Helical Tape Inserts Research Articles

Experimental analysis of W/EG based Al2O3-MWCNT non-Newtonian hybrid nanofluid by employing helical tape inserts inside a corrugated tube

Experimental analyses have been undertaken on friction factors and convective heat transfer using a helically corrugated tube (HCT) equipped with inserts, under laminar flow conditions. Water-ethylene glycol mixture with Al2O3-MWCNT hybrid nanofluids has been employed. The investigation focused on examining the synergistic effects of hybrid nanofluids, triangularly helical tape (THT) inserts and helical corrugation within the tubes on the friction factor, Nusselt number, and thermal performance factor (TPF). The fluid displayed non-Newtonian behaviour at volume fractions greater than 0.1 %. The study indicated that augmenting the concentration of Al2O3-MWCNT in the hybrid nanofluid and decreasing the helix ratio of the THT inserts led to increased heat transfer rates and TPF. The peak TPF of 2.31 was recorded when using the W/EG based Al2O3-MWCNT hybrid nanofluid with a 1 % volume fraction in an HCT equipped with THT inserts with a helix ratio of 2 at a Reynolds number of 2000. Moreover, Al2O3-MWCNT exhibits an average Nusselt number of 42.5 %, 49.47 %, and 56.2 % higher than the base fluid at φ = 0.1 %, 0.5 %, and 1 %, respectively.

Analysis of numerical and grey relation method of the effect of helical tape insert density on the hydrothermal performance

In this study, the hydrothermal performance of the Double pipe heat exchangers(DPHEs) with a continuous and variable helical tape insert(HTI) conducted on the outer surface of the inner pipe was numerically investigated by using the generated three-dimensional(3D) computational fluid dynamics(CFD) models. The numerical analyzes were performed under variable pitch ratios (0.167≤λ≤0.500), annulus side Prandtl number(Pr) (5.9≤Pran≤7.8) and Reynolds numbers(Re) (4200≤Rean≤16000) conditions. The numerical model was first validated for the conventional equal HTI DPHE model by comparison with experimental data obtained from the literature and empirical correlations. The validated model was then used to determine the effects of the variable HTI on the outer surface of the inner pipe. The relationship between the Nusselt number(Nu) and Darcy friction factor(f) was examined by using Grey Relation Analysis(GRA) method. The using of the denser HTIs on the tube side inlet region increases Nu about 9% compared with the conventional model. The f values of the models with variable HTI densities were calculated as higher than the Equal model under all Re conditions. The obtained results from the GRA method, conventional Equal model can be used for low Re, but the Inlet model can be preferred for 14000 and above Re conditions.

Thermohydraulic performance and second law analysis of a tube embedded with multiple helical tape inserts

ABSTRACT The present investigation deals with the analysis of the heat exchanger tube by inserting the multiple helical tape geometry to determine the heat transfer, friction factor, thermal performance, and entropy generation experimentally. The helical tapes designed for current investigation are analyzed in terms of geometrical parameters namely number of tape (1,2,3), twist ratio (2,3,4), and width ratio (0.4). The experiments are conducted in the range of Reynolds number lying in turbulent region from 5000 to 29000. The experimentation affirms an enhancement of the thermal performance. The experimental data reveal that there is 3.95 times enhancement in the heat transfer for twist ratio of 2 and number of tapes of 3. The thermal performance factor is enhanced by 1.23 times over smooth tube for the twist ratio of 2 and number of tapes of 1. It is observed that the maximum heat transfer enhancement is found for low and high values of twist ratio and number of tapes, respectively. The rate of entropy generation is less for the tube equipped with helical tape inserts for all possible cases than smooth tube. The minimum entropy generation value of 0.27 is observed for twist ratio of 2 and number of tapes 3. The developed empirical correlations for Nusselt number, friction factor, and thermal performance factor are in good agreement with experimental results.

Convection Heat Transfer and Friction Factor of AL2O3/ Water Nanofluid Flows inside Circular Tube with Inserting Helical Tape.(Dept.M)

Forced convection heat transfer and friction factor for nanofluid flows inside circular horizontal tube with and without inserting helical tape, was experimentally studied. Electric heater was wrapped around the outer surface of the tube to obtain a constant and uniform heat flux at the tube wall. Experiments are conducted with adding nano-particles (AI2O3) to water up 10, 2% by volume 10 obtain diffrerent concentrations of nanonfluids. An experimental test loop equipped with the required measuring instruments was designed and constructed to assess the effects of nano-particles concentration, mass flow rate, and applied heat flux on the convection heal transfer process and pressure drop. The tested tube fitted with screw helical tape inserts to evaluate its effects on heal transfer rate and friction factor with nanofluid as the working fluid compared with pure water. The measurements of temperature, now rate, applied volt and pressure drop are recorded and manipulated to calculate the convection heat transfer coefficient and friction factor. The obtained experimental results show that, wall temperature was reduced by using nanofluid compared with pure water. Accordingly. the convection heal transfer coefficient;' increased when using nanofluid and increased also with increasing heat flux and mass now rate (Reynolds number). Higher rates of heat transfer and pressure drop are obtained from the tube fitted with screw helical tape insert compared to flow in a plain/tube under similar conditions. This improvement in the heat transfer coefficient characterized by a swirling flow as a result of the secondary flow of the fluid flow inside tube with helical tape. The average value for the thermal-hydraulic performance(ŋ) for tube with inserting helical tape was 1.4 for water only , and 1.8 for nanofluid at concentration 0.8% comparison with the previous work gave good agreement.

Heat and Fluid Flow in a Tube with Helical Tape around Rod (Dept.M)

Forced convective heat transfer and friction factor for nanofluid flows inside circular horizontal tube with inserting helical tape, is experimentally studied. Electric heater is wrapped around the outer surface of the tube to obtain a constant and uniform heat flux at the tube wall. Experiments are conducted with adding nano-particles (Al2O3) to water up to 0.35% by volume to obtain different concentrations of nanofluids. An experimental test loop equipped with the required measuring instruments was designed and constructed to assess the effects of nano-particles concentration, mass flow rate, and applied heat flux on the convection heat transfer process and pressure drop. The tested tube fitted with screw helical tape inserts to evaluate its effects on heat transfer rate and friction factor with nanofluid and pure water as a working fluid. The measurements of temperature, flow rate, applied volt and pressure drop are recorded and manipulated to calculate the convective heat transfer coefficient and friction factor. The obtained experimental results show that, wall temp erature is reduced by using nanofluid compared with pure water. Accordingly, the convection heat transfer coefficient increased when using nanofluid and it also increased with increasing heat flux and mass flow rate (Reynolds number). Higher rates of heat transfer and pressure drop are obtained from the tube fitted with screw helical tape insert compared to flow in a plain tube under similar conditions. This imp rovement in the convection heat transfer coefficient characterized by a swirling flow as a result of the secondary flow of the fluid flow inside tube with helical tape and the area of the tape inserted. The average value for the thermal hydraulic performance (ŋ) for tube with inserting helical tape was 1.4 for water only, and 1.8 for nanofluid at concentration 0.2%. Comparison with the previous work shows fairly agreement. A correlation is obtained between Nusselt number and op erating parameter.

Parametric study on the heat transfer characteristics in a circular tube with helical tape insert under laminar flow conditions

AbstractIn the present study, the effect of a helical coiled tape on the heat transfer characteristics in a tubular heat exchanger has been studied. Numerical analysis is carried out in a tubular heat exchanger with a helical coiled tape insert under laminar flow conditions. The heat transfer characteristics, like Nusselt number (Nu) and friction factor (f), have been determined. Numerical modeling is undertaken and validated using analytical results. To study the parametric variation, simulation is carried out for different width ratios (WR) and twist ratios (TRs). It is observed that Nu increases as the WR is increased and the TR is reduced. The thermohydraulic performance index (THPI) is measured and found to be higher for a combination of a higher WR and a higher TR. From the tested values, it is seen that for a combination of WR = 3 and TR = 1.25, the maximum THPI was observed. It is concluded that both the tape width and pitch will significantly influence the thermohydraulic characteristics in a tubular heat exchanger with a helical tape insert inserted.

Evaluation of velocity distribution utilizing the helically coiled tape in a conical diffuser

Numerical analyses study is reported on the flow characteristics in a conical diffuser with a helical tape insert. In this study, a rectangular tape of 5 mm width and 2 mm thickness is used inside the inner wall of the diffuser to induce additional recirculation. The numerical results are achieved for different Reynolds numbers (58035, 116072, 174108 and 232144) based on the inlet hydraulic diameter. The simulations are carried out with constant inlet condition considering the flow turbulent and incompressible. Air is used as a working fluid and maintained at constant room temperature. From a similar inlet condition, the results indicated that the velocity distribution is well enhanced.

Experimental investigation on the hydrothermal performance of a double-pipe heat exchanger using helical tape insert

This study experimentally examines the hydrothermal performance of horizontal Double Pipe Heat Exchangers (DPHEs) with and without continuous Helical Tape Insert (HTI) conducted on the outer surface of the internal pipe. Ten DPHEs of counter-flow configurations were constructed; nine of them were with HTI fabricated with different ratios of HTI height to the clearance between the two pipes (δ), and different ratios of HTI pitch to HTI diameter (λ). The experiments were performed with pure water in both sides with 2050≤Rean≤15925, and Ret≈26700. Compared with plain annulus-case, the results showed that using the HTI increases both annulus average Nusselt number (Nu¯an) and Fanning friction factor (fan), with average increases of 69.4–164.4% and 48.6–113.1%, respectively, when δ increases from 0.275 to 1, and with average increases of 78.1–183.2% and 67.6–99.2%, respectively, when λ decreases from 1 to 0.333. The hydrothermal performance index (HTPI) was determined to compare the performance of DPHEs with HTI to that of plain annulus case. The results demonstrated that HTI of δ = 0.667 provides the highest HTPI, while HTPI increases with decreasing λ. Finally, correlations for Nu¯an, fan, and HTPI for DPHEs with HTI in the annulus as a function of the investigated parameters were proposed.

Experimental Study on Laminar Forced Convection of Al2O3/Water and Multiwall Carbon Nanotubes/Water Nanofluid of Varied Particle Concentration with Helical Twisted Tape Inserts in Pipe Flow

ABSTRACTIn this study an experimental investigation has been carried out to analyze the laminar forced convection of Al2O3/water and multiwall carbon nanotubes (MWCNT)/water nanofluids through uniformly heated horizontal circular pipe with helical twisted tape inserts. Tests were conducted for varied range of nanoparticle volume concentration (0.15%, 0.45%, 0.60%, and 1%) and helical tape inserts of twist ratios of 1.5, 2.5, and 3. The heat transfer enhancement and the increase of friction factor of nanofluids with helical inserts are compared with that of pure water results with plain tube without inserts. The Nusselt number is found to increase with the increase in Peclet number and nanofluid concentration. The MWCNT/water nanofluids with helical screw tape inserts exhibits higher thermal performance compared to Al2O3/water nanofluid. The maximum thermal performance factor was found to be 1.79 and 1.99 for Al2O3/water and MWCNT/water nanofluids with helical twisted tape inserts, respectively. The pressure drop for Al2O3 nanofluid is found to be higher compared to the MWCNT nanofluid for all the twist ratio of helical screw tape inserts.

Heat transfer and nanofluid flow characteristics through a circular tube fitted with helical tape inserts

Numerical investigations are performed using finite volume method to study laminar convective heat transfer and nanofluids flows through a circular tube fitted with helical tape insert. The wall of tube was subjected to a uniform heat flux boundary condition. The continuity, momentum and energy equations are discretized and the SIMPLE algorithm scheme is applied to link the pressure and velocity fields inside the domain for plain tube. Four different twist ratios of 1.95–4.89, two different types of nanoparticles, Al2O3 and SiO2 with different nanoparticle shapes of spherical, cylindrical and platelets, and 0.5–2.0% volume fraction in base fluid (water) and nanoparticle diameter in the range of 20–50nm were used to identify their effect on the heat transfer and fluid flow characteristics through a circular tube fitted with helical tape insert geometries. The results indicate that the four types of nanofluid achieved higher Nusselt number than pure water. Nanofluid with Al2O3 particle achieved the highest Nusselt number. For all the cases studied, the Nusselt number increased with the increase of Reynolds number and with the decrease of twist ratio of helical tape insert.

Heat transfer performance evaluation and prediction of correlation for turbulent flow through a tube with helical tape inserts at higher Reynolds number

An experimental investigation was accomplished to evaluate the performance of heat transfer for turbulent flow through a tube with helical tape inserts. The mild steel helical tape inserts with different twist ratios of 1.88, 3.13, 4.69, 6.41 and 7.81 were used in the flow field. Heat transfer and pressure drop data were prompted for a wide range of Reynolds number from 7200 to 50,000. The experimental results indicated that the Nusselt number, friction factor and thermal performance factor were increased with decreasing twist ratio. The results also showed that helical tape inserts of different geometries in a circular tube enhanced the heat transfer rate significantly with corresponding increase in friction factor. Nusselt number and friction factor for the tube with inserts were found to be increased up to 260 and 285 %, respectively, than those over the plain tube values at the comparable Reynolds number. The heat transfer performance was evaluated and found to be 44 % higher compared to the plain tube based on the constant blower power. Finally, new correlations were proposed for the twist ratios ranging from 1.88 to 7.81 for predicting the heat transfer, friction factor and thermal performance factor for turbulent flow through a circular tube fitted with helical tape inserts.

Experimental study of heat transfer and friction factor of Al2O3 nanofluid in U-tube heat exchanger with helical tape inserts

Turbulent forced convection heat transfer and friction of Al2O3–water nanofluid flowing through a concentric tube U-bend heat exchanger with and without helical tape inserts in the inner tube were studied experimentally. The experiments were conducted in the Reynolds number range from 3000 to 30,000, volume concentrations of 0.01%, 0.03% and helical tape inserts of p/d=5, 10, 15 and 20. The results indicate that an increase in Reynolds number and Prandtl number yields to an increase in the average Nusselt number, and augmentation of thermal conductivity in the nanofluid contributes to heat transfer enhancement. The Nusselt number of entire pipes for 0.03% concentrations of nanofluid with helical tape inserts of p/d=5 shows an enhancement of 32.91%, as compared to water. The friction factor for the entire inner tube for 0.03% concentration of nanofluid with helical tape inserts of p/d=5 has increased by 1.38-times, as compared to water; in general and consistent with theory, the pressure drop in the inner tube increases with an increase in nanoparticle volume concentration and aspect ratio of the inserts. The empirical correlations for the Nusselt number and friction factor are obtained as functions of the Reynolds number, Prandtl number, volume concentration and aspect ratio.

Heat transfer and friction characteristics of Al2O3/water and CNT/water nanofluids in transition flow using helical screw tape inserts – a comparative study

The convective heat transfer characteristics of Al2O3/water and CNT/water nanofluids through uniformly heated horizontal circular tube in transition regime with helical twisted tape inserts are estimated experimentally. Tests were performed with varied range of particle volume concentration (0.15%, 0.45%, 0.60% and 1%) and helical tape inserts of twist ratio (TR)=1.5, 2.5 and 3. It is observed that the heat transfer performance of both the nanofluids increases with the increase in the particle volume fraction. The CNT/water nanofluids with helical screw tape inserts exhibits higher thermal performance compared to Al2O3/water nanofluid. The maximum enhancement in heat transfer was obtained by using CNT/water nanofluid (ϕ=1%) with helical tape inserts of twist ratio 1.5. For all the twist ratio of helical screw tape inserts the pressure drop for Al2O3 nanofluid with helical screw tape inserts is higher compared to the CNT nanofluid.

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.

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.

Numerical Investigation of Heat Transfer and Friction Factor Characteristics in a Circular Tube Fitted with V‐Cut Twisted Tape Inserts

Numerical investigation of the heat transfer and friction factor characteristics of a circular fitted with V-cut twisted tape (VCT) insert with twist ratio (y = 2.93) and different cut depths (w = 0.5, 1, and 1.5 cm) were studied for laminar flow using CFD package (FLUENT-6.3.26). The data obtained from plain tube were verified with the literature correlation to ensure the validation of simulation results. Classical twisted tape (CTT) with different twist ratios (y = 2.93, 3.91, 4.89) were also studied for comparison. The results show that the enhancement of heat transfer rate induced by the classical and V-cut twisted tape inserts increases with the Reynolds number and decreases with twist ratio. The results also revealed that the V-cut twisted tape with twist ratio y = 2.93 and cut depth w = 0.5 cm offered higher heat transfer rate with significant increases in friction factor than other tapes. In addition the results of V-cut twist tape compared with experimental and simulated data of right-left helical tape inserts (RLT), it is found that the V-cut twist tape offered better thermal contact between the surface and the fluid which ultimately leads to a high heat transfer coefficient. Consequently, 107% of maximum heat transfer was obtained by using this configuration.

Heat transfer performance for turbulent flow through a tube using double helical tape inserts

The augmentation of heat transfer for turbulent fluid flow through a tube by using double helical tape inserts was investigated experimentally in the present work. The effects of insertion of the helical tape turbulators with different helix angles (9°, 15°, 21° and 28°) on heat transfer and pressure drop in the tube for Reynolds number ranging from 22,000 to 51,000 were examined. Experimental results showed that the heat transfer and thermal performance of the inserted tube were significantly increased compared to those of the plain tube. The study showed the Nussselt number, friction factor as well as thermal enhancement efficiency were increased with decreasing helix angles under the same operating conditions. The results indicated that the Nusselt number and friction factor were increased up to 305% and 170%, respectively, than those over the plain tube while the maximum thermal performance was found to be 215% for using the double helical tape insert with helix angle 9° at high Reynolds number. Furthermore, correlations of the Nusselt number and friction factor were developed in terms of the helix angle (α), Reynolds number (Re) and Prandtl number (Pr) based on the experimental data.

Heat transfer enhancement and development of correlation for turbulent flow through a tube with triple helical tape inserts

Influence of triple helical tapes inserted for turbulent flow through a tube on heat transfer enhancement was studied experimentally. The triple helical tapes made of mild steel with different helix angles, α = 9°, 13°, 17°, and 21° were examined for Reynolds number ranging from 22,000 to 51,000. The experiment showed that the Nusselt number, effectiveness and friction factor for the inserts were found to be up to 4.5, 3.45 and 3.0 times, respectively, over the plain tube. The highest enhancement efficiency achieved was 3.7 for the inserts based on constant blower power. Finally, new correlations for predicting heat transfer and friction factor for turbulent flow through a circular tube fitted with the inserts were proposed.

Heat transfer behaviour of nanofluids in a uniformly heated circular tube fitted with helical inserts in laminar flow

The CFD simulation of heat transfer characteristics of a nanofluid in a circular tube fitted with helical twist inserts under constant heat flux has been explained using Fluent version 6.3.26 in laminar flow. Al 2O 3 nanoparticles in water of 0.5%, 1.0% and 1.5% concentrations and helical twist inserts of twist ratios 2.93, 3.91 and 4.89 has been used for the simulation. All thermophysical properties of nanofluids are temperature dependent. The heat transfer enhancement increases with Reynolds number and decreases with twist ratio with maximum for the twist ratio 2.93. By comparing the heat transfer rates of water and nanofluids, the increase in Nusselt number is 5%–31% for different helical inserts and different volume concentrations. The maximum heat transfer enhancement is 31.29% for helical insert of twist ratio 2.93 and for the volume concentration of 1.5% corresponding to the Reynolds number of 2039. The data obtained by simulation match with the literature value of water with the discrepancy of less than ±10% for plain tube and tube fitted with helical tape inserts for Nusselt number.

Study on the potential use of helical swirl generators in enhancing the thermal performance of solar air heaters

SYNOPSIS The thermal performance of a solar air heater may be enhanced by means of twisted tapes, inserted inside the fluid flow tubes, which induce swirl flow acting as turbulence promoters. Experiments were carried out to investigate the effect of helical tape inserts of two different twist ratios (23 and 11) on the friction factor and heat transfer coefficient for a flow in a circular tube maintained at uniform heat flux conditions. The data were recorded at low Reynolds numbers, well in the turbulent region, for a wide range, 8.05 × 103 − 1.36 × 104. The results confirm that this system with helical tape inserts could enhance heat transfer by about 1. 15 to 1.7 times compared to that of plain tube. Also, the study shows that higher heat transfer rates were recorded for lower twist ratios.