Papers by Keyword: Forced Convection

Abstract: In this paper, we will discuss how to cope with the smoother growth front and higher growth rate by the forced convection. When the rotation rate of the upper part of the solution is different from that of the lower part in the crucible, the centrifugal force of the upper part is different from that of the lower part. As a result, a forced convection occurs in the solution. This kind of convection was achieved with accelerating/decelerating rotation of crucible and a plate fixed on the bottom of the crucible. By optimizing conditions of rotation program patterns and the crucible design for the forced convection, the growth rate could almost be doubled while maintaining smooth morphology.

Abstract: An experiment sturdy has been carried out for jet impingement cooling on the spherically convex surface is the development of mechanism. The effect of curvature, Space between jet exit and target surface, and Reynolds number on heat transfer is investigated for around air jet on hemispherical surface. The flow at the jet exit has fully developed velocity profile. A uniform heat flux boundary is created on the heated surface. The experiments are performed for 5000<Re<25000, 2<L/d<10, and jet diameters ranging from 1.3, 2.1, 3.4, 4.0 and 5.2 cm. In the mean time effect of curvature on local heat transfer is negligible at the wall jet region corresponding to r/d>0.5. From the experimental results the variation of the D/d ratio with local Nusselt number (Nu_st) for various Reynolds numbers and various L/d ratios are plotted. The results show that Nu_st increase with increase in curvature and the effect of the curvature will high at high Reynolds number. i.e. Nu_st at Re=25000 is 25% higher than at Re= 5000 This may be attributed to an increase in curvature increases acceleration, & size of three dimensional counter rotating vortices at stagnation point and the increment of Reynolds number increases the jet momentum, and also enhances the vortices creation. Nu_st is peaking in the L/d ratio of 6 because of high turbulence intensity as this distance.

Abstract: This paper presents numerical study of turbulent nanofluid (Fe₃O₄ - water) flow in a square straight channel. An ANSYS FLUENT commercial software was employed to investigate the flow and thermal characteristic of the flow in the range of Reynolds number 10,000 to 50,000 and nanoparticle volume concentration from 0% to 2%. The results show that by increasing the Reynolds number, the Nusselt number increased for both pure water and nanofluid cases. The thermal conductivity and viscosity of the nanofluid were increased with an increase in the particle volume concentration and yields enhancement of heat transfer.

Abstract: The rapid development of lithium ion battery has provided a broad space for every profession and trade, but the temperature change of the lithium ion battery is relatively sensitive, should strengthen the lithium ion battery thermal management system. In this paper, using COMSOL MUTILPHYSICS software, the lithium-ion battery forced convection cooling numerical simulation research , comparing its temperature changes. We conclude: when forced convection temperature is high, the flow speed is high, the cooling effect is better; near the cooling entrance closer, the cooling effect is more obvious, and has important significance to the lithium ion battery radiating and rational utilization.

Abstract: The experimental study has been made to investigate heat transfer and pressure drop for air flow around finned flat tube banks in-line configurations with laminar forced convection. Measurements were conducted for twelve tubes in the flow direction, four tubes in the row. Four air velocity (0.2, 0.5, 0.8 and 2.0 m/s) identical to the Reynolds number, Re_Dh based hydraulic diameter was varied between 124 and 1238. The total heat flux supplies in all tubes change four times from 473.2 to 3871.7 W/m². The study results indicate that the average heat transfer coefficient, and the average Nusselt number, of all tubes has increased 113.6%–150.3% with Re_Dh numbers varying from 124 to 1238 at the fixed heat flux. Likewise, the friction factor decreases 57.7% with a Re_Dh number range 124 – 1238.

Abstract: Recently several experiments on directional solidification of Al-6.5wt.Si-0.93wt.%Fe (AlSi7Fe1) alloy were performed under terrestrial conditions and onboard the International Space Station (ISS) in the Materials Science Lab (MSL) with use of electromagnetic stirring and without it. Analysis of the samples showed that stirring with a rotating magnetic field lead to the accumulation of iron-rich intermetallics in the center of the sample and influenced the primary dendrite spacing while the secondary dendrite arm spacing were not affected. In the present paper the accumulation of the intermetallics b-Al₅SiFe in the center of the samples due to RMF stirring is demonstrated numerically and the evolution of primary and secondary dendrite arm spacing is discussed.

Abstract: Experiments are conducted to investigate heat transfer characteristics of finned loop heat pipe (FLHP) for heat input range from 20 W to 100 W. The experiments are carried out by manufacturing the FLHP, which the setup consists of a water tank with pump, a flat evaporator, condenser installed with two pieces of fans and air flow fins, two transportation lines (vapor and liquid lines), copper pipe sections for attachment of the thermocouples and power supply. The unique of the current experimental setup is the vapor and liquid lines of FLHP are made of transparent plastic tube to visualize the fluid flow patterns. In this study, the total thermal resistance (R_t) is estimated for both natural and forced convection modes under steady state condition, by varying the air velocity from 2 m/s to 10 m/s. The coolant velocity and heat input to achieve minimum R_t are found out and the corresponding effective thermal conductivity is calculated. The transient temperature distribution in the FLHP is also observed. The experimental observations are verified by simulation using Finite Element Method (FEM). The results reveal that the air velocity and power input have significant effects on the performance of FLHP. As the heat input and air velocity increase, total thermal resistance decreases.

Abstract: This paper established the thermal Lattice Boltzmann model of fluid flow and heat transfer, which is based on double lattice Boltzmann distribution model [. The temperature distribution adopted the higher accuracy velocity model. Based on this thermal lattice Boltzmann model, this paper simulated forced convection of circular tube fluid. Comparing the simulation results with the traditional CFD calculation results, we could find that the thermal lattice Boltzmann method have unique advantages in effectiveness and flexibility than the traditional calculation method.

Abstract: In this study, forced convective heat transfer is considered in channel over a backward facing step having a baffle on the top wall. Four different geometries with different expansion ratios and different type of baffles are numerically investigated. The study clearly shows that the geometry with expansion ratio 2 and solid baffle has the highest Nusselt number compared to other geometries. Considering both Nusselt number and skin friction coefficient for all four geometries clearly illustrated an increase in average Nusselt number by increasing the expansion ratio. This study clearly shows that mounting a slotted baffle at the top wall instead of a solid baffle caused a decline in average Nusselt number. It is also found that for geometry with expansion ratio of 3 and a slotted baffle on the top of the channel, skin friction coefficient in both bottom wall and step wall has its minimal compared to other geometries.

Abstract: Nanofluids are engineered colloids made of a base fluid and nanoparticles, which become potential candidate for next generation heat transfer medium. Nanofluids have higher thermal conductivity and single-phase heat transfer coefficients than their base fluids. The use of additives is a technique applied to enhance the heat transfer performance of base fluids. Recent articles address the unique features of nanofluids, such as enhancement of heat transfer, improvement in thermal conductivity, increase in surface volume ratio, Brownian motion, thermophoresis, etc. A complete understanding about the heat transfer enhancement in forced convection in laminar and turbulent flow with nanofluids is necessary for the practical applications. There are many controversies and inconsistencies in reported arguments and experimental results on various thermal characteristics such as effective thermal conductivity, convective heat transfer coefficient and boiling heat transfer rate of nanofluids. As of today, researchers have mostly focused on anomalous thermal conductivity of nanofluids. Although investigations on boiling, droplet spreading, and convective heat transfer are very important in order to exploit nanofluids as the next generation coolants, considerably less efforts have been made on these major features of nanofluids. This review summarizes recent research on fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows and identifies opportunities for future research.