1st Nordic Drying Conference - NDC'01, Trondheim, Norway, June 27-29, 2001

A DRYING HEAT PUMP USING CARBON DIOXIDE AS WORKING FLUID K. Klöcker, E.L. Schmidt, R. Schrey, F. Steimle Institute of Applied Thermodynamics and Air Conditioning, University of Essen, Universitätsstra e 15, 45141 Essen, Germany Phone: +49 201 1832598 FAX: +49 201 1832584 E-mail: karsten.kloecker@uni-essen.de, rainer.schrey@uni-essen.de Keywords: heat pump dryer, carbon dioxide, energy savings ABSTRACT The application of carbon dioxide as working fluid in refrigeration and heat pump systems is regaining increasingly importance in view of the CFC problem. It is under ecological and economical aspects an attractive alternative to the HFC working fluids being in practical use. The thermophysical properties and characteristics of carbon dioxide are quite different from those refrigerants used in conventional vapour compression cycles. Its application in conventional vapour compression refrigerating systems is limited by its critical parameters (tc = 31.1°C and pc = 73.8 bar). The possibility to use carbon dioxide also beyond these limits in high temperature processes, e.g. heat pumps, is given by the application of a trans-critical process. The design and construction of a commercial drying heat pump system (batch type cabinet dryer with 12 kW heating capacity and closed air circuit) using the natural working fluid carbon dioxide is shown and experimental results of investigations carried out are presented. Possible energy savings theoretically calculated and experimentally obtained are given for comparison.

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