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Chapter 8 Solutions
Fundamentals of Heat and Mass Transfer
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- 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forwardA 1-in Sch 40 stainless steel pipe with a thermal conductivity of 45 W/m-K can move 1,000 kg of saturated steam per hour at 150 °C. Refractory material 0.25 inches thick with a thermal conductivity of 0.025 W/m-K insulates the pipe. At a temperature of 25 °C, the pipe is exposed to the outside air. There is a 1135 W/m2 internal heat transfer coefficient.40 W/m2-K is the outside heat transfer coefficient, whereas -K. Suppose that only the radial direction is involved in steady-state heat transfer and that radiation effects are negligible. ✓ Determine how much heat is being lost through these pipes to the environment.a. 399.1 W/mb. 1525.0 W/mc. 618.4 W/md. 1128.7 W/me. none of the above √ How about the insulated pipe's surface temperature?a. 118.5 °Cb. None of the abovec. 101.5 °Cd. 216.3 °Ce. 292.2 °Carrow_forwardA furnace wall comprises three layers of thickness 250 mm, 100 mm, and 150 mm with thermal conductivities of 1.65, k and 9.2 W/m K respectively. The inside is exposed to gases at 1250 °C with convection of 25 W/m2K, and the inside surface is at 1100 °C, the outside surface air at 25 °C with convection of 12 W/m2K. Determine the overall heat transfer coefficient in W/m2-K to 2 d.p. ?arrow_forward
- QUESTION 3: Warm air is blown over the inner surface of the windshield of an automobile to defrost ice accumulated on the outer surface. The windshield has a thickness of 5 mm and thermal conductivity of 1.4 W/m-K. The outside ambient temperature is -10°C and the convection heat transfer coefficient is 200 W/m²-K, while the ambient temperature inside the automobile is 25°C. Determine the value of the convection heat transfer coefficient for the warm air blowing over the inner surface of the windshield necessary to cause the accumulated ice to begin melting.arrow_forwardA pipe carrying steam of 5 cm inside diameter and 6.5 cm outside diameter is covered with a 2.75 cm of high temperature insulation(k = 0.1 W/m.K). The convection heat transfer coefficient for inside and outside surfaces are 4650 W/m2.K and 11.5 W/m2.K, respectively. The thermal conductivity of the pipe material is 45 W/m.K. If the flow fluid temperature is 200°C and ambient air temperature is 25°C, determine the Overall heat transfer coefficient * U إضافة ملفarrow_forwardOil whose temperature is 30°C is flowed through a pipe with a diameter of 50 cm. The pipe is in an environment where the temperature is 20°C. So that not a lot of heat comes out of the pipe, the pipe is wrapped with an insulating material (k = 0.007 W/mK) as thick as 5 cm. If the convection coefficient of the outer surface of the pipe is 12 W/m²K, calculate the heat flow from the pipe per meter of length.arrow_forward
- 3- Pipes with inner and outer diameter of 50mm and 60mm, respectively, are used for transporting superheated vapor in a manufacturing plant. The pipes with thermal conductivity of 16 W/m.K are connected together by flanges with combined thickness of 20mm and outer diameter of 90mm. Air condition surrounding the pipes has a temperature of 25C and a convection heat transfer coefficient of 10 W/m².K. If the inner surface temperature of the pipe is maintained at a constant temperature of 150C, determine the temperature at the base of the flange and the rate if heat loss through the flange. Air, 25 °C h= 10 W/m².ºC D;= 90 mm D;, = 50 mm T; = 150 °C Pipe, k = 16 W/m•°C D,= 60 mm t= 20 mmarrow_forwardThe building is in an environment of 30 ° C. The walls are covered with an insulating layer of 4 cm thickness whose thermal conductivity is 1.8 W / (m K), and the temperature of the inner wall of the insulation is 320 ° C. Wall heat loss to the environment occurs by convection. Calculate the convection heat transfer coefficient value on the outer surface of the insulation to ensure that the outer surface temperature does not exceed 40 ° C. Convection coefficient = AnswerW / m² ° C.arrow_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 steam pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe that needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam only decreases slightly to 95%. The temperature of the outer surface of the insulation is assumed to be 25 ° C. The conductive of the pipe material and the situation of no pressure drop in the pipe. A. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam that comes out = Answer kJ / kg. c. Determine the change / loss of steam heat along the flow = Answer watt. d. Determine the minimum required insulation thickness = Answer cm.arrow_forward
- 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…arrow_forwardThe thickness of one wall is 0.07 m. The right side of the wall is exposed to ambient air with a temperature of T = 310 K and Tsur= 300 K. If the external surface temperature of the wall (right side) is 500 K and the coefficient of heat transfer is h=30W/m²K, the rate of propagation is 0.78, and the coefficient of heat transmission of the wall is k=0.86 W/m²K, what is the temperature of the inner wall?arrow_forwardA central heating system from a house consists of 50m of 15mm outside diameter copper pipe with a wall thickness of 1mm. This pipe is used to distribute water at a temperature of 70 degrees C. Calculate the rate of heat loss from the length of pipe if it is fitted with a 15mm radial thickness of insulation. Take the ambient air temperature to be 15 degrees C and the internal and external surface heat transfer coefficients to be 100 W/m².K and 8 W/m2.K respectively. The thermal conductivity of the copper is known to be 400 W/m.K and 0.05 W/m.K for the insulation. State your answer correct to three significant figures in Watts. Assume steady state radial heat transfer. Answer: Ensure that you consider the overall effects of radial heat transfer through conduction and convection. Additionally ensure that you consider the overall length of the copper pipe.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
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