This paper presents a theoretical investigation of solar air heater using phase change material (PCM). PCM used in present configuration is homogenous mixture of paraffin wax with Aluminium powder. The purpose of using Aluminium powder with paraffin wax is to increase the thermal conductivity. PCM mixtures are encapsulated in cylinders and are used as solar absorbers. Using MATLAB program, the effect of different parameters is studied. It has been observed that with increase in mass flow rate, air outlet temperature decreases and freezing time of cylinder decreases. However, at constant mass flow rate, with increase in cylinder radius, air temperature decreases and while freezing time increase sharply. The different parameters have  to be chosen such that performance of solar air heater can be optimized.

In the present work, thermo-fluidic behavior of a heat exchanger tube with conical shaped insert has been investigated with the help of finite volume method. To enhance the heat transfer rate, two different types of roughness has been used in conical insert i.e. protrusion and dimple roughness. A three-dimensional computational model with  RNG turbulence model is used for the simulation and it has been performed for three different diameters (3 mm, 6 mm and 9 mm) and two different pitch space (120 mm and 180 mm) for both protrusion and dimple roughness. The present model has been validated with Dittus-Boelter equation and with Blasius equation for Nusselt number and friction factor, respectively. For a constant heat flux of 1200 W/m2, effect of roughness, diameter and pitch on Nusselt number and friction factor has been predicted for Reynold number range of 5000 to 30000. From the result, it is found that, the protrusion shaped roughness has better thermal performance factor than dimple shape and diameter of 6 mm has performed better than 3 mm and 9 mm for both the cases of roughness due to favorable flow dynamics.

Extended surfaces are used in a variety of heat transfer applications owing to their ability in reducing the convection resistance by exposing a large surface area to the surrounding fluid. Surface modification in the form of perforations is a passive method of increasing the heat transfer rates with the additional benefit of weight reduction. This work deals with numerical investigation of heat transfer and friction from a perforated fin (with and without slot) subjected to forced convection. The perforated fin with slot has been found to have a maximum enhancement in heat transfer with the simultaneous increase in frictional losses versus that of a solid fin. Further, the perforated fin without slot has been able to transfer heat at a relatively higher rate with a considerable reduction in energy loss due to friction in comparison to a solid fin. C⃝

Present work deals with experimental analysis in which various observation takes place related to performance characteristics like HTR, effectiveness and fluid flow peculiarities like Nu, Re, f, NTU, TPF etc in a cascaded spiral concentric tube type heat exchanger consisting of a GI shell and a cascaded spiral copper inner tube having conical shape inserts, hemispherical insert and plane profile unit for parallel flow. Five spiral cascades with three turns in each are used for the inner side copper tube unit. Water enters at 304°K from the innermost turn along the cascaded spiral tube, and leaves at the outermost turn. The hot fluid inlet for heat exchanger is from bottom of one end of the shell at 333°K, flowing radically across the cascades, and then leaving the exchanger from the top of another end. This paper based on comparative experimental study of the behavior of such system for parallel flow with different shape of inserts, and then compared with the simulation results for same. In this analysis comparative approach is considered for evaluating optimum fluid flow and thermal properties on the basis of geometrical parameters. The results predicted that out of three profiles of insert, plain, conical and half cut elliptical profile, which located over inner copper tube of exchanger, half cut elliptical profile insert shows best results on fluid flow and thermal peculiarities, for mass flow rate range 0.012 to 0.049 Kg/s and Reynolds number range 4236 to 18540, heat transfer rate varies from 1128.06 to 2374.77, Nusselt number varies from 75.15 to 144.05, Friction factor varies from 0.00376 to 0.00305 and effectiveness varies from 0.77 to 0.40 and Number of transfer unit varies from 2.08 to 0.68 for half cut elliptical profile.

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