In the central receiver concept of solar energy collection, a large number of heliostats (reflectors) provide a concentrated solar flux of
The receiver wall is exposed to the solar flux at its outer surface and to atmospheric air for which
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Fundamentals of Heat and Mass Transfer
- Determine the heat transfer that occurs by radiation between two surfaces that are co-axial and parallel to each other, full and semicircular. Assume that the surfaces only exchange radiation with each other. T1 = 700 °C; ɛ1 = 0.8; T2 = 20 °C; e2 = 0.4. фб ст (2) to 4 cm 6 8 cm (1 t.arrow_forwardLiquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. answers: a) 375K b) 22.1kWarrow_forwardLiquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x106 W. Calculate the surface temperature of the end (facing the sun) of a tank. Calculate the conductive heat transfer through the end (facing the sun)of a tank.arrow_forward
- Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. DATA FOR QUESTION: Thermal conductivity, polyurethane foam = 0.02 W/mKStefan’s Constant = 5.67x10^-8 W/m^2K^4Emissivity, steel = 0.95 answers: a) 375K b) 22.1kWarrow_forwarda) Explain how Fourier's law of conduction (in one-dimensional cartesian system) can be applied to experimentally measure the thermal conductivity of solid materials. What are the necessary conditions and assumptions? b) 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 ε₁0 (T₁ - T₂).arrow_forwardConsider a large plane wall of thickness L = 0.8 ft and thermal conductivity k = 1.2 Btu/h-ft-°F. The wall is covered with a material that has an emissivity of ε = 0.80 and a solar absorptivity of a = 0.60. The Inner surface of the wall is maintained at T₁ = 524 R at all times, while the outer surface is exposed to solar radiation that is incident at a rate of q solar = 300 Btu/h-ft2. The outer surface is also losing heat by radiation to deep space at O K. 0 Plate a solar o = 0.1714 x 10-8 Btu/h ft2 R4 Sun If the temperature of the outer surface of the wall is 556.39 R, determine the rate of heat transfer through the wall when steady operating conditions are reached. (Round your answer up to 2 decimal places.) 51 Btu/h-ft2 (per The rate of heat transfer through the wall when steady operating conditions are reached unit area)arrow_forward
- Ex1. A thin-walled cubical container that is 0.5 m by 0.5 m by 0.5 m is filled with ice water. The container is inside another .cubical container and the 3 cm gap between the containers is a vacuum. The outer surface of the inner container has an emissivity of 0.1 and a temperature of 1 C. The inner surface of the outer container has an emissivity of 0.3 and a temperature of 19 C. (a) What is the rate of heat transfer to the ice water? (b) If the container initially contains 1/2 ice and 1/2 water by volume, how long will it take for all the ice to be melted?arrow_forwardEx2. Two large parallel plates are exchanging radiation. One plate has a temperature of 1000 K and an emissivity of 0.8. The other plate is at 350K and has an emissivity of 0.4. (a) What is the radiant heat flux between the plates? (b) It is desired to reduce the heat transfer between the plates by inserting a thin radiation shield between them. The shield has an emissivity of 0.1 on one side and 0.05 on the other. What is the new rate of heat transfer after the shield is in place, and what is the temperature of the shield? (c) An additional shield like the one of Part (b) is placed in the system to further reduce the heat transfer. What is the resulting heat flux, and what are the temperatures of the two shie lds?arrow_forwardAt midday when a black paved airport runway is directly under the Sun, it receives 800 W of solar power per square meter of surface from the Sun. If this hot surface loses energy only by radiation back into the atmosphere, what is its equilibrium temperature (in K)? You may use an emissivity of e = 1 for a black surfacearrow_forward
- A small sphere (emissivity = 0.745, radius = r1) is located at the center of a spherical asbestos shell (thickness = 1.72 cm, outer radius = r2; thermal conductivity of asbestos is 0.090 J/(s m Co)). The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 727 °C, while the temperature of the inner surface of the shell is 406 °C, both temperatures remaining constant. Assuming that r2/r1 = 6.54 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.arrow_forwardTwo parallel discs pf 1m diameter are situated 2m part in surroundings at a temparature 20 C. The inner side of one disc has an emissivity of 0.5 and is manintained at 500 C by electric resistance heating and the outer side of the disc is well insulated. The other disc is Two parallel discs of 1m diameter are situated 2m apart in surroundings at a temperature of 20 oC. The inner side of one disc has an emissivity of 0.5 and is maintained at 500 oC by electric resistance heating and the outer side of the disc is well insulated. The other disc is open to radiation on both sides and reaches an equilibrium temperature. Calculate this equilibrium temperature and the heat flow rate from the first disc, assuming heat transfer is entirely by radiation.arrow_forwardConsider 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/m°C, b) free flowing air with h = 7.5 W/m2°C, c) evacuated, d) filled with urethane insulation with k = 0.026 W/m°C, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/m°Carrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning