Water enters a circular tube whose walls are maintained at constant temperature at specified flow rate and temperature. For fully developed turbulent flow, the Nusselt number determined from Nu -0.023 can be law of cooling in this case is Re0.8 PrO.4. The correct temperature difference to use in Newton's (a) the difference between the inlet and outlet water bulk temperature (b) the difference between the inlet water bulk temperature and the tube wall temperature (o) the difference between the average water bulk temperature and the tube temperature (d) the log mean temperature difference (e) None of the above. Explain.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?