A single-cylinder air-cooled lawn mower engine operates under steady conditions. The cylinder temperature cannot exceed 300 ⁰C. To cool the engine, annular fins are placed around the cylinder. The fins are 0.3 cm thick and are 2 cm long from base to tip. The fins are made of cast iron (k = 52 W/mK). The outside diameter of the engine cylinder at the base of the fin is 0.3 m. Assume that the engine operates in 30 ⁰C air and that the heat transfer coefficient on the sides and tip of the fin is 12 Wm^-2K^-1. Determine the number of fins needed to cool a 3 kW engine to the given temperature if the engine has an efficiency of 30 % and 50 % of the total heat given off by the engine actually is dissipated through the fins ?

A single-cylinder air-cooled lawn mower engine operates under steady conditions. The cylinder temperature cannot exceed 300 ⁰C. To cool the engine, annular fins are placed around the cylinder. The fins are 0.3 cm thick and are 2 cm long from base to tip. The fins are made of cast iron (k = 52 W/mK). The outside diameter of the engine cylinder at the base of the fin is 0.3 m. Assume that the engine operates in 30 ⁰C air and that the heat transfer coefficient on the sides and tip of the fin is 12 Wm^-2K^-1. Determine the number of fins needed to cool a 3 kW engine to the given temperature if the engine has an efficiency of 30 % and 50 % of the total heat given off by the engine actually is dissipated through the fins ?

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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2.55 A long, 1-cm-diameter electric copper cable is embedded in the center of a 25-cm-square concrete block. If the outside temperature of the concrete is 25oC and the rate of electrical energy dissipation in the cable is 150 W per meter length, determine temperatures at the outer surface and at the center of the cable.
During a picnic on a hot summer day, the only available drinks were those at the ambient temperature of 90°F. In an effort to cool a 12-fluid-oz drink in a can, which is 5 in high and has a diameter of 2.5 in, a person grabs the can and starts shaking it in the iced water of the chest at 32°F. The temperature of the drink can be assumed to be uniform at all times, and the heat transfer coefficient between the iced water and the aluminum can is 30 Btu/h·ft2·°F. Using the properties of water for the drink, estimate how long it will take for the canned drink to cool to 40°F.
One wall of a refrigerated warehouse is 10.0-m-high and 5.0-m-wide. The wall is made of three layers: 1.0-cm-thick aluminum (k = 200 W/m·K), 8.0-cm-thick fibreglass (k =0.038 W/m·K), and 3.0-cm thick gypsum board (k = 0.48 W/m·K). The warehouse inside and outside temperatures are 210°C and 20°C, respectively, and the average value of both inside and outside heat transfer coefficients is 40 W/m2·K. (a) Calculate the rate of heat transfer across the warehouse wall in steady operation. (b) Suppose that 400 metal bolts (k = 43 W/m·K), each 2.0 cm in diameter and 12.0 cm long, are used to fasten (i.e., hold together) the three wall layers. Calculate the rate of heat transfer for the “bolted” wall. (c) What is the percent change in the rate of heat transfer across the wall due to metal bolts?
‏Q1 / A5 - cm - diameter steel pipe is covered with a 1 - cm layer of insulating material having k = 0.22 W / m . ° C followed by a 3 - cm - thick layer of another insulating material having k = 0.06 W / m . ° C . The system is exposed to a convection surrounding condition of h = 60 W / m² . ° C and T -15 ° C . The outside surface temperature of the steel pipe is 400 ° C . Calculate the heat lost by the pipe - insulation assembly for a pipe length of 20 m . Express in Watts .
A rectangular fin with k=43 W/m.C , thickness t=2 cm , length L=14 cm and width W=1 m. The base of the fin is maintained at a temperature of 200 C while the fin is exposed to a convection environment at T∞= 15 C and h∞ = 20 W/m2 .C .Using the chart , calculate the heat lost from the fin .
The roof of an electrically heated home is 9 m long, 12 m wide, and 0.50 m thick, and is made of a flat layer of concrete whose thermal conductivity is k = 0.8 W/m · °C . The temperatures of the inner and the outer surfaces of the roof one night are measured to be 25°C and 5°C, respectively, for a period of half a day. Determine the rate of heat loss (hp) through the roof that night.
A cylindrical body having 10 cm diameter and lenth of 30 cm passes through a heat treatment furnace which is 6 m in length. The body must reach a temperature of 800°C before it comes out of the furnace. The furnace gas is at 1250°C and body initial temperature is 90°C. How much time it will take to attain the required temperature ? Take h = 100 W/m² °C. Take K(steel) = 40 W/m°C and a (thermal diffusivity of steel) = 1.16 x 10-5 m²/s.
Which of the following provides the basis of convection heat transfer? Group of answer choices Newton’s Law Fourier’s Law Stefan-Boltzmann Law Toricelli’s Principle
A 12-m-long and 5-m-high wall is constructed of two layers of 1-cm-thick sheetrock (k = 0.17 W/m·K) spaced 16 cm by wood studs (k = 0.11 W/m·K) whose cross section is 16 cm * 5 cm. The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation (k = 0.034 W/m·K). The house is maintained at 20°C and the ambient temperature outside is 29°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m2·K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.
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You are using a silver spoon to stir water that just started boiling so that you can achieve a more even heat distribution in your water. The spoon is partially immersed in boiling water and a thermometer in your kitchen reads 27 °C. The handle of the spoon has a cross section of 2mm × 1cm and extends 15 cm in the air from the free surface of the water. The heat transfer coefficient at the exposed surfaces of the spoon handle is 3 W/m2 ×K. Part A : Determine the temperature difference across the exposed surface of the spoon handle. Follow the problem-solving guide on the front page. At the minimum, your analysis should answer the following questions providing detailed justifications: -What are the modes of heat transfer that the spoon is exposed to? -Is this a time dependent or steady state problem? Why or why not? -Is this a 1-D, 2-D or 3-D problem? Why or why not? - What is the thermal conductivity of the material? - The heat transfer coefficient is a function of many variables.…
A 6-m-long 2-kW electrical resistance wire is made of 0.2-cm-diameter stainless steel(? = 15.1 W/mK). The resistance wire operates in an environment at 30°C with a heattransfer coefficient of 140 W/m2K at the outer surface. Determine the maximumtemperature in the wire;(a) by using the applicable relations.(b) by setting up the proper differential equation and solving it.