![]() Wet material is fed in at the bottom and is conveyed up by hot air or gas. It consists mainly of a vertically upward section of duct. Flash dryingĪ flash dryer is essentially a pneumatic conveying system. This shows that the cooling effect of water, because of the very high enthalpy of evaporation, h fg, can be very effective, and that the enthalpy term for vapor should always be included in any energy analysis of a system. ![]() 0.01 kg/s of water (2% of 0.5) at a temperature of 20 ☌ is sprayed into the airstream at exit from the compressor.įrom which the relative humidity is 75%, and so all the water will have evaporated, residence time permitting. ![]() The air is delivered at a pressure of 201.3 kN/m 2 absolute (1 bar gauge) and at a temperature of 100 ☌. It will be assumed that 0.5 kg/s of air (24.5 m 3/min at free air conditions), having a relative humidity of 70%, is drawn into the compressor at a pressure of 101.3 kN/m 2 absolute (standard atmospheric pressure) and at a temperature of 20 ☌. This case will be used as an example of applying the steady-flow energy equation. A water consumption figure was given as 2% of the airflow rate. In dealing with the staging of positive-displacement blowers, in Chapter 6, which describes air movers, it was mentioned that water sprays could be used to reduce the temperature of the outlet air, instead of a conventional heat exchanger. 29.16 to 29.18, instead of absolute values, which are essential for the ideal gas law. This means that Celsius temperatures can be used directly, as shown in Eqns. The datum for the specific enthalpy values in Fig. 29.17 is taken as 273.16 K, which is the triple point of water, which = 0.01 ☌, and so 0 ☌ is taken as the datum for all thermal energy quantities in the steady-flow energy equation. Variation of specific enthalpy of saturated vapor with saturation temperature, for steam
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