A mercury-in-glass thermometer having a diameter of 6 mm is placed in a verti- cal position to measure the air temperature in a metal warehouse in the summer. The walls of the warehouse are at 50°C. The convection coefficient is 7 W/m² - °C, and the emissivity of the thermometer may be taken as = 0.9. Calculate the temperature indicated by the thermometer if the air temperature is 32°C. €

A mercury-in-glass thermometer having a diameter of 6 mm is placed in a verti- cal position to measure the air temperature in a metal warehouse in the summer. The walls of the warehouse are at 50°C. The convection coefficient is 7 W/m² - °C, and the emissivity of the thermometer may be taken as = 0.9. Calculate the temperature indicated by the thermometer if the air temperature is 32°C. €

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.29P: 1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that...

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An electronic box that consumes 200 W of power is cooled by a fan blowing air into the box enclosure. The dimensions of the electronic box are 15 cm * 50 cm * 50 cm, and all surfaces of the box are exposed to the ambient except the base surface. Temperature measurements indicate that the box is at an average temperature of 32°C when the ambient temperature and the temperature of the surrounding walls are 25°C. If the emissivity of the outer surface of the box is 0.75, determine the fraction of the heat lost from the outer surfaces of the electronic box.
The vertical 0.8-m-high, 2-m-wide double-pane window consists of two sheets of glass separated by a 2-cm air gap at atmospheric pressure. If the glass surface temperatures across the air gap are measured to be 12°C and 2°C, determine the rate of heat transfer through the window.
The passenger compartment of a minivan traveling at 60 mph can be modeled as a 3.2-ft-high, 6-ft-wide, and 11-ftlong rectangular box whose walls have an insulating value of R-3 (i.e., a wall thickness-to-thermal conductivity ratio of 3 h?ft2?°F/Btu). The interior of a minivan is maintained at an average temperature of 70°F during a trip at night while the outside air temperature is 90°F. The average heat transfer coefficient on the interior surfaces of the van is 1.2 Btu/h?ft2?°F. The air flow over the exterior surfaces can be assumed to be turbulent because of the intense vibrations involved, and the heat transfer coefficient on the front and back surfaces can be taken to be equal to that on the top surface. Disregarding any heat gain or loss by radiation, determine the rate of heat transfer from the ambient air to the van. Assume the air flow to be entirely turbulent because of the intense vibrations involved. Use a film temperature of 80°F for evaluations of air properties at 1 atm.
Consider a hot automotive engine, which can be approximated as a 0.5-m-high, 0.40-m-wide, and 0.8-m-long rectangular block. The bottom surface of the block is at a temperature of 100°C and has an emissivity of 0.95. The ambient air is at 20°C, and the road surface is at 25°C. Determine the rate of heat transfer from the bottom surface of the engine block by convection and radiation as the car travels at a velocity of 80 km/h. Assume the flow to be turbulent over the entire surface because of the constant agitation of the engine block.
A 10-m-long section of a 6-cm-diameter horizontal hot-water pipe passes through a large room whose temperature is 27°C. If the temperature and the emissivity of the outer surface of the pipe are 73°C and 0.8, respectively, determine the rate of heat loss from the pipe by (a) natural convection and (b) radiation.
In a new residential project, you strongly believe thatdouble-paned windows are ‘better’ than single-paned windows.Compare the rate of heat loss between single and double-panedwindows (1.5 m x 1 m) if the thickness of each pane is (th = 0.4 cm)and (k = 0.9 W/m.K). The indoor and outdoor temperatures are 18°C and 2 °C, respectively. Thickness of the air gap between thedouble-paned windows is (th = 1 cm), and (k = 0.022 W/m.K).Image credit: Windowwhirl.
During a picnic on a hot summer day, the only available drinks were those at the ambient temperature of 90°F. In an effort to cool a 12-fluid-oz drink in a can, which is 5 in high and has a diameter of 2.5 in, a person grabs the can and starts shaking it in the iced water of the chest at 32°F. The temperature of the drink can be assumed to be uniform at all times, and the heat transfer coefficient between the iced water and the aluminum can is 30 Btu/h·ft2·°F. Using the properties of water for the drink, estimate how long it will take for the canned drink to cool to 40°F.
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