**A: **Much of the professional work of an engineer is not too different from that of an accountant. The engineer often accounts for different quantities with different rules of exchange: forces, energy, materials, momentum, stress, and so on.

The calculations for pressure drops in fluid flow are important for the sizing of pumps, fittings, and pipes. The formalisms and nomenclature used in such procedures may take inspiration from the form of the energy balance or Bernoulli equation; that is, we can represent pressure drops (measured in units of pressure) equivalently as head losses (measured in units of length) or energy losses. In fact, we could devise a completely arbitrary system for doing the accounting of energy losses in piping systems, but that would be like doing your taxes in an imaginary currency.

I encourage you to look up the variety of online pressure-drop calculators available (type “pressure drop calculator” into a search) and compare the language used and the ultimate results for test cases that you devise. As a start, you might consider the flow of water at 10 gallons per minute through a 50m long, 5 cm ID pipe with a 90-degree bend. Compare the results you get from different online calculators. I get about 22 mbar for the pressure drop.

Tags: Flow, Pressure Drop, Resistance Coefficient