Heat Transfer Coefficients on the Downstream Face of an Abrupt Enlargement or Inlet Constriction in a Pipe

1980 ◽  
Vol 102 (3) ◽  
pp. 408-414 ◽  
Author(s):  
E. M. Sparrow ◽  
J. E. O’Brien
Keyword(s):  
Heat Transfer ◽  
Transfer Coefficient ◽  
Working Fluid ◽  
Downstream Face ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Diameter Pipe ◽  
Naphthalene Sublimation ◽  
Flow Configurations

Measurements were made of the local and average heat transfer coefficients on the downstream face of an enlargement step in a pipe. Two flow configurations were investigated: (a) an abrupt enlargement from a smaller diameter pipe to a larger diameter pipe and (b) partial constriction of a pipe inlet by a large baffle plate. Air was the working fluid. The transfer coefficients were determined by means of the naphthalene sublimation technique; axial pressure distributions were also measured. The highest values of the local transfer coefficient were found to occur on the portion of the enlargement face adjacent to the aperture through which the flow enters the enlarged space. On the other hand, the lowest coefficients occur in the corner where the enlargement face meets the wall of the enlarged pipe. The radial distributions of the transfer coefficient on the enlargement face vary with the Reynolds number. With regard to average transfer coefficients, higher values (by at least 50 percent) are attained for the constricted inlet than for the abrupt enlargement. The average coefficients for the enlargement face are much higher (by a factor of two or three) than those on the wall of the enlarged pipe for fully developed flow conditions.

Heat Transfer Characteristics of an Obliquely Impinging Circular Jet

1980 ◽  
Vol 102 (2) ◽  
pp. 202-209 ◽  
Author(s):  
E. M. Sparrow ◽  
B. J. Lovell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Local Heat ◽  
Maximum Point ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Local Coefficients ◽  
Naphthalene Sublimation

Measurements of local heat (mass) transfer coefficients were made on a surface on which a circular jet impinges at an oblique angle. The angle of inclination of the jet relative to the surface was varied from 90 deg (normal impingement) to 30 deg. The Reynolds number and the distance between the jet orifice and the impingement plate were also varied parametrically. To facilitate the experiments, the naphthalene sublimation technique was employed, and the resulting mass transfer coefficients were converted to heat transfer coefficients by the well-established analogy between the two processes. It was found that the point of maximum mass transfer is displaced from the geometrical impingement point, with the extent of the displacement increasing with greater jet inclination. The local coefficients on the uphill side of the maximum point drop off more rapidly than do those on the downhill side, thus creating an imbalance in the cooling/heating capabilities on the two sides. Neither the maximum transfer coefficient nor the surface-averaged transfer coefficient are highly sensitive to the inclination of the jet; during the course of the experiments, the largest inclination-induced decreases in these quantities were in the 15 to 20 percent range.

Heat Transfer on Rotating Channel With Various Heights of Pin-Fin

2008 ◽  
Author(s):  
Jun Su Park ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Pin Fins ◽  
Naphthalene Sublimation ◽  
Pin Fin Array

Pin-fins have been used to enhance the heat transfer near the trailing edge of a turbine airfoil. Previous pin-fin heat transfer studies focused mainly on the array geometry of pin height-to-diameter equal to unity in a stationary frame. This study experimentally examines the effects of pin height-to-diameter ratio (Hp/Dp) from 2 to 4 and rotation number (Ro) from 0 to 0.2. The tested model used a staggered pin-fin array with an inter-pin spacing of 2.5 times the pin-diameter (S/D = 2.5) in both longitudinal and transverse directions. Detailed heat/mass transfer coefficients were measured using the naphthalene sublimation technique with a heat-mass transfer analogy. The data measured suggest that an increase in Hp/Dp increases the level of array heat/mass transfer. Array averaged Sherwood numbers for Hp/Dp = 3 and Hp/Dp = 4 are approximately 10% and 35% higher than that of Hp/Dp = 2. The effect of rotation induces notable difference in heat/mass transfer between the leading surface and the trailing surface. The heat transfer coefficients change a little although the rotating number increases in the tested range because the pin-fins break the rotation-induced vortices.

Measurements of Heat Transfer and Pressure Drop for an Array of Staggered Plates Aligned Parallel to an Air Flow

1980 ◽  
Vol 102 (3) ◽  
pp. 426-432 ◽  
Author(s):  
E. M. Sparrow ◽  
A. Hajiloo
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Air Flow ◽  
Plate Thickness ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Naphthalene Sublimation

The heat transfer and pressure drop characteristics of an array of staggered plates, aligned parallel to the direction of a forced convection air flow, have been studied experimentally. During the course of the experiments, the plate thickness and Reynolds number were varied parametrically. Mass transfer measurements employing the naphthalene sublimation technique were made to obtain the heat transfer results via the heat-mass transfer analogy. For a given operating condition, the per-plate heat transfer coefficients were found to be the same for the second and all subsequent rows. The fully developed heat transfer coefficients increase with Reynolds number for all the plate thicknesses investigated, but in a different manner for the different thicknesses. In general, thicker plates give rise to higher heat transfer coefficients, especially at the larger Reynolds numbers. The measured friction factors also increase with plate thickness. For the thickest plates, the friction factor was found to be independent of the Reynolds number, signalling the dominance of inertial losses.

A New Analogy Function for the Naphthalene Sublimation Technique to Measure Heat Transfer Coefficients on Turbine Airfoils

1995 ◽  
Author(s):  
M. Häring ◽  
B. Weigand
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Schmidt Number ◽  
Numerical Solutions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Transfer Equations ◽  
Naphthalene Sublimation ◽  
Sublimation Technique

The naphthalene sublimation technique is based on the analogy between mass and heat transfer. This analogy is only fully valid for incompressible flow and if the Prandtl and Schmidt number are equal. In the present investigation the energy- and mass transfer equations were solved simultaneously to establish an analogy function which allows the calculation of the Nusselt number from the Sherwood number in function of the Mach, the Prandtl and the Schmidt number. For a laminar flow this new analogy function is based on similarity solutions of the conservation equations for high Mach number flows. Also a numerical investigation was conducted to study the influence of the pressure gradient and the Soret effect as well as varying fluid properties. For a turbulent flow, a flat plate solution was established for Pr=1. Energy and mass transfer equations were additionally solved for a two dimensional duct flow to study the influence of the Prandtl number on the analogy function independently. The resulting analytical and numerical solutions are shown for various pressure gradients, Prandtl and Mach numbers. In addition, approximations for the analogy function are derived. The influence of the present theory on heat transfer measurements on a turbine airfoil is shown. The theory is validated against experimental results in Häring et. al. (1995) showing a good agreement between the heat transfer coefficients calculated with the new analogy function and measurements of actual heat transfer.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

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.

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.

Calculation of Hourly Output of a Solar Still

1993 ◽  
Vol 115 (4) ◽  
pp. 231-236 ◽  
Author(s):  
V. B. Sharma ◽  
S. C. Mullick
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Balance ◽  
Solar Still ◽  
Balance Equations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hourly Output ◽  
The Heat Balance

An approximate method for calculation of the hourly output of a solar still over a 24-hour cycle has been studied. The hourly performance of a solar still is predicted given the values of the insolation, ambient temperature, wind heat-transfer coefficient, water depth, and the heat-transfer coefficient through base and sides. The proposed method does not require graphical constructions and does not assume constant heat-transfer coefficients as in the previous methods. The possibility of using the values of the heat-transfer coefficients for the preceding time interval in the heat balance equations is examined. In fact, two variants of the basic method of calculation are examined. The hourly rate of evaporation is obtained. The results are compared to those obtained by numerical solution of the complete set of heat balance equations. The errors from the approximate method in prediction of the 24-hour output are within ±1.5 percent of the values from the numerical solution using the heat balance equations. The range of variables covered is 5 to 15 cms in water depth, 0 to 3 W/m2K in a heat-transfer coefficient through base and sides, and 5 to 40 W/m2K in a wind heat-transfer coefficient.

The Measurement of Full-Surface Internal Heat Transfer Coefficients for Turbine Airfoils Using a Non-Destructive Thermal Inertia Technique

2002 ◽  
Author(s):  
Nirm V. Nirmalan ◽  
Ronald S. Bunker ◽  
Carl R. Hedlung
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbine Airfoils ◽  
Non Destructive ◽  
Internal Heat Transfer

A new method has been developed and demonstrated for the non-destructive, quantitative assessment of internal heat transfer coefficient distributions of cooled metallic turbine airfoils. The technique employs the acquisition of full-surface external surface temperature data in response to a thermal transient induced by internal heating/cooling, in conjunction with knowledge of the part wall thickness and geometry, material properties, and internal fluid temperatures. An imaging Infrared camera system is used to record the complete time history of the external surface temperature response during a transient initiated by the introduction of a convecting fluid through the cooling circuit of the part. The transient data obtained is combined with the cooling fluid network model to provide the boundary conditions for a finite element model representing the complete part geometry. A simple 1D lumped thermal capacitance model for each local wall position is used to provide a first estimate of the internal surface heat transfer coefficient distribution. A 3D inverse transient conduction model of the part is then executed with updated internal heat transfer coefficients until convergence is reached with the experimentally measured external wall temperatures as a function of time. This new technique makes possible the accurate quantification of full-surface internal heat transfer coefficient distributions for prototype and production metallic airfoils in a totally non-destructive and non-intrusive manner. The technique is equally applicable to other material types and other cooled/heated components.

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