A spherical vessel has an inner radius r1 and an outer radius r2. The inner surface
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Heat and Mass Transfer: Fundamentals and Applications
- Consider steady heat transfer between two large parallel plates at constant temperatures T1 = 300 K and T2 = 200 K that are L = 1 cm apart, as shown below. Assuming the surface to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is a) filled with still air with k = 0.0219 W/moC, b) free flowing air with h = 7.5 W/m2oC, c) evacuated, d) filled with urethane insulation with k = 0.026 W/moC, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/moCarrow_forwardThe wall of an oven in an industrial plant, made of fire brick (k = 0.71 W/m/K) has thickness of L = 15 cm. The oven is exposed to air at 28oC and the surfaces of the far surroundings are at 20oC. If the temperature of the outer surface of the wall is 92oC and the heat transfer coefficient and emissivity are 20 W/(m^2*K) and 0.8 respectively, determine the temperature of the inner surface of the wall.arrow_forwardThe heat is dissipated from the plate by convection and radiation into surrounds at 20 C . Take ε =0.8 , σ =5.67×10**-8 and h∞ = 6 W/m**2. K. If the surface temperature of the plate is 50 C ,the value of the heat flux from the plate is :arrow_forward
- Calculate the rate of heat energy emitted by 100 m 2 of a polished iron surface (emissivity=0.06). The temperature of the surface is 37°C. where Stefan boltmans constant is = 5.669 x 10^-8 W/(m^2 K^4)arrow_forwardA 2-m x 1.8-m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°C. The temperature of the furnace room is 30°C, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m² • °C. It is proposed to insulate this section of the furnace wall with expanded perlite insulation (k = 0.052 W/m • °C) in order to reduce the heat loss by 90%. Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used. ANSWER:_______cmarrow_forwardConsider a room whose door and windows are tightly closed, and whose walls are well-insulated so that heat loss or gain through the walls is negligible.arrow_forward
- A 5 m long section of a steam pipe whose outer diameter is 10 cm passes through an open space at 30°C. The average temperature of the outer surface of the pipe is measured to be 150°C, and the average heat transfer coefficient on that surface is determined to be 180 W/m^2.k. Determine (a) the rate of heat loss through convection from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace, and the price of natural gas is 0.05 Rs/Kwh, consider a 250 working-day year.arrow_forwarda) Coolant flowing through a radiator at the rate of 3 kg/s are cooled from 105 0C to 81 0C. The specific heat capacity of coolant and air are 4.19 kJ/kg K and 1.13 kJ/kJ/K respectively. Th overall heat transfer coefficient from gas to water is 140 W/m2 K. Calculate the surface area required for the radiation if the vehicle speed is 100 km/h. Consider the density of air as 1.225 kg/m3arrow_forwardThe furnace wall shown in the figure is made of a material with a thermal conductivity of 5 W / m ° C, the radiant emission coefficient of the outer surface of the wall is 0.95, Stefan Boltzman constant is 5.67x104 W / m ^ 2 (K ^ 4), ambient temperature and air temperature 297 K is. The heat transfer coefficient between the outer surface of the wall and the air is h = 20 W / m (K ^ 2). Wall inner surface temperature 573 K, outer surface temperature 308 K Since the value is kept constant a) Find the layer thickness of the wall? b) Find the layer thickness of the wall if the moving fluid medium on the outer surface of the wall is corroded?arrow_forward
- The blades of a wind turbine turn a large shaft at a relatively slow speed. The rotational speed is increased by a gearbox that has an efficiency of 0.93. In turn, the gearbox output shaft drives an electric generator with an efficiency of 0.95. The cylindrical nacelle, which houses the gearbox, generator, and associated equipment, is of length L = 6 m and diameter D = 3 m. If the turbine produces P = 2.5 MW of electrical power, and the air and surroundings temperatures are T = 25 oC and Tsur = 20 oC, respectively, determine the minimum possible operating temperature inside the nacelle. The emissivity of the nacelle is 0.83, and the convective heat transfer coefficient is h = 35 W/m2 .K. The surface of the nacelle that is adjacent to the blade hub can be considered to be adiabatic, and solar irradiation may be neglected. Use Fin or N number of fins to reduce the Ts of the nacelle less than 143 oCarrow_forwardA spherical container with an inner radius r1 = 1 m and an outer radius r2 = 1.05 m has its inner surface subjected to a uniform heat flux of q1=7kw/m^2. The outer surface of the container has a temperature T2 = 25°C, and the container wall thermal conductivity is k = 1.5 W/m·K. Show that the variation of temperature in the container wall can be expressed as and determine the temperature of the inner surface of the container at r = r1.arrow_forwardA 2-m × 1.8-m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°C. The temperature of the furnace room is 30°C, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m2·C. It is proposed to insulate this section of the furnace wall with perlite insulation (k = 0.052 W/m·C) in order to reduce the heat loss by 90 percent, Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning