

April 9, 2020 at 5:31 pmkashokbhSubscriber
Hi Community,
I am trying to use a nonconstant film coefficient for convection boundary condition. I know the thermal resistance of my heat sink, lets call it "Rhs". I want to define the film coeffcient as 1/(Rhs*Area). I have parametrized the geometry and have parameters for area. For Rhs, I want to add a new parameter. Workbench is allowing me to only insert a dimensionless/constant parameter. Am I missing something?

April 9, 2020 at 9:57 pmpeteroznewmanSubscriber
From Wikipedia, Absolute thermal resistance is the temperature difference across a structure when a unit of heat energy flows through it in unit time.
So R = (Ths  Tamb)/Q where R is Thermal Resistance in units of K/W, Q is heat flow in W and (Ths  Tamb) is the change in temperature in Kelvin across the thermal boundary layer, where Ths is the hot surface temperature and Tamb is the ambient temperature.
This could be written
Q = (Ths  Tamb)/R
ANSYS implements convective heat transfer using a film coefficient h in units or W/K.m^2 and that is applied to a surface. ANSYS calculates the area of that surface to know a value for A.
ANSYS will calculate Q using the equation Q = hA(Ths  Tamb)
Therefore 1/R = hA or as you said, h = 1/(R*A)
If your Area comes from SpaceClaim without units as P7, you can add units as shown in P9. Note that P8 is coming from Mechanical from the Convective boundary condition.
Let's say the value of R will be entered as an input. In this example, R = 7
Now you can type the equation for h.
Edit the Properties of P8, which came from Mechanical Convective boundary condition.
Now the value of h used in the Convective BC is calculated from R and A
Type in a range of R values and Areas in the Parameter Set table.
P2 is an output from Mechanical measuring a specific Named Selection Face in the model.

 You must be logged in to reply to this topic.
Simulation World 2022
Check out more than 70 different sessions now available on demand. Get inspired as you hear from visionary companies, leading researchers and educators from around the globe on a variety of topics from lifesaving improvements in healthcare, to bold new realities of space travel. Take a leap of certainty and check out a session today here.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Ansys Blog
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
 How to calculate the residual stress on a coating by Vickers indentation?
 An Unknown error occurred during solution. Check the Solver Output…..
 Saving & sharing of Working project files in .wbpz format
 Solver Pivot Warning in Beam Element Model
 Understanding Force Convergence Solution Output
 whether have the difference between using contact and target bodies
 Colors and Mesh Display
 The solver engine was unable to converge on a solution for the nonlinear problem as constrained.
 Massive amount of memory (RAM) required for solve
 What is the difference between bonded contact region and fixed joint

1862

1677

917

670

351
© 2022 Copyright ANSYS, Inc. All rights reserved.