Fluid Types
This website, all Irrigation Craft products, and all technical articles assume the fluid being pumped has the following properties:
Newtonian fluids are non-viscous (not sticky), do not resist deformation, and flow freely. The exact definition is a fluid where viscosity does not change in relation to shear rate at a constant temperature and pressure. Examples of Newtonian fluids are gases such as air, water, gasoline, mineral spirits, and light oils.
Pressure has no effect on fluid volume at a constant temperature. Therefore gases are not included in any discussion on this website regarding pumps. Non-Compressible fluids are sometimes called Liquids.
Unless otherwise noted, all discussions of pumps on this website assume there are no gas bubbles in the pumpage.
Discussions of pumps on this website assume there are little or no entrained solids (such as sand) in the pumpage.
Non-Saturated & Non-Supersaturated
All discussions of pumps on this website assume the pumpage is not saturated, not close to saturated, and not supersaturated with dissolved gasses or substances. Roto-Dynamic pumps reduce pressure in their intakes and internally as they add velocity energy to the fluid. If a fluid is close to or completely saturated with a gas then that gas may come out of solution inside the pump resulting in a two phase flow regime inside the pump, reducing pump efficiency and performance.
Discussions of pressure on this website mostly ignore the effect of temperature on the density of water because temperatures ranging from 40 degrees F to 120 degrees F change water density by only 1.14%, which we consider to be irrelevant for most of our purposes. Density variations based on temperature are greater for other types of fluids and therefore temperature and density may be more relevant for discussions of other types of fluids.
The one area where water temperature and density is not ignored is in the area damage resulting from cavitation. In short, the cooler the water, the more damage will occur under cavitation conditions. To learn more on this topic follow these two links:
The small amount of heat added during the centrifugal pumping process is often insignificant for purposes of pump analyses and performance testing, therefore the heat is ignored and the process is considered to be adiabatic, defined as no change in temperature in the pumpage or pump casing. This adiabatic behavior is less true when pumps are operated well below their BEP however, as evidenced by the rapid heating that can be observed when centrifugal pumps are operated at very low flow rates.
For control purposes the pumping process is not adiabatic. Some heat actually is added to the fluid during the pumping process due to friction within the pump. If a pump operates under low flow conditions for a long enough period of time, significant heat can accumulate and cause a noticeable temperature rise so that the control system must account for this accumulation of heat in the pump and fluid held within the pump.
There are some high head low flow centrifugal pumps (very low Specific Speed), that add a larger amount of heat to the pumpage. But these are unusually high head pumps reaching pressures of 50,000 psi and more, and they are not a part of Irrigation Craft's normal business.
Learn More About the Properties of Water on this Website
Learn more about Heat Accumulation in Pumps on this Website
