Bruheat/Electrim Bin - Evaporation rate

[SteveD]

Hi Chaps

I'm brewing a smaller (2.5 gal) batch of strong stuff fairly soon and I'll be boiling in an old Electrim bin fitted with the usual single 2.4kw element. I can't for the life of me remember the evaporation rate you get with one of these - open boil, full tilt, as I haven't used one to boil wort for about 13 years. Does anyone know? It'd help me with my volume calcs.

Cheers,

Steve

[SteveD]

Cheers, Chris

10% per hour seems about right, I'll go with that.

[David Edge]

10% per hour seems about right, I'll go with that.

"I - I - I corwumph!" exploded Mr Wilkins...

One of the most useful things in GW's big book (and not one I've seen anywhere else) is that 3kW will evaporate 5 litres per hour, so 2.4kW will give you four litres per hour. Laws of physics and all that.

It works for me with a 45-litre 3-kW Burco, although as it is insulated (an inch of air between galvanised outer and copper vessel) the rate might be a little less from an un-insulated vessel where more heat is lost through the walls.

But I'd suggest that using a percentage may lead to disappointment.

[steve_flack]

One of the most useful things in GW's big book (and not one I've seen anywhere else) is that 3kW will evaporate 5 litres per hour, so 2.4kW will give you four litres per hour. Laws of physics and all that.

Doesn't that depend on the volume being boiled, the ambient temperature etc. The reason I say that is a) I use 3kW elements b) They sure as hell don't boil off 5L in an hour on a five gallon batch on my system c) they boil off even less on a ten gallon batch.

[steve_flack]

.
If you go for 10%/hr and are flexible on boil time it's easier to cut the boil short than have to extend it.

What I do...and some people are probably going to shake heads here....is boil for 45 minutes and then see how I'm doing with a refractometer. If I'm a bit over gravity I add some water. If I'm under I boil a bit more. Once I'm where I want to be, I add my 15 minute hops and whirlfloc and carry on a usual.

[David Edge]

Cast your mind back to O-level physics. At steady state (ie once you've reached boiling point for the atmospheric pressure and sugar concentration), the energy input comes out as:

1) losses (radiation, convection) through the vessel walls
2) latent heat of evaporation of liquid
3) radiation, convection from liquid surface

If you have some data that suggests that 1 and 3 are significant compared to 2 please share it!

[David Edge]

a) I use 3kW elements b) They sure as hell don't boil off 5L in an hour on a five gallon batch on my system c) they boil off even less on a ten gallon batch.

ok, my last one crossed in the post with Steve's.

That does suggest that your copper has significant losses through the walls and that more liquid heats more wall hence more radiation and less evaporation.

So my insulated system has minimal losses and evaporates 5 litres, if you can say how much your non-insulated system boils off with 5 and 10 gallons those would be very useful data points - along with the vessel wall material.

[steve_flack]

I'd wager that 1 is pretty important and is the main reason I get a much stronger boil with 5 gallons than 10. In fact if I seriously want to get a decent boil off with 10 gallon I need two elements on.

[steve_flack]

I reckon in an hour I lose about 3L on a 5 gallon batch and about two on a 10 gallon batch. The boil is also noticeably less vigorous in a 10G batch - it's more of a simmer. The kettle is made of uninsulated stainless steel so, whilst compared to other metals, stainless steel is a rubbish conductor of heat, it's probably better at it than your kettle.

[David Edge]

I'd wager that 1 is pretty important

If this were hbd we'd already have three nuclear physicists trundling proton synchrotons into their garden sheds as we speak! But yes, it looks like it is. I do like my insulated copper!

My simple model ignores losses from any lid upon which vapour condenses and then drips back too.

But, seriously folks, who's got data for 5 and 10 gal and stainless and plastic vessels?

What I do...and some people are probably going to shake heads here...

Perfectly reasonable empirical method! I'm lucky - if I hit start of boil I also hit end of boil - but that's because I calculate boil off in litres per hour and not as a percentage. Do you brew in a lift <g>?

[David Edge]

stainless steel is a rubbish conductor of heat, it's probably better at it than your kettle.

Dead right - I can touch my kettle and it's quite cool!

[steve_flack]

[
If this were hbd we'd already have three nuclear physicists trundling proton synchrotons into their garden sheds as we speak!

As a British scientist I prefer a more arm waving, 'shall we have a cup of tea and a biscuit to discuss it?' sort of answer....

[steve_flack]

Dead right - I can touch my kettle and it's quite cool!

I can't and it isn't. Warms up the garage nicely though (so does the RIMS).

[David Edge]

As a British scientist I prefer a more arm waving, 'shall we have a cup of tea and a biscuit to discuss it?' sort of answer....

Oh quite so, the US method is to identify one insignificant variable - eg the material of the rivets holding the makers plate on - and then start a flame war of epic proportions illustrated with ASCII art and equations. It's just not cricket!

[SteveD]

Er...ok. I just can't remember what my electrim bin did when I used it as a boiler, but my current 70L plastic one with 5.4kw of elements will lose about 16L over a 90min. It's got quite a surface area.

What I'm going to do is guess at between 3-5L per hour, and 10% ish divided by the weather forecast, and multiplied by the tide, and do as I usually do, (and Steve F) and check the gravity as I go, adding liquor if it looks like over shooting.

Cheers, chaps