This study demonstrates the performance improvements that can be achieved by accounting for the in-situ air flow distribution during the design phase of a heat exchanger. The heat exchanger used in this study was a two-slab, A-shaped finned-tube evaporator installed in a horizontal duct with a condensate collection pan and condensate droplet collection metal sheet. The installation configuration and attachments resulted in a large degree of air maldistribution, with approximately 20 % more air passing through the upper slab than the lower slab. We used the NIST heat exchanger model EVAP-COND and Intelligent System for Heat Exchanger Design (ISHED) to examine options for improving the evaporator design for its performance with the actual, measured air velocity profile. Optimization of the refrigerant flow distribution between the two slabs provided 1.1 % capacity improvement, while optimization of refrigerant circuitry for both slabs improved the capacity by 5.6 %. Simulations also showed that the tubes with minimal air flow had a very small contribution to the overall capacity, and that eliminating them from the assembly may prove to be an attractive cost saving method. Evaporator designs with optimized circuitry and reduced number of tubes had better capacities than the original 120 tube evaporator, showing an improvement of 5.2 % for a 108 tube design and 4.0 % for a 102 tube design.
Proceedings Title: Sustainable Refrigeration and Heat Pump Technology
Conference Dates: June 13-16, 2010
Conference Location: Stockholm, -1
Pub Type: Conferences
air flow, EVAP-COND, heat exchanger, ISHED, refrigerant circuitry