A furnace is shaped like a long equilateral-triangularduct where the width of each side is 2 m. Heat is supplied fromthe base surface, whose emissivity is «1 = 0.8, at a rate of800 W/m2 while the side surfaces, whose emissivities are 0.5,are maintained at 500 K. Neglecting the end effects, determinethe temperature of the base surface. Can you treat this geometryas a two-surface enclosure?

A furnace is shaped like a long equilateral-triangularduct where the width of each side is 2 m. Heat is supplied fromthe base surface, whose emissivity is «1 = 0.8, at a rate of800 W/m2 while the side surfaces, whose emissivities are 0.5,are maintained at 500 K. Neglecting the end effects, determinethe temperature of the base surface. Can you treat this geometryas a two-surface enclosure?

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter1: Temperature And Heat

Section: Chapter Questions

Problem 100P: One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a...

See similar textbooks

Similar questions

The thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m K and 0.020 W/m K, respectively, while other tissues inside the body have conductivities of about 0.50 W/m K. Assume that between the core region of the body and the skin sin face lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. (b) Find the rate of energy loss when the core temperature is 37C and the exterior temperature is 0C. Assume that both a protective layer of clothing and an insulating layer of unmoving air a absent, and a body area of 2.0 m2.
One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a house. Suppose a single-story cubical house already had 15 cm of fiberglass insulation in the attic and in all the exterior surfaces. If you added an extra 8.0 cm of fiberglass to the attic, by what percentage would the heating cost of the house drop? Take the house to have dimensions 10 m by 15 m by 3.0 m. Ignore air infiltration and heat loss through windows and doors, and assume that the interior is uniformly at one temperature and the exterior is uniformly at another.
To help prevent frost damage, 4.00 kg of water at 0 is sprayed onto a fruit tree. (a) How much heat transfer occurs as the water freezes? (b) How much would the temperature of the 200-kg tree decrease if this amount of heat transferred from the tree? Take the specific heat to be 3.35k J/kg. , and assume that no phase change occurs in the tree.
The two concentric spheres of diameters Di = 20 cmand Do = 30 cm are separated by air at 1 atm pressure. Thesurface temperatures of the two spheres enclosing the air areTi = 320 K and To = 280 K, respectively. Determine the rateof heat transfer from the inner sphere to the outer sphere bynatural convection.
If the air temperature isthe same as the temperature of your skin (about 30°C), your body cannotget rid of heat by transferring it to the air. In that case, it gets ridof the heat by evaporating water (sweat). During bicycling, a typical70 kg person’s body produces energy at a rate of about 500 W due tometabolism, 80% of which is converted to heat. (a) How many kilogramsof water must the person’s body evaporate in an hour to get ridof this heat? The heat of vaporization of water at body temperature is2.42 * 10^6 J/kg. (b) The evaporated water must, of course, be replenished,or the person will dehydrate. How many 750 mL bottles of watermust the bicyclist drink per hour to replenish the lost water? (Recall thatthe mass of a liter of water is 1.0 kg.)
In a cylinderical furnace of 1.5 m dia and 2 m length the curved surface is maintained at 1400 K,its emissivity being 0.7. The two ends are maintained at 800 K and 600 K. The emissivities are 0.65 and 0.55. Determine the heat flow to each of the surfaces by radiation.
An ideal air conditioner keeps the temperature inside a roomat 21°C when the outside temperature is 32°C. If 4.8 kWof power enters a room through the windows in the form ofdirect radiation from the Sun, how much electrical powerwould be saved if the windows were shaded so only 500 Wenters?
(a) Calculate the rate of heat transfer by radiation from a car radiator at 110C into a 50.0C environment, if the radiator has an emissivity of 0.750 and a 1.20 m2 surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of 200hp (1.5 kW) and the efficiency of automobile engines as 25%.
(a) Calculate the rate of heat transfer by radiation from a car radiator at 110°C into a 50.0ºC environment, if the radiator has an emissivity of 0.750 and a 1.20-m2 surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of 200 hp (1.5 kW) and the efficiency of automobile engines as 25%.
(a) A typical student listeningattentively to a physics lecture has a heat output of 100 W. Howmuch heat energy does a class of 140 physics students release into alecture hall over the course of a 50 min lecture? (b) Assume that allthe heat energy in part (a) is transferred to the 3200 m3 of air in theroom. The air has specific heat 1020 J/kg. K and density 1.20 kg>m3.If none of the heat escapes and the air conditioning system is off,how much will the temperature of the air in the room rise during the50 min lecture? (c) If the class is taking an exam, the heat output perstudent rises to 280 W. What is the temperature rise during 50 minin this case?
You plan to add a certain amount of heatto a gas in order to raise its temperature. (a) If you add the heat atconstant volume, is the increase in temperature greater than, lessthan, or equal to the increase in temperature if you add the heatat constant pressure? (b) Choose the best explanation from amongthe following:I. The same amount of heat increases the temperature by thesame amount, regardless of whether the volume or the pressure is held constant.II. All the heat goes into raising the temperature when added atconstant volume; none goes into mechanical work.III. Holding the pressure constant will cause a greater increase intemperature than simply having a fixed volume.
(a) If the heat capacity of an electric jug is 500 J °c1, how much heat energy does it absorb when heating 1.5 L of water, specific heat 4200 J kg1 0c1, from 20°C to 95°C?