EXP2 Thermal Conductivity Experiment Handout PDF

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Machines laboratary course...

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T.C. BEYKENT UNIVERSITY FACULTY OF ENGINEERING-ARCHITECTURE MECHANICAL ENGINEERING DEPARTMENT

T H ER M A L CO N DUCT IV IT Y T ES T R I G EXPERIMENT SHEET

CONTENTS INTRODUCTION ........................................................................................................................................ 3 BASIC CONSEPTS .................................................................................................................................... 3 THEORETICAL PRINCIPLES ................................................................................................................... 3 EXPERIMENT SET AND ITS SPECIFICATIONS 8 EXPERIMENT PRINCIPLE SCHEMES ................................................................................................... 10 TEST NO: .........-01.................................................................................................................................. 11 TEST NO: .........-02.................................................................................................................................. 15

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INT INTRO RO RODU DU DUCTI CTI CTION ON Thermal conductivity experiment set is a training set for mechanical engineering students who will be able to visually and experimentally consolidate their theoretical knowledge about heat conduction within the context of ‘Machine Laboratory’ course. The aim of the experiment is to provide the students understanding of heat transfer in terms of linear and radial thermal conductivity applications and gaining psychomotor skills. It is basically scheduled for at least 2 different experimental studies. In this sheet, firstly basic information about heat conduction and theoretical equations to be used in analyses are given. Afterwards, each tests are discussed separately.

BA BASIC SIC CON CONSE SE SEPTS PTS Heat: Depending on temperature difference, it is a kind of energy which is transferred from one point to another. Heat Transfer: According to the 2nd law of thermodynamics, it is flow of heat from a high temperature environment to a low temperature environment between two environments with a temperature difference. Heat transfer depends on environment surface properties and temperature differences. Heat transfer has three different methods. These are conduction, convection and radiation. Thermal Conductivity: It is the ability of a substance or object to transfer hea t. Thermal conductivity is also defined as the ratio of the quantity of heat delivered by an object to the quantity of heat it receives. Thermal Conductivity Coefficient (λ (W/m.K)): It defines the ability of a substance or object to transfer heat. Heat Transmission Coefficient (U (W/m2K)): It is the resistance of a substance or object to heat

transfer. Heat transmission coefficient depends on thermal conductivity coefficient (λ) and thickness of the object.

TH THEOR EOR EORET ET ETICA ICA ICALL PR PRIN IN INCIP CIP CIPLES LES In a structure having two different temperature environments, heat moves from a high temperature environment to a low temperature environment. This process which is defined as the transfer of heat, depends on three different methods such as conduction, convection and radiation. The transfer conditions of heat are related to the convection modules as can be understood from the methods. If the temperature difference is the value between two surfaces for a solid form, the molecules for solids are primarily a movement from the hot surface to the cold surface with a convection characteristic. If this is 3

the transfer of heat from one environment to another it means that the heat is transferred by liquid or gas fluid. In this case, the heat is transferred by a fluid. If there is a distance between the environment to be heated and the surface to be heated and if the heating source has a property of radiation (such as sun, flame), then the heat is transferred by direct radiation. For solid forms, the heat transfer method described in these methods is heat transfer by conduction. Heat conduction describes the internal structure dynamism with the rotation and vibration of the molecular forms starting directly on the hot surface. Briefly, it is the movement of heat from hot to the cold by interaction of lower energy particles and particles having high energy charge. While the heat conduction form takes place in gases and liquids like a solid property via molecular collision and diffusion, in solids it is energy transfer depend on direct molecular vibration and free electrons. Principally, heat transfer is a function of heat transfer rate. However, conduction and conduction rate of the heat depends on temperature difference, geometry and surface area, thickness and type of the defined structure or structure component (or for defined system boundaries). This relationship which is defined as Fourier's law, is the heat transfer rate in relation to the amount of heat in any direction within a structure (herein direction x), temperature gradient and heat transfer surface area. Fourier's law is as follows:

𝑄 =−𝑘𝐴

𝑑𝑇 𝑑𝑥

Figure 1 Heat transfer mechanism where is temperature gradient, A is surface area and k is coefficient of thermal conductivity. Herein, (-) describes the direction of heat flow. If the heat increases in x direction in a flow like in the figure 1, it is positive and negative if it decreases.

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𝑑𝑇 >0 𝑑𝑥

T

𝑑𝑇...