20. A continuous, horizontal tube evaporator is fed with a 5% caustic soda solution and the product is continuously discharged and contains 30 lb of caustic soda per 100 lb of water. How many pounds of water evaporated per 100 lb of dilute water per hour? a. 21 b. 78 c. 17 d. 83 e, none of these

28.21 A 1 x 10-2 m spherical pellet is sprayed with a very thin coat of paint. The paint contains a volatile solvent. To dry the pellet, a 300 K and 1.013 × 105 Pa air stream flows around it with a bulk velocity of 1 m/s. The estimated loading of the solvent in the wet paint is 0.12 g solvent/cm³. Physical properties are vapor pressure of the solvent = 1.27 x 104 Pa mass diffusivity of solvent in air = 9.62 x 10-6 m²/s kinematic viscosity of air density of air = 1.569 x 10-5 m²/s = 1.177 kg/m³ thermal conductivity of air thermal diffusivity of air heat capacity of air = 2.624 x 10-2 J/m.s. K = 2.216 x 10-5 m²/s = 1.006 J/g. K = 78 g/g mole molecular weight of the solvent Use the McAdam's¹¹ equation Nu = 0.37(Redp) 0.6 (Pr) 1/3, where Redp dp vx V to evaluate (a) the heat-transfer coefficient, h; (b) the mass-transfer coefficient, ke; (c) the molar flux of the solvent into the air stream.

Design a hydrocooling unit that can cool fruits and vegetables from 30°C to 5°C at a rate of 20,000 kg/h under the following conditions: The unit will be of flood type that will cool the products as they are conveyed into the channel filled with water. The products will be dropped into the channel filled with water at one end and picked up at the other end. The channel can be as wide as 3m and as high as 90 cm. The water is to be circulated and cooled by the evaporator section of a refrigeration system. The refrigerant temperature inside the coils is to be –2°C, and the water temperature is not to drop below 1°C and not to exceed 6°C. Assuming reasonable values for the average product density, specific heat, and porosity (the fraction of air volume in a box), recommend reasonable values for the quantities related to the thermal aspects of the hydrocooler, including how long the fruits and vegetables need to remain in the channel, the length of the channel, the water velocity through…

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