Pomiary oporów przepływu podczas skraplania w minikanałach rurowych

Badanie i analiza oporów przepływu podczas skraplania czynników chłodniczych w minikanałach rurowych ma duże znaczenie dla poznania procesu skraplania. W artykule tym przedstawiono wyniki przeprowadzonych badań, które mają na celu ułatwienie projektowania, konstrukcji i eksploatacji kompaktowych wymienników ciepła. W wyniku analizy rezultatów badań autorka proponuje własną zależność pozwalającą na wyznaczenie średnich i lokalnych oporów przepływu w minikanałach.

Nowadays, much attention is paid to miniaturization of devices while increasing their efficiency. The same is with heat exchangers which have to exchange a lot of heat from a small area. By using minichannels and phase transitions, miniaturization of heat exchangers with intensification of heat exchange is possible. Unfortunately, the decrease in internal diameter creates problems associated with an increased flow resistance, which is a negative phenomenon because it causes increases in energy consumption for refrigerant transportation. The understanding of the dependence between the flow resistance and the flow parameters, refrigerant properties as well as internal diameter of a minichannel can improve design, construction and exploitation of compact heat exchangers. It will also enable optimization of the heat transfer coefficient α and flow resistance (Δp/L) growth. For this purpose, investigations were performed on three different refrigerants: R134a, R404A, R407C in minichannels with an internal diameter of the range dw = 0.31 mm - 3.3 mm. Miniaturization of compact heat exchangers and use of environmentally friendly CFC substitutes also help to reduce harmful effects on the environment and costs due to the absorptivity of material decrease. Based on the analysis of the investigation results the author has developed own correlation describing change of the pressure drop on the minichannel length, depending on its internal diameter, flow parameters and refrigerant properties.