Apr 25, 2020 - 10:51 AM
Capillary action is the ability of a liquid to flow vertically and horizontally along narrow spaces without the assistance or even in opposition to external forces like gravity. This phenomenon is used by trees and plants to transport water and nutrients up from their roots to their leaves. The forces of capillary action can be quite amazing such as how water is transported to the top a 500ft sequoia tree with no physical movement or pumping action. For capillary action to exist you need to have very small spaces with no openings or blockages to stop the flow of the fluid.
In SLIC systems we most often see issues with capillary action with Ethernet cables which do not have a fully molded on connector or open ended outer sheathing where one end of the cable is immersed in Dielectric Coolant and the other end is attached to a router or switch. In this instance it is not unusual to see Coolant dripping out very slowly (a drop or two an hour) from the router / switch connector side. This can also be seen in some unmolded power supply and video cabling where the fluid can enter into the cable at the immersed end. This can also occur when using stranded power cables which have unsealed connector ends..
Generally cables that have multiple strands of wire in them or twisted pairs in an outer sheath and are not sealed on the ends provide an excellent medium for capillary action to occur, as they have many small spaces in which the coolant can travel. This is exactly why Ethernet Cables can be an issue, as they have 4 pairs of twisted solid core wire in an external sheath, the gap between the twisted pairs and the sheathing provide the perfect sized spacing needed for the Dielectric Coolant to travel up the cable
There are a couple of quick fixes that you can use to avoid Coolant traveling up the cabling from your tank:
1) Stripping off the outer sheathing on cables.
Since capillary action requires the small gaps you can eliminate it by stripping off about 2cm of the external sheathing on an Ethernet cable about 1-6" above the tank and then flaring out the twisted pairs to increase their spacing ( just grab the cable on either side of where you removed the sheathing and push the end together to flare out or increase the gaps between the pairs of wires). This removal of the other sheathing and the flaring eliminate the small gaps that characterize capillary action. This method is not acceptable for use with power and other stranded wiring carrying power, but it can certainly work with video and other insulated wires inside of a common sheath.
2) Sealing the cable ends at the connector
Sealing the joint between the connectors and wires is another simple method, we typically use a small dab of clear silicon spread around the exposed twisted pairs going into the Ethernet connector and area at the entry of the twisted pairs into the sheath. Make sure to get the silicon into the entire end of the sheathing and around all the twisted pairs, again flaring the cable works well. Cables with molded on connectors are typically already sealed.
3) Moving the cable connection out of the Coolant
In large systems we will typically use some short jumper cables that exit the fluid and then use a butt connector or back to back connector to create the break in the cable above the level of Dielectric Coolant. This has the added benefit of allowing for simple changing of cables without the need to touch the inside of the tank. We also have used patch panels to accomplish this same approach.
In sealed tanks, or open tanks with lids another great way to stop capillary action and to provide for ease of use in cabling is to mount connectors in the wall of the tank and then use jump cables to connect the connectors to the device. You can seal the connectors with 2-part epoxy on the tank walls.
See the attached diagram for a description on potting cables into acrylic tanks with Epoxy. You can also pot connectors mounted in the tank wall the same way.