Reynolds Number 1

[ChipFuller]

I asked the manufacturer of chemical reactor at our plant what's the Reynolds number at 60 gpm. The manufacturer replied back at 60 gpm the reactor has an overall heat transfer coefficient of 75 KCal/m2h degree C with a pressure drop of 0.28 bar. I'm trying to back into the Reynolds number but it seems like I'm missing some data. Am I right?

 

[TD2K]

Reynold's number are an indication typically of the flow characteristic in the system (laminar versus turbulent). Typically, my experience is with the Reynold's number of a flow through a piping system but the concept can be applied to different geometries.

The Reynold's number is a 'diameter' * 'velocity' * 'density' / 'viscosity'.

The heat transfer coefficient (what the vendor has given you as 75 kcal/hm2) is affected by the Reynold's number as well as other fluid properties.

I'm unclear what type of system you are trying to get the Reynold's number for. Is the 60 gpm through the reactor flowing through some sort of catalyst or packing?

 

[ChipFuller]

Thanks for the reply. I'm working with a Chemical Process Engineer and he says that he needs turbulent flow through the water jacket of the reactor. He doesn't know what the turbulent flowrate is, so I contacted the vendor in Italy and this was the information provided. I'm flowing 55% ethlyene glycol and 45% deionized water.

 

[rmw]

Go to

http://www.processassociates.com,

explore around, and you will find information that correlates the function of reynolds number and OHTC. I found this site via Eng-Tips.com, and have found it very helpful. You should be able to calculate your Reynolds numbers there, if you know or can approximate the dimensions of the flow area of the water jacket.

 

[ChipFuller]

I haven't done the Reynolds number for a reactor. Do I use the inside diameter of the nozzle or some dimension from inside the water jacket of the reactor?

 

[Ti85]

The actual Reynolds Number in the jacket will depend on the type of jacket and the jacket internals. The manufacturer may have empirical data on heat transfer used this information to answer your question. You may not be able to accurately calculate the Reynolds number. Wihtout any details about your set-up or guarantees of accuracy you could try the following.

This should yield a very conservative Re number.

Calculate the cross-sectional area of the jacket, A.
Flowrate/A = estimated velocity, v.
For the diameter a crude estimate would be 2 x (the distance from the inside of the jacket to the outside of the reactor). You then need the viscosity & density of the liquid in the jacket. Watch you're units.

This is very much a back of the napkin calculation and is the type of thing I normally keep to myself until I can do a more accurate calculation. If your answer looks totally off the wall then crumple up the napkin and toss it. One other note, if your chemical engineer is any good he should be able judge if the flow is or isn't turbulent if he has the reactor jacket specifications and flowrates in front of him.

 

[Mike6158]

Just curious about something. In this particular casem wouldn't the Reynolds number change as the fluid medium heated up? In this case, process modeling software (Hysis for instance) might give you the answer that you need.

 

[25362]

If the dominant resistance to heat flow is on the internal reactor side, then the OHT coefficient would be fixed by -and lower than- the coefficient in the reactor. In this case any change in the jacket's HT coefficient by changing the Re number (i.e., degree of turbulence), would have little influence on the OHTC.

 

[Ti85]

I agree with 25362, you already have the information you're really looking for, OHTC (minus the reactorside coefficient). The Reynold's Number in the jacket is irrelevant.

 

[aliihsan]

hi
if you have convection heat transfer number, you can get back to Nusselt number which is related with Reynolds number and Prandtl number. prandtl number is identical for the mixture you handle.