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Thermohydraulic performance evaluation of a heat exchanger mounted with oval inclined twisted rings
(2025-03-01)
Samruaisin, P.
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Chuwattanakul, V.
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Thapmanee, P.
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Kumar, M.
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Naphon, P.
This research examines the effects of oval inclined twisted rings (I-TRs) on thermal performance characteristics. Heat transfer enhancement, friction factor, and thermal enhancement factor tests were conducted under uniform wall heat flux with Reynolds numbers (Re) varying from 6000 to 20,000. A systematic investigation was carried out to examine the influence of different pitch ratios (p/D) and oval-ring inclination angles (θ) on thermal enhancement factor (TEF). The experimental results reveal that the Nusselt number increases with decreasing pitch ratio (p/D) and inclination angle (θ) of the I-TRs. At p/D = 1.5, the Nusselt numbers are approximately 8.59 % to 18.78 % higher than those for I-TRs with p/D values of 2.0 and 2.5. At the smallest inclination angle, θ = 30°, the Nusselt numbers are approximately higher than those at θ = 45°, 60°, 75°, and 90° by around 1.56 %, 7.21 %, 13.74 %, and 27.14 %, respectively. At a p/D ratio of 1.5 and an inclination angle of θ = 30°, the resulting thermal enhancement factor (TEF) consistently exceeds unity across the entire Reynolds number (Re) range. In contrast, for other geometries and configurations, some TEF values fall below unity at higher Re. Within the studied range, the highest TEF of 1.12 is achieved at θ = 30°, p/D = 1.5, and Re = 6,000. The key finding suggests that the performance of the thermal system is highly dependent on both the configuration and operational conditions.
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Experimental Study of the Effects of Inclusion of Rectangular-Cut Twisted Tapes on Heat Transfer and Pressure Drop in a Round Tube
(2019-12-01)
Ruengpayungsak, K.
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Kumar, Manoj
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Chuwattanakul, V.
;
Eiamsa-ard, S.
Twisted tape inserts were used as swirl generators in the flow through a tube for enhancing heat transfer. Twisted tapes have commonly been applied in many thermal applications used in industry. Several modified twisted tapes have been investigated for improving the thermal performance of heat exchangers. The effects in tubes with modified rectangular-cut twisted tape (RC-TT) inserts with various free-spacing ratios (s/w = 2.0, 2.5, 3.0, 3.5 and 4.0) and edge–width ratios (t/W = 0.1, 0.15, 0.2 and 0.25) on heat transfer and pressure losses are reported. The RC-TT used in this work had a fixed thickness of 1.2 mm, width of 60 mm, length of 2000 mm and twist ratio (y/W) of 3.0. Experiments were performed over a range of Reynolds numbers, 10,000 ≤ Re ≤ 20,000, using air as a test fluid. A tube with a classical/typical twisted tape was also tested for comparison. In all cases, the Nusselt number tended to increase with the Reynolds number, while the friction factor and thermal performance showed the opposite trend. For the rectangular-cut twisted tape inserts, the friction factor and Nusselt number decreased, while thermal performance increased with increasing free-spacing ratios (s/w) and edge–width ratios (t/W). Furthermore, the maximum thermal performance was achieved at the lowest free-spacing ratio (s/w), edge–width ratio (t/W) and Reynolds number (Re).
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Parametric study on thermal enhancement and flow characteristics in a heat exchanger tube installed with protruded baffle bundles
(2019-11-01)
Eiamsa-ard, S.
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Ruengpayungsak, K.
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
Influence of protruded baffle turbulators (P-BTs) on turbulent convective heat transfer rate and thermal performance behavior in round tubes was experimentally studied. The following geometrical parameters of P-BTs were considered (i) spacing ratio (SR = s/D<inf>ob</inf> = 1.0–3.0), (ii) diameter ratio (DR = d/D<inf>ob</inf> = 0.2–0.4), (iii) baffle orientation angle (θ = 0° (without rotation), 60°, 120° and 180°), and (iv) Reynolds number (Re = 6000 to 20,000). Air was used as working fluid at Prandtl number of Pr = 0.71. The plain tube data was examined for comparison with tube installed with protruded baffle turbulators (P-BTs). The experimental results obvious that increasing baffle orientation angle (θ), increasing diameter ratio (DR) and decreasing spacing ratio (SR) lead to the significant increases in heat transfer (Nu) and pressure loss (f). It can be also reveal that thermal performance (η) at a given Re considerably increases with the increasing spacing ratio (SR) and the reduction of diameter ratio (DR) and baffle orientation angle. The P-BTs with larger baffle orientation angle, induce stronger vortex ring and longitudinal vortex behind the baffles, give higher the thermal performance. Furthermore, all of empirical correlations (Nu, f and η) were derived as a function of Re and the protruded baffle turbulator (P-BT) geometry parameters including spacing ratio (SR), and protrusion-diameter ratio (DR).
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Flow and thermal mechanisms in a heat exchanger tube inserted with twisted cross-baffle turbulators
(2017-03-05)
Nanan, K.
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
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Eiamsa-ard, S.
The turbulent forced convective heat transfer behaviors in a tube inserted with baffle turbulators (typical straight baffles, straight cross-baffles, straight alternate-baffles, twisted-baffles, alternate twisted-baffles, and twisted cross-baffles) have been experimentally and numerically investigated. The influence of pitch ratio (P/D) from 1.0 to 2.0 and Reynolds numbers (Re) from 6000 to 20,000 are also reported. Among the studied turbulators, the twisted cross-baffles gave the highest heat transfer enhancement and thermal enhancement factor while the straight cross-baffles gave the lowest heat transfer rate and thermal enhancement factor. The twisted-baffles, alternate twisted-baffles, and twisted cross-baffles created high longitudinal vortex/swirl around the tube core. The strongest longitudinal vortex/swirl was achieved by the use of twisted cross-baffles. The recirculation flows were found in the tube fitted with straight baffles (a recirculation flow), straight alternate-baffles (double recirculation flows) and straight cross-baffles (quadruple recirculation flows). The heat transfer rate, friction factor and thermal enhancement factor increased with decreasing pitch ratio (P/D) and increasing Reynolds number (Re). At the optimum condition of the smallest pitch ratio (P/D = 1.0) and the lowest Reynolds number (Re = 6000), the twisted cross-baffles offered the highest thermal enhancement factor of 1.7.
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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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Turbulent heat transfer enhancement in round tubes by inserting triple twisted-tapes
(2015-01-01)
Eiamsaard, S.
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Promthaisong, P.
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Chuwattanakul, V.
Turbulent flow characteristics and heat transfer performances in a round tube equipped with triple twisted tapes are investigated numerically. Effects of the triple twisted tapes at different twist ratios on the heat transfer and thermal performance characteristics are reported. The results of velocity and temperature fields, and the local heat transfer coefficients as well as the flow structure in tube with tape inserts are also given. A round tube wall is subjected to a constant wall temperature condition. Thermal field, heat transfer and fluid flow characteristics are studied using computational fluid dynamics (CFD) analysis. Computations, based on a finite volume method, are carried out by utilizing the Renormalized Group (RNG) k-e turbulence model. The investigation is carried out for triple twisted tapes with y/W = 2.0, 3.0 and 4.0 in round tubes for laminar air flow with Reynolds numbers between 500 and 2000. It is found that the use of triple twisted tapes with smallest twist ratio of y/W =2.0 results in the highest heat transfer and friction factor while the use of the tapes with the largest twist ratio (y/W = 4.0) results in the highest thermal performance. The highest thermal performances based on the constant pumping power criterion of the tubes equipped triple twisted tapes with y/W = 2.0, 3.0 and 4.0 are 2.43, 2.63 and 2.73, respectively.

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