Resolving Field Failure of a Heat Exchanger using Simulations

Background

A heat exchanger design & manufacturer in United States wanted find out the root cause of a field failure. They wanted to evaluate the heat transfer rate, flow distribution and solid particle sedimentation from multiphase flow in the heat exchanger.

Problem definition

The challenge was to design process parameters for the desired heat transfer rate without solid particle sedimentation in heat exchanger tube. The heat exchanger model consisted of 785 tubes with 4 passes. The flow was multiphase with a liquid-solid mixture having 7 different sizes of solid particles. Computational Fluid Dynamics was used to study the flow field, heat transfer rate, solid particle sedimentation and flow distribution.

Technical approach

  • Complex Geometry was made simulation-ready by removing noncontributing geometry features.
  • The mesh count was about 17 million.
  • RANS equation with energy & k-e turbulent equations was solved.
  • Eulerian multiphase model was used to solve multiphase flow equation.

 

Conclusions

We studied different inlet flow rates and selected an optimum flow rate to prevent solid sedimentation. We finalized the process with optimum velocity to achieve desired heat transfer rate.

It was difficult to accomplish the same study with an experimental set-up because the operation time of a heat exchanger in measured in hours making it impossible to visualize solid sedimentation in tubes.

The CFD simulation done by our team made it possible to visualize solid sedimentation and the solve sedimentation issue in few days’ time without further trial & error approach on the installed site.

Our simulation study reduced problem resolution time from months to a few days.