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Nanofluid Heat Transfer in Tubes with Wires

The research was conducted at Tehran University under supervision of Dr akhavan and Dr Sedaghat.

Nanofluid Heat Transfer in Tubes with Wires

Ali Akbar Shamshiri

In this work, an experimental study is carried out to investigate the effect of adding MWCNT nanoparticles to the heat transfer oil on flow heat transfer and pressure drop characteristics. Thanks to many studies is performed in recent two decays on nanofluids, investigate on usage of nanofluids heat transfer is in preliminary stage and it is necessary to known mechanisms of increase in heat transfer and complete the present studies. The other technique usually have been used for increase in heat transfer is use of inserted devices tube such as wire coils. They show several advantages in relation to other enhancement techniques such as Low cost and Easy installation and removal. The experiments are done for pure base oil and nanofluids flow inside plain tube and wire coil inserted tubes on constant wall temperature boundary condition in laminar flow and low Reynolds number in turbulent region. To reach constant wall temperature, entire test section is surrounded by saturated vapor. The flow is considered hydrodynamically developed, but thermally developing so it is in thermal entrance region in laminar flow. Heat transfer oil (HT-B) and MWCNT- Heat transfer oil nanofluids with weight concentrations of 0.1, 0.2 and 0.4% are considered as the working fluids. The experimental study was carried out on six test sections including a circular tube with 1500 mm length, 14.5 mm inner diameter and 15.6 mm outer diameter and five wire coils fitted in the plain tube within a geometrical range of helical pitch 1.12 < p/d < 2.79 and wire diameter 0.069 < e/d < 0.097. Base fluid and nanofluids characteristics like density, viscosity, thermal conductivity coefficient and specific heat capacity have been measured by means of accurate apparatuses. The experimental measurements showed that adding nanoparticles to the base fluid would lead to the increase in density, thermal conductivity and viscosity of the base liquid, but specific heat capacity decreases as nanoparticle concentration increases. The maximum increasing of the value of thermal conductivity up to 15.3% is achieved for nanofluid with the highest concentration. The experimental results of the convective heat transfer of flow inside plain tube and wire coil inserted tubes showed that by increasing the flow rate and nanoparticles concentration, the convective heat transfer coefficient is increased. The maximum enhancement of convective heat transfer coefficient of up to 73% and 1014% are obtained for the nanofluid flow with 0.4% wt. concentration for plain tube and wire coil inserted tube, respectively. On the other hand, results obtained for pressure drop in plain tube and wire coil inserted tubes showed that the pressure drop was enhanced by increasing the flow rate and nanoparticles concentration. Furthermore, the performance evaluation of the two enhanced heat transfer techniques studied in this investigation showed that dilute nanofluids have better efficiency.

Keywords: nanofluid, heat transfer, pressure drop, constant temperature and wire coil inserts.

 

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