Refrigerant distribution effects on the performance of microchannel evaporators.
The performance of air to refrigerant heat exchangers can be affected greatly by both refrigerant and air flow distribution. Maldistribution of either fluid stream can lead to reduced heat transfer effectiveness of the heat exchanger and thus lower system efficiency and capacity. Microchannel evaporators are especially susceptible to refrigerant maldistribution as they typically have many parallel channels fed by a common header or manifold. This paper outlines general trends in refrigerant flow distribution in such evaporators taking into account various heat exchanger orientations. In addition, links between heat exchanger performance and refrigerant flow distribution characteristics in microchannel evaporators are made using both analytical and experimental methods. These results show that unification of the liquid refrigerant flow distribution in the evaporator can lead to quantifiable improvements in evaporator performance.
Quantification of Refrigerant Distribution and Effectiveness in Microchannel Heat Exchangers Using Infrared Thermography
Microchannel heat exchangers, specifically evaporators, are known to be susceptible to maldistribution of both the refrigerant and air streams. This maldistribution leads to reduced heat transfer effectiveness of the heat exchanger and thus lower system efficiency and capacity. Besides these reductions in performance, maldistribution in evaporators can also lead to liquid slugging of the compressor. Quantifying the refrigerant distribution using a single parameter in a non-invasive manner for an operable system is difficult and expensive. It is desirable to use a non- dimensional rating parameter that can be applied over a wide variety of heat exchangers: evaporators, gas-coolers, condensers, geometries, and slab configurations. This paper outlines a statistical methodology for quantifying in such a way both the refrigerant distribution and the effective use of heat transfer area using infrared thermography. The parameter was developed to rate heat exchanger distribution on a scale from zero to one; zero being the highest degree of maldistribution and one being uniform distribution. This method also has the advantage of being both non- invasive and low cost.
Modelling environmental impacts of marine finfish aquaculture
Summary Our understanding of the interactions between fish farms and the environment has reached the stage where it is reasonable to expect that quantitative estimates of the possible environmental consequences of aquaculture development can be provided for regulatory and mitigation purposes. This paper summarizes recent developments in this area and provides several case histories of areas where theoretical analyses appear to have direct practical relevance. Fish wastes