Flow Cells

Flow cells are used for a variety of column experiments. They are used most often for column leaching experiments. Such studies are designed to determine rates of movement of water and chemicals (i.e. nutrients, tracers, organics, metals etc.) through soil, and to determine chemical transport parameters.

Flow cells are also used to study the hydraulic properties of soils, such as the saturated hydraulic conductivity, the unsaturated hydraulic conductivity, and soil water retention.

By using SMS flow cells all of these hydraulic properties (the saturated hydraulic conductivity, the unsaturated hydraulic conductivity, and soil water retention) can all be determined on the same soil core. Column tensiometers are recommended, for determining the unsaturated hydraulic conductivity. Small column tensiometers, with or without pressure transducers, are available from SMS.

A flow cell is usually made of cast acrylic, but aluminum and stainless steel flow cells can be made on special order. A flow cell consists of a tube, which holds the soil or other porous medium, and two removable end-plate assemblies, one mounted on each end of the tube. The tube and the top and bottom end-plate assemblies are held together with 3 rods.

Each end-plate assembly consists of two parts: a round doughnut shaped part containing an o-ring slides over the end of the column, and a flat round plate which holds a perforated aluminum support disc. There is a flat o-ring between the two plates, as well as a porous nylon membrane (bubbling pressure 30 mbar) or a membrane filter (bubbling pressure 600 mbar). When needed, the membranes can easily be replaced. The round doughnut shaped part of the end plate assembly for 5.25 inch OD flow cells is made of aluminum.

Flow cells come in nine standard tube diameters: 1.5, 2.0, 2.25, 2.5, 3.0, 3.25, 3.5, 4.0, and 5.25 inches outside diameter. The inside diameters are 0.5 inches less than the outside diameters. For different diameters (including metric sizes) contact SMS. Flow cells can be made in nearly every length.

Frequently asked questions:

Question 1: How much pressure can I apply to the flow cells?

Answer:

The flow cells are designed for pressures up to 1 bar. However, the porous membrane has a bubbling pressure less than 1 bar, so the flow cell will start leaking if subjected to air pressures of 1 bar or more.

Question 2: Can other membranes be used in the flow cell?

Answer:

Yes, they can be used if they are relatively thin (less than 0.2 mm thick).

Question 3: I took soil samples (undisturbed) in metal rings, which have a different outside diameter than standard flow cells. Can I use the SMS flow cells for these cores?

Answer:

If many flow cells are required, SMS can make special flow cells to fit the non-standard cores.

An alternate approach would be to place the non-standard cores inside larger flow cells, which are long and wide enough to accommodate the cores. This works well for determining water retention data.

Question 4: Are tubing connectors provided for the outlets in the top and bottom end plates?

Answer:

Tubing connectors may be ordered with the flow cells. They can be screwed into the outlets, which are standard 1/8 inch NPT, or 1/4 inch NPT (National Pipe Thread) threaded outlets. Quick release connectors are recommended for hydraulic property determinations. They are especially useful when determining soil water retention (soil water release curves) curves. These connectors fit directly into the 1/8 or 1/4 inch NPT outlets of the flow cells.

Question 5: Can tensiometers be used with the flow cells?

Answer:

Yes, tensiometers can readily be used. When ordering the flow cells, specify the number of access ports and tensiometers required, as well as the desired placement of the access ports in the flow cell wall (i.e. 7 cm from the top of the flow cell, 15 cm from the top of the flow cell, etc.). SMS column tensiometers may be ordered with a three-way valve to make it easy to fill the tensiometers with water, to readily remove all air from the tensiometers, and to attach the pressure transducers.

Question 6: Can I order flow cells with more than one inlet/outlet in the top and/or the bottom of the flow cells?

Answer:

Yes, extra holes, either threaded or straight, in the top and bottom can be ordered.