Author Topic: Mash Tun Specific Heat Calculation  (Read 2345 times)

Offline brewmot60

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Mash Tun Specific Heat Calculation
« on: February 24, 2020, 09:36:00 PM »
I get the idea behind the Mash Tub Specific Heat value. A mash tun will absorb some heat of the strike water. Different mash tuns of different sizes and design will absorb different amounts of heat from your strike water. The Mash Tun Specific Heat value accounts for this fact and provides an offset for the loss of heat.

Here is what I do not get.

Let's say I start a brew session and the mash tun has been in garage and the ambient temperature is 42? F and the mash tun is also 42?. It will absorb X percent of the heat from the strike water.

If everything else is the same, but the ambient temperature is 100? F,  the mash tun will be 100? and absorb less heat when compared to my 42? brew day.

Beersmith treats the Mash Tub Specific Heat value the same for all ambient temperature conditions.

The only thing I come up with is Beersmith assumes that your grain and mash tun have been exposed to the same ambient temperature and are the same temp. The Mash Tub Specific Heat offset will track up and down with the grain temp setting found elsewhere in the calculator. Which makes sense.

In my case, I have my grains inside the house and the mash tun is out in the garage. My house could be 70? and the garage could be 40?, or 70? or 90?.

Thanks in advance.

Offline Oginme

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Re: Mash Tun Specific Heat Calculation
« Reply #1 on: February 25, 2020, 02:44:46 AM »
The amount of heat absorbed by your mash tun is defined by the heat capacity (specific heat) of the mash tun, the mass of the mash tun, and the differential temperature between the heat source (the strike water) and the ambient temperature of the mash tun.  While the mass of the mash tun and the specific heat are both constants, the differential temperature is what determines how much thermal energy is required to bring the mass of the mash tun up to the desired mash temperature.  The program uses this equation to solve for both the thermal energy required for the mash tun as well as the grains and then adds that energy to the water to determine the strike water temperature which would contain that extra energy.
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Offline BOB357

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Re: Mash Tun Specific Heat Calculation
« Reply #2 on: February 25, 2020, 10:55:02 AM »
It appears that you're missing  the tun temperature entry, right under the grain temperature entry. With that, all the blanks are filled in and everything needed for the calculations have values.

When I stored my mash tun in an unheated shed, I'd put a gallon or 2 of hot tap water in it and let it sit while heating my strike water. I'd also take the grain temperature. Once the strike water was up to temperature I'd dump the tap water out and pour the strike water in, followed by the grains. When doing it this way, I just left the tun temperature at the default value of 72 degrees. When I started keeping the mash tun in the house I also left the default tun temperature be, as it was only a couple of degrees warmer than we keep the inside temperature.

I used this for with both 5 and 10 gallon round coolers with good results. Like other inputs, you may need to make minor adjustments after a couple of batches, but you'll be very close after following these steps provided your equipment profile and mash profiles have been adjusted to closely reflect your gear and procedures.

Bob

Offline Oginme

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Re: Mash Tun Specific Heat Calculation
« Reply #3 on: February 25, 2020, 11:00:34 AM »
Good catch, Bob!  I meant to reference that input on the mash tab.  My only excuse was that I was writing the reply while out in the barn milking and should have saved it for inside when i had a chance to make sure I covered everything.
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Offline BOB357

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Re: Mash Tun Specific Heat Calculation
« Reply #4 on: February 25, 2020, 05:25:56 PM »
I was actually just clarifying to the OP. Nice to know that I'm not the only that finds it difficult to concentrate on multiple things at the same time. I will warn you though, it doesn't get any better with age :)
Bob

Offline Lost Lantern Brewing

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Re: Mash Tun Specific Heat Calculation
« Reply #5 on: February 25, 2020, 07:09:20 PM »
Here's a link to the math behind specific heat. Basically, water is towards the high end of the materials spectrum, and metals are near the low end.  Water has a very high specific heat and stainless steel has a very low specific heat.  It's an expression of a material's capacity to store heat.  It's why a large pot of very hot water takes a relatively long time to cool off, but you can use bare hands on a sheet of aluminum foil just seconds after coming out of a hot oven.

Offline Lost Lantern Brewing

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Re: Mash Tun Specific Heat Calculation
« Reply #6 on: February 25, 2020, 08:10:39 PM »
Sorry.  I forgot to post the link...The Wikipedia entry for Specific Heat at the link has the formulas for calculating exactly what should happen in the scenario you described.  Brad would have to comment on the exact math he uses, but it's likely that it follows the formulas listed in the article at the link.

https://en.wikipedia.org/wiki/Specific_heat_capacity

Offline brewmot60

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Re: Mash Tun Specific Heat Calculation
« Reply #7 on: February 25, 2020, 08:29:27 PM »
I revisited the Help topic on the Infusion Tool.

It appears the answer is found in "Starting Conditions" section under "Initial Mash Temperature" It says to use room temperature if this is the first step.

I am going believe the tool assumes the grain and the mash tun have been sitting in the same environment and start at the same temperature.

If you are going to use this tool, plan ahead ensure the grain and the mash tun start off at the same point.

Offline BOB357

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Re: Mash Tun Specific Heat Calculation
« Reply #8 on: February 26, 2020, 07:56:45 AM »
The instructions you're citing are for the stand alone infusion tool.  If you're willing to deal with making sure your grain and mash tun are both at a defined temperature and enter that temperature in both of the appropriate places in the mash tab, you'll be just fine.
Bob

Offline brewmot60

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Re: Mash Tun Specific Heat Calculation
« Reply #9 on: February 26, 2020, 09:09:38 PM »
The instructions you're citing are for the stand alone infusion tool.  If you're willing to deal with making sure your grain and mash tun are both at a defined temperature and enter that temperature in both of the appropriate places in the mash tab, you'll be just fine.

There you go. Thank you. That helps knit things together. You are right, I was using the stand alone tool, not the mash tab on the recipe.

I was stymied for a while until I discovered the "Adjust Temp For Equip" check box on the design tab, not the mash tab. (why isn't on the mash tab?) ETA Found it at the top of the section under the description
« Last Edit: February 26, 2020, 09:54:45 PM by brewmot60 »

 

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