How to specify ambient temp in a heat exchanger simulation in Sub-ambient simulation

BharathB · June 19, 2018, 15:04

Heat transfer is between fluid (water) in a pipe placed adjacent to an array of small heat sources, temperature at fluid inlet is less than ambient, How do i specify the ambient temperature (of surrounding air in gaps between heat sources) in this sub-ambient cooling simulation. Do i need to model a separate air domain (with the surrounding air) and assign a fixed temperature in cell zone conditions (in the fixed term option)?

Thank You

`e` · June 20, 2018, 02:23

The temperature at the boundaries are defined with boundary conditions. If you do not assume that the pipe wall is a known temperature then you would need to also model the external fluid (to determine the temperature on this boundary).

BharathB · June 21, 2018, 09:40

Thank You 'e'

also instead of modelling the air domain, could i give a convection boundary condition at the walls where air is in contact(with approximate analytically calculated heat transfer coefficient of air at the temperature and speed for the geometry) to obtain an approximate solution?

thank you for your reply.

`e` · June 23, 2018, 02:47

Yes, you could add a convective heat transfer boundary condition and apply a UDF to calculate the heat transfer coefficient with an analytical equation, using the DEFINE_PROFILE macro. Discussion at: UDF to change heat transfer coefficient with wall temperature

June 19, 2018, 15:04	How to specify ambient temp in a heat exchanger simulation in Sub-ambient simulation	#1
BharathB New Member Bharath Join Date: Jun 2018 Posts: 3 Rep Power: 8	Heat transfer is between fluid (water) in a pipe placed adjacent to an array of small heat sources, temperature at fluid inlet is less than ambient, How do i specify the ambient temperature (of surrounding air in gaps between heat sources) in this sub-ambient cooling simulation. Do i need to model a separate air domain (with the surrounding air) and assign a fixed temperature in cell zone conditions (in the fixed term option)? Thank You

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June 20, 2018, 02:23		#2
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	The temperature at the boundaries are defined with boundary conditions. If you do not assume that the pipe wall is a known temperature then you would need to also model the external fluid (to determine the temperature on this boundary).

June 21, 2018, 09:40		#3
BharathB New Member Bharath Join Date: Jun 2018 Posts: 3 Rep Power: 8	Thank You 'e' also instead of modelling the air domain, could i give a convection boundary condition at the walls where air is in contact(with approximate analytically calculated heat transfer coefficient of air at the temperature and speed for the geometry) to obtain an approximate solution? thank you for your reply.

June 23, 2018, 02:47		#4
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	Yes, you could add a convective heat transfer boundary condition and apply a UDF to calculate the heat transfer coefficient with an analytical equation, using the DEFINE_PROFILE macro. Discussion at: UDF to change heat transfer coefficient with wall temperature