A manufacturing process calls for heating long copper rods, which are coated with a thin film having
(a) What is the initial rate of change of the rod temperature!
(b) How long must the rods remain in the oven to achieve a temperature of 1000 K?
(c) The heating process may be accelerated by routing combustion gases, also at 1650 K, through the oven. For convection coefficients of 10, 100, and
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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_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_forwardA 30 x 30 cm door in a brick kiln is at a distance of 3.5 m from a wall 12 m wide and 5 m high. The door is so located that a normal from the center of the door strikes the wall midway from the ends and 1.5 m above the floor. The opening into the kiln may be considered a black body; the wall is painted flat paint (Ɛ = 0.46). The temperature inside the kiln is 1 400 C and the wall temperature is 60 C. Determine (a) the configuration factor F12 and (b) the net radiant heat exchange between the opening and the wall when the fire door is open?arrow_forward
- A dryer is shaped like a long semicylindrical duct of diameter 1.5 m. The base of the dryer is occupied with water soaked materials to be dried, and maintained at a temperature of 370 K and emissivity of 0.5. The dome of the dryer is maintained at 1000 K with emissivity of 0.8. Determine the drying rate per unit length experienced by the wet materials.arrow_forwardThe surface temperature of the sun is about 6000K. Accordingly, which wavelength corresponds to the greatest value of the electromagnetic radiation intensity from the sun? Interpret your result according to the sensitivity of the human eye.arrow_forwardThis experiment is conducted to determine the emissivity of a certain material. A lone cylindrical rod of diameter D1 = 0.01 m is coated with this new material and is placed in an evacuated lone cylindrical enclosure of diameter D2 = 0.1 m and emissivity E2 = 0.95, which is cooled externally and maintained at a temperature of 200 K at all times. The rod is heated by passing electric current through it. When steady Operating conditions are reached, it Is observed that the rod Is dissipating electric power at a rate of 8 W per unit or its leneth and its surface temperature is 500 k, Based on these measurements, determine the emissivity of the coatine on the rodarrow_forward
- An 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_forwardHeat is generated in a sphere of radius 1 m at a rate of 1000 W/m3. The sphere is surrounded by air at 27 oC.A. Balance total energy produced by the total energy lost from the surface by convection and radiation tocalculate the surface temperature.B. Solve the heat transfer problem in the sphere and use the temperature calculated in A as the boundarycondition to determine the temperature at the center of the sphere.Assume that the sphere can be treated as a black body for calculating radiation losses.Properties The thermal conductivity is given to be k =2.5 W/m°C.σ = 5.67 × 10−8 W / (m2 x K4). Heat transfer coefficient h = 10 W/(m2 K)arrow_forwardA loaf of bread having a surface temperature of 373 K is being baked in an oven whose walls and the air are at 477.4 K. The bread moves continuously through the large oven on an open chain belt conveyor. The emissivity of the bread is estimated to be 0.85, and the loaf can be assumed to be a rectangular solid 114.3 mm high × 114.3 mm wide × 330 mm long. Calculate the radiation heat-transfer rate (in SI and AES units) to the bread, assuming that it is small compared to the oven and neglecting natural convection heat transfer.arrow_forward
- A 3-in-diameter cylindrical wire is coated in 3 inches of polyethylene insulation. The wire can be modeled as a grey body with an emissivity of .85. Due to the electrical resistance, the wire is at a temperature of 300 degrees Celsius. The insulation is also a great body with an emissivity of .95, at a temperature of 40 degrees Celsius. (Assume F12=1). What is the heat flux (W/m^2) of the energy going from the wire to the insulation?arrow_forwardA furnace is of cylindrical shape with a diameter of 1.2 m and a length of 1.2 m as shown in Figure 3. The top surface has an emissivity of 0.70 and is maintained at 500 K. The bottom surface has an emissivity of 0.50 and is maintained at 650 K. The side surface has an emissivity of 0.40. Heat is supplied from the base surface at a net rate of 1400 W. Estimate the temperature of the side surface and the net rates of heat transfer between the top and the bottom surfaces, and between the bottom and side surfaces.arrow_forwardA house located in Boulder, Colorado (40° N latitude), has ordinary double-pane windows with 6-mm-thick glasses and the total window areas are 8, 6, 6, and 4 m2 on the south, west, east, and north walls, respectively. Determine the total solar heat gain of the house at 9:00, 12:00, and 15:00 solar time in July. Also, determine the total amount of solar heat gain per day for an average day in January. The shading coefficient of a double pane window with 6-mm thick glasses is SC = 0.82. The incident radiation at different windows at different times are given as in the table.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning