Thermal Radiation Thermal Engineering Lab ME-4111 Professor: Eduardo Cabrera Damian Luna - 33509 Yetziel Sandoval – 78820 Alberto Gonzales – 80546 Fernando Fresse – 56319 Jaen Soto – 51080

Outline Objective Introduction Theoretical Background Theory Experimental Procedure

Objective Validate the principles of Heat Transfer by Radiation The effects of surface emission and absorption. Also interconnect the geometry phenomenon to it.

Introduction Radiation energy emitted by matter in the form of electromagnetic waves as a result of the changes in the electronic configurations of the atoms or molecules. Heat transferred by thermal radiation respect to other objects Surface reflectivity, absorptivity, emissivity, surface area, temperature and geometric orientation. Fundamentals laws to demonstrate in this experiment Emission Absorption Propagation

Theoretical Background Radiation is a mode of heat transfer in which radiation is emitted by a heated surface in all directions and travels at the speed of light, Radiation does not require a medium for its propagation. Thermal Radiation is radiation confined in the range of 0.1μm to 100 μm of the spectrum that includes a little portion of UV radiation, visible light and a fair portion of infrared radiation.

Radiation Radiation that leaves a surface can propagate in all possible directions, and we are often interested in knowing its directional distribution. Radiation incident upon a surface may come from different directions, and the manner in which the surface responds to this radiation depends on the direction.

Radiation The radiation emitted by a surface propagates in all directions and its characterized by Radiation Intensity that can be expressed by:

Blackbody A black body is defined as a theoretical object that absorbs0% of the radiation received. In other words is a perfect emitter and absorber of radiation. At a specified temperature and wavelength, no surface can emit more energy than a blackbody. A blackbody absorbs all incident radiation, regardless of wave- length and direction. Also, a blackbody emits radiation energy uniformly in all directions per unit area normal to direction of emission. A blackbody is a diffuse emitter. The term diffuse means independent of direction and is expressed by: Eb= emissive power of Blackbody λ=wavelength c=speed of light C1,2=Constants T=Blackbody Temperature

Stefan-Boltzmann Law This law states that the total energy radiated of a black body across all wavelengths is directly proportional to the fourth power of the black body's temperature. The law becomes: Stefan-Boltzann constant: The Stefan-Boltzmann Law enables the calculation of the amount of radiation emitted.

Emissivity Represents the ratio of the radiation emitted by the surface at a given temperature to the radiation emitted by a blackbody at the same temperature. The emissivity of a surface is denoted by E, and it varies between zero and one. Emissivity is a measure of how closely a real surface approximates a blackbody which emissivity is 1.

Area Factor The heat transfer rate from one radiating black surface to another is dependent on the amount that each surface can see from the other surface. In order to solve radiant heat transfer problems an area factor F12 is introduced, where F12 is defined by the fraction of energy emitted per unit time by one surface at T1 that is intercept by the other surface at T2 as shown in the figure. Thus the time of radiant heat transfer (Q12) between two black surfaces of area A1 and A2 at their respective temperatures T1 and T2, is expressed by the following equation:

Thermal Radiation Unit Equipment Thermal Radiation Unit

Thermal Radiation Unit The Hilton H960 Thermal Radiation Unit consist of horizontal bench with a defined reversible scale in mm, fitted with electrically heat radiation source. The equipment include an interface console that is controlled by solid stage regulator where the temperature and flux of radiation is monitored. A transformer that provides a low voltage supply for the heat source and metal plates with a thermocouple attached it The equipment is capable to demonstrate the fundamental laws of radiation.

Radiation Detector Is a Device that is used to measure the intensity flux of radiation unit or Watts per square meter. The intensity of radiation that the digital meter indicates comes from the radiometer and not the surface. The mathematical relationship between radiation received and emitted is: q”= R/sin2Θ= 5.59R R = Radiometer reading Q = Energy emitted by heat surface Θ= Half angle of the radiometer window This constant: 5.59 = 1/sin2(25°)

Radiation Detector In this experiment is important to calculate de propagation of uncertainty due to thermocouple and radiometer reading use the information table 2.1

Experimental Procedure Inverse Square Law for Heat 1. Set the radiometer at a initial distance of 100(mm) from the heat source 2. Turn on the power control unit and set the power control knob to 6 mark. This setting will be maintained throughout the entire task. 3. Allow the radiometer reading stabilizes and then note the value of distance and power. reading. 4. Move the radiometer away of the heat source by increasing the distance in 100(mm) 5. Repeat step 4 until you have 7 values

Experimental Procedure Stefan-Boltzmann Law 1.Set the matt black plate at a distance of 50 mm from the heat source. 2.Set the radiometer at a distance of 110 mm from the heat source. 3.Turn on the power control unit and set the power control knob to maximum. 4.After radiometer reading stabilizes , note the value of the plate’s temperature and radiometer readings simultaneously. Also note the value of the ambient temperature at the same time since this value will be used in the equations. 5.Decrease the temperature of the plate by turning down the power control knob to the next mark and repeat step d until you record at least 5 data points.

Experimental Procedure Emissivity 1 1. Metal plate distance set to 50 mm 2. Radiometer distance set to 110 mm 3. Turn on power and set to max 4. Allow radiometer to stabilize and take note of readings of temp in plate and radiometer readings 5. Decrease the power with the knob and repeat the previous step 5 times. 6. Change plate and repeat procedure.

Experimental Procedure Emissivity 2 1. Set Matt Black Plate at 50mm from the heat source 2. Set the Radiometer at 110mm from the heat source 3. Turn on the power control unit and put in the max mark 4. Allow for the radiometer reading to stabilize and note the temperature and read the radiometer 5. The silver plate at 20mm from the first plate

Experimental Procedure Area factors 1. Black plate distance set to 50mm. 2. Aperture plate distance set to 200mm. 3. Radiometer distance set to 300mm. 4. Turn on the power and set to the maximum position. 5. Aperture plate set at 60mm. 6. Close the aperture by 10mm relative to track 7. Repeat the step 6 with increments of 10mm until 0 mm

References Heat and Mass Transfer Fundamentals & Applications, 5th Edition Fundamentals of Heat and Mass Transfer, 7th Edition Thermal Engineering Laboratory Manual.