Many of our membrane test systems rely on positive pressure on the feed side to push water through the membrane. Due to the goals of a recent project, we switched to a suction approach with a peristaltic pump on the permeate side pulling water through the membrane. After this update the suction pump created a pulsating flow that caused high-amplitude noise in the sensitive permeate flow meter. The system relies on that flow meter when in Flux-Control mode, so the noise was untenable. The peristaltic pump head is shown in Figure 1; a roller squeezes the tubing and traps water between the roller cylinders. When the water is discharged from the pump head, the driving force from the roller disappears, which decreases the flow rate until the next roller squeeze comes.
Figure 1. Peristaltic pump head
In previous version of our system the pulsation did not cause too much trouble for the flow meter since the flow was buffered by the membrane and its module. However, in the new approach the pump outlet line is directly connected to the flow meter.
Figure 2 shows the flow rate right after the peristaltic pump. In this case, the flux data (which is calculated from flow rate) cannot be used for controlling the peristaltic pump speed. Even a 4-data-point average and 8-data-point average values were too dispersed (Figures 3 and 4).
Figure 2. Flow rate from a 2018-08-29 flux control test.
Figure 3. 4-data-point average flow rate from a 2018-08-29 flux control test.
Figure 4. 8-data-point average flow rate from a 2018-08-29 flux control test.
In this situation, a pulsation dampener is necessary. Dampeners are common in industrial applications to decrease the pulsation and avoid water hammer effects. The dampener can absorb the extra water during the peak flow rate and release it on the downside to smooth the signal. Here we used a self-made pulsation dampener (Figure 5) created with a syringe.
Figure 5. Self-made pulsation dampener.
The syringe is air-sealed, which means the gas inside works as a “space buffer” where extra water can be temporarily stored. This temporary storage increases the air pressure, which pushes the water out when the flow rate from the pump decreases. After the dampener was installed, the flow rate showed a stable enough result (Figure 6) for data analysis and system control.
Figure 6. Flow rate from a 2018-09-03 pressure control test after the pulsation dampener was installed.
Very sweet. Thank you!
Great! Thank you!
I enjoyed this, thanks team
Very interesting, I am wondering how you are able to air-seal the syringe without loss to the pump. What kind of separator is being used, and why is the syringe taped and secured so that it will not compress. I plan to make a similar device for my research and any response will be greatly appreciated.
The funny thing here is that the syringe doesn’t really need to be a syringe. It just needs to be some vessel to hold air. We happened to have a syringe available, which had a convenient nozzle to connect to the tubing. But it could have been any air-filled vessel.
Great work! Just wondering what kind of flowrate transducer or senor you used to generate those figures?
We are using a flowmeter from Alicat.
Nice! Is there a particular 3-way tube fitting you’re using, or will any do? Thank you!
Here is a three-way connector with three tube adapters to connect them together. I think you can find a three-way connector for tubing directly.
Why is there a clip at the back of the syringe?
That is the not the necessary item. I use it for hanging up the device.
This is fantastic, I have been struggling with pulsation in my microfluidic system for studying endothelial cells. Just curious- if the 3-way connector and syringe were oriented properly (vertically) would it also act as a bit of a bubble trap? Thanks for this protocol, great idea!
Hi Bob, that will probably happen according to my experience; however, it also depends on your velocity. On the other hand, when you disarm (decrease the pressure in) the system, these bubbles will enter back into your flow again. For this reason, I usually get rid of the bubbles before the beginning.