Investigation of the heat transfer enhancement effects of nanofluids in process heating and cooling

The global energy system faces a dual challenge; the need for more energy and less carbon emission. Out of the 50 billion tonnes of greenhouse gases emitted each year, 24.2 % comes from energy use in industries such as processing and manufacturing that require constant heating and cooling. Heat transfer improvements in heating and cooling industries cause energy saving thus reducing operational costs, increase the operational life of heat transfer systems and reducing greenhouse gas emissions. While nanofluids usage in heat exchangers presents a critical step for emission reduction, several factors including instability of suspended nanoparticles, the effect of a surfactant on physical property measurements and combining nanofluids with inserts have not been adequately assessed. This thesis investigates the use of highly conductive nanofluids as a potential alternative to conventional working fluids with low thermal conductivity, such as water, currently used in heat exchangers for heating and cooling systems. A distinguishing feature of this study is the consideration of the effect of surfactants on the stability of nanofluids, the physical properties of the nanofluids and the thermal performance of the nanofluids. The use of nanofluids in combination with hiTRAN® heat transfer inserts was also investigated. Activated carbon (C), copper oxide (CuO) and alumina (Al₂O₃) nanoparticles were suspended in distilled water (H₂O) and Ethylene glycol (EG). Surfactants were added including sodium dodecyl benzene sulfonate (SDBS), cetyltrimethyl ammonium bromide (CTAB), sodium lauryl sulphate (SDS) and Arabinogalactan (ARB) to create 20 combinations of nanofluids. ARB as a surfactant kept C/H₂O and CuO/EG nanofluid stable for 29 days. Whereas CTAB and SDBS surfactants kept C/H₂O and Al₂O₃/H₂O nanofluids stable for 17 and 11 days respectively. Viscosity results showed that in some cases the surfactant caused a slight increase in viscosity and in some cases viscosity decreased.