Status Report on Polyalkylene Glycol Lubricants For Use With HFC-134A In Refrigeration Compressors
نویسنده
چکیده
The objective of this work is to assess the sensibility of a computer simulation program, employed to analyse the transient behaviour of· domestic refrigerators, to the adopted capillary tube and condenser mathematical modelling approach. Although all the comparisons, presented in this work, are related to a specific computer program, it is believed that, at least in a qualitative way, they are also valid for most of the computer simulation programs of vapor compression refrigerating systems, available in the open literature. A c Cp D ~ e f G H h he j K k L M m Nu p Pr Q R Re St T v NOMENCLATURE area, m~ thermal capacity, kJ/K specific heat, J/kgK diameter, m hidraulic diamet~r, m fin thickn@ss, m friction factot mass velocity based on tube cross-sectional area, kg/sm 2 stagnation enthalpy, kJ/kg specific enthalpy, kJ/kg conv. heat transfer coef., W/m K Colburn factor (hcPr 21 o/qcp) entrance loss factor thermal conductivity, W/mK length, m distance betwe@n adjacent fins, ~ mass, kg mass flow rate, ke/s Nusselt number (hcD/k) pressure, N/m Prandtl number (~Cp/k) mass velocity in the coil ~here the minimuM area occurs, kg/sm 2 thermal resistance, K/kW Reynolds number (4Q/oD~) Stanton number (hc/QCp) temperature, K time, s volume, m v specific volume, m 3 /kg x vapor quality Xa transverse tub@ spacing, m Xb longitudinal tube spacing, m y fin height, m Z compressibility factor ~ constant ~T temperature drop across condensate film, K \ latent heat, J/kg u absolute viscosity, kg/ms p density, kg/m' 0 ratio of minimum flo~ area to frontal area Subscripts a air i inlet, inside f fin t liquid o outlet, outside t two-phase flow v vapor w wall 1 superheated region 2 saturated vapour region 3 saturated liquid region 4 subcooled region surroundings previous tim@ step
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