Thermal Diffusivity.pptx

Thermal Diffusivity Presentation

1. In the name of Allah , the Most Merciful , the Most Kind

2. Experimental Methods to Find Thermal Diffusivity Presented to: Dr. Anis-Ur-Rehman Muhammad Ahsan CIIT/FA20-PPH-001/ISB

3. Layout

4. Thermal diffusivity (with a unit mm 2 /s) is the thermal conductivity divided by density and specific heat capacity at constant pressure while thermal conductivity is a measure of how easily one atom or molecule of a material accepts or gives away heat. Thermal diffusivity measures the rate of transfer of heat of a material from the hot end to the cold end. Thermal diffusivity is usually denoted by . The formula is   is thermal conductivity  (W/( m·K )) is specific heat capacity  (J/( kg·K )) is density  (kg/m³)   WHAT IS THERMAL DIFFUSIVITY?

5. Several thermal diffusivity measurement methods exist, and the proper method depends on many factors, such as sample type, temperature range, and available resources. Some of the methods are: Laser Flash Method Transient Hot Plate Method Experimental Methods to Find Thermal Diffusivity Hot Wire Method

6. A heated wire is inserted into the material. The heat flows out radially from the wire into the sample and the temperature change in the wire is recorded. The plot of the wire temperature versus the logarithm of time is used to calculate thermal diffusivity, provided that density and capacity are known. Since this is an intrusive measure, it cannot be used for solids; it works well for foams, fluids and melted plastics. Hot Wire Method

7. Hot Wire Method Advantages: Fast and Accurate Minimum Conduction and Radiation losses Minimize (or even avoid) Convection Classification of Hot-Wire Methods Standard Cross Wire Method Single Wire, Resistance Method Potential Lead Wire Method Parallel Wire Method

8. The Flash Method is a method for the determination of the  thermal diffusivity   of different materials. The sample is subjected to a high intensity short duration radiant energy pulse. The power source can be a laser or a flash lamp. Laser Flash Method

9. With a reference sample specific heat can be achieved and The thermal diffusivity is calculated. It is suitable for a multiplicity of different materials over a broad temperature range (−120°C to 2800°C). The energy will then be absorbed by the specimen and emitted again on the top of the sample. This radiation results in a temperature rise on the surface of the sample. This temperature rise is recorded from an infrared (IR) detector. The detector signal shows the duration of the measurement and the normalized temperature rise on the surface of the sample, where the light pulse occurs. Laser Flash Method

10. Absolute method for the measurement of thermal conductivity and thermal diffusivity , with calculation of specific heat and thermal effusivity . No calibration required in order to make measurements. No contact agent required between sensor and sample Thermal conductivity from 0.001 W/ m•K up to 1800 W/ m•K Temperatures from - 250 °C up to 1000 °C Transient Plane Source Method

11. Transient Plane Source Method It utilizes a plane sensor and a special mathematical model describing the heat diffusivity, combined with electronics, enables the method to be used to measure “ ” .  

12. The Transient Plane Source technique typically employs two samples halves, in between which the sensor is sandwiched. The sensor is placed between two halves of the sample to be measured. During the measurement, a constant electrical effect is passes through the conducting spiral, increasing the sensor temperature. The heat generated dissipates into the sample on both sides of the sensor, at a rate depending on the thermal transport properties of the material. By recording temperature vs. time response in the sensor, the thermal conductivity, thermal diffusivity and specific heat capacity of the material can be calculated . Transient Plane Source Method

13. Different testing modules are available: Standard: for measurement of bulk thermal conductivity and thermal diffusivity of isotropic solids, liquids, pastes and powders. Anisotropic: for measurement of directionally-dependent (in-plane and through-plane) thermal conductivity and thermal diffusivity. Slab: for thin, highly thermally conducting materials. Thin film: for measurement of coatings and stand-alone films. 1-Dimensional: for 1D measurement of elongated materials like rods. Specific Heat: direct measurement of specific heat. TPS Testing Modules

14. Direct thermal property measurement, no complex calibration required. Is multi-property: thermal conductivity, thermal diffusivity and specific heat. Homogeneous and heterogeneous Isotropic and anisotropic Solids, liquids, pastes and powders No contact agent required Two-sided and single-sided sensors Advantages