A performance evaluation plot of enhanced heat transfer techniques oriented for energy-saving

On the basis of the existing performance evaluation criteria analysis and four assumptions, a performance evaluation plot has been proposed in this paper. This plot takes the ratios of heat transfer enhancement and friction factor increase as its two coordinates. The quadrant of the coordinate where both (Nue/Nu0), (fe/f0) are greater than 1.0 can be divided into four regions. In Region 1 heat transfer is actually deteriorated based on identical pumping power, in Region 2 heat transfer is enhanced based on identical pumping power but deteriorated based on identical pressure drop, in Region 3 heat transfer is enhanced based on identical pressure drop but the increase in friction factor is larger than the enhancement of heat transfer at identical flow rate, and in Region 4 heat transfer enhancement ratio is larger than friction factor increase ratio based on identical flow rate. For some techniques which lead to the reduction of both heat transfer rate and friction factor, the proposed plot is still applicable. Different enhanced techniques for the same reference one can be easily and clearly compared for their effectiveness when enhancement study is based on energy-saving. Five practical examples are provided to show the functions of the plot.