Stability Issues and Operating Limitations of Nanofluid filled Heat pipe: A Critical Review

Abstract

It has been proved by researchers that #nanofluids are good alternatives to conventional fluids in heat pipes. Typically, application of nanofluids in heat pipes results in improved #thermal #performance but some contradictions were also reported by the researchers. Although nanofluids are widely used in heat pipes some issues are yet to be resolved like the stability of nanofluids and operational limitations. The stability problem is a big issue for #researchers either before or after the #operational cycle. Therefore, it is important to enhance the nanofluid stability for the #commercialization of the heat pipe. In this regard, this paper aims to study and summarise the outcomes of applications of nanofluids in different heat pipes. The authors emphasized on #stability problems of nanofluids in heat pipes. Moreover, the #impacts of operating #limitations are also reviewed in this article.

Conclusion

• The heat pipe thermal performance has been #improved in most cases, by using nanofluids as a working medium.
• It happens due to the good thermal #conductivity of the nanofluids.
• The thermal performance of the heat pipe depends on the #concentration of the nanoparticles in the nanofluid, tilt angle, charging volume, #wick structure, thermophysical properties, and power input to the #evaporator.
• The stability of nanofluids is the main hurdle for its commercialization.
• Some methods are employed by researchers for improving the stability like sonication, different types of stirring, addition of #surfactant, surface #modification and pH variation but it needed more research for #optimum solution of the stability issue.
• Addition of surfactant beyond a limit will decrease the thermal conductivity of nanofluids which results in decrease in thermal performance of the heat pipe.
• It is clear that more work is to be done on the stability issue of the heat pipes for its commercialization.
• The range of operation of a heat pipe is decided by the operating limitations.
• The main cause of the occurrence of operating limitations is the incapability of the wick structure to return the condensate to the evaporator in sufficient amount to avoid the dry-out condition of the evaporator.
• The operating Limitations can be divided into two categories as - Capillary limit or Wicking Limit, Boiling Limit, and Entrainment or pickup limit are comes under failure limitations. The main cause of occurrence of these limitations is insufficient condensate flow to the evaporator at a particular input power, which leads to dry out condition of the evaporator thus towards the chances of failure of the heat pipe.
• The Sonic, Viscous, and Condenser limits come under non-failure limits.
• Capillary, Entrainment, Sonic, and Viscous limits are due to axial heat transfer whereas boiling limit is due to radial heat transfer in the evaporator.