The Optimum Dimensions of Circular Fins with Variable Thermal Parameters

1980 ◽  
Vol 102 (3) ◽  
pp. 420-425 ◽  
Author(s):  
P. Razelos ◽  
K. Imre
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Variable Thermal Conductivity ◽  
Linear Variation ◽  
Transfer Coefficients ◽  
Base Thickness ◽  
Optimum Length ◽  
Heat Transfer Coefficients ◽  
Trapezoidal Profile ◽  
The Heat Transfer Coefficient

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.

A Model of Heat Transfer in Fluidized Beds

1972 ◽  
Vol 94 (1) ◽  
pp. 105-110 ◽  
Author(s):  
Benjamin T. F. Chung ◽  
L. T. Fan ◽  
C. L. Hwang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Fluidized Beds ◽  
Transfer Coefficients ◽  
Surface Renewal ◽  
Heat Transfer Coefficients ◽  
Fluidized System ◽  
The Heat Transfer Coefficient

An expression for estimating the heat transfer coefficient in a fluidized bed has been developed based on the surface renewal and penetration concept. The predicted heat transfer coefficients between walls and beds agree well with experimental results. The result of this analysis shows that, in general, the effect of thermal conductivity of particle on heat transfer is insignificant. The maximum possible Nusselt number for the gas fluidized system is determined theoretically as 13.5. This value appears to be reasonable in light of the majority of available experimental data.

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.

scholarly journals Numerical simulation of variable thermal conductivity on 3D flow of nanofluid over a stretching sheet

2020 ◽  
Vol 9 (1) ◽  
pp. 233-243 ◽  
Author(s):  
Nainaru Tarakaramu ◽  
P.V. Satya Narayana ◽  
Bhumarapu Venkateswarlu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Stretching Sheet ◽  
Three Dimensional ◽  
Variable Thermal Conductivity ◽  
Normal Velocity ◽  
Transfer Coefficients ◽  
Similarity Transformations ◽  
Frictional Coefficients ◽  
The Impact

AbstractThe present investigation deals with the steady three-dimensional flow and heat transfer of nanofluids due to stretching sheet in the presence of magnetic field and heat source. Three types of water based nanoparticles namely, copper (Cu), aluminium oxide (Al2O3), and titanium dioxide (TiO2) are considered in this study. The temperature dependent variable thermal conductivity and thermal radiation has been introduced in the energy equation. Using suitable similarity transformations the dimensional non-linear expressions are converted into dimensionless system and are then solved numerically by Runge-Kutta-Fehlberg scheme along with well-known shooting technique. The impact of various flow parameters on axial and transverse velocities, temperature, surface frictional coefficients and rate of heat transfer coefficients are visualized both in qualitative and quantitative manners in the vicinity of stretching sheet. The results reviled that the temperature and velocity of the fluid rise with increasing values of variable thermal conductivity parameter. Also, the temperature and normal velocity of the fluid in case of Cu-water nanoparticles is more than that of Al2O3- water nanofluid. On the other hand, the axial velocity of the fluid in case of Al2O3- water nanofluid is more than that of TiO2nanoparticles. In addition, the current outcomes are matched with the previously published consequences and initiate to be a good contract as a limiting sense.

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

1999 ◽  
Author(s):  
Kal R. Sharma
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Empirical Correlations ◽  
Transfer Coefficients ◽  
Minimum Fluidization Velocity ◽  
Heat Transfer Coefficients ◽  
Fluidization Velocity ◽  
Minimum Fluidization ◽  
Semi Empirical ◽  
The Heat Transfer Coefficient

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.

Diffusion Layer Theory for Turbulent Vapor Condensation With Noncondensable Gases

1993 ◽  
Vol 115 (4) ◽  
pp. 998-1003 ◽  
Author(s):  
P. F. Peterson ◽  
V. E. Schrock ◽  
T. Kageyama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Transfer ◽  
Vapor Condensation ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Noncondensable Gases ◽  
Vertical Tubes

In turbulent condensation with noncondensable gas, a thin noncondensable layer accumulates and generates a diffusional resistance to condensation and sensible heat transfer. By expressing the driving potential for mass transfer as a difference in saturation temperatures and using appropriate thermodynamic relationships, here an effective “condensation” thermal conductivity is derived. With this formulation, experimental results for vertical tubes and plates demonstrate that condensation obeys the heat and mass transfer analogy, when condensation and sensible heat transfer are considered simultaneously. The sum of the condensation and sensible heat transfer coefficients becomes infinite at small gas concentrations, and approaches the sensible heat transfer coefficient at large concentrations. The “condensation” thermal conductivity is easily applied to engineering analysis, and the theory further demonstrates that condensation on large vertical surfaces is independent of the surface height.

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

1997 ◽  
Vol 119 (2) ◽  
pp. 381-389 ◽  
Author(s):  
M. E. Taslim ◽  
C. M. Wadsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

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.

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

1965 ◽  
Vol 13 (2) ◽  
pp. 153 ◽  
Author(s):  
GI Pearman
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Wind Tunnel ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Free And Forced Convection ◽  
Wind Velocities ◽  
The Heat Transfer Coefficient

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.

scholarly journals The Influence of Different Facings of Polyisocyanurate Boards on Heat Transfer through the Wall Corners of Insulated Buildings

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1991 ◽  
Author(s):  
Tomas Makaveckas ◽  
Raimondas Bliūdžius ◽  
Arūnas Burlingis
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Insulation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermal Bridge ◽  
Thermal Bridges ◽  
The Impact ◽  
Heat Flow Meter

Polyisocyanurate (PIR) thermal insulation boards faced with carboard, plastic, aluminum, or multilayer facings are used for thermal insulation of buildings. Facing materials are selected according to the conditions of use of PIR products. At the corners of the building where these products are joined, facings can be in the direction of the heat flux movement and significantly increase heat transfer through the linear thermal bridge formed in the connection of PIR boards with facing of both walls. Analyzing the installation of PIR thermal insulation products on the walls of a building, the structural schemes of linear thermal bridges were created, numerical calculations of the heat transfer coefficients of the linear thermal bridges were performed, and the influence of various facings on the heat transfer through the thermal bridge was evaluated. Furthermore, an experimental measurement using a heat flow meter apparatus was performed in order to confirm the results obtained by numerical calculation. This study provides more understanding concerning the necessity to evaluate the impact of different thermal conductivity facings on the heat transfer through corners of buildings insulated with PIR boards.

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

1999 ◽  
Author(s):  
Michael Gritsch ◽  
Stefan Baldauf ◽  
Moritz Martiny ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Cooling Flows ◽  
Heat Transfer Coefficients ◽  
High Density Ratio ◽  
The Heat Transfer Coefficient

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

2005 ◽  
Vol 1 (3) ◽  
Author(s):  
Michael Ngadi ◽  
Julian N. Ikediala
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Correlation Equation ◽  
Deep Fat Frying ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Increasing Temperature ◽  
The Heat Transfer Coefficient

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.

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