ABSTRACT According to thermodynamics, thermal radiation is the electromagnetic radiation emitted by a body as a result of its temperature. In this experiment, the thermal radiation of a body is determined. The radiometer was moved along horizontally to measure the thermal radiation of that body from a different distance. The plotted graph show the relationship between the distance and the radiation. Moreover, from the graph, the order of proportionality of thermal radiation intensity can be measured. The emissivity of the experimented sample was found to be 0.62, this justifies the accuracy of the test. Introduction and Background The electromagnetic radiation emitted by a body as a result of its temperature is called thermal radiation, which does not require an intervening medium to carry it. All bodies emit such radiation to their surroundings and absorb such radiation from them. When thermal equilibrium is reached the rates of emission and absorption are equal. On the electromagnetic spectrum, thermal radiation is characterized by a wavelength of 0.1100 µm. All matter with temperature above absolute zero exchange thermal radiation with their environment. The amount of radiation emitted by a surface depends on the type of material, the condition of the surface and its temperature. Thus, two different substances at the same temperature may emit different amount of radiation due to the nature of their surface. Black bodies are considered as perfect emitter and absorber of thermal radiation and therefore have higher emissivity and absorptivity than polished shiny surfaces. Thermal Radiation Name: Manea Alabbas Date:03-14-2017 MEEN 317 The objective of this lab is to demonstrate that the intensity of radiation on a surface in inversely proportional to the square of the distance of the surface from the source of the thermal radiation. Theory The rate at which thermal radiation is emitted by a surface to its surrounding is described by Stefan-Boltzman quation as: ( Qrad = As Ts4 − T4 ) (1) Where,  = emissivity of the surface, For a black body,  = 1  = Stefan Boltzmann constant (5.67x10-8 W m-2K-4) As = Surface area Ts = Surface temperature of material T∞ = ambient temperature Equipment and materials 1. HT 10X Heat Transfer Service Unit 2. HT 13 Laws of Radiant Heat Transfer and Radiant Heat Exchange Accessory Procedure 1. First, Locate and setup the HT 10X Heat Transfer Service Unit and the HT 13 Laws of Radiant Heat Transfer and Radiant Heat Exchange Accessory 2. Identify and position the radiometer at a distance 890mm on the track away from the heated plate. Department of Mechanical Engineering NC A&T STATE UNIVERSITY Thermal Radiation Name: Manea Alabbas Date:03-14-2017 MEEN 317 3. Connect the lead from the radiometer to the socket marked R on the front of the HT 10X service unit. Allow the radiometer to stabilize at room temperature. 4. Adjust the zero potentiometer until the reading on the HT 10X is zero. 5. Connect the thermocouple on the heated plate and the polished plate to the Data Acquisition System. 6. Set the Voltage Control potentiometer to minimum with the selector switch to manual and then connect the power lead from the heated plate on the HT13 to the socket at the rear of the HT 10X service unit. 7. Set the heater voltage to 20V. 8. At stability, record the temperatures of the heated plate and the polished plate and then take the radiometer reading. R (W/m2) at the 890mm distance. 9. Repeat the experiment by moving only the radiometer 100mm towards the heated plate. Part B 1. With the same setup, replace the radiometer with a black surfaced body and record the temperature at stability. The surface should be at a distance 310mm from the heat surface 2. Repeat the process at the same distance, 310mm, with a different surface. Discussion of Results From the plotted graph of Log X vs Log R, the order of proportionality of thermal radiation intensity versus radiometer distance was found 2nd degree, which means they Department of Mechanical Engineering NC A&T STATE UNIVERSITY Thermal Radiation Name: Manea Alabbas Date:03-14-2017 MEEN 317 are proportional to at a square relation. From the second graph of distance vs black body temperature, the square relation also hold true for their relation. The emissivity of the experimented body was found to be 0.62. Conclusions This experiment was done to determine the thermal radiation of a particular body. the order of proportionality of thermal radiation intensity versus radiometer distance was also obtained. The emissivity of the body was found 0.62 which is acceptable value. Though great care was taken to measure all the data and thus the experiment gave accurate result, more accurate result could be obtained by more trials. Department of Mechanical Engineering NC A&T STATE UNIVERSITY
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