Heat Transfer Behaviour with ZnO-water Nanofluids Om Shankar Prajapati and A.K. Rajvanshi Department of Mechanical Engineering Malaviya National Institute of Technology Jaipur, Rajasthan, India omshankar.prajapati@gmail.com
Boundary conditions:
Nanofluid: Nanofluids as a new, innovative class of heat transfer fluids represent a rapidly emerging field where nanoscale science and thermal engineering meet. Nanofluids, engineered by dispersing nanometer-sized solid particles in conventional heat transfer fluids have been found to possess superior thermal performance compared to their base fluids. They can offer numerous potential benefits and applications in important fields such as microelectronics, microfluidics, transportation, and biomedical. Preparation of nanofuids is the first key step in applying nanophase particles to changing the heat transfer performance of conventional fluids. Some special requirements are necessary, such as even suspension, stable suspension, durable suspension, low agglomeration of particles and no chemical change of the fluid. In general, these are effective methods used for preparation of suspensions: (1) changing the pH value of suspension, (2) using surface activators and/or dispersants, (3) using ultrasonic vibration.
Preparation of Nanofluid: ZnO + Distilled water
Ultrasonication
S. No.
Parameter
Range
1
Volume fraction
0 - 0.1%
2
Heat flux (kW/m2)
0 - 200
3
Mass flux (kg/m2 s)
400
4
Pressure (bar)
1
5
Degree of subcooling (oC)
20
Results: The variation of thermal conductivity of ZnO-water nanofluid shown with particle volume fraction (0.001%, 0.01% and 0.1%). The thermal conductivity of base fluid (distilled water) is 0.61 (W/mK). The increment of thermal conductivity with particle volume fraction is shown. Experimental data shows that heat transfer coefficient, h (kW/m2K) of ZnO-water nanofluid increases gradually with heat flux. Study reveals that heat transfer increases with heat flux applied at all given range of percentage ZnO-water nanofluids due to increased energy gain to the nanoparticles.
Volume Conc. 0.001% vol. 0.01% vol. 0.1% vol.
Ultrasonic Vibration Mixer (UVM) with ZnO-nanofluid
Experimentation: The closed loop test facility of 10 liter capacity mainly consists of ultrasonic vibration mixer, storage reservoir, circulating pump, flow meter, electrically heated horizontal annular test section, condenser and heat exchanger. The working fluid is pumped from the reservoir to the test section via flow meter. The mixture of working fluid and steam from the exit of the test section passes through a horizontal condenser and counter flow heat exchanger before returning to the reservoir. The heated length of 500 mm is located 230 mm downstream of the inlet plenum and thus allowing for the flow to fully develop. An input 415 V, 3 phase AC power is stepped down to 0–32 V DC power by using 64 kVA DC regulated power supply by which a large range of heat fluxes are applied to the test section.
Thermal conductivity enhancement of ZnO-Water nanofluid
Variation of heat transfer coefficient with heat flux
Conclusions: An experimental facility with adequate instrumentation has been modified and erected to study heat transfer characteristics of ZnO-water nanofluid and report information on heat transfer characteristics of ZnO-water nanofluid in convective heat transfer within the boundary conditions. The working fluid was electrically heated in horizontal annular test section. All the instruments in test set up were properly calibrated as per guidelines given by American Society of Mechanical Engineers. Convective heat transfer experiments were carried out to study heat transfer behavior of ZnO-water nanofluid, compare them with base fluid (distilled water) and obtain data on heat transfer characteristics. Finally, the results of the present investigation are summarized as follows: 1. The thermal conductivity of base fluid increases with addition of ZnO nanoparticles. 2. Heat transfer coefficient increases with heat flux. 3. Heat transfer performance improved with particle volume fraction of ZnO-water nanofluid.
Acknowledgement The financial help given by Board of Research in Nuclear Science (BRNS), Department of Atomic Energy, India is gratefully acknowledged.
References Schematic of experimental setup
Test section and position of thermocouples
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