Wetting specific heat

Equation (4.137) is almost exactly the same as the approximation equation (4.123) derived for wet bulb temperature. When the partial pressure of water vapor is low compared with the total pressure—in other words when the humidity x is low—the specific heat of humid air per kilogram of humid air, Cp, and the specific heat of humid air per kilogram of dry air, Cp, are al most the same Cp = Cp. Therefore, in a situation where the humidity is low and Le s 1, the thermodynamic wet bulb temperature is very nearly the same as the technical wet bulb temperature dy... 

The wetted surface area of the 2 m3 reactor during two-phase relief has been estimated as 8.6 m2. This is the full surface area of the bottom and the sides of the reactor because, if two-phase relief occurs, this whole area will be wetted inside the reactor with liquid. The heat input rate from the fire is estimated as 252 kW l For a closed reactor containing 793 kg of material, and using the average, specific heat capacity of 2.25 kJ/kg K, the effective rate of temperature rise due to the fire is given by ... 

The balance between conduction and diffusion still operates for a much larger isolated wet object, provided radiation is excluded. This is the basis of the wet bulb thermometer method for measuring humidity. The actual rate of evaporation now is not as simply determined and is influenced by wind. The wet bulb temperature is almost independent of wind condition, owing to a convenient accident. Heat conduction is a diffusion process, and the diffusion coefficient for water vapor in air (0.24 sq. cm./sec.) is numerically close to the diffusion coefficient of temperature in air (thermal conductivity/specific heat = 0.20 sq. cm./sec.). Hence, the exact way in which each molecular diffusion process merges into the more rapid eddy diffusion process is not important because no matter how complex the transition is, it must be quantitatively similar for the two processes. 

A dryer produces 180 kg/hr of a product containing 8% water from a feed stream that contains 1.25 g of water per gram of dry material. The air enters the dryer at 100°C dry-bulb and a wet bulb temperature of 38°C the exit air leaves at 53°C dry-bulb and 60% relative humidity. Part of the exit air is mixed with the fresh air supplied at 21°C, 52% relative humidity, as shown in Fig. P4.169. Calculate the air and heat supplied to the heater, neglecting any heat lost by radiation, used in heating the conveyor trays, and so forth. The specific heat of the product is 0.18. 

Another common method used for measuring T Is thermal analysis. The glass transition is associated wfth changes in specific heat, not with latent heat. Thus the transition occurs as a base-line shift rather than as distinct endotherms in DSC or differential thermal analysis (DTA). As shown In Figure 3, wet determinations are more difficult than dry determinations, since the wet fibers must be sealed In DSC capsules to prevent moisture vapor from escaping during the determination. Further, the baseline shift is usually very small, and an accurate measure is difficult to accomplish. 

Average relative volatility Phase equilibrium Molecular proportions Solubility of the liquid components Density of the vapour and reflux Viscosity of the vapour and reflux Surface tension of the vapour and reflux Specific heat of the components Heat of evaporation of the components Wetting properties... 

Knowing k, the thermal conductivity coefficient X of the wet material can be calculated from Equation 2.21 when Cjw, the specific heat of the wet material, and pos, the density of the dry material, are known ... 

Specific heat of a moist agricultural product can be related to its dry, or wet, mass. From the relationships between dry and wet masses it follows that... 

The mass-transfer coefficient A e can be approximated analogically with the Lewis relation from the heat-transfer coefficient h and specific heat of wet air Cg for the water-air system. 

Cwm Om ( moisture rcprcsent the specific heats of wet material, bone dry material, and liquid moisture, respectively... 

The drying material is a liquid. Feed solid mass content = 57% wet basis. Feed temperature = 97°C. Feed pressure = 101.3 kPa. The material goes through a spray dryer to be dried to a moisture content of 8.5% wet basis. Material outlet temperature is 50°C. Then it goes through a vibrated fluidized bed dryer to get the product dried to the final moisture content of 0.3% wet basis. Material product temperature is 52°C. Specific heat of the bone dry material = 1.26 kJ/kg °C. Mass flow rate of wet material = 5000 kg/h. 

The drying material is wet solid particles. Feed moisture content = 22% wet basis. Feed temperature = 20°C. Product temperature = 50°C. Product moisture content = 0.2% wet basis. Specific heat of the absolute dry material = 1.26 kJ/kg°C. Mass flow rate wet basis = 2000 kg/h. 

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