Let's practice how to use energy conservation in conjunction with Nusselt number correlations. A coolingsystem cools air from 80°C to 20°C by passing air via a 20-cm diameter circular duct. The duct providesa uniform cooling at a rate of 200 W/m². The air flows at a steady rate of 3 m/s. What is the requiredlength of the cooling system*? What is the temperature of the duct surface at 15-m from the entrypoint?

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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 6.53P

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1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical hairdryer is idealized as a thin-walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of this appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of to an outlet temperature of and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that heat loss from the outside of the dryer duct is neglected.
For a water flow over a steel surface, the temperature of water at a specific location was found to change with the vertical distance from the surface (y) up to a distance of 0.015 m as T(y) = 60 + 20y + tan(y), where temperature is in °C and y is in cm. The surface temperature and ambient temperature was measured as 60°C and 105°C, respectively. The thermal conductivity of steel and water are, respectively, 48 W/m-K and 0.6 W/m-K. What is the local convection coefficient at this location?
Q: Air enters a rectangular duct. Determine the exit temperature of the air and find the rate of heat transfer loss . Taking k = 0.02662 W/m."C. v= 1.702x10 m'/s, Pr 0.7255, C-1007 J/kg. C ,p=1.127 kg/m u= 2.325 kg/m.s Ans : 34.2°C 3776 W Air dact 15 em 2 em L7m Q. Hot air enters a sheef metal duct located in a basement. Determine
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(heat transfer ) thanks The velocity of the fluid flowing in parallel over a 500mmx500mm flat heater surface is U= 19 m/s and the inlet velocity temperature is T_∞15 C. The surface temperature of this plate is T_s140 C, the friction force is F_D=0.4 N and the surface area of the plate is A=0.32 m2. According to this;(F_D= 0.4N A=32 m2)a) Surface shear stressb) Find the coefficient of frictionc) Heat transfer coefficientd) What is the amount of heat transfer (electric power) that must be given to maintain a constant surface temperature?
An electric motor is to be connected by a horizontal steel shaft (k 42.56 W/m.K), 25 mm in diameter to an impeller of a pump, circulating liquid metal at a temperature of 540°C. If the temperature of electric motor is limited to a maximum value of 52°C with the ambient air at 27°C and heat transfer coefficient of 40.7 W/m2.K, what length of shaft should be specified between the motor and pump? Steel shaft
Conduction 1. A thermodynamic analysis of a proposed Brayton cycle gas turbine yields P= 5 MW of net power production. The compressor, at an average temperature of T. = 400°C, is driven by the turbine at an average temperature of T₁ = 1000°C by way of an L = 1m-long, d= 70mm - diameter shaft of thermal conductivity k = 40 W/m K. Compressor min T Combustion chamber Shaft L Turbine Th out (a) Compare the steady-state conduction rate through the shaft connecting the hot turbine to the warm compressor to the net power predicted by the thermodynamics- based analysis. (b) A research team proposes to scale down the gas turbine of part (a), keeping all dimensions in the same proportions. The team assumes that the same hot and cold temperatures exist as in part (a) and that the net power output of the gas turbine is proportional to the overall volume of the device. Plot the ratio of the conduction through the shaft to the net power output of the turbine over the range 0.005 m s Ls 1 m. Is a…
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Q1: (5pt) In a cylindrical fuel element for a gas-cooled nuclear reactor, the generation rate of thermal energy within the fuel element due to fission can be approximated by the relation q(1) W/m³ %3D where a is the radius of the fuel element and is constant.The boundary surface at r = a is maintained at a uniform temperature Tɔ. (a) Assuming one-dimensional, steady-state heat flow, develop a relation for the temperature drop from the centreline to the surface of the fuel element. (b) For a radius of a = 30 mm, the thermal conductivity k = 10 W/(m °C) and qo = 2 x 107 W/m³, calculate the temperature drop from the centreline to the surface. 02: (5pt)
43% uo 7:52 * ZAIN IQ I. sheet No.3.pdf Homework 01-03 -2021 one-dimensional heat transfer and disregarding radiation, determine the rate of heat transfer through the wall. Q4/ Steam at Te1-320°C flows in a cast iron pipe (k=80W/m.°C) whose inner and outer diameters are D =5cm, and D=5.5cm, respectively. The pipe is covered with 3 cm thick glass wool insulation with k=0.05W/m.°C. Heat is lost to the surroundings at T02=5°C_by natural convection and radiation, with a combined heat transfer coefficient to be h,=18W/m.C. Taking the heat transfer coefficient inside the pipe to be h,=60W/m.C, determine the rate of heat loss from the steam per unit length of the pipe. Also determine the temperature drops across the pipe shell and the insulation. 05/ Determine the overall heat transfer coefficient U based on the outer surface of a D=2.5cm, and D=3.34 cm steel pipe (k=54.0W/m.°C) for the following conditions: inside and outside heat transfer coefficients are 1200W/m."C. and 2000W/m."C…
A composite plane wall consisting of materials, 1.5-in steel (k = 312 BTU-in/HR.ft2.0F) and 2-in aluminum (k = 1400 BTU-in/HR.ft2.0F), separates a hot gas at Ti = 2000F, hi = 2 BTU/HR.ft2.0F, from cold gas at To = 80 deg F, ho = 5. If the hot fluid is on the aluminum side, find: a) Transmittance, U; b) The heat through 100 sq. ft of the surface under steady state condition and c) The interface temperature at the junction of the metals.
Carbon steel balls (p=7833 kg/m', k=54 W/m.C, Cp=0.465 kJ/kg.K ) 10 mm in diameter are annealed by heating then first 910 °C in a furnace and then allowing them to cool slowly to 120 °C in ambient air at 36 °C. If the average heat transfer coefficient is 80 W/m?.°C.

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