In a two-dimensional cylindrical configuration, the radial
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Fundamentals of Heat and Mass Transfer
- Natural Convection Cooling of an Orange.An orange 102 mm in diameter having a surface temperature of 21.1°C is placed on an open shelf in a refrigerator held at4.4°C. Calculate the heat loss by natural convection, neglecting radiation. As an approximation, the simplified equation for vertical planes can be used withLreplaced by the radius of the sphere (M1). For a more accurate correlation, see (S2).arrow_forwardThis food product is produced in the form of small spheres or pellets by freezing it in the water freezer. Blast freezer air freezers operate at a temperature of -35 degrees Celsius The initial product temperature is 25 degrees Celsius.The pellets have a diameter of 0.5 cm and a density of 980 kg / m³ temperature initial freezing is -2.5 degrees Celsius latent heat of product manufacture is 280 kj / kg the thermal conductivity of frozen products is 1.9 W / (m degrees Celsius). Convection heat transfer coefficient is 50 W / (m² degrees Celsius) calculated freezing time. tf =arrow_forwardA furnace wall consists of 200 mm of refractory fireclay brick, 100 mm of kaolin brick, and 6 mm of steel plate. The fire side of the refractory is at 1150°C and the outside of the steel is at 30°C. An accurate heat balance over the furnace shows the heat loss from the wall to be 300 W/m2. It is known that there may be thin layers of air between the layers of brick and steel. To how many millimeters of kaolin are these air layers equivalent? The thermal conductivities of the fireclay brick, the kaolin brick and the steel are 1.7, 0.17, 17, respectivelyarrow_forward
- The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.arrow_forwardThe production line of a special biscuit at 30 ̊C and 1 atm has a 0.8 X 0.8 (m) square plate. One side of the plate is maintained at a temperature of 100 ̊C, while the other side is insulated. Determine the rate of heat transfer from the plate by natural convection if the plate (i) Is horizontal with the hot surface facing down; (ii) Is horizontal with the hot surface facing up; Data: The properties of air at the film temperature are: thermal conductivity, k= 0.0279 W/m.k); kinematic viscosity= 1.815 x 10-5 m2/s; Pr = 0.709arrow_forwardA small sphere (emissivity =0.503 radius=r1) is located at the center of a spherical abestos shell ( thickness =1.74 cm, outer radius= r2; thermal conductivity of abestos is 0.090 J/ (sm c degrees) The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 695 degrees Celsius while the temperature of the inner surface of the shell is 352 degrees Celsius, both temperatures remaining constant. Assuming that r2/r1 =8.75 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.arrow_forward
- The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is -196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and 196°C. The tank is exposed to 22°C ambient air with a heat transfer coefficient of 22 W/m2 · °C. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air in kg/sec. Answer in…arrow_forwardA black thermocouple is inside a chamber with black walls. If the air around the thermocouple is 20 oC, the walls are at 100 oC and the heat transfer coefficient between the thermocouple and the air is 75W/m2- K. What temperature will the thermocouple read?arrow_forwardA copper sphere with density 8900 kg/m3, radius 5.00 cm,and emissivity e = 1.00 sits on an insulated stand. The initial temperatureof the sphere is 300 K. The surroundings are very cold, so the rateof absorption of heat by the sphere can be neglected. (a) How long doesit take the sphere to cool by 1.00 K due to its radiation of heat energy?Neglect the change in heat current as the temperature decreases. (b) Toassess the accuracy of the approximation used in part (a), what is thefractional change in the heat current H when the temperaturechangesfrom 300 K to 299 K?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning