A water oxygenator consists of a cylindrical gas-permeable tube that is 1 mm in diameter and 200 cm in length. The water properties are such that its viscosity is close to 1 cP and its density is 1 g cmâ3. The tube wall is highly permeable to oxygen and the concentration of oxygen at the inside surface of the tube where the water is flowing is constant along the length of the tube at 5.6 μg cmâ3. The diffusivity of oxygen in the water flowing through the tube is equal to 2.1 à 10â5 cm2 sâ1. The water is flowing through the oxygenator tube at a flow rate of 2 cm3 minâ1.

If there is no oxygen in the water entering the oxygenator and the exiting oxygen concentration in the water leaving the oxygenator tube is equal to 4.0 ug cm", use these data to find the average mass transfer coefficient in cm s-1.

Acommercial grade cubical freezer, 4 m on a side, has a composite wall consisting of an exterior sheet of 5.0-mm thick plain carbon steel (kst= 60.5 w/m k), an intermediate layer of 100-mm thick polyurethane insulation (kins 0.02 w/m k), and an inner sheet of 5.0- mm thick aluminium alloy (kal polyurethane insulation and both metallic sheets are each characterized by a thermal contact resistance of r 2.5 x 104 m2 k/w. (a) what is the steady-state cooling load that must be maintained by the refrigerator under conditions for which the outer and inner surface temperatures are 25°c and -5°c, respectively? (b) for power saving purpose, which wall material should be increased/reduced in. thickness in order to reduce 50% of the cooling load found in part (a)? redesign the thickness of the proposed material. 177 w/m-k). adhesive interfaces between the q=575.93 w