A hybrid Ejector and CO2 Compression Refrigeration System
Lead Research Organisation:
University of Nottingham
Department Name: Division of Architecture & Urbanism
Abstract
The proposed project aims to investigate a high-performance, low energy refrigeration system for refrigeration in general and for food transport vehicles in particular. The proposed system is based on the integration of a trans-critical CO2 mechanical driven compression cycle and a compact ejector cooling system. The system will be driven by heat rejected from the vehicle exhaust system and heat recovered from the CO2 gas in the mechanical compression cycle. The ejector evaporator replaces the ambient air in the CO2 mechanical compression cycle, by utilizing the cooling effect produced in the ejector cycle to provide sub-cooling of the high-pressure CO2 fluid below ambient temperature. This is thought to help improve the performance of the CO2 cycle. The ejector cycle is integrated in a way to enhance sub-cooling of the high pressure gas, but not to limit the overall system performance to that of the ejector cycle. The system could be operated using two working fluids i.e., CO2 for the mechanical compression cycle and an environmentally friendly working fluid e.g., water or methanol. The proposed system is efficienct, compact and requires minimal energy to operate, features which make the system particulary suitable for applications in transport vehcles. The research programme will involve:1. Thermodynamics and energy transfer analysis of the combined CO2 mechanical compressor -ejector refrigeration system2. Computer modelling for components sizing and performance analysis of the combined refrigeration system.3. Laboratory evaluation of the performance of the system components;4. Analysis of the environmental impact of application of the system.Development of the proposed system would enable refrigeration to be provided for food storage in food transport vehicle with minimum energy consumption owing to utilisation of the waste heat and improvement of the performance of the CO2 mechanical compression cycle. The improved system performance would reduce energy consumption in this sector and also reduce the impact of the global warming attributed to the use of HFC refrigerants.
People |
ORCID iD |
| Siddig Omer (Principal Investigator) |
Publications
Mark Worall (Author)
(2010)
Design analysis of a hybrid jet-pump CO2 compression system
Worall M
(2011)
A hybrid jet-pump CO 2 compression system for transport refrigeration
in International Journal of Low-Carbon Technologies
| Description | Analysis of the transcritical CO2 system showed that the discharge pressure and temperature were independent and that there was an optimum COP that depended on pressure, temperature and gas cooler outlet temperature. As gas cooler discharge temperature increased, the peak in COP occurred at higher pressure and temperature but the COP was reduced. Analysis of the jet-pump showed that for a given generator temperature and evaporator temperature, entrainment ratio decreased with increasing condenser temperature. The analysis led to the conclusion that an ejector designed for one condenser temperature would be inadequate for another. It was important to select the correct operating conditions for the ejector to operate efficiently but without the loss of ejector function. A comparison of five refrigerants, HFE7000, HFE7100, methanol, ethanol, water, that were possible candidates for use in the system showed that the synthetic refrigerants HFE7000 and HFE7100 were superior in their performance and thermophysical properties but a global warming potential (GWP) of over 150 made them unacceptable for mobile air conditioning and inappropriate for transport refrigeration. Methanol and ethanol were superior to water, but methanol was highly toxic, explosive and flammable. Ethanol was much less toxic and flammable and had superior properties to water. Water was the safest but had the poorest performance and would require large heat transfer area, with the subsequent increase in weight and reduction in space. It was concluded that for small sub-cooling requirements water could be used successfully but for higher cooling requirements ethanol would be a better candidate. Refrigerated transport is responsible for substantial energy consumption and emission of gases contributing to radiative forcing and therefore a global warming effect. TEWI is a concept that takes account of the direct impact of a refrigeration system due to leakage during operation and at end of life and its indirect effect due to the energy consumed by the refrigeration system and the vehicle on which it operates. The analysis has found that for a small rigid trailer, corresponding cooling capacity, cold space temperature and environmental conditions analysed in this project, energy consumption was approximately 9% of the vehicle's and that implementation of subcooling reduced this to approximately 7% at 10K subcooling and 6% at 25K subcooling. Although the proportion appears low, a substantial reduction in energy consumption is achieved. The reduction in the emission of global warming gases is much more substantial. By replacing traditional fluorocarbon refrigerant such as R404a with CO2 the TEWI is reduced by half. Subcooling by 10K reduces TEWI by 60% and subcooling by 25K reduces it by 65%. This shows that the environmental benefits of using CO2 as a refrigerant are substantial and subcooling enhances its environmental benefits. Average exhaust gas heat exchanger temperature increased linearly from 64_C at 374W to 81_C at 607W through to 124_C at 1642W. This validated the design of the heat exchanger and showed that the temperatures and heat available were suitable for use in the CO2 ejector compression system. |
| Exploitation Route | meetings and seminars open to the public Articles in local and national newspapers Television and radio articles Academic papers Conference presentations Seminars Industry exhibitions and expositions Public meetings Newspaper articles Website publication |
| Sectors | Energy,Environment,Transport |
| Description | collaboration with Venturi Jet Pumps Ltd |
| Organisation | Venturi Jet Pumps Ltd |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | The project involved mathematical modelling,prototype design, component manufacture and testing. The ejector operating conditions were determined by modelling and these parameters were passed on to venturi Jet Pumps Ltd to design and manufacture an ejector for the design conditions. |
| Start Year | 2009 |