Fluids are pumped at elevated temperatures for a number of reasons: The fluid needs to be heated to change it from a solid or semi-solid into a liquid so it can be more easily moved, processed or applied. A process where heat is used as a catalyst to initiate or sustain a chemical reaction.
Full Answer
How does temperature affect the performance of a pump?
Temperature can be an issue in the field because pumps are frequently sized and sold to pump a viscous liquid at some stated temperature, but then the pumps are actually operated at a lower temperature, which yields a higher viscosity and, of course, a higher required hp with less flow and head than desired or promised.
Does water temperature affect the performance and cavitation of centrifugal pump?
The effect of water temperature on performance and cavitation inception of a centrifugal pump has been studied experimentally. A special test rig with a testing centrifugal pump was constructed in the laboratory of fluid mechanics at Higher Institute of Engineering-Hoon.
What happens to a pump when it starts up?
Once a pump is at its startup temperature, the metal temperatures within the pump are uniform and the fluid within the pump is approaching its normal operating viscosity. This is important for fluids that solidify at ambient temperatures.
How does the viscosity of a fluid affect the pump performance?
Fluid viscosity or thickness will affect how it will behave in a pump. However, this is where things start becoming complicated because the viscosity of fluids/liquids can change under different conditions. Viscosity remains constant regardless of changes in shear rate or agitation. As pump speed increases, flow increases proportionately.
How does temperature affect pump performance?
The results showed that the pump head and pump efficiency increase with the decrease of water temperature. The results showed that increasing water temperature speeds up cavitation.
What are the factors affecting pump performance?
Important factors affecting pump performance are surface roughness; internal clearances; mechanical losses, such as those related to bearings, lip seals, mechanical seals, and packing; high suction specific speed; impeller trim; and the viscosity of the fluid pumped.
Does temperature increase in pump?
To calculate the pressure at the outlet of a pump we use pump performance characteristics i.e. charts giving pump head as a function of volumetric flow. When the fluid flows through a pump, it's temperature slightly rises.
How does the temperature of liquid affect Npsha?
The temperature of the Liquid impacts the NPSH req of a pump. As the pumping liquid temperature increases, the size of the vapor bubbles due to cavitation get smaller, hence leading to lesser damage.
What decreases pump efficiency?
Undertaking routine maintenance on your pump can also reduce energy consumption, as like with any equipment, wear can reduce efficiency.
What factors must be considered when selecting a pump to be used in a process?
Below are process liquid properties that must be considered before selecting a pump.Liquid viscosity.Temperature.Specific gravity.Vapor pressure.Solids present & concentration.Shear sensitive.Abrasive or Non-abrasive.
Does water temperature affect flow rate?
As the temperature increases, the difference in water flow increases.
How would a rise in the temperature of a liquid affect the maximum possible pump lift?
As the submerged ratio and liquid temperature increase, the efficiency of the pump increases also at the same air flow rate. For the same submergence ratio, varying the liquid temperature affects the airlift performance.
What causes pump to overheat?
Pump overheating is one of the most common problems with a pump. It can be caused by several factors, including lubrication, damaged bearings, clogged filters and others. Overheating can cause a pump to seize up and fail, leading to costly repairs or replacement.
How the NPSH will affect the pump performance?
NPSH increases as the square of the pump flow rate near and above the design flow rate of a pump. It does not increase this fast at flow rates much below the rated flow rate. Good design practices on the inlet piping help insure an adequate NPSH.
What are the factors that affect NPSHr?
To determine an acceptable NPSH margin, three factors must be considered:NPSHR: the minimum NPSH given by the pump manufacturer.NPSHA (Available): the amount of absolute suction available to suppress boiling at the impeller eye. ... NPSH3: the net positive suction head available based on a 3% head drop.
How do you increase the NPSH of a pump?
How to Increase the NPSH Margin to a PumpIncrease the liquid level in the suction vessel.Eliminate any flow restrictions in the suction piping (such as a strainer)Operate at a flow rate less than the pump bep (see figure 3).Install an Inducer, if available.Change to a low NPSHR impeller, if available.More items...•
What factors affect efficiency of centrifugal pump?
There are basically two components that can affect the hydraulic efficiency of the centrifugal pump. The impeller, and the volute casing. The affinity laws tell us quite a bit about the inner workings of an impeller. We know that, for any given impeller, the head it produces varies as the square of a change in speed.
What is performance of water pump?
The centrifugal pump converts mechanical energy into hydraulic energy (flow, velocity and pressure), and the AC motor converts electrical energy into mechanical energy. Many medium and larger centrifugal pumps offer efficiencies of 75 to 93 percent and even the smaller ones usually fall into the 50 to 70 percent range.
How does density affect pump performance?
Considering the volume flow rate, head and efficiency remain unchanged an increase in density increases the absorbed power and a decrease in density decreases the absorbed power for the pump. This principle is important when a motor rating is to be provided for a pumped liquid which has a cold start-up.
What are the factors that affect Npshr?
To determine an acceptable NPSH margin, three factors must be considered:NPSHR: the minimum NPSH given by the pump manufacturer.NPSHA (Available): the amount of absolute suction available to suppress boiling at the impeller eye. ... NPSH3: the net positive suction head available based on a 3% head drop.
What happens to the viscosity of a pump as the size of the pump increases?
As the physical size of the pump increases, the maximum viscosity that it can handle also increases. For example:
What are the effects of viscosity on a pump?
Two effects on pump performance must be discussed: viscosity and gas content. Figures 20.23 and 20.24 illustrate the effects of viscosity change on centrifugal and positive displacement pumps, respectively. Figure 20.23 shows the deterioration of centrifugal pump performance, and it may be noted that if v is greater than 100 centistokes, water performance must be corrected. Figure 20.24 indicates that in a positive displacement pump the volumetric efficiency improves and power requirement increases (with increasing viscosity).
What is the average HSPF for a heat pump?
The HSPF can be thought of as the “average COP” for the entire heating system. To estimate the average COP, one divides the HSPF by 3.4. Hence, an HSPF of 6.8 corresponds roughly with an average COP of 2. HSPFs of 5–7 are considered good. The higher the HSPF, the more efficient the heat pump is on a seasonal basis.
How is centrifugal pump performance tested?
Centrifugal pump performances are tested by using clean cold water or viscous oil. Pump efficiency is determined by principally two parameters, head and flow rate, in addition to other factors such as properties of the fluid, impeller design and motor speed selected.
What is the HSPF rating for a heat pump?
Many heat pumps meet this requirement, and some have HSPF ratings above 9. More efficient heat pumps are generally more expensive, so financial assessments must also account for the annual energy savings, along with the added cost.
What is SEER in heat pump?
The SEER is the ratio of the total cooling of the heat pump to the total electrical energy input during the same period, that is , (4.5) SEER = Total seasonal cooling output / Total electrical energy input. The SEER rates the seasonal cooling performance of the heat pump.
What is a pump head?
The pump head is a term derived from the Bernoulli formulation, an energy balance around the pump. It is expressed as:
What happens to the temperature of a pump when the flow through the pump is reduced?
If the flow through the pump is reduced by thrott ling the discharge valve the temperature rise increase. If the flow is reduced to 2 m3/h (0.00056 m3/s), brake power slightly reduced to 0.095 kW and the pump efficiency reduced to 15% (0.15) - the temperature rise can be calculated as
Is a pump perfect?
No pump is perfect with 100% efficiency. Energy lost in friction and hydraulic losses transforms to heat - heating up the fluid transported through the pump.
What happens when you put hot fluid in a cold pump?
Thermal Shock. The rapid introduction of hot fluid into a cold pump (or the reverse) can result in thermal shock that may result in permanent damage or failure, and can have detrimental effects on the mechanical seal including seal face fracturing.
Why is high temperature pumping important?
Fluids are pumped at elevated temperatures for a number of reasons: The fluid needs to be heated to change it from a solid or semi-solid into a liquid so it can be more easily moved, processed or applied.
How much clearance does a multistage pump need?
Additionally, many multistage pumps have tilting pad thrust bearings that can have axial clearance up to 0.025 inches (0.65 millimeters [mm]). Increased thrust bearing clearance is frequently required for pumps with specialized spring-loaded thrust compensation devices. The bearing clearance and expected shaft motion during startup should be shared between pump and seal engineers to ensure a full understanding of shaft axial position during operation.
Why do pumps have mechanical seals?
The challenge for the mechanical seal is the design of the seal arrangement needs to be able to tolerate this displacement without negatively impacting seal performance , and the key to achieving this is knowing the magnitude of the displacement and the direction (into the seal chamber or out). This is typically determined by field measurements or analytically by the pump manufacturer for the specific operating temperature of the pump.
Why are there differences in thermal expansion rates of the pump casing and shaft?
Differences in thermal expansion rates of the pump casing and shaft due to different materials of construction ( that produce shaft growth during preheat and while at temperature).
Why is the shaft of a pump subject to axial displacement?
When sealing the pump shaft of high-temperature pumping applications, the mechanical seal is often subjected to axial displacement as a result of dimensional changes. Pump operating temperature and differences in thermal expansion and heating rates of the pump casing relative to the pump shaft, can result in axial growth of the shaft in the seal chamber.
What happens if you heat a pump too fast?
Heating too fast will create temperature gradients that can produce uneven thermal expansion resulting in damage to the pump casing, rotating elements and close clearance wear rings, and the mechanical seal. The manufacturer can recommend heating rates as they are dependent on the type and size of the pump.
Why is it important to keep in mind the operating temperature of hydraulic fluid?
It is very important to keep in mind the system’s expected range of operating temperatures so that the hydraulic fluid remains stable and is able to maintain the desired viscosity. This can be a significant issue for equipment that is exposed to outdoor temperatures, especially when temperatures drop below freezing. In addition, the fluid needs to be able to dissipate the heat that is generated by pressure drops and friction.
Why do hydraulic pumps fail?
Pumps may become inefficient or even catastrophically fail simply because the wrong type of hydraulic fluid is used. How do you know if you are using the right kind of fluid for your hydraulic pump? The answer to that question is dependent on several factors, including the type of pump, its maximum operating temperature, its maximum operating pressure, and even the type of material the pump’s seals are made from.
Why is hydraulic fluid viscous?
It is closely related to temperature, with hydraulic fluids becoming more viscous as temperatures drop. If a hydraulic fluid has a viscosity that is too high, the system will not perform efficiently due to the losses involved in overcoming the resistance of the fluid to motion.
What is the viscosity of a vane pump?
For vane pumps with an operating pressure of 500 psi, the ISO VG viscosity can range from 15 to 22. When the maximum operating pressure is around 1000 psi, the viscosity is heavily dependent on the maximum operating temperature. For operating temperatures up to 104°F, the viscosity should be between 10 and 15; for temperatures between 104 and 140°F, the recommended viscosity is 15 to 32. When maximum operating temperatures are expected to reach 158°F, a higher viscosity fluid on the order of 22 to 46 is highly recommended.
What is hydraulic fluid?
Hydraulic fluid (sometimes referred to as hydraulic oil) can serve multiple purposes in a hydraulic system and its individual components — including pumps. These purposes include the following: Transmitting energy. Dissipating heat.
What is the maximum pressure for a gear pump?
Most gear pumps need a fluid that can handle a maximum temperature and pressure of 158°F, 500 psi. Gear pumps work best with fluids that have an ISO VG viscosity of 15 to 32 for a max temperature of 140°F and 32 to 68 for a max temperature of 158°F.
What happens if you use a hydraulic pump?
In fact, the use of a fluid that is poorly matched to the pump can lead to a catastrophic failure that can cause cascading issues throughout the system. Issues that can arise as a result of poor ...
Who published the paper The influence of viscosity on centrifugal pump performance?
The influence of viscosity on centrifugal pump performance, Ingersoll Rand technical paper issued 1957 in conjunction with Lehigh University, Arthur Ippen
Why is a centrifugal pump curved?
The major factors are a combination of mechanical, leakage, shock and disc friction losses . Disk friction is the major contributor and most important factor when quantifying the losses. The curves as mentioned are based on water performance, but with applications on viscous fluids those water curves must be corrected for the viscosity to be accurate. The head, flow, efficiency and brake horsepower (BHP) curves will all require modification (viscous corrections).
What is the viscosity limit of a centrifugal pump?
Depending on the pump size and impeller geometry, the viscosity limits for the average centrifugal pump will vary from 250 to 700 centipoise, and I have witnessed many pumps successfully pumping fluids in excess of 1000 centipoise. If your application is above 250 centipoise, I recommend you work with your pump manufacturer/vendor to arrive at the answer. The two important points to take into consideration are these:
What is the best centipoise for a pump?
The pump manufacturer is the best source for this value, as it will depend on the application, fluid personality and the pump geometry. Note that at 100 centipoise, the viscous effects will be significant. I will state that at 30 to 40 centipoise or greater, you should use the corrections or risk adverse effects. I also recommend that somewhere in the area of 5 to 10 centipoise, you must at least be aware and conscious of the effects however minor.
Why does fluid have more friction?
When pumping fluid, the more viscous the liquid the more friction will occur. The resistance (friction) is due to the shear stress properties of the fluid and the wall surface of the pipe/pump. Note that the smother the pump and pipe surfaces/walls are the less effect the viscous fluid friction will have.
Why is disc friction higher?
The smaller an impeller is, the more likely the disc friction effects will be higher simply because the surface area of the impeller and casings have more interaction with the fluid than in a larger pump.
Does viscosity affect NPSHR?
Intuitively, you would think that changes in viscosity will effect NPSHR (aka NPSH3), but most published empirical data disputes that line of thinking. On pump suction line applications where highly viscous fluids have issues flowing in the pipe to the pump suction come to mind, but these issues would normally be covered in the friction component of the NPSHA calculation. That is, the friction factor would be higher for the viscous fluid and consequently reduce the NPSHA. My advice on viscous fluids is to increase the margin between available and required NPSH.
What is the most important aspect to understand before any pump selection?
Pump Knowledge. One of the most important aspect to understand before any pump selection is the viscosity of the fluid which is going to be pumped. Fluid viscosity or thickness will affect how it will behave in a pump. However, this is where things start becoming complicated because the viscosity of fluids/liquids can change under different ...
What is the most important factor in pump selection?
What is most important about viscosity during pump selection? Kinematic viscosity is a real physical factor that influences pump curves, and thus the choice of pump.
Why do pumps stall?
Viscosity of fluid increases with agitation until they become almost solid. As a result, pumps can bog down and stall after initially pumping dilatant liquids.
How much viscosity does water have?
Based on the table above, water has a low viscosity of 1 cSt at 20°C, while motor oil has a high viscosity of more than 500 cSt at the same temperature. Viscosity is essentially resistance to flow and this has implications for pumps. If you have a high-viscosity, sticky fluid on your hands, it clings and it’s much harder to remove ...
What is kinematic viscosity?
Kinematic viscosity is a real physical factor that influences pump curves, and thus the choice of pump.
What is the fastest way to pump tomato paste?
Graco is the Fastest Way to Pump 1500kg Tomato Paste
What happens if you put sticky fluid on your hands?
If you have a high-viscosity, sticky fluid on your hands, it clings and it’s much harder to remove than a low-viscosity fluid. It is the same in a pump, where you use impellers instead of your hands, to move the fluid.
How does a centrifugal pump cause a liquid to flash?
The greater the flow velocity through the pump the greater this pressure drop. If the pressure drop is great enough , or if the temperature of the liquid is high enough, the pressure drop may be sufficient to cause the liquid to flash to steam when the local pressure falls below the saturation pressure for the fluid that is being pumped . These vapor bubbles are swept along the pump impeller with the fluid. As the flow velocity decreases the fluid pressure increases. This causes the vapor bubbles to suddenly collapse on the outer portions of the impeller. The formation of these vapor bubbles and their subsequent collapse is cavitation .
How much pressure does a centrifugal pump produce?
Normally, a centrifugal pump produces a relatively low pressure increase in the fluid. This pressure increase can be anywhere from several dozen to several hundred psid across a centrifugal pump with a single stage impeller. The term PSID (Pounds Force Per Square Inch Differential) is equivalent to ΔP.
How to avoid cavitation in pump?
It is possible to ensure that cavitation is avoided during pump operation by monitoring the net positive suction head of the pump. Net positive suction head (NPSH) for a pump is the difference between the suction pressure and the saturation pressure of the fluid being pumped. NPSH is used to measure how close a fluid is to saturated conditions. Equation 3-19 can be used to calculate the net positive suction head available for a pump. The units of NPSH are feet of water.
What is the relationship between the volumetric flow rate and the pressure differential?
Analysis of the relationship between the volumetric flow rate ( V ˙ ) that a centrifugal pump can maintain and the pressure differential across the pump ( ΔP pump) is based on various physical characteristics of the pump and the system fluid. Variables evaluated by design engineers to determine this relationship include the pump efficiency, the power supplied to the pump, the rotational speed, the diameter of the impeller and blading, the fluid density, and the fluid viscosity. The result of this complicated analysis for a typical centrifugal pump operating at one particular speed is illustrated by the graph in Figure 7.
How does a centrifugal pump work?
As the impeller and blading rotate, they transfer momentum to incoming fluid. A transfer of momentum to the moving fluid increases the fluid's velocity. As the fluid's velocity increases its kinetic energy increases. Fluid of high kinetic energy is forced out of the impeller area and enters the volute.
Why are centrifugal pumps used in parallel?
In order to increase the volumetric flow rate in a system or to compensate for large flow resistances , centrifugal pumps are often used in parallel or in series.
What is centrifugal pump?
Centrifugal pumps are one of the most common components found in fluid systems. In order to understand how a fluid system containing a centrifugal pump operates, it is necessary to understand the head and flow relationships for a centrifugal pump.
What is viscosity in pumps?
Viscosity is a measure of a fluid’s resistance to flow. Pumped liquids are generally considered vis-cous when their absolute viscosity exceeds 40 centipoise. This is the point at which the effect on pump performance becomes appreciable; at 100 centipoise the effect is pronounced.
What is a centrifugal pump curve?
A pump curve in its simplest form is a plot of the pump’s impeller performance indicating change in discharge head (pressure) versus pump capacity, i.e., flow rate. These graphs are also referred to as pump performance curves or characteristic curves.