study investigates the performance of a CO2 trans-critical system with heat recovery from the de-superheater. The influence of sub-cooling (or further cooling) in the condenser/gas cooler on system performance is investigated. Following the suggested control strategy in this study, the extra operating energy demand required to recover the needed heating energy from the analyzed CO2 system is smaller than what a typical heat pump would require for the same load. This is the case for almost all ambient temperatures over a full season. When taking the simultaneous heating and cooling loads into account, the CO2 trans-critical system has lower annual energy usage in an average size supermarket in Sweden when compared to a conventional R404A refrigeration system with separate heat pump for heating needs. CO2 trans-critical systems are efficient solutions for simultaneous cooling and heating needs in supermarkets in relatively cold climates.

On the suitability of carbon dioxide in forced circulation-type secondary loops

A recent spurt in the universal interest to study alternatives to the conventional DX refrigeration systems and use of natural refrigerants as secondary fluids has been visible. This investigation presents a comparative analysis between carbon dioxide and other working fluids for use in forced circulation-type secondary loops suitable for various refrigeration and air conditioning applications. The comparison is made on the basis of equal heat transfer rate, frictional pressure drop per unit length, temperature drop/ rise of secondary fluid and mean temperature difference between the secondary fluid and heat exchanger tube wall. Employing friction factor and heat transfer correlations, equations are obtained for diameter ratio, area ratio, mass ratio and pumping power ratio. Results show that employing carbon dioxide in place of other conventional secondary fluids except water leads to compact and lightweight heat exchangers, despite the high-pressure operation of carbon dioxide-based loops. The pumping power required is much smaller as well in case of carbon dioxide compared with all other fluids for the wide range of operating temperatures. Though results are presented here for the case of cooling only, calculations indicate similar trends for the heating configuration as well. Carbon dioxide appears to be an excellent secondary fluid for a wide range of refrigeration and air conditioning applications and it could turn out to be a disruptive technology for such applications in view of its benign environmental footprint.

Alternative designs for a 24-h operating solar-powered absorption refrigeration technology

The air-conditioning and refrigeration systems in the Kingdom of Saudi Arabia consume more than 60% of the electrical energy of the building sector. Most of the used systems are of the vapor-compression type. Using solar energy to power such systems will save a large amount of energy (primary or electrical) that can be utilized by the production sectors such as industries. Therefore in the present study, alternate designs for a 24-h operating solar-powered absorption refrigeration technology have been developed in detail. The development includes an in-depth review of the design and operation of the conventional and solar-assisted absorption refrigeration systems coming-up with new alternative designs, detailed thermodynamic analysis of some of the new alternative designs and selection of the most suitable alternative design. The analysis indicates that continuously operating solar-powered aqua-ammonia absorption system with refrigerant storage is the most suitable alternative design for an uninterrupted supply of cooling effect.

Performance Analysis of Solar-Assisted Refrigeration Cycle

Energy-conservation and environmental protection are keys to sustainable development of domestic economy. The solar-assisted cascade refrigeration cycle system is developed. The system consists of electricity-driven vapor compression refrigeration system and solar-driven vapor absorption refrigeration system. The vapor compression refrigeration system is connected in series with vapor absorption refrigeration system. Refrigerant and solution reservoirs are designed to store potential to keep the system operating continuously without sunlight. The results indicate that the system obtains pretty higher COP as compared with the conventional vapor compression refrigeration system. COP of the new-type vapor compression refrigeration system increases as sunlight becomes intense.

Study on the Hybrid Liquid Desiccant Evaporative Cooling Air-Conditioning Refrigeration Circulation System

This article presents a new hybrid evaporative cooling air-conditioning refrigeration system using two-stage liquid desiccant, and carries off the theoretical study on it. Compared with the conventional liquid desiccant air-conditioning refrigeration system, the new system adopts direct mixing heat transfer technology and evaporative cooling technology instead of water-cooled or air-cooled technology. Thus the cooling water usage is reduced. Using the two-stage adiabatic absorber and using refrigerant rather than water as the cooling medium of desiccant solution, the pressure difference of mass transfer is increased. Compared with the conventional system, the heat of regenerating solution is decreased because the mass ratio of air to desiccant solution is increased which gives rise to the decline of solution's mass rate. The results of theoretical calculation show that the new system has the better performance in power consumption, usage of water and equivalent coefficient of performance than the conventional system.

Study on Solar-Assisted Cascade Refrigeration System

Energy-conservation and environmental protection are keys to sustainable development of domestic economy. The solar-assisted cascade refrigeration system is developed. The system consists of electricity-driven vapor compression refrigeration system and solar-driven vapor absorption refrigeration system. The vapor compression refrigeration system is connected in series with vapor absorption refrigeration system. Refrigerant and solution reservoirs are designed to store potential to keep the system operating continuously without sunlight. The results indicate that the system obtains pretty higher COP as compared with the conventional vapor compression refrigeration system. COP of the new-type vapor compression refrigeration system increases as sunlight becomes intense.

Development of a novel refrigeration system for refrigerated trucks incorporating phase change material

An innovative refrigeration system incorporating phase change material (PCM) is proposed to maintain refrigerated trucks at the desired thermal conditions. The advantage of using PCM to maintain low temperatures is that a conventional refrigeration system does not have to be located on-board the vehicle. In addition, the system consumes less energy and produces much lower local greenhouse gas (GHG) emissions. The phase change thermal storage unit (PCTSU) is charged by a refrigeration unit located off the vehicle when stationary. The PCM is discharged and provides cooling when in service. A new PCM with a lower cost than currently available PCMs was developed, suitable for maintaining the refrigerated truck at a temperature of −18 °C. The PCM has a melting temperature of −26.7 °C and a latent heat of 154.4 kJ kg −1. A prototype system was constructed and test results proved that the proposed refrigeration system is feasible for mobile transport. An analysis shows that delivery of refrigerated products can be made with a PCM system having a weight comparable to that of an on board conventional refrigeration system with less than half of the energy cost.

Performance evaluation of integrated trigeneration and CO2 refrigeration systems

Food retailing is one of the most energy intensive sectors of the food cold chain. Its environmental impacts are significant not only because of the indirect effect from CO2 emissions at the power stations but also due to the direct effect arising from refrigerant leakage to the atmosphere. The overall energy efficiency of supermarkets can be increased by integrating the operation of CO2 refrigeration and trigeneration systems. This paper compares three alternative schemes in a medium size supermarket. Experimental results and simulation studies have shown that the best scheme for energy and GHG emissions savings is the one where the cooling produced by the trigeneration system is used to condense the CO2 fluid in the refrigeration system to ensure subcritical operation throughout the year. It is shown that this system can produce 30% energy savings and over 40% greenhouse gas emissions savings over conventional refrigeration and indoor environment control systems in supermarkets.

Performance analysis of a multi-mode thermochemical sorption refrigeration system for solar-powered cooling

A multi-mode thermochemical sorption refrigeration system is presented for solar-powered cooling. The proposed system consists of three sorption refrigeration thermodynamic cycles that can be alternately operated based on the available solar energy insolation viz: combined double-way cycle, double-effect cycle and two-stage cycle. The working performance of the different sorption refrigeration cycles were theoretically analyzed and compared. For combined double-way sorption cycle, both adsorption refrigeration and resorption refrigeration were combined to improve the cooling capacity. For double-effect sorption cycle, one internal heat recovery process was employed to enhance the energy utilization efficiency. For two-stage cycle with internal heat recovery process, a secondary reactive salt was used to lower the driving regeneration temperature. Thermodynamic analysis showed that the working modes of the proposed system can be switched according to the different driving heat source temperatures. In comparison with the conventional solar solid-gas sorption refrigeration system, the presented multi-mode system can contribute to improving the utilization efficiency of solar energy and widening the scope of application of solar thermochemical sorption refrigerator.

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.

A REVIEW OF EJECTOR TECHNOLOGY FOR REFRIGERATION APPLICATIONS

This paper provides a comprehensive review of ejector technology for refrigeration applications, combining an understanding of basic fluid flow fundamentals within the ejector with application in cycle-level development. An ejector is a passive device that requires no external mechanical input or moving parts. A high-velocity motive stream produces a low-pressure region into which a suction flow is entrained, resulting in a pressure rise of the suction flow and mixing between the two streams to provide a pumping effect. The first part of this review addresses the progression from experiment-based analytical models to computational modeling of the ejector itself from the early 1950s to 2009. Included is an assessment of the most recent work in CFD modeling, and an exploration into what is needed to develop these models further. Suggestions for future research include better modeling of shock phenomena and the effects of two-phase flow in ejectors. The second part of this review focuses on ejector applications in refrigeration cycles with special emphasis on the vapor-jet refrigeration cycle. Important connections are made between ejector component and system level studies, an understanding of which would enable improvement of system level performance to the extent where they could be used in some niche applications instead of conventional refrigeration systems.

Performance evaluation of locality-based compact solar refrigeration system

Cooling system with low capacity utilising solar power can be widely used for remote and rural cooling applications. This paper describes the trend of solar insolation for a period of one year at Tiruvannamalai town, a district capital in Tamil Nadu state, South India which is geographically located at latitude 12.229 N, longitude 79.076 E. The performance of a compact solar refrigeration system attached with micro spray nozzles in the evaporator chamber during specified period was studied. The analysis of the result shows that the coefficient of performance of the compact solar refrigeration system is consistent in the range between 0.3 and 0.5 during the period when the solar insolation was high and also performs well during low solar insolation days due to the fewer loads on the system. The trend signifies that the area of the solar collector can be reduced to 20 to 30 percentages for the required load during winter seasons. Also the cost analysis made for operating the system with conventional vapour compression refrigeration system of the same capacity was compared and the proposed system was found economical during operation.

Performance evaluation and optimal design of supermarket refrigeration systems with supermarket model “SuperSim”, Part I: Model description and validation

Conventional supermarket refrigeration systems are responsible for considerable CO 2 emissions due to high energy consumption and large quantities of refrigerant leakage. In the effort to conserve energy and reduce environmental impacts, an efficient design tool for the analysis, evaluation and comparison of the performance of alternative system designs and controls is required. This paper provides a description of the modelling procedure employed in the supermarket simulation model ‘SuperSim’ for the simulation of the performance of centralised vapour compression refrigeration systems and their interaction with the building envelope and HVAC systems. The model which has been validated against data from a supermarket has been used for the comparison of R404A and CO 2 refrigeration systems and the optimisation of the performance of transcritical CO 2 systems. These results are presented in Part II of the paper.

Simulation and experiment of a hydrogen liquefaction test rig using a multi-component refrigerant refrigeration system

A small-scale laboratory hydrogen liquefaction plant that contains a new innovative MR (multi-component refrigerant) refrigeration system is proposed. A test rig was constructed to verify the simulation of this system. Initial experiments indicated that the rig were able to adequately cool normal hydrogen gas from 25 °C to −158 °C at a flow rate of 0.6 kg/h using a simplified five-component MR mixture refrigeration system. The power consumption of pre-cooling from the MR compressor was 1.76 kW h per kilogram of feed hydrogen gas. After two weeks, the lowest temperature was about −180 °C when a few additional grams of nitrogen gas were charged into the rig. The simulation and experimental data were in good agreement, and the primary conclusion was that pre-cooling hydrogen gas with the MR refrigeration system resulted in a lower energy consumption per kilogram of feed hydrogen gas compared to conventional refrigeration systems.