Helical Screw-tape Inserts Research Articles

Comparative Study on Heat Transfer Enhancement of Low Volume Concentration of Al2o3–Water and Carbon Nano-Tube–Water Nano-Fluids in Transition Regime Using Helical Screw Tape Inserts

This study reports the comparison of heat transfer and friction factor characteristics of helical screw inserts in Al2O3–water and carbon nano-tube–water nano-fluids through a straight pipe in transition regime with constant heat flux boundary condition. Experiments were carried out by using 0.15% volume concentration of Al2O3–water and carbon nano-tube–water nano-fluid with helical tape inserts of twist ratio, TR = 1.5, 2.5, and 3. The thermal performance of helical screw tape inserts with the carbon nano-tube–water nano-fluid is found -to be higher when compared to the Al2O3–water nano-fluid. In addition, the maximum enhancement in heat transfer was obtained for the carbon nano-tube–water nano-fluid with helical tape inserts of twist ratio 1.5. The increase in pressure drop of the Al2O3–water nano-fluid with helical screw tape inserts is found to be higher compared to the carbon nano-tube–water nano-fluid helical screw tape inserts at lower value of twist ratio.

Laminar heat transfer and friction factor characteristics of carbon nano tube/water nanofluids.

This paper presents an experimental investigation on the convective heat transfer and friction factor characteristics of CNT/water nanofluid through a circular tube fitted with helical screw tape inserts with constant heat flux under laminar flow condition. Nanofluids of 0.1% and 0.2% volume fractions are prepared by two step method. Thermo-physical properties like thermal conductivity and viscosity are measured by using KD2 thermal property analyzer and Brooke field cone and plate viscometer respectively. From the measurements, it is found that the viscosity increase is substantially higher than the increase in the thermal conductivity. The helical screw tape insets with twist ratios Y = 3, 2.44 and 1.78 are used to study the convective heat transfer and friction factor characteristics under laminar flow in the Reynolds number range of 520-2500. It is observed that, in a plain tube, maximum enhancement in Nusselt number for 0.1% and 0.2% volume fractions of nanofluids compared to pure water is 15% and 32% respectively. With the use of inserts, maximum enhancement in Nusselt number corresponding to twist ratios of 1.78, 2.44 and 3 are obtained as 8%, 16% and 4.6% for 0.1% volume fraction of nanofluid and 5%, 4% and 12% for 0.2% volume fraction of nanofluid when compared with water in plain tube. Thermal performance factor evaluation revealed that the values at all Reynolds number for all twist ratios and both concentration of CNT nanofluid are greater than unity which indicates that helical screw tape inserts with twist ratios considered are feasible in terms of energy saving in laminar flow.

Mixing performances of swirl flow and corrugated channel reactors

Four different geometrical solutions for tubular reactors are compared for transfer intensification in fluid processes: (1) a compact multi-tube with helical screw-tape inserts, (2) a plain corrugated channel with a smooth bend curvature, called “wavy channel”, (3) a plain corrugated channel with a herringbone pattern, called “zigzag channel”, and (4) a plain straight pipe serving as the reference case. The single-phase mixing abilities of these four devices are compared by the chemical probe method (Villermaux/Dushman iodide/iodate system) for a range of main-flow Reynolds numbers between 100 and 4000. The chemical probe method is used here to investigate the global mixing time in the entire reactor volume, as deduced from the segregation index by a phenomenological model. Experimental results reveal better mixing performance and reduced energy expenditures in the helical-insert tube, in both the laminar and turbulent regimes.

Comparative Study on Heat Transfer Enhancement of Low Volume Concentration of Al2O3–Water and Carbon Nanotube–Water Nanofluids in Laminar Regime Using Helical Screw Tape Inserts

An experimental study has been carried out to evaluate the heat transfer and friction factor characteristics of helical screw inserts in Al2O3–water and carbon nanotubes (CNT)–water nanofluids through a straight pipe in laminar flow regime with constant heat flux boundary condition. Tests have been performed by using 0.15% volume concentration Al2O3–water and CNT–water nanofluid with helical tape inserts of twist ratio (TR) = 1.5, 2.5, and 3. The helical screw tape inserts with CNT–water nanofluid exhibits higher thermal performance compared to Al2O3–water nanofluid. The maximum enhancement in heat transfer was obtained for CNT–water nanofluid with helical tape inserts of TR = 1.5. The increase in pressure drop of Al2O3–water nanofluid with helical screw tape inserts is found to be higher compared to CNT–water nanofluid with helical screw tape inserts at lower value of TR. For both the nanofluids (CNT–water and Al2O3–water), the thermal performance factor was found to be greater than unity for all TRs.

THERMOHYDRAULICS OF LAMINAR FLOW THROUGH A CIRCULAR TUBE HAVING INTEGRAL HELICAL CORRUGATIONS AND FITTED WITH HELICAL SCREW-TAPE INSERT

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral helical corrugations and fitted with a helical screw-tape insert are presented. Predictive friction factor and Nusselt number correlations are also presented. The thermohydraulic performance was evaluated. The major findings of this experimental investigation are that the helical screw-tape insert in combination with integral helical corrugations performs significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of the fin parameter. This research finding is useful in designing tubes carrying solar thermal mass of viscous oil in a parabolic trough solar collector used in environmentally sound and increasingly cost-effective solar thermal electric power plants. The result is also useful in designing heat exchangers used in process industries.

Numerical studies on heat transfer and friction factor characteristics of a tube fitted with helical screw-tape without core-rod inserts

The principle of heat transfer enhancement in the core flow of tube has been proposed to improve the temperature uniformity and reduce flow resistance, which is different from that of heat transfer enhancement in the boundary flow of tube. Helical screw-tape inserts with four different widths (w=7.5mm, 12mm, 15mm and 20mm) have been investigated for different inlet volume-flow rates ranging from 200L/h to 500L/h. A three-dimensional turbulence analysis of heat transfer and fluid flow is performed by numerical simulation. The simulation results show that the average overall heat transfer coefficients in circular plain tubes are enhanced with helical screw-tape of different widths by as much as 212∼351% at a constant tube-side temperature and the friction factor are enhanced by as much as 33% to 1020%. The PEC value of the helical screw-tape inserts of different width varies between 1.58 and 2.35. Physical quantity synergy analysis is performed to investigate the mechanism of heat transfer enhancement. The synergy angles α, β, γ, θ and η are calculated, and the numerical results verify the synergy regulation among physical quantities of fluid particle in the flow field of convective heat transfer, which can guide the optimum design for better heat transfer units and high-efficiency heat exchangers. Entropy generation analysis is also performed to explain how to get the optimum helical screw-tape.

Enhancement of heat transfer of laminar flow of viscous oil through a circular tube having integral helical rib roughness and fitted with helical screw-tapes

The experimental friction factor and Nusselt number data for laminar flow of viscous oil through a circular duct having integral helical rib roughness and fitted with helical screw-tape insert have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts in combination with integral helical rib roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of fin parameter.

Laminar Flow Heat Transfer and Pressure Drop in a Circular Tube Having Wire-Coil and Helical Screw-Tape Inserts

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having wire-coil and helical screw-tape inserts have been presented. Peripherally and axially local temperatures on the duct outside wall have been measured. The temperature drop across the duct wall has been calculated to obtain the duct inside wall temperatures. Peripherally averaged and axially local temperatures have been used to get axially local Nusselt numbers. These axially local Nusselt numbers have been averaged over the whole length of the duct to get the mean Nusselt number. Predictive friction factor and Nusselt number correlations developed by log-regression analysis have also been presented. Nusselt number correlation takes care of the thermal development length represented by the Graetz number, swirl and inertia force due to forced convection at large Reynolds number, buoyancy force due to natural convection at low Reynolds number represented by Rayleigh number and the geometrical parameters of wire-coil and helical screw-tape inserts. The thermohydraulic performance has been evaluated. The helical screw-tape inserts in combination with wire-coil inserts perform better than the individual enhancement technique acting alone for laminar flow through a circular tube up to a certain value of fin parameter.

Laminar Flow Heat-Transfer Enhancement Using Transverse Ribs and Helical Screw-Tape Inserts

DOI: 10.2514/1.T3819 The experimental friction factor and axially averaged Nusselt number data have been presented for laminar flow throughacircularductthathasintegraltransverseribroughnessandhasbeen fittedwithhelicalscrew-tapeinserts. Peripherally local temperatures at several locations along the periphery of the duct have been measured. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts in combination with integral transverse rib roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of the fin parameter.

Friction and Thermal Characteristics of Laminar Flow of Viscous Oil Through a Circular Tube Having Axial Corrugations and Fitted With Helical Screw-Tape Inserts

The experimental friction factor and Nusselt number data for a laminar flow through a circular duct having axial corrugation and fitted with helical screw-tape inserts have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts, in combination with axial corrugation, perform better than the individual enhancement technique acting alone for laminar flow through a circular duct.

A comparison of thermal characteristics of Al2O3/water and CuO/water nanofluids in transition flow through a straight circular duct fitted with helical screw tape inserts

A comparison of thermal characteristics of Al2O3/water and CuO/water nanofluids in transition flow through a straight circular duct fitted with helical screw tape inserts was made in this study. The helical screw tape inserts with twist ratios Y=1.78, 2.44 and 3 were used in the experimental study using 0.1% volume concentration Al2O3/water and CuO/water nanofluid. The average enhancements in Nusselt number for water with twist ratios of 1.78, 2.44 and 3 were 156.24%, 122.16% and 89.22% respectively when compared to plain tube. The average increase in Nusselt number corresponding to the twist ratios of 1.78, 2.44 and 3 were 166.84%, 128.67% and 89.22% respectively for Al2O3/water nanofluid. In the case of CuO/water nanofluid, the enhancements in Nusselt number were 179.82%, 144.29% and 105.63% for twist ratios 1.78, 2.44 and 3 respectively. Thermal performance analysis based on the constant pumping power criteria shows that helical screw tape inserts give better thermal performance when used with CuO/water nanofluid than with Al2O3/water nanofluid.

Comparative study on thermal performance of helical screw tape inserts in laminar flow using Al 2O 3/water and CuO/water nanofluids

This paper presents a comparison of thermal performance of helical screw tape inserts in laminar flow of Al 2O 3/water and CuO/water nanofluids through a straight circular duct with constant heat flux boundary condition. The helical screw tape inserts with twist ratios Y = 1.78, 2.44 and 3 were used in the experimental study using 0.1% volume concentration Al 2O 3/water and CuO/water nanofluids. Nanofluids with required volume concentration of 0.1% were prepared by dispersing specified amounts of Al 2O 3 and CuO nanoparticles in deionised water. The performance analysis of helical screw tape inserts in laminar flow of Al 2O 3/water and CuO/water nanofluids is done by evaluating thermal performance factor for constant pumping power condition. Thermal performance factor of helical screw tape inserts using CuO/water nanofluid is found to be higher when compared with the corresponding value using Al 2O 3/water. Therefore, the helical screw tape inserts show better thermal performance when used with CuO/water nanofluid than with Al 2O 3/water nanofluid.

Heat transfer and friction factor inside elliptic tubes fitted with helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of elliptic tubes with different twist ratios (Y) and pitch ratios (S) has been conducted under laminar flow condition. All data are obtained using cold water flowing in the tube side and hot water flowing in the annuli side of the heat exchanger. The experiments covered a range of Reynolds numbers, 5.7×102≤Re≤1.31×103. Heat transfer and friction factor analyses are presented for different conditions of Re, S, and Y. The results indicate that the helical screw element of different Y and S has an effect on the results of heat transfer coefficient and friction factor. The averaged Nusslet number (Nu) increases with an increase in Re and it decreases with an increase in Y and S. For a fixed Reynolds number, the friction factor (f) increases with a decrease in Y and S for the elliptic tubes. The thermal performance factor (η) is introduced to indicate the percentage increase in Nu over the percentage increase in f. The maximum percentage increase in Nu over the percentage increase in f (maximum increase in η) is 19.7% and 42.3% at the values of S and Y equal to 1 and 0.22, respectively. Correlations of the average Nusselt number and friction factor with Re, S, and Y are presented.

Augmentation of laminar flow and heat transfer in flat tubes by means of helical screw-tape inserts

The heat transfer a characteristics and friction factor in the horizontal double pipes of flat tubes with full length helical screw element of different twist ratio and helical screw inserts with different spacer length are investigated. Cold and hot water are used as working fluid in tube side and shell side respectively. The experiments covered a range of Reynolds numbers 5.7 × 10 2 ⩽ Re ⩽ 1.31 × 10 3. The effect of spacer length on the heat transfer augmentation and friction factor and the effect of twist ratio on heat transfer augmentation and friction factor have been presented separately. The study shows that, the Nusslet number (Nu) and friction factor ( f) decrease with the increase of S or Y for flat tube. The comparison between the data of present plain circular with that of previous plain circular tube showed a good agreement between them but the data of present plain flat tube showed a higher in heat transfer and pressure drop than that of plain circular tube. The correlations of average Nusselt number and friction factor with Re, S and Y are presented.

Numerical investigations of circular tube fitted with helical screw-tape inserts from the viewpoint of field synergy principle

3-D numerical simulations are performed for heat transfer and fluid flow characteristics of the tubes fitted with helical screw-tape inserts. The comparison between the RNG k-epsilon turbulence model and the SST k-omega turbulence model in prediction of swirling flow shows that the latter has better qualitative and quantitative agreements with the experimental results than the former. The simulation results show that the novel helical inserts with right and left twists alternately have better heat transfer performance than that of the helical inserts with uniformly right twists. The simulation results are analyzed from the viewpoint of field synergy principle, it is found that the principle could explain well the mechanism of heat transfer enhancement of the helical twist inserts. The smaller the mean intersection angle between the temperature gradient and velocity vector, the larger the Nusselt number; in addition, the smaller local intersection angle also implies the higher local heat transfer coefficient.

Studies on heat transfer and friction factor characteristics of laminar flow through a circular tube fitted with right and left helical screw-tape inserts

Experimental investigation on heat transfer and friction factor characteristics of circular tube fitted with right-left helical screw inserts of equal length, and unequal length of different twist ratio have been presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer coefficient enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left helical twist length on heat transfer and friction factor were presented. The empirical relation for Nusselt number, friction relating Reynolds number, twist ratio and right-left distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor, respectively. Performance evaluation analysis has been made and the maximum performance ratio of 2.85 and 2.97, respectively were obtained for 300 R and 300 L, and 400 R and 200 L type inserts.

Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with regularly spaced helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and helical screw inserts with spacer length 100, 200, 300, and 400 mm have been studied with uniform heat flux under turbulent flow condition. The experimental data obtained are verified with those obtained from plain tube published data. The effect of spacer length on heat transfer augmentation and friction factor, and the effect of twist ratio on heat transfer augmentation and friction factor have been presented separately. The decrease in Nusselt number for the helical twist with spacer length is within 10% for each subsequent 100 mm increase in spacer length. The friction factor for helical twist insert with spacer length 100 mm is very much close to value of friction factor for full-length helical twist for all Reynolds number and decreases by 5% for each 100 mm increment space length indicating that there is no much reduction in pumping power. Hence the helical screw inserts with spacer can only be used for heat augmentation only in turbulent flow with less reduction in pumping power. Empirical correlation were formed for explaining data and found to fit experimental data within ±10%, and ±20%, respectively, for Nusselt number and friction factor.

Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and increasing and decreasing order of twist ratio set have been studied with uniform heat flux under turbulent flow conditions. The Reynolds number was varied from 2700 to 13 500. The experimental data obtained are compared with those obtained from plain tube published data. The maximum Nusselt number for the twist of 1.95 was obtained. The performance of the helical twist insert was compared with the twisted tape performance reported in the literature and found that it is better than twisted tape performance. The heat transfer augmentation for helical twist of increasing and decreasing order twist were also presented. The empirical correlations developed relating twist ratio and Reynolds number, are fitting the experimental data within ±13% and ±15% for Nusselt number and friction factor, respectively. The performance evaluation study has been presented to check the potential of using the helical twist insert.

Experimental studies on heat transfer and friction factor characteristics of laminar flow through a circular tube fitted with regularly spaced helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and helical screw inserts with spacer length 100, 200, 300 and 400 mm have been studied with uniform heat flux under laminar flow condition. The experimental data obtained are verified with those obtained from plain tube published data. The effect of spacer length on heat transfer augmentation and friction factor, and the effect of twist ratio on heat transfer augmentation and friction factor have been presented separately. The decrease in Nusselt number for the helical twist with spacer length is within 10% for each subsequent 100 mm increase in spacer length. The decrease in friction factor is nearly two times lower than the full length helical twist at low Reynolds number, and four times lower than the full length helical twist at high Reynolds number for all twist ratio. The regularly spaced helical screw inserts can safely be used for heat transfer augmentation without much increase in pressure drop than full length helical screw inserts.

Experimental studies on heat transfer and friction factor characteristics of laminar flow through a circular tube fitted with helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and increasing and decreasing order of twist ratio set have been studied with uniform heat flux. The experimental data obtained are compared with those obtained from plain tube published data. The heat transfer coefficient increases with twist ratio. There is no much change in the magnitude of heat transfer coefficient enhancement with increasing twist ratio and with decreasing twist ratio set, as the magnitude of swirl generated at the inlet or at the outlet in the order of increasing twist ratio or decreasing twist ratio, is same in both the cases. The empirical correlations developed in terms of twist ratio and Reynolds number, are fitting the experimental data within plus or minus 15% and 13% for Nusselt number and friction factor, respectively.