Helical Screw-tape Inserts Research Articles

Hydro-thermal characteristics of laminar flow through a square duct having transverse ribs and helical screw-tape inserts

The hydro-thermal characteristics of transverse ribs combined with helical screw tape inserts in square duct are numerically investigated and compared the numerical findings with very little available experimental results. Moreover, the experimental data is available only with circular duct. No other cross-sectioned duct has ever been investigated. The motivation and novelty of the present work is to fill this hiatus. Finite volume method-based solver, ANSYS Fluent has been used for simulation. The uniform heat flux boundary condition has been imposed and a wide range of Prandtl number with five different fluids has been used for this investigation. This is never ever possible in a single experimental programme. Only numerical simulation can do the job and this is the inherent beauty of the present investigation. The results of experimental and computational findings proved that the present configuration produces good mixing and enhanced boundary layer separation. The results of the effect of rib height, rib pitch and screw tape parameter on Nusselt number and friction factor are presented. The numerical investigation has shown that Servotherm oil is the best fluid. The Nusselt number is increasing with increase in rib height and Reynolds number and it is decreasing with increase in rib pitch and screw tape parameter value. Also, the friction factor is increasing with increase in rib height and Reynolds number but the increment in Nusselt number is larger than the increment in friction factor. Therefore, the present fin geometry is recommended for industrial use.

Experimental performance analysis of a parabolic trough solar air collector with helical-screw tape insert: A comparative study

Heat transfer improvement efforts in parabolic trough air collectors (PTAC) are long-sought and much anticipated by many researchers, however, alternative heat transfer improvement methods such as helical screw tape insert inside the receiver tube has yet to be experimentally investigated. Therefore, in this study, a dual-function PTAC for low-medium temperature applications was experimentally tested in an indoor environment to assess its thermal characteristics. To increase the heat transfer performance, a helical screw tape was inserted along the pathway of air flow inside the receiver tube. To observe the effect, the PTAC system was tested with a helical screw tape insert and smooth absorber tube and the results were compared. Moreover, energy, exergy and thermal–hydraulic analysis of the PTAC was performed. Results show that the helical screw tape inserted PTAC always yields a much better performance in terms of overall collector efficiency and exergy efficiency. Overall results prove that the temperature rise improvement across the PTAC was remarkable, improving the efficiency by 56%–71% so that the role of the helical screw tape insert is to ensure an improved heat exchange. The findings validate the potential and elucidate specific conclusions for the practice of such heat exchange improvement methods in parabolic trough air collectors.

Augmentation of laminar flow heat transfer in annular flat tubes by means of helical screw-tape inserts in the inner tube.(Dept.M)

The heat transfer characteristics and friction factor in 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*102 ≤ Re ≤ 1.31*103. The effect of spacer length and twist ratio on the heat transfer augmentation and friction factor on heat transfer have been presented separately. The study shows that, Nusslet number (Nu) and friction factor (f) decrease with the increase of spacer length (S) and twist ratio (Y) for flat tube. The comparison between the data of present plain circular tube with that of previous plain circular tubes showed good agreement 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 and experimental thermal performance with entropy generation analysis on tube with helical screw tape inserts at number of strips in turbulent flow

In the heat exchangers, twisted tape insert is a technique to enhance heat transfer. In this paper, the experimental and numerical investigations are arranged to analyze thermal performance with entropy generation analysis on single and double strip helical screw tape inserts. The finite volume method is used with shear stress transport K-ω model to analyze fluid flow in tube with inserts. The Nusselt number attained enhancement with double strip as compared to single strip helical screw inserts at decreased values of twist ratio and increased values of Reynolds number. However, the Nusselt number attained maximum enhancement of 112% with double strip helical screw insert than plain tube at 4000 of Reynolds number (Re). The common correlations for Nusselt number and friction factor are generated with respect to Reynolds number, number of the strips and twist ratio. Entropy generation analysis is also performed. The thermal performance factor attained its enhancement with double strip than single strip helical screw inserts at twist ratio of 2.5 and 3; whereas, double strip helical screw insert attained maximum value of 1.5 at twist ratio of 2.5 and Reynolds number of 16000. The double strip helical screw inserts are suitable for miniaturization of heat exchanger.

Thermohydraulic Analysis on Helical Screw Insert at Different Strips with Nanofluid

The experimental analysis is conducted to evaluate the thermal hydraulic performance of nanofluid flow in a tube with a helical screw insert at a number of strips and different twist ratios in a transition flow regime. The Nusselt number is achieved the enhancement with nanofluid flow in the double-strip helical screw tape (DS-HST) as compared with the single-strip helical screw tape (SS-HST) insert with decreased values of twist ratios and increased values of Reynolds number. Maximum values of Nusselt number are found at 1.5 of twist ratio and higher values of Reynolds number. Common correlations of the Nusselt number and friction factor are developed. Thermal performance factor achieves maximum values with the DS-HST insert at 2.5 of twist ratio as compared with the SS-HST inserts in the range of Reynolds number. This analysis shows suitability of DS-HST inserts for enabling the miniaturization of heat exchanger.

Experimental analysis on thermal and friction factor characteristics of fluid flow in tube with novel double strip helical screw tape

An experimental analysis has been carried out to investigate the thermal and friction factor characteristics of fluid flow in a tube with double strip helical screw tape (DS-HST) inserts with different values of twist ratio and compared with single strip helical screw tape inserts and plain tube. Water is used as a working fluid at different flow rates with constant heat flux conditions. CFD analysis is also carried out to visualize thermal and fluid flow characteristics of fluid flow in tube with inserts. Experimental results have showed that Nusselt number and friction factor have attained excellent enhancement with double strip helical screw tape inserts in the range of flow rates than single strip helical screw tape inserts at the value of twist ratio 1.5. Correlation is also developed for Nusselt number with a range of Reynolds number, twist ratio and number of strips. Moreover, the performance ratio has attained maximum value at twist ratio of 2.5 with high values of flow rate. It is concluded that DS-HST is able to attain enhancement in the efficiency of heat exchanger, causing a reduction in size for thermal applications.

Thermal performance analysis of CuO/water nanofluid flow in a pipe with single and double strip helical screw tape

This paper presents the experimental analysis to evaluate thermo-hydraulic characteristics of single and double strip helical screw tape inserts in the copper tube with water and CuO/water nanofluid at constant heat flux conditions at twist ratio of 1.5, 2.5 and 3. Results show that Nusselt number and friction factor with double strip helical screw tape inserts achieves substantial enhancement as compared to single strip helical screw tape insert. The Nusselts number with nano-fluid increases and achieves the increment by 182% and 170% for double strip and single strip helical screw tape inserts respectively, at a twist ratio of 1.5. Whereas at twist ratio of 2.5 and 3, thermal performance factor shows excellent performance for double strip helical screw tape inserts, that makes it suitable for heat exchanger to reduce the size of it for thermal applications. Correlations for Nusselt number and friction factor are also developed within the range of Reynolds number, twist ratio and Number of strips.

Experimental thermal performance analysis of fluid flow in a heat exchanger pipe with novel double strip helical screw tape inserts for utilization of energy resources

ABSTRACT Heat transfer enhancement is an essential parameter of heat exchangers, that can increase by increasing the value of heat transfer coefficient. So, researchers used different types of inserts, in which, single strip helical screw tape showed excellent enhancement in heat transfer, due to the formation of high-intensity swirl flow. However, to increase more intensity of swirl flow, Double strip helical screw tape inserts (DS-HST) used in present work. An experimental analysis is carried out to analyze thermal and friction factor characteristics of fluid flow in heat exchanger tube, with DS-HST, at twist ratio of 1.5, 2.5, and 3, in the range of Reynolds number from 4000 to 16000, at constant heat flux condition. Experimental results showed that Nusselt number and friction factor achieved excellent enhancement with double strip helical screw tape insert than single strip helical screw tape insert (SS-HST) with decreasing value of twist ratio. The correlation developed for Nusselt number at a range of Reynolds number, twist ratio and a number of strips. Moreover, Thermal performance factor achieved maximum value at twist ratio of 2.5 and 3 for DS-HST, than SS-HST inserts in the higher values of Reynolds number, at constant pumping power. So this range of turbulent flow showed the suitability of DS-HST inserts, which can reduce the size of heat exchangers or thermal applications, utilize energy resources, and decrease pollution in the environment.

Laminar flow heat transfer enhancement in square and rectangular channels having: (1) A wire-coil, axial and spiral corrugation combined with helical screw-tape with and without oblique teeth and a (2) spiral corrugation combined with twisted tapes with oblique teeth

Heat transfer enhancement is a vital area of research as it helps to design heat exchangers of reduced sizes and improved heat transfer rates. Thus, there is a pressing need for techniques which result in significantly increased heat transfer over and above increased pressure drop. In this paper, the benefits of different compound techniques using (1) wire-coil inserts and helical screw-tape inserts with oblique teeth, (2) wire-coil inserts and helical screw-tape inserts without oblique teeth, (3) spiral corrugation and helical screw-tape inserts without oblique teeth, (4) axial corrugation and helical screw-tape inserts without oblique teeth, and (5) spiral corrugation and twisted-tape inserts with oblique teeth were studied experimentally for laminar flow in a non-circular duct (aspect ratio = 1, 0.5 and 0.33). Servotherm medium oil with Prandtl number ranging from 430 to 530 was used as working fluid. The experiment was conducted for a uniform heat flux boundary condition. The effect of geometric parameters of the inserts such as wire-coil diameter, wire-coil helix angle, tooth angle and tooth horizontal length of the screw tape and the twisted tape, corrugation height and corrugation pitch, etc. on heat transfer and pressure drop characteristics was presented. The influence of duct geometry (aspect ratio) on Nusselt number and friction factor was also studied. Correlations for Nusselt number and friction factor were developed and a performance evaluation was done.

New combined heat transfer enhancement techniques used in laminar flow through non-circular ducts

The problem of heat transfer enhancement using different combinations of transverse ribs, transverse corrugations and twisted-tape insert with oblique teeth, twisted tape with centre clearance and helical screw-tape insert in square and rectangular channel was investigated. The study also involved the thermohydraulic performance of inserts in non-circular channels in the laminar regime. Non-circular channels having aspect ratios of 1, 0.5 and 0.33 were considered. The techniques used for heat transfer augmentation in the present study were and the problem was (1) transverse ribs with twisted tape with oblique teeth, (2) integral transverse corrugation and centre-cleared twisted-tape insert, (3) transverse rib and helical screw-tape insert, (4) axial ribs and centre-cleared twisted-tape insert and (5) integral transverse rib and centre-cleared twisted-tape insert. These combined fin geometry are supposedly important from possible heat transfer enhancement point of view. In the channels, the combined influence of insert geometry such as rib pitch, rib height, twist ratio of twisted tape, twisted tape tooth horizontal length and twisted tape tooth angle was studied. The experiment was carried out using Servotherm oil as the working fluid, which had a wide range of Prandtl number (430–530). Uniform heat flux boundary condition was used. The methods used in the experiment have been discussed in the text of the presentation. The important results of the experimental investigation showed that the thermohydraulic performance using a combination of inserts was better than that of bare ducts and that of the individual enhancement technique acting alone. Both the increase in pressure drop and heat transfer augmentation occurred due to the addition of inserts, but heat transfer enhancement dominated over the increase in pressure drop. Nusselt number and friction factor correlations have also been developed and are presented in this paper. The experimental program considered different fin arrangements with various parameters and therefore, it should be very helpful in designing heat exchangers of different shapes and sizes used for industrial purpose. It is concluded from the present investigation that 31–52 per cent increase in heat duty at constant pumping power and 25–36 per cent reduction in pumping power at constant heat duty are achievable. This is the novelty of the present work since no such study and the observations have been made earlier. These types of combined fin configurations have not been tried before. The findings are likely to have good impact in the industry.

CFD study of heat transfer enhancement and fluid flow characteristics of laminar flow through tube with helical screw tape insert

In this study, a three-dimensional (3D) computational fluid dynamics (CFD) analysis is performed to investigate the heat transfer performance and fluid flow characteristics using a helical screw tape insert in pipe flow. An inserted tube geometry was improved using a helical coil i.e., wire-wrapped with 1.92 twist ratio. Single-phase, horizontal, and a laminar flow (200 < Re <2300) through an annular channel is considered. A flow domain is created first, and then discretized, later all boundary conditions are applied and finally, simulated it using ANSYS FLUENT. The results are analyzed and processed further to check for mesh sensitivity and experimental validation. The simulated results showed that the heat transfer rate in terms of Nusselt number increased 1.34-2.6 times, whereas, the friction factor also increased 3.5-8 times for wire-wrapped-tube i.e., the tube with helical screw tape insert in comparison to the plain tube. The thermal performance factor was evaluated and the maximum value is found 3.79 at a constant pumping power. The pressure drop was estimated which was increased due to the increased flow restriction by inserted coils.

Thermal Uniformity Study in a Circular Divergent Diffuser with Swirl Flow Generator

In this work, numerical and experimentally study of thermal uniformity coefficient is performed in an annular diffuser fitted with a swirl generator. Temperature distribution and thermal uniformity are studied. For this research paper, the swirling and the helical motion are induced by a helical screw tape placed on the hub. The experimental measurement is reported for helical screw-tape with H = 0.005 m width and t= 0.002 m thickness in a constant inlet condition. The effect of the helical screw-tape inserts is investigated at an inlet Reynolds number (Re) of 7.7 x 104 based on the hydraulic diameter and the flow is considered as turbulent and incompressible. Numerical simulations are carried out using NUMECA FINE™/Open v3.1 applying standard k-ε model as a turbulence model. The effect of the helical screw-tape on the thermal uniformity is investigated at the same Reynolds number. Results show that the experiment gave results that match the numerical simulation results very well. This swirling flow leads to thermal fluid mixing between the core flow and the wall regions of the annular diffuser, and consequently, improves the thermal uniformity rate significantly.

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.

Thermo-hydraulic analysis for a novel eccentric helical screw tape insert in a three dimensional tube

The effects of eccentricity between the centers of helical screw tapes and tube on heat transfer, friction factor and performance evaluation criteria are numerically studied in this paper. A three-dimensional turbulence model is used to simulate the flow inside the tube with helical screw tape insert. All simulations are performed for four values of eccentricity (0, 0.5, 2, and 3.5) and Reynolds numbers in the range of 5000 to 12000. The obtained results indicated that the swirling effects created by helical screw tape insert are transferred from the tube core to near wall of the tube. This leads to the more mixing of fluid and centrifugal force near the wall, which has significant ability to improve the heat transfer rate at this region. There are 33%, 16.94%, 8.45%, and 7.3% increments in performance evaluation criteria for Re=5000, 7500, 10233, and 12000 when the eccentricity value is increased from 0 to 3.5.

Thermo-fluid performance and entropy generation analysis for a new eccentric helical screw tape insert in a 3D tube

In this paper, a new application is presented for a helical screw tape insert in a 3D tube. In this application, an eccentricity is created between the centrelines of helical screw tape and tube. Accordingly, the effects of this eccentricity on thermal-hydraulic performance and entropy generation are investigated numerically. A three-dimensional SSTk−ω turbulence model is applied to simulate this problem. All simulations are made for eight values of the eccentricity in the range of 0 to 3.5 and Reynolds numbers in the range of 5000 to 12,000. The calculated results showed that incorporating the helical screw tape near the tube wall (by increasing the eccentricity value) diverts the swirling flow from the core region towards the tube surface where high velocity flow impinges over the tube wall, hence extracting higher amount of thermal energy. Moreover, 42% and 237% increments are observed in the frictional and thermal entropy generations, respectively for an eccentricity in the range of 0 to 3.5.

Experimental Studies on Natural Circulation Solar Water Heating System Fitted with Helical Screw Tape Inserts

Experimental investigation of heat transfer and friction factor characteristics of thermosyphon solar water heater with helical screw tape of various twist ratios(Y=3, 4, 5 and 6) has been studied. Compared to other twist ratio, the minimum twist ratio 3, offers higher Nusselt number, friction factor and Thermal performance. The average Nusselt number, friction factor and thermal efficiency for helical screw tape collector with minimum twist ratio 3 are 13.86, 0.111 and 63.62% respectively. Whereas the increasing twist ratio decreases the above performance. The heat removal factor for screw tape collector with twist ratio 3 has 54.4% higher than plain tube collector. Correlations developed for friction factor and Nusselt number has been verified and deviation falls within ±13%.

Heat Transfer Performance through a Flat Tube Using Rotary Helical Screw-tape Inserts

Heat transfer characteristics and friction factor in the horizontal double pipes of a flat tube with full and varied spacer length helical screws at various rotational speeds are investigated for Reynolds numbers ranging from 580 to 1,582. The heat transfer and friction factor of the inserted tube are significantly increased compared to those of the plain tube. The Nusselt number, friction factors, and thermal enhancement efficiency were increased with decreasing spacer length at increasing rotational speed under the same operating conditions.

Thermal and friction characteristics of laminar flow through a circular duct having helical screw-tape with oblique teeth inserts and wire coil inserts

Helical screw-tape inserts and wire coil inserts both individually are enhancement techniques. Naturally, therefore, it is worthwhile to try their combinations as a potential enhancement technique. The experimental friction factor and Nusselt number data for laminar flow through a circular duct having helical screw-tape and wire coil 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 wire coil inserts 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.

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.

A numerical study of parabolic trough receiver with nonuniform heat flux and helical screw-tape inserts

Effect of solar incidence angle was analyzed in order to accurately simulate the heat flux distribution around the absorber tube outer surface. Helical screw-tape inserts was proposed to homogenize the absorber tube temperature distribution and improve the thermal efficiency. Three dimensional periodical models of flow and heat transfer were established and solved with the heat flux of different transversal angle (β). The results show that β affects the flux distribution more greatly than longitudinal angle (φ). Transversal angle (β) of 11.567 mrad increases the relative change of heat loss (Qloss) as inlet temperature rises, and also increases the maximum temperature on absorber tube (Tmax) and the maximum circumferential temperature difference (ΔT). But its effect reduces as Reynolds number rises. Within the range of studied Re, the helical screw-tape inserts of given geometrical parameters greatly reduce the Qloss, Tmax and ΔT, which indicates that helical screw-tape inserts is a feasible way to enhance the heat transfer inside the receiver.