Microfluidics in pressures lower than one atmosphere

Click For Summary

Discussion Overview

The discussion revolves around an experiment involving microfluidics, specifically focusing on the behavior of liquid flow under pressures lower than one atmosphere. Participants explore the mechanics of a setup that includes a reservoir, valves, tubing, and a pump, while investigating the causes of liquid flow issues at low pressures.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes an experimental setup where liquid is pushed from a reservoir into a chamber under varying pressures, noting that flow issues arise when pressures drop below 200mbar.
  • Another participant questions the specifics of the setup, asking about the length of the capillary and other flow impediments, as well as the saturation percentage at 10^-2 bar.
  • A participant provides details about the tubing used, including dimensions and the operation of a volumetric plunger pump, while seeking clarification on the vapor pressure of water.
  • There is a query regarding the vapor pressure of water, with one participant suggesting it is approximately 31mbar at room temperature.
  • Another participant reiterates the question about the vapor pressure of water, indicating a need for further insights.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the causes of the liquid flow issues at low pressures, with multiple questions raised about the experimental setup and the properties of water. No consensus is reached on the underlying reasons for the observed behavior.

Contextual Notes

Participants have not fully defined the conditions under which the experiment operates, such as the specific characteristics of the tubing and the implications of vapor pressure on the experiment. There are also unresolved questions about the effects of capillary action and other flow impediments.

Who May Find This Useful

This discussion may be of interest to researchers and practitioners in microfluidics, fluid dynamics, and related fields who are exploring low-pressure systems and the behavior of liquids in micro-scale environments.

cedric goossens
Messages
4
Reaction score
0
Hi everyone

I am trying to build an experiment with microfluidics. I have a reservoir containing a bellow. This bellow is a compensation mechanism and makes sure that the liquid (in this case water) can be pushed out of the reservoir. Before storing the fluid in the reservoir, the reservoir is evacuated up to 10^-2bar and the fluid is degassed. Right after the reservoir I have a first valve followed by stainless steel tubing with a diameter of 0.35mm. THis tubing also contains a pump. After the tubing I have a second valve which connects the tubing to a controlled (pressure and temperature) and closed chamber. My experiment is as follows:
- reservoir valve is closed
- chamber valve is opened
- chamber and tubing are evacuated
- pressure is set in chamber and tubing
- reservoir valve is opened
- reservoir valve is closed when liquid reaches chamber
- chamber valve is closed
- chamber is evacuated
- pressure is reset (same value as before)
- chamber valve is opened
- pump is used to inject liquid

Now this works perfectly fine when the set pressure is 1bar, 400mbar,...
But when the pressure is below 200mbar the liquid keeps on flowing out of the tubing. I was wondering what the cause is of this. Is this due to the capillary effect or is it something else that I am missing?
 
Physics news on Phys.org
cedric goossens said:
10^-2bar and the fluid is degassed.
Through a capillary? Of what length? Containing a pump? And what other impediments to flow? For how long? And what percentage of saturation is 10-2 bar?
 
Well the liquid lines consist of a few types of tubing. First of all there is a 1.6mm diameter tubing approximately 20cm in length, as a sidebranch of this tubing there is a volumetric plunger pump to push the liquid out. Behind the final valve there is a tube of 0.35mm diameter tubing of approximately 2cm. The pump is set to work at a speed of 10µl/s and needs to pump out volumes between 2 and 130µl.
The last question I don't quite get. Before filling the reservoir with degassed liquid, it is set to 10^-2 bar. After that the reservoir is filled.
 
cedric goossens said:
The last question I don't quite get.
What's vapor pressure of water?
 
Considering it's at room temperature this should be about 31mbar
 
Bystander said:
What's vapor pressure of water?

Sorry to bother you but do you have any insights?
 

Similar threads

Solving the Problem of Capillary Action in Tiny Peristaltic Pumps
  • · Replies 9 ·
Replies
9
Views
3K
Bubble formation in 4 mm gap vessel
  • · Replies 6 ·
Replies
6
Views
1K
Graduate (Fluids) Difference in stress or pressure between setups?
  • · Replies 10 ·
Replies
10
Views
2K
Graduate Does Fluid Dynamics Explain Pressure Gradients in a Frictionless Tube?
  • · Replies 48 ·
2
Replies
48
Views
6K
Gas conductance through tube at low pressure
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Why does atmospheric pressure increase as you go closer to the Earth's surface?
  • · Replies 16 ·
Replies
16
Views
3K
High School What causes liquid to rise in a capillary tube?
  • · Replies 1 ·
Replies
1
Views
3K
Just curious about many things like hydrostatics
  • · Replies 28 ·
Replies
28
Views
4K
Graduate Help needed on calculating system pressure during rapid phase transition of CO2
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Measuring Steam Condensate from my Steam Cleaner
  • · Replies 8 ·
Replies
8
Views
3K