Heat Exchanger Development for Compact Water/LiBr Sorption Systems

For energy efficient tri-generation, solar cooling or residential heating compact sorption appliances using the working pair water/lithium bromide (LiBr) can be applied. Standard plant technology established in the field of large capacity chillers and heat pumps with conventional tube-and-shell configuration cannot be easily adapted to compact units for economic and operational reasons. For a successful marketing of compact sorption units, major effort is required to achieve tolerable plant dimensions and weight together with affordable first cost and reliable operation. In a research project, the design of all key components, i.e. main heat exchangers - evaporator, absorber, condenser and generator - and the liquid pumps for refrigerant and absorbent solution has been revised. In order to achieve uncomplicated manufacturing and improved vacuum tightness, concepts for standardized heat exchanger modules have been developed. A single effect absorption plant has been erected for the experimental investigation of the newly designed finned heat exchangers and plate heat exchanger configurations as main heat exchangers in an absorption cycle. Concepts for sizing these compact heat exchanger units in compliance with the given thermo-hydraulic conditions of a water/lithium bromide absorption cycle will be presented. Estimations of the wetting of the heat exchangers, the pressure drop in the vapor flow, as well as the achieved heat transfer per heat exchanger volume will be discussed. Experimental results for falling film absorption with compact heat exchangers will be presented.