Optimum flowrate history for cooldown and energy storage processes

This paper considers the basic thermal design problem of cooling or heating an object using the minimum amount of working fluid. It is shown analytically that if the duration of the cooling or heating process is fixed, then there exists a unique operating regime (flowrate-time function) which insures the minimum consumption of working fluid. The optimum flowrate is proportional to ( U Cp ) 1 2 , where U is the overall heat transfer coefficient and C p is the specific heat of the working fluid ; the optimum flowrate changes with time as ( U Cp ) 1 2 varies with the temperature of the system. Numerical examples of cooldown and energy storage processes show that the implementation of this optimum operating regime can lead to significant savings in working fluid.