The two-phase flows in horizontal headers with multiple connected parallel channels have been investigated by numerical simulations and analyses with the Computational Multi-Fluid Dynamic (CMFD) method. First, the experimental conditions with available detailed measurements of the header inlet and outlet two-phase flow rates have been simulated in order to investigate the ability of the applied CMFD method to predict complex header two-phase flow conditions with phase separation. The obtained results show the acceptable agreement of numerical results with measured values. Afterwards, the refrigerant R134a two-phase flow in the header of plate and fin evaporator is investigated with the aim of finding out reasons for the non-uniformity of the liquid and vapour outflow rates from the header, as well as of defining a retrofit for the problem diminishing. The refrigerant flow rate through the evaporator and corresponding refrigerant velocity are decreased at the reduced evaporator load. The obtained results clearly show that this velocity decrease in the horizontal header leads to the formation of the liquid layer on the bottom of the header that is transferred mainly to the first downward connected outlet evaporating channel, while the liquid feeding of the remaining outlet channels is much lower. This effect is the cause of the problem with exit air temperature stratification. The performed numerical simulations show that the introduction of the fins over outlet channels improves the uniformity of the liquid and vapour phase distribution from the header towards the outlet channels and, thus, reduces the temperature stratification of air at the evaporator exit plane. Presented results show that the developed CMFD method provides reliable results for different geometry and flow conditions.
A numerical investigation of the refrigerant maldistribution from a header towards parallel channels in an evaporator of automotive air conditioning system
International Journal of Heat and Mass Transfer ; 55 , 13/14 ; 3335-3343
2012
9 Seiten, 11 Bilder, 16 Quellen
Aufsatz (Zeitschrift)
Englisch
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