Use of nanoparticles to enhance heat transfer

[jwseifed]

Hey guys. I have a counterflow heat exchanger which passes liquid nitrogen through tubes and hot exhaust gas over them externally. At the same time, we are injecting nanoparticles into our inlet pipe so that it mixes with the exhaust gas prior to entering the heat exchanger. The purpose of this is to enhance heat transfer, which has been shown to occur on some lower scale experiments in the past (albeit for cross-flow configurations). However, it is having the opposite affect in our case. The exiting temperature of the LN2 is decreasing and the exiting air temperature does not change compared to the baseline test.

There is most likely some frost enveloping the LN2 pipes, which is reducing heat transfer, but it still doesn't explain why the nanoparticles would be REMOVING heat from the coolant. I've attached a screenshot of the plot to help illustrate better.

Green - inlet temp of hot air
Black - outlet temp of hot air
Blue - outlet temp of cold LN2
Red - inlet temp of cold LN2

Nanoparticles were injected during the period between the vertical black dots shown. Steady state starts at around 300. Note the rapid drop in LN2 outlet temp (blue) and rising air outlet temp (black), these should theoretically be trending in the opposite directions. I also don't know why the temperatures continued to change even after the injection was completed. If anyone has some insight on this I would most definitely appreciate it. Thank you

 

[hacksaw]

Basically, boundary layer flow, where time evolved multi-phase flow where phase change is occurring.

Beyond consulting the research literature and various texts, you'll need your current flow tests and sophisticated CFD resources.