During its manufacture, plate glass at 600°C is cooledby passing air over its surface such that the convectionheat transfer coefficient is
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Fundamentals of Heat and Mass Transfer
- A spherical ball (15 cm in diameter) with a density of 1000 kg/m³, specific heat capacity of 4180 J/kg-K and thermal conductivity of 0.62 W/m-K is removed from an oven at a uniform temperature of 150 °C. The ball is then left to cool down in steady air at 10 °C. Calculate the heat transfer coefficient for this process and the time for the surface of the ball to drop to 20 °C. Use the following equation to solve this problem (characteristic dimension of the sphere is the diameter). 0.589 . Ra* Nu = 2+ 0.469 16 Prarrow_forwardCalculate the thermal conductivity (in W/m-K) of a material having a heat loss of 1028 watts, inside diameter of 59.4cm and thickness of 118.4mm passing through a 14.5m long pipe at 55˚C. Assume ambient temperature of 4˚C.arrow_forwardA square thermal window is constructed of two sheets of flat glass, each 4.00 mm thick, separated by 5.00 mm of stationary air. If the inside of the window is at 20.0 oC, the external one at -30.0 oC and the cross-sectional area of the window is 6.00 m2, determine for the steady state: kglass= 0,80 W/(m*K); kair= 0,024 W(m*K) a) The temperatures between the air layer ?1 and ?2 indicated in the figure.b) The flow of heat through the windowarrow_forward
- A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 2000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = AnswerkJ / kg. b. Determine the enthalpy of steam coming out = AnswerkJ / kg. c. Determine the vapor heat change / loss along the flow = Answerwatt. d. Specify the minimum required insulation thickness = Answercm.arrow_forward[2] Consider a 1.2-m-high and 2-m-wide double-pane window consisting of two 3-mm-thick layers of glass (k = 0.78 W/m °C) separated by a 12-mm-wide stagnant air space (k = 0.026 W/m- °C). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 24°C while the temperature of the outdoors is -5°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1 = 10 W/m2.°C and h2 = 25 W/m2.°C, and disregard any heat transfer by radiation. Glass 3 12 3 mm Frame a.) Steady rate of heat transfer. А. 318 W B. 214 W C. 114 W D. 321 W b.) Temperature of its inner surface. A. 25°C B. 17.5°C С. 15°С D. 19.2°Carrow_forwardA pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.arrow_forward
- The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is -196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and 196°C. The tank is exposed to 22°C ambient air with a heat transfer coefficient of 22 W/m2 · °C. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air in kg/sec. Answer in…arrow_forwardA 10 cm outer diameter pipe carrying saturated steam at a temperature of 195C is lagged to 20 cm diameter with magnesia and further lagged with laminated asbestos to 25 cm diameter. The entire pipe is further protected by a layer of canvas. If the temperature under the canvas is 20°C, find the mass of steam condensed in 8 hrs on a 100m length of pipe and interface temperature. Take thermal conductivity of magnesia as 0.07 W/m – K and that of asbestos as 0.082 W/m – k. Neglect the thermal conductivity of the pipe material. The latent heat of steam for given conditions can be taken as 1951 kJ/kg–K.arrow_forwardA furnace wall consists of 2 ft of brick . The brick has athermal conductivity of 0.6 Btu/ hr sq ft ( ° F /ft), a specific heat of0.2 Btu/ lb ° F, and a density of 110 lb/cu ft. The temperature atthe inside surface of the wall is 1100 ° F , and at the outside surface,200 ° F .(a) Calculate the thermal diffusivity of the brick .(b) Calculate the heat loss per hour through a wall 10 ft high and10 ft long(c ) Calculatearrow_forward
- A soil with thermal diffusivity 6X106 m2/s and thermal conductivity 30 w/m.K is initially at a uniform temperature of 35°C. Suddenly, the surface is exposed to a coolant at 15°C for which the convection heat transfer coefficient is 100 W/m2 .K. Determine temperatures at the surface and at a depth of 20 cm after 5 min have elapsed.arrow_forwardA pipe 30 m long with an outer diameter of 75 mm is used to carry steam at a rate of 1000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.arrow_forwardWater hardening process of 2 m long and 0.05 m diameter steel bars will be carried out. The steel bar, which is heated up to 900 °C in the oven, is cooled to an average temperature of 100 °C in a water bath. The water bath is kept at a uniform temperature of 30 °C and the heat transfer coefficient between the water and the rod surface is 325 W/m2K. Accordingly, calculate the time required for the steel bar to cool to 100°C in the water bath. (Steel bar p=7832 kg/m3, cp=434 J/kgK, k=63.9 W/mK)arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning