Learning Forum

[jijojose2024]

Hii all,

When I tried hand calculation for the temperature of exhaust gas cooled using mCpdt equation it is found that mass weighed avg is within 1 or 2 deg of the hand calculation but most tutorials and some opinions i personnaly got says it is area weighed avg to get the temp at the outlet of an exhaust pipe. 

so which one is correct??

[Rob]

For flow boundaries I'd use mass weighted (except for pressure) and for solid surfaces it's generally area weighted.  For the flow bc you need to account for the (small region) of high velocity flow carrying a larger proportion of the mass/heat/species. 

[jijojose2024]

but why most tutorial videos suggest area weighted average??

[Rob]

No idea, Ansys tutorials or from other sources?

[jijojose2024]

i cant say specifically but i hardly remember anyone using mass weighted average.... mostly youtube

 

[Rob]

Area weighted tends to be used for walls etc, ie non-flow surfaces and values. Mass weighted for flow. 

So, on a wall I'd look at area weighted temperature. On a flow boundary I'd use mass weighted temperature as that will account for the small fast (or slow) region holding the most (or least) energy.