In order to increase heat transfer between a stainless steel (k = 15 W/m-K) wall and the surrounding air, eight parabolic fins made of aluminum (k = 186 W/m-K) are attached to the surface of the wall. The surrounding air is a temperature of 20°C and the convection coefficient between the wall and the air is found to be h = 200 W/m^2 -K. The wall has a height of 50 mm and a width of 200 mm, while each fin has a base thickness of 4 mm and a length of 10 mm. The surface temperature of the wall is 300°C. Required:
a. Calculate the efficiency of a single fin, ηf
b. Calculate the overall surface efficiency, ηe for the finned surface.

Amass of m 1.5 kg of steam is contained in a closed rigid container. initially the pressure and temperature of the steam are: p 1.5 mpa and t 240°c (superheated state), respectively. then the temperature drops to t2= 100°c as the result of heat transfer to the surroundings. determine: a) quality of the steam at the end of the process, b) heat transfer with the surroundings. for: p1.5 mpa and t 240°c: enthalpy of superheated vapour is 2900 kj/kg, specific volume of superheated vapour is 0. 1483 m/kg, while for t 100°c: enthalpy of saturated liquid water is 419kj/kg, specific volume of saturated liquid water is 0.001043m/kg, enthalpy of saturated vapour is 2676 kj/kg, specific volume of saturated vapour is 1.672 m/kg and pressure is 0.1 mpa.

Two technicians are discussing the intake air temperature (iat) sensor. technician a says that the computer uses the iat sensor as a backup to the engine coolant temperature (ect) sensor. technician b says that the powertrain control module (pcm) will subtract the calculated amount of fuel if the air measures hot. who is correct

Burgers vector is generally parallel to the dislocation line. a)-true b)-false