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DOI: 10.1615/ICHMT.2008.CHT.1050
page 17

Fatma Salman Marhoon
University of Bahrain

Peter R. Senior
School of Chemical Engineering and Analytical Science, The University of Manchester, PO Box 88, Sackville Street, Manchester, M60 1QD, UK

Peter J. Heggs
School of Chemical and Process Engineering, University of Leeds, Leeds, UK; Dept of Chem Eng, UMIST, Sackville St., Manchester, M60 1QD


The increased emphasis on energy savings and environmental protection has resulted in much more attention being paid towards the modelling of heating, ventilation and air-conditioning (HVAC) equipment. These models permit the prediction of the system performance and the optimization of the system components during design. In addition they can be used to develop new air conditioning techniques and also allow the modification of the energy efficiency of an existing vapour compression system.
Heat exchangers are widely used in the process industries. In the HVAC sector, they are integral to the performance of a vapour compression system. In addition, these have the most potential for modification in the design of HVAC systems.
The main objective of this report is to develop performance models for two phase heat exchangers: evaporators and condensers that are used in refrigeration circuits and use them as tools for improving the energy usage.
Steady state models have been developed for the heat exchangers in a 5 kW cold storage refrigeration unit: a flooded evaporator (thermosyphon heat exchanger) and an air cooled condenser. Experimental data have been collected at various cold storage temperatures: 5°C, 0°C, −10°C and −20°C.
The model for the flooded evaporator provides the predictions the following outlet conditions: the spatial averages of the temperatures of the air and refrigerant, the outlet pressure and vapour quality of the refrigerant. In addition, the overall heat duty, the length of each region and the temperature distribution in each flow path, and the three dimensional temperature distributions on the air side are detailed. The simulator predictions are in reasonable agreement with both the design and the experimental data to within an error of 20 %.
These models can be used in the redesign of heat exchangers in the refrigeration system for the newly mandated environmentally friendly refrigerants and to meet the increasing regulatory minimum system efficiencies.

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