If there is steady flow, nothing changes with time.
1. The properties of the fluid at entry and exit are constant.
2. The properties of the fluid at any point in the control volume are constant.
3. dm_{1}/dt=dm_{2}/dt and both are constant.
4. Q and Wx are constant.
E_{cf} = E_{ci} and m_{1} = m_{2} = m
This equation can also be written as a rate equation
where is the mass flow rate [kg/s] and and are the heat transfer rate and rate of doing work [kW].