An Evaluation of the Wind Chill Factor: Its Development and Applicability

1998 ◽  
Vol 120 (2) ◽  
pp. 255-258 ◽  
Author(s):  
M. Bluestein
Keyword(s):  
Heat Transfer ◽  
Wind Velocity ◽  
Air Temperature ◽  
Wind Effect ◽  
Transfer Coefficients ◽  
Wind Chill ◽  
Heat Transfer Coefficients ◽  
Economic Significance ◽  
Two Factors ◽  
Transfer Principles

The wind chill factor has become a standard meteorologic term in cold climates. Meteorologic charts provide wind chill temperatures meant to represent the hypothetical air temperature that would, under conditions of no wind, effect the same heat loss from unclothed human skin as does the actual combination of air temperature and wind velocity. As this wind chill factor has social and economic significance, an investigation was conducted on the development of this factor and its applicability based on modern heat transfer principles. The currently used wind chill factor was found to be based on a primitive study conducted by the U.S. Antarctic Service over 50 years ago. The resultant equation for the wind chill temperature assumes an unrealistic constant skin temperature and utilizes heat transfer coefficients that differ markedly from those obtained from equations of modern convective heat transfer methods. The combined effect of these two factors is to overestimate the effect of a given wind velocity and to predict a wind chill temperature that is too low.

Heat transfer from starlings sturnus vulgaris during flight

1999 ◽  
Vol 202 (12) ◽  
pp. 1589-1602 ◽  
Author(s):  
S. Ward ◽  
J.M.V. Rayner ◽  
U. Möller ◽  
D.M. Jackson ◽  
W. Nachtigall ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Convective Heat Transfer ◽  
Heat Loss ◽  
Convective Heat ◽  
Air Temperature ◽  
Sturnus Vulgaris ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Infrared thermography was used to measure heat transfer by radiation and the surface temperature of starlings (Sturnus vulgaris) (N=4) flying in a wind tunnel at 6–14 m s-1 and at 15–25 degrees C. Heat transfer by forced convection was calculated from bird surface temperature and biophysical modelling of convective heat transfer coefficients. The legs, head and ventral brachial areas (under the wings) were the hottest parts of the bird (mean values 6.8, 6.0 and 5.3 degrees C, respectively, above air temperature). Thermal gradients between the bird surface and the air decreased at higher air temperatures or during slow flight. The legs were trailed in the air stream during slow flight and when air temperature was high; this could increase heat transfer from the legs from 1 to 12 % of heat transfer by convection, radiation and evaporation (overall heat loss). Overall heat loss at a flight speed of 10.2 m s-1 averaged 11. 3 W, of which radiation accounted for 8 % and convection for 81 %. Convection from the ventral brachial areas was the most important route of heat transfer (19 % of overall heat loss). Of the overall heat loss, 55 % occurred by convection and radiation from the wings, although the primaries and secondaries were the coolest parts of the bird (2.2-2.5 degrees C above air temperature). Calculated heat transfer from flying starlings was most sensitive to accurate measurement of air temperature and convective heat transfer coefficients.

The Thermodynamic Performance of Liquid-Vapor Separation Air-Cooled Condenser in ORC System at Low Ambient Temperature

2014 ◽  
Author(s):  
Ying Chen ◽  
Wenxian Zheng ◽  
Tianming Zhong ◽  
Nan Hua
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Tube Wall ◽  
Ambient Air ◽  
Working Fluid ◽  
Heat Transfer Area ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermodynamic Performance ◽  
Liquid Vapor

This paper investigated the thermodynamic performance of a novel condenser, liquid-vapor separation condenser (LSC), under the ORC conditions with extreme ambient air temperature. By contrast, a common parallel flow condenser (PFC) with the identical structure of tube and fin, together with the heat transfer area was measured under the same condition. The average condensing temperature was chosen as 35°C, R134a was chosen as the working fluid. The experimental results announced that the in-tube average heat transfer coefficients (AHTCs) of the LSC were 96.7% to 109.1% of the PFC when the initial air temperature varied from −10°C to 10°C, at the R134a inlet mass flux from 437kg/(m2s) to 750kg/(m2s), and heat flux from 3kW/m2 to 5 kW/m2. Specially, the pressure drop was only 35.1% to 53.2% of the PFC under the experiment conditions. The tube wall temperatures of the LSC decreased slower than the PFC. The thermodynamic performance of the LSC was superior to the PFC under the ORC conditions. The result indicates the LSC is a promising condenser in ORC system.

scholarly journals APPROACH TO DETERMINING BOUNDARY CONDITIONS ON THE EXTERNAL SURFACE OF THE HEIGHT CASE OF THE ADMINISTRATIVE BUILDING

2021 ◽  
pp. 73-79
Author(s):  
N.О. ORLOVA
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Wind Speed ◽  
Air Temperature ◽  
Thermal Regime ◽  
Energy System ◽  
Building Envelope ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Mathematical Model

Problem statement. The influence of the external climate on the thermal regime of the enclosures of premises and buildings is complex. The calculated values and combinations of parameters are determined, as a rule, taking into account the security factor of the calculated conditions. The main indicators of the cold season are the outdoor temperature and wind speed. As you know, an increase in wind speed with a constant outside air temperature causes an increase in pressure on the windward facade of the building, as a result of which the heat loss of the room, associated with heating of the incoming air, increases. Wind speed and direction have a stronger influence on the distribution of air flows in the ventilation system and on the infiltration costs than the outside temperature. A change in the outside air temperature from −15 to −30 °С leads to the same increase in air exchange in the apartment as an increase in wind speed from 3 to 6 m/s. The purpose of the article is to determine the heat transfer coefficients on the outside of an office building. Results. The basic principles of calculating heat transfer coefficients are presented. The zoning of the premises of the Institute is proposed, taking into account their thermal regime and boundary conditions on external surfaces. Scientific novelty and practical significance. The original values of the heat transfer coefficients, which are considered on the example of the climatic conditions of the city of Kharkov for the IP Mash complex of the NAS of Ukraine. On the basis of the presented methodology for determining the heat transfer coefficients, it is planned to present this building as a single energy system with three main energetically interconnected subsystems: the energy effect of the external climate on the building envelope; energy that is contained in the building envelope, that is, in the external building envelope; energy, which is contained within the volume of the building, that is, in the internal air, internal equipment, internal structures, etc. Then the mathematical model of the building as a unified energy system will consist of three submodels: the mathematical model of the influence of the external climate on the building envelope; mathematical model of heat transfer through the building envelope; mathematical model of radiant and convective heat transfer in the premises of the building.

Design and Performance Analysis of Air Pre heater for Water Tube Boiler to improve its Efficiency

2021 ◽  
pp. 01-06
Author(s):  
V. Karthikeyan ◽  
M. Sambathkumar ◽  
K. Arulkumar
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Flue Gas ◽  
Transfer Coefficients ◽  
Air Preheater ◽  
Software Application ◽  
Heat Transfer Coefficients ◽  
Performance Requirements ◽  
Specific Performance ◽  
And Performance

Air preheater is a heat transfer surface in which air temperature is raised by transferring heat from other media such as flue gas which is coming from boiler exhaust. The paper presents the design of regenerative –air preheater to designed to meet specific performance requirements, using the software application CFD (Computational Fluid Dynamics) / CADD. An analytical study was planned to find out the various heat transfer performance parameters like outlet and inlet air temperature of the air preheater and the boiler, Pressure drop inside the Air preheater and the boiler heat transfer coefficients, heat transfer rate, overall heat transfer coefficient and Velocity of the air and flue gas also Conduction and convection modes of heat transfer were found. These heat transfer parameters are critical in designing and functioning of the air Preheater and to calculate the efficiency of the boiler.

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