Cold storage using phase change material in refrigerated display cabinets: experimental investigation

Refrigerated display cabinets are the main energy consumers in supermarkets. Cold thermal energy storage (CTES) using phase change materials (PCM) can significantly reduce temperature variations in a display cabinet during loading of warm items, defrost cycles or power outages. This contributes to reduced loss in product quality and less food being wasted. With an increasing share of intermittent renewables in the power grid, PCM-enhanced systems benefit from low-cost electricity during periods with low demand. Stored excess cooling can be later used during periods with high demand. A CTES prototype was developed using water as PCM integrated in an evaporator. This system was experimentally compared to a reference case not using the PCM capabilities. The results show the potential for PCM-CTES to consistently keep the cabinet air temperature low, thus prolonging shelf life and product quality. Charged PCM-CTES systems provide cooling for several hours after the main evaporator is deactivated. Keywords: Refrigerated Display Cabinet, Thermal Energy Storage, Cold Storage, Phase Change Material, Supermarket Refrigeration, Defrost Cycle.acceptedVersio

Experimental evaluation of CO2 ejector cooling system for supermarkets at tropical zones

Cooling system for supermarkets, now-a-days in developing countries like India, mainly use man-made synthetic refrigerants/mixtures such as R134a, R404A and R410A (HFCs). These fluorinated refrigerants possess outrageous impact on the environment/ambient due of their high GWP and ODP. The EU F-gas regulation is formulated recently and came into force in 2014 in order to restrict the use of synthetic refrigerants for various HVAC applications. Under this regulation, it is also illegal to vent any such synthetic refrigerants to the atmosphere during the system servicing or end-of-life decommissioning. Sudden phase down of HFCs forced the present scenario to identify a potential replacement of these synthetic refrigerants. The influence of the same is comparatively high for developing countries. In the present study, the performance of a multi-ejector based supermarket cooling system is experimentally evaluated using natural refrigerant carbon dioxide (CO2). 33 kW cooling capacity of the system which is capable of maintaining three simultaneous different temperatures such as -29 °C for freezing, -6 °C for refrigeration and 7-11 °C for air-conditioning is examined at high ambient temperature context (up to 46 ºC gas cooler outlet temperature). The maximum COP of the supermarket cooling system appeared as 4.2. It is also observed that the maximum exergy efficiency of system is 0.316 obtained corresponding to 3.2 PIR of the system

An experimental study of an ejector-boosted transcritical R744 refrigeration system including an exergy analysis

The field of refrigeration witness a massive transition in the supermarket with a strong focus reflected on energy consumption. The use of ejector allows for overcoming the significant exergy destruction lays on the expansion processes of the cooling systems and led to spark improvement in the system performance by recovering some of the expansion work. In this study, a detailed experimental work and exergy analysis on the R744 transcritical ejector cooling system was investigated. The experiment was implemented on the commercial ejector cartridge type (032F7045 CTM ELP60 by Danfoss). The impact of different operating conditions determined by exit gas cooler pressure and temperature, evaporation temperature and receiver pressure was examined. The ejector performance of the pressure lift, mass entrainment ratio, work rate recovery and efficiency were evaluated. In addition, exergy efficiency and the variation of exergy produced, consumed, and destruction were assessed based on the transiting exergy. The result revealed better overall performance when the ejector operated at transcritical conditions. The ejector was able to recover up to 36.9% of the available work rate and provide a maximum pressure lift of 9.51 bar. Moreover, it was found out that the overall available work recovery potential increased by rising the gas cooler pressure. Out of the findings, the ejector could deliver maximum exergy efficiency of 23% when working at higher motive nozzle flow temperatures along with providing lower exergy destruction. The experiment results show that the amount of the exergy consumed and destruction were gradually increased with higher gas cooler pressure and, in contrast, decreasing with higher motive nozzle flow temperature. © 2021 Elsevier LtdacceptedVersio

Multiejector CO2 cooling system with evaporative gascooler for a supermarket application in tropical regions

In the present study, the performance of a 33 kW multiejector trans-critical CO2 cooling system is experimentally evaluated for a supermarket application with/without internal heat exchanger and evaporative cooling. In order to enhance the overall performance of the system for tropical regions, the testing is carried out at high ambient temperature (up to 46 °C) with 5 cm, 10 cm and 15 cm cooling pad thickness arrangements. The experimental results clearly projects that the evaporative cooler capacity reaches a maximum of 10 cm pad thickness. However, a minor improvement is observed in terms of Coefficient of Performance and Power Input Ratio beyond 10 cm pad thickness. Maximum improvement in COP with internal heat exchanger and evaporative cooler is 11% and 40% respectively. On the other hand, a maximum reduction in the system Power Input Ratio with internal heat exchanger and evaporative cooler is 8.5% and 26% respectively. However, a minor enhancement in Coefficient of Performance and Power Input Ratio of 4% and 6% are observed respectively with 15 cm cooling pad thickness. Furthermore, a comparative analysis is carried out with the existing and present experimental study to project the compatibility of an evaporative condenser in the ejector based CO2 cooling system. From the study, it is evident that the evaporative cooling arrangement for the gascooler of the CO2 system is suggested as a potential solution to the supermarket application at a high ambient temperature context. © 2021 Elsevier LtdacceptedVersio

Experimental and computational analysis of a R744 flashing ejector

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Monitoring of Thermal and Flow Processes in the Two-Phase Spray-Ejector Condenser for Thermal Power Plant Applications

The paper deals with the problem of accurate measuring techniques and experimental research methods for performance evaluation of direct contact jet-type flow condensers. The nominal conditions and range of temperature, pressure and flow rate in all characteristic points of novel test rig installation were calculated using the developed model. Next, the devices for measurement of temperature, pressure and flow rate in a novel test rig designed for testing the two-phase flow spray ejector condensers system (SEC) were studied. The SEC can find application in gas power cycles as the device dedicated to condensing steam in exhaust gases without decreasing or even increasing exhaust gas pressure. The paper presents the design assumptions of the test rig, its layout and results of simulations of characteristic points using developed test rig models. Based on the initial thermal and flow conditions, the main assumptions for thermal and flow process monitoring were formulated. Then, the discussion on commercially available measurement solutions was presented. The basic technical parameters of available sensors and devices were given, discussed with details. © 2022 by the authors.Monitoring of Thermal and Flow Processes in the Two-Phase Spray-Ejector Condenser for Thermal Power Plant ApplicationspublishedVersio

Energy efficient multiejector CO2 cooling system for high ambient temperature

Experimental evaluation of a multiejector CO2 cooling system of 33 kW cooling capacity is conducted for an Indian supermarket at high ambient temperature context. The test-rig is designed to depict the actual supermarket cooling requirements in India with three different cooling temperature levels simultaneously; freezing, medium refrigeration and air-conditioning. The rig is equipped with a novel design consisting of two multiejectors; low ejection ratio ejector (LERE) and high ejection ratio ejector (HERE), in a series configuration. It is observed that the maximum pressure lift of 5.5 bar is obtained with this new design. Moreover, improvement in the overall system performance with the support of the internal heat exchanger (IHX) is evaluated. Enhancements observed in the maximum COP and PIR are 7.2% and 6.2% respectively. Furthermore, the test-rig performance with the flooding and non-flooding of the medium temperature evaporator (refrigeration) is evaluated. It is observed that the evaporator flooding reduces its superheat at the exit by 83.84%, leading to the overall reduction of PIR by 6.51%. The performance of the proposed system is also compared with the reported field data obtained at a low ambient temperature context. The results projected that the proposed cooling system with series multiejector configuration is a reliable choice for higher ambient temperatures and it is expected to outperform the existing systems at lower ambient temperatures.acceptedVersio

Performance evaluation of CO2 ejector system with parallel compressor for supermarket application

Evolution in modifications for CO2 system configuration came across from the last two decades has proven to hold the potential in order to improve the overall performance of the CO2 cooling system for various applications. However, performance of the CO2 system at high ambient context is not promising and comparable with popular conventional refrigerants. Due to its unique properties, the CO2 system possesses substantial losses at high ambient temperature due to the throttling process. System configuration with parallel compressor is proven as the most popular and efficient configuration for high ambient temperature (up to 46 °C). In this study performance evaluation of a CO2 multi-ejector based supermarket cooling system of 33 kW cooling capacity with compressor configuration is experimentally evaluated at high ambient temperature (up to 46 °C). Test facility is equipped with two-phase multi-ejector resulting in pressure lift due to the expansion work recovery. Removed flashes in flash gas tank or separator after passing through two-phase ejector, are further compressed with the help of auxiliary compressor configured in parallel but with an additional possession of low compression ratio. High stability with high gascooler pressure and CO2 system consistency at high gascooler outlet temperature is observed. Maximum reduction in the AUX compressor energy consumption observed is 8% for 46 bar & 10.7% for 48 bar receiver pressure at 36 ºC gascooler outlet temperature. Also, the Exergy efficiency of the system observed is 0.315 corresponding to 3.2 PIR at 46 ºC gascooler outlet temperature

Monitoring of solids behaviour during gravitional flow in rectangular silo

This paper is focused on the application of Electrical Capacitance Tomography (ECT) to gravitational flow of bulk solid in rectangular silo investigation. In order to measure the materials distribution inside a vessel, a dedicated, spatial 16 electrode sensor is designed. Reconstructed images are presented in 3D domain space. The investigated silo model consists of rectangular bin and a cone-like hopper section. The flow behaviour of material (friable sand) is studied for two silo model configurations having different lower section slopes. The slope angle is a silo geometrical parameter affecting the type of the flow regime - mass or funnel type

Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climates

The novel configuration presented in this work simplifies the layout of ejector-supported booster systems while maintaining all the benefits of an ejector implementation. The basic version of the solution is based on: i) MT and LT compressor suction groups, ii) flooded MT evaporation with increased evaporation temperature, and iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'). With lower ambient temperatures the ejector is operated passively, and the high-pressure control is performed by individual metering devices upstream of the different evaporators ('winter mode'). The feasibility tests performed in the laboratory proved that energy-wise this novel system configuration outperforms traditional and parallel compression supported booster systems under any condition. The pressure lift measured with active ejector is sufficient for liquid refrigerant distribution to the evaporators, while the pressure drop recorded in passive mode is negligible for practical applications.Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climatesacceptedVersio