Experimental and numerical heat transfer studies of nanofluids with an emphasis on nuclear fusion applications

A nanofluid is a mixture of a low concentration of solid particles (10-100nm in size at concentrations below 10%vol.) and a carrier fluid (usually conventional coolants). These novel fluids exhibit anomalous heat transfer phenomena which cannot be explained using classical thermodynamic models. The fluids can be designed to offer unsurpassed heat transfer rates for heat transfer related applications at low costs of manufacturing. This PhD thesis describes the efforts to test whether these fluids can be utilised for high heat flux applications (similar to those encountered in proposed future fusion reactors) and also to discover the mechanisms which give rise to the phenomenal heat transfer enhancements observed. A broad metadata statistical analysis was performed on published literature which provided qualitative results regarding the heat transfer enhancement to be expected from nanofluids, indicated trends connecting by part mixture properties and heat transfer enhancement values exhibited and provided probable explanations of the heat transfer mechanisms involved. This study was performed to tackle the novelty and scientific uncertainty issues encountered in the field. Optical laser diagnostics experiments were performed on a high heat flux device (HyperVapotron) in isothermal conditions. The study provided extensive information regarding the flow structures formed inside the device using conventional coolants and nanofluids. This helped to both, understand the conventional operation of the device as well as review probable suitable geometries for the utilisation of the device using nanofluids. Finally, a Molecular Dynamics Simulation code was composed to model heat conduction through a basic nanofluid. The code results suggested the formulation of a new type of complex heat transfer mechanism that might explain the augmentation of heat transfer encountered experimentally. A new low cost high throughput platform (HTCondor®) has been used to run the code in order to demonstrate the capabilities of the system for less financially able institutions.Open Acces

Anomalous heat transfer modes of nanofluids: a review based on statistical analysis

Abstract This paper contains the results of a concise statistical review analysis of a large amount of publications regarding the anomalous heat transfer modes of nanofluids. The application of nanofluids as coolants is a novel practise with no established physical foundations explaining the observed anomalous heat transfer. As a consequence, traditional methods of performing a literature review may not be adequate in presenting objectively the results representing the bulk of the available literature. The current literature review analysis aims to resolve the problems faced by researchers in the past by employing an unbiased statistical analysis to present and reveal the current trends and general belief of the scientific community regarding the anomalous heat transfer modes of nanofluids. The thermal performance analysis indicated that statistically there exists a variable enhancement for conduction, convection/mixed heat transfer, pool boiling heat transfer and critical heat flux modes. The most popular proposed mechanisms in the literature to explain heat transfer in nanofluids are revealed, as well as possible trends between nanofluid properties and thermal performance. The review also suggests future experimentation to provide more conclusive answers to the control mechanisms and influential parameters of heat transfer in nanofluids.</p