An Experimental Investigation of Reflux Condensation Phenomena in Multiple U-Tubes With and Without Noncondensible Gas

Condensation Mode ◽

Series Of Experiments ◽

Pure Steam ◽

Abstract A series of experiments were performed to investigate the thermal-hydraulic phenomena inside U-tubes in a reflux condensation mode. A total of 512 data for local condensation heat transfer coefficients (108 for pure steam flow and 404 for steam-air flow conditions, respectively) have been obtained for various inlet flow rates of steam and air under atmospheric condition. A new correlation, which includes the effects of flow rates of steam and noncondensible gases (air) on the heat transfer coefficient and is applicable to the reflux condensation mode, has been developed using the concept of degradation factor based on the steam-air experimental results. In addition, the effects of multiple U-tubes with different lengths (i.e., two-long and two-short U-tubes) and noncondensible gases on the onset of flooding during a reflux condensation have been examined.

Systematic heat transfer measurements in highly viscous binary fluids

Heat and Mass Transfer ◽

10.1007/s00231-021-03087-w ◽

2021 ◽

Author(s):

Ann-Christin Fleer ◽

Markus Richter ◽

Roland Span

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Volatile Component ◽

Test Tube ◽

Heat Fluxes ◽

Transfer Coefficients ◽

Low Viscosity ◽

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 Measurements for Rotating Turbine Discs

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/89-gt-236 ◽

1989 ◽

Cited By ~ 3

Author(s):

G. Qureshi ◽

M. H. Nguyen ◽

N. R. Saad ◽

R. N. Tadros

Keyword(s):

Heat Transfer ◽

Coolant Flow ◽

Flow Conditions ◽

Transfer Coefficients ◽

Rotating Disc ◽

Nusselt Numbers ◽

Rotating Discs ◽

Turbine Disc ◽

State Technique

To optimise the turbine disc weight and coolant flow requirements, the aspect of improving thermal analysis was investigated. As a consequence, an experimental investigation was undertaken to measure the rates of convective heat transfer. The constant temperature steady state technique was used to determine the local and average heat transfer coefficients on the sides of rotating discs. The effects of coolant flow rates, CW (3000 ≤ CW ≤ 18600) with two types of cavity in-flow conditions and of the rotational speeds, Reθ (from 4×105 to 1.86×106) on the disc heat transfer were studied and correlations developed. For a rotating disc in confined cavities with superimposed coolant flows, Nusselt numbers were found to be higher than those for the free rotating disc without confinement.

Convective Heat Transfer at Minimum Fluidization Velocity for Gas-Solid Fluidized Beds

10.1115/imece1999-1017 ◽

1999 ◽

Author(s):

Kal R. Sharma

Keyword(s):

Heat Transfer ◽

Fluidized Beds ◽

Empirical Correlations ◽

Transfer Coefficients ◽

Minimum Fluidization Velocity ◽

Fluidization Velocity ◽

Minimum Fluidization ◽

Semi Empirical ◽

Abstract Experimentally measured values for the minimum fluidization velocities and time averaged local surface heat transfer coefficients are provided for 16 different cases of fluidizing conditions for gas-solid dense fluidized beds. Semi-empirical Correlations for the minimum fluidization velocity and the heat transfer coefficient at minimum fluidization velocities are provided. The implications of the Peclet number dependence in terms of diffusion and convection is discussed.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

Journal of Turbomachinery ◽

10.1115/1.2841122 ◽

1997 ◽

Vol 119 (2) ◽

pp. 381-389 ◽

Cited By ~ 55

Author(s):

M. E. Taslim ◽

C. M. Wadsworth

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Thermal Performance ◽

Blockage Ratio ◽

Transfer Coefficients ◽

Height Ratio ◽

Average Heat ◽

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

The Optimum Dimensions of Circular Fins with Variable Thermal Parameters

Journal of Heat Transfer ◽

10.1115/1.3244316 ◽

1980 ◽

Vol 102 (3) ◽

pp. 420-425 ◽

Cited By ~ 66

Author(s):

P. Razelos ◽

K. Imre

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Variable Thermal Conductivity ◽

Linear Variation ◽

Transfer Coefficients ◽

Base Thickness ◽

Optimum Length ◽

Trapezoidal Profile ◽

Optimum dimensions of circular fins of trapezoidal profile with variable thermal conductivity and heat transfer coefficients are obtained. Linear variation of the thermal conductivity is considered of the form k = k0(1 + εT/T0), and the heat transfer coefficient is assumed to vary according to a power law with distance from the bore, expressed as h = K[(r − r0)/(r0 − re)]m. The results for m = 0, 0.8, 2.0, and −0.4 ≤ ε ≤ 0.4, have been expressed by suitable nondimensional parameters which are presented graphically. It is shown that considering the thermal conductivity as constant, the optimum base thickness and volume of the fin are inversely proportional to the thermal conductivity of the material of the fin, while the optimum length and effectiveness are independent of the properties of the material used.

Preliminary studies of the loss of heat from leaves under conditions of free and forced convection

Australian Journal of Botany ◽

10.1071/bt9650153 ◽

1965 ◽

Vol 13 (2) ◽

pp. 153 ◽

Cited By ~ 6

Author(s):

GI Pearman

Keyword(s):

Heat Transfer ◽

Wind Tunnel ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Transfer Coefficients ◽

Free And Forced Convection ◽

Wind Velocities ◽

An account is given of techniques and methods used in measurement of convective heat transfer from leaves of the succulent Carpobrotus. Heat transfer was studied under still air conditions and in wind (in a specially constructed wind-tunnel) up to velocities of 300 cm sec-1. A correlation was demonstrated between experimentally obtained values of heat transfer coefficients and theoretical values calculated from empirical formulae. At wind velocities of 300 cm sec-1 the heat transfer coefficient for Carpobrotus was increased to seven times its value still air.

The Superposition Approach to Local Heat Transfer Coefficients in High Density Ratio Film Cooling Flows

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/99-gt-168 ◽

1999 ◽

Cited By ~ 17

Author(s):

Michael Gritsch ◽

Stefan Baldauf ◽

Moritz Martiny ◽

Achmed Schulz ◽

Sigmar Wittig

Keyword(s):

Heat Transfer ◽

Film Cooling ◽

Density Ratio ◽

Two Dimensional ◽

Transfer Coefficients ◽

Cooling Flows ◽

High Density Ratio ◽

The present paper reports on the use of the superposition approach in high density ratio film cooling flows. It arises from the linearity and homogeneity of the simplified boundary layer differential equations. However, it is widely assumed that the linearity does not hold for variable property flows. Therefore, theoretical considerations and numerical calculations will demonstrate the linearity of the heat transfer coefficient with the dimensionless coolant temperature θ as long as identical flow conditions are applied. This makes it necessary to perform at least two experiments at different θ but with the coolant to main flow temperature ratio kept unchanged. A comprehensive set of experiments is presented to demonstrate the capability of the superposition approach for determining heat transfer coefficients for different film cooling geometries. These comprise coolant injection from two dimensional tangential slots, single holes, and rows of cylindrical holes. Particularly, two dimensional local distributions of the heat transfer coefficient will be addressed.

Natural Heat Transfer Coefficients of Chicken Drum Shaped Bodies

International Journal of Food Engineering ◽

10.2202/1556-3758.1000 ◽

2005 ◽

Vol 1 (3) ◽

Cited By ~ 3

Author(s):

Michael Ngadi ◽

Julian N. Ikediala

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Correlation Equation ◽

Deep Fat Frying ◽

Heat Transfer Correlation ◽

Transfer Coefficients ◽

Increasing Temperature ◽

Average heat transfer coefficients of chicken drum shaped bodies were estimated using aluminum chicken drum shaped models. Three model drum sizes namely small, medium and large, and three frying oil viscosities for three temperature differences were used. Estimated heat transfer coefficients were in the range from 67 to 163 W/m²K. Increasing temperature difference increased heat transfer coefficient. Conversely, increasing the size of the chicken drum model bodies and oil viscosities decreased the heat transfer coefficient. A heat transfer correlation equation between average Nu and Ra was derived. The methodology developed in this study could be used to estimate heat transfer coefficients of chicken drum during deep-fat frying.

The Effect of Turbulator Lean on Heat Transfer and Friction in a Square Channel

Volume 5: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38137 ◽

2003 ◽

Cited By ~ 7

Author(s):

Ronald S. Bunker ◽

Sarah J. Osgood

Keyword(s):

Heat Transfer ◽

Flow Direction ◽

Standard Form ◽

Bulk Flow ◽

Transfer Coefficients ◽

Square Channel ◽

Friction Factors ◽

Lean Angle ◽

Series Of Experiments

An experimental study has been performed to investigate the convective heat transfer coefficients and friction factors present in square cooling passages with non-normal, or leaned turbulators. The standard form of turbulated channels used in virtually all turbine vanes and blades is that of nearly square turbulators, or rib rougheners, cast in an orthogonal orientation to the channel surface. While turbulators may be oriented at an angle to the bulk flow direction, the projection of the turbulator is still normal to the cast surface. Non-orthogonal lean angle presents an additional variable which may be used to improve or optimize performance, a factor hitherto not investigated. The present study has performed a series of experiments measuring both detailed heat transfer coefficient distributions and friction factors within a square channel with flow Reynolds numbers up to 400,000. Turbulator lean angles of 45, 22.5, 0, −22.5, and −45-degrees to the surface normal have been tested with a turbulator configuration of 45-degree orientation to the bulk flow, pitch-to-height ratio of 10, and height-to-hydraulic diameter ratio of 0.1. Results show up to a 20% reduction in heat transfer capability, and as much as 30% increase in friction factor. The local distributions of heat transfer are also more variable with lean angle. The conclusion is made that normal turbulators provide the best overall performance.

Heat Transfer from Immersed Slender Bodies

International Journal of Mechanical Engineering Education ◽

10.1177/030641909502300304 ◽

1995 ◽

Vol 23 (3) ◽

pp. 203-211 ◽

Cited By ~ 1

Author(s):

P. J. Erens ◽

A. A. Dreyer

Keyword(s):

Heat Transfer ◽

Low Cost ◽

Cylindrical Tube ◽

Transfer Coefficients ◽

Shaped Tube ◽

Cylindrical Tubes ◽

Slender Bodies ◽

Effects Of Radiation ◽

This article describes a simple, low-cost experiment which could be used as a good educational example for students, combining the effects of radiation, natural convection, forced convection and condensation into one experiment. Many correlations are available for the calculation of the heat transfer from single, slender bodies (or tubes) immersed in a moving fluid. Even for a simple cylindrical tube the predicted heat transfer coefficients differ significantly from correlation to correlation. For more complex tube geometries fewer correlations could be found in the literature. The correlation by Gnielinski [1] appeared the most favourable since this single correlation is valid for many tube geometries (not just for cylindrical tubes). A simple experimental technique is described to measure the heat transfer coefficient on the outside of various tubular profiles in a fluid stream. This technique was then used to evaluate heat transfer coefficients on six different tubes, ranging from a circular cylinder to a complex T-shaped tube. The experimental data for all six tubes showed very good agreement with the correlation of Gnielinski.