Numerical performance analysis of a counter-flow double-pipe heat exchanger with using nanofluid and both sides partly filled with porous media

Simultaneous application of nanofluid and porous media in a counter-flow double-pipe heat exchanger is studied in order to enhance its heat transfer with minimum power increase. Both channels of the heat exchanger are partially/completely filled with porous media, and different configurations of porous layers with various Darcy values are analyzed in different Reynolds numbers. Nanofluid flow is simulated using two-phase mixture model and flow through porous media obeys from Darcy-Brinkman-Forchheimer rule. Results are presented in terms of the performance evaluation criterion. First, the inner and outer pipes were filled with porous media having the same Darcy number. Depending on Darcy value, two optimal regions exist: 1partial filling of only the inner pipe and 2complete filling of the both pipes. Next, different combinations of Darcy number of the inner and outer pipes have been investigated for various filling portions and Reynolds numbers. Depending on Re and Da numbers, three different optimum situations exist: 1partial filling of the inner pipe; 2partial filling of the outer pipe; and 3complete filling of the both pipes. For instance at Re-i=500 and Da(o)=10(-4), when a very low (Da(i)=10(-4)), moderate (Da(i)=10(-2)) or high (Da(i)=10(-1)) permeable porous medium is used in the inner pipe, the optimal situations are, respectively, the first, third and second situations. Based on the working conditions of the heat exchanger, proper porous layer thickness and Darcy configuration have to be selected to meet the maximum performance.