I am working on Welding Modelling in APDL. I am applying variable heat transfer coefficient. So, I have defined a table based on various temperature as follows,
SF, ALL, CONV, %TCONV%, Tinf
where, Tinf is ambient temperature.
Can anyone tell me, whether way of applying heat transfer coefficient which depends on temperature is correct or not?
With Regards
Vinayak S Matur
I do not know what´s APDL, but in principles, in forced convection the heat transfer coefficient doesn´t depend on the temperature. Only heat flux associated with the heat transfer coefficient. Different situation is with natural or free convection where the temperature of the body, or if you want temperature difference between the body and ambiance is the driving force for the fluid movement and thus influences the heat transfer coefficient. So to sum-up, it depends on your situation.
But I suppose that in welding application the natural convection might be strong enough to account for the heat transfer coefficient being temperature dependent.
regards
Miroslav
Variable heat transfer coefficient, I have used for study of temperature distribution in brake rotors and drums during brake application. For a welding modelling, I assume that you are trying to analyse the temperature distribution while welding a length. In Ansys, to use the data in APDL, better to contact the Ansys support team. They will help you.
Hope this helps you.
Thanks
HRS
In forced convection, heat transfer rate depends on mainly velocity, fluid properties such as thermal coductivity, dynamic viscosity, specific heat, density, etc., characteristic length. Nu = f( Re, Pr). It also depends on temperare difference as rate of heat tranfer is proportional to area, and temperature difference according to Newtons law of convection.
Dear Vinayak, Like Miroslav I too do not understand what is APDL. And like him, I also feel that natural convection and radiation may be important, radiation more so. Since you are welding metals, heat will leak away rapidly by conduction. At the temperatures of welding, the emissivity of the junction will be quite close to unity. While natural convection is likely to be stronger than forced convection, I think that radiation will be more important. As for natural convection vs. forced convection, please calculate the value of Gr/Re^2 to judge if forced convection is important.
Just for the record, the temperature dependence of heat transfer coefficient is a function of Prandtl no., but may be ignored in air if the temperature difference is less than about 100 K.
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