Consider a plane composite wall that is composed of two materials of thermal conductivities ka 0.1 w/mk and kb 0.04 w/mk and thicknesses la 10 mm and lb 20 mm. the contact resistance at the interface between the two materials is known to be 0.30 m2 k/w. material a adjoins a fluid at 200°c for which h = 10 w/m2 k, and material b adjoins a fluid at 40°c for which h = 20 w/m2 k.
a)what is the rate of heat transfer through a wall that is 2.5 meters high by 2 meters side?
b)what is the temperature at the exposed surface of material a?
c)what is the temperature at the exposed surface of material b?
d)sketch the temperature distribution.

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.

Aplate clutch has a single pair of mating friction surfaces 250-mm od by 175-mm id. the mean value of the coefficient of friction is 0.30, and the actuating force is 4 kn. a) find the maximum pressure and the torque capacity using the uniform-wear model. b) find the maximum pressure and the torque capacity using the uniform-pressure model.

At 12 noon, the count in a bacteria culture was 400; at 4: 00 pm the count was 1200 let p(t) denote the bacteria cou population growth law. find: (a) an expression for the bacteria count at any time t (b) the bacteria count at 10 am. (c) the time required for the bacteria count to reach 1800.