# Thermo heat transfer

1. Feb 1, 2005

### bird91

Hello all,

I am a little confused on this problem and want to be clear on it.

Given: Water is boiled at 1 atm pressure in a 20-cm i.d. pan. Water level in pan drops by 10cm in 30 min, determine the rate of heat transfer to the pan.

Now correct me if I'm wrong but water boils at 100 (degrees C) at 1 atm pressure, and 1 atm pressure is equal to 101.3 kPa.

Heres where I get confused, do I need to find the internal energy of saturated water at that pressure? If so than do i just take the difference between the sat. vapor and the saturated liquid? Where does the water level dropping come into effect? I know the larger the temp difference, the higher rate of heat transfer. Can you point me in the right direction, I would ask the teacher but I can't make the office hours.Thanks for your time.

2. Feb 2, 2005

### ehild

You need simply the latent heat of vaporization of water at its boiling point. It is 2260 kJ/kg. This latent heat is needed to convert 1 kg water into 1 kg water vapour. You can determine the amount of water evaporated in 30 min, don't you? I hope you can proceed from here.

ehild