An experimental study is done to study the convection heat transfer from the outer surface of a group of helical coils that have the same external surface area which is (0.1 m2). These coils are wrapped to form different helical coils with different geometrical dimensions. Five pipe diameters are used in this study also; the pipes are wrapped by different values of coil diameter ranges from 75- 300 mm. The effect of the coil pitch on the heat transfer process has been studied, to reach the value that gives the best performance for each coil. The heat source is steam flowing inside the coil. These coils are tested at different air speeds inside the wind tunnel, which made the Reynolds number (Re) changes from 239 - 3990. The obtained results showed that the Nusselt number enhances with the increase of D/do and P/do to reach the maximum value at the optimum values of D/do and P/do then the Nusselt number begins to decrease. Nusselt number increases with the increase of Reynolds number under all conditions. A correlation for Nusselt number as a function of Reynolds number and the other studied operating parameters reported. By comparing this work with literature, one can find an acceptable agreement in the results.
This paper focuses on the melting of phase change material capsulated in the elliptical cross-section horizontal cylinder under convective boundary conditions. Different parameters are discussed, namely, the HTF inlet temperature and velocity and the axes ratio of the capsule cross-section. The effect of HTF inlet temperature, inlet velocity, and the capsule axes ratio was studied using the CFD software FLUENT 6.3.26. A comparison between the numerical and experimental results was made for the system. The experimental results matched well with the heat transfer model. It is shown that the inlet temperature of the heat transfer fluid (HTF) has a great effect on the process of paraffin wax melting. The increase of HTF inlet temperature increases the PCM liquid fraction at constant charging time and decreases at the same time the total time of the capsulated paraffin wax melting. The geometry of the capsule crosssection represented by its axes ratio has a sensible effect on the process of paraffin wax melting. Increasing the axes ratio of the capsule, i.e. elongated the capsule in the perpendicular direction of flow increasing the PCM liquid fraction at constant charging time and decreases the total time of the capsulated paraffin wax melting. The increase of HTF inlet velocity has a weak effect on the process of paraffin wax melting in the inlet velocity range 0.003-0.012 m/s.
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