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As the subject states I have hit a wall in a fluid mechanics associated problem in designing an experiment for my grad project.

Long story short, I'm an engineering undergrad who got a broad education in formal engineering topics (thermo, heat and mass, classical mechanics, systems, circuits, etc. etc.), but literally only did 1 fluid mechanics course. I am now a Masters student doing more biologic focused research. I am working with stem cells and I need to perform a flow experiment in which I run continuous fluid over my cells in a flow chamber at a specified flow rate.

My problem is that I have been using a syringe pump as it was what the facility provided and it's less than optimal. Only 30 mL at a time and at my specified flow rate I end up having to change it a lot and therefore flow is discontinuous and not really up to the rigor of my experiment. I get ok results, but I think it can be better.

What I'd like to do, and my problem is, that I'd like to run a circulating system with a continuous pump. I just don't know how to figure out what pump to use. I have some support and money from the lab, and I'd prefer to be able to tweak the flow rate if possible.

To set up the problem:

I am using an Ibidi mu VI 0.4 chamber slide. Full literature available here:

https://ibidi.com/channel-slides/57--slide-vi-04.html

Quick and dirty dimensions:

Outer dimensions (w x l) 75.5 x 25.5 mm² Adapters Female Luer Number of channels 6 Channel volume 30 µl Channel height 0.4 mm Channel length 17 mm Channel width 3.8 mm Volume per reservoir 60 µl

Using their literature provided I have already calculated that I need to provide a flow rate of:

4.73 mL/min

which corresponds to a shear stress of: 6 dyne/cm^2 (0.6 Pa)

my tubing dimensions are:

L = 20 cm inner d = 1.6 mm

I have a reservoir of cell media of maximum 50 mL which needs to sit beside the microscope in a heater to provide the maximum "comfort" and conditions that my cells like (37 degrees C)

Now, for the life of me I can't figure out how to determine an appropriate set up/pump to make this into a continuous flow, needed to pump/circulate for 2 hours

Can anybody at least put me on the right path to designing this?? I don't have the time to relearn all my fluids, but I don't mind brushing up on topical required reading to solve.

I can also attempt to make a diagram if you need a better visual representation. I hope I explained my problem thoroughly though.

Thank you,

A frustrated grad student

EDIT:

A few constraints as per suggestion (thanks for the suggestion)

1.) Steady flow of ~4.73 mL/min

2.) Acceptable range of +/- 10% preferably at least consistently averaging out to the desired flow rate of the span of minutes and not hours (I.E. if it drops below or above only stays for minutes on the time scale of 10-15 minutes, not averaging out over a span of hours).

3.) I unfortunately have lost some of the lingo so I hope this is correct, but I need to DELIVER a shear stress of 0.6 Pa, which according to the Ibidi Flow Chamber literature (as above, mu chamber VI 0.4) by using my tubing of 1.6 mm inner diameter, by providing that flow rate, that is the pressure that will occur at that flow rate. This could be my misunderstanding, if I am grossly misunderstanding this I would love an explanation

4.) THE most important thing is delivering approximately 0.6 Pa of shear stress to the cells (+/- 10%)

5.) Flow must be continuous for 2 hours, breaks of tens of seconds for switching/resetting things is acceptable but not minutes of switching thing (reservoir switches, etc.)

To be continued if there are any other suggestions... as far as I know those are my only constraints.

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  • $\begingroup$ Have you considered peristaltic pump? $\endgroup$ – user207455 Jul 23 at 18:59
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    $\begingroup$ You might get more responses over at Engineering. $\endgroup$ – jacob1729 Jul 23 at 19:03
  • $\begingroup$ I have not, actually. It looks like a peristaltic pump creates a pulsation in the flow? I mean, what really matters is that I can deliver a mostly continuous flow at my specified rate, it's a hell of a lot better to have tiny "no flow" moments throughout than the massive disconnections every time I have to change the syringe. I'm pretty open to any solution, lower tech and lower expense is preferred so if you think that's something that could provide those things I would be open to it. $\endgroup$ – BMEGrad2020 Jul 23 at 19:07
  • $\begingroup$ Fair, sorry, I didn't know there was an engineering stack exchange. I think I've only ever seen/read physics. Figured a few physicists in here would be wizards enough to help. It's not a super tough problem, I think? But I guess engineers deal with pumps more often. I'll cross post there. Thanks. $\endgroup$ – BMEGrad2020 Jul 23 at 19:08
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    $\begingroup$ @BMEGrad2020, it would be helpful if you would declare all of your constraints. Example: 1) steady flow of 4.37 ml/min; 2) minimum and maximum acceptable deviation from this flow (every process and measurement has its precision), and how long this deviation can be tolerated; 3) any pressure or differential pressure requirements. $\endgroup$ – David White Jul 23 at 19:57
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Your solution, as pointed out by Solar Mike, is a peristaltic pump. With proper setup and operation, flow pulsation is minor.

You buy these in three parts: a motor drive unit, a pump head that bolts onto it, and tubing that fits into the pump head. Appropriate selection of these three will furnish you with the correct flow rate for your application.

Motor drives come in fixed rate, variable rate, and computer-controlled variable rate types. The tubing comes in a variety of types, for compatibility with a range of different liquids. Multiple pump heads can be attached to a single drive unit, for parallel dispensing of different liquids at identical flow rates.

The brand name of choice is masterflex.

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