Consider steady heat transfer between two large parallel plates at constant temperatures of
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Chapter 1 Solutions
Heat and Mass Transfer: Fundamentals and Applications
- Consider a person whose exposed surface area is 1.7 m2, emissivity is 0.7, and surface temperature is 32°C. Determine the rate of heat loss from that person by radiation in a large room having walls at a temperature of (a) 300 K and (b) 280 K.arrow_forwardQuestion 4:Consider a person standing in a room maintained at20°C at all times. The inner surfaces of the walls, floors, andceiling of the house are observed to be at an average temperature of 12°C in winter and 23°C in summer. Determine therates of radiation heat transfer between this person and the surroundingsurfaces in both summer and winter if the exposedsurface area, emissivity, and the average outer surface temperatureof the person are 1.6 m2, 0.95, and 32°C, respectively.arrow_forwardA group of 25 power transistors, dissipating 1.5 W each, are to be cooled by attaching them to a black-anodized square aluminum plate and mounting the plate on the wall of a room at 30°C. The emissivity of the transistor and the plate surfaces is 0.9. Assuming the heat transfer from the back side of the plate to be negligible and the temperature of the surrounding surfaces to be the same as the air temperature of the room, determine the size of the plate if the average surface temperature of the plate is not to exceed 50°C.arrow_forward
- Two very large walls are at constant temperature of 658oF and 856oF. Assuming that the walls behave like black bodies, how much heat in Btu/hr-ft2 must be removed from the colder wall in order to maintain a constant pressure (σ=0.1714x10-8 Btu/hr-ft2-R)arrow_forwardA thermocouple shielded by a layer of aluminum foil and copper with an emissivity of 0.05 and 0.02 is used to measure the temperature of hot gases flowing in a duct whose walls are maintained at T= 380K. Assuming emissivity of the thermocouple junction is 0.7 and convection heat transfer coefficient to be h= 130 W/m2.C, determine the radiation heat transfer from thermocouple junction to duct wall.arrow_forwardThe door of an oven in the kitchen of a house is 0.5 m high and 0.7 m wide. When the oven is operating, the outside temperature of the door reaches 32°C. Calculate the heat transfer from the oven door towards the room at 22°C, taking into account the effects of radiation. The emissivity of the oven door is 1 and the walls of the kitchen are at 22°C. (σ = 5.67 x 10-8 W/m2K4 , g = 9.81 m/s2 ) NOTE: More precise values for weather characteristics can be obtained from resources on the internet. Also indicate the source you received.arrow_forward
- A 5-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steel (k = 15 W/m-°C) is used to store iced water at 0°C. The tank is located in a room whose temperature is 30°C. The walls of the room are also at 30°C. The outer surface of the tank is gray (emissivity = 0.9), and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are 80 W/m²-°C and 10 W/m²-°C, respectively. Determine the amount of ice at 0°C that melts during a 24-h period. The heat of fusion of water at atmospheric pressure is hfg = 333.7 kJ/kg.\ ANSWER:_____kgarrow_forwardA vertical 1.5-m-high and 3.0-m-wide enclosure consists of two surfaces separated by a 0.4-m air gap at atmospheric pressure. If the surface temperatures across the air gap are measured to be 280 K and 336 K and the surface emissivities to be 0.15 and 0.90, determine the fraction of heat transferred through the enclosure by radiation.arrow_forwarda certain body at 20 C is display on a top of a building during the night. the body sees nothing but the sky which has effective temperature of 110 k. determine the heat transfer rate from the body to the sky if the body temperature is maintained at 23 C. the surface to the sky emissivity of the body is equal to 0.92arrow_forward
- Consider a 0.6-m × 0.6-m thin square plate in a room at 30°C. Both sides of the plate are maintained at a temperature of 90°C. Determine the rate of heat transfer from the plate by natural convection if the plate is (a) vertical and (b) horizontal. (c) If the plate surface with an emissivity of ε= 0.6, also loses heat by radiation to the room walls at 30°C, can radiation loss be neglected?arrow_forwardDetermine the heat transfer that occurs by radiation between two surfaces that are co-axial and parallel to each other, full and semicircular. Assume that the surfaces only exchange radiation with each other. T1 = 700 °C; ɛ1 = 0.8; T2 = 20 °C; e2 = 0.4. фб ст (2) to 4 cm 6 8 cm (1 t.arrow_forward(b) Consider a sealed 20-cm-high electronic box in Figure 1 whose base dimensions are 50 cm x 50 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 120 W of power and the outer surface temperature of the box is not to exceed 55°C, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. 50 cm 120 W € = 0.95 T₁ = 55°C 20 cm Stand 50 cm. Figure 1 Electronic boxarrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning