Modelling and Evaluation of the Thermohydraulic Performance of Finned-Tube Supercritical Carbon Dioxide Gas Coolers

This paper investigates the thermohydraulic performance of finned-tube supercritical carbon dioxide (sCO2) gas coolers operating with refrigerant pressures near the critical point. A distributed modelling approach combined with the ε-NTU method has been developed for the simulation of the gas cooler. The heat transfer and pressure drop for each evenly divided segment are calculated using empirical correlations for Nusselt number and friction factor. The model was validated against test results and then used to investigate the influence of design and operating parameters on local and overall gas cooler performance. The results show that the refrigerant heat-transfer coefficient increases with decreasing temperature and reaches its maximum close to the pseudocritical temperature before beginning to decrease. The pressure drop increases along the flow direction with decreasing temperature. Overall performance results illustrate that higher refrigerant mass flow rate and decreasing finned-tube diameter lead to improved heat-transfer rates but also increased pressure drops. Design optimization of gas coolers should take into consideration their impact on overall refrigeration performance and life cycle cost. This is important in the drive to reduce the footprint of components, energy consumption, and environmental impacts of refrigeration and heat-pump systems. The present work provides practical guidance to the design of finned-tube gas coolers and can be used as the basis for the modelling of integrated sCO2 refrigeration and heat-pump systems.UK Engineering and Physical Sciences Research Council; European Union’s Horizon 2020 research and innovation progra

Energy analysis of alternative CO 2 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.This study was supported by the Research Councils UK Energy programme, Grant No: EP/K011820/1 and GEA Searle, now Kevlion. The authors wish to acknowledge the cash and in-kind contributions of these organisations as well as the support received from Brunel University London and the RCUK National Centre for Sustainable Energy use in Food Chains (CSEF)

Analysis of an R744 typical booster configuration, an R744 parallel-compressor booster configuration and an R717/R744 cascade refrigeration system for retail food applications. Part 1: Thermodynamic analysis

This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) In this paper, the performances of a typical R744 booster configuration, a R744 parallel-compressor booster refrigeration system, and a R717/R744 cascade system configuration are presented based on the 1 st and 2 nd law of thermodynamics, for food retail applications. The results for a supermarket application with a total 145 kW cooling capacity show that the typical booster system and parallel-compressor booster system have better performances than the cascade system. However, for convenience store applications with 30 kW total cooling capacity the cascade system shows better performance beyond 26 °C ambient temperature which limits the applications of the cascade system for low capacity systems and the parallel refrigeration system solution appears to be a better option. In addition, the most critical components of each system based on the 2 nd law are identified in this paper.Research Councils UK for the researc

CFD comparisons of open-type refrigerated display cabinets with/without air guiding strips

© 2017 The Authors. Published by Elsevier Ltd. Open-type vertical refrigerated display cabinets are used widely in supermarkets and grocery stores due to its attraction for customers and food merchandisers. These cabinets, however, are less energy efficient than cabinets with glass doors because of the interactions between the air curtain, that is used to provide an artificial barrier between the air in the cabinets, and the air in food premises. To improve the energy efficiency of open fronted refrigerated display cabinets, many types of air curtains have been designed, including single layer air curtains, multi-layer air curtains and shelf tip air curtains amongst others. An approach, considered in recent years to improve the efficiency of air curtains is the use of air guiding strips at the front face of the shelves of open-type vertical refrigerated display cabinets with single layer air curtains. This paper uses Computational Fluid Dynamics modelling to investigate the influence of air guiding strips on the performance of vertical multi-deck refrigerated display cabinets. The results showed that the air guiding strips accelerate the air curtain vertically; leading to a stronger and stiffer air curtain, consequently inhibit the infiltration of the ambient warm air into the cabinet. The average temperature of simulated food in the cabinet decreases by 4.9°C compared to the cabinet without the strip due to the improved protection of the stiffer air curtain. The cooling capacity required to maintain the food chilled decreases by 34%

Experimental Study on the Influences of Air Flow in an Integral Hydrocarbon Display Cabinet to its Temperature and Energy Performances

This paper presents results on temperature energy performance tests of an integral refrigerated hydrocarbon (HC) display cabinet for retail food applications. Heat from the condensing unit of the cabinet is rejected to both ambient air and water/glycol mixture flowing in a closed water circuit. Air flow in the cabinet loaded with M-packages as test products was studied in order to analyze effects of air flow rate in the cabinet to its temperature and energy performances. The product and air temperatures as well as energy consumption of the cabinet were measured. The tests were conducted in a test chamber at climate class 3. It was found that the HC display cabinet with integral condensing unit was found to provide excellent energy performance with an Energy Efficiency Index below the requirement to qualify for enhanced capital allowances. The refrigeration system of the cabinet could also achieve a COP of 3.15. The study also found that higher air flow rate in the cabinet could make the product temperatures a little bit better, but the energy consumption increased approximately 7% when air flow rate was increased from 1200 m 3 h -1 to 1800 m 3 h -1 . Air flow distribution in the cabinet was necessary to be optimized in order to comply with M0 classification cabinet.WR Refrigeration and Arneg SP

Experimental and CFD investigation of overall heat transfer coefficient of finned tube CO <inf>2</inf> gas coolers

This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) The overall heat transfer coefficient of two CO2 gas coolers was investigated through experiment and Computational Fluid Dynamics (CFD). The CFD modelling provided prediction accuracy for the overall heat transfer coefficient with a maximum error of 9% compared to the CFD predictions. Comparing the two gas cooler designs, and from the experimental and modelling results it has been shown that the performance of the gas cooler can be improved by up to 20% through optimization of the circuit design of the gas cooler. A horizontal slit between the 1 st and 2 nd row of tubes of the gas cooler can increase the overall heat transfer coefficient by 8% compared with the a fin without the slit.DRPM RISTEK DIKTI and RCU

Development of corn-oil ester and water mixture phase change materials for food refrigeration applications

This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This research aims to investigate development of corn-oil ester and water mixtures as novel solid-liquid phase change material candidates for chilled and frozen food refrigeration applications. Thermal properties of both water and its mixture with corn-oil ester were tested by DSC and T-history methods. The results showed that corn oil could mix well in water solutions. Phase transition temperatures of the mixtures were lower than those of individual water. Corn-oil ester in the mixtures was acted as a nucleate agent and it was able to lower freezing point and to trigger ice nucleation in water which could diminish super-cooling. Addition of corn oil ester by 5% to 35% in water solutions could decrease freezing temperature from 0°C down to respectively -3.5°C to -28°C. The PCM candidates were also found to have excellent thermal properties that could fulfill requirements of thermal energy storage systems for food refrigeration applications.Higher Education Directorate General of the Ministry of Education and Culture of the Republic of Indonesi

Analysis of typical booster configuration, parallel-compressor booster configuration and R717/R744 cascade refrigeration system for food retail applications. Part 2: Energy performance in various climate conditions.

This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This paper compares three different natural refrigerants based system configurations in terms of cooling performance, total equivalent warming impact per year and annual power consumption for the proposed refrigeration systems. Two different cooling load levels were selected to represent a typical supermarket and a convenience store applications. The systems selected in this study include the R717/R744 cascade system configuration, a typical R744 booster configuration and a R744 parallel-compressor booster refrigeration system. The weather conditions of London, UK and Larnaca, Cyprus, were used for the modelling of energy consumption and environmental impacts to represent moderate and warm climatic conditions respectively.Research Councils UK Energy programm

Energy savings potential in using cold-shelves innovation for multi-deck open front refrigerated cabinets

This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) An approach considered in recent years to improve the efficiency of open-type refrigerated display cabinets is to install air guiding strips at the front face of the shelves with a single layer air curtain. This paper presents experimental results comparing a conventional open-type vertical refrigerated cabinet and a cold shelf innovation, which integrates both air-guiding strips and air supply at the front of individual shelves. In addition, a comprehensive and detailed Computational Fluid Dynamics model using ANSYS Fluent has been created to further investigate the influence of the cold shelve innovation on the performance of vertical multi-deck refrigerated display cabinets. The experimental results showed energy savings of 16.7 kWh/24 hrs for the guiding strips and cold shelf innovation compared to the conventional cabinet due to the more efficient air curtain and lower air temperature entering the evaporator coil.Research Councils UK Energy programm