Abstract
Forced convective heat transfer from a vertical circular tube conveying deionized (DI) water or very dilute Ag-DI water nanofluids (less than 0.02% volume fraction) in a cross flow of air has been investigated experimentally. Some experiments have been performed in a wind tunnel and heat transfer characteristics such as thermal conductance, effectiveness, and external Nusselt number has been measured at different air speeds, liquid flow rates, and nanoparticle concentrations. The cross flow of air over the tube and the liquid flow in the tube were turbulent in all cases. The experimental results have been compared and it has been found that suspending Ag nanoparticles in the base fluid increases thermal conductance, external Nusselt number, and effectiveness. Furthermore, by increasing the external Reynolds number, the external Nusselt number, effectiveness, and thermal conductance increase. Also, by increasing internal Reynolds number, the thermal conductance and external Nusselt number enhance while the effectiveness decreases.
Highlights
Prediction of forced convective heat transfer from a circular tube conveying a hot nanofluid is a basic but important problem in the field of heat transfer enhancement in recent years
The results clearly showed that the use of nanofluids significantly improves the convective heat transfer at higher Reynolds numbers
Results and discussion the results of experiments are presented for different internal Reynolds numbers, various volume fractions of Ag/DI water nanofluid (i.e., 0.005%, 0.01%, and 0.02%), as well as different external Reynolds numbers
Summary
Prediction of forced convective heat transfer from a circular tube conveying a hot nanofluid is a basic but important problem in the field of heat transfer enhancement in recent years. Researchers and engineers are confronted with this problem in a wide variety of industries ranging from transportation, HVAC, heat exchangers, and textiles. All of these industries are limited by heat transfer; they have a strong need for improved fluids that can transfer heat more efficiently. Adding small particles such as metallic or metal oxide particles with high conductivity in micro and nano sizes to the heat transfer fluids such as water, ethylene glycol, and oils is an effective method for heat transfer enhancement [1,2,3].
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