Experimental analysis of the refrigerant flow maldistribution in braze plate heat exchangers

Abstract

[EN] Braze plate heat exchanger (BPHE) are used widely in heating and cooling systems and the efficiency of heat pumps depends critically on the proper performance of them. One of the most common factors affecting the performance of BPHE is the not uniform distribution of the refrigerant. This problem is especially important in the evaporator as the refrigerant enters in it in two phase flow and usually the distribution of liquid and vapor is not uniform over all the channels. This problem is very well known in the literature, and manufacturers have implemented some technical solutions like introducing distributors in the inlet port in order to minimize this effect. Nevertheless, the applied solutions usually are developed only for the nominal conditions and when the BPHE work in other conditions is difficult to know which is going to be its behavior. In this contribution, an experimental analysis of the refrigerant distribution in an evaporator BPHE as a function of the inlet and outlet conditions has been done. The BPHE has been tested working at several inlet conditions (quality) and outlet conditions (superheat) for different temperature difference in the secondary fluid and the refrigerant distribution inside the BPHE has been registered using thermography. From the obtained results, it has been seen that: i) the flow maldistribution is present in most of the test, ii) the quality of the refrigerant at the inlet has an influence in the flow distribution, iii) the superheat has also a very important influence in the refrigerant maldistribution. In fact, the obtained results have shown that conditions working with low superheat show a better refrigerant distribution. Saturation temperature reduction at the evaporation seems to be a result of the refrigerant maldistribution. The COP degradation because of the refrigerant maldistribution is quite important for the performed test. In fact, it is important enough to remove any possible advantage derived for working at high superheat when the temperature lift in the water side is high.