scholarly journals Influence of environmental boundary conditions on convective heat transfer coefficients of wall internal surface

2021 ◽  
Vol 312 ◽  
pp. 02012
Author(s):  
Tullio de Rubeis ◽  
Luca Evangelisti ◽  
Claudia Guattari ◽  
Roberto De Lieto Vollaro ◽  
Francesco Asdrubali ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Internal Surface ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Air Speed ◽  
Velocity Changes ◽  
Forced Air

In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus. An experimental setup characterized by air and surface temperature probes, and a hot-wire anemometer was used. Five small fans were installed in the metering chamber to generate a forced air flow characterized by different velocity values. So, the GHB was used for investigating the influence of different air speed values on internal convective coefficients. Considering horizontal heat fluxes, an internal convective coefficient values of 2.5 W/m2K is reported in the Standard ISO 6946. However, no exhaustive description about this value is provided. The aim of this work is to experimentally determine the internal thermal surface resistance, quantifying how the convective heat transfer coefficient varies as air velocity changes.

scholarly journals CONVECTIVE HEAT TRANSFER CHARACTERISTICS OF AQUEOUS TiO2 NANOFLUID UNDER LAMINAR FLOW CONDITIONS

2008 ◽  
Vol 07 (06) ◽  
pp. 325-331 ◽  
Author(s):  
S. M. SOHEL MURSHED ◽  
KAI CHOONG LEONG ◽  
CHUN YANG ◽  
NAM-TRUNG NGUYEN
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Enhancement Of Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Constant Wall Heat Flux

This paper reports an experimental investigation into force convective heat transfer of nanofluids flowing through a cylindrical minichannel under laminar flow and constant wall heat flux conditions. Sample nanofluids were prepared by dispersing different volumetric concentrations (0.2–0.8%) of nanoparticles in deionized water. The results showed that both the convective heat transfer coefficient and the Nusselt number of the nanofluid increase considerably with the nanoparticle volume fraction as well as the Reynolds number. Along with the enhanced thermal conductivity of nanofluids, the migration, interactions, and Brownian motion of nanoparticles and the resulting disturbance of the boundary layer are responsible for the observed enhancement of heat transfer coefficients of nanofluids.

Effect of Mixed Convective Heat Transfer on Interior Helium Temperature of High-Altitude-Cruising Airships

2013 ◽  
Vol 470 ◽  
pp. 516-520 ◽  
Author(s):  
Yong Qiang Yang ◽  
Yun Peng Ma ◽  
Zhe Wu
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
High Altitude ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Pressure Difference ◽  
Convective Heat Transfer Coefficient ◽  
Analysis Model ◽  
Forced Convective Heat Transfer ◽  
Air Speed

This paper aims to establish a thermal analysis model for stratospheric airships. Mixed convective heat transfer between envelope and air has been specially considered. Thermal analysis of HAB on the summer solstice was carried out in this paper, results show that forced convective heat transfer coefficient increases obviously as the air speed decreasing, which will enhance the heat transfer between envelope and atmospheric. The pressure difference decreases obviously as air speed increasing during the whole day. Therefore HAB(high altitude balloon) should increase the air speed to reduce the pressure difference, which will enhance the safety of HAB.

scholarly journals Determination of Heat Transfer Coefficients Over Ribbed Surfaces With Infrared Thermography

1997 ◽  
Author(s):  
Francisco P. Brójo ◽  
Luís C. Gonçalves ◽  
Pedro D. Silva
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Stanton Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The scope of the present work is to characterize the heat transfer between a ribbed surface and an air flow. The convective heat transfer coefficients, the Stanton number and the Nusselt number were calculated in the Reynolds number range, 5.13 × 105 to 1.02 × 106. The tests were performed inside a turbulent wind tunnel with one roughness height (e/Dh = 0.07). The ribs had triangular section with an attack angle of 60°. The surface temperatures were measured using an infrared (IR) thermographic equipment, which allows the measurement of the temperature with a good spatial definition (10.24 × 10−6 m2) and a resolution of 0.1°C. The experimental measures allowed the calculation of the convective heat transfer coefficient, the Stanton number and the Nusselt number. The results obtained suggested a flow pattern that includes both reattachment and recirculation. Low values of the dimensionless Stanton number, i.e. Stx*, are obtained at the recirculation zones and very high values of Stx* at the zones of reattachment. The reattachment is located at a dimensionless distance of 0.38 from the top of the rib. That distance seems to be independent of the Reynolds number. The local dimensionless Stanton number remains constant as the Reynolds number varies. The convective heat transfer coefficient presents an uncertainty in the range of 3 to 6%.

Heat transfer between Phaseolus vulgaris and the environment

1971 ◽  
Vol 49 (6) ◽  
pp. 833-838 ◽  
Author(s):  
T. F. Saldin ◽  
N. Barthakur
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Phaseolus Vulgaris ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Forced Air ◽  
Theoretical Results ◽  
Infrared Radiometer

Heat transfer was studied from intact leaves of greenhouse-grown Phaseolus vulgaris L. under still and forced air conditions. Microwaves were used to heat the leaves without disturbing the thermal equilibrium of the environment. Leaf temperatures were measured by thermocouples and an infrared radiometer. Convective heat transfer coefficient for a leaf was obtained by two experimental methods and compared with the theoretical results. The unsteady-state method proved to be quite satisfactory.Typical values of heat transfer coefficient for free convection varied from 1.86 × 10−4 to 3.64 × 10−4 cal cm−2 s−1 °C−1, as the temperature difference between the leaf surface and the surrounding air increased from 1.0 to 3.9 °C. Forced convective heat transfer coefficient, however, increased to about 10 × 10−4 cal cm−2 s−1 °C−1 at 610 cm s−1.

Experimental Investigation of Convective Heat Transfer of Supercritical Pressure Hydrocarbon Fuel in a Horizontal Section of a Rotating U-Duct

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Zelong Lu ◽  
Yinhai Zhu ◽  
Yuxuan Guo ◽  
Peixue Jiang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotational Speed ◽  
Convective Heat Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Horizontal Section ◽  
Static Conditions

Abstract The experimental and numerical investigations of the heat transfer of supercritical pressure n-decane flowing through a pipe at various rotational speeds, mass flow rates, heat fluxes, and pressures, are presented. This pipe is 2 mm in diameter, 200 mm in length, with a radius of 0.328 m, and is parallel to the rotating axis. The wall temperature was measured at four positions around the periphery of the pipe at each of the five selected cross section along the pipe's length. Maximum convective heat transfer was observed at the outer edge of the horizontal section, while its corresponding minimum was observed at the inner edge. The heat transfers at the two sides of the channel were observed to be similar. The density and pressure differences between the outer and inner edges increased at increasing rotating speeds. However, the temperature difference between the outer and inner edges decreased with increased rotational speed mainly because of the increase of secondary flows in the section. The section's average convective heat transfer coefficient increased with an increase in the rotational speed, and its value at 1000 rpm was approximately twice than that at static conditions. The phenomenon of oscillation was observed near the exit of the horizontal section, and was caused by the flow and considerable property changes near the pseudo critical temperature. A computational fluid dynamics (CFD) model was developed using the real gas thermal properties and was coupled with the heat transferred owing to fuel flow. The predicted fuel and wall temperatures were in good agreement with the experimental data. A new local Nusselt number correlation of the heat transfer of n-decane in a rotating horizontal section was proposed.

Experimental study on heat and mass transfer for heating milk

2011 ◽  
Vol 22 (3) ◽  
pp. 45-53
Author(s):  
Mahesh Kumar ◽  
K.S. Kasana ◽  
Sudhir Kumar ◽  
Om Prakash
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Linear Regression Analysis ◽  
Convective Heat Transfer Coefficient ◽  
Simple Linear Regression ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rate Of Heating ◽  
Convective Heat Transfer Coefficients

In this paper, an attempt has been made to estimate the convective heat transfer coefficient for sensible heating of milk in a stainless steel pot during khoa, made by traditional method. Various indoor experiments were performed for simulation of a developed thermal model for maximum evaporation by varying heat inputs from 240 watts to 420 watts. The experimental data was used to determine values of constants in the well known Nusselt expression by simple linear regression analysis and, consequently, convective heat transfer coefficients were determined. It is found that the convective heat transfer coefficients decrease with an increase in rate of heating. The experimental error in terms of percent uncertainty was also evaluated.

Subcooled-Boiling and Convective Heat Transfer to Heptane Flowing Inside an Annulus and Past a Coiled Wire: Part I—Experimental Results

1986 ◽  
Vol 108 (4) ◽  
pp. 922-927 ◽  
Author(s):  
H. Mu¨ller-Steinhagen ◽  
A. P. Watkinson ◽  
N. Epstein
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Direction ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Order Effects ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients

Heat transfer coefficients for subcooled heptane were measured in two flow geometries for different heat fluxes, flow rates, bulk temperatures, and system pressures. Regimes of convective heat transfer and of nucleate boiling were delineated for a concentric annular test section containing an internally heated rod, and for a resistance-heated coiled wire mounted in crossflow. Second-order effects such as flow direction, hysteresis, and method of pressurization were also investigated.

scholarly journals A determination methodology for the spatial profile of the convective heat transfer coefficient on building components

2016 ◽  
Vol 27 (4) ◽  
pp. 512-527 ◽  
Author(s):  
Evy Vereecken ◽  
Hans Janssen ◽  
Staf Roels
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Spatial Profile ◽  
Order Of Magnitude

Several experimental procedures have been established to determine the convective heat transfer coefficient, a frequently used parameter in many engineering disciplines. Almost all of these methodologies focus on point or spatially averaged values. Yet, in many studies the spatial profile of the local convective heat transfer is of importance. In this paper, a methodology to determine such spatial profile is proposed. In this method, experiments are combined with Monte Carlo simulations. Such an approach makes it possible to account for inaccuracies in the input data. As an example, the methodology is applied to determine the spatial profile of the local convective heat transfer coefficient near a corner for two thermal bridge configurations. The temperature difference between interior surface and indoor air is found to restrict the applicability of the method. Nonetheless, for the case with a sufficient temperature difference, the order of magnitude of the convective heat transfer coefficients further away from the corner is in line with literature data. An important limitation of the technique at this stage of its development is, however, its requirement for prior knowledge of the equation that describes the spatial profile of the convective heat transfer coefficient. Despite these drawbacks, the methodology shows much potential and can be valuable for other applications as well.

Parametric Study of Convective Heat Transfer Coefficients at the Tire Surface

1980 ◽  
Vol 8 (3) ◽  
pp. 37-67 ◽  
Author(s):  
A. L. Browne ◽  
L. E. Wickliffe
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal State ◽  
Convective Heat Transfer Coefficient ◽  
Operating Conditions ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract Analyses have shown that the thermal state of a tire is influenced by both the size of and variation in the value of the convective heat transfer coefficient at the tire surface. In the work reported here, a test facility was constructed to permit the determination of convective heat transfer coefficients under a broad range of operating conditions. Data were obtained to show the effects of air speed, boundary layer thickness and turbulence level, humidity, tire surface contamination, tire surface roughness and unevenness, and tire surface wetness on convective heat transfer coefficients. The significance of these results to tire power loss is discussed.

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