how to avoid bubble formation in hexane I have faced this problems when I was working in lab with hexane for the first time. 

I was trying to guide dispersion of nano-particles in hexane solution to a fluid cell (vacuum chamber) with a syringe and a flexible tubing (about 2mm or 3mm diameter). All the materials that I use are hexane resistant. 
The fluid cell is kept on very low pressure, so the goal is not to have any bubble formed in it. 
When I inject hexane fluid, midway before it reaches the chamber, the vapor bubble are formed ( I think because of low boiling point of hexane ) , which is bad I don't want any bubbles go in the chamber. 
However, I figured that if the flow is not horizontal or parallel to the ground (i.e when i inject vertically up ward to chamber) I can avoid the bubble flow. 

I also thought to do the injection process fast, however the whole flow has to be very slow for the experiment.
 I would like to know what exactly causing it and what are your suggestions to avoid the bubble formation in a horizontal flow. 

I was thinking maybe adding some other solution with higher boiling point would be a case to avoid it. But I don't know exactly what solution. And also it is important to keep in mind that hexane solution contains magnetic nanoparticles and I don't want any effect (like aggregation and so on) of added solution into the dispersion nanoparticles.
Thank you,
As you state, hexane has a low boiling point. If the bubbles are hexane vapor, as opposed to an air leak, then cool the fluid and apparatus more. You might pre-chill the hexane in a dry ice bath. The sublimation temperature of $\ce{CO2}$ at 1 atmosphere is about 195 K, and the melting point of a mix of hexane's various isomers is about 179 K, so there should be no problem with crystals blocking the flow.

Be careful with the cold -- frostbite is not painful at first, but is as damaging as a burn!