Flow boiling of R134a and ammonia in a plate heat exchanger

This paper presents experimental results on evaporation heat transfer for flow boiling of ammonia and of R134a in a chevron-pattern corrugated plate heat exchanger (PHE). The measurements enable the evaluation of a quasi-local heat transfer coefficient along the plate, which in turn allows discussing the two-phase distribution and the heat transfer mechanism during evaporation in a plate channel. The saturation temperature varied between 268 K < T-NH3(S) < 283 K (3.55 bar < p(R)(S) < 5.73 bar) for ammonia and 265 K < T-R134a(S) < 283 K (2.157 bar < p(R)(S) < 4.14 bar) for R134a. The heat transfer coefficient is discussed in relation to the vapor quality, mass flux, heat flux and the type of refrigerant. The secondary fluid is a water/ethylene glycol mixture flowing in counter flow or parallel flow arrangement within the PHE. It is shown that the parallel flow case yields better overall performance than the counterflow case, and that plates with low chevron angle corrugations increase the evaporation heat transfer. Comparison with the limited data available from the literature shows good agreement. The Danilova equation and the Steiner boiling correlation are adapted to PHEs and show the need for further theoretical development. (C) 2008 Elsevier Ltd. All rights reserved.