Multiple Twisted Tapes Research Articles

Analytical investigation of solar parabolic trough receiver with multiple twisted tapes using exergy and energy analysis

Exergy analysis is an important thermodynamic approach to studying the system's actual output, considering all losses. The present study is an analytical approach to calculating the thermal and exergetic efficiencies of the parabolic trough receiver using MATLAB R2018a simulation software. These efficiencies are evaluated considering temperature rise characteristics and parametric design factors. The influence of the solar air heater's thermal and exergy analysis-based mathematical model on all design parameters is examined. The receiver tube has multiple twisted tape inserts with three varying parameters, i.e., twist ratio (y/w) = 3 to 5, perforation ratio (dp/w) = 0.05 to 0.25, and winglet ratio (d/w) = 0.1 to 0.3. The twisted tape with y/w, dp/w, and d/w having values 3, 0.1, and 0.05 perform better regarding energy and exergy with values 84.27% and 4.28%, respectively. This thorough examination can prove to be highly effective and advantageous in generating the design model for the specified twisted tape parameter value without requiring extensive investment in actual experimentation while also furnishing an evaluation of the performance of the solar air heater design.

Thermal and Flow Analysis of TiO2 Nanofluid Flow in Circular and Square Ducts with Multiple Twisted Tape Inserts

A numerical study is conducted to observe the thermal and flow performance of TiO2 nanofluid in the circular and square ducts with different twisted tape arrangements. The presence of the twisted tape in the tube induces swirl flow, which aids in the heat transfer, but at the penalty of a higher friction factor. The results also reveal that the maximum Nusselt number enhancement is obtained in the circular tube when the counter-triple twisted tape arrangement (C-TTs) is adopted while it is co-triple twisted tape arrangement (Co-TTs) for the case of square duct. Besides, the highest friction factor is observed for the Co-TTs for both circular and square ducts. The heat transfer and friction factor in the circular duct are greater than that of the square duct. The highest thermal performance factor of 1.286 is obtained when the single twisted tape and 1.5% nanofluid are used in the circular tube. However, multiple twisted tape inserts in the square duct contributes to improved thermal performance at a relatively lower friction factor when compared to the circular tube. Therefore, it is recommended to implement the square duct with multiple inserts for compact or microchannel heat exchanger for heat transfer application.

Turbulent thermal-hydraulic characteristics in a spiral corrugated waste heat recovery heat exchanger with perforated multiple twisted tapes

Waste heat recovery technology can undoubtedly improve energy saving and reduce carbon emissions, as one of the key equipment, heat exchangers always determine the waste heat recovery efficiency. In this study, to improve the heat transfer potentiality of conventional plain tube heat exchangers, a synergistic thermal enhancement technology of a spiral corrugated tube (SCT) with multiple twisted tapes (TTs) was devised by taking liquid-gas heat exchanging as a typical waste heat recovery scenario. The impacts of the TTs numbers, transverse space ratios (S/D), and longitudinal perforation length ratios (L/D) on tubular turbulent heat transfer-fluid flow characteristics were numerically investigated, consisting of flow fields, temperature contours, local Nusselt number (Nu) distributions, vortex structures, and turbulent kinetic energy contours, as well as average Nu, friction factor (f), and overall thermal performance evaluation index (η). The findings proved that the fitting of multiple TTs into the SCT greatly homogenized the flow fields and temperature distributions, and increased the Nu and f, in which both of them also raised with the increase of the number of TTs. The η dropped and subsequently augmented as the quantity of TTs increased. Furthermore, perforations on the surface of the quadruple TTs could attenuate the f with a relative less reduction in the Nu, which caused higher η values than the ones without perforations. Notably, as demonstrated by the vortex structures, this could be ascribed to the fact that the perforations reduced excessive longitudinal vortex interactions in the mainstream regime without reducing the impingement to the thermal boundary layer too much. Both the Nu and f generally declined with rising S/D and L/D. Overall, by means of simple mounting perforations on the surface of the quadruple TTs, the maximum η could be further enhanced up to around 7.9% and a maximum η of 1.23 was obtained by the SCT with S/D = 0.152 and L/D = 0.348.

Pressure drop and nanoparticle deposition characteristics for multiple twisted tape inserts with partitions in turbulent duct flows

In this study, the pressure-drop (flow resistance) and nanoparticle deposition characteristics of multiple twisted tapes (MTTs) with partitions were experimentally investigated in turbulent duct flows using air as working fluid. Penetration tests for nano-sized particles and pressure drop measurements were performed in the empty duct and ducts fitted with twisted tapes (TTs), and zones under the same pumping power condition. A co-swirling arrangement was used for MTT inserts. Different nanoparticle diameters (5–100 nm), Reynold numbers (4000–11000), TT twist ratios (3 and 7), number of tapes (1, 2, and 4), and partition schemes were considered in the present investigation. It was found that the penetration efficiency of nanoparticles generally increased with the diameter of nanoparticles and Reynold number. The nanoparticle deposition velocity was always higher in ducts fitted with MTTs than in ducts equipped with a single twisted tape (STT). The results also showed that the ratios of nanoparticle deposition velocities for TT-equipped ducts to the empty duct ranged from 1.8 to 13.7, while the corresponding ratios of friction factor varied from 1.4 to 3.2. Beside, TTs with a smaller twist ratio offered higher particle deposition velocities and flow resistances than TTs with a larger twist ratio. Furthermore, empirical correlations for friction factor, nanoparticle penetration efficiency, and deposition velocity were proposed, respectively. The fouling resistance caused by accumulation of deposited particles was analyzed and the results showed that the maximum resistance decreased with the increasing Reynolds number, but was comparable for particle size between 50 nm and 100 nm.

Impact of new multiple twisted tapes on treatment of solar heat exchanger

Impact of new multiple twisted tapes on treatment of solar heat exchanger

Performance evaluation of solar parabolic trough receiver using multiple twisted tapes with circular perforation and delta winglet

A parabolic trough collector (PTC) is one of the concentrating types of a solar collector working in the medium range of temperature from 100–400 °C, for this reason, the efficiency of the solar parabolic trough is less than other types of concentrating solar collector (Point focusing types) in terms of solar to thermal energy conversion, the improvement in efficiency is achieved by various passive heat augmentation techniques in the receiver tube. One of the promising passive techniques is twisted tape inserts used in the receiver due to its simplicity in design and the various possibility of geometric modification. This paper deals with the performance evaluation of the solar parabolic trough receiver system by using passive techniques in the receiver. The testing of the receiver of PTC was done by using multiple perforated twisted tapes with winglets having different perforation ratios ([Formula: see text]) of 0.05, 0.15, 0.25, twist ratios ([Formula: see text]) of 3, 4, 5 and wing depth ratios ([Formula: see text]) of 0.1, 0.2 and 0.3. The number of twisted tapes was fixed at 4. The examination was conducted for Reynolds numbers ([Formula: see text]) varying from 3000–21,000 using air as working fluid. The outcome shows that the use of perforation and winglet in twisted tapes augment the Nusselt number as compared to that of smooth twisted tapes. The maximum thermohydraulic performance ([Formula: see text]) of 2.40 is received by using multiple twisted tapes with perforation and winglet having [Formula: see text] = 0.3, [Formula: see text] = 3, and [Formula: see text] = 0.05 at the Re = 21,000. The correlations for Nusselt number ([Formula: see text]) and friction factor ([Formula: see text]) are also developed with ± 8.5% and ± 8.3% accuracy, respectively.

Heat Enhancement Effectiveness Using Multiple Twisted Tape in Rectangular Channels

Heat enhancement and heat removal have been the subject of considerable research in the energy system field. Flow-through channels and pipes have received much attention from engineers involved in heat exchanger design and construction. The use of insert tape is one of many ways to mix fluids, even in a laminar flow regime. The present study focused on the use of different twisted tapes with different pitch-to-pitch distances and lengths to determine the optimum design for the best possible performance energy coefficient. The results revealed that twisted tape of one revolution represented the optimal design configuration and provided the largest Nusselt number. The length of the tape played a major role in the pressure drop. The results revealed that the insertion of a shorter twisted tape can create mixing while minimizing the changes in the pressure drop. In particular, the best performance evaluation criterion is found for a short tape located towards the exit of the channel. The highest performance energy coefficient was obtained for the half-twisted tape for a Reynolds number varying between 200 and 600.

Analyzing entropy and thermal behavior of nanomaterial through solar collector involving new tapes

In the present examination, the effect of Aluminum oxide suspended in water at concentration of 0.03% as nanomaterial for turbulent flow using multiple twisted tapes (TTn) in a solar flat plate collector was scrutinized. Properties are estimated by utilizing previous correlations. Outputs are described for a different number of turbulator and Reynolds number (Re). The increase in Sgen,f (1604.672) is more significant for higher Re = 20,000. The highest Sgen,th (15,788.13) is observed for TTn = 1 and Re = 4000. The highest number of Be is 0.9987 when the TTn = 1 and Re = 4000. Both the Be number and the Фs shows the same trend for the reported results. The increase in the number of Re and TTn reduces the values of Be and Фs. Output results verify that the use of turbulators enhances the nanofluid flow resulting in enhanced heat transfer, which also provides higher flow disturbance. Therefore, it can be concluded that using twisted tapes and nanofluids can result in reduces exergy losses.

NUMERICAL INVESTIGATION OF NON-UNIFORM HEAT TRANSFER ENHANCEMENT IN PARABOLIC TROUGH SOLAR COLLECTORS USING DUAL MODIFIED TWISTED-TAPE INSERTS

In this paper, a numerical investigation is presented on heat transfer augmenting by using various kinds of modified multiple twisted tape inserted in solar parabolic trough collectors. The pressurized water is considered as working fluid and Reynolds number varying from 10000 to 20000. The received heat flux on the solar absorber was assumed non-uniform due to hemispheric insolation of sun. The obtained numerical results for the Nusselt number, friction factor and thermal performance are presented for each cases. Various types of twisted tape including single twisted tape, normal, perforated, center-cleared, square, and V-cut dual twisted tape are considered and analyzed. The numerical simulations are performed by a commercial CFD code, ANSYS FLUENT 18.2. The obtained results revealed that at Re=10000 and 20000, the average Nusselt numbers of case with dual v-cut twisted tapes are more than plaine tube by 19.58 and 17.44%, respectively. Moreover, thermal performance of all cases with various twisted tapes is larger than 1 which means that utilizing twisted tape with various configurations leads to more thermal performance than plain tube. The thermal performances of case with dual square-cut twisted tapes (as the best case) for Re=10000 and 20000 are more than plain tube by about 16 and 12% improvement, respectively. Furthermore, for the case with perforated dual twisted tape (as the case with lowest thermal performance), the thermal performances for Re=10000 and 20000 are more than plain tube by about 9.2 and 7% improvement, respectively.

Numerical investigation on the heat transfer characteristics in a circular pipe using multiple twisted tapes in laminar flow conditions

AbstractIntroducing passive devices in the form of inserts helps to increase the heat transfer characteristics in a circular pipe. In the present work, the feasibility of using two twisted tapes has been numerically studied under laminar flow conditions. Two twisted tapes with configurations of co‐swirl and counter‐swirl conditions were simulated for Re ranging from 1000 to 2500. Heat transfer characteristics like Nusselt number, friction factor, and thermohydraulic performance index (THPI) were investigated. Even the effect of spacing of the tubes inside the pipe was numerically studied. Results indicated that the insertion of two tapes will improve the performance of the circular tube compared with a single tape in terms of a higher Nu and higher THPI. It is observed that for the co‐swirl condition for a Reynolds number of 1000, Nu and THPI is 38% and 29% higher than using a single tape, whereas, for the counter‐swirl condition, they are 43% and 34% higher than that of the single tape condition. Also, it is revealed that counter swirl positioning of the tape with an L/D ratio 0.56 outperformed all other configurations with the highest THPI.

Thermal-hydraulic performances in multiple twisted tapes inserted sinusoidal rib tube heat exchangers for exhaust gas heat recovery applications

The article presents a numerical investigation on turbulent thermal and fluid flow characteristics of multiple twisted tapes (MTTs) inserted sinusoidal rib tube (SRT) heat exchangers based on exhaust gas heat recovery background. The effects including geometric parameters of tape number (single, twin, triple and quadruple twisted tapes) and tape arrangements (clockwise and anticlockwise or co-swirl and counter-swirl) in the SRT were comparably studied. A periodic RNG k-ε numerical model was employed to depict the heat transfer behaviors and flow structures in the SRTs at a constant wall temperature condition. The results showed that the alone use of the SRT yielded enhanced heat transfer of about 27.4%–39.5% and increased friction loss of around 49.4%–74.7% higher than that in the baseline of spirally corrugated tube (SCT). In addition, it was found that the diverse thermo-hydraulic performances in the SRTs fitted with MTTs were dominated by flow structures of swirl flows and shear flows. By the synergy of longitudinal vortexes from SRT and MTTs, the Nusselt number and friction factor obtained from the SRTs fitted with MTTs were, respectively, larger than that from SCT at about 1.43–1.87 times and 2.66–10.07 times. In contrast to the SCT, the overall thermal performance evaluation criterion (PEC) was enhanced up to 1.59 for the alone use of SRT. Moreover, the PEC could be improved under increased heat transfer and reasonable pressure drop via suitable tape arrangements in the SRTs mounted with MTTs, of which the best PEC was 1.49. At last, the comparisons of present results with previous studies proved that the proposed enhanced devices held some competitive advantages.

Hydrodynamics investigation of pepper drying in a swirling fluidized bed dryer with multiple-group twisted tape swirl generators

The present work aims to investigation the behavior of drying peppers in a swirling fluidized bed dryer (S-FBD) fitted with multiple twisted tape swirl generators. A multiple-group twisted tape swirl generator was located at the air inlet at the bottom of the bed. The effects of the superficial air velocity (U*=U/Umf = 1.0, 1.1 and 1.2) on the moisture content (MC), moisture content ratio (MR) and drying rate (DR) were examined. The experimental results showed that the S-FBD can reduce the moisture content of peppers more rapidly than a conventional fluidized bed dryer (FBD). The S-FBD gave a higher DR and decreased drying time compared to that of a FBD. The results also indicated that operation at higher superficial air velocities resulted in a greater DR, especially at the beginning stage of the drying process. For the S-FBD, the reduced of MC, MR and DR at a high superficial air velocity (U*=U/Umf = 1.2) was better than at low superficial air velocities (U* = 1.0 and 1.1). Furthermore, five different drying models were evaluated to predict the performance of the S-FBD.

Performance of a beta Stirling refrigerator with tubular evaporator and condenser having inserted twisted tapes and driven by a solar energy heat engine

This paper investigates the performance of a beta-type Stirling refrigerator. The proposed refrigerator has twin tubular evaporator and condenser. The tubes of both evaporator and condenser have insertions of multiple twisted metallic tapes inside them. In the proposed refrigerator, a wire net regenerator is suggested. The working fluid is selected to be Helium. Rhombic drive mechanism controls the synchronization of the reciprocation of both the displacer and the piston. A computer program in the form of a spreadsheet is prepared to solve the refrigerator cycle numerically. The results get the more suitable dimensions of the evaporator, the condenser, the regenerator, and the more suitable stroke to bore ratio of both piston and displacer. The refrigerator develops 0.000283 TR/cc, COP = 0.5297 at 800 rpm. The comparison among the present work and previous ones shows that; the present refrigerator explores an enhancement in COP up to 100%, especially at low-speed levels.

Intensification of thermo-hydraulic performance in heat exchanger tube inserted with multiple twisted-tapes

The present work presents the thermo-hydraulic characteristics in the heat exchanger tube inserted with multiple-twisted tapes (M-TT). Multiple-twisted tapes consisted of a larger twisted tape and small twisted tapes which were placed along with the larger twisted tape. The study encompassed 6 different twist ratios of the small twisted tapes (y/w = 2.5, 5, 10, 15, 20 and 25) and 5 different numbers of the small twisted tapes (N = 2, 3, 4, 5 and 6). Experiments were conducted under uniform wall heat flux condition by using air as the testing fluid for Reynolds numbers from 6000 to 20,000. A large single twisted tape in a tight-fit form (T-TT) and that in a loose-fit form (L-TT) were tested as the reference cases for comparison. The experimental results found that the use of multiple-twisted tapes (M-TT) with N = 3, 4, 5 and 6 leads to the considerable increases in heat transfer enhancement and friction factor as compared to those of single twisted tape. For multiple twisted tapes (M-TT), Nusselt number (Nu), friction factor (f) and thermo-hydraulic performance factor (η) increase with increasing number (N) and decreasing twist ratio (y/w) of small twisted tapes. The maximum thermo-hydraulic performance factor of 1.2 is obtained by the use of M-TT with N = 6 and y/w = 2.5. In addition, the numerical work on flow and thermal behaviors was also performed for a better understanding of heat transfer mechanisms.

Experimental determination of enhancement of heat transfer in a multiple square perforated twisted tape inserts heat exchanger tube

ABSTRACTThis paper presents an experimental determination of Nusselt number and friction factor of heat exchanger tube with multiple square perforated twisted tape inserts. The effect of geometrical parameters, especially, perforation width ratio and twist ratio, has been investigated. The perforation width ratio and twist ratio have been varied from 0.083 to 0.333 and 2.0 to 3.5, respectively. The optimum values of parameters for multiple square perforated twisted tape inserts arrangement have been obtained and discussed. The effect of multiple square perforated twist tape inserts has been investigated for the range of Reynolds number from 5,000 to 27,000. The effect of important parameters on the and has been discussed, and the results are compared with the results of without square perforated multiple twisted tape inserts and smooth surface heat exchanger tube under similar flow conditions. The optimum values of parameters for multiple square perforated twisted tape inserts heat exchanger tube arrangement have been obtained and discussed. The maximum enhancement is observed at a of 0.250 and of 2.5, respectively.

Turbulent thermal, fluid flow and thermodynamic characteristics in a plain tube fitted with overlapped multiple twisted tapes

Turbulent thermal–hydraulic characteristics in a plain tube by using overlapped multiple twisted tapes (MTTs) with counter large/small combinations (C-L/S-C) were experimentally investigated. Reynolds number (Re) ranged from 5800 to 19200, tape number changed from 3 to 5 and overlapped twisted ratios (P1:P2) were 0.74 to 2.97. By using air as working fluid, heat transfer tests were performed under the constant heat flux conditions and pressure drop experiments were conducted at the isothermal conditions. Nusselt number (Nu) and friction factor (f), overall thermal performance evaluation criterion (PEC), entropy generation and entransy dissipation in the MTTs were compared. The results show that Nu and f increase with increasing tape number and decreasing overlapped twisted ratio. The experimental results demonstrates that both increasing tape number and decreasing overlapped twisted ratio result in the reduction of entropy generation due to heat transfer and the rise of entropy generation due to friction resistance. It is found that the indicator of equivalent temperature difference, reflecting entransy dissipation and heat transfer ability, has the same sequence to that of the heat transfer behaviors. In the scope of this study, both the maximum Nu and the largest increased f are obtained in the 5MTTs with values respectively about 98.4% higher and 9.13 times than that in the plain tube while the highest PEC is found in the 3MTTs with P1:P2=0.74 with a value of being about 1.08. The least total entropy generation is gained by the 3MTTs with P1:P2=0.74 at Re=17090 and the smallest entransy dissipation per unit energy is achieved by the 5MTTs under Re=17294. Furthermore, thermal–hydraulic empirical correlations with deviations of ±5% are developed and comparisons with previous studies are also conducted.

Heat transfer enhancement of heat exchanger tube with multiple square perforated twisted tape inserts: Experimental investigation and correlation development

The present study examines the augmentation in heat transfer and friction in a flow through heat exchanger tube with multiple square perforated twisted tape inserts. The experimental outcomes pertaining to Reynolds number (Ren) from 5000 to 27000, perforation width ratio (a/WT) from 0.083-0.333 and twist ratio (TL/WT) from 2.0-3.5 have been presented and discussed. Multiple square perforated twist tape brought out considerable enhancement in heat transfer rates over without square perforated multiple twisted tape and plain tube. The maximum enhancement is observed at a a/WT of 0.250 and TL/WTof 2.5. Correlations of Nusselt number, friction factor and thermal hydraulic performance are established in term of Reynolds number and geometrical parameter of twisted tape which can be used to predict the values of Nusselt number, friction factor and thermal hydraulic performance with considerably good accuracy.

Heat transfer and fluid flow characteristics of heat exchanger tube with multiple twisted tapes and solid rings inserts

Heat transfer and fluid flow characteristic of a roughened tube is investigated for constant heat flux. The inserts were employed for the swirl flow generation in the test section through the tube. Pitch ratios (l/D)=1 and 2 of the solid ring tubular (SRT) and twist ratios (y/W)=2, 3 and 4 of the twisted tapes (TT) are introduced into the core flow. The Reynolds number covered in the range of 6300–22500 for co-twist arrangements for the turbulent flow of air in the tested heat exchanger tube. The study reveals that the Nusselt number, friction factor and thermal performance factor of the integrated SRT and TT are in the range of 107–293, 0.93–0.99 and 1.46–1.61, respectively. The highest thermal performance factor in the order of 1.61 over smooth tube heat exchanger was obtained for the integrated device consisting of the SRT with l/D=1.0 and y/W=2. The quadruple co-twisted tape insert provides the maximum Nusselt number, friction factor, thermal performance factor. The correlations for the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices were also developed in terms of flow and geometrical parameters.

Experimental investigation of heat transfer and pressure drop in a circular tube with multiple inserts

The heat transfer ability of a convectional heat exchanger needs to be improved in order to transport a desired rate of energy at the reduced size and cost. Among the different means to increase the heat transfer coefficient, use of inserts emerged as a promising technique to bring out the enhancement in heat transfer at the cost of bearable increase in frictional losses. The present work aims to investigate the heat transfer and fluid flow characteristics of a circular tube fitted with multiple inserts arranged in co-swirl and counter-swirl orientations. The experimental data have been collected for single, twin and four twisted tape inserts having twist ratios of 2.5, 3 and 3.5 while the Reynolds number is varied in the range of 4000 to 14000. A significant rise in the heat transfer has been registered by the use of multiple twisted tapes having twist ratio of 2.5 with the concurrent rise in friction losses with respect to the smooth tube. The maximum enhancement in the heat transfer and friction are found to be 2.42 and 6.96 times that of smooth tube while the maximum value of the thermo-hydraulic performance factor is found to be 1.26 for a set of four counter-swirl twisted tapes with the twist ratio of 2.5. The correlations of Nusselt number and friction factor as function of Reynolds number and twist ratio are developed for different twisted tape configurations.

Numerical study of nanofluid flow in flat tubes fitted with multiple twisted tapes

In this paper, while numerically simulating the Al2O3–water nanofluid flow in flat tubes fitted with twisted tapes, the effects of three different Heat Transfer Enhancement (HTE) methods are also separately evaluated and compared. These three HTE mechanisms include the use of nanofluid instead of the base fluid, use of flat tubes instead of circular tubes and the use of twisted tapes inside the tubes. The obtained results indicate that although all the three mentioned mechanisms improve the heat transfer within the tubes, the HTE due to the use of twisted tapes is greater than that caused by the other two mechanisms. After discovering that the simultaneous use of the three mentioned mechanisms can considerably increase the amount of heat transfer, three different arrangements of the twisted tapes in the nanofluid-containing flat tubes are also evaluated and compared. These three arrangements include the use of one twisted tape, use of two twisted tapes in the same direction and the use of two twisted tapes in different directions. The obtained results indicate that the use of two twisted tapes in different directions leads to the highest amounts of heat transfer and pressure drop in flat tubes.