Experimental investigation on forced convection heat transfer of water - ethylene glycol based TIO2 nanofluid / Khamisah Binti Abdul Hamid

Faculty of Mechanical Engineering

Thesis (Master of Engineering (Mechanical)) -- Universiti Malaysia Pahang – 2016

Bibliography : p. 100-113

Nanofluid as a new heat transfer fluid have overcome the limitations in thermal performance faced by conventional fluids such as water (W), ethylene glycol (EG) and oil based fluids. However, researches conducted on nanofluid with specific liquid mixture based such as water/EG are limited. In conjunction with that, experimental investigations using nanofluid in mixture base fluid are required for determination on heat transfer performance. The objective of the study is to investigate the thermophysical properties and the heat transfer performance of TiO2 nanofluid in a base fluid composed of mixture of water and EG at three different operating temperatures. The nanofluid was prepared by dispersing TiO2 of 50 nm in size in the base fluid (60W:40EG) for volume concentrations in the range of 0.5 to 1.5%. The nanofluid thermal conductivity and viscosity were measured using analytical laboratory equipment, whereas the density and specific heat were obtained using mixture formula. The forced convection heat transfer investigation was conducted using the existing experimental set up at Reynolds number that ranges from 3,000 to 24,000 for bulk temperature of 30, 50 and 70oC under constant heat flux boundary conditions. The measurements of the properties indicated that the thermal conductivity of nanofluid increased with the increase of temperature and concentration. The maximum enhancement of thermal conductivity achieved was 15.4% at 1.5% volume concentration, compared to the base fluid. On the other hand, the nanofluid dynamic viscosity increased with increase in volume concentration but decreased exponentially with temperature. The maximum enhancement in nanofluid viscosity was observed to be 33.3% for the concentration of 1.5%, compared to the base fluid. The heat transfer coefficients of the nanofluid increased with the increase of Reynolds number at concentrations of 1.3% and 1.5% for a working temperature of 30oC. The enhancements in heat transfer coefficient at this condition were 7.2% and 9.7%, respectively. However, most enhancements in heat transfer coefficient for nanofluid concentrations in the range of 0.5% to 1.0% showed negative values. The heat transfer coefficient for the range of concentrations studied with temperatures of 50oC and 70oC showed an enhancement compared to the base fluid. The maximum enhancements were found to be 22.8% and 28.9% for temperatures of 50oC and 70oC, respectively. The friction factor for nanofluid is slightly increased with the increase of concentration at about 1.1 times of the base fluid. The heat transfer performance evaluated through the Performance Energetic Criterion (PEC) of TiO2 nanofluid showed that the effect of high temperature is dominant at concentrations greater than 1%. It is recommended to use TiO2 nanofluid in a mixture of water and EG (60W:40EG) based at a high temperature of 70oC and concentrations of 1.5% for various heat transfer applications.