Browse Groups

• Hi all, The internet has provided me with far too many conflicting rates and formulae for calculating whether an external water bath for a stainless steel
Message 1 of 13 , Jun 1, 2005
View Source
Hi all,

The internet has provided me with far too many conflicting rates and
formulae for calculating whether an external water bath for a stainless
steel boiler will or will not provide sufficient heat.

I'd very much appreciate it if an engineer on the list would give this a
once over:

T1 = 105 degC (water + table salt jacket)
T2 = 78 degC (mash)
Heat transfer coefficient = no idea... Ignoring it for the moment.
K = approx 14 W(m2 . K) (I have seen more figures for SS than I care to
poke sticks at. This is the most conservative, and is for 270K, so
anything better would be super).
Q = Watts
A = Area = .64m2
D = thickness of the SS wall = approx 2 mms

Q/A = (T1 - T2) / (D . 1/K)

Q/A = (27) / (.002 / 14)
= 27 . 7000
= 189,000

Q = 189,000 . 0.64
= 120.96 kW

So, what I'd like to know is -- will a 2mm stainless steel wall for an
area of .64m2 allow heat to pass through at a rate of up 120kW for that
temperature differential? Even approximately? As long as it's higher
than 3 or 4kW I'm happy. Unfortunately some formulae I've found
suggested the figure would be closer to 800W...

Cheers and thanks,
Andrew
• Andrew, a mash temperature will typically vary inbetween 90C (~17%) - 99C (~1%) during operation. IMO you ll get missleading results by using 78C for mash
Message 2 of 13 , Jun 1, 2005
View Source
Andrew, a mash temperature will typically vary inbetween 90C (~17%) -
99C (~1%) during operation. IMO you'll get missleading results by
using 78C for mash temperature.

- Riku

--- In Distillers@yahoogroups.com, Andrew Forsberg <andrew@u...>
wrote:
> Hi all,
>
> The internet has provided me with far too many conflicting rates and
> formulae for calculating whether an external water bath for a
stainless
> steel boiler will or will not provide sufficient heat.
>
> I'd very much appreciate it if an engineer on the list would give
this a
> once over:
>
> T1 = 105 degC (water + table salt jacket)
> T2 = 78 degC (mash)
> Heat transfer coefficient = no idea... Ignoring it for the moment.
> K = approx 14 W(m2 . K) (I have seen more figures for SS than I
care to
> poke sticks at. This is the most conservative, and is for 270K, so
> anything better would be super).
> Q = Watts
> A = Area = .64m2
> D = thickness of the SS wall = approx 2 mms
>
> Q/A = (T1 - T2) / (D . 1/K)
>
> Q/A = (27) / (.002 / 14)
> = 27 . 7000
> = 189,000
>
> Q = 189,000 . 0.64
> = 120.96 kW
>
> So, what I'd like to know is -- will a 2mm stainless steel wall for
an
> area of .64m2 allow heat to pass through at a rate of up 120kW for
that
> temperature differential? Even approximately? As long as it's higher
> than 3 or 4kW I'm happy. Unfortunately some formulae I've found
> suggested the figure would be closer to 800W...
>
> Cheers and thanks,
> Andrew
• That s a very good point. Well, even at only 1 deg C difference the rate is 4.4kW for that area of 2mm SS wall. The other problem will have to be how to
Message 3 of 13 , Jun 1, 2005
View Source
That's a very good point. Well, even at only 1 deg C difference the rate
is 4.4kW for that area of 2mm SS wall. The other problem will have to be
how to insulate the jacket optimally. One thing at a time.

So, do those calculations look even roughly correct to you?

Cheers
Andrew

abbababbaccc wrote:

>Andrew, a mash temperature will typically vary inbetween 90C (~17%) -
>99C (~1%) during operation. IMO you'll get missleading results by
>using 78C for mash temperature.
>
>- Riku
>
>
>
• Hate to bring bad news, but I m guessing the conduction of heat through the steel will not be your limiting factor, and your 120kW sounds about right. It will
Message 4 of 13 , Jun 1, 2005
View Source
Hate to bring bad news, but I'm guessing the conduction of heat
through the steel will not be your limiting factor, and your 120kW

It will more likely be the convection of the water bath and the wash
inside the boiler, more so the water bath once it is boiling, that
will limit heat transfer.

Agitation of both will provide better heat transfer. Trying to
calculate heat transfer for such a system would be a nightmare.

I'd say your best bet is an experiment, unless you're a hardcore nerd
that wants to create a computer model, or a hardcore physicist/maths
guru who has way too much spare time =). Let us know how you get on.

knarl.

--- In Distillers@yahoogroups.com, Andrew Forsberg <andrew@u...>
wrote:
> Hi all,
>
> The internet has provided me with far too many conflicting rates and
> formulae for calculating whether an external water bath for a
stainless
> steel boiler will or will not provide sufficient heat.
>
> I'd very much appreciate it if an engineer on the list would give
this a
> once over:
>
> T1 = 105 degC (water + table salt jacket)
> T2 = 78 degC (mash)
> Heat transfer coefficient = no idea... Ignoring it for the moment.
> K = approx 14 W(m2 . K) (I have seen more figures for SS than I
care to
> poke sticks at. This is the most conservative, and is for 270K, so
> anything better would be super).
> Q = Watts
> A = Area = .64m2
> D = thickness of the SS wall = approx 2 mms
>
> Q/A = (T1 - T2) / (D . 1/K)
>
> Q/A = (27) / (.002 / 14)
> = 27 . 7000
> = 189,000
>
> Q = 189,000 . 0.64
> = 120.96 kW
>
> So, what I'd like to know is -- will a 2mm stainless steel wall for
an
> area of .64m2 allow heat to pass through at a rate of up 120kW for
that
> temperature differential? Even approximately? As long as it's higher
> than 3 or 4kW I'm happy. Unfortunately some formulae I've found
> suggested the figure would be closer to 800W...
>
> Cheers and thanks,
> Andrew
• ... Hey Knarl, Bad news is still news, and it s far better to be brought it in the form of advance notice than to jump in first, only to swear and curse later.
Message 5 of 13 , Jun 2, 2005
View Source
On Wed, 2005-06-01 at 22:52 +0000, dearknarl wrote:
> Hate to bring bad news, but I'm guessing the conduction of heat
> through the steel will not be your limiting factor, and your 120kW
>
> It will more likely be the convection of the water bath and the wash
> inside the boiler, more so the water bath once it is boiling, that
> will limit heat transfer.
>
> Agitation of both will provide better heat transfer. Trying to
> calculate heat transfer for such a system would be a nightmare.
>
> I'd say your best bet is an experiment, unless you're a hardcore nerd
> that wants to create a computer model, or a hardcore physicist/maths
> guru who has way too much spare time =). Let us know how you get on.
>
> knarl.

Hey Knarl,

Bad news is still news, and it's far better to be brought it in the form
of advance notice than to jump in first, only to swear and curse later.

The other problem with the jacket proposal was the thought that it will
need to be a stainless steel jacket that's welded to the stainless steel
tank. Through tubes might improve the situation, as might encroaching
further under the tank... But, tbh, the last thing I want after all that
is to need to build an automated stirring paddle mechanism.

On a brighter note: the L-bend at the bottom of the tank, before the
gate valve, has a couple of small 3/4"-ish OD screw fittings with caps.
They look decidedly like they were designed for a steam mixer... :->
Hmmmmmmmm.

Cheers & thanks,
Andrew
Your message has been successfully submitted and would be delivered to recipients shortly.
• Changes have not been saved
Press OK to abandon changes or Cancel to continue editing
• Your browser is not supported
Kindly note that Groups does not support 7.0 or earlier versions of Internet Explorer. We recommend upgrading to the latest Internet Explorer, Google Chrome, or Firefox. If you are using IE 9 or later, make sure you turn off Compatibility View.