Pressure Drop In Rectangular Channel Research Articles

Research on frictional pressure drop of air-water Co-current upward flow in vertical rectangular channels with different sizes

An experiment of air-water two-phase co-current upward flow has been conducted in adiabatic vertical channels under atmospheric conditions to investigate the frictional pressure drop affected by cross-sectional sizes of rectangular channels. Four channels with a cross-section of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm, 10 × 100 mm were selected, and the superficial velocities of water and air were 0.25–3 and 0–20 m/s, respectively. The void fraction was measured by flat electrodes. Based on the Lockhart-Martinelli and Chisholm correlations, the result shows that with the increase of the hydraulic diameter of the channel, the parameter C rises to 28. In this study, the mechanism of frictional pressure drop was analyzed, and a new model was proposed based on the Chisholm model. In addition, the other frictional multiplier model was proposed based on the effects of void fraction, Reynolds number, and hydraulic diameter. Both of the models proposed in this study can predict the frictional pressure drop in rectangular channels well with a high accuracy, and the errors are below 15% in most conditions.

Heat transfer and pressure drop in rectangular channels with crossing fins (a Review)

Channels with crossing finning find wide use in the cooling paths of high-temperature gas turbine blade systems. At different times, different institutions carried out experimental investigations of heat transfer and pressure drop in channels with coplanar finning of opposite walls for obtaining semiempirical dependences of Nusselt criteria (dimensionless heat-transfer coefficients) and pressure drop coefficients on the operating Reynolds number and relative geometrical parameters (or their complexes). The shape of experimental channels, the conditions of experiments, and the used variables were selected so that they would be most suited for solving particular practical tasks. Therefore, the results obtained in processing the experimental data have large scatter and limited use. This article considers the results from experimental investigations of different authors. In comparing the results, additional calculations were carried out for bringing the mathematical correlations to the form of dependences from the same variables. Generalization of the results is carried out. In the final analysis, universal correlations are obtained for determining the pressure drop coefficients and Nusselt number values for the flow of working medium in channels with coplanar finning.

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

Experimental investigation of the two-phase flow regimes and pressure drop in horizontal mini-size rectangular test section

Abstract An experimental study was conducted in order to investigate two-phase flow regimes and fully developed pressure drop in a mini-size, horizontal rectangular channel. The test section was machined in the form of an impacting tee junction in an acrylic block (in order to facilitate visualization) with a rectangular cross-section of 1.87-mm height on 20-mm width on the inlet and outlet sides. Pressure drop measurement and flow regime identification were performed on all three sides of the junction. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. Accuracy of the pressure-measurement technique was validated with single-phase, laminar and turbulent, fully developed data. Two-phase experiments were conducted for eight different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations for the fully developed two-phase pressure drop in rectangular channels with similar sizes. Wide deviations were found among these correlations, and the correlations that agreed best with the present data were identified.

Experimental investigation on frictional pressure drop of water in vertical rectangular channel

Experimental investigation on saturated flow boiling frictional pressure drop was made during a phase-change process with water. The outlet pressure ranged from 12.1 to 16.1MPa, mass fluxes from 500 to 1501kg/(m2s), heat flux from 737 to 1211kW/m2, and average quality in test section from 0.05 to 0.38. The rectangular channel had the following dimensions: gap size 2mm, width 40mm, and heated length 1000mm. The experiments were performed with the channel oriented uprightly.Analysis of the experimental data showed that the effects of pressure, mass flux, and quality on frictional pressure drop agreed with those of a conventional channel. Seven state-of-the-art correlations for conventional channel or rectangular channel were evaluated, but they failed to predict the experimental data. According to the results, the quality was an important parameter on predicting frictional pressure drop for steam–water fluid. The Nconf (Nconf=(1/Dh)(4σ/(g(ρl−ρg))) could not offer any advantage for the present experiment condition. A new correlation for two-phase frictional pressure drop in rectangular channel was developed on the basis of C coefficient method, all the data were within ±15% of error of prediction. The mean deviation was 3.4%.

Endwall heat transfer and pressure drop in rectangular channels with attached and detached circular pin-fin array

Endwall heat transfer and pressure drop characteristics in four rectangular channels with a channel aspect ratio of 4 and the staggered arrays of circular pin-fins with four clearances ( C) between pin-tips and the measured endwall of 0, 1/4, 1/2 and 3/4 pin-diameter ( d) are examined comparatively at Reynolds numbers ( Re) of 10,000, 15,000, 20,000, 25,000 and 30,000 to determine the effects of pin-tip leakages on the endwall heat transfer and on channel inlet-to-exit pressure drops. The accelerated flows through pin-to-endwall clearances modify the protrusion-endwall interactions that affect the horseshoe vortices as well as the downstream wakes and shear layer separations. By way of increasing C/ d ratio from 0 to 3/4, the area averaged endwall Nusselt numbers decrease with substantial reductions in channel inlet-to-exit pressure drops. The endwall heat transfer level with detached pin-fins at C/ d = 1/4 is somewhat less than that with attached pin-fins but the pressure drop coefficient of the former is much lower than that of the later, which leads to the highest thermal performance factor among the four comparative cases in the Re range examined by this study. A set of correlations that evaluate the area averaged endwall Nusselt number and the pressure drop coefficient with Re and C/ d as the controlling parameters are derived.

Heat transfer and pressure drop in rectangular channel with compound roughness of V-shaped ribs and deepened scales

A novel heat transfer enhancement (HTE) roughness with V-shaped ribs and deepened scales is devised. Performances of heat transfer and pressure drop in a rectangular channel fitted with such HTE surfaces are experimentally examined for both forward and backward flows in the Re range of 1000–30000. Relative to the smooth-walled pipe flow conditions, HTE ratios for the present test channel with forward and backward flows, respectively, reach 9.5–13.6 and 9–12.3 for laminar flows and 6.8–6.3 and 5.7–4.3 for turbulent flows. Comparisons of heat transfer data, pressure-drop measurements and thermal performance factors with previous results collected from varieties of HTE devices demonstrate the superiorities of this compound HTE device. The decrease of HTE ratio as Re increases for turbulent flows, which is a common setback for several HTE elements, is almost diminished in the channel fitted with present compound HTE surfaces. Experimental correlations of heat transfer and friction coefficient for the tested channel with forward and backward flows are derived for design applications.

Heat transfer performance comparisons of five different rectangular channels with parallel angled ribs

This paper systematically presents the results of heat transfer and friction factor data measured in five short rectangular channels with turbulence promoters. The project investigated the combined effects of the channel aspect ratio, rib angle-of-attack, and flow Reynolds number on heat transfer and pressure drop in rectangular channels with two opposite ribbed walls. The channel aspect ratio (width-to-height, W/ H, ribs on side W) varied from 1 4 to 1 2 , to 1, 2. and 4, while the corresponding rib angles-of-attack a were 90°, 60°, 45°, and 30°, respectively. The Reynolds number range was 10,000–60,000. The results suggest that the narrow aspect ratio channels ( W/ H < 1) give much better heat transfer performance than the wide aspect ratio channels ( W/ H > 1). For the square channel ( W/ H = 1), the 60° 45° angled ribs provide the best heat transfer performance. For the narrow aspect ratio channel ( W/H = 1 4 or 1 2 ), the 45° 60° angled ribs are recommended while the 30° 45° angled ribs are better for wide aspect ratio channels ( W/ H = 4 or 2).