Density detection of ice slurry

R

Richard Gue

I'm hoping that someone on our list with experience in the process control
field can suggest a reasonably inexpensive method of determining the
density of a seawater and ice slurry in a mixing tank. It is not a batch
mixing application, so the tank level is variable and I cannot just
measure the load on the mixer motor. Fortunately, ballpark accuracy is
acceptable. We just need to make sure the slurry is not too thin or
thick, and that it is well mixed before we pump it to the use point.
TIA

Richard Gue
Controls Engineer
North Star Ice Equipment Corp.
Seattle, WA
(206) 763-7300 voice
(206) 763-7323 fax

A

Anthony Kerstens

If ballpark is OK...

1. Measure the tank weight.
2. Measure the tank level (to calculate volume).
3. Divide.

Anthony Kerstens P.Eng.

T

Tom Bering, P.Eng.

This looks like a straight forward density meter problem. If you get a float containing water, the height of the float above the surface will tell you the density.

The float does not actually have to be in the tank, it can be in a pipe attached to it. This can make reading the height of the float easier.

B

Bob Pawley

The float is simple and inexpensive.

However, if you need an electronic indication hook up and calibrate a DP cell for density measurement.

Bob Pawley

C

C. Ward Yelverton

??? Since water is denser than ice, wouldn't a water filled float SINK in a ice slurry? Or am I missing something vital?

A

Anthony Kerstens

Or eventually freeze and break the float??

Anthony Kerstens P.Eng.

H

Heavner, Lou

I think what he was attempting to describe is a hydrometer. Imagine a
testtube with markings on the side. The test tube will have enough air in
it to keep it partially afloat, regardless whther there is water in it or
not. The hydrometer with fixed density (more or less) will rise or sink
depending on the density of the icewater. The scale markings can be
calibrated to give you specific gravity or density.

E

Erich Mertz

It seems to me that the hydrometer would be floating in the water and measuring the density of the water alone since the ice particles are descrete particles also "floating" in the water. However, it would be interesting to go to 7eleven and and buy a slush drink to check it,

Regards
Erich Mertz

D

dooley

There is a big difference between the electrical conductivities of ice and salt
water so the electrical conductivity of the mixture is equal to (conductivity of
salt water)x(1-ice fraction by volume)^3/2.( ref... Frick... about 1890).
Electrical conductivity or resistivity using two probes a reasonable distance
apart in the vessel should work. Insulate the probes so that the distance from the tips (effective electrodes) to surface/wall or floor is reasonably greater than the distance between the probe tips. Use a large size for the electrodes relative to the ice particle size so that there is no local shielding effect from the ice particles although if it is agitated it may not matter.

Alternatively, if the ice particles are small enough you could use an
electrodeless (toroidal) system either in the vessel or since it is a continuous
process, in the discharge line. Rosemount and Foxboro both have toroidal probes
with reasonably large holes (38mm?)

Vince Dooley

R

Richard

Hi,
Just thought I would write as we share the same name!
In the UK Gue is not a very common name at all.
Anyway that was it really.

Regards
Richard Gue