Heat Efficiency Calculations?

[AndrewQLD]

I am getting a 2400 watt immersion heater and I need to work out how long it will take to heat a 40 lt pot of water to 75c. My water temp is around 18c. I am going to set a timer up so that I can mash in when I get out of bed in the morning .

Does anyone have the formula to calculate this??

Cheers
Andrew

 

[sosman]

I am getting a 2400 watt immersion heater and I need to work out how long it will take to heat a 40 lt pot of water to 75c. My water temp is around 18c. I am going to set a timer up so that I can mash in when I get out of bed in the morning .

Does anyone have the formula to calculate this??

Cheers
Andrew

[post="70443"][/post]​

Andrew, the physical constant you need is the specific heat capacity of water. You will also need to give some consideration to heat losses.

Latent heat of evaporation  2270	2270 kJ/kg

Specific heat capacity water 	 4.19	kJ/kgK

40 L of water is ~ 40 kg
assuming tap water is 20C then temperature rise is 75-20 = 55C (same diff for Kelvin).

=> 4.19 x 40 x 55 ~ 10 MJ

Watts * seconds = Joules

=> 10e7/2400 ~ 4000 seconds or a bit over an hour assuming no losses.

I have had a few beers so don't quote me :chug:

 

[AndrewQLD]

Sosman, I knew I could count on you thanks for the info this will help me to shave another hour of my brewday . I am having a beer too, Bosun Best Bitter all EKG yumm.

Thanks again.

Andrew

 

[PeterS]

I am getting a 2400 watt immersion heater and I need to work out how long it will take to heat a 40 lt pot of water to 75c. My water temp is around 18c. I am going to set a timer up so that I can mash in when I get out of bed in the morning .

Does anyone have the formula to calculate this??

Cheers
Andrew

[post="70443"][/post]​

Andrew, I am no Einstein and can not give you equation as to how long. On the other hand, I can give you an idea of how long it took me the first time (which happened to be yesterday). This is what I did:

On Friday night, I filled my 60l kettle with 40L of cold water, ploncked my immersion heater (2400W) in it on a string to ensure that not all of it is immersed. (the bent arm sits nicely on a string, set to your height). Next, I set my cheap Arlec timer to activate at 4.30AM and swtich off at 7AM, the time I intended to get up. I happened to get up slightly earlier and decided to check how the timer went. It was boiling at 6.45AM. Since this was a first time try, I can only tell you that it takes less than 2 hours to get it up to mash in temp. Teherfore, next time I will set the time accordingly and adjust it until I am close to what temp I need.

I hope that helps.

Bye the way, I have to think of immersing the element a different way. Since I had a lid on the kettle, I found that the steam was sufficiently hot enough to cause me concerne about the electrical lead tthat was within the kettle. Even the bacalite or whatever material that was within the inside of the kettle was a tad hot. Probably no great concern as I always switch those things off when I move it..
:beer:
PeterS....