# Simcenter STAR-CCM+ Is radiation included in HTC?

2021-01-22T17:21:36.000-0500
Simcenter STAR-CCM+ Simcenter STAR-CCM+ Virtual Reality Teamcenter Share Simcenter STAR-CCM+ Viewer Simcenter STAR-CCM+ Application Specific Solutions

## Summary

When exchanging thermal boundary conditions between simulations it’s common to use a temperature and a HTC.

## Details

When exchanging thermal boundary conditions between simulations it’s common to use a temperature and a HTC. Consider Newton's law of cooling:
q˙s′′=h(Ts−Tref)
The local surface heat flux, q˙s′′, and the surface temperature, Ts, and are known and for every choice of heat transfer coefficient, h, there is a reference temperature, Tref, that satisfies the equation.
In Simcenter STAR-CCM+ there are 4 different field functions for HTC,
• Local Heat Transfer Coefficient (LHTC)
• Specified y+ Heat Transfer Coefficient (Y+HTC)
• Heat Transfer Coefficient (HTC)
• Virtual Local Heat Transfer Coefficient (does not need the energy equation and will not be considered here)
The major difference between LHTC, Y+HTC and HTC is the choice of Tref.
• LHTC uses the temperature of the cell closest to the wall
• Y+HTC uses the temperature at a specified distance (y+). Needs y+ as input, default is 100
• HTC uses a user specified temperature. Needs temperature as input, default is 300K
There is one other difference between the 3 and that comes from what q˙s′′ is used. HTC uses the conduction heat flux whereas LHTC and Y+HTC uses the total heat flux. What this means is that the contribution from radiation (and boiling) will be included in the LHTC and Y+HTC but not in the HTC.
To illustrate this, please see the attached testcase of a solid cube given a heat source of 1000W with radiation activated. In the example the surface integral of h(Ts−Tref) does add up to 1000W for LHTC and Y+HTC but not for HTC. If you add the contribution from HTC with the radiated heat flux you get to the desired 1000W.