As far as diathermy concern, we use microwaves to deposit its energy in the surface of fatty layers where as the infrared waves most of it energy is deposited in deep area with fatty layers. O true False
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- 1.13 If the outer air temperature in Problem is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air, assuming radiation is negligible.Three thin sheets of polished aluminum are placed parallel to each other so that the distance between them is very small compared to the size of the sheets. If one of the outer sheets is at 280C and the other outer sheet is at 60C, calculate the temperature of the intermediate sheet and the net rate of heat flow by radiation. Convection can be ignored.Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.
- 8.15 A mercury bath at is to be heated by immersing cylindrical electric heating rods, each 20 cm tall and 2 cm in diameter. Calculate the maximum electric power rating of a typical rod if its maximum surface temperature is .A horizontal, 3-mm-thick flat-copper plate, 1-m long and 0.5-m wide, is exposed in air at 27C to radiation from the sun. If the total rate of solar radiation absorbed is 300 W and the combined radiation and convection heat transfer coefficients on the upper and lower surfaces are 20 and 15W/m2K, respectively, determine the equilibrium temperature of the plate.A man is working in a chamber enclosed with black walls. If the air around the worker is at 20oC, the walls are at 100oC, and the heat transfer coefficient between the worker and the air is 15 W/m2-oC, what temperature will the worker feel? Assume the radiation emissivity of the worker’s cloth is about 0.8.
- The basal metabolic rate isthe rate at which energy is produced in the body when a person is at rest.A 75 kg (165 lb) person of height 1.83 m (6 ft) has a body surface areaof approximately 2.0 m2. (a) What is the net amount of heat this personcould radiate per second into a room at 18°C (about 65°F) if his skin’ssurface temperature is 30°C? (At such temperatures, nearly all the heatis infrared radiation, for which the body’s emissivity is 1.0, regardless ofthe amount of pigment.) (b) Normally, 80% of the energy produced bymetabolism goes into heat, while the rest goes into things like pumpingblood and repairing cells. Also normally, a person at rest can get rid ofthis excess heat just through radiation. Use your answer to part (a) to findthis person’s basal metabolic rate.9. What is diffusion and convection? Provide an example for each!40% of incident radiant energy on the surface of thermally transparent body is reflected back, if the transmissivity of the body be 0.15 then emissivity of the surface is–
- During hot summer weather, many people put “koozies” around their beverages to keep the drinks cold. In addition to preventing a warm hand from heating the container through conduction, what other mechanisms slow the process of warming beverages?Problem 3: At 2pm in the afternoon, the surface temperature was 70 deg. F and 560 W/m2 of solar radiation was being absorbed by the surface. Determine how much radiation is being emitted by the surface, and whether the temperature was increasing or decreasing at this time.The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.