Shivering onset, metabolic response, and convective heat transfer during cold air exposure

1991 ◽  
Vol 70 (5) ◽  
pp. 1996-2002 ◽  
Author(s):  
P. Tikuisis ◽  
D. G. Bell ◽  
I. Jacobs
Keyword(s):  
Heat Transfer ◽  
Metabolic Rate ◽  
Body Fat ◽  
Convective Heat ◽  
Heat Fluxes ◽  
Air Exposure ◽  
Cold Air ◽  
Convective Heat Loss ◽  
Norm Group ◽  
Lean Group

The onset and intensity of shivering of various muscles during cold air exposure are quantified and related to increases in metabolic rate and convective heat loss. Thirteen male subjects resting in a supine position and wearing only shorts were exposed to 10 degrees C air (42% relative humidity and less than 0.4 m/s airflow) for 2 h. Measurements included surface electromyogram recordings at six muscle sites representing the trunk and limb regions of one side of the body, temperatures and heat fluxes at the same contralateral sites, and metabolic rate. The subjects were grouped according to lean (LEAN, n = 6) and average body fat (NORM, n = 7) content. While the rectal temperatures fluctuated slightly but not significantly during exposure, the skin temperature decreased greatly, more at the limb sites than at the trunk sites. Muscles of the trunk region began to shiver sooner and at a higher intensity than those of the limbs. The intensity of shivering and its increase over time of exposure were consistent with the increase in the convective heat transfer coefficient calculated from skin temperatures and heat fluxes. Both the onset of shivering and the magnitude of the increase in metabolic rate due to shivering were higher for the LEAN group than for the NORM group. A regression analysis indicates that, for a given decrease in mean skin temperature, the increase in metabolic rate due to shivering is attenuated by the square root of percent body fat. Thus the LEAN group shivered at higher intensity, resulting in higher increases in metabolic heat production and convective heat loss during cold air exposure than did the NORM group.

Radiative and Convective Conducting Fins on a Plane Wall, Including Mutual Irradiation

1971 ◽  
Vol 93 (1) ◽  
pp. 41-46 ◽  
Author(s):  
R. C. Donovan ◽  
W. M. Rohrer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Considerable Increase ◽  
Radiative Heat ◽  
Plane Surface ◽  
Heat Fluxes ◽  
Fluid Medium ◽  
Radiant Exchange ◽  
Radiative Component

The radiative and convective heat transfer from a fin array consisting of longitudinal rectangular fins on a plane surface has been theoretically investigated by mathematically describing the interaction among the heat conduction in the fin, the convective heat transfer to the fluid medium, and the radiant exchange of the fin with the neighboring elements. Solutions for the fin temperature distribution, the local radiative heat fluxes over the fin and base surfaces, the total radiative heat transfer, the total convective heat transfer, and the effectiveness of the fins were found. In the primary range of physical interest, the fins usually cause a considerable increase in the convective component of the heat transfer but either cause decreases or only slight increases in the radiative component. Thus convection is generally the more effective mode of heat transfer in fin arrays, and the effectiveness of the fins decreases as the radiative component increases.

scholarly journals Conjugate Effect on the Thermal Characteristics of Air Impinging Jet

CFD Letters ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 25-35
Author(s):  
Ghassan Nasif ◽  
Yasser El-Okda
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat ◽  
Thermal Characteristics ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Stagnation Region ◽  
Jet Cooling ◽  
Air Jet ◽  
Finite Volume Approach

A computational fluid dynamics (CFD) investigation to determine the conjugate heat transfer (CHT) effect on the stagnation and local thermal characteristics due to an impinging process has been carried out in this study using STAR-CCM+ - Siemens PLM commercial code. The transient Navier-Stokes’s equations are numerically solved using a finite volume approach with k-ω SST eddy viscosity as the turbulence model. A fully developed circular air jet with different Reynolds numbers, impinging vertically onto a heated flat disc with different metals, thicknesses, and boundary heat fluxes are employed in the current study to examine the thermal characteristics and provide an enhanced picture for the convection mechanism that used in jet cooling technology. It is found that the thermal characteristics are influenced by the thermal conductivity and thickness of the target upon using air as a cooling jet. The CHT process enhances the local convective heat transfer at the fluid-solid interface due to the variation in transverse and axial conductive heat transfer inside the metal up to a certain redial extent from the stagnation region compared to the process with no CHT. The extent of the radial enhancement depends on the thermal conductivity of the metal. For a given thermal conductivity, the CHT process acts to increase the temperature and convective heat flux of the stagnation region as the metal thickness increases.

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.

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.

scholarly journals An analytical model of icicle growth

1994 ◽  
Vol 19 ◽  
pp. 141-145 ◽  
Author(s):  
Krzysztof Szilder ◽  
Edward P. Lozowski
Keyword(s):  
Heat Transfer ◽  
Analytical Solution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Differential Forms ◽  
Heat Fluxes ◽  
Time Interval ◽  
Dimensionless Form ◽  
Conservation Of Energy ◽  
Dimensionless Variables

A model of icicle growth has been developed based on an analytical solution of the differential forms of the conservation of energy and mass. The problem has been formulated using dimensionless variables defined as the ratios of the various heat fluxes which determine the icicle’s growth. The evolution of the dimensionless icicle shape has been expressed as a function of the variation of the convective heat transfer with icicle radius. The time interval needed for the icicle to reach its maximum length and the variation of the icicle mass and drip rate are expressed in dimensionless form.

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 Study on Convective Heat Transfer from Hot Water to Cold Air Flow with Evaporation

2013 ◽  
Vol 26 (5) ◽  
pp. 523-530
Author(s):  
Tatsuya HIROTA ◽  
Yutaka EBIHARA ◽  
Yasuo KOIZUMI ◽  
Kouji OHIRA ◽  
Tatsuya YAMAJI ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Hot Water ◽  
Cold Air

Numerical Investigation of Heat Transfer From a Surface Under the Influence of Two Impinging Pulsating Slot Jets

2002 ◽  
Author(s):  
A. K. Chaniotis ◽  
D. Poulikakos ◽  
Y. Ventikos
Keyword(s):  
Heat Transfer ◽  
Convective Heat ◽  
Research Work ◽  
Jet Impingement ◽  
Basic Research ◽  
Convective Heat Exchange ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Non Linear System ◽  
Two Jets

The problem of gas jet impingement on a surface has many applications in the processing and manufacturing industries, ranging from convective heat exchange in a variety of practical implementations to surface coating. The present basic research work considers two air jets, exiting from two slots and impinging on a target solid surface, heated with constant heat flux. The jet impingement arrangement is attractive due to its simplicity and to the high convective heat transfer coefficients it yields, corresponding to high heat fluxes. The simulations of this process are conducted using an improved Smooth Particle Hydrodynamics (SPH) methodology. The simulation of an array of two slot jets impingement focuses on the investigation of the flow field and the energy exchange between jets and surface, with an emphasis on the oscillatory characteristics of the two jets relative to one another. The effect of the main problem parameters is examined within the paper. The strong aerodynamic and thermal interaction that exists between the gaseous jets and the impingement surface leads to non-linear system responses; their dynamic behavior and heat transfer implications are also discussed in the paper. The numerical results indicate that within the investigated parametric domain, the phase angle difference between the two jets and the amplitude of the pulsation have a significant effect on the surface temperature and overall heat transfer.

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