Ahot air balloon roughly spherical in shape has a volume of 70,000 ft3 and a weight of 500 lb (including passengers, basket, ballon fabric, if the outside air temperature is 80 of and the temperature within the balloon is 165 of, estimate the rate at which it will rise under steady state conditions if the atmospheric pressure is 14.7 psi.

The mass flow rate of the fluid remains constant in all steady flow process. a)- true b)- false

Awall of 0.5m thickness is to be constructed from a material which has average thermal conductivity of 1.4 w/mk. the wall is to be insulated with a material having an average thermal conductivity of 0.35 w/mk so that heat loss per square meter shall not exceed 1450 w. assume inner wall surface temperature of 1200°c and outer surface temperature of the insulation to be 15°c. calculate the thickness of insulation required.

Asolid steel sphere (k=63.9 w m-1 k-1 , ? =7832 kg m-3 , c=0.523 kj kg-1 k-1 ), 100 mm in diameter is initially at a uniform temperature of 500o c and is suddenly quenched in a large oil bath for which t? = 100o c and h = 3200 w m-2 k-1. estimate the time required for the sphere to cool to 200o c and to 110o c