Channel is wide with width 6 mm, height 0.4 mm, length 60 mm. I want to achieve flow rates from 1 ul/min to 25 ul/min in my system. Flow rates below say 100 ul/min (using syringe pump with 2 ml syringe) are not having any effect on fluid movement. Why can this be happening? What can be done?
I have checked and eliminated all leaks as well.
What liquid are you pumping? What degree of accuracy do you need? Has the liquid been degassed (failure to degas the liquid can result in compressing a gas, not a liquid, which results in no or little initial flow)?
Syringe pumps (and the syringes used) come in a wide variety of specifications (accuracy and flow delivery). Perhaps you have mismatched the two to meet your requirement or are working outside of the range of the syringe/syringe pump specification? The manufacturer's provide tables of accuracy and range which are worth consulting before use.
Perhaps the passages are blocked or obstructed? Have you made sure to use high purity liquids and filter everything through a 0.22 micron filter before use?
You may want to consider using a high performance HPLC capillary pump. Many manufacturers offer these with ranges below 40 ul/min (e.g. 0.01 to 40.00 ul/min). When installed and operated with appropriate applications, they can provide the highest level of precision and stability over time. They also provide back-pressure feedback which is valuable in determining if you have an obstruction or blockage.
Besides, your channel is too large for such low flow rates. If the flow rate is 1 uL/min, you need almost 2.5 hours to fill the channel. In practical, the cross section area should be 100 times less the the current design ( 6 mm width x 0.4 mm height). Did any one try uL/min flow rates with your dimension before, like publications?
I agree with Hongzhu Lia, you have a problem of relative orders of magnitute. The channel is much too big for the flow rate you want.
I agree that the channel volume is very large relative to the flow rates used, but that does mean you can not use those low flow rates.
As is often the case with these very generalized student questions, no information was provided regarding the actual application, system design or what type of monitoring/measuring equipment is used to evaluate the flow at the outlet. Based on the information supplied and assuming this is a closed-system, once the channel has filled with liquid (depending on flow rate, this could take minutes to hours), flow should occur and be measurable at the outlet. The fact that his total channel volume is enormous, compared to the range of flow rates described, does not change the result that flow should still be seen. Provided there are no leaks, if you add fluid to the channel, then you better be able to measure the change. *BTW: If this is open-system (again, no information was provided), then evaporation alone would probably make it impossible to measure at low levels of flow.
We are trying to measure how the flow rate will effect the immunological reaction, and hence the use of such low flow rates. Also, high flow rates will not satisfy our overall project goals. I had used low flow rates of magnitude 20-30 ul/min earlier in similar channels (width 5mm, height 0.5 mm), and didn't face any problem.
The system is closed. I am using negative pumping pressure on one side while the other side of the channel is open to atmosphere via a tubing. Syringe pump used is a New Era Syringe Pump, syringe is a 2ml plastic syringe.
As of now I have not degassed the liquid, and will see if that makes a difference. Thank you for help.
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