In climates with low night-time temperatures, an energy efficient way of cooling a house is to install a fan in the celling that draws air from the interior of the house and discharges it to a ventilated attic space. Consider a house whose interior air volume is 450 m3.

If air in the house is to be exchanged once every 5 min determine:

(a) the required flow rate of the fan and

(b) the average discharge speed of air if the fan has a diameter of 1.20 m.

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.

During a steady flow process, the change of energy with respect to time is zero. a)- true b)- false

The higher the astm grain size number, the finer the gran is. a)-true b)-false