Emergency cooling of superheated surfaces by nanofluids additives in the event of a water boiling crisis

摘要

In order to prevent accidental overheating in metallurgy, electrical engineering, power engineering, nuclear power plants (NPP) etc., we have developed a series of nanofluids (NFs) which are stable under high temperature, boiling and radiation conditions. In our work, a new AlSi-7 nanofluid based on natural aluminosilicates with unique thermal behavior was developed for the first time. The boiling curve, covering all modes including transient and film boiling and burnout heat flux up to 3.7 MW/m~2 is presented. The possibility of using this NF for emergency cooling of a superheated heat exchange surface was studied. For this purpose, the automatic unit for simultaneous recording of NFs boiling curves and the changes of the main heat transfer parameters (such as heat flux, heat transfer coefficient and temperature of the heating surface) in real time conditions under a constant rise of heat flux are presented. These NFs consisted of metals oxides, natural aluminosilicates and carbon nanomaterials (including nano-diamonds, multi-walled carbon nanotubes (CNTs) and thermo-expanded graphite (TEG)). Results showed the possibility of increasing the heat transfer coefficient (HTC) and critical heat flux (CHF) by 1.5-3.0 times compared with those of distilled water. By adding nanofluids to boiling water in the event of a boiling crisis, emergency cooling of an overheated heat transfer surface resulted in a sharp decrease in temperature of the heating surface from 700 to 125 °C without reducing the heat load has been proven.