2. In this example, we will calculate the theoretical minimum power needed for an ice machine to take water at 15 C and produce 1 Tonne ( = 1000 kg) of ice at 0 C in 1 hour. For this example, we use the expression for ideal work or power: Wideal = mwmas AH) where Wideal is the ideal minimum power needed for this process, riaw is the mass owrate of the water, and AS and AH are the total entropy and enthalpy change of the water in process, respectively. The heat capacity of liquid water Cp = 4.18 kJ/kg. Enthalpy of phase change (fusion) of water = 79.72 kJ/kg. Surroundings To = 25 C. Find the enthalpy change of cooling water from 15 C to 0 \"C. [Answerr -62.7 kJ/kg.] Find the entropy change of cooling water from 15 C to 0 C. [Answerz -0.224 kJ/kg-K.] Find the entropy change of freezing liquid water at 0 0C. Answer: [-0.292 kJ/kg-K.] Calculate the quantity ToAS, [Answerz -153.8 kJ/kg.] Calculate the total enthalpy change AH for this process. [Answer: -142.4 kJ/kg.] Calculate Wideal for this process from the above equation. [Answerz -3.l7 kW.] r6099 ,crsv Note that the answer is negative, meaning that work (power) is needed for the process, that is, work is done on the system. Work is done to cool the water to the freezing point of water, then freeze the water, and to overcome the entropy change of cooling and freezing the water. This is the theoretical minimum power required and there is no real process that can achieve this. The actual process would require at least twice the theoretical amount of power