The cylinder of an engine is I m long and has an outside diameter of 6 cm. The outside surface temperature of the cylinder is 200°C when the ambient temperature is 30°C. The film coefficient of heat transfer is 25 W/m K. The cylinder is provided with 12 longitudinal straight fins of 0.1 cm thickness and 3 cm length. The thermal conductivity of cylinder and fin material is 75 W/m K. Assuming that the fins have insulated tip, determine (a) the percentage increase in heat dissipation due to addition of fins, (b) the temperature at the centre of the fin, (c) the fin efficiency and fin effectiveness, and (d) the overall fin effectiveness. EXAMPLE 4.6

The cylinder of an engine is I m long and has an outside diameter of 6 cm. The outside surface temperature of the cylinder is 200°C when the ambient temperature is 30°C. The film coefficient of heat transfer is 25 W/m K. The cylinder is provided with 12 longitudinal straight fins of 0.1 cm thickness and 3 cm length. The thermal conductivity of cylinder and fin material is 75 W/m K. Assuming that the fins have insulated tip, determine (a) the percentage increase in heat dissipation due to addition of fins, (b) the temperature at the centre of the fin, (c) the fin efficiency and fin effectiveness, and (d) the overall fin effectiveness. EXAMPLE 4.6

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.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.36P

See similar textbooks

Similar questions

1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
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.
A long stainless-steel (AISI 316) steam pipe, with an inside diameter of 6.00 cm and an outside diameter of 8.00 cm, is covered with a layer of asbestos insulation (k = 0.150 W/m-K) 1.00 cm thick, which in turn is covered with foam insulation (k = 0.044 W/m-K) 6.00 cm thick. The inside surface temperature of the stainless-steel steam pipe is measured to be 250.0°C, while the outside surface of the foam is exposed to convection, T_inf = 25.0°C, h_inf = 15.0 W/m^2-K. • Draw and label a sketch of this system. Include dimensions, known temperatures, etc. • Draw and completely label the corresponding 1-D steady-state conduction resistor diagram. • Determine the heat transfer rate through the pipe per unit length. • Calculate the temperature at the asbestos/foam interface.
An uninsulated 100-mm diameter steam pipe runs for 25-meters inside a room whose walls and air are at a temperature of 25C .The superheated steam inside the pipe maintains the temperature at the pipe surface at 150C. If the natural convection heat transfer coefficient of the air outside the pipe is 10 W/(m^2)(k)and the surface emissivity is 0.8, compute for the total thermal resistance at the outside surface of the pipe in K/W.
Calculate the quantity of heat conducted per minute through a duralumin circular disc 119mm diameter and 22.65mm thick when the temperature drop across the thickness of the plate is 9.3°F take the coefficient of thermal conductivity of duralumin as 150 W/m-K. Answer: 22.833 kJ/min
The plumbing system of a house involves a 0.5-m section of a plastic pipe (k = 0.16 W/m-C) of inner diameter 2 cm and outer diameter 2.4 cm exposed to the ambient air (refer to figure 3). During a cold and windy night, the ambient air temperature remains at about -5°C for a period of 14 h. The combined convection and radiation heat transfer coefficient on the outer surface of the pipe is estimated to be about 40 W/m2-°C, and the heat of fusion of water is 333.7 kJ/kg. Assuming the pipe to contain stationary water initially at 0°C. (20 pts.) determine (a) if the water in that section of the pipe will completely freeze that night. (b) What is to be done to be sure that water doesn't freeze during the period of 14 h.
A 10-m long pipe carrying brine at – 8°C passes through a room at 30°C. The outside diameter of the pipe is 15 cm and the convection coefficient has a value of 18 W/m2 ·K. In order to reduce the heat gain, molded insulations of 2.5 cm, 4 cm, 6 cm and 8 cm thicknesses with conductivities of 0.06 W/m-K, 0.05 W/m-K and 0.03 W/m-K, respectively, were installed to the pipe. Determine the heat loss on the pipe.
A 5-mm-diameter spherical ball at 50 oC is covered by a 1-mm-thick plastic insulation (k=0.13 W/m.oC). The ball is exposed to a medium at 15 oC, with a combined convection and radiation heat transfer coefficient of 20 W/m2.oC. Determine if the plastic insulation on the ball will help or hurt heat transfer from the ball.
A hot surface at 100°C is to be cooled by attaching3-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. Thetemperature of the surrounding medium is 30°C, and the heattransfer coefficient on the surfaces is 35 W/m2·K. Determine therate of heat transfer from the surface for a 1-m * 1-m sectionof the plate. Also determine the overall effectiveness of the fins.
In a food industry, pieces of meat with approximately 30 cm in diameter and 20 mm in thickness are stored in a industrial freezer and thawed by exposure to ambient air at 15°C with convective heat transfer coefficient equal to 10W/(m2.K). Consider a piece of meat that, when removed from the freezer, had a temperature of -12°C. For defrosting, the piece is hung on a "line", so that both larger surfaces are exposed to the ambient air. For frozen meat, the following properties can be assumed ρ=1090 kg/m3, cp=3.54 kJ/(kg.K), k=0.47 W/(m.K). Ask: (1) Indicating the control volume and the simplifications adopted, obtain the differential energy balance equation for the cooling the piece of meat and describe the conditions of outline and initial that apply to the process, justifying them; (2) Use the appropriate analytical solution to determine the time necessary for the complete defrosting of the part. The part is considered to be completely thawed when a minimum temperature of 5oC is reached…
A 2 m X 1.5 m section of wall of an industrial furnace burning gas is not insulated, and the temperature at the outer surface of this section is measured to be 80oC. The temperature of the furnace room is 30oC, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 w/oC. It is proposed to insulate this section of the furnace wall with glass wool insulation (K=0.038 W/moC) in order to reduce the heat loss by 90 percent. Assuming the outer surface temperature of the section remains at about 80oC, determine i) the thickness of the insulation that is needed and ii) the outer surface temperature of the insulation after installation.