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1.
The experimental data for heat transfer during nucleate pool boiling of saturated liquid metals on plain surfaces are surveyed and a new correlation is presented. The correlation is h = Cq0.7prm, where C and m are, respectively, 13.7 and 0.22 pr < 0.001 and 6.9 and 0.12 for pr > 0.001 (h is in W/m2 K and q in W/m2). This correlation has been verified with data for K, Na, Cs, Li, and Hg from 17 sources over the reduced pressure (pr) range of 4.3 × 10−6 to 1.8 × 10−2. The correlation of Subbotin et al. was found unsatisfactory, but a modified correlation was developed that also gives good agreement with most of the data.  相似文献   

2.
Strain rate and temperature effects on the flow stress of 304N stainless steel were investigated using data obtained from torsion tests on thin-walled tubular specimens, at given strain rates of between 10−3 and 10−1 with temperatures ranging from 83 to 296 K. Initially, the apparent strain rate sensitivity of the flow stress, obtained at test temperatures of 83, 153, 213, and 296 K, was examined. The strain dependence and the strain rate dependence of the mechanical threshold stress (the flow stress at O K) at strains less than 0.1 and at strain rates of 2.4 × 10−3 and 8.3 × 102 s−1, is also discussed. It was concluded from the experimental results that the mechanical threshold stress depends not only on the strain but also on the strain rate.  相似文献   

3.
Experimental measurements of heat transfer are made from the inner peripheral surface of a rotating test rig designed to be similar to a gas turbine high pressure compressor internal air system. The test rig comprises a number of annular discs sealed at their periphery by a shroud. An axial throughflow of cooling air enters the test rig and flows through the annular section between the disc bores and a central shaft. Tests were carried out for the following range of rotational speeds and axial throughflow rates: 540 < NR < 10,800 rev/min and (corresponding to the range of rotational and axial Reynolds numbers 4 × 105 < Re < 7.7 × 106 and 3.3 × 104 < Rez < 2.2 × 105).

The shroud Nusselt numbers are found to depend on the shroud Grashof number. They are relatively insensitive to changes in axial Reynolds number and two geometrically similar cavities give similar values of Nusselt number. The heat transfer from the shroud is governed by the mechanism of free convection. It is recommended that a modified form of a correlation for Rayleigh–Bénard convection in a gravitational force field be used, with appropriate modification, to predict shroud heat transfer.  相似文献   


4.
Experiments were made for the flow over two side-by-side normal plates for which the gap ratios are in the range 1.4–2.1 and the Teynolds numbers are at 6.6 × 103 and 1.8 × 104. At low gap ratios, i.e., 1.4–1.6. the gap flow appears always to be biased and flip-flops to the preferred side non-periodically with respect to time. As the gap ratio becomes larger, the percentage of time occupied by the gap flow in the biased state decreases and the non-biased state of the gap flow becomes prevalent. A comparison of the experimental results obtained under five free stream turbulence conditions further shows that the addition of artificial disturbance into the free stream promotes gap flow flopping at low gap ratios.  相似文献   

5.
The results of an experimental study of a temperature field and its statistical characteristics in turbulent water flow upon a sudden change of heat generation in the channel wall are reported. Measurements were performed in 5 mm × 40 mm, 10 mm × 40 mm, and 20 mm × 40 mm channels in the regions of thermal stabilization and stabilized heat transfer at Reynolds numbers of (0.8–6.8) × 104. The measurement results are generalized using a dimensionless time scale. The results of the calculation of heat transfer coefficients at unsteady heat transfer are presented.  相似文献   

6.
The general momentum equation for fluid flow within a porous medium is supposedly valid for any fluid-porous medium configuration. One of the main concerns of using the general equations refers to the inclusion of both inertia terms, namely, the convective inertia term and the Forchheimer term. In this study, we go beyond the important discussion about the correctness of including both terms in the general momentum equations by focusing upon the effect of the convective inertia term on the heat transfer results. The fluid-porous medium system considered here is a cavity bounded by solid surfaces with vertical walls maintained at constant but different temperatures. The natural convection problem is solved numerically, and the results are compared with a general theory developed by using the method of scale analysis. It is demonstrated that the convective inertia term effect upon the heat transfer results is minor for 0.01 ≤ Pr ≤ 1, 10 ≤ RaD ≤ 104, 10−8 ≤ Da ≤ 10−2, and porosities 0.4 and 0.8. It is also shown that, contrary to the general belief, the convective inertial effect upon the heat transfer within the cavity is minimized when the Prandtl number is reduced.  相似文献   

7.
An experimental investigation was carried out on the heat transfer due to a submerged slot jet of water impinging on a circular cylinder in crossflow. The cylinder diameter and the slot width are of the same order of magnitude, specifically Ds = 2.0 and 3.0 mm and Dc = 2.5 and 3.0 mm. The experimental apparatus allowed variation of the slot width, the cylinder diameter, and the distance from nozxle exit to heater. Conditions of impingement from the bottom (ascending flow) were taken into consideration as well as impingement from above (descending flow). The Nusselt number was determined as a function of Reynolds and Prandtl numbers in the range 1.5 × 103 < Re < 2.0 × 104, 2.7 < Pr < 7.0, and 1.5 ≤ z/Ds ≤ 10. The experimental data were correlated with a simple equation that fits 90% of the data with a precision of 20%.  相似文献   

8.
Computational and experimental study of annular photo-reactor hydrodynamics   总被引:1,自引:0,他引:1  
The performance of ultraviolet (UV) reactors used for water treatment is greatly influenced by the reactor hydrodynamics due to the non-homogeneity of the radiation field. Reliable modeling of the reactor flow structures is therefore crucial for the design process. In this study, the turbulent flow through two characteristic annular UV-reactor configurations, with inlets concentric (L-shape) and normal (U-shape) to the reactor axis, was investigated through computational fluid dynamic (CFD). The modeling results were evaluated with the velocity profiles from particle image velocimetry (PIV) experiments. The influence of mesh structure and density, as well as three turbulence models: Standard κ, Realizable κ, and Reynolds stress model (RSM), on the simulation results were evaluated. Mesh-independent solutions were achieved at mean cell volumes of 5 × 10−9 m3. The Realizable κ displayed the best overall match to the experimental PIV measurements. In general, the CFD models showed a close agreement with the experimental data for the majority of the reactor domain and captured the influences of reactor configuration and internal reactor structures on the flow distribution. The validated CFD hydrodynamic models could be integrated with kinetic and radiation distribution models for UV-reactor performance simulation.  相似文献   

9.
Over a range of Reynolds numbers from 0·6 × 105 to 1·75 × 105 tests were made on a seven rows deep tube bank. These tests were made using a specially instrumented porous cylinder which could be located in any position within the bank. Mass transfer through the porous surface simulating the condensation process in a surface condenser, was applied, and its effect on local parameters investigated. The distribution of static pressure and skin friction was determined around tubes in different rows in the bank. From these measurements, the pressure drag and friction drag were estimated. The total pressure drop across the bank was also measured.

Results showed that, for typical steam condenser loadings, the contribution of the pressure drag to the total drag does not change appreciably with suction. However, the skin friction contribution does change considerably with suction.  相似文献   


10.
Mean and fluctuating velocities have been measured in a sodium mixing layer experiment, i.e. in a fluid with very low Prandtl number (Pr10−2), with a miniature permanent-magnet velocity probe in the presence of strong temperature gradients. A mathematical model for the probe, based upon Faraday's law of induction and including thermoelectric as well as inertia effects due to the finite response time of thermocouples, is presented together with a new dynamic method to compensate for these effects. The sensitivity of the four different probes used in this experiment is in the range of 81–65 (μV/ms−1). Electrical pertubations arising from large-scale thermoelectric effects inside the test section and their influence on the velocity signal are also discussed. The electronic measurement system, combining low noise and high resolution, was specially developed to match the experimental requirements. With this system it was possible to measure velocity RMS-values down to 1 mm/s corresponding to a voltage of 100 nV, and mean velocities with an accuracy of about 6 mm/s. This paper deals with the peculiarities of the measurement technique and its performance, but does not analyze the experimental results, which will be presented in a separate publication.  相似文献   

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