Concept explainers
It is well known that wind makes the cold air feel much colder as a result of the wind-chill effect that is due to the increase in the convection heat transfer coefficient with increasing air velocity. The wind-chill effect is usually expressed in terms of the wind-chill temperature (WCT), which is the apparent temperature felt by exposed skin. For an outdoor air temperature of
For heat transfer purposes, a standing man can be modeled as a 30-cm-diameter, 170-cm-long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of
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HEAT+MASS TRANSFER:FUND.+APPL.
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- The roof of a building is well insulated on its lower surface and the upper surface is made of black material. The upper surface is exposed to ambient air at 310 K with a convective heat transfer coefficient of 15 W m⁻² K⁻¹. The temperature of clear sky can be taken as 50 K. To the nearest 5 K, what temperature would be measured on the outer surface of the roof by a thermography camera on a clear night once the system had reached a steady state? State clearly the assumptions you are using.arrow_forwardA classroom type room with 45students taking an exam in thermodynamics is expected to release a body heat of about 8kJ/hr per person. In order to compensate this heat dissipation, an air-conditioning unit is to be installed. If specific heat capacity and density of air is 1.0062kJ/kg-K and 1.2kg/m3, determine the volume of air flow required in examination room if the air is to be cooled down from 290C to 200C. a. 8.5177Li/s b. 9.1262Li/s c. 9.2022Li/s d. 9.0501Li/sarrow_forwardA classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360kJ/h. There are 10 light bulbs in the room, each with a rating of 100W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.arrow_forward
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- How would you define a system to determine the temperature rise created in a lake when a portion of its water is used to cool a nearby electrical power plant?arrow_forwardIn determining the average rate of heating of a tank of 20% sugar syrup, thetemperature at the beginning was 20°C and it took 30 min to heat to 80°C. Thevolume of the sugar syrup was 50 ft3 and its density 66.9 lb/ft3. The specific heat ofthe sugar syrup is 0.9 Btu lb-1°F-1.(a) Convert the specific heat to kJ kg-1°C-1.(b) Determine the rate of heating, that is the heat energy transferred in unit time, in SI units (kJ s-1)arrow_forwardWhat are the mechanisms of heat transfer?arrow_forward
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