Square cross-section generates the highest entropy, followed by ellipse and circular. Helical tubes offer higher heat transfer and lower entropy generation. Heat transfers of helical coiled tube with several cross section profiles are evaluated.
Finally, the improvement in Nusselt number was obtained by (68 %) at Dean number of 590 and particle concentration of 3.0% vol., but, the minimum enhancement in the Nusselt number was obtained by (31 %) at Dean number of 65 and particle concentration of 0.5 % vol Moreover, there is a significant enhancement in the Nusselt number when increasing the duct aspect ratio and coil radius ratio as well as with increasing the Reynolds and Dean number for water and nanofluid. Also, the pressure drop increases with increasing the duct aspect ratio and coil radius ratio but it decreases with increasing pitch ratio of the coiled duct. The results indicate that the heat transfer performance improves significantly when using volume fraction up to 0.5 % vol. The heat transfer and flow behavior performance of these nanofluid suspensions were studied as a function of various parameter such as rectangular tubes aspect ratio, radius of coil, number of turns, Reynolds number and Dean number. In this study, the nanofluid thermo-physical properties are formulated as functions of nanoparticle volumetric fraction. Steady state laminar flow of a single phase nanofluid in helical duct was solved by the computational fluid dynamics (CFD) approach presented by finite volume method. The nanofluid suspensions is water-Al2O3 with volume of fraction of 0.5, 1, 2 and 3 % vol. A numerical simulation on pressure drop and heat transfer of vertical rectangular helical coiled duct by utilizing nanofluid as the test fluid is presented. Heat transfer enhancement in horizontal annuli using variable nanoparticles concentrations of Al2O3-water nanofluid is investigated. Among the considered mass flow rates in 4 ¼ 0.06 and 0.10%, mass flow rate of 0.002 kg/s has the highest thermo-fluid efficiency. The highest and lowest values of outlet temperature are reported for fluid with highest solid nanoparticle volume concentration and distilled water, respectively. Also, by increasing mass flow rate, the heat transfer between hot surfaces and cooling fluid is enhanced. Surfaces with angular corners create greater velocity variations in comparison with surfaces with curved corners and this behavior leads to higher pressure loss as well as more pumping power. By increasing the nanoparticles concentration, the highest Nusselt number belongs to tube with elliptical cross-section. The results show that variations of average Nusselt number in lower mass flow rates is not dependent to the shape of flow cross-section. Uniform temperature and velocity distributions with several mass flow rates are applied to geometry at inlet and constant wall temperature as boundary conditions. Different shapes including rectangle, elliptic, trapezoid and circle are selected as tube cross-sections. Simulations are performed for different mass flow rates between 0.0005 and 0.005 kg/s. Water-graphene nanoplatelet/platinum hybrid nanofluid with 0.02, 0.06 and 0.10% volume concentration has used as working fluid. In this study, effects of nanofluid concentrations and different cross-sections of tube on thermal performance of horizontal spiral-coil in laminar fluid flow are investigated numerically. Today, one of the most common methods for heat extraction from the solar ponds is using spiral piping system.
0 kommentar(er)
