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HUMIDIFICATION

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Humidification operation is a classical example for an interphase transfer of mass and energy, when a gas and a pure liquid are brought into intimate contact. The term humidification is used to desi ... gnate a process where the liquid is transferred to gas phase and dehumidification indicates a process where the transfer is from gas phase to liquid phase. The matter transferred between phases in both the cases is the substance which constitutes liquid phase and it either vaporizes or condenses indicating either humidification process or dehumidification process. 5.1 Definitions The substance that is transferred (vapor) is designated by ‘A’ and the main gas phase is designated by ‘B’. 5.1.1 Molal absolute humidity (Y) It is defined as the moles of vapor carried by a unit mole of vapor free gas. Y = yA/ yB = (pA/ pB) = [pA/ (Pt-pA)] = moles of A/ moles of B (5.1) where yA,yB are moles of A and B respectively, PA is the partial pressure of A and PT is total pressure When the quantities yA and yB are expressed in mass, then it is called mass absolute humidity (Y’ ) or Grosvenor humidity. Y’ = Y. MA/ MB = [pA/ (PT-pA)] (MA/ MB) = mass of A/ mass of B (5.2) 5.1.2 Saturated absolute humidity (YS) When the vapor – gas mixture is saturated, then the partial pressure becomes equal to the vapor pressure of that substance. YS = PA/ PB = [PA/ (Pt – PA)] (5.3) When the quantities are expressed in mass, YS’ = (PA/ PB) (MA/MB) = [PA/ (Pt – PA)](MA/MB) (5.4) 5.1.3 Dry bulb temperature (DBT) The temperature indicated by the thermometer by ordinary immersion in the vapor – gas mixture is called dry bulb temperature [Show More]

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