Small-scale Refrigeration System Research Articles

A detailed study of the transient behavior of dual-skin chest-freezer with R290

• Detailed transient behavior of dual-skin chest-freezer operating with R290 is described. • Two mathematical models for freezer transient simulation are developed. • Experimental results of transient system operation are provided in Excel file. • Thermal load influence is simulated with a maximum relative error of 2.7%. • The optimum refrigerant charge of 200g of R290 is calculated. This work reports on a numerical and experimental study of the transient behavior of a dual-skin chest-freezer refrigeration system, operating with R290. A simpler dynamic mathematical model, called thermal, and a more sophisticated one, called capacitive, which models the mass distribution in the systems components, were evaluated. The experiments provided measured data for the characterization of the transient operation of the appliance, supply of models’ input data, and validation of the models. Comparisons between simulation and experimental results showed a very good agreement for both transient and time-averaged systems behavior and performance. The maximum relative error for temperatures at pull-down and on/off operations was 5.5 % . The capacitive model simulated the transient experimental behavior of the refrigeration system well when goods were inserted in the freezer’s cabinet, showing a 2.7 % maximum relative error for the systems performance parameters. Moreover, it yielded a parametric analysis of the refrigerant charge, determining a 200g mass of R290 for the optimum performance. The thermal model is an excellent feature for a first design, simulating 100 min of a real operation in few seconds. The capacitive model provides more complex results, and is a very good tool for a detailed systems design. The experimental data can be used by other researchers for validating their simulations and experimental studies. The paper provides new findings for a system operating with R290, a fluid that has been widely used in small scale refrigeration systems for household applications.

Experimental investigations on the performance of mini-channel evaporator refrigeration system for thermal management of power batteries

The vapor compression refrigeration system possesses excellent thermal performance owing to two phase boiling with large latent heat, which can be a promising option for refrigerant cooling of battery modules. In this work, the battery thermal management equipped with a small-scale refrigeration system was built up, which primarily consisted of the mini-channel evaporator directly mounted with a battery module, compressor, throttle valve and fan-cooled condenser. The influencing factors such as the refrigerant charge, openness of throttling valve (OTV) and the heating power were examined experimentally. It is found that, with the increase in the refrigerant charge, the system coefficient of performance (COP) first increased and then decreased. When the heating power is between 100 W to 200 W, the temperature of the battery module could be controlled in a suitable range, namely 10°C-45°C, by adjusting the OTV within the range of 48.8%-72.1%. As the OTV increased, the heat transfer coefficient of the mini-channels first increased and then levelled off. As the heat power increased, the heat transfer coefficient of the mini-channels first increased and then decreased. The present study helps better understanding of thermal management using the vapor compression refrigeration system in the battery thermal management.

Steady-state performance of capillary tubes for small-scale vapour compression systems using different refrigerants

• Fixed capillary tube geometry with straight, helical and SLHX sections. • A model was proposed to determine the steady-state operation of the capillary tubes. • Refrigerant velocity was shown to increase with the capillary tubes elongation. • Refrigerant outlet state of the capillary tube is determined. • Refrigerants R134a, R1234yf, R1234ze (E), R513A, R600, R600a are investigated. The operational performance of small-scale refrigeration systems is mainly decided by their capillary tubes outlet parameters, wherein an accurate determination of the pressure and vapour quality is a prerequisite. Experiments have been performed for a capillary tube (CT) with specified geometry consisting of a straight, a helical and a suction line heat exchanger (SLHX) section. The capillary tube is incorporated in a small refrigeration system operated with R600a. In addition, a model was developed to determine the steady-state operation of the capillary tubes (activated with R134a, R1234yf, R1234ze(E), R600, R600a, R152a and R513A refrigerants) and validated. The highest and lowest value of the vapour quality was discerned to be 0.3132 (for R1234yf) and 0.2124 (for R600), respectively. The relative errors between the experimental and model results for the CT outlet pressure and temperature were ranged from 1.16 to 5.35% and 0.12–0.81%, respectively. It is asserted that the present strategy may contribute towards the precise estimation of the pressure and vapour quality to customize the working performance of small scale refrigeration systems.

Progress in two-phase flow-induced noise of small scale refrigeration system

Progress in two-phase flow-induced noise of small scale refrigeration system

Experimental studies on the performance improvement of household refrigerator connected to domestic water system with a water-cooled condenser in tropical regions

The consumption of electrical and thermal energies in the residential building sector is growing fast and many strategies are being followed to overcome the energy demand in this sector. Among the various strategies, performance enhancement of refrigeration systems has been identified as one of the important areas for investigation. Due to the increase in the use of small-scale appliances and their impact on global energy requirements, specific research has to be focused on small scale systems with water-cooled condensers to reduce the energy consumption in residential buildings. In this study, the water-cooled condenser of a refrigeration system was connected to the prevailing water distribution system of a house with suitable changes in the existing arrangements. The proposed system was analysed for energy savings and environmental benefits. The experimental work was conducted in the tropical region, and the experimental findings indicated that the brazed plate condenser in small-scale refrigeration systems could decrease 21 to 27% of daily energy consumption. The total equivalent warming impact was found as 26.8% lower than that of conventional systems. Among the refrigerants, R290/R600a (45.2:54.8 – mass percentage) mixture showed 5.9% lower per day energy consumption and 8.9% higher COP than that of R134a. Compared to R134a, the R1234yf showed an increase of 4.7% and 7.3% in per day energy consumption and pull-down time respectively for all tested conditions. However, this small reduction in the performance of R1234yf may be tackled by optimizing the system components. Thus the building energy-efficiency could be improved by integrating the household refrigerator with the use of general water supply in a residential building.

Energy and exergy analysis on hydrofluoroolefin/ hydrofluorocarbon (HFO/HFC) refrigerant mixtures in low and medium temperature small-scale refrigeration systems

The new refrigerants such as HFO-1234yf and HFO-1234ze have been considered as long-term replacements for HFC-134a to comply with the Kyoto protocol. In small size refrigeration systems, these refrigerants have poor performance than HFC-134a besides their minor flammability. Previous studies reveal that the addition of HFC-134a in small quantity can improve the performance of a system without exceeding the global warming potential limit (150) prescribed by the European Union. However, this concept is not studied in small-scale refrigerators. Therefore, the performance of low and medium temperature systems of capacity 190 and 285 litre, respectively, working with different hydrofluoroolefin/ hydrofluorocarbon (HFO/HFC) mixtures, has been studied by mathematical simulation. The software tool ‘MATLab’ and the refrigerant property database ‘REFPROP’ have been used in the simulation. The results showed that the coefficient of performance (COP) of Hydrofluoroolefin (HFO) refrigerants and its mixtures decreases from 2.4 to 15.7% than that of HFC-134a. Among the mixtures, HFO-1234ze/HFC-134a (90/10) shows better performance and its predicted coefficient of performance (COP) and exergetic efficiency are 4–8.3% and 5.1–10.5%, respectively, higher than that of other mixtures considered in this study.

Investigation of energy and exergy performance on a small-scale refrigeration system with PCMs inserted between coil and wall of the evaporator cabin

Domestic refrigerators have become an indispensable part of the modern life. Since they are connected to the electric mains and operate throughout the day and year, they consume a lot of energy. Several experimental studies show that the addition of phase change material in the refrigerators at various locations improves the energy efficiency of the refrigerators. In this work, an experimental study was conducted to explore and reveal the improvement in energy efficiency of a small-scale refrigeration system when PCM was applied between the evaporator coil and the insulation. It was observed that the addition of PCM for a thickness of 0.03 m could reduce the heat ingress inside the evaporator by 15–19%. Moreover, the compressor ON cycle time and the temperature fluctuation inside the freezer cabinet were also relatively lesser. The per day energy consumption was reduced by 15.7–17.3% and the improvement in COP was found to be 17.4% with the addition of PCM. The refrigeration system was able to retain its desired temperature level for a period of 5 h even after the power supply was switched OFF. This idea of incorporating PCM between coil and insulation could be extended to household refrigerators so as to reduce the energy consumption. This would come handy in case of power outages which are very common in places having low grid reliability.

A small scale remote cooling system for a superconducting cyclotron magnet

Through a technology transfer program CERN is involved in the R&D of a compact superconducting cyclotron for future clinical radioisotope production, a project led by the Spanish research institute CIEMAT. For the remote cooling of the LTc superconducting magnet operating at 4.5 K, CERN has designed a small scale refrigeration system, the Cryogenic Supply System (CSS). This refrigeration system consists of a commercial two-stage 1.5 W @ 4.2 K GM cryocooler and a separate forced flow circuit. The forced flow circuit extracts the cooling power of the first and the second stage cold tips, respectively. Both units are installed in a common vacuum vessel and, at the final configuration, a low loss transfer line will provide the link to the magnet cryostat for the cooling of the thermal shield with helium at 40 K and the two superconducting coils with two-phase helium at 4.5 K. Currently the CSS is in the testing phase at CERN in stand-alone mode without the magnet and the transfer line. We have added a “validation unit” housed in the vacuum vessel of the CSS representing the thermo-hydraulic part of the cyclotron magnet. It is equipped with electrical heaters which allow the simulation of the thermal loads of the magnet cryostat. A cooling power of 1.4 W at 4.5 K and 25 W at the thermal shield temperature level has been measured. The data produced confirm the design principle of the CSS which could be validated.

Experimental investigation of the refrigerant flow of isobutane (R600a) through adiabatic capillary tubes

Capillary tubes are widely used as expansion device in small scale refrigeration systems. Despite the simple geometry one finds complex physical processes during the throttling in the capillary tube, which were subject of many studies in the last decades. However, there is currently only one source of experimental data for the refrigerant isobutane (R600a) and adiabatic capillary tubes (Melo et al., 1999). In order to close this gap a test rig was built and experimental data in the range of typical small scale refrigeration systems was collected. The measured mass flow rates span from 0.64 kg h−1 to 1.93 kg h−1. Additionally, the effect of critical flows (Choked Flow) is shown by means of an extra performed test. The semi-algebraic equation from Hermes et al. (2010) showed a remarkable level of agreement by predicting 94% of all points within a ±10% error band.

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.

Performance of microchannel condensers with metal foams on the air-side: Application in small-scale refrigeration systems

Abstract The thermal-hydraulic performance of microchannel condensers with open-cell metal foams to enhance the air-side heat transfer is investigated in this paper. Three different copper metal foam structures with distinct pore densities (10 and 20 PPI) and porosities (0.893 and 0.947) were tested. A conventional condenser surface, with copper plain fins, was also tested for performance comparison purposes. The experimental apparatus consisted of a closed-loop wind tunnel calorimeter and a refrigerant loop, which allowed the specification of the mass flow rate and thermodynamic state of R-600a at the condenser inlet. The experiments were performed at a condensing temperature of 45 °C. The air-side flow rate ranged from 1.4 × 10 −3 to 3.3 × 10 −3 m 3 /s (giving face velocities in the range of 2.1–4.9 m/s). The heat transfer rate, the overall thermal conductance, the Colburn j -factor, the friction factor and the pumping power were calculated as part of the analysis.

Cycle performance studies on HFC-161 in a small-scale refrigeration system as an alternative refrigerant to HFC-410A

In this paper, the refrigerant HFC-161 as an alternative refrigerant to HFC-410A is presented in a small scale refrigeration system. Theoretical cycle performances of HFC-410A, HFC-32 and HFC-161 are calculated and analyzed under the rated working condition. The results show that the COP of HFC-161 is 10.0% and 17.8% higher than that of HFC-32 and HFC-410A, respectively, and the discharge temperature of HFC-161 is the lowest among these refrigerants. Experimental tests were also performed on a vapor-compression refrigeration system with a rotor compressor which was originally designed for HFC-410A to compare the cycle performance of the HFC-410A, HFC-32 and HFC-161 under different working conditions. Experimental results show that the HFC-161 can achieve higher COP by 15–25% than HFC-410A and HFC-32, and the discharging temperature of HFC-161 is much lower than that of HFC-410A and HFC-32. The power consumption and cooling capacity of HFC-161 are the smallest among these refrigerants. The cooling capacity and COP of HFC-32 is very similar to those of HFC-410A, but discharging temperature and power consumption of HFC-32 are slightly higher those of HFC-410A under most working conditions. These results show that HFC-161 is a promising alternative refrigerant to HFC-410A for small-scale refrigeration systems, which supply a very valuable reference for the actual system of HFC-161.

Mini-channel evaporator/heat pipe assembly for a chip cooling vapor compression refrigeration system

We investigate a novel evaporator design for a small-scale refrigeration system whose function is to assist the existing heat pipe technology currently used in chip cooling of portable computers. A heat transfer model for the evaporator/heat pipe assembly was devised specifically for sizing the evaporator in order to keep the chip surface temperature below a certain value. A prototype was tested with R-600a at saturation temperatures of 45 and 55 °C, mass flow rates between 0.5 and 1.5 kg h −1 and heat transfer rates between 30 and 60 W. The experimental results demonstrated that the average refrigerant-side heat transfer coefficient is more sensitive to a change in the refrigerant mass flux than to changes in the saturation temperature and heat transfer rate. The agreement between the calculated heat transfer coefficient and the data was within ±10% for the conditions evaluated.

Condensation heat transfer coefficients for R22 and R407C in gravity driven flow regime within a smooth horizontal tube

The quasi local heat transfer coefficients of R22 and R407C in the coaxial counterflow condenser (20 mm ID) of a refrigerating vapour compression plant have been experimentally measured. The experimental conditions under which the heat transfer coefficients were determined reflect a typical working situation for small scale refrigeration systems. The plant runs with low mass fluxes of refrigerant within the range of 45.5–120 kg/m2/s. During the experimental tests the pressure at the inlet of the test condenser varies within a fixed range between 15.2 and 14.3 bar. The results illustrate that the R22 heat transfer coefficient is always greater than that of R407C. Furthermore, comparisons between the experimental data and the values predicted by means of the most credited literature relationships for gravity-driven condensation are reported.

Experimental evaluation of R22 and R407C evaporative heat transfer coefficients in a vapour compression plant

The mean heat transfer coefficients of R22 and R407C in the coaxial counterflow evaporator (20 mm ID) of a refrigerating vapour compression plant have been experimentally measured. The experimental conditions under which heat transfer coefficients were determined reflect a typical working situation for small-scale refrigeration systems. The heat flux ranged from 1.9 to 9.1 kW/m 2 and the mass flux was varied from 30 to 140 kg/m 2 s. The results illustrate that the R22 heat transfer coefficient is always greater than that of R407C. Furthermore, a comparison carried out between the experimental data and those predicted by means of the most credited literature relationships showed a strongly overprediction for R407C coefficients.

Dynamic simulation and optimal matching of a small-scale refrigeration system

This paper describes a principle and method of optimal matching to reduce energy consumption in small-scale refrigeration systems, based on systems analysis. A knowledge of the dynamic characteristics of a refrigeration system is important for predicting the performance of the system. A simulation model of a refrigeration system consisting of a compressor, an evaporator, a condenser and a capillary tube has been established to illustrate optimal matching. For each component a mathematical model has been developed, in which the concept of transient and distributive is introduced. On the basis of dynamic simulation, a method of optimal matching to minimize power consumption is recommended. To test the reliability of the theoretical models, an experiment was carried out on a small-scale refrigeration system. The experimental data were compared with the theoretical results and it is shown that the theory is valid.

Hydrogen sulphide, its uses and dangers

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.