[dyemeduke]

I am working at a site that has no insulation on some outdoors water piping that will be exposed to harsh winter conditions (-40 degC and wind).  The system has not been started up yet, but there is a bypass jumper between the supply and return line that will keep water flowing.  The jumper/bypass is 1 1/2" NPS.

Me and another engineer are working on this, and we both feel that this presents a cause of concern.  Insulation will be costly at this point, so our other option is to increase the bypass size in order to ensure the pipe doesn't freeze due to the mass of water.  Him and I disagree though on one fact - the kinetic energy of the system.

In your opinions, do we need to account for the kinetic energy of the moving water mass?  Specifically, we've calculated the heat loss over the length of pipe at various water flow rates.  He feels that we just need to calculate the water flow required that will keep the return water line above 0 degC.  I feel that this is just the first step, because we need to compare our heat loss to the kinetic energy of the moving water and the latent heat of freezing the mass of water.  If our heat loss is close to these summed values (KE and latent heat), then we NEED to increase the flow.  Our main debate is over the KE.  To me, the water is moving, so heat losses must overcome KE at the pipe/water interface.  The flow is turbulent, so if the KE of the system is sufficiently (don't know how to quantify what "sufficiently" is yet) above the heat loss, it seems like we should be fine.

Your thoughts?  My colleague is making some strong arguments to why I don't need to account for KE, but this just feels wrong to me...and I've exhausted my time on this subject - need to look at other issues.  Thank you to anybody for your help.