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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FUNDAMENTAL CONCEPTS Heat transfer is energy in transit‚ which occurs as a result of temperature gradient or difference. This temperature difference is thought of as a driving force that causes heat to flow. The concepts of heat transfer and temperature‚ the key words in the discipline of heat transfer‚ are 2 of the most basic concepts of thermodynamics. dffffffffff rifffff orfff ffffffffff fv ing ff ce Rate of transport process= fffffffffff or rate = coefficient B driving force resist
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Practice Problems Set – 1 MEC301: Heat Transfer Q.1 The slab shown in the figure is embedded on five sides in insulation materials. The sixth side is exposed to an ambient temperature through a heat transfer coefficient. Heat is generated in the slab at the rate of 1.0 kW/m3. The thermal conductivity of the slab is 0.2 W/m-K. (a) Solve for the temperature distribution in the slab‚ noting any assumptions you must make. Be careful to clearly identify the boundary conditions. (b) Evaluate T at the
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overall heat transfer coefficient on the outer surface of the covered pipe is 10 W/m2.K. if the velocity of the steam is 10 m/s‚ at what point along the pipe will the steam begin condensing and what distance will be required for the steam to reach a mean temperature of 100 oC? Question 2: Consider a horizontal‚ thin walled circular tube of diameter D = 0.025 m submerge in a container of n-octadecane (paraffin)‚ which is used to store thermal energy. As hot water flows through the tube‚ heat is
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HEAT TRANSFER MECHANISMS Heat energy is being transferred from one location to another because of a temperature difference. The three mechanisms for heat transfer are: • Conduction. When you grip the hot handle of a pan on a stove‚ you feel conduction in action. Heat flows from the pan and along the length of the handle to its cooler free end. This is because one end of the rod is held at the high temperature‚ and the other end stays at the lower temperature. Although the rod itself doesn’t
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resistance R0 = 100 Ω at 0o C. If the resistance RT = 197.7 Ω in an oil bath‚ what is the temperature of the oil in the bath‚ given that RT = R0(1+αT)? Take R0 = 100 Ω R0 = resistance at 0o C α = 3.9083 x 10-3 /o C (2 marks) NDE Thermodynamics and Heat Transfer Exam 2008 Name: _______________________________________ Read all the instructions before starting Do not open this paper until instructed Time allowed: 2 hours (plus 5 minutes reading time) Attempt ALL question in Section A (questions 1 – 12)
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Heat & Mass Lab 1: | | | 2/10/2011 2/10/2011 Executive Summary This experiment was conducted using a heat transfer unit. Many relationships were obtained and calculated from the observed results. To name a few; the log mean temperature difference‚ heat transfer coefficient‚ Reynolds‚ Nusselt and Graetz numbers. The main focus of this experiment is the heating and cooling of the oil fluid. This was achieved using the heating component in the heat exchanger and water flowing
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and observe the concept of Heat Transfer‚ by measuring the temperature distribution for steady state conduction of energy through a specific efficient unit. • Understand the Fourier Law of heat conduction and the usage of its equation in determining the rate of heat flow via solid materials. II. Theory : The Fourier Rate Equation: When a plane section of ∆x and a constant area A maintains a temperature difference ∆T‚ then the heat transfer rate per unit time by conduction
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FREESTUDY HEAT TRANSFER TUTORIAL 2 CONVECTION AND RADIATION This is the second tutorial in the series on basic heat transfer theory plus some elements of advanced theory. The tutorials are designed to bring the student to a level where he or she can solve problems ranging from basic level to dealing with practical heat exchangers. On completion of this tutorial the student should be able to do the following. • • Explain the use of the surface heat transfer coefficient. • Explain
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State Heat Transfer laboratory were to study the rates of heat transfer for different materials of varying sizes‚ to develop an understanding of the concepts of forced and free convection and to determine the heat transfer coefficients for several rods. These objectives were met by heating several rods and allowing them to cool through free convection in air‚ free convection in water and forced convection in water- while monitoring their change in temperature over change in time. Seven heat transfer
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Heat Transfer Through Jacket Objective The objective of this example is to analyze heat transfer in a pilot plant using simulation models. The first step is to use pilot plant data to calculate heat transfer parameters. The second part involves using simulation models to examine the trade-off between jacket parameters and heating times. Process Description Assumptions: The stirred tank is assumed to be perfectly mixed. The contributions of agitator work‚ heat loss to environment
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