I'm trying to calculate how much water do I need to evaporate to cool down the skin of a combustion chamber of a rocket engine after a test. You can approximate its shape with a cylinder with a 50 cm diameter and a wall 2mm thick. Overall the combustion chamber is 60cm long.
You can use the heat capacity of s235 steel. 
At the end of a 1 minute test the engine is at 1000K. explain your steps
To calculate how much water is needed to evaporate to cool down the skin of a combustion chamber of a rocket engine after a test, we need to determine the amount of heat that needs to be removed from the combustion chamber.

Here are the steps to calculate this:

Determine the volume of the combustion chamber.

Volume of the cylinder = πr²h, where r = radius = 25cm and h = length = 60cm

Therefore, the volume of the combustion chamber = π(25cm)²(60cm) = 2.356 x 10^5 cm³

Determine the mass of the combustion chamber.

Mass of the cylinder = density x volume

Assuming the density of S235 steel is 7.85 g/cm³, the mass of the combustion chamber = 7.85 g/cm³ x 2.356 x 10^5 cm³ = 1.85 x 10^6 g = 1850 kg

Calculate the heat energy stored in the combustion chamber.

The specific heat capacity of S235 steel is about 0.49 J/g·K.

Assuming that the initial temperature of the combustion chamber is room temperature (25°C or 298 K), the heat energy stored in the combustion chamber after the test is:

Q = m x c x ΔT, where m = mass of combustion chamber, c = specific heat capacity of S235 steel, and ΔT = change in temperature.

ΔT = 1000 K - 298 K = 702 K

Q = 1850 kg x 0.49 J/g·K x 702 K = 5.39 x 10^8 J

Determine the amount of water needed to evaporate to remove this heat energy.

The heat of vaporization of water is 2.26 x 10^6 J/kg.

Therefore, the amount of water needed to evaporate to remove 5.39 x 10^8 J of heat energy is:

m = Q ÷ Hv, where Hv = heat of vaporization of water

m = (5.39 x 10^8 J) ÷ (2.26 x 10^6 J/kg) = 238.5 kg

Therefore, approximately 238.5 kg of water would need to be evaporated to cool down the skin of the combustion chamber of the rocket engine after a 1-minute test at 1000K.
Thanks, that was just what I was looking for, you helped me out a lot here.