The Role of Temperature in Pump SelectionBy Welcome / February 12, 2021
The anticipated temperature range that a pump will need to handle during operation is crucially important to making the right choices about not just which pump to install, but what kinds of components should be installed along with it. Although temperature seems like a familiar concept, in industrial applications it can quickly get complicated.
How hot or cold is the fluid in a system? How much heat is generated by the pump and other equipment? What are the specific temperature requirements for the operation?
Answering questions like these can require careful analysis. Read on to understand the relationship between pressure and temperature, then use our pump selection software to find the perfect solution for your operation.
The Basics of Temperature
At the most rudimentary level, temperature is simply a measure of the heat present in a gas, liquid, or solid. The common temperature scales familiar to everyone are Fahrenheit and Centigrade, two systems invented in the 1700s. The two systems vary in important ways:
- The freezing point of water is equal to 0 oC or 32 o
- The boiling point of water is equal to 100 oC or 212 o
To confuse matters more, the Fahrenheit and Centigrade scales converge at -40 degrees: -40 oF and -40 oC are the same temperature. Converting between the two scales involves simple math:
oF = (oC x 9/5) + 32
oC = (oF – 32) x 5/9
The scale below illustrates the conversion between the two.
Beyond static measurements of Fahrenheit and Centigrade, discussion of temperature quickly gets more complex. For example, temperature intervals, which measure the relative rise or fall in temperature, cannot be converted using the formulas above.
A few European countries use the Reaumur scale, expressed as oRe. In the Reaumur scale, the freezing temperature of water is equal to 0 oRe, while the boiling point of water is defined as 80 oRe. Simple formulas are used to convert between Reaumur and the more familiar scales:
oRe = (oC x 4/5)
oRe = (oF – 32) x 4/9
oC = (oRe x 5/4)
oF = (oRe x 9/4) + 32.
As with pressure, temperature can be measured according to two distinct reference bases, standard and absolute.
In temperature, absolute zero is defined as the lowest possible temperature; it is the point when the atoms in a substance are completely stationary, transmitting no thermal energy whatsoever. Measures of temperature against absolute zero are expressed in Kelvins (K) in the Centigrade system (0 K = -273.15 oC) or degrees Rankine (oR) in the Fahrenheit system (0 oR = 459.67 oF). Note that Kelvin is a “degreeless” unit of measure.
Here is an illustration of these different units and how they compare:
The Interaction of Temperature and Pressure
In a pump system, temperature influences not only the operational stability and efficiency of components but also the system’s pressures. The graph below illustrates the pressure of a gas held at a constant volume. As a gas’s temperature approaches absolute zero, it becomes a liquid (as illustrated by the dotted lines). As the temperature rises, the gas’s pressure rises as well. The various gas lines demonstrate that gasses of different elements will undergo different pressure changes in response to temperature changes.
Because different elements build up pressure in distinct ways from one-another, a system must be designed around the specific characteristics of the materials that it will handle. If inadequate attention is paid to how gasses will respond to temperatures within a system, dangerous faults can occur.
Cryogenic Fluids Raise Special Challenges
Cryogenic liquids are extremely cold, -150 oC (-238 oF) and below. Such liquids are also often referred to as liquified gasses. Liquified natural gas, or LNG, is a well-known example of a cryogenic liquid.
LNG is often pumped in liquid form at -196 oC (-320 oF). Such cold temperatures will embrittle many materials, like standard carbon steels, so systems that pump LNG or other cryogenic liquids must be built with specialized components. By adding certain elements or forging metal with certain grain structures, parts can be built to hold up even at these extremes.
When pumping cryogenic fluids care must also be taken to control pressure and system temperatures. If a cryogenic fluid is raised past its boiling point, it will turn to a gas and create significant pressure and containment problems.
Call PumpWorks to Talk About Your Pump Needs
The team at PumpWorks deals with pressures and temperatures day in, day out, helping customers find the right solutions for their complex pumping requirements. Whether you require ANSI process pumps, API process pumps, or custom pump skid packages, we are ready to assist.