# Heating Water by Injecting Steam

## Water can be heated by injecting steam.

For some applications a direct heating of the water by injecting steam may be convenient. A direct heating system is very simple since it don't require any heat exchangers. Fouling of surfaces, which may be a major problem in certain processes, are avoided.

The required steam flow rate in an steam injection process can be calculated as

*m _{s} = P / (h_{g} - (t c_{p})) (1)*

*where*

*m _{s} = steam flow rate (kg/s)*

*P = heat transfer rate or power (kW)*

*h _{g} = specific total enthalpy of the steam before the control valve (kJ/kg)*

*t = final temperature of the water after the heating ( ^{o}C) *

*c _{p} = specific heat water (kJ/kg)*

### Example - Heating a Water Volume by Injecting Steam

100 liter (kg) of water is heated from 20 ^{o}C to 80 ^{o}C in 5 minutes (300 s). The specific heat of water is* **4.2 kJ/kg ^{o}C *and the power required can be calculated as

*P = (100 kg) (4.2 kJ/kg ^{o}C) ((80 ^{o}C) - (20 ^{o}C)) / (300 s)*

* = 84 kW*

The absolute steam pressure is *220 kPa* and the total enthalpy of the steam is *2711 kJ/kg*. The required steam flow rate can be calculated as

*m _{s} = (84 kW) / ((2711 kJ/kg) - ((80 ^{o}C) (4.2 kJ/kg^{o}C)))*

* = 0.035 kg/s*

* = 127 kg/h *

The total steam consumption for the heating process can be calculated as

*q = (0.035 kg/s) (300 s)*

* = 10.5 kg *