Panda, DebashisSatapathy, Ashok K.Sarangi, Sunil Kr.
16页
查看更多>>摘要：Most one-dimensional simulation models developed so far to estimate the theoretical performance of pulse tube cryocoolers ignore the effect of heat loss arising out of thermal dispersion in porous media and turbulent conduction in pipes。 In this paper one-dimensional numerical simulation of an inertance type pulse tube cryocooler has been carried out to illustrate the effect of thermal dispersion and turbulent conduction on the oscillating gas flow and heat transfer behavior。 The study has been conducted under three conditions: simulation of cryocooler without considering gas axial heat conduction effects， simulation of cryocooler with gas axial heat conduction but neglecting the influence of thermal dispersion and turbulent conduction， and simulation of the cryocooler with gas axial heat conduction including the influence of thermal dispersion and turbulent conduction。 The effect of thermal dispersion and turbulent conduction in the gas phase has been expressed in terms of an axialconduction-enhancement-factor in the gas energy equation。 It is revealed that the inclusion of axialconduction enhancement factor in the porous media and tubes of the pulse tube cryocooler creates a positive phase shift in all oscillating physical quantities。 This phase change causes an adverse effect on the cooling mechanism of the pulse tube cryocooler。 It is found that， the coefficient of performance decreases by 8。6% and the minimum cooling temperature increases by 6。67% when the axial-conduction enhancement factor is included in the one-dimensional simulation model。
查看更多>>摘要：In this study， an experimental study on the spray cooling using liquid nitrogen (LN2) as the coolant was studied。 Accordingly， an open-cycle experimental setup for cryogenic spray cooling was built。 Investigation of spray cooling heat transfer performance on both plain and straight-grooved surfaces was carried out。 The spray morphology was captured using the visual technique in the cryogenic system and the spray angles under different injection pressures were obtained。 Additionally， a parametric study of heat transfer characteristics on the straight-grooved surfaces was carried out。 The results have shown that the spray angle， at first， increases as with the inlet pressure， which is followed by a decrease。 The straight-grooved surface significantly improved the spray cooling heat transfer compared to its plain counterpart by the maximum improvement rate of 64。2%。 However， temperature uniformity was poorer。 As the groove depth increases， the heat flux experiences increases at first， followed by a decrease。 Finally， it was observed that the increase in groove width reduces the heat flux。
NSTL
Elsevier