Heat Transfer and Pressure Drop Characteristics Induced by a Slat Blockage in a Circular Tube

1980 ◽  
Vol 102 (1) ◽  
pp. 64-70 ◽  
Author(s):  
E. M. Sparrow ◽  
K. K. Koram ◽  
M. Charmchi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Pipe Flow ◽  
Turbulent Pipe Flow ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Cross Sectional ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Flow Experiments

Complementary heat transfer and fluid flow experiments were performed to determine transfer coefficients and pressure drops associated with the presence of a slat-like blockage in a tube. Water was the working fluid for the heat transfer studies (Pr = 4), while for the fluid flow experiments, which were performed under isothermal conditions, air was employed. The flow was turbulent in all cases, with the Reynolds number ranging from 10,000 to 60,000. Three blockage elements were used which respectively blocked 1/4, 1/2, and 3/4 of the tube cross-sectional area. Downstream of the blockage, heat transfer coefficients were measured around the circumference of the tube as well as along its length. The heat transfer coefficients in the region just downstream of the blockage were found to be several times as large as those for a corresponding conventional turbulent pipe flow. With increasing downstream distance, the coefficients diminish and thermal development is completed (to within five percent) at about 10, 15, and 18 diameters from the respective blockages. The blockage-induced circumferential variations of the heat transfer coefficient are dissipated by about five diameters. The pressure losses induced by the blockage are high, with values for the respective blockages that are 1.2, 5.2, and 33.2 times the velocity head in the pipe flow in which the blockage is situated. These losses are comparable to those for a gate valve.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

An Experimental Investigation of Condensation Heat Transfer Coefficients and Pressure Drops of Refrigerants Inside Multiport Mini-channel Tubes

2017 ◽  
Vol 25 (02) ◽  
pp. 1750013 ◽  
Author(s):  
Pham-Quang Vu ◽  
Kwang-Il Choi ◽  
Jong-Taek Oh ◽  
Honggi Cho
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients

The condensation heat transfer coefficients and pressure drops of R410A and R22 flowing inside a horizontal aluminum multiport mini-channel tube having 18 channels are investigated. Experimental data are presented for the range of vapor quality from 0.1 to 0.9, mass flux from 50 to 500[Formula: see text]kg/m2s, heat flux from 3 to 15[Formula: see text]kW/m2 and the saturation temperature at 48[Formula: see text]C. The pressure drop across the test section was directly measured by a differential pressure transducer. At a small scale, the noncircular cross-sections can enhance the effect of the surface tension. The average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux. Under the same test conditions, the heat transfer coefficients of R22 are higher than those for R410A, the pressure drops for R410A are 7–19% lower than those of R22. The lower pressure drop of R410A has an important advantage as an alternative working fluid for R22 in air-conditioning and heat pump systems.

Heat Transfer in Rotating Serpentine Coolant Passage With Ribbed Walls at Low Mach Numbers

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Shang-Feng Yang ◽  
Je-Chin Han ◽  
Salam Azad ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Low Mach Number ◽  
Heat Transfer Coefficients ◽  
Rotation Numbers ◽  
Wide Range ◽  
Mach Numbers

This paper experimentally investigates the effect of rotation on heat transfer in typical turbine blade serpentine coolant passage with ribbed walls at low Mach numbers. To achieve the low Mach number (around 0.01) condition, pressurized Freon R-134a vapor is utilized as the working fluid. The flow in the first passage is radial outward, after the 180 deg tip turn the flow is radial inward to the second passage, and after the 180 deg hub turn the flow is radial outward to the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers up to 0.6 and Reynolds numbers from 30,000 to 70,000. Heat transfer coefficients were measured using the thermocouples-copper-plate-heater regional average method. Heat transfer results are obtained over a wide range of Reynolds numbers and rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Regional heat transfer coefficients are correlated with Reynolds numbers for nonrotation and with rotation numbers for rotating condition, respectively. The results can be useful for understanding real rotor blade coolant passage heat transfer under low Mach number, medium–high Reynolds number, and high rotation number conditions.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

scholarly journals Experimental Study of Forced Convective Heat Transfer in a Coiled Flow Inverter Using TiO2–Water Nanofluids

2020 ◽  
Vol 10 (15) ◽  
pp. 5225
Author(s):  
Barbara Arevalo-Torres ◽  
Jose L. Lopez-Salinas ◽  
Alejandro J. García-Cuéllar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Thermal ◽  
Convective Heat Transfer Coefficients

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed.

Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity With and Without the Trailing-Edge Cooling Holes

2014 ◽  
Author(s):  
Mohammad Taslim ◽  
Joseph S. Halabi
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Flow Direction ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Cross Sectional ◽  
Heat Transfer Coefficients ◽  
Cfd Models ◽  
Cooling Cavity ◽  
Rib Roughened

Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Realizable k–ε turbulence model in conjunction with enhanced wall treatment approach for the near wall regions, was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results.

scholarly journals Real Gas Effects in Carbon Dioxide Cycles

1969 ◽  
Author(s):  
G. Angelino
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Cooling Water ◽  
Working Fluid ◽  
Moderate Pressure ◽  
Transfer Coefficients ◽  
Good Efficiency ◽  
Real Gas ◽  
Heat Transfer Coefficients ◽  
Real Gas Effects

The potential performance of carbon dioxide as working fluid is recognized to be similar to that of steam, which justifies thorough thermodynamic analysis of possible cycles. The substantially better results achievable with CO2 with respect to other gases are due to the real gas behaviour in the vicinity of the Andrews curve. Simple cycles benefit from the reduced compression work, but their efficiency is compromised by significant losses caused by irreversible heat transfer. Their economy, however, is appreciably better than that of perfect gas cycles. More complex cycle arrangements, six of which are proposed and analyzed in detail, reduce heat transfer losses while maintaining the advantage of low compression work and raise cycle efficiency to values attained only by the best steam practice. Some of the cycles presented were conceived to give a good efficiency at moderate pressure which is of particular value in direct-cycle nuclear applications. The favourable influence on heat transfer coefficients of the combined variation with pressure of mechanical, thermal and transport properties, due to real gas effects, is illustrated. Technical aspects as turbo-machines dimensions and heat transfer surfaces needed for regeneration are also considered. Cooling water requirements are found to be not much more stringent than in steam stations.

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