Hello everyone and welcome back to this course
on Chemical Engineering Thermodynamics. Today we are going to talk about the first
law of thermodynamics for open systems. For example, in the case where I had a fluid
that is mixed well with a stirrer work is done on the fluid which is my system of interest
through this tower, and we call this type of work as shaft work. Similarly, in case of a turbine the fluid
does work on the turbine or in case of a centrifugal pump it pushes the fluid through
the pipes in all these cases there is a shaft work that is being done on the system or delivered
shaft work being delivered by the system as in case of a turbine. The essential feature of this shaft
work is that there would be no change in the control volume of our system. So, to differentiate it from other forms of
work typically we will denote the shaft work with a subscript s. So,
W_s?shaft work W ?_s?rate of shaft work
The other type of work that is important is what we call as the flow work
for an open system. It is a work associated with the flow as the
name indicates. For example, when a gas is released from a
tank into the atmosphere which is at a lower pressure it is by opening a valve it is going
to push the fluid outside so that it can come out. Or in the other case if I have a high-pressure
reservoir and I am trying to fill it tank by opening a valve then the fluid in the reservoir
is going to push the fluid inside the tank which is the system of my interest so that
it can end the tank. In both cases there is a work that is being
done by pushing the fluid. In one case the system is doing work on the
surrounding fluid, in the other case there is an external work that is being done on
the fluid inside the tank, right. This type of work is what we call as
flow work, right.
