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-   -   heat transfer in two-phase flow (http://www.cfd-online.com/Forums/cfx/25612-heat-transfer-two-phase-flow.html)

Leonid Fromzel April 8, 2008 05:57

heat transfer in two-phase flow
 
I tried to model two-phase air/oil flow inside the cavity. Oil is delivered from one inlet hole, whereas air is delivered from another inlet hole. Air-oil mixture is evacuated from outlet hole. Mixture model was applied with air and oil both treated as continuous phases.

I did this analysis in the following subsequent steps: - first stage - I modeled isothermal flow - oil and air temperatures are the same, cavity walls are adiabatic. Results were obtained with sufficient accuracy. OK.

- second stage - different temperatures of the air and oil at the respective inlets, homogeneous heat transfer model, results from the first stage were used as initial conditions. Results were obtained with sufficient accuracy. OK.

- third stage - different temperatures of the air and oil at the respective inlets, inhomogeneous heat transfer model with user supplied correlation for heat transfer coefficient (HTC) between the phases, results from the second stage were used as initial conditions. Solution failed because oil maximum temperature exceeds reasonable limits in one small local area near air inlet. To fix this problem I tried to implement or change the following -correlation for Nu number instead correlation for HTC -very big constant HTC (10^6) -very small constant HTC (actually zero) -constant oil properties instead of user supplied temperature dependent properties -different time steps -different advection schemes for energy equations -etc

No one of these approaches led to sucsess.

I am totally confused because from my point of view homogeneous heat transfer model and inhomogeneous heat transfer model with very big HTC should give just the same results.

What do you think about this problem? Thanks



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