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_forwardTwo 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_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 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_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 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_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_forwardA 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.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_forwardAn electronic box that consumes 200 W of power is cooled by a fan blowing air into the box enclosure. The dimensions of the electronic box are 15 cm * 50 cm * 50 cm, and all surfaces of the box are exposed to the ambient except the base surface. Temperature measurements indicate that the box is at an average temperature of 32°C when the ambient temperature and the temperature of the surrounding walls are 25°C. If the emissivity of the outer surface of the box is 0.75, determine the fraction of the heat lost from the outer surfaces of the electronic box.arrow_forwardA black body of finite dimension at 1000 K is inserted into an infinite medium at 300 K. Given Stefan Boltzman constant as 1.8x10-8 W/m²K4, Determine heat transfer coefficient.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning