1) An aluminium pan of 15 cm diameter is used to boil water and the water depth at the time of boiling is 2.5 cm. The pan is placed on an electric stove and the heating element raises the temperature of the pan to 110°C. Determine the power input for boiling and the rate of evaporation. Take Csf = 0.0132.
2) Suppose the sun (diameter = 1.4 X 109) having a surface temperature of 5750°K and at a mean distance of 15 X 1010 m from the earth (diameter = 12.8 X 106m). Evaluate the following:
a) The total energy emitted by the sun,
b) The emission received per m2 just outside the atmosphere of the earth,
c) The total energy received by the earth if no radiation is blocked by the atmosphere of the earth, and
d) The energy received by a 1.6 m X 1.6 m solar collector whose normal is inclined at 50° to the sun. The energy loss through the atmosphere is 42 percent and diffuse radiation is 22 percent of direct radiation.
3) What is meant by heat exchanger? Derive an expression for logarithmic mean temperature difference for the counter flow heat exchanger.
4) Ammonia and air are in equimolar counter diffusion in a cylindrical tube of 2.5 mm diameter and 15 m length. The total pressure is 1 atmosphere and the temperature is 25°C. One end of the tube is connected to a larger reservoir of ammonia and the other end of the tube is open to atmosphere. If the mass diffusivity for the mixture is 0.28 X 10-4 following:
a) Mass rate of ammonia in kg/hr
b) Mass rate of air in kg/hr.
5) Classify heat pipes. describe the working principle of heat pipe with neat sketch.