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slurry viscosity 2
- Thread starter cement001
- Start date
HamishMcTavish
Nuclear
I think the short answer is no, there is no particular viscometer / rheometer to measure slurry viscosity. There are different reasons for using each type - a google search will provide you with some of them.
Could you provide more background information to assist provision of a better answer?
Regards, HM
No more things should be presumed to exist than are absolutely necessary - William of Occam
Could you provide more background information to assist provision of a better answer?
Regards, HM
No more things should be presumed to exist than are absolutely necessary - William of Occam
-
2
- #3
I assume you mean, inline or online.
Invariably, when you encounter any non-Newtonian fluid in the process there will be a great deal of debate about the "right" viscometer to use.
There is a problem too that in many (most cases) there is no prior history of successful process measurements, for whatever reason (mostly the lack of available technoloies but also a lack of applications skills and knowledge to devise a solution. If there are enough such applications then a manufactured solution will become available e.g. PMI sensors (Polymer Melt Index) but in others you may find the user has fabricated his own solution... sometimes found in chocolate manufacture.
There are some established off-the-shelf solutions for a range of applications but once you get outside of this areas of familiarity you are going to find it tough going and you may need to be prepared to try several different solutions and work with someone used to exploring unusual applications.
Much of the discussion you will have with manufacturers and your own laboratory people will be based on the wrong assumptions.
With difficult or complex rheologies, the solution will probably need to be based on a combination of a laboratory where samples can be evaluated and a process instrument that will give repeatable readings even though it may only give a repeatable number.
The problems are two fold:
[ul][li]find a technology that will survive the process envirnment[/li]
[li]find a technology that will respond predictably and repeatably to changes in fluid behaviour[/li][/ul]
Chalk and cement slurries can be quite challenging, especially chalk because it often has flints and fragments of quarry machinery entrained.
Drilling muds are another example of a difficult application.
These are the sort of applications that used to use a rotational style technique with a large pear shaped bob that rotated in an open tank through which the slurry flowed and where the motor torque was a function of viscosity.
Many will tell you that whenever you encounter a non-Newtonian fluid the only way to measure viscosity is with a rotational viscometer where you have a controlled shear rate.
This isn't necessarily true.
For example, with water based auto paint there was considerable debate as to whether it should use constant sheer rate or constant sheer strain. The solution is a variation of a couette style rotational viscometer using a fixed shear rate and one that exploits the operational conditions and identifies the true process objectives. In the end, no one actually cared what the viscosity was, just how many cars needed a respray.
At Mercedes, I understand, the 10% respray rate was eliminated almost entirely by this rotational viscometer (ProRheo).
In other cases where the fluid is shear sensitive the answer is to control the flow rate and use a non-rotational viscometer which can be "calibrated" against the lab analysis.
All too often you will find that the difficulties of process measurement, historically, have meant that processes have come to rely on lab analysis.
There are two problems with this.
The one is that your in-house knowledge base is laboratory based and necessarily rather purist and the objective will be asserted as being to know the viscosity online.
The other is that when using the lab to control process, the sample collection and handling and the lab procedures become corrupted because speed of result is as important as accuracy.
In some processes off line sampling can become very crude indeed simple because the speed of analysis is critical e.g. methylmethacrylate polymerisation control where the operator dips a sample and makes a very fast but very crude measurement using a very coarse cup type measurement.
Making a process measurement means taking control of the objectives but also redefining the role of the laboratory and this may require some tact.
Process viscosity is difficult enough to measure analytically (for quality purposes) even with Newtonian fluids and the result is that the many process viscometers end up being rather specialised into niche market solutions which don't adapt well to new applications and especially if they have the wrong starting assumptions and especially if the manufacturer's representatives are unfamiliar with other applications.
If you really want to know what the viscosity is, then you will have to measure in the laboratory and the more complex the rheology, the more complex the laboratory measurements. For this reason many laboratory rotational viscometers have an associated PC which allows them to profile the fluid behaviour across a variety of different shear rate conditions.
However, if you ultimate objective in measuring viscosity in the process is quality control (rather than quality analysis) and you define quality as something tangible other than viscosity e.g. reject rate in auto headlight lacquer coatings with a secondary objective to reduce excess lacquer/solvent use, then you really don't care what the viscosity is.
Let the lab worry about it.
Your concern is to use some kind of repeatable measure to control your reject rate.
That opens the door to the newer viscometer technologies that may be more suitable for a process environment. e.g. vibrational, ultrasonic etc.
So, as HamishMctavish says, please post more details.
The process conditions and the objectives will be most helpful.
JMW
Invariably, when you encounter any non-Newtonian fluid in the process there will be a great deal of debate about the "right" viscometer to use.
There is a problem too that in many (most cases) there is no prior history of successful process measurements, for whatever reason (mostly the lack of available technoloies but also a lack of applications skills and knowledge to devise a solution. If there are enough such applications then a manufactured solution will become available e.g. PMI sensors (Polymer Melt Index) but in others you may find the user has fabricated his own solution... sometimes found in chocolate manufacture.
There are some established off-the-shelf solutions for a range of applications but once you get outside of this areas of familiarity you are going to find it tough going and you may need to be prepared to try several different solutions and work with someone used to exploring unusual applications.
Much of the discussion you will have with manufacturers and your own laboratory people will be based on the wrong assumptions.
With difficult or complex rheologies, the solution will probably need to be based on a combination of a laboratory where samples can be evaluated and a process instrument that will give repeatable readings even though it may only give a repeatable number.
The problems are two fold:
[ul][li]find a technology that will survive the process envirnment[/li]
[li]find a technology that will respond predictably and repeatably to changes in fluid behaviour[/li][/ul]
Chalk and cement slurries can be quite challenging, especially chalk because it often has flints and fragments of quarry machinery entrained.
Drilling muds are another example of a difficult application.
These are the sort of applications that used to use a rotational style technique with a large pear shaped bob that rotated in an open tank through which the slurry flowed and where the motor torque was a function of viscosity.
Many will tell you that whenever you encounter a non-Newtonian fluid the only way to measure viscosity is with a rotational viscometer where you have a controlled shear rate.
This isn't necessarily true.
For example, with water based auto paint there was considerable debate as to whether it should use constant sheer rate or constant sheer strain. The solution is a variation of a couette style rotational viscometer using a fixed shear rate and one that exploits the operational conditions and identifies the true process objectives. In the end, no one actually cared what the viscosity was, just how many cars needed a respray.
At Mercedes, I understand, the 10% respray rate was eliminated almost entirely by this rotational viscometer (ProRheo).
In other cases where the fluid is shear sensitive the answer is to control the flow rate and use a non-rotational viscometer which can be "calibrated" against the lab analysis.
All too often you will find that the difficulties of process measurement, historically, have meant that processes have come to rely on lab analysis.
There are two problems with this.
The one is that your in-house knowledge base is laboratory based and necessarily rather purist and the objective will be asserted as being to know the viscosity online.
The other is that when using the lab to control process, the sample collection and handling and the lab procedures become corrupted because speed of result is as important as accuracy.
In some processes off line sampling can become very crude indeed simple because the speed of analysis is critical e.g. methylmethacrylate polymerisation control where the operator dips a sample and makes a very fast but very crude measurement using a very coarse cup type measurement.
Making a process measurement means taking control of the objectives but also redefining the role of the laboratory and this may require some tact.
Process viscosity is difficult enough to measure analytically (for quality purposes) even with Newtonian fluids and the result is that the many process viscometers end up being rather specialised into niche market solutions which don't adapt well to new applications and especially if they have the wrong starting assumptions and especially if the manufacturer's representatives are unfamiliar with other applications.
If you really want to know what the viscosity is, then you will have to measure in the laboratory and the more complex the rheology, the more complex the laboratory measurements. For this reason many laboratory rotational viscometers have an associated PC which allows them to profile the fluid behaviour across a variety of different shear rate conditions.
However, if you ultimate objective in measuring viscosity in the process is quality control (rather than quality analysis) and you define quality as something tangible other than viscosity e.g. reject rate in auto headlight lacquer coatings with a secondary objective to reduce excess lacquer/solvent use, then you really don't care what the viscosity is.
Let the lab worry about it.
Your concern is to use some kind of repeatable measure to control your reject rate.
That opens the door to the newer viscometer technologies that may be more suitable for a process environment. e.g. vibrational, ultrasonic etc.
So, as HamishMctavish says, please post more details.
The process conditions and the objectives will be most helpful.
JMW
- Thread starter
- #4
You need to provide some process details if only to figure out what sort of viscometer solution you will need.
It isn't simply a case of picking a viscometer and sticking it inline (if you want it to deliver some meaningful measurement) and there may not be a solution at this time.
If you want behavioural measurement (viscosity at the process conditions e.g. process temperature- the conditions at some point in the process which is not necessarily the same point that you can install the viscometer) the installation requirements can be quite different from an analytical measurement (viscosity at reference conditions usually a reference temperature).
For example, a behavioural measurement of fuel oil (heater control prior to burners or engines) can cost around $3-4k but an analytical measurement of fuel oil in a refinery can cost around $200,000 - or more and both using the same viscometer technology - the measurement is more than the instrument.
The system requirements are very different.
Process conditions can also have a profound influence on system design and cost.
So you may have to do a great deal more to establish the viscometer type and installation before you can even guess at what happens to the fluid flow. Plus, for a new application, you may find that it doesn't work and you have to start again.
Process Viscosity measurement is not simple and sometimes not achievable (or affordable) which is why so many processes are still controlled by taking lab samples.
JMW
It isn't simply a case of picking a viscometer and sticking it inline (if you want it to deliver some meaningful measurement) and there may not be a solution at this time.
If you want behavioural measurement (viscosity at the process conditions e.g. process temperature- the conditions at some point in the process which is not necessarily the same point that you can install the viscometer) the installation requirements can be quite different from an analytical measurement (viscosity at reference conditions usually a reference temperature).
For example, a behavioural measurement of fuel oil (heater control prior to burners or engines) can cost around $3-4k but an analytical measurement of fuel oil in a refinery can cost around $200,000 - or more and both using the same viscometer technology - the measurement is more than the instrument.
The system requirements are very different.
Process conditions can also have a profound influence on system design and cost.
So you may have to do a great deal more to establish the viscometer type and installation before you can even guess at what happens to the fluid flow. Plus, for a new application, you may find that it doesn't work and you have to start again.
Process Viscosity measurement is not simple and sometimes not achievable (or affordable) which is why so many processes are still controlled by taking lab samples.
JMW
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