In an experiment, the temperature of a hot gas stream is to be measured by a thermocouple with a spherical junc-tion. Due to the nature of this experiment, the response time of the thermocouple to register 99 percent of the initial tem-perature difference must be within 5 s. The properties of the thermocouple junction are k = 35 W/m⋅K, rho = 8500 kg/ m 3 , and c p = 320J/kg⋅K. If the heat transfer coefficient between the thermocouple junction and the gas is 250 W/ m 2 ⋅K, deter-mine the diameter of the junction.

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