Lesson 6 - Principles of Fluid Mechanics 3
This lesson considers the factors which contribute to pressure loss when fluid follows through a pipe or duct system. It will examine in detail, the factors which contribute to frictional pressure losses and also losses due to the presence of fittings in the pipeline.
Point of Reflection – Reconvene
Welcome back! So, what were your thoughts?
How did you get on? Well, pressure does not really get ‘lost’ as lone socks and pens do, but rather it gets converted. The concept on what the pressure gets converted to is the conservation of energy. We know from our previous studies that pressure can be considered a form of energy. If the pressure value is reduced, due to flow through a fitting, then we know from the conservation of energy, that is must have been converted into another form of energy. Unlike our representation of Bernoulli’s equation, it is not conserved as either kinetic energy or gravitational potential energy, but rather initially converted into kinetic energy and then to thermal energy. The next section deals with this conversion in more detail.
Ultimately, the promotion of turbulence and eddies downstream from the fittings, which creates a loss in pressure, promotes the conversion of quantities of pressure energy into kinetic energy and ultimately into heat. (Remember the conservation of energy?). The quantities of heat produced are exceptionally small and would probably not reflect using standard temperature instrumentation, but the conversion of pressure energy is reflected in a noticeable loss of pressure across the fitting. So much for the mechanisms of pressure loss through fittings!
So, how do we represent and calculate how much pressure is lost through various fittings? We will deal with this next.