The focus of this thesis is to establish the current use of nanofluids during experiments, examine some of the areas of research that need to be performed and undertake an experimental analysis of the boiling heat transfer of nanofluids. Although nanofluids in microchannels have been thoroughly examined with some models being produced, the models in these regimes are rather complex and require specific conditions to be accurate and experiments designed for the boiling regime are few and far between. The aim of this thesis is to present a simple design of a heat exchanger which can be used to collect data and create a model for the boiling regime using nanofluids. As the main focus is to reduce costs and simplify, a highly concentrated silica suspension was purchased and diluted with deionised water and a small amount of 0.05 M sodium hydroxide (for stabilisation purposes) to a low volume concentration (< 1 vol%) This process of dilution would be significantly cheaper than producing a nanofluid in-situ and would make the production of nanofluids readily available to anyone who may wish to use them. Four methods of dilution were tested to determine whether the dilution method had any significant effect on the average particle size within the nanofluid. After examination it was determined that the method of dilution did not have a significant effect on the average particle size whereas there was a correlation between the volume concentration and the average particle size. As the nanofluid was diluted further the average particle diameter increased in an exponential manner, with the most noticeable change being at approximately 3 vol%. The silica nanofluid was then to be used in a simple single pass heat exchanger which was created to boil the nanofluid and collect the temperature and pressure data to allow for the critical heat flux to be calculated. The heat exchanger design was originally a bespoke piece of glass equipment with a central copper tube and an outer ring of jackets, one of which would contain the silica nanofluid whilst the outermost sealed jacket would contain air for insulation. This design was then simplified due to infeasibility when producing the sampling locations, this resulted in the design of a removeable air jacket and further design considerations such as the stability of the system during operation. Unfortunately, due to the Covid 19 pandemic the experimental analysis could not be performed. However, this led to a Computational Fluid Dynamics (CFD) analysis approach being taken as CFD modelling has been an up-and-coming method for fluid analysis due to the availability of software and ability to test transient effects on a system before making any direct changes.
|Date of Award
|13 Jan 2023
|Lande Liu (Main Supervisor) & Jonathan Hinks (Co-Supervisor)