A steam-carrying steel-pipe has inner and outer diameter of 85 mm and 110 mm, respectively. It is covered with an insulation having a thermal conductivity of 1.8 W/mK. The convective heat transfer coefficient between the surface of insulation and the surrounding air is 14.5 W/m²K. Determine the critical radius of insulation.
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- 2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)The front window of an automobile has a thickness of 4 mm and is defrosted by the passage of a stream of hot air through the inner surface. The thermal conductivity of glass is around 0.78 W/(m oC). Assume the ambient air temperature is -10°C and the external convection coefficient is 65W/(m2 K). If the hot air blowing to defog the glass internally is at 40 ºC and the internal convection coefficient corresponds to 30 W/(m2 K), the internal surface temperatures will be _____________. However, if the car accelerates and maintains high speed, the external convection coefficient should _____________ [increase or decrease?] and if the condition is maintained long enough the temperature of the inner surface of the glass should _____________ [increase or decrease?].1. Saturated steam at 500 K flows in a 0.20 m inside diameter, 0.21 m outside diameter pipe. The pipe is covered with 0.075 m of insulation with a thermal conductivity of 0.10 W/m-K. The pipe's conductivity is 52 W/m-K. The ambient temperature is 300 K. The unit convective coefficients are hi = 18,000 W/m²-K and ho 12 W/m²-K. Determine the heat loss (kJ/min) from 5 m of pipe.
- Consider a long, insulated cable supplying power to a community. It is elevated in the air by using poles. The ambient air temperature is 20oC and the convective heat transfer coefficient is h = 20 W/m2.K. Radiation exchange between the cable surface and the environment can be neglected. Make your calculations considering per meter-length. The wire carries 500 Amp current and has a resistance of 0.0001 Ohm/m. The diameter of the solid core wire is 1.0 cm and has a thermal conductivity of k = 20 W/m.K The electrically insulating material covering the wire-core has a thickness of 0.5 cm with a thermal conductivity of k = 0.01 W/m.K a) What is the rate of heat loss from the cable to the environment in kW/meter? b) What is the outside surface (exposed to air) temperature of the cable? c) What is the temperature of the interface between the insulation sleeve and the core-wire carrying the electric power? If the sleeve material has to remain below 100 oC for the long term, would this…A steel pipe 150mm diameter conveys steam at a temperature of 260 degrees and is covered by two layers of lagging, each 50mm thick. The thermal conductivity coefficient of the inside layer of lagging is 0.086W/m.K while that of the outside layer is 0.055W/m.K. The outside surface temperature of the steel pipe can be taken as the same as the temperature of the system. The ambient temperature is 27 degrees. Calculate the heat lost per hour for pipe length 30m. Calculate the interface temperature between the two layers of laggingSoru 1 A steel pipe (k=43 W/m.K) has inner and outer diameters are 5 cm and 6 cm, Henüz respectively. The pipe is covered with high temperature insulation material. Thermal cevaplanmadı conductivity and thickness of the insulation are 0.11 W/m.K and 0.012 m, respectively. Steam at 115,82°C flows in the pipe. The unit thermal resistance at the inner wall is 0.0026 m2.K/W. The heat transfer coefficient at the outer surface is 17 W/m2.K. The 35,00 üzerinden işaretlenmiş P Soruyu işaretle ambient temperature is 55,54°C. Estimate the rate of heat loss per unit length (W/m). Yanıt:
- One vessel having a carbon-steel wall of thickness 5 mm carrying saturated steam and water at 423K. The vessel is insulated with magnesia of thickness 50 mm. If the ambient air temperature is 321 K, determine the heat loss from the vessel. Given: i. thermal conductivity of carbon steel is 52 W/m.K ii. thermal conductivity of magnesia is 0.5 W/m.K iii. surface coefficient of insulation surface is 3 W/m2.K6. A 1.5 m pipe of negligible thickness holding a hot fluid at 140°C and having an outer diameter of 0.4 m is insulated with three layers of each 50 mm thick insulation of k₁ = 0.02; k2 = 0.06; and k3= 0.16 W/m-K (starting from inside). The outside surface temperature is 30°C. Determine a. the heat loss in Watts, b. the temperatures between interfaces of insulating layers in °CThe oven of a stove must have a sufficient insulation so that the surface temperature of the stove is not greater than 50 oC. To accomplish this, insulation, k = 0.11 W/m-K, is used between the inside and outside metal surfaces. The room temperature is 20 oC, and the outside unit convective coefficient is 8 W/m2-K. Neglecting the resistance of the metal, what is the minimum thickness of insulation required, if the outside temperature reaches 315 oC?
- Calculate the heat loss through a 100-ft² wall with an inside temperature of 65°F and an outside temperature of 35°F. Assume the exterior wall is composed of 2- in. of material having a 'k' factor of 0.80, and 2-in. of insulation having a conductance of 0.16. RTotal = 8.75 & Q = 342-Btu/hr RTotal = 9.2 & Q = 399-Btu/hr RTotal = 8.75 & Q = 399-Btu/hr RTotal = 9.2 & Q = 342-Btu/hr Hide hint for Question 3 Utilize the (RTotal = 1/C + x1/k1) equation.Please answer:Calculate the correct rate of heat loss through the vertical walls of a boiler furnace of size 4 m by 3 m by 3 m high (A=12 m ). Thewalls are constructed from an inner fire brick wall 25 cm thick of thermal conductivity 0.4 W/mK, a 2 mm thick steel protective layerof thermal conductivity 55 W/mK, and a layer of ceramic blanket insulation of thermal conductivity 0.2 W/mK and 8 cm thick. Theinside temperature of the fire bricklayer was measured at 600 deg C and the temperature of the outside of the insulation 60 deg C.A room is well insulated apart from a single-glazed window measuring 1 m2 and 4 mm thick. The internal air temperature is 22oC and outside it is -12oC. If the external convective heat transfer coefficient, hout, is double that of the inside coefficient, and the conductivity in the glass is negligible. Determine hout if Q = 100 W.