You’re talking about specific heat capacity (energy required to change temperature).
Bizzybee is talking about heat of vaporization (the energy required for a liquid/vapor phase change - aka vaporizing or condensing).
You just made a minor math error at the end (aside from units being all over the place you still got them right in the end). Bizzybee’s calculations should have also included the energy required to cool the butane, not solely condense it. Though it’s a small value relative to the energy for vaporization/condensing, it still makes a difference as you scale up.
Was half way through sending you a private message but figured I’d share these tidbits here too, to clear up the picture.
187.2 is the energy required in BTU’s, not a temperature change in degrees. And your units are all over the place. You also multiplied degrees by seconds and ended up with BTU/hr.
I’m not saying this to shame you, but to actually get you to think about why the math is working the way it is (or why you messed up)…hate that I even have to make that disclaimer…
Start at the top: Write everything down in fractions so you can more easily keep track of units and visualize how they “cancel out.”
4 lbs × .39 btu/(lb • °F) × 120 °F = 187.2 BTU = total energy required
187.2 BTU/min = 11,232 BTU/hr …now I follow you again.
1 kilowatt = 3412.14 BTU/hr
(x kW) / (1 kW)= (11,232 BTU/hr) / (3412.14 BTU/hr)
x = 3.29
3.29 kW is the power required.
Look at that last conversion from BTU/hr to kW that you did. The digits are the same in both values (2,9,3, respectively). You could only get that by multiplying by a factor of 10 (aka you just shifted the decimal placement). I didn’t follow much of your math until this point haha. You almost had it, just messed up that final multiplication.
Now, as far as Bizzybee’s calculations, he has a typo in his units. He multiplied (mol/lb) by (kJ/mol) and ended up with (kJ/min). It should be 175 kJ/lb. Guess he just shorthanded the conversion…Otherwise, he’s right. Here is a more explicit unit conversion:
3600 kJ = 1 kWh
175 kJ = 0.0486 kWh
[ 0.0486 kWh ] / [ (1/60) hr ] = 2.916 kW
This is what happens when I eat 300+ mg THC and it somehow wakes me up. I’ll be wired all night😂. That being said, I’m pretty stoned and typing this all from my phone. Someone double check me for what it’s worth.