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1.
This work experimentally studies the flow characteristics and forced convective heat transfer in a sintered porous channel that filled with sintered copper beads of three average diameters ( 0.830, and 1.163 mm). The pressure drop and the local temperature measurements can be applied to figure out the distributions of the friction coefficient and the heat transfer coefficient. Three sintered porous channels differ in the arrangement of obstacle blocks. Model A has no obstacle. Models B and C have five obstacle blocks facing down and up, respectively, in a sintered porous channel. The range of experimental parameters, porosity, heat flux, and effect of forced convection are 0.370 ≤ ɛ ≤ 0.385, q=0.228, 0.872, 1.862 W/cm2, and 200 ≤ Re d ≤ 800. The permeability and inertia coefficient of each of the three sintered porous channels are analyzed. The results for Model A agree with those obtained by previous investigations in C f distribution. The heat transfer of Model C exceeds that of Model A by approximately 20%. Finally, a series of empirical correlation equations were obtained for practical applications and engineering problems.  相似文献   

2.
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 Nu= 0.945(Pe 1/3) Fo–1/2.  相似文献   

3.
This study experimentally examines the forced convective flow over two sequentially heated blocks mounted on one principal wall of a channel. The experiments, involving mass transfer, were carried out via the naphthalene sublimation technique (NST). By virtue of the analogy between heat and mass transfer, the results can then be converted to determine the heat transfer. In the experiments, the block spacings were set at 2, 4, 6, 8, 12, 16, and 22 and the Reynolds numbers were set at 1300 and 104 which correspond to the laminar and the turbulent convective flow cases, respectively. Results show that the Sherwood number increases or decreases monotonically along the block surfaces in the laminar convection cases; while the hump and sharp increase in the Sherwood number can be found in the turbulent convection cases. This is attributed to the reattachment of the separating bubble and the flow impingement, respectively. Comparison between the experimental and numerical results is made and the effect of the block spacing on heat transfer is discussed.  相似文献   

4.
The present study introduces a new correlation predicting critical heat flux (CHF) for a saturated forced convective boiling with an impinging jet. The new correlation is able to predict all the CHF data inV-regime with a good accuracy of +-20% to which the correlations existing until now could not be applicable for 15l/?r<100 and D/d>36. The new correlation seems to support a new criterion of CHF mechanism applicable for not only pool boiling but also forced convective boiling, recently proposed by Katto and Haramura.  相似文献   

5.
The structure of free-convection flow in a plume channel formed as a result of melting above a local heat source placed on the basement of a solid mass is experimentally investigated. The channel shape and the flow pattern in it are functions of the relative power Ka = N/N 1, where N is the plume source power and N 1 is the heat removed to the surrounding mass. When the heat is withdrawn from the plume channel by heat conduction, the channel represents a system of convective cells on whose boundaries there are channel constrictions. The temperature fields and the cell flow patterns are investigated. For mantle plumes, such as the Hawaiian, Iceland, and Bouvet plumes and extended igneous provinces, the basement diameter and the values of the criterion Ka are determined.  相似文献   

6.
Nonsimilarity solutions for non-Darcy mixed convection from a vertical impermeable surface embedded in a saturated porous medium are presented for variable surface heat flux (VHF) of the power-law form. The entire mixed convection region is divided into two regimes. One region covers the forced convection dominated regime and the other one covers the natural convection dominated regime. The governing equations are first transformed into a dimensionless form by the nonsimilar transformation and then solved by a finite-difference scheme. Computations are based on Keller Box method and a tolerance of iteration of 10−5 as a criterion for convergence. Three physical aspects are introduced. One measures the strength of mixed convection where the dimensionless parameter Ra* x /Pe3/2 x characterizes the effect of buoyancy forces on the forced convection; while the parameter Pe x /Ra*2/3 x characterizes the effect of forced flow on the natural convection. The second aspect represents the effect of the inertial resistance where the parameter KU /ν is found to characterize the effect of inertial force in the forced convection dominated regime, while the parameter (KU /ν)(Ra*2/3 x /Pe x ) characterizes the effect of inertial force in the natural convection dominated regime. The third aspect is the effect of the heating condition at the wall on the mixed convection, which is presented by m, the power index of the power-law form heating condition. Numerical results for both heating conditions are carried out. Distributions of dimensionless temperature and velocity profiles for both Darcy and non-Darcy models are presented. Received on 26 May 1997  相似文献   

7.
We consider steady-state combined (forced and free) turbulent convection in a vertical circular channel in a uniform solid medium for the case in which a constant vertical temperature gradientis maintained in the solid mass, far from the channel. The velocity and temperature distributions are found, and the critical values of the Rayleigh number for axisymmetric and antisymmetric fluid motions are calculated. The problem is solved by the Galerkin method.Notation v(0) forced convection velocity - v(1) free convection velocity - v velocity with combination of forced and free convection - v average velocity across channel section - T temperature with combined forced and free convection - Tw channel wall temperature - y distance from channel wall - y* dimensionless distance from wall - r0 channel radius - r distance from centerline - vt turbulent viscosity - t turbulent thermal diffusivity - P0 averaged pressure corresponding to constant fluid ternperature - z coordinate along channel axis, directed upward - Q quantity of heat released by internal sources per unit fluid volume per unit time - fluid thermal conductivity (e for the surrounding mass) - R Reynolds number - R* Rayleigh number - P Prandtl number - G Grashof number - V* dynamic viscosity  相似文献   

8.
In this paper, a correlation for estimating the fin Nusselt number of natural convective heat sinks with vertically oriented plate-fins is suggested. For this purpose, extensive experimental investigations are performed for various channel widths, heights and input powers. A numerical simulation is conducted by using a commercial tool to verify the present experimental results and examine fluid flow and heat transfer characteristics of a natural convective heat sink. By comparison of the present study and the previous studies, it is shown that the present correlation is widely applicable for Elenbaas numbers between 0.5 and 2 × 106 and is more accurate than previous correlations. Based on an asymptotic approach, it is found that the optimal channel width is independent of the heat sink height but dependent of the heat sink length, the difference between the heat sink base and the ambient temperatures, and fluid property.  相似文献   

9.
The influence of free stream direction on mixed (natural and forced) convective heat transfer from a circular cylinder is investigated. The cylinder, which has an isothermal surface, is placed with its axis horizontal and normal to the oncoming flow. The free stream direction varies between the vertically upward (parallel flow) and the vertically downward (contraflow) directions. The investigation is based on the time integration of the unsteady, two-dimensional equations of motion and energy until reaching steady conditions. The study is limited to Reynolds numbers up to Re = 40 and Grashoff numbers of Gr = Re2. The results are compared with the available experimental data and the agreement is satisfactory.  相似文献   

10.
Enhancements of nucleate boiling critical heat flux (CHF) using nanofluids in a pool boiling are well-known. Considering importance of flow boiling heat transfer in various practical applications, an experimental study on CHF enhancements of nanofluids under convective flow conditions was performed. A rectangular flow channel with 10-mm width and 5-mm height was used. A 10 mm-diameter disk-type copper surface, heated by conduction heat transfer, was placed at the bottom surface of the flow channel as a test heater. Aqueous nanofluids with alumina nanoparticles at the concentration of 0.01% by volume were investigated. The experimental results showed that the nanofluid flow boiling CHF was distinctly enhanced under the forced convective flow conditions compared to that in pure water. Subsequent to the boiling experiments, the heater surfaces were examined with scanning electron microscope and by measuring contact angle. The surface characterization results suggested that the flow boiling CHF enhancement in nanofluids is mostly caused by the nanoparticles deposition of the heater surface during vigorous boiling of nanofluids and the subsequent wettability enhancements.  相似文献   

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