Consider a thin opaque, horizontal plate with an electrical heater on its backside. The front side is exposed to ambient air that is at
What is the electrical power
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Fundamentals of Heat and Mass Transfer
- 1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .arrow_forward11.41 Determine the steady-state temperatures of two radiation shields placed in the evacuated space between two infinite planes at temperatures of 555 K and 278 K. The emissivity of all surfaces is 0.8.arrow_forwardDetermine the rate of radiant heat emission in watts per square meter from a blackbody at (a) 15C, (b) 600C, and (c) 5700C.arrow_forward
- Determine the amount of acres of land necessary to generate 50 MW of solar power at noon in Philadelphia with an array of panels positioned horizontally. Assume that the panels are 21 % efficient and that the solar irradiation at noon is 900 W/m².arrow_forwardA certain body at 20C is displayed on a top of a building during the night. The body sees nothing but the sky which has an effective temperature of 110K. Determine the heat transfer rate from the body to the sky if the body temperature is maintained at 23C, the surface emissivity of the body is equal to 0.92, and none of the radiation going out of the comes backarrow_forwardA flat-plate solar collector, as shown in Fig. 1, is used to heat water by having water flow through tubes attached at the back of the thin solar absorber plate. The absorber plate has an emissivity and an absorptivity of 0.8. The top surface (* = 0) temperature of the absorber is To = 35 °C, and solar radiat ion is incident on the absorber at 600 W/m? with a surrounding temperature of 0 °C. The convection heat transfer coefficient at the absorber surface as 8 W/m?-K. Assuming constant thermal conductivity and no heat generation in the wall, i express the differential equation and the boundary conditions for steady one- dimensional heat conduct ion through the wall, obtain a relation for the variation of temperature in the wall by solving the differential equation, and ii iii. determine the net heat flux, ġo absorbed by the collector ε, α, Τ. Absorber plate Water tubes Insulation Fig. 1arrow_forward
- •A thin disk-shaped wafer (diameter-=30cm) is maintained at T=100oC. The wafer loses heat to the room by convection and radiation from its upper surface while heat is supplied constantly from below. Assuming the surrounding air at 20oC and all surrounding surfaces (isothermal/blackbodies) at T=15oC. How much heat (in W) must be supplied to the wafer? h wafer-air= 30W/m2K Emissivity of wafer’s surface(gray body)=0.85arrow_forwardA plate-type solar energy collectorr with an absorbing surface covered by a glass is to receive an incident radiation of 800 W/m2. The glass plate has a reflectivity of 0.12 and a transmissivity of 0.80. The absorbing surface has an absorptivity of 0.90. The area of the collector is 5 m2. How much solar energy in watts is absorbed by the collector? ANSWER: 3060 WATTSarrow_forwardA composite wall is comprised of two large plates separated by sheets of refractory insulation. In the installation process, the sheets of thickness L = 50 mm and thermal conductivity k = 0.05 W/mK are separated at 1-m intervals by gaps of width w = 10 mm. The hot and cold plates have temperatures and emissivities of T1 = 400 deg C, emissivity1 = 0.85 and T2 = 35 deg C, emissivity2 = 0.5, respectively. Assume that the plates and insulation are diffuse-gray surfaces. %3D Determine the heat loss by radiation through the gap per unit length of the composite wall (normal to the page). Recognizing that the gaps are located on a 1-m spacing, determine what fraction of the total heat loss through the composite wall is due to transfer by radiation through the insulation gap. Hot side Gap w = 10 mm A. 47 W/m, 9.2% T1 = 400°C B. 47 W/m, 10.2% L = 50 mm C. 37 W/m, 10.2% D. 37 W/m, 9.2% T2 = 35°C Cold side 1 m Insulation, k = 0.05 W/m-Karrow_forward
- Two surfaces make up an enclosure where surface 1 is flat and has area A₁, temperature T₁ and emissivity. Surface 2 is black and has temperature T₂. Show that the net power transfer rate (net heat flux) in W/m² at surface 1 is given by ε₂0 (T₁-T₂).arrow_forwardConsider a black spherical ball, with a diameter of 25 cm, is being suspended in air. Determine the surface temperature of the ball that should be maintained in order to heat 11.7 kg of air from 20°C to 30°C in the duration of 5 minutes.Given: cv = 718 J/kg∙K Stefan-Boltzmann constant (σ) = 5.67 × 10–8 W/m2∙K The surface temperature of the ball is Ts = _____ °C.arrow_forwardA one-dimensional plane wall is exposed to convective and radiative conditions at x = 0. The ambient and surrounding temperatures are T = 20°C and Tsur = 40°C, respectively. The convection heat transfer coefficient is h = 20 W/m².K, and the absorptivity of the exposed surface is a = 0.78. Determine the convective and radiative heat fluxes to the wall at x = 0, both in W/m², if the wall surface temperature is T = 25°C. Assume the exposed wall surface is gray, and the surroundings are large. q'conv i W/m² = grad = i W/m²arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning