Drying 737 a higher saturation limit and therefore, a lower relative humidity, given the same absolute humidity Wet basis--means of measuring moisture content in terms of quantity of moisture per quantity of wet material. For example, if we have 1000 lbs of wet cake with 200 lbs of water our moisture content is 20% on a wet basis and 25% on a dry basis. (See Dry basis. Wet bulb temperature-the dynamic equilibrium temperature attained by a water surface when the rate ofheat transfer by convectionequals the rate of mass transfer away from the surface 3.0 PSYCHROMETRIC CHARTS There are many forms of psychrometric charts available from various technical sources as well as many manufacturers of process equipment who have tailored the chart for use with their equipment. These charts are usef for determining moisture content in the air at a given temperature and relative humidity or wet bulb temperature. The type of information obtainable from these charts depends upon which chart one uses, because each is designed differently. Usually, accompanying the chart is a set of instructions for Please see the references for examples of these charts and the various forms in which they exist 4.0 DRYING THEORY The process of drying solids is usually quantified into three phases 1. Initial adjustment period--this is the stage at which the wet feed material heats up or cools down to the starting drying temperature which is basically referred to as the wet cake temperature. For example, the wet feed is introduced to the heated dryer at ambient temperature During this period the material temperature will start to rise to the wet bulb temperature which may be different from the initial feed temperature. The reason the tempera ture of the wet cake remains low relative to the gas temperature is a phenomenon known as evaporative 2. Constant rate period--this is the stage at which the free moisture is evaporating from the solids at a constant rateDrying 737 a higher saturation limit and, therefore, a lower relative humidity, given the same absolute humidity. Wet basis-means of measuring moisture content in terms of quantity of moisture per quantity of wet material. For example, if we have 1000 Ibs. of wet cake with 200 Ibs. of water, our moisture content is 20% on a wet basis and 25% on a dry basis. (See Dry basis.) Wet bulb temperature-the dynamic equilibrium temperature attained by a water surface when the rate ofheat transfer by convection equals the rate of mass transfer away from the surface. 3.0 PSYCHROMETRIC CHARTS There are many forms of psychrometric charts available from various technical sources as well as many manufacturers of process equipment who have tailored the chart for use with their equipment. These charts are usehl for determining moisture content in the air at a given temperature and relative humidity or wet bulb temperature. The type of information obtainable from these charts depends upon which chart one uses, because each is designed differently. Usually, accompanying the chart is a set of instructions for use. Please see the references for examples of these charts and the various forms in which they exist. 4.0 DRYING THEORY The process of drying solids is usually quantified into three phases: 1. Initial adjustment period-this is the stage at which the wet feed material heats up or cools down to the starting drying temperature which is basically referred to as the wet cake temperature. For example, the wet feed is introduced to the heated dryer at ambient temperature. During this period the material temperature will start to rise to the wet bulb temperature which may be different fromthe initial feed temperature. The reason the tempera￾ture of the wet cake remains low relative to the gas temperature is a phenomenon known as evaporative cooling. 2. Constant rate period-this is the stage at which the free moisture is evaporating from the solids at a constant rate