Flow and heat transfer measurements of film injectant from a row of holes with compound angle orientations

An experiment has been conducted on the flow and heat transfer characteristics of film coolant injected from a row of five holes with compound angle orientations of 35° inclination angle and 45° orientation angle. The Reynolds number number based on the mainstream velocity and injection hole diameter 3.58 x10⁴. Three-dimensional velocity, film cooling effectiveness and heat transfer coefficient data are presented at three different mass flux ratios of 0.5, 1.0 and 2.0. Flow entrainment has been found between the vortices generated by adjacent injectants. The injectant with compound angle orientation entrains not only the mainstream boundary layer flow but also the adjacent injectant. Because of the flow entrainment, the injectant. With compound angle orientation is characterized by a single vortex while two bound vortices are usually observed in the case of simple angle injection. The strength of the secondary flow depends strongly on the mass flux ratio, which shows significant influence on the film cooling effectiveness and heat transfer coefficient.     

Direct numerical simulation of flow characteristics and heat transfer enhancement in a rib-dimpled cooling channel

The present study reports the numerical investigation on the flow characteristics and heat transfer enhancement of the rib-dimpled channels. Two geometric variables were considered: the rib angle, θ, and the length between the rib center and the dimple rim, l. Nine cases were investigated by combining three different rib angles with three different lengths. Direct numerical simulations were conducted with a Reynolds number of 2800. As θ and l changed, the flow characteristics of the rib-dimpled channel were altered, which lead to different characteristics in the flow mixing and heat transfer rate. The span-wise rotating flow and the up-wash counter rotating vortices played an important role in the augmentation of heat transfer rate. The rib-dimpled channel with l = 0.15 and θ = 70° showed the maximum increase of 32 % in the volume goodness factor, in comparison with the general dimpled channel.

     

Numerical study on flow and heat transfer characteristics of air-jet cooling system

Journal of Mechanical Science and Technology - The present study aims to numerically analyze the cooling characteristics of the air-jet array in designing more efficient air-cooling system. Heat...     

A numerical study on the flow and heat transfer characteristics in a noncontact glass transportation unit

Vertical sputtering systems are key equipment in the manufacture of liquid crystal display (LCD) panels. During the sputtering process for LCD panels, a glass plate is transported between chambers for various processes, such as deposition of chemicals on the surface. The minimization of surface scratches and damage to the glass, the rate of consumption of gas, and the stability of the floating glass-plate are key considerations in the design of a gas pad. To develop new, non-contact systems of transportation for large, thin glass plates, various shapes of the nozzle of a gas pad unit were considered in this study. In the proposed nozzle design, negative pressure was used to suppress undesirable fluctuations of the glass plate. After the nozzle’s shape was varied through numerical simulations in two dimensions, we determined the optimal shape, after which three-dimensional analyses were carried out to verify the results from the two-dimensional analyses. The rate of heat transfer from the glass plate, as a result of the gas jet, was also investigated. The average Nusselt number at the glass surface varied from 22.7 to 26.6 depending on the turbulence model, while the value from the correlation for the jet array was 23.5. It was found that the well-established correlation equation of the Nusselt number for the circular jet array can be applied to the cooling of the glass plates.     

A numerical study of the heat transfer and fluid flow of micro-channeled water block for computer CPU cooling

Thermal and fluid flow characteristics of a micro-channeled water-block with pass variations in 8 samples were studied. The results of a numerical analysis using ANSYS CFX-11 were compared with the results of experiments. The numerical analysis and experiments were conducted under an input power of 150 W, inlet temperature of 35°C and mass flow rates of 0.7 ∼ 2.0 kg/min. The numerical results showed reasonably good agreement, within 3–5%, with the experimental results. Also, the numerical results showed that 2-pass samples give better performance than 1-pass samples in terms of heat transfer. However, the pressure drop for 2-pass samples was relatively higher.     

An experimental study on the heat transfer and pressure drop characteristics of electronics cooling heat sinks with FC-72 flow boiling

Journal of Mechanical Science and Technology - An experimental study was performed to measure FC-72(C6F14) flow boiling heat transfer and pressure drop in heat sinks for electronics cooling. The...     

A numerical study on dynamic characteristics of a catenary

Dynamic characteristics of a catenary that supplies electrical power to high-speed railway is investigated. The catenary is a slender structure composed of repeating spans. Each span is in turn composed of the contact and messenger wires connected by the hangers in regular intervals. A finite element based dynamic model is developed, and numerical simulations are performed to determine the dynamic characteristics of the catenary. The influence of the structural parameters on the response characteristics is investigated. The structural parameters considered include tension on the contact and messenger wires, stiffness of the hangers, and the hanger and span spacing. The hanger characteristics are found to be the dominant factors that influence the overall dynamic characteristics of the catenary.     

An experimental study on heat transfer characteristics with turbulent swirling flow using uniform heat flux in a cylindrical annuli

An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000-70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.     

螺旋槽管内传热及阻力特性的数值研究

为了深入分析螺旋槽管内传热及阻力特性,基于Fluent对16根具有不同结构参数的单头螺旋槽管进行了数值研究。分析了雷诺数Re、槽深e和螺距p对螺旋槽管内传热及阻力特性的影响,结果表明,在研究的雷诺数Re范围内(10000~45000),螺旋槽管的努塞尔数Nu是光管的1.34~2.01倍,且随Re的增加而增加;阻力系数f是光管的2.01~6.40倍,随Re的增加而减小;Nu和f随e的增加而增加,随p的增大而减小。通过回归分析,得到了螺旋槽管传热和阻力的准则关联式,供相关工程设计参考。     

Numerical study on flow characteristics at blade passage and tip clearance in a linear cascade of high performance turbine blade

A numerical analysis has been conducted in order to simulate the characteristics of complex flow through linear cascades of high performance turbine blade with/without tip clearance by using a pressure-correction based, generalized 3D incompressible Navier-Stokes CFD code. The development and generation of horseshoe vortex, passage vortex, leakage vortex, tip vortex within tip clearance, etc. are clearly identified through the present simulation which uses the RNG k-ε turbulent model with wall function method and a second-order linear upwind scheme for convective terms. The present simulation results are consistent with the generally known tendency that occurs in the blade passage and tip clearance. A 3D model for secondary and leakage flows through turbine cascades with/without tip clearance is also suggested from the present simulation results, including the effects of tip clearance height.     

A numerical study of the fluid flow and heat transfer around a single row of tubes in a channel using immerse boundary method

The analysis of the time-dependent and two-dimensional fluid flow and heat transfer around a single row of tubes in a channel is performed numerically. Due to its fundamental significance and practical importance, aerodynamic and heat transfer characteristics of tube bundle have been paid great attention by many researchers. In the present study, the immersed boundary method is applied by using a Cartesian grid system. Numerical solution for the governing equations of mass, momentum and energy conservation is obtained with the finite volume method. To validate the numerical approach with the immersed boundary method, the results have been compared with published data. The generation and evolution of vortical structures, wake interactions and their effects on the drag, lift and heat transfer are analyzed at different Reynolds numbers. The effect of hydraulic boundary layer development on the fluid flow and heat transfer is also investigated.     

Measurement and simulation of fuel injection pipe pressure and study of its effect on the heat release in a direct injection diesel engine

Fuel injection pipe pressures are measured and simulated to study the effect of fuel injection system characteristies on the heat release in a direct injection diesel engine. The fuel injection simulation is based on a linear model. The governing equations are solved by the finite difference method. The measured fuel pipe pressures and the simulated fuel pipe pressures matched well to each other except for the interval when the nozzle is closing. The effects of the fuel pipe length and the nozzle opening pressure are tested. The longer fuel pipe length causes proportional retardation of the fuel injection time. The higher nozzle opening pressure results in increase of the maximum fuel pipe pressure and shorter combustion duration.     

Numerical simulation of fully developed flow and heat transfer characteristics in a curved tube with pulsating pressure gradient

Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.     

A study of sliding between rollers and races in a roller bearing with a numerical model for mechanical event simulations

A numerical model of a roller bearing is presented in this paper. These simulations provide us with the spatial and time distributions of stress and strain values, as well as all the nodal displacements at every time step. The model was developed with the finite element method (FEM) for mechanical event simulations (MES) with the commercial code Algor^TM. The model has been validated by verifying that the contact force distributions correspond to those predicted by the analytical model of Harris-Jones.As an application, a study of sliding between the rollers and the races has been carried out. For each roller, a rolling zone can be defined in which local sliding (computed between two consecutive time steps) is negligible. According to the simulations, we conclude that the rolling zone is practically the same for all the rollers in the same simulation; that this rolling zone is smaller than the corresponding load zone, and that rolling and load zones are angularly centered with respect to each other.     

A study on the behavior characteristics of diesel spray by using a high pressure injection system with common rail apparatus

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 22 MPa to 112 MPa using a high pressure injection system (ECD-U2). Also, we conducted simulation study by modified KIVA-II code. The results of simulation study are compared with experimental results. The images of liquid and vapor phase for free spray were simultaneously taken by exciplex fluorescence method. As experimental results, the vapor concentration of injected fuel is leaner due to the increase of atomization in the case of the high injection pressure than in that of the low injection pressure. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.