Investigation Of Heat Transfer Fluid In Internally Ribbed Tubes

Hydrodynamics and convective heat transfer characteristics of heat transfer fluid in the internally ribbed(rifled)tube,which is widely used in solar power technologies,are measured and simulated by means of computational fluid dynamics(CFD).Therminol 66 liquid phase heat transfer fluid is used as heat transfer fluid,and the single-head internally ribbed tube with the outer diameters of 25.0 and 19.0 mm,and the four-head internally ribbed tube with the outer diameter of 28.8 mm are used for heat transfer tube.The convective heat transfer and flow behavior of Therminol heat transfer fluid are measured.Based on heat transfer theory and fluid dynamics,the flow behavior and heat transfer are simulated using CFD method.The enhancement of heat transfer in the internally ribbed tube is analyzed.The experimental equipment and measurements are established to test the heat transfer and hydrodynamics of Therminol heat transfer fluid 66 in the smooth tube with the outer diameter of 19.0 mm.The convective heat transfer coefficient and friction factor of Therminol heat transfer fluid are measured in the smooth tube.The comparison of measurements and calculations using empirical correlations shows that the measured heat transfer coefficients are in agreement with calculations.This indicates the measuring system and statistical method for data are acceptable and credible.The convective heat transfer coefficient and frictional factor of Therminol heat transfer fluid 66 are measured in the single-head internally ribbed(rifled)tubes with the outer diameters of 19.0 and 25.0 mm.Experimental measurements show that the measured friction factor in the internally ribbed tube 19.0 mm increases by 1.8 to 4.0 times comparing to the smooth tube.Compared to heat transfer in the smooth tube,the measured heat transfer in the internally ribbed tube 19.0 mm increases by 1.8 to 4.6 times.Experimental results show that the heat transfer and thermal performance of Therminol 66 heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number is from 1.7 to 4.7 times over the smooth tube.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 1.9 and 3.2 times over the smooth tube.The empirical correlations for convective heat transfer coefficient and frictional facto r are proposed on the basis of experimental measurements.The convective heat transfer coefficient and frictional factor of Therminol heat transfer fluid 66 are measured in the four-head internally ribbed(rifled)tube with the outer diameter of 28.8 mm.C omparing to the smooth tube,the measured friction factor in the four-head ribbed tube increases by 1.3 to 1.9 times.The measured heat transfer increases by 1.05 to 1.67 times compared to heat transfer in the smooth tube.The correlations of Nu number and friction factor are proposed on the basis of experimental data.Heat transfer coefficient and friction factor of Therminol heat transfer fluid 66 are simulated in an internally ribbed(rifled)tube by means of computational fluid dynamics using five different turbulence models.The distributions of velocity and temperature are predicted as a function of Reynolds number.Simulated results show that the vortexes formed enhance heat transfer by the reduction of heat transfer resistance.The flow direction by ribs will result in the formation of centrifugal force which will effect on heat transfer and pressure drop.Comparing to four-head ribbed tube,the single-head ribbed tube provide high performance of convective heat transfer and low friction factor of Therminol heat transfer fluid 66.More ribs will give high pressure drop and low heat transfer due to the vortex formed within the ribs.Thus,the single-head ribbed tube is recommended in applications of solar heatersThe effect of rib height,pitch and rib width on heat transfer and friction factor of Therminol heat transfer fluid 66 is discussed based on CFD.The convective heat transfer is reduced with the decrease of rib heights.The simulated thermal enhancement factor and synergy angle decrease first,and then increase with the decrease of rib height.The heat transfer decreases with the increase of rib pitches.Simulations prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.Comparing experimental results and simulations using laminar flow model,RNG k-? model,realizable k-? model and shear-stress transport(SST)k-? model,k-kl-? transition model and transition SST model,respectively,The SST k-? model is recommended to predict heat transfer of Therminol heat transfer fluid in internally ribbed tube.The transition k-kl-? model is suitable in the predictions from laminar flow to turbulent flow of Therminol heat transfer fluid in ribbed tube.From experiments and simulations,the design of fluid heater using Therminol heat transfer fluid is performed.T he effect of plates on flow behavior is discussed in water-Therminol heat transfer fluid heater.The performance of water-Therminol heat transfer fluid heater is investigated by the optimum of configuration of plates for applications of solar power.The op timized flow field improves heat transfer,and can be utilized in development of heat transfer enhancement in the solar heaters.