Calculate the individual resistance of this composite wall and the resistances at the surfaces, and the overall conductance. (b) Draw the thermal circuit. (c) For the air temperature inside the refrigerator at 6.50C and outside of 250oC determine the rate at which heat must be removed from the refrigerator. Also, calculate the temperature on the outer surface of

Calculate the individual resistance of this composite wall and the resistances at the surfaces, and the overall conductance. (b) Draw the thermal circuit. (c) For the air temperature inside the refrigerator at 6.50C and outside of 250oC determine the rate at which heat must be removed from the refrigerator. Also, calculate the temperature on the outer surface of

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.38P: 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from...

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Hot water at an average temperature of 70°C is flowing over a 15-m section of a cast iron pipe (k = 52 W/m·K) whose inner and outer diameters are 4 cm and 4.6 cm, respectively. The inner surface of the pipe exchanges heat by convection and radiation to the cold air at 10°C inside the pipe, with a convective heat transfer coefficient of 15 W/m2·K and heat transfer coefficient for radiation is 6.157 W/m2·K. The heat transfer coefficient at the outer surface of the pipe in the hot water side is 120 W/m2·K, Draw the thermal resistance network and determine the rate of heat loss from the hot water.
Pulverized coal particles are used in oxy-fuel combustion power plants for electricity generation. Consider a situation where coal particles are suspended in hot air flowing through a heated tube, where the convection heat transfer coefficient is 100 W/m2·K. If the average surface area and volume of the coal particles are 3.1 mm2 and 0.5 mm3, respectively, determine how much time it would take to heat the coal particles to two-thirds of the initial temperature difference.
The walls of the refrigerated storage room are 10 m long and 3 m high and constructed with 90 mm concrete blocks (k = 0.935 W / [m ° C]) and 8 cm fiber insulation board (k = 0.048 W). / [m ° C]). The cold room temperature is -10 ° C and the convective heat transfer coefficient is 40 W / (m² K); the outside air temperature is 30 ° C with the outer wall surface convection heat transfer coefficient of 10 W / (m² K). Calculate the overall heat transfer coefficient. Overall heat transfer coefficient = Answer W / (m² K).
A hot surface at 100°C is to be cooled by attaching 3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m·K) to it, with a center-to-center distance of 0.6 cm. The temperature of the surrounding medium is 30°C, and the heat transfer coefficient on the surfaces is 35 W/m2 ·K. Determine the rate of heat transfer from the surface for a 1-m x 1-m section of the plate. Also determine the overall effectiveness of the fins.
Hot oil flows at a temperature of 165 oC through a steel pipe with an outer diameter of 38.0mm and a wall thickness of 3.0mm. Since the heat conduction coefficient of the pipe material is 40W / m oC, the inner and outer surface heat transfer coefficients of the pipe are 4000 and 15W / m2 oC, respectively, and the outdoor temperature is 22 oC a) The insulation material on the pipe is removed, that is, when the bare pipe is a total of 50 (m) Find the total heat flux from the long pipe to the outside. b) If the pipe surface is covered with an insulation material with a thickness of 5 cm and a heat transfer coefficient of 0.065W / moC, how many% decrease in heat loss?
Question 2 Consider a 1.5-m-high electric hot-water heater that has a diameter of 40 cm and maintains the hot water at 60 °C. The tank is located in a small room whose average temperature is 27 °C, and the heat transfer coefficients on the inner and outer surfaces of the heater are 50 and 12 W/m2⋅K, respectively. The tank is placed in another 46-cm-diameter sheet metal tank of negligible thickness, and the space between the two tanks is filled with foam insulation (k = 0.03 W/m⋅K). The thermal resistances of the water tank and the outer thin sheet metal shell are very small and can be neglected. The price of electricity is $0.08/kWh, and the homeowner pays $280 a year for water heating. Determine the fraction of the hot-water energy cost (in %) of this household that is due to the heat loss from the tank. Heat transfers through the top and bottom of the tank are negligible. In continuation of Question 2, hot-water tank insulation kits consisting of 3-cm-thick fiberglass insulation…
In a meat processing plant, 4 cm-diameter spherical meat balls (k=0.45 W/m-K and α=0.91×10-7 m²/s) that are initially at 25 °C are to be cooled by passing them through a refrigeration room at -10 °C. The heat transfer coefficient in the cold room is 22.5 W/m²-K. If surface of the meat balls is to be cooled to 3 °C, determine how long the meat balls should be kept in the refrigeration room. What will be the center temperature of the meat balls at the end of the process?
Consider a steam pipe of length 15 ft, inner radius 2 in., outer radius 2.4 in., and thermal conductivity 7.2 Btu/hr-ft-°F. Steam is flowing through the pipe at an average temperature of 250°F, and the average convection heat transfer coefficient on the inner surface is given to be 1.25 Btu/hr-ft2-°F. If the average temperature on the outer surfaces of the pipe is 160°F, determine the rate of heat loss from the steam through the pipe. ANSWER:______Btu/hr
Consider a 2-m-high electric hot-water heater thathas a diameter of 40 cm and maintains the hot water at 55°C.The tank is located in a small room whose average temperatureis 27°C, and the heat transfer coefficients on the innerand outer surfaces of the heater are 50 and 12 W/m2·K,respectively. The tank is placed in another 46-cm-diametersheet metal tank of negligible thickness, and the spacebetween the two tanks is filled with foam insulation (k =0.03 W/m·K). The thermal resistances of the water tank andthe outer thin sheet metal shell are very small and can be neglected. The price of electricity is $0.08/kWh, and the home owner pays $280 a year for water heating. Determine the fraction of the hot-water energy cost of this household that is due to the heat loss from the tank. Hot-water tank insulation kits consisting of 3-cm-thick fiberglass insulation (k = 0.035 W/m·K) large enough to wrap the entire tank are available in the market for about $30. If such an insulation is installed on…
A 4-mm-diameter and 10-cm-long aluminum fin (k = 237 W/m·K) is attached to a surface. If the heat transfer coefficient is 12 W/m2·K, determine the percent error in the rate of heat transfer from the fin when the infinitely long fin assumption is used instead of the adiabatic fin tip assumption.
Hot water is flowing at an average velocity of1.5 m/s through a cast iron pipe (k = 52 W/m·K) whose innerand outer diameters are 3 cm and 3.5 cm, respectively. Thepipe passes through a 15-m-long section of a basement whosetemperature is 15°C. If the temperature of the water dropsfrom 70°C to 67°C as it passes through the basement and theheat transfer coefficient on the inner surface of the pipe is400 W/m2·K, determine the combined convection and radiationheat transfer coefficient at the outer surface of thepipe.
/ Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.