Condenser Size.

[YHB]

I have been meaning to ask this for a while.

Lets say you are running 90% reflux, therefore the Dephleg is knocking 90% of the vapour down and passing 10 % of the vapour.

Why then is the Product Condenser always much bigger than the Dephleg if it is doing less work?

Tell me what I am missing?

[Eucyblues]

I'm sure if you do the numbers the internal water capacity of the dephleg will be greater than the shotgun ....

However...the transfer surface area in the dephleg will probably be smaller than in the SG  - so a higher water flow would be needed

On the other hand, the rate of heat transfer depends on the temperature difference between the fluids, so the rate is higher in the depghleg than in the SG ie: it takes more effort to reduce the temp when the distillate is only a bit warmer than the coolant

Hope that tidies it up - clear as mud eh 

[ShiFu]

The dephleg is for "knocking down" the vapors - turning hot vapors into hot liquid - to cycle back in the still repeatedly.
You don't really want that liquid to be too cold, that would make the column unstable and unproductive. Just enough to phase change back into a liquid and not much more than that. Over-chilling the hot liquid should be avoided.   

The product condenser is to not only knock the hot vapors down but to chill the distillate enough that the alcohol does not quickly evaporate into the atmosphere (causing a loss of alcohol and a fire hazard). 
Oversizing the product condenser can help to save cooling water as the distillate has more contact area and time.   
And because most alcoholmeters are calibrated to read at 20C. 

The most efficient (shotgun style) product condenser I've seen so far is really two condensers. A small "pre-condenser" that takes the brunt of the heat exchange and knocks down the hot vapors into a hot liquid. The next, bigger, condenser can more effectively chill the hot liquid into a cool liquid. 
My all-time favorite condenser for water effeciency is a copper worm (coil) in a bucket. But it's not as elegant and compact as a shotgun (tube in shell) condenser. 


I wouldn't think the product condenser is doing less work than the dephlegmator. 

[YHB]

Thanks for the answers, yes I was only referring to condensing the vapour, not cooling the distillate.

I have been using a BOK for years with the condensate coming off steaming. It only took a very small heat exchanger (15 over 10) with a trickle of coolant to chill the distillate down.

 
And because most alcoholmeters are calibrated to read at 20C. 

Not a consideration with Digital alcoholmeters

[Eucyblues]

The dephleg is for "knocking down" the vapors - turning hot vapors into hot liquid - to cycle back in the still repeatedly.

That's what i should have said....

[Myles]

One other thing. The PC is also often used in strip mode with no dephlegmator coolant flow.

Either on a dedicated strip run or when running out tails at the end of a spirit run.

[YHB]

OK - I will build a big expensive one, I much preferred the small cheap idea.

So - 8 barrel Gatling Gun condenser with 400mm long 15 over 10 barrels and teak Caps.

That should keep me busy for a few weeks.

[Myles]

The previously mentioned 2 stage condenser is a good idea. Your condenser requirements realy can change quite a lot dependent on your mode of operation.

If you want, for strip runs you can relocate the dephlegmator into the downstream vapour path and use it as a precondenser. It can be an efficient use of equipment.

One traditional method used in some of Alex's Boka designs is to include a product cooler in the coolant supply line to the reflux condenser.

I have more condensers than I need and in hindsight should not have built some of them, but it was a learning process.

[law-of-ohms]

I run two condensers.

Full  3in shotgun, then a 45d bend, then a 2in shotgun. I find the bend creates turbulence and better cooling efficiency.

I can trickle out the water from them at ~65c, but the product comes out cold. use the hot water coming out to create the next mash