Lectures Lectures of Heat Transfer Heat Transfer Rate Processes Mode Conduction Convection Radiation Transfer Mechanism Diffusion of energy due to random molecular motion Diffusion of energy due to random molecular motion plus bulk motion Energy transfer by electromagnetic waves Rate of heat transfer (W) q = - kA dT dx q = h A(Ts-T∞) q = σ ε A(Ts4-Tsur4) By Mr. Amjed Ahmed Ali Syllabus of Heat Transfer (English)‚ (2 hours/ week‚ Applied 2 hours /week) 1.Heat transfer by conduction‚ convection
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Mechanisms of Heat Transfer Prepared by: Ms. Ana Antoniette C. Illahi 1 Conduction • conduction (or heat conduction) is the transfer of thermal energy between regions of matter due to a temperature gradient. Heat spontaneously flows from a region of higher temperature to a region of lower temperature‚ and reduces temperature differences over time‚ approaching thermal equilibrium. Prepared by: Ms. Ana Antoniette C. Illahi 2 (Heat Current in Conduction) • • • • • • • • H - Heat Current
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Fi l +m = Fil + Fim Ji Gij qij i‚ Ji‚ Ai qij=(JiJj)/(1/AiFij) blackbody Ji=Ei(T) function of temperature Radiation network to find flux or potential 40 to 50 % ison radiation Heat exchanger U fouling factor will increase the resistance of heat transfer. how to include into the overall equation (mcp)h Th‚ in Tc‚ out (mcp)c Tc‚in You want to know the cooling effect energy conservation Q= {mcp(Th‚iTh‚o)}h ={mcp(Tc‚oTc‚i) }c Delta Tlm log mean
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situation for thick pipes is‚ however‚ more complex. [pic] The figure shown above represents the condition in a thick walled pipe. The area for heat flow is proportional to the radius – as may be seen‚ the area at the outside wall of the pipe is much greater than the middle. As a result the temperature gradient is inversely proportional to the radius. The heat flow ‘per unit length of pipe’ at any radius r‚ is [pic] cf. [pic] Note: Area‚[pic] Note there is no length of pipe (l) in this equation
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The University of Sydney Aerospace‚ Mechanical and Mechatronic Engineering MECH3260 Thermal Engineering Heat Transfer Quiz 3 2007 Time: 40 minutes Answer ONE question only. Question 1 Consider the cylindrical receiver in a solar thermal power plant shown below. The receiver is made of opaque material and has a diameter D = 8m and length L = 14m. At a particular time‚ the heliostats direct a concentrated solar flux of q”S = 80 kW/m2
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Heat transfer Heat transfer is the transition of thermal energy from a hotter object to a cooler object ("object" in this sense designating a complex collection of particles which is capable of storing energy in many different ways). When an object or fluid is at a different temperature than its surroundings or another object‚ transfer of thermal energy‚ also known as heat transfer‚ or heat exchange‚ occurs in such a way that the body and the surroundings reach thermal equilibrium‚ this means that
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Heat transfer is a discipline of thermal engineering that concerns the generation‚ use‚ conversion‚ and exchange of thermal energy and heat between physical systems. Heat transfer is classified into various mechanisms‚ such as thermal conduction‚ thermal convection‚ thermal radiation‚ and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species‚ either cold or hot‚ to achieve heat transfer. While these mechanisms have distinct characteristics
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HEAT TRANSFER Heat transfer‚ also known as heat flow‚ heat exchange‚ or simply heat‚ is the transfer of thermal energy from one region of matter or a physical system to another. When an object is at a different temperature from its surroundings‚ heat transfer occurs so that the body and the surroundings reach the same temperature at thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature‚ as required by the second
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UNSTEADY STATE HEAT TRANSFER Heat transfer processes are prominent in engineering due to several applications in industry and environment. Heat transfer is central to the performance of propulsion systems‚ design of conventional space and water heating systems‚ cooling of electronic equipment‚ and many manufacturing processes (Campos 3). Unsteady state conduction is the class of heat transfer in which the temperature of the conducting medium varies with time and position. This occurs frequently in
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DEFINITION OF HEAT TRANSFER | Heat transfer is energy in transit due to temperature difference . Whenever there exists a temperature difference in a medium or between media‚ heat transfer must occur. The basic requirement for heat transfer is the presence of temperature difference . There can be no net heat transfer between two mediums that are at the same temperature. The temperature difference is the driving force for heat transfer‚ just as the voltage difference is the driving force for electric
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