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Cooling water flow calculation:

Basic concept of specific heat

Heat exchangers calculations


In our case, the heat exchanger already exists we want to calculate the flow of water needed. We're going to use this equation:

Q = M . Cp1. (Te - Ts) = m. Cp2. (ts - te)


with: M: flow of steam (kg/s)

m: flow of water (kg/s)

Cp1: Steam Specific heat (kj/kg.k)

Cp2: water Specific heat (kj/kg.k)

Te: Temperature of entering steam

Ts: Temperature of exiting steam

ts: Temperature of exiting water 

te: Temperature of entering water


First, we have to find the specific heats:

at a pressure of 1.5 bar, the specific heat of steam is 2.0768 Kj/Kg.k

the specific heat of fresh water is around 4.19 kj/kg.k

 The temperature of cooling water used as the inlet is around 25 °C so te = 25 °C and will exit the condenser with a temperature around 50 °C.

The steam exiting the turbine and entering the condenser is around 120 °C so Te =120 °C, it should be cooled to over 90 °C so Ts = 90°C.

We also have the flow of steam around 50 g/s. We are now able to calculate the flow of water needed using the equation stated above.

Calculation and results

Q = M . Cp1. (Te - Ts) = m. Cp2. (ts - te)

50 g/s x 2.0768 kj/kg.k x (120-90) k = m x 4.19 kj/kg.k x (50-25) k 

0.05 kg/s x 2.0768 kj/kg.k x (120-90) k = m x 4.19 kj/kg.k x (50-25) k 

 3.1152 Kj/s = 104.75 kj/kg x m 

m = 0.029 kg/s = 30 g/s 

multiplied by a safety factor of 1.5 we'll need around 45 g/s of fresh water. That means 162 liters/hour.