Heating Up Water

[kevinprior 0]

Hi, I have a project at the moment where we have to heat up approx 40 litres of water to about 90°C, does anybody have any formulas or calculations I can use to determine how much heat input in KW to acheive this? I am planning on using electric elements to do this. Thanks Kev

[OZEE 5]

Need a little more info to accurately make that calculation. What is the starting temp? How fast do you need to get it from StartingTemp to EndingTemp? (i.e., you can get an ice-cube heated up to 90C with a cigarette lighter if you wait long enough...)

[finfin 0]

Interesting.... need to know how fast you need to heat it and how fast heat is being lost from it. Mostly how fast is fast enough(assuming losses are negligible). 1 Watt is 0.2390585 calories/second. 1 calorie is the amount of heat required at a pressure of one atmosphere to raise the temperature of one gram of water one degree Celsius that is equal to about 4.19 joules — abbreviation cal —called also gram calorie small calorie. Oh yeah... Pressure too. I assume it is at 1 atmosshere but it could easily be higher if it is pressurized water.

[finfin 0]

So we have 40000 cc (grams) of water we need 40000 calories. 40000 calories/second is 167323.1 watts. That means 139.4359 watts could raise the temp 1 degree C in 20 minutes (at one atmosphere pressure assuming no losses). Forgot to ask what the starting temp was... You get the idea though. And don't forget that more is better. And PLEASE check my math.

[kevinprior 0]

the starting temp will be approx 60° heating up to 90°, I imagine about 20 mins to heat up would be a good assumption, the water will be in an open tank so the pressure will be atmospheric. Thanks for your calculation finfin, using online calculators I got about 4 Kw, so your working out looks good. The only other thing I may to consider is water loss, this is for a food process where the water could become contaminated and require replenishment. However the difficult thing I have, is that this is for a prototype machine to determine if what we are trying to do will actually work. So I don't know how many l/min etc to account for. I don't think the loss will be too great, so I was considering going for 4.5Kw and see how it goes. Thanks Kev

[finfin 0]

Remember that there are losses other than water used. If you knew how long the water took to cool down in the system with no heat applied... You need to add for that also. If it is well insulated it MAY be negligible.

[alex31 0]

From my expirience 3kw is inaff! or 6kw with SSR control Edited 22 May 2007 by alex31