You’ve experienced convection cooling if you’ve everextended your hand out the window of a moving vehicle or into a flowing water stream. With the surface ofyour hand al a temperature of 30°C, determine the convection heal flux for (a) a vehicle speed of 35 km/h inair at
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Fundamentals of Heat and Mass Transfer
- A spherical communications satellite, 2 m in diameter, is placed in orbit around the earth. The satellite generates 1000 W of internal power from a small nuclear generator. If the surface of the satellite has an emittance of 0.3, and is shaded from solar radiation by the earth, estimate its surface temperature.arrow_forwardThe air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specifiedarrow_forwardDetermine the rate of heat loss from the wall of a building resulting from a 16 km/h wind blowing parallel to its surface. The wall is 24 m long and 6 m high, its surface temperature is 27C, and the temperature of the ambient air is 4C.arrow_forward
- calculate the convection heat transfer rate over a surface of area 1 m^2 having heat convection coefficient of 40 W/m^2K and temperature difference of 25 °Carrow_forward1. (a) Consider a room with a 1.8-m-high and 2.0-m-wide double-pane window consisting of two 4-mm-thick layers of glass separated by a 10-mm-wide stagnant air space. The convection heat transfer coefficients on the inner and outer surfaces of the window are 12 W/m2 K and 25 W/m2 K, respectively, while the average thermal conductivity of glass is 0.78 W/m K; and the air, 0.026 W/m K. If the room is maintained at 22 oC, the outside temperature is -4 oC and heat transfer due to radiation can be neglected, determine: (i) Draw the sketch and thermal resistance network; (ii) the total thermal resistance; (iii) the steady rate of heat transfer through this double-pane window; (iv) the temperature of the inner surface of the window.…arrow_forwardReconsider Prob. 9-20. Using the EES (or other) software, evaluate the effect of the plate thickness on the surface temperature exposed to the cold air. By varying the plate thickness from 0.01 to 0.1 m, plot the plate surface temperature on the cold air side as a function of the plate thickness. Prob A 0.2-m-long and 25-mm-thick vertical plate (k = 1.5 W/m∙K) separates the hot water from the cold air at 2°C. The plate surface exposed to the hot water has a temperature of 100°C, and the surface exposed to the cold air has an emissivity of 0.73. Determine the temperature of the plate surface exposed to the cold air (Ts,c).arrow_forward
- Consider a 50-cm-diameter and 95-cm-long hot water tank. The tank is placed on the roof of a house. The water inside the tank is heated to 80°C by a flat-plate solar collector during the day. The tank is then exposed to windy air at 18°C with an average velocity of 40 km/h during the night. Estimate the temperature of the tank after a 45-min period. Assume the tank surface to be at the same temperature as the water inside, and the heat transfer coefficient on the top and bottom surfaces to be the same as that on the side surface. Evaluate the air properties at 50°C.arrow_forwardWrite the comparison between forced and free convection in a non-isothermal system?arrow_forwardIn presence of an external flow when will the convective heat transfer be dominated by free convection and not by the forced convection due to the external flow? Gr ≫ Re². Gr ≪ Re. Gr ≫ Re. Gr ≪ Re For ideal gases, the specific heat capacity at constant pressure, thermal conductivity, dynamic viscosity, and Prandtl number are independent of pressure. How will the ratio of thicknesses of velocity boundary layer and thermal boundary layer change if pressure is increased from 1 atm to 5 atm for the flow of an ideal gas over a flat plate? It will decrease by a factor of 5. It will remain the same. It will increase by a factor of 5. We need to know the actual fluid properties to tell.arrow_forward
- Why is heat transfer faster in forced convection compared to natural convectionarrow_forwardIllustrate the concept of convection in heat transfer operation and also differentiate forced convection and natural convection with suitable examples. Why thermal conductivity of liquid decreases whereas that of gas increases by increasing temperature?arrow_forwardIn a new residential project, you strongly believe that double-paned windows are ‘better’ than single-paned windows. Compare the rate of heat loss between single and double-paned windows (1.5 m x 1 m) if the thickness of each pane is (th = 0.4 cm) and (k = 0.9 W/m.K). The indoor and outdoor temperatures are 18 °C and 2 °C, respectively. Thickness of the air gap between the double-paned windows is (th = 1 cm), and (k = 0.022 W/m.K).arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning