Optimization of heat transfer enhancement and pumping power of a heat exchanger tube using nanofluid with gradient and multi-layered porous foams

Nanofluids and porous inserts are two traditional methods of enhancing heat transfer. Porous media improve heat transfer along with increasing the pressure drop. This study aims to use gradient and multi-layered porous media (GPM and MLPM) with optimized properties and arrangement to maximize the heat transfer and minimize the pressure drop. Fluid flow in a pipe filled with GPM or MLPM is numerically simulated using ANSYS-FLUENT; where the properties of each layer consisting the porosity and the particle size (or permeability) of the porous medium can be adopted independently. First, simple arrangements of porous layers including constant, linear or stepwise increasing or decreasing of particle size (Case I) or porosity (Case II) of layers with respect to the radius are investigated. Results show that the stepwise and linear profiles both in Case I and Case II have nearly the same performance evaluation criteria (PEC) values. Particle swarm optimization (PSO) algorithm is used to find the optimal arrangements of porous layers in the both cases to maximize PEC value. Results show that the optimal arrangement of Case I and Case II gives PEC of 0.845 and 0.789, respectively. In addition, simultaneous optimization of Case I and Case II gives a higher PEC (0.856). Finally, using alumina/water nanofluid (5%) in the simultaneous optimized conditions improves PEC about 3 times.