Transient Forced Convection Heat Transfer Research Articles

1811 増加熱入力による気流中の水平平板発熱体過渡熱伝達(G06-2 伝熱(2),G06 熱工学)

Forced convection transient heat transfer for helium gas at various periods of exponential increase in heat input to a horizontal plate (ribbon) was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over a horizontal plate. The gas flow velocities ranged from 4 to 10m/s, the gas temperatures ranged from 313 to 353K, and the periods of heat generation rate, τ, ranged from 46ms to 17s. Empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was obtained that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function.

F213 指数関数状増加熱入力に伴う水平平板発熱体におけるヘリウムガスの強制対流過渡熱伝達(強制対流)

Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a horizontal plate (ribbon) was theoretically studied. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. The values of numerical solution for surface temperature and heat flux were compared and discussed with authors' previous experimental data. It was clarified that the values of numerical solutions for surface temperature and heat flux at the velocity of 6m/s agree well with the experimental data, though they show some differences at other velocities.

Transient Forced Convection Heat Transfer for Helium Gas Flowing Over a Horizontal Plate

Transient heat transfer coefficients for helium gas flowing over a horizontal plate (ribbon) were measured under wide experimental conditions. The platinum plate with a thickness of 0.1 mm was used as test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q{sub 0}exp(t/t). The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate, t, ranged from 50 ms to 17 s. The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period t longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The dependence of transient heat transfer on the gas flowing velocity becomes weaker when the period becomes very shorter. The gas temperature in this study shows little influence on the heat transfer coefficient. Empirical correlation for quasi-steady-state heat transfer was obtained based on the experimental data. (authors)

Transient convective heat transfer to water near the critical region in a vertical tube

Numerical analysis has been carried out to investigate transient forced convective heat transfer to water near the critical region in developing flow through a vertical tube. With large variations of thermophysical properties such as density, specific heat, viscosity, and thermal conductivity near the thermodynamic critical point, heat transfer in the tube is strongly coupled with fluid flow. Buoyancy force parameter has also large variation with fluid temperature and pressure in the tube. Time dependent characteristics of fluid velocity, temperature, and heat transfer coefficient with water properties are presented and analyzed. Transient Nusselt and Stanton number distributions along the tube are also compared for various pressures in the tube. Because of heat transfer from the wall transition behavior from liquid-like phase to gas-like phase of heat transfer coefficient occurs when the fluid passes through pseudocritical temperature region in the tube. Turbulent viscosity ratio also has steep variation near the pseudocritical temperature close to the wall.

Effect of flow geometry parameters on transient heat transfer for turbulent flow in a circular tube with baffle inserts

The effect of the flow geometry parameters on transient forced convection heat transfer for turbulent flow in a circular tube with baffle inserts has been investigated. The characteristic parameters of the tubes are pitch to tube inlet diameter ratio H/ D = 1, 2 and 3, baffle orientation angle β = 45°, 90° and 180°. Air, Prandtl number of which is 0.71, was used as working fluid, while stainless steel was considered as pipe and baffle material. During the experiments, different geometrical parameters such as the baffle spacing H and the baffle orientation angle β were varied. Totally, nine types of baffle inserted tube were used. The general empirical equations of time averaged Nusselt number and time averaged pressure drop were derived as a function of Reynolds number corresponding to the baffle geometry parameters of pitch to diameter ratio H/ D, baffle orientation angle β, ratio of smooth to baffled cross-section area S o/ S a and ratio of tube length to baffle spacing L/ H were derived for transient flow conditions. The proposed empirical correlations were considered to be applicable within the range of Reynolds number 3000 ⩽ Re ⩽ 20,000 for the case of constant heat flux.

Theoretical and Experimental Studies on Transient Heat Transfer for Forced Convection Flow of Helium Gas over a Horizontal Cylinder

Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input (Q0exp(t/τ)) to a horizontal cylinder (heater) was theoretically and experimentally studied. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was clarified that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The values of numerical solution for surface temperature and heat flux agree well with the experimental data for the cylinder diameter of 1mm. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over horizontal cylinders under wide experimental conditions. The platinum cylinders with diameters of 1.0mm, 0.7mm, and 2.0mm were used as test heaters. The gas flow velocities ranged from 2 to 10m/s, and the periods ranged from 50ms to 15s. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1s, and it becomes higher for the period shorter than around 1s. The heat transfer shifts to the quasi-steady-state heat transfer for longer periods and shifts to the transient heat transfer for shorter periods. The transient heat transfer coefficients show significant dependence on cylinder diameters, there are higher for smaller cylinder diameters. The empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data.

An experimental and numerical investigation of heat transfer during technical grade paraffin melting and solidification in a shell-and-tube latent thermal energy storage unit

The latent thermal energy storage system of the shell-and-tube type during charging and discharging has been analysed in this paper. An experimental and numerical investigation of transient forced convective heat transfer between the heat transfer fluid (HTF) with moderate Prandtl numbers and the tube wall, heat conduction through the wall and solid–liquid phase change of the phase change material (PCM), based on the enthalpy formulation, has been presented. A fully implicit two-dimensional control volume Fortran computer code, with algorithm for non-isothermal phase transition, has been developed for the solution of the corresponding mathematical model. The comparison between numerical predictions and experimental data shows good agreement for both paraffin non-isothermal melting and isothermal solidification. In order to provide guidelines for system performance and design optimisation, unsteady temperature distributions of the HTF, tube wall and the PCM have been obtained by a series of numerical calculations for various HTF working conditions and various geometric parameters, and the thermal behaviour of the latent thermal energy storage unit during charging and discharging has been simulated.

Experimental study of transient forced convection heat transfer from simulated electronic chips

Experiments are performed to study the single-phase transient forced convection heat transfer on an array of four in-line, flush-mounted simulated electronic chips in a vertical rectangular channel. Water is the coolant media and the flow covers the wide range of laminar flow regime with Reynolds number, based on heat source length, from 800 to 2,625. The heat flux ranges from 1 W/cm2 to 7 W/cm2. The heat transfer characteristics are studied and correlations are presented. The transient correlation for overall data recommended is Nul= 0.945(Pel1/3) Fo−1/2.

Second law analysis of transient heat transfer for turbulent flow in a circular tube with baffle inserts

This paper presents the results of an experimental investigation of transient forced convective heat transfer for turbulent flow of nine circular tubes with baffle plate inserts using different pitch to tube inlet diameter ratios and baffle orientation angles in the range of Reynolds number 3000≤Re≤20000 in the case of constant heat flux. The characteristic parameters of the tubes are: pitch to tube inlet diameter ratio H/D = 1, 2 and 3; baffle orientation angle β = 45, 90 and 180 degree. Air, having a Prandtl number of 0.71 was used as the working fluid, while stainless steel was considered as the pipe material. The data show that unsteady entropy generation numbers for the baffled tubes are higher than those from the steady one. A generalised correlation for the unsteady entropy generation number relative to the steady dimensional entropy generation number for the baffle inserted tubes has been developed.

1203 ヘリウムガスの強制対流過渡熱伝達の数値解析(GS-6 強制対流・沸騰,研究発表講演)

1203 ヘリウムガスの強制対流過渡熱伝達の数値解析(GS-6 強制対流・沸騰,研究発表講演)

Study of transient forced convection heat transfer from discrete heat sources in a FC-72 cooled vertical channel

Experiments are performed to study the transient forced convection heat transfer from a four-in-line chip module that are flush-mounted to on one wall of a vertical rectangular channel using FC-72 as coolant. The flow covers the wide range of laminar flow regime with Reynolds number based on heat source length, from 800 to 2625. The heat flux ranges from 1 to 7 W⋅cm −2. The heat transfer characteristics are studied and correlations are presented. The transient correlation for overall data recommended is Nu ℓ = 0.776 ( Pe ℓ 1 / 3 ) Fo −0.74 . Finally the data obtained from FC-72 are compared with the data from water coolant and found that the Nusselt number data from FC-72 are higher than those from water.

Temperature regulator unit for fluid flow in a channel using phase change material

A numerical study was conducted to evaluate the thermal characteristics of a temperature regulator unit (TRU). The unit employs a phase change material (PCM) to stabilize the temperature of fluid flow in a channel. The PCM is placed outside the channel to dynamically absorb or release thermal energy to the channel flow. Melting and solidification of the PCM and transient forced convection heat transfer for the fluid are solved as a conjugate problem. A two-dimensional finite element model was developed to predict the performance of the TRU under constant and cyclic flow inlet temperatures. The results show that the unit was effective in reducing the flow exit temperature for a significant amount of time when there is a sudden temperature jump of the flow at the inlet. In addition, there was a substantial reduction in temperature fluctuations at the flow exit when a cyclic flow inlet temperature is applied. A parametric study was conducted to assess the effect of different design parameters, such as the effect of the Reynolds number and PCM quantity in the system.

An Experimental Study of Transient Heat Transfer From Discrete Heat Sources in Water Cooled Vertical Rectangular Channel

Experiments are performed to study the single-phase transient forced convection heat transfer on an array of 4×1 flush-mounted discrete heat sources in a vertical rectangular channel during the pump-on transient operation. Water is the coolant media and the flow covers the wide range of laminar flow regime with Reynolds number, based on heat source length, from 800 to 2625. The applied uniform heat flux ranges from 1 to 7W∕cm2. For flush-mounted heaters the heat transfer characteristics are studied and correlations are presented for four chips as well as for overall data in the transient regime. The experimental results indicate that the heat transfer coefficient is affected strongly by the number of chips and the Reynolds number. Finally the general impacts of heat source protrusions (B=1, 2 mm) on heat transfer behavior of four chips are investigated by comparing the results obtained from flush-mounted (B=0) heaters.

618 水平円柱におけるヘリウムガスの定常及び非定常強制対流熱伝達における発熱率上昇周期及び試験発熱体直径の影響(GS-6 熱工学(2))

The knowledge of forced convection transient heat transfer at various periods of exponential increase of heat input to a heater is important as a database for understanding the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity. The transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder were measured using a forced convection test loop. The platinum heaters with diameters of 0.7mm, 1.0mm, 2.0mm are heated by electric current with an exponential increase of Q_0exp(t/π). It was clarified that the heat transfer coefficient decreases when the diameter of test heater becomes larger, and it increases when the diameter of test heater becomes smaller. Semi-empirical correlations for quasi-steadystate and transient heat transfer were developed based on the experimental data.

Analytical solution for conjugated heat transfer in pipes and ducts

The conjugated transient forced convection heat transfer for laminar, thermally developing, steady slug flow of a Newtonian fluid of constant thermal properties in semi-infinite pipes and ducts is considered. An analytical solution for three cases, namely (1) steady state, (2) transient with negligible axial conduction in the wall and (3) early stages of time, is obtained.

Transient Heat Transfer for Forced Convection Flow of Helium Gas.

The knowledge of forced convection transient heat transfer at various periods of exponential increase of heat input to a heater is important as a database for understanding the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity. The transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder were measured using a forced convection test loop. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponential increase of Q 0 exp(t/r)

水平円柱に直交した低レイノルズ数領域の種々気体の過渡強制対流熱伝達

水平円柱に直交した低レイノルズ数領域の種々気体の過渡強制対流熱伝達

Transient boundary-layer heat transfer from a flat plate subjected to a sudden change in heat flux

We examine the transient forced convection heat transfer from a fixed, semi-infinite, flat plate situated in a fluid which, at large distances, is moving with a constant velocity parallel to the plate. Both the fluid and the plate are initially at a constant temperature and the transients are initiated when the zero heat flux at the plate is suddenly changed to a constant value. The thermal boundary-layer equations are solved using numerical techniques to extend a series which is valid for small times and describe fully the development from the initial unsteady state solution (small times) to the ultimate steady state solution (large time).

Transient forced convection heat transfer from a circular cylinder embedded in a porous medium

Studies of the transient heat transfer past a circular cylinder in a steady-state viscous flow are presented for some fluid saturated fibrous porous media. Numerical results have been obtained according to the Darcy-Brinkman model by means of the finite element method. Analysis of the influence of the Darcy and Peclet numbers on the mean Nusselt number exhibits the successive conduction, transition and convection regimes. The duration necessary to reach the steady-state convection heat transfer appears as a function of the Peclet and Darcy numbers.

Transient forced convection heat transfer in a vertical rib-heated channel using a turbulence promoter

An experimental investigation for transient forced convection heat transfer in a vertical rib-heated channel with a turbulence promoter has been systematically performed. Parametric studies including the steady-state convective heat flux, channel inlet velocity, channel spacing, and promoter location and height on transient heat transfer performance in a vertical rib-heated channel have been explored. A generalized distribution for transient convective heat flux is proposed; the channel inlet velocity is verified to be the most significant parameter affecting transient convective heat flux and Nusselt number distributions. Besides, the use of a turbulence promoter can effectively enhance transient heat transfer performances for all the ribs in both the entrance and the fully-developed regions of the channel. Furthermore, the present results reveal that the effect of channel inlet velocity is more significant on the heat transfer performance of ribs in the entrance region than in the fully-developed region of the channel, while the effect of promoter height is reverse. The effect of promoter height compared with that of promoter location has more significance on heat transfer performance in the fully-developed region.