Phase change heat transfer of liquid nitrogen upon injection into aqueous based TiO₂ nanofluids

This paper reports an experimental study on the cryogenic phase change behaviour of liquid nitrogen upon injection into a relatively large pool of aqueous based titanium dioxide nanofluids under ambient temperatures. Stable TiO₂ are formulated at concentrations between 1% and 4% by particle weight, and characterized in the experiments. Both transient pressure and temperature profiles are measured and analysed in the range of liquid nitrogen Reynolds number of 2,200-11,000 and Webber number of 9-220. The results, however, do not show obvious influence of nanoparticles' concentration on the pressure build up and heat transfer under the condition of this work. Very similar results are observed for liquid nitrogen injection into pure distilled water and into different concentrations of TiO₂ nanofluids; both the pressure and the rate of pressure rise during the injection process increase linearly with injection velocity irrespective of nanoparticle concentrations. Further discussion shows that a higher rate of pressure rise could be achieved if operating conditions were optimised to induce the fragmentation and subsequent vapour explosion.