ME401_ConvectionRadiation

ME401_ConvectionRadi - COMBINED CONVECTION AND RADIATION YEDITEPE UNIVERSITY DEPARTMENT OF MECHANICAL ENGINEERING 1 YEDITEPE UNIVERSITY ENGINEERING

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1 COMBINED CONVECTION AND RADIATION YEDITEPE UNIVERSITY DEPARTMENT OF MECHANICAL ENGINEERING
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2 YEDITEPE UNIVERSITY ENGINEERING FACULTY MECHANICAL ENGINEERING LABORATORY Combined Convection and Radiation 1. Objective: & To determine the combined heat transfer (Qradiation + Qconvection) from a horizontal cylinder in natural convection over a wide range of power inputs and corresponding surface temperatures.To demonstrate the relationship between power input and surface temperature in free convection. & To compare the contribution of heat transfer by convection with heat transfer by radiation and from the measurements to show the domination of the convective heat transfer coefficient Hc at low surface temperatures and the domination of the radiation heat transfer coefficient Hr at high surface temperatures. & To determine the effect of forced convection on heat transfer from the surface of a cylinder at varying air velocities and surface temperatures.To demonstrate the relationship between air velocity and surface temperature for a cylinder subjected to forced convection. 2. Equipment: & The 'Combined Convection and Radiation' accessory A centrifugal fan with a vertical outlet duct at the top of which is mounted a heated, horizontal cylinder. & One K type Thermocouple is fitted in the wall of the duct and one K type thermocouple attached to the heated cylinder. & HT10X Heat Transfer Service Unit & IFD5 PC Interface Console & IBM Compatible PC
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3 3. Theory: 3.1 Natural Convection and Radiation If a surface, at a temperature above that of its surroundings, is located in stationary air at the same temperature as the surroundings then heat will be transferred from the surface to the air and surroundings. This transfer of heat will be a combination of natural convection to the air (air heated by contact with the surface becomes less dense and rises) and radiation to the surroundings. A horizontal cylinder is used in this exercise to provide a simple shape from which the heat transfer can be calculated. Note: Heat loss due to conduction is minimised by the design of the equipment and measurements mid way along the heated section of the cylinder can be assumed to be unaffected by conduction at the ends of the cylinder. Heat loss by conduction would normally be included in the analysis of a real application. In the case of natural (free) convection the Nusselt number Nu depends on the Grashof and Prandtl numbers and the heat transfer correlation can be expressed in the form: Nu = f(Gr, Pr) and the Rayleigh number Ra = (Gr Pr) The following theoretical analysis uses an empirical relationship for the heat transfer due to natural convection proposed by VT Morgan in the paper "The Overall Convective Heat Transfer from Smooth Circular Cylinders" published in TF Irvine and JP Hartnett (eds.), Advances in Heat Transfer vol. 16, Academic, New York, 1975, pp 199-269. Ts = Surface temperature of cylinder (K) D = Diameter of cylinder (m) L = Heated length of cylinder Ta = Ambient temperature of air (K) Heat transfer area (surface area) As = (pDL)
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This note was uploaded on 11/30/2010 for the course UNKNOWN a taught by Professor A during the Spring '10 term at Boston Conservatory.

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ME401_ConvectionRadi - COMBINED CONVECTION AND RADIATION YEDITEPE UNIVERSITY DEPARTMENT OF MECHANICAL ENGINEERING 1 YEDITEPE UNIVERSITY ENGINEERING

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