# Sizing a Herms heat exchanger



## Nodrog (12/7/13)

Am trying to figure out what sort of size hx I will need for herms system. Ie what length of what diameter copper tube? Ideally want it small enough to fit in a domestic kitchen kettle, save building another vessel, but not sure if its possible.

What size / length of tube are people using??
My Mash tun is a 40 litre Eski, looking to yield 25 to 30 liters wort including sparge water.

Think my basic maths has got me partly there?

max power into the hot water bath / kitchen kettle is 2kW
I want to be able to raise the temperature of the fluid flowing inside the pipe by a maximum of 1C per minute, up to 70 Deg C. 

I 'think' it takes 4200 Joules to heat 1litre of water by 1deg C. Am i right? Is this the same from 20 to 21 as 60 to 61Degrees? Is it roughly the same if its wort, SG=1050? Assuming it is, think that means 70W will heat litre 1 degree in 1 minute, which seems pretty impressive for a light bulb? Anyway, if it does that means 2 kW 'should' heat a flow of 29litres by 1degree over 1 minute?? Max published flow rate of march 809c is 15litres per min, but realistically 10, and can throttle down to 5 or less if i need to. So I have more heat than I need if element goes full bore, which is good, as the PID will flick the element on and off, and i can have a constant flow rate.

My copper tube is 14.73mm OD, wall thickness 1.02mm.
Assuming the water bath is near boiling, say 95C, so at worst case temp difference is 25 Deg C, is there a formula that tells me the surface area / length of copper tube i need for 5l/min, 10 l/min and 15l/min flow rates to give 1Deg C per minute rate of temperature change??

Plenty of questions!


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## Yob (12/7/13)

http://aussiehomebrewer.com/topic/41110-dedicated-herms-guide-problems-and-solution-thread/

Many people say 7m of coil, personally I use 3 in a 19lt Big W special and an OTS 2400w element and get 1'c per min (just over a min actually) which is comparable with what Ive read from other peoples flasher systems.

The thread linked above is extensive but well worth the read through in it's entirety... most of the issues you'll face are answered in there.

:icon_cheers:


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## AndrewQLD (12/7/13)

The longer the length of the herms coil the faster your flow can be and the faster your ramp speed becomes, however there is a point where your flow becomes so fast that the grain bed compacts and the flow becomes reduced or you get a stuck mash.
For my system I have ended up with 3mt coil and around 2-3 lt/minute flow.


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## mxd (12/7/13)

I use a 1.7ltr kettle (2000 watt I think) and the stainless coil from (some retailer here ??) for an 80 lts MLT, before that I used a 9ltr urn with a 2400 watt element with as much coper as I could fit in.

Both of the above ramp around 2 Degree every 3 mintutes.


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## Nodrog (12/7/13)

Think its Gryphon who have the coil to fit a kettle.
Would be good, but think he's in WA, I'm in Auckland, doesn't get much further apart without leaving the south pacific...


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## Truman42 (12/7/13)

With the stainless coil from Gryphon and the hermit build he posted on here (Coil sits inside some PVC pipe with a cordless kettle element) I get a good 2C per minute ramp.

So maybe ask Nev for some info on postage to Unzud, or if he knows of a supplier/seller of the same coil over there etc etc. they fit in a standard 3 kg postbag so I cant see it being that much dearer to post to Unzud.

Standard air mail for 1 kg is $20.00, 2kg $38.00 I doubt if they weigh more than a kg though.


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## Nodrog (12/7/13)

Yup, pm-ed gryphon, they're closed for a couple of weeks, guess you've got to take break sometime!


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## Tex083 (16/7/13)

Cant rate the Hermit coil high enough.
On the same site I got the SS compression fittings and a SS T to put the temp sensor, much like the Coil Kit for $180
http://gryphonbrewing.com.au/product_info.php?cPath=80&products_id=585
But you can do it cheaper if you DIY a bit.


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