Consider a person standing in a room maintained at
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HEAT+MASS TRANSFER:FUND.+APPL.
- 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.arrow_forwardConsider 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_forwardHeat transferarrow_forward
- Determine the net heat transferred by radiation from a 9-ft square hot plate to a cold plate of equal size that are parallel to one another, and 20 ft apart if the hot plate is oxidized steel at 700°F and the cold plate is dull brass at 175°F.Ans: 2,863 Btu/hrarrow_forwardConsider a sealed 20-cm-high electronic box whose base dimensions are 40 cm × 40 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 100 W of power and the outer surface temperature of the box is not to exceed 55 °C, determine the (maximum) temperature (in °C) 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. Round your answer to 2 decimal places.arrow_forward1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron. 2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.arrow_forward
- Consider a person standing in a room maintained at 20°C at all times. The inner surfaces of the walls, floors, and the ceiling of the house are observed to be at an average temperature of 15°C in winter and 30°C in summer. Determine the rate of radiation heat transfer between this person and the surrounding surfaces if the exposed surface area and the average outer surface temperature of the person are 1.2 m2 and 34°C, respectively. Given: εskin = 0.95, σ = 5.67x10^(-8) W/(m^2∙K^4 ). Heat Radiation in Winter (W) = Heat Radiation in Summer (W) =arrow_forwardA 50-cm * 50-cm circuit board that contains 121 square chips on one side is to be cooled by combined natural convection and radiation by mounting it on a vertical surface in a room at 25°C. Each chip dissipates 0.18 W of power, and the emissivity of the chip surfaces is 0.7. Assuming the heat transfer from the back side of the circuit board to be negligible, and the temperature of the surrounding surfaces to be the same as the air temperature of the room, determine the surface temperature of the chips. Evaluate air properties at a film temperature of 30°C and 1 atm pressure. Is this a good assumption?arrow_forwardexplain why summer is warmer than winter. Specifically, how can summer be warmer than winter if Earth is farther away from the Sun at that time?arrow_forward
- Solve asaparrow_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_forwardConsider a person standing in a room kept at 22°C at all times. Your house It has been observed that the inner surfaces of the walls, floor and ceiling are at an average temperature of 15°C. If this person's exposed surface area is 1.4 m2 and if the average external surface temperature is 30°C, this person and the surrounding surfaces Determine the radiation and heat transfer rate between One's emissivity, the Stefan-Boltzmann constant a=5,67x10 -8 W/m 2 K 4arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning