David Paulson

Flow Prediction Vs. Actual results

Discussion created by David Paulson on May 1, 2009
Latest reply on Sep 3, 2009 by Joe Galliera
I am a new user of the Flow component to SolidWorks. I recently purchased Flow to reverse engineer a product design that did not perform as expected. And, of course, to improve our design insight in the future.

The specific project was a helical oil separator which is expected to separate gaseous ammonia from liquid mineral oil as a component to a refrigeration system. The velocity profiles computed by Flow and the particle studies seem to be realistic.

However, the actual thermal surface plots on the vessel are in stark disagreement with the Flow thermal predictions. This leads to a few questions that some of you out there might have insight:

1. Does Flow calculate turbulent vs. laminar flow based upon fluid velocity, tempertature, etc. or is this an input criteria? With velocities of NH3 gas of about 300 fps max. I would expect the flow to not be turbulent, and thus the heat exchange with the NH3 gas and the vessel and the ambient would be calculated upon the temperature gradient of the gas at a somewhat low velocity relative to the vessel wall. There shoud be a temperature gradient in the gas flow at this low velocity, which does not seem to be modeled correctly by Flow.

2. Is the thermal properties of the particles (mineral oil liquid) taken into account in the thermal calculations?? There is a large difference between the specific heat of gas and liquid. The thermal properties of the mass flow of the liquid is way more significant than the thermal properties of the vapor. But the Flow calculation seems to be solely based upon the vapor. Am I missing the method wherein the thermal properties of the particle (liquid) mass flow is included in the calculation?

In my reality, the temperature drop (inlet to outlet) on the surface of the oil separator was about 5 degrees F. The Flow prediction was about 35 degrees F.

Any insight is greatly appreciated.

David Paulson