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This paper presents the performance of a simple five-layers-type gas to gas heat exchanger, which is simple to construct, easy to maintain and has low space requirements, under different laminar gaseous flow rates and temperatures. The merits and drawbacks of the use of porous material inserts to improve the performance of this type of heat exchanger are investigated. An experimental work was carried out to investigate the influence of the insertion of porous segments with different thicknesses on heat transfer enhancement and the associated pressure drop as these are the many determining factors in most engineering applications. During these experiments the volume flow rates of the hot and cold air streams were varied such that the volume flow rate of both of the streams was the same in any of the experimental runs. These experiments were conducted for different values of hot air inlet temperature, while keeping the cold air inlet temperature nearly constant. Also the results obtained in this work was compared with the corresponding results obtained previously using a similar three layered heat exchanger under similar operating hydro-thermal conditions. The investigations showed that the thermal performance of the heat exchanger due to the two additional layers was pronouncedly improved on the expense of an increase in pressure drop of much lower cost.

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In this study, a numerical investigation has been carriedout for single phase flow behavior for thirty six internally finnedtubes to demonstrate the effect of axial pitch to fin height ratio(p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internalfin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di)with 14 mm and Reynolds number (Re) of single-phase flow for10000≤Re≤50000 on enhancement of forced convection heattransfer and reduction of friction factor by using ANSYS CFXprogram. It solves the three-dimensional Navier-Stokes equationsfor steady state turbulent with SST model and enhance walltreatment. The numerical analysis provided at fully developedvelocity and temperature. Numerical results showed that thesmallest axial pitch to fin height ratio (p/e) =0.8 and with apexangle α=10 degree provided enhancement of heat transfer of 2.8 to3.55 times higher than of smooth tube. Finally, present numericalresults are seen to be in good agreement with literatureexperimental correlations.