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Heat transfer performance evaluation of a solar air heater duct with multiple tapered V-baffles
(2025-12-01)
Thianpong, C.
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Kaewkosum, P.
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Woncharee, K.
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Keaitnukul, W.
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Maruyama, N.
This report aims to study the heat transfer enhancement, pressure loss characteristics, and thermal performance of a channel equipped with multiple tapered V-shaped baffles (MTVBs). The effects of up-facing and down-facing orientations, converging (C) and diverging(D) configurations, variations in the taper ratio (e<inf>CR</inf> and e<inf>DR</inf> = 0.0 and 0.5), and Reynolds number (6000 ≤ Re ≤ 24,000) are examined. The performance of UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs is analyzed and compared with that of the conventional transverse baffles (TBs) and MVBs (e<inf>DR</inf> = 1.0). The experimental setup maintained a constant attack angle (α) of 45°, pitch ratio (p/H) of 1.5, width-shaped ratio (W<inf>b</inf>/W) of 0.25, and blockage ratio (e/H) of 0.3. Tests were conducted at a fixed Prandtl number of 0.71, and a thermochromic liquid crystal sheet was utilized to assess the local Nusselt number distribution on the wall installed with UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs. The results reveal that the channel with MVBs (e<inf>DR</inf> = 1.0) achieves the greatest heat transfer rate, with a Nu/Nu<inf>s</inf> ratio of up to 4.37 while a f/f<inf>s</inf> ratio reaching 48.12. In contrast, D-MTVBs at e<inf>DR</inf> = 0.0, despite having a lower Nu/Nu<inf>s</inf> ratio (maximum 3.87), attain the maximum thermal performance of 1.39 at Re = 6000, owing to their optimized design that effectively enhances heat transfer while minimizing pressure drop.
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Experimental investigation and ANN prediction of heat transfer enhancement in a heat exchanger tube utilizing twin corrugated twisted tapes
(2025-12-01)
Du, Y.
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Wongcharee, K.
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Thianpong, C.
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Chuwattanakul, V.
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Chamoli, S.
This report introduces a novel twin-corrugated twisted tape (TC-TT) insert designed to enhance heat transfer in exchanger tubes. The key innovation lies in the twin-corrugated structure, which generates a twin-swirl flow effect. The corrugated surface synergistically increases flow disturbance and expands the effective heat transfer area. The studied parameters were twist ratios (y/w = 3.0, 3.5, and 4.0) and corrugation angles (θ = 45°, 60°, 75°, and 90°) at 6,000 ≤ Re ≤ 20,000. The results show that using twin-corrugated twisted tapes increases the average Nusselt number by roughly 60–135% compared to a plain tube and by 16–35% compared to a conventional single-twisted tape, confirming the effectiveness of this structural modification. This enhancement is primarily due to the combination of double swirling-flows and enhanced effective heat transfer generated by the corrugated surface. Reducing the corrugation angle (θ) and twist ratio (y/w) led to increases in the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). Within the studied range, the Nusselt number, friction factor, and thermal performance factor reached maximum values of 5.18, 0.153, and 1.44, respectively, at a twist ratio of 3.0, a corrugation angle of 45°, and Re = 6,000. Regression analysis was utilized to develop correlations for the Nu and f, considering the Re, Pr, y/w, and θ as influencing variables. The proposed correlations for predicting the friction factor and Nusselt number have errors within ±3% and ±2%, respectively. In addition, an artificial neural network (ANN) was developed for predicting the thermal performance values occurring below the experimental study range. The optimal state ANN model shows remarkable prediction accuracy with R<sup>2</sup> of 0.965.
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Performance of a heat exchanger with compound inclined circular-rings and twisted tapes
(2022-09-01)
Pimsarn, M.
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Samruaisin, P.
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Thianpong, C.
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Ruengpayungsak, K.
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Eiamsa-Ard, P.
Optimization was done of the aerothermal performance factor (η) of a tube into which a combination of inclined circular-rings (ICRs) and twisted-tapes (TTs) were installed. The key contribution of this research is determination of the appropriate ICR and TT sizes to produce the best heat exchanger performance. An ICR's purpose is to produce counter-rotating vortices, whereas the TT's role is to create swirl flow within a tube to improve turbulence and transfer cold fluid from the core region to the heated-wall zone. The influence of circular-ring inclination angle (α = 30o, 45o, 60o and 90o), number of twisted tapes (H = 2, 4, and 6) and twist ratios (TR = 1.0, 2.0, and 3.0) on heat transfer and pressure losses were assessed to determine an optimum η condition. The heat transfer and friction factor tend to increase with H values and decreasing TR. The heat transfer of ICRs together with TTs is higher than in a plain tube by up to 128.7% and 155.3%, respectively, while it is better than the transverse circular-ring (α = 90o) and twisted-tape by up to 116.9% and 146.5%, respectively. Furthermore, due to moderate heat transfer and low pressure losses, a maximal η of 1.66 was achieved for α = 30o, H = 2 and TR = 3.0 within the examined range.
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Multi objective optimization of TiO2/water nanofluid flow within a heat exchanger enhanced with loose-fit delta-wing twisted tape inserts
(2022-02-01)
Thianpong, C.
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Wongcharee, K.
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Safikhani, H.
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Chokphoemphun, S.
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Saysroy, A.
A hybrid technique by using TiO<inf>2</inf>/water nanofluid together with loose-fit delta-wing twisted tape (LTT-W) was employed for heat transfer enhancement. Experiments encompassed the TiO<inf>2</inf>-water nanofluids having concentration (φ) of 0.05%–0.15 vol% and the loose-fit delta-wing twisted tapes having two different wing arrangements (co- and counter arrangement) and three loose-fit ratios (c/D) of 0.0, 0.15, and 0.2. Experimental revealed that the system with combined enhancement technique gave considerably higher heat transfer than the one without enhancement technique. This can be attributed to the combined influences of swirling flow and higher thermal conductivity of the working fluid. Heat transfer rate and thermohydraulic performance rose with the decrease of loose-fit ratio and the rise of nanofluid concentration. The maximum thermohydraulic performance (TPF) of 1.36 was obtained at c/D = 0.0 and φ = 0.15%. The Multi-Objective Optimization (MOO) was also performed to study the optimal thermohydraulic performance by using GMDH models and NSGA II algorithms. The Pareto front, which contains very useful information, were extracted for both co and counter arrangements. The Pareto fronts have recognized very accurately, the best boundary of the experimental data with respect to the lowest friction factor and highest Nusselt number.
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Influence of regularly spaced quadruple twisted tape elements on thermal enhancement characteristics
(2018-06-01)
Samruaisin, P.
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Changcharoen, W.
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Thianpong, C.
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Chuwattanakul, V.
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Pimsarn, M.
The present work explores the heat transfer, pressure loss and thermal enhancement factor (TEF) behaviors of a tube fitted with regularly spaced quadruple twisted tape elements (RS-QTTs). The effects of free space ratio and twisted tape arrangement (co, counter and cross arrangements) were investigated in turbulent flow regime. Experiments were carried out using all twisted tapes with constant twist ratio of 2.5 under constant heat flux condition. The results show that RS-QTTs in all arrangements yield lower heat transfer rate and cause lower friction loss than full-length quadruple twisted tapes (QTTs) due to the weaker swirling intensity caused by the decaying of swirling flow. Heat transfer rates given by the RS-QTTs with s/y of 0.5, 1.0, 1.5 and 2.0 are lower than those given by the QTTs by around 6.2%, 8.13%, 10.6% and 12.8%, respectively. For RS-QTTs, heat transfer rate, friction loss and TEF increase with decreasing s/y. Over the range reported, the RS-QTTs in cross-arrangement with s/y = 0.5 gives heat transfer rate up to 6.6% over than that of the QTTs and the maximum TEF of 1.27. Moreover, the flow and thermal behaviors were also numerically studied for a better understanding on heat transfer mechanism.
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Intensification of thermo-hydraulic performance in heat exchanger tube inserted with multiple twisted-tapes
(2018-05-25)
Piriyarungrod, N.
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Kumar, Manoj
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
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.
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Heat transfer evaluation of turbulent flows through gear-ring elements
(2017-01-01)
Ruengpayungsak, K.
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Wongcharee, K.
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
Heat transfer and friction loss characteristics in tubular heat exchangers with gear-ring turbulators (GR-Ts) have been experimentally and numerically investigated. The GR-Ts with different free-space length ratios (SR = s/D = 1.0, 2.0 and 3.0) and tooth numbers (N = 8, 16 and 24), were experimentally tested under constant wall heat flux in turbulent flow (Reynolds numbers from 6000 to 20,000). Air was used as the working fluid. The behaviors in a plain tube and the tube with a conventional ring turbulators (N = 0) were also studied for comparison. The results show that utilizing tubes with GR-Ts leads to the increases of heat transfer coefficient and pressure loss as compared to those associated with the use of a plain tube. Heat transfer enhancement and friction increase with decreasing free-space length ratio (SR) and tooth number (N). Among the investigated inserts, the conventional ring turbulators (N = 0) with free-space length ratio, SR = 1.0 give the highest heat transfer rate and friction factor at 2.7 times and 15.5 times of those of the plain tube. However, the maximum thermal performance factor of 1.3 is obtained by using the GR-Ts with the largest free-space length ratio and maximum tooth number (SR = 3.0 and N = 24). At SR = 3.0, the GR-Ts with tooth numbers (N) of 0, 8, 16 and 24 yield thermal performance factors up to 1.24, 1.26, 1.28 and 1.3, respectively. The numerical results are given for a better understanding of flow and heat transfer characteristics associated with the use of GR-Ts.
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Influence of three-start spirally twisted tube combined with triple-channel twisted tape insert on heat transfer enhancement
(2016-04-01)
Eiamsa-ard, S.
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Promthaisong, P.
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
In the present article, heat transfer enhancement by three-start spirally twisted tube combination with triple-channel twisted tape is studied numerically using RNG k-ε turbulence model. Influences of the tape width ratio (w/D = 0.1, 0.25, 0.34 and 0.5) and tube/tape arrangement (belly-to-belly and belly-to-neck arrangements) are described. The numerical results of a twisted tube without tape and a circular plain tube are also given for comparison. The results are reported in terms of velocity field, temperature field, turbulent kinetic energy, local Nusselt number distribution, average Nusselt number, pressure loss and thermal performance factor. It is found that heat transfer and friction factor increase with tape width ratio. At a given tape width, the systems in belly-to-neck arrangement are more efficient for heat transfer enhancement than the ones in belly-to-belly arrangement. The three-start spirally twisted tubes with twisted tapes in belly-to-neck arrangement at w/D = 0.1, 0.25 and 0.34 give higher Nusselt numbers than the twisted tube without tape up to 1.2%, 21% and 36%, respectively. The twisted tubes with triple-channel twisted tape in belly-to-belly arrangement provide higher Nusselt numbers than the twisted tube without tape up to 1.23%, 6.7%, 10% and 17%, respectively. The superior heat transfer of the combined devices in belly-to-neck arrangement (especially at large w/D) is attributed to the stronger interaction between the swirling flows induced by the tubes and those induced by the tapes. Moreover, the systems in belly-to-neck arrangement cause lower friction loss than the ones in belly-to-belly arrangement. Thus, the systems in belly-to-neck arrangement yield higher thermal performance factors. Among the studied cases, the twisted tube combined with triple-channel twisted tape in belly-to-neck arrangement at w/D = 0.34 possesses the maximum thermal performance of 1.32 at Reynolds number of 5000.
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Investigation of heat transfer enhancement by perforated helical twisted-tapes
(2014-03-01)
Nanan, K.
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Thianpong, C.
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Promvonge, P.
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Eiamsa-ard, S.
Influence of perforated helical twisted-tapes (P-HTTs) on the heat transfer, friction loss and thermal performance characteristics under a uniform heat flux condition is reported. The P-HTTs were obtained by perforating typical helical twisted-tapes (HTTs) with a prospect to reduce the friction loss of fluid flow. The experiments were conducted using P-HTTs' three different diameter ratios (d/. w) of 0.2, 0.4 and 0.6, and three different perforation pitch ratios (s/. w) of 1, 1.5 and 2. The helical pitch ratio and twist ratio were fixed at P/. D=2 and y/. w=3. Tests were performed for Reynolds number between 6000 and 20,000. The experiments using the plain tube and the tubes with HTTs were also carried out for assessment. The experimental results reveal that the use of P-HTTs leads to the reduction of friction loss as compare to that of HTT. Heat transfer, friction loss and thermal performance factor increase as d/. w decreases and s/. w increases. For the present range, the maximum thermal performance factor of 1.28 is obtained by using the P-HTT with d/. w=0.2 and s/. w=2.0 at the Reynolds number of 6000. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor give accurate predictions within ±. 4%, ±. 6% and ±. 3%, respectively. © 2014 Elsevier Ltd.
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A case study on thermal performance assessment of a heat exchanger tube equipped with regularly-spaced twisted tapes as swirl generators
(2014-01-01)
Eiamsa-Ard, P.
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Piriyarungroj, N.
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Thianpong, C.
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Eiamsa-Ard, S.
Effects of the regularly-spaced twisted tape (RS-TT) on the heat transfer, friction factor and thermal performance factor behaviors in a heat exchanger are reported along with those of a full length twisted tape. The full length (or typical) twisted tapes with two different twist ratios (y=P/W = 6.0 and 8.0), and the regularly-spaced twisted tape (RS-TT) with two different twist ratios (y=6.0 and 8.0) and three free space ratios (s=S/P = 1.0, 2.0, and 3.0) were employed for comparative study. The article also presents the application of a mathematical model for numerical simulation of the swirling flow in a tube induced by regularly-spaced twisted tape (RS-TT) insertion. The numerical simulation was performed in order to gain an understanding of physical behavior of the fluid flow (decaying swirling flow field), fluid temperature and local Nusselt number characteristics of a tube fitted with RS-TT in the turbulent flow regime. The Navier-Stokes equation in common with the energy equation was solved using the SIMPLE technique with the RNG k-ε turbulence model. The experimental results show that heat transfer rate and friction increased with decreasing twist ratio and space ratio. At similar conditions, full length twisted tapes (s=0) offered higher heat transfer rate, friction factor and thermal performance factor than RS-TT ones (s = 1.0, 2.0 and 3.0) as they induced more consistent swirling flows and thus turbulence. This reveals that it is possible to gain promising tradeoff between enhanced heat transfer and increased friction by selecting the twisted tape with proper geometries.

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