End correction for regenerator heat transfer calculation using symmetrical cycle theory27 (courtesy Plenum Press): A= 4 H S ( T + r,) = reducedlength U C 1C + ^W 1W TT = 12H0(7"C -f Tw) ^ ^ 5 ^ — = reduced period Cp5C/ 1 [1 U ° = 4 U + —J where Tw, T0 = switching times of warm and cold streams, respectively, hr S = regenerator surface area, m2 U0 = overall heat transfer coefficient uncorrected for hysteresis, kcal/m2 • hr • 0C U = overall heat transfer coefficient Cw, C0 = heat capacity of warm and cold stream, respectively, kcal/hr • 0C c = specific heat. | INSULATION SYSTEMS 1939 0 10 20 30 40 50 60 70 80 90 100 Reduced period ir Fig. End correction for regenerator heat transfer calculation using symmetrical cycle theory27 courtesy Plenum Press A reduced length UcTe CWTW 12H0 Tc Tw . . 77 ----S reduced period cpsd r where TW TC switching times of warm and cold streams respectively hr S regenerator surface area m2 Uo overall heat transfer coefficient uncorrected for hysteresis kcal m2 hr C U overall heat transfer coefficient Cw Cc heat capacity of warm and cold stream respectively kcal hr C c specific heat of packing kcal kg C d particle diameter m ps density of solid kg m3 phases are well distributed in the flow stream approaching the distribution point. Streams that cool during passage through an exchanger are likely to be modestly self-compensating in that the viscosity of a cold gas is lower than that of a warmer gas. Thus a stream that is relatively high in temperature as would be the case if that passage received more than its share of fluid will have a greater flow resistance than a cooler system so flow will be reduced. The opposite effect occurs for streams being warmed so that these streams must be carefully balanced at the exchanger entrance. INSULATION SYSTEMS Successful cryogenic processing requires high-efficiency insulation. Sometimes this is a processing necessity as in the Joule-Thomson liquefier and sometimes it is primarily an economic requirement as in the storage and transportation of cryogens. For large-scale cryogenic processes especially those operating at liquid nitrogen temperatures and above thick blankets of fiber or powder insulation air 1940 CRYOGENIC SYSTEMS 1 at warm end 100 150 200 250 300 High-pressure gas temperature K Fig. AT limitation for contaminant cleanup in a regenerator. or N2 filled have generally been used. For lower temperatures and for smaller units vacuum insulation has been enhanced by adding one or many radiation shields sometimes in the form of .
