CF042 Crossflow Cell

Q. What is the difference between Sepa CF and Sterlitech HP4750?

A. The Sterlitech HP4750 is an enclosed batch system (limited to 300ml) with direct filtration under pressure. There is a stir bar mixing the solution and pressures up to 1000 psi may be applied.

The Sepa CF is a crossflow system that allows continuous sampling and testing under different pressure and flow rate parameters depending on the pump and fluid.

Q. Does the feed spacer penetrate the membrane?

A. The mesh spacer usually leaves an imprint on the membrane which is not a problem - unless too thick of a mesh is used - then it could damage the membrane.

Q. How do I calculate Reynolds number based on the feed cross-flow velocities for the various feed spacers?

A. The Sepa CF cell for use with high fouling spacer has a flow area width and height of 3.7 inches by 0.068 inches. Once a spacer material is placed in the channel the actual flow channel cross section is significantly reduced. We have not calculated that. We typically operate the cell and estimate the Reynolds number at the transition from laminar to turbulent flow by monitoring the increase in pressure drop as the crossflow is increased.

Another usage implementation which we have used is the placement of a rubber gasket in the flow channel. A specifically sized flow channel can be cut out of the gasket to define a flow channel of the desired cross section.

We actually have done more study of the CF cell for use with standard spacer (3.7 in. by 0.034 in. cell cross-section). We evaluated that cell for various cross flow velocities at various feed flow rates.

Q. How do I distinguish between the low foulant (34ml) feed spacer and the high foulant (68ml) feed spacer when I hold them in my hands?

A. The low foulant has smaller squares and bends slightly easier.  It feels lighter.  It is not stiff like the medium foulant.  The high foulant spacer has corragated ridges in it like cardboard.  No holes.

Q. Is the low foulant spacer the same as the permeate carrier?

A. No, the low foulant spacer is under the membrane and the permeate carrier is on top. The membrane is sandwiched between the spacer and permeate carrier.

Q. In the instruction manual of the Sepa CF, tubular and mesh spacers are mentioned. Can I conclude that the tubular is the low foulant and the mesh is the high foulant?

A. The mesh spacer is a low (34 ml) and also the medium spacer (68 ml).

The tubular spacer is for high foulants (68 ml) and looks like corregated cardboard.

Q. Could the filter cloth of industrial filters be used in the Sepa filtrations units, after cutting it to proper size?

A. The Sepa CF can potentially work for any media that can be fitted into the chamber.

One thing that could be an issue for some types of filter media is whether or not a sufficient seal is made between the O-ring and the media. For membranes, this is not a problem because membranes have a relatively smooth surface, which affords good mechanical seal when pressed together. A large fiber woven material, for example, may need to be modified or filled with some type of potting compound to level the surface in order to get a non-bypass seal.

Q. Can I use the Sepa CF membrane cell without spacers?

A. Using the cell without any spacers will usually cause wrinkles in the membrane. The depth of the cell is made to accommodate the spacer that will fit in it (34 or 68 ml).

Q. How can I set the maximum flow from my Sepa CF?

A. Most separations and flux through membranes are controlled by the nature of the fluid. For salt rejecting membranes, such as RO and NF, the dominant variables are operating pressure and osmotic pressure (a solute concentration-dependent property which reduces net operating pressure with increased solute concentrate).

Q. What is the definition of GFD?

A. GFD = Gallons Per Square Foot of Membrane Per Day

Q. Will there be a difference in flow rate on the Sepa CF if it is run continuously or in intervals?

A. If permeate flow rate verses time for both membranes are plotted will there be a difference?

There should be a difference in the plots - at least initially. There is typically a "conditioning" affect that occurs as the result of mechanical compression, some of this affect is reversible to an observable amount if operation is intermittent.

This will yield a "zigzag" appearance to a graph of operation vs. time or cumulative hours of operation. The trend with the intermittent operation would be to gradually approach a standard.

Q. What fluid do I use in my Hydraulic hand pump for my Sepa CF?

A. The unit uses standard grade hydraulic oil. It has a reservoir located under the handle at the furthest end with a cap on the reservoir.

The amount of oil used will depend on the length of line, hose.

The recommended oil has a viscosity rating at 100°F.

SUS rating 150-165

SAE 10 wt oil Hydraulic oil (do not use other types of oils)

General purpose

150-165 thickness

Rating 210°F 42-45

Q. What is the proper way to store the membranes for the Sepa CF after they have been used?

A. We recommend that the membranes for the Sepa CF be kept wet once used. Either keep the water fresh (change every couple of days), or add ~0.5 sodium metabisulfite (preferred) to keep bacteria from growing.

Q: What are the torque settings for the CF042 and Sepa CF Cells?

A: Best practices for plumbing of polymer (Acrylic, Delrin, and PTFE cells) CF042 cells, include the use of Teflon tape properly installed on 1/4npt threaded coupling, and the use of a light coat of Teflon based pipe thread sealant, then the coupling needs to be seated in the base of the cell using the following torque settings:

• Delrin- 60 inch pounds
• Acrylic -70 inch pounds
• PTFE -15 inch pounds OR until the fitting "shoulders" out on the base of the CF042 cell*

*extreme caution should be used to assure that the fitting is not started incorrectly (cross-threaded).  In normal installation, the fitting should easily turn in several turns without tooling (by "hand") before using the torque wrench.