Drying 735 heat transfer. In essence, the moisture that is evaporated from the product is recycled and reheated. It replaces air or inert gas and this hot vapor is used to strip off additional liquid from the wet product. The excess vapors are removed via a vent condenser outside of the closed vapor loop. This procedure can be applied in any of the drying processes mentioned here. One advantage to this method of drying is that the product sees only the vapor with which it is already in contact in the liquid state. a possible reason for using this method is product oxidation when air drying. This method may reduce oxidation if the solvent is used. This method is also more energy efficient when solvents are present since the inert gas that is recycled in the former method needs to be reheated after it has been cooled down to condense the solvents 2.0 DEFINITIONS Absolute Humidity--the ratio of mass of vapor(moisture) to mass present in the carrier gas stream. Example: 0.02 pounds of water per pound of air. This number can be used to find the relative humidity on the psychrometric charts. It is also useful for cu quantities in a stream due to such items as products of combustion (when a gas fired heater is used), and evaporation and ambient quantities. This is necessary for calculating condenser or venting amounts Bound Moisture--liquid which is bound to a solid by chemical bonds or physical adsorption in the molecular interstices of the solids Capillary flow-the flow of liquid through the pores of a solid Critical moisture content-the average moisture in the solids when the constant rate drying period ends Diffusion--the process of mass transfer of the liquid from the interstices of the solid to the surface of the solid Dry basis--means of measuring moisture content in terms of moisture content per quantity of dry product, forexample, pounds of water per pound of dry product. (Also see Wet Basis.) Equilibrium moisture content-the limiting moisture content to which a product can be dried under fixed conditions such as temperature humidity and pressure Evaporative cooling-when drying a solid with free or bound moisture the effect of a phase change from the liquid state to the vapor state removes energy from the liquid-solid mass. This results in a reduction of temperature in a nonadiabatic operation, whereas in anDrying 735 heat transfer, In essence, the moisture that is evaporated from the product is recycled and reheated. It replaces air or inert gas and this hot vapor is used to strip off additional liquid from the wet product. The excess vapors are removed via a vent condenser outside of the closed vapor loop. This procedure can be applied in any of the drying processes mentioned here. One advantage to this method ofdrying is that the product sees onlythe vapor with which it is already in contact in the liquid state. A possible reason for using this method is product oxidation when air drying. This method may reduce oxidation ifthe solvent is used. This method is also more energy efficient when solvents are present since the inert gas that is recycled in the former method needs to be reheated after it has been cooled down to condense the solvents. 2.0 DEFINITIONS Absolute Humid@-the ratio of mass of vapor (moisture) to mass present in the carriergas stream. Example: 0.02 pounds ofwater per pound of air. This number can be used to find the relative humidity on the psychrometric charts. It is also usehl for cumulative quantities in a stream due to such items as products of combustion (when a gas fired heater is used), and evaporation and ambient quantities. This is necessary for calculating condenser or venting amounts. BoundMoisture-liquid which is bound to a solid by chemical bonds or physical adsorption in the molecular interstices of the solids. Capillaryflow-the flow of liquid through the pores of a solid. Critical moisture content-the average moisture in the solids when the constant rate drying period ends. Dijfision-the process of mass transfer ofthe liquid from the interstices of the solid to the surface of the solid. Dry basis-means of measuring moisture content in terms of moisture content per quantity of dry product, for example, pounds of water per pound of dry product. (Also see Wet Basis.) Equilibrium moisture content-the limiting moisture content to which a product can be dried under fixed conditions such as temperature, humidity and pressure. Evaporative cooling-when drying a solid with free or bound moisture, the effect of a phase change from the liquid state to the vapor state removes energy from the liquid-solid mass. This results in a reduction of temperature in a nonadiabatic operation, whereas in an