Two kg of refrigerant R134a, initially at P1 = 1 MPa, u1 = 312.70 kJ/kg, is contained within a
well-sealed copper tank. A paddle wheel is fitted into the tank to transfer energy to the
refrigerant at constant rate of 0.1 kW. The refrigerant loses heat to its surroundings at a
rate K·t2
, in kW, where K is a constant, in kW per minute squared, and t is time, in minutes.
After 10 minutes of stirring, the refrigerant is at p2 = 0.6 MPa and u2 = 231.05 kJ/kg. No
overall changes in kinetic and potential energy occur. (a) For the refrigerant, determine the
work and heat transfer, each in kJ. (b) Determine the value of the constant K appearing in
the given heat transfer relation, in kW/min2
.