Consider the cylindrical. 0.12-m-diamter radiation shield of Example 9.5 that is installed concentric with a 0.10-m-diameter tube carrying steam. The spacing provides an air gap of
(a) Calculate the heat loss per unit length of the tube by convection when a second shield of 0.14-mdiameter is installed, with the second shield maintained at 35°C. Compare the result to that for thesingle shield of the example.
(b) In the two-shield configuration of part (a), the air gaps formed by the annular concentric tubes are
Want to see the full answer?
Check out a sample textbook solutionChapter 9 Solutions
Fundamentals of Heat and Mass Transfer
- A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.arrow_forwardThree 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.arrow_forward1.13 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.arrow_forward
- A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation. b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. can you solve part b please?arrow_forwardA long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. Specifically need help with part barrow_forwardThe small horizontal metal tube with an OD of 0.05 m, 0.1 m long, and with a surface temperature of 25 C is in a very large furnace enclosure with firebrick walls and the surrounding air at 500 C. The emissivity of the metal tube is 0.6. Calculate the net heat transfer to the tube by radiation in Watts.arrow_forward
- A 4.0-cm-diameter sphere is heated to a temperature of 200°C and is enclosed in a large room at 20 C. Calculate the radiant heat loss if the surface emissivity is 0.6.arrow_forwardThe temperature of a hot gas stream flowing in a duct (90cm) length and (30cm) diameter is to be measured by using a spherical thermocouple junction (2mm) in diameter placed at the center of the duct. The duct wall is at (30 ° C) and the gas stream is at (110 ° C). If the heat is being transferred to the thermocouple at the rate of (560 W / m²) from the gas, and both the thermocouple and the duct are considered black, what will be the reading of the thermocouple?arrow_forwardAn astronaut performing an extra-vehicular activity(space walk) shaded from the Sun is wearing a spacesuitthat can be approximated as perfectly white (e = 0) exceptfor a 5 cm × 8 cm patch in the form of the astronaut’snational flag. The patch has emissivity 0.300. The spacesuitunder the patch is 0.500 cm thick, with a thermalconductivity k = 0.0600 W/m °C , and its inner surface isat a temperature of 20.0 °C . What is the temperature of thepatch, and what is the rate of heat loss through it? Assumethe patch is so thin that its outer surface is at the sametemperature as the outer surface of the spacesuit under it.Also assume the temperature of outer space is 0 K. You willget an equation that is very hard to solve in closed form,so you can solve it numerically with a graphing calculator,with software, or even by trial and error with a calculator.arrow_forward
- A furnace is located next to a dense array of cryogenic fluid piping. The ice-covered piping approximates a plane surface with an average temperature of Tp = 0°C and a total, hemispherical emissivity of εp = 0.53. That is, the piping can be replaced by a flat surface with the given properties. The furnace wall has a temperature of Tf = 206°C and a total, hemispherical emissivity of εf = 0.83. To minimize the heat loading on the regirgeration equipment and piping, a reflective aluminum radiation shield with a total, hemispherical emissivity of εs = 0.14 on each of its sides is installed between the pipiing and the furnace wall as shown. Assume that all surfaces are diffuse and gray and treat the problem as one-dimensional (surfaces form infinite parallel plates). What is the heat load on on the refrigeration unit? That is, what is the net radiative power at the surface which approximates the dense array of ice-cold piping, qrad,p in Watts?arrow_forwardConsider a hemispherical furnace of diameter D = 5 mwith a flat base. The dome of thefurnace is black, and the base has an emissivity of 0.7. Thebase and the dome of the furnace are maintained at uniformtemperatures of 400 and 1000 K, respectively. Determine thenet rate of radiation heat transfer from the dome to the basesurface during steady operation.arrow_forwardA circular grill of diameter 0.35 m and emissivity 0.7 is maintained at a constant surface temperature of 130 °C in a horizontal position. What electrical power is required when the room air and surroundings are at 24 °C?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning