Papers by Keyword: Convective Heat Transfer

Abstract: For the first time, the time dependences of the temperature of aluminum, zinc and zinc-aluminum alloys alloyed with II A group elements under spontaneous cooling mode were obtained; an anomalous course and two characteristic times of the cooling process were found, and their mechanism was explained; the temperature dependence of the thermophysical properties of the investigated metals and alloys was established; the temperature dependence of the coefficients of convective heat transfer and radiation of Al, Zn and Zn55Al and Zn5Al alloys was experimentally determined; the influence of the concentration of II A group elements and temperature on the heat capacity and thermodynamic functions of Zn55Al and Zn5Al alloys was revealed.

Abstract: The turbulent convective heat transfer in a transversely grooved tube of molten salt with natural convection effect has been numerically investigated. In general, the average Nusselt number with and without considering natural convection in transversely grooved tube was almost equal. According to the simulated results, the heat transfer coefficient of transversely grooved tube in upside region was lower than that of downside region. The effect of natural convection on unilateral heat transfer in transversely grooved tube was more obvious with lower Reynolds number and higher inlet temperature, and the effect of natural convection on unilateral heat transfer was lower with bigger groove deep.

Abstract: In order to meet the demand of heat rejection requirement of heavy-duty engine, a novel nanofluid heavy-duty coolant was developed in this paper by taking advantage of nanofluid heat transfer technique and organic acid technique. Comparing with conventional heavy-duty coolant, the heat transfer capacity increased more than 10%, which solved the problems of limited thermal conductivity and convective heat transfer performance. The coolant possessed the characteristics of a qualified engine coolant should have and could be a promising engine coolant.

Abstract: The aim of the research work describe in this paper is to investigate correlation of water, air massflow rate and calor fluks to heat transfer coefficient. The investigation was carried out toward a pipe section test developed from acrylic with diameter of 60 mm and 210 mm length, therefore, the buble can be easier to shoot. A concurrent water were flowed upward and air was injected from the bottom. The wall of the heater was heated using two thermocouple installed at the outer surfece of the heater. The fluid flow was measured using thermocouple installed along the annulus pipe. A heater with transparent tube diameter of 50 mm and 1800 mm length was also installed, and supplied with 1000 Watt electric power. Result of the experiment showed that heat transfer coefficient incresed along with the air massflow rate increased, and its decreased with the increasing of water mass flow rate. The maximum heat transfer coefficient of 4340,602 W/m² °C at electric fluck calor of 29582,448 W/m² was echieved on water volume flow rate of 3 lpm and 9 lpm of air volume rate.

Abstract: An experimental investigation was conducted to study the heat transfer and pressure drop characteristics of an array of divergent straight minichannels (DSM) and was compared with straight minichannels (SM). The experiment was conducted in hydro dynamically developed and thermally developing laminar and turbulent regimes. The minichannel heat sink array consisted of 15 rectangular channels machined on a 30x30mm² and 11mm thick Aluminium substrate. Each minichannel was of 0.9mm width, 1.8mm pitch and a depth of 1.3 mm at entrance and 3.3 mm at exit for increasing the cross sectional area. DI water and 0.5% and 0.8% volume concentrations of Al₂O₃/water nanofluid were used as working fluids. The Reynolds number was varied from 1000 to 3500; and the heat flux was maintained as 45kW/m². It was observed that the heat transfer performance of the DSM channel was higher than that of the SM channel.

Abstract: A finite element model was developed to simulate the 3-D velocity and temperature distributions in a vessel system including a bifurcated blood vessel and two branches. The effect of the angel between vessels and bifurcation ratio were taken into account, and the local Nusselt number at three typical radial angels and the mean Nusselt number on a section in the branching vessel were obtained. Results show that: the flow and temperature fields were highly unlike the distributions of a single vessel; the local Nusselt number were different at different radial angels; In the entrance region of the branching vessel the mean Nusselt number on a section was larger than that in a single vessel, and there was a maximum of mean Nusselt number whose value and location varied as the different furcating angel or bifurcation ratio; the mean Nusselt number decays rapidly at a small bifurcation ratio.

Abstract: According to kiln structure and material movement features, the transient heat conduction model of material bed and the contact heat transfer model at the interface of covered kiln wall and material bed are built. Considering their contribution to the convective heat transfer of material bed, the convective heat transfer coefficient between covered kiln wall and material bed is proposed, and its formula is obtained, with which the convective heat transfer between covered kiln wall and material bed can be calculated conveniently, so the heat transfer prediction within the rotary kiln can be done more easily.

Abstract: Convective heat transfer in microchannels of two-stage Y-branch bifurcation structures at different inlet velocities and branch angles were simulated, and the temperature, static pressure drop as well as the relationship between Reynolds Number (Re) and Nusselt Number (Nu) of fluid were compared and analyzed. The results indicate that the flow in microchannels with 30° branch angle has the minimum pressure drop for the velocities from 0.5 m/s to 2.5 m/s, while it comes at 60° for the velocities from 2.5 m/s to 3.5 m/s. It can also be found that the laminar-turbulent transition comes in advance compared with the common round channels. The critical Reynolds Number is found to be in 1997-2224, which is smaller than the known value of 2300. The Nu increases with increasing Re with a same trend for the different branch angles.

Abstract: Carbon nanotubes (CNTs) are said to be among the most potential materials in applications of nanodevices, nanocomposites and nanostructure due to their excellent mechanical and physical attributes. CNTs were first discovered by S. Iijima in 1991 where he has reported in his article the synthesis of needle-like tubes by using an arc-discharge evaporation. After the immense discovery, the number of research on CNTs has increased significantly, focusing on their mechanical characteristics, dynamics properties and applications in nanotechnology. This paper attempts to present a review of a quite number of publications on CNTs and their dynamic properties. The main topics covered in this review are the applications of CNTs, their dynamic characteristics including the modeling and simulation of vibrating CNTs, and finally the vibration modes of CNTs.

Abstract: With the convective heat transfer theory, numerical analysis of fluid-solid-heat coupling is implemented for the engine combustion chamber cooling structure based on finite element method and computational fluid dynamic method, thus to obtain valuable simulation results. Different components of the mesh generation method used which have different influences on the computational results are thought over during this analysis process, including different grid type, grid density and boundary layer meshes. Moreover, MPI parallel technique is also used to resolve the computation demands. The temperature distributions of the key parts in the cooling structure are investigated, which can be used as a significant reference for the thermal protection design of the engine combustion chamber.