**Thermal contact conductance** is the study of heat conduction between solid or liquid bodies in thermal contact¹. It is a measure of the **thermal conductivity**, or ability to conduct heat, between two bodies in contact¹. The **thermal contact conductance coefficient** is a property indicating the thermal conductivity between two bodies in contact¹. The inverse of this property is termed **thermal contact resistance**¹.
When two solid bodies come in contact, such as A and B in Figure 1, heat flows from the hotter body to the colder body. A temperature drop is observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces¹. Thermal contact resistance is defined as the ratio between this temperature drop and the average heat flow across the interface¹.
Most experimentally determined values of the thermal contact resistance fall between **0.000005 and 0.0005 m²K/W** (the corresponding range of thermal contact conductance is **200,000 to 2000 W/m²K**). The significance of thermal contact resistance depends on the thermal resistances of the layers compared to typical values of thermal contact resistance. It is significant and may dominate for good heat conductors such as metals but can be neglected for poor heat conductors such as insulators¹.
Thermal contact conductance is an important factor in various applications, including electronics, electronic packaging, heat sinks, brackets, industry, nuclear reactor cooling, gas turbine cooling, internal combustion engines, heat exchangers, thermal insulation, press hardening of automotive steels, hypersonic flight vehicles, thermal supervision for space vehicles, and residential/building science¹.
Please note that thermal contact resistance arises due to improper contact between two bodies due to irregularities like scratches, ruptures, or dirt on the surface, which causes less contact area available for heat conduction².
Source:
(1) Thermal contact conductance - Wikipedia. https://en.wikipedia.org/wiki/Thermal_contact_conductance.
(2) Thermal contact resistance: Definition, Formula (Heat transfer). https://mechcontent.com/contact-resistance-heat-transfer/.
(3) Thermal Contact Resistance | Neutrium. https://neutrium.net/heat-transfer/thermal-contact-resistance/.
(4) What is Thermal Contact Resistance - Thermal Engineering. https://www.thermal-engineering.org/what-is-thermal-contact-resistance-thermal-contact-conductance-definition/.
How to define Thermal contact resistance in Transient Thermal Ansys Workbench ?
**Thermal contact resistance** is created by the air gap between the contacting surfaces². It depends on surface roughness, how much pressure is applied on the surfaces in contact, and the kind of thermal paste used to fill up the air gap².
In **Transient Thermal Ansys Workbench**, you can define thermal contact resistance by specifying the **thermal contact conductance coefficient**¹. The inverse of thermal contact conductance is thermal contact resistance¹. The thermal contact conductance coefficient quantifies a contact's ability to conduct heat¹. It is used to calculate the amount of heat transferred through conduction between two bodies in contact¹.
To define thermal contact resistance in Transient Thermal Ansys Workbench, you can follow these steps:
1. Open your Transient Thermal Ansys Workbench project.
2. Select the surfaces that are in contact and for which you want to define thermal contact resistance.
3. Right-click on the selected surfaces and choose "Properties" or "Contact Properties".
4. In the properties window, look for the option to define thermal contact conductance or thermal contact resistance.
5. Enter the desired value for thermal contact conductance coefficient or thermal contact resistance.
6. Save the changes and run the simulation.
Please note that the specific steps may vary depending on the version of Ansys Workbench you are using. It is recommended to refer to the official documentation or user guide for detailed instructions specific to your version of Ansys Workbench.
I hope this helps! Let me know if you have any further questions.
Source:
(1) Thermal contact resistance - Ansys Learning Forum. https://forum.ansys.com/forums/topic/thermal-contact-resistance/.
(2) Thermal Contact Conductance - ANSYS Innovation Courses. https://courses.ansys.com/wp-content/uploads/2020/03/Lesson-3-Thermal-contact.pdf.
(3) Intro to Transient Thermal Analysis - ANSYS Innovation Courses. https://courses.ansys.com/wp-content/uploads/2020/05/Lesson-1-Introduction-to-transient-analysis.pdf.
(4)https://www.engineersedge.com/heat_transfer/thermal_contact_conductance_13849.htm.
To calculate the contact thermal conductance between two steel plates, you need to know the following parameters:
- The thermal conductivity of the steel plates, denoted by k (W/m•K).
- The thickness of each steel plate, denoted by L (m).
- The contact area between the plates, denoted by A (m2).
- The contact pressure between the plates, denoted by P (MPa).
- The surface roughness of the plates, denoted by R (μm).
- The interface fluid between the plates, such as air or oil.
The contact thermal conductance, denoted by h (W/m2K), is a measure of how well heat is transferred across the interface between the plates. It depends on the factors mentioned above, as well as the temperature of the interface. There is no simple formula for contact thermal conductance, but there are some empirical correlations that can be used to estimate it. One such correlation is given by Yovanovich (1981) as:
This correlation is valid for steel plates with surface roughness between 0.1 and 10 μm, contact pressure between 0.1 and 10 MPa, and interface temperature between 20 and 200 °C. It assumes that the interface fluid is air with a thermal conductivity of 0.026 W/m•K.
To use this correlation, you need to plug in the values of k, L, P, R and h into the equation and solve for h. Alternatively, you can use an online calculator such as this one to compute h for you.
I hope this helps you understand how to calculate contact thermal conductance between two steel plates. If you have any further questions, please feel free to ask me. 😊
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