[Gasification] heat exchanger flow

[Mark Ludlow]

Toby,

Turbulent flow is also characterized by a velocity profile of the fluid
within the conduit. Laminar flow has a parabolic profile while turbulent
flow has a velocity profile that is much flatter, with relatively higher
velocities closer to the conduit wall. Also, since it is turbulent, it has
many flow vectors that are not aligned with the "apparent" streamline and
even flow vectors that may oppose the overall direction of the mass flux.

Mark

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Bob Stuart
Sent: Tuesday, September 18, 2007 12:54 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] heat exchanger flow


On 18-Sep-07, at 1:21 PM, Toby Seiler wrote:

> Oscar, Jim and list,
>
>   Turbulence in flow is not going to improve heat transfer.  Is it  
> possible the term has been misapplied?  Turbulence causes  
> resistance to flow.  Wiping the surface with lots of molecules  
> moves the heat along.  If you restrict the flow, there are less  
> molecules to do the transfer thing.  Please provide a reference so  
> I can understand what may be referred to as "turbulent" flow versus  
> "swirl" or convoluted flow path in heat exchange.
>
>   Regards,  Toby Seiler

In laminar flow, only a few molecules get close enough to the surface  
to pick up heat.  In turbulent flow, there is a continuous exchange  
of molecules between the surface and the main stream of the flow, so  
that the center does not come out almost unchanged.

Best,
Bob Stuart




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