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【正文】 rs ??? 1() 6. Humid volume of an air–water vapor mixture PtHvH27318291 ??????????? ??? ?PtHvH273 ??????7. Total enthalpy of an air–water vapor mixture ? ? ? ?? ? 0000 HrttHccHrttcI wa i rs ???????? ? HtHI 5 0 0 ???8. Humidity chart of air–water vapor mixtures Adiabatic Saturation Temperatures This means that the total enthalpy of the entering gas mixture = enthalpy of the leaving gas mixture. sssssrHrcttHH ?????Wet Bulb Temperature wyBwyBwwrkMhrkMhttHH /????This means that the adiabatic saturation temperature is approximately equal to wet bulb temperature. EQUILIBRIUM MOISTURE CONTENT OF MATERIALS After exposure of the solid sufficiently long for equilibrium to be reached, the solid will attain a definite moisture content. Effect of temperature ? Often, for moderate temperature ranges, the equilibrium moisture content will be assumed constant when experimental data are not available at different temperatures. Bound and Unbound Water in Solids Bound water Free and Equilibrium Moisture of a Substance ? Free moisture content in a sample is the moisture above the equilibrium moisture content. Free and Equilibrium Moisture of a Substance ? Free moisture content in a sample is the moisture above the equilibrium moisture content. ? Free moisture can be removed by drying under the given percent relative humidity. Free moisture content equilibrium moisture content RATEOFDRYING CURVES ? . Rate of Drying Curves for ConstantDrying Conditions Drying in the ConstantRate Period ? In the constantrate drying period, the surface of the solid is initially very wet and a continuous film of water exists on the drying surface. This water is entirely unbound water and it acts as if the solid were not present. ? The rate of evaporation under the given air conditions is independent of the solid and is essentially the same as the rate from a free liquid surface. ? The surface temperature is approximately the same as the wet bulb temperature Drying in the FallingRate Period 3. Effect of shrinkage ? It is desirable to dry with moist air. ? to decrease the temperature of air This decreases the rate of drying so that the effects of shrinkage on warping or hardening at the surface are greatly reduced. CALCULATION METHODS FOR CONSTANTRATE DRYING PERIOD Drying time for constant rate period csXXsRXXALRdXAL 2112??? ??)()( WwWHwc ttrhHHkArqR ?????Effect of Process Variables on ConstantRate Period ? 1. Effect of air velocity ? 2. Effect of g
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