On The Rheological Properties And Transport Behaviors Of Polymer Aqueous Solutions And Nanofluids

The fluid pipeline transportation systems are inherently encountered in every area of our life.They play an increasingly pivotal role in the construction and development of the industrial and civil infrastructure in our country.The development of a new generation heat exchanger featured with low pump power consumption and high energy transport efficiency is the key to improve the capability of the existing fluid pipeline transportation systems.This could be realized by,for instance,using the non-Newtonian fluids with drag reduction properties such as polymer and surfactant in turbulent pipe flow and nanofluids characteristics with excellent energy transport performance.It is seen that the extensive studies have been conducted on the thermo-physical property,fluid flow,and heat transfer behaviors of polymer aqueous solutions and nanofluids from both theoretical and practical engineering standpoint.Nevertheless,the rheological properties of non-Newtonian fluids with low concentrations,to the best of our knowledge,have not been assessed or understood and this motives the presented experimental investigation.The aim here is to focus on the rheological properties and energy transfer performance of non-Newtonian fluids revealing the principles of fluid mechanics and mass and heat transfer.It provides some references for the design of the multifarious heat transfer components and modern fluid pipeline transportation systems.The presented work investigates the rheological characteristics of polymers solutions(CMC,XG,PEO)and two kinds of nanofluids(MWCNT,TiO2)with different concentrations using an accurate rotational rheometer.Based on the theory of non-Newtonian fluid mechanics,the effects of shear rate,concentration,and temperature on the viscosity and other rheological behavior of non-Newtonian fluids are examined and analyzed in detail.At the same time,shear degradation,flow and mass transfer characteristics of polymer solutions are explored as well.To obtain the reproducible and reliable experimental results of the viscosity and thixotropic properties for low concentrated nanofluids,an improved 3ITT experimental test method is proposed,which effectively expands the range of low testing shear rates.With the analysis of the viscosity-temperature characteristics of water-based MWCNT nanofluids,the addition of refrigerants could effectively and controllably solve the problem of viscosity hysteresis for high concentrated nanofluids.Based on the experimental data,the dependency of the relative viscosity of the nanofluids on shear rate,temperature,and solid volume fraction is obtained and a new and accurate correlation is developed for engineering application.Besides,a critical point quantifying the transition from Newtonian to non-Newtonian is obtained for nanofluid containing MWCNT and this critical concentration is independent of temperature.The drag reduction and mass transfer characteristics of polymer fluids such as XG and CMC under laminar pulsatile flow have been investigated.The experiment setup is established based on five types of wavy-walled tubes.The influences of geometric parameters of the wave wall tube as well as operating conditions on the mass transfer performance are analyzed using particle image velocimetry(PIV)flow field visualization technology.It is found that XG solution with more prominent visco-elastic rheological behavior exhibits superior drag reduction effect and there is an optimal drag reduction concentration.The increasing concentration makes the mass transfer performance degradation of CMC solutions.However,the mass transfer rate could be improved by the increasing amplitude of wavy-walled tubes in pulsating flow.The presence of reverse flow promotes the mass transfer and they are mostly distributed in the deceleration regime in one pulsating cycle.An optimal oscillatory fraction corresponding to the highest mass transfer enhancement is obtained.To investigate the effect of MWCNT nanofluid on the shear degradation of the PEO solution,the drag reduction effect in turbulent flow for the PEO solutions with a low concentration and polymer-based nanofluid are evaluated using a double-gap geometry rotational rheometer.The experimental data have proved that the optimal drag reduction concentration of the PEO solution is 50 ppm and the addition of 0.0047%MWCNT-water nanofluid significantly improves the drag reduction performance as well as the shear resistance for the 50 ppm PEO solution at 25?.Furthermore,the absence of viscosity hysteresis in the polymer-based nanofluids implies that the addition of polymer strengthens the suspension stability of MWCNT nanofluids.As a result,the applicable temperature range of MWCNT nanofluids has been expanded.Based on the above analysis,it can be concluded that polymer-based nanofluid as a new heat exchanger working medium has considerable practical application value in the heat and mass transfer fields.