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# Spray cooling

## Spray cooling

(OP)
I have tried to do a search on these forums and have found nothing, but it may be i am using the wrong keyword, if that is the case please direct me to the correct thread.

That said I am looking for equations for calculating the length of time it takes for sprayed droplets to evaporate into a hot vapour stream. if anybody could point me in the right direction i would be gratefull. I expected Perry's to have something, but unless I am looking in the wrong sections I cant find anything.

### RE: Spray cooling

(OP)
Dont seem to be able to edit posts here, so looking abit more into the subject it seems its not physics as it where, and seems to be reliant on the reaction too, so i should point out its ammonia I am talking about spraying for denox

### RE: Spray cooling

Not knowing the details of the issue in hand, I pressume that you can apply performance of spray dryers in which the droplets' settling time depends on their size and other properties of the vaporizing liquid as well as of the warm fluid flowing upwards. Thus, one can estimate the settling velocity of the droplets and given the size of the drying chamber one can estimate the average residence time.

As an example the terminal velocity for the intermediate Re values, 2<Re<500, would be:

Vt=[0.072D1.6*(RhoL-Rhogas)/(visc0.6*Rhogas0.4)]0.714

Vt, m/s; RhoL and Rhogas, densities, kg/m3; visc, viscosity of the gas, Ns/m2

After doing an estimate of the terminal velocity, one re-estimates the value of Re=Vt* RhoL*D/visc
to verify whether the applied formula is the correct one for the pre-selected flowing regime.

### RE: Spray cooling

(OP)
Thanks for the reply, but I dont think I can apply the above in this case. Still trying to get more details from the client, but its an exhaust gas moving at about 1m/s so the flow is likely to be turbulent.

I think i either need some way to calculate the evaporation rate of the droplets, or some reaction kenetics for this one depending on which is the governing factor.

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