CHAPTER-5CONCLUSIONSIn this study, heat transfer enhancement in a heat exchanger with the tube wall inserts has been investigated experimentally with four working fluids namely (40:60) Ethylene Glycol/Water and three different volume concentrations of (40:60) Ethylene Glycol/Water based Fe2O3 nanofluids. It is found that the presence of Fe2O3 nanoparticle in (40:60) Ethylene Glycol/Water can enhance the heat transfer rate.
The degree of the heat transfer enhancement depends on the quantity of nanoparticles added to the base fluid. The inlet temperature was maintained constant at 70°C, and water flow rate was kept constant, and volume flow rate of nanofluids was varied. The experiment was carried out with volume concentrations of 0.
05, 0.1 and 0.2% iron oxide in 40:60 mixture of ethylene glycol-water base fluid.
The variation of Nusselt Number, Reynolds Number and percentage increase in Nusselt Number, Overall heat transfer coefficient and heat transfer with various volume concentrations of nanofluids were evaluated.5.1 CONCLUSIONS:The thermal characteristics of nanofluids were experimentally studied, and the following conclusions were drawn:i) The heat transfer coefficient of experimental data for the base fluid show good agreement with the Dittus-Boelter equation, and that of nanofluid shows good agreement with Pak and Cho equation.ii) The Overall heat transfer coefficient has increased with the increasing volume concentration of nanofluids. Hence heat transfer also increased accordingly. At 70°C inlet temperature and 15 LPM, the overall heat transfer coefficient and heat transfer rate were increased to 593 W/m2K and 2420 W respectively.
iii) The Nusselt Number showed an increasing trend with increasing volume concentration (up to 0.2%) of the nanoparticle. It is due to increase in heat transfer coefficient and Brownian movement.
At 70°C inlet temperature and 15 LPM, Nusselt Number increased 285 when volume concentration of nanoparticle increased up to 0.2%. iv) It seems that the increase in the effective thermal conductivity and the variations of the other physical properties are not solely responsible for the significant heat transfer enhancement. Brownian motion of nanoparticles maybe one of the major factors in the enhancement of heat transfers.
The presence of nanoparticles and their random motion within the base fluid causes the thinning of the thermal boundary layer, and it has important, contributions to such heat transfer improvement.v) The Pressure drop also increased the flow rate as well as with the increase in concentrations of nanofluids. Another major reason for the increase is the tube wall inserts which increase the turbulence and hence leading to increment in pressure drop.5.2 SCOPE OF FUTURE WORK:The present work was conducted to understand the heat transfer enhancement in the heat exchanger with the tube wall inserts using Fe2O3/Ethylene Glycol-Water (40:60) nanofluids. For further research understanding, the following suggestions can be considered:i) The experiment can be carried out with other types of nanoparticle-like Alumina, CuO, SiO2, ZnO, etc.
ii) The optimum heat transfer rate can be found at by increasing the concentration of Fe2O3 nanoparticle above 0.2% by volume and keeping a balance on friction factor.iii) The twisted tapes twist ratio can be varied to balance the heat transfer and pressure drop.iv) Other shapes of fins (trapezoidal, parabolic, pin fins, etc.) as well as its dimensions can be varied and experimentally checked for the enhancements in heat transfer characteristics.v) The numerical analysis can be done and can be compared with the experimental results.