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Old   July 15, 2000, 01:34
Default Offset strip-fin heat exchanger
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Hello, Thanks a lot to CHAM and for opening PHOENICS user forum. I'm using PHOENICS 3.2 for fluid flow and heat transfer analysis in plate-fin heat exchanger. I started with rectangular offset strip-fin for which i have to find j and f data upto Re=10,000. I found a published paper(webb & joshi) where the equation for the critical Reynolds number has been developed. Below this critical number(laminar), i have used laminar model of PHOENICS and the results agreed well with the experimental results. Now my question is regarding which model have to be used to predict the flow friction and heat transfer above the critical reynolds number.

Thanks. Dipak
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Old   July 19, 2000, 10:46
Default Re: Offset strip-fin heat exchanger
Mike Malin
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Presumably the critical value refers to the onset of turbulence, so that above this the flow will be transitional at moderate Re, and fully-turbulent at still higher Re. In the first instance, one might as well use the standard high-Re form of the k-e model or perhaps the Wilcox-Kolmogorov k-f model.

At transitional Re, there is a case for using a low-re k-e or k-f model, but more mesh will be required to grid near-wall regions to capture the rapid variation in fluid variables. The k-f model usually converges much better than the k-e model which can be problematic to converge due the stiffness problem with the k-e equations. The 2-layer k-e model or LVEL model ( a pragmatic algebraic low-Re model ) might also be used, although the latter takes no account of turbulent transport of velocity fluctuations and scale.
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