Thermal Conductivity.pptx

Thermal Conductivity Presentation

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

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

3. Outlines Thermal Conductivity Experimental Methods Steady State Method Guarded Hot Plate Method Concentric Sphere Method Unsteady State Method Transient Plane Source Method Laser Flash Method

4. “Ability to Convey” Thermal: “Heat” Conductivity: Means Means

5. Thermal conduction is the phenomenon by which heat is transported from high to low temperature regions of a substance. The property that characterizes the ability of a material to transfer heat is the thermal conductivity . It is best defined in terms of the expression:   heat flux thermal conductivity temperature gradient Thermal Conductivity

6. Several thermal conductivity 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: Steady State Methods Unsteady State Methods (constant temperature) (temperature varies with time) Experimental Methods to Find Thermal Conductivity

7. Definition: These methods are used when the materials are in equilibrium state. (when temperature of the materials is constant) Advantages: • Accurate readings can be taken. • Its steady state implies constant signals. Disadvantage: As material takes long time to reach equilibrium state so it is slow method. Steady State Methods

8. A solid sample of material is placed between two plates. One plate is heated and the other is cooled or heated to lesser extent. Temperature of the plates is monitored using thermo couple until they are constant. The steady state temperatures, the thickness of the sample and the heat input to the hot plate are used to calculate thermal conductivity. Guarded Hot Plate Method

9. The apparatus consists of two concentric thin spherical chambers with grain sample filled inside the annular space properly. The inner sphere is heated electrically, and the outer space is cooled in a water bath. The thermal conductivity ‘k’ will be: Q= kA₂A ₁(T₂ - T₁ / R₂ - R₁) Where Q= rate of heat flow A= area T= temperature 1,2 is suffix for outer and inner sphere Concentric Sphere Method

10. Definition: These methods are used during the heating of material. Advantage: Do not require the signal to obtain a constant value. Readings can be taken during heating of material. Disadvantage: Readings are not accurate. Mathematical analysis of the data is in general more difficult. Unsteady State Methods

11. Transient Plane Source Method It utilizes a plane sensor and a special mathematical model describing the heat conductivity, combined with electronics, enables the method to be used to measure “ k ” . Range between at least 0.01-500 W/m/K

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. This method is used to measure thermal diffusivity of a thin disc in the thickness direction. This method is based upon the measurement of the temperature rise at the rear face of the thin-disc specimen produced by a short energy pulse on the front face. With a reference sample specific heat can be achieved and with known density the thermal conductivity results as follows α = k/ ρ C It is suitable for a multiplicity of different materials over a broad temperature range (−120°C to 2800°C). Laser Flash Method

14. Laser Flash Method

15. Thank You