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Performance Assessment of Solar Air Heater Channel with Inclined Groove Turbulators
(2025-05-19)
Koolnapadol, N.
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Promvonge, P.
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Khanoknaiyakarn, C.
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Promthaisong, P.
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Hoonpong, P.
An experimental investigation was carried out to explore the thermal performance and frictional loss features in a solar air heater (SAH) channel that was intentionally roughened on the absorber surface using multiple inclined groove turbulators. The working fluid, air, flows into the SAH channel, which has a consistent surface heat flux for Reynolds numbers (Re) varying between 5290 and 22,600 in the current research. Thermal characteristics at a single inclination angle (a = 45°) are investigated in this research by comparing the effects of three distinct relative groove frequencies (P/H=PR=0.8, 1.2 and 1.6) and groove depth ratios (D/H=DR=0.16, 0.24 and 0.32). The findings highlight that the employ of inclined grooves results in a noticeable rise in Nusselt number (Nu) from 1.24 to 2.82 times relative to the smooth absorber plate (smooth channel), as well as a 1.88 to 7.9 times increase in friction factor (f). The Nu and f show an increasing trend when Re increases, whereas the opposite pattern occurs as DR and PR increase. At PR = 0.8 and DR = 0.32, the inclined groove roughness has the largest thermal effectiveness factor (TEF) of around 1.64. The Nu and f correlations, which are functions of inclined groove features, have also been established.
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Heat transfer of a coil-tube heat exchanger in the freeboard zone of a rice husk fluidized-bed combustor
(2021-10-01)
Chokphoemphun, S.
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Eiamsa-ard, S.
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Promvonge, P.
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Thongdaeng, S.
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Hongkong, S.
This research presents an investigation on heat recovery from a fluidized-bed combustor by using coil-tube heat exchangers positioned inside the freeboard zone. Rice husk was used as a fuel at a constant mass flow rate of 8 kg/h. Heat recovery experiments were performed at four different air mass flow rates (6.0248, 6.8077, 7.8163, and 8.8646 kg/h) using coil-tube heat exchangers wrapped around with steel wires in three different configurations (2_Coil wires, 4_Coil wires and Full length). Air was supplied to the coil-tube heat exchanger with two different air flows corresponding to flue gas flow: co-flow and counter-flow. The results showed that the outlet temperature tended to decrease with an increase in air flow rate in the coil-tube heat exchanger. The outlet temperatures obtained from the system with co-flow were greater than the one with counter-flow by 7–17 °C (2–15%) depending on the coil-tube heat exchanger configuration. The heat transfer rates in heat recovery process were in the range of 279–425 J/s. In addition, it was found that the heat transfer rate and the outlet temperature of the air from the coil-tube heat exchanger increased with an increase in the number of coil wires wrapped around the outer surface of the coil-tube heat exchanger.
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Characterization of heat transfer and artificial neural networks prediction on overall performance index of a channel installed with arc-shaped baffle turbulators
(2021-08-01)
Promvonge, P.
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Eiamsa-Ard, S.
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Wongcharee, K.
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Chuwattanakul, V.
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Samruaisin, P.
Influences of baffle pitch ratio (p/w) and attached angle of arc-shaped baffles (AB) on the overall performance index (OPI) of a channel installed with AB have been carefully studied. In addition, an artificial neural network (ANN) model for predicting the OPI of the channel was reported. The arc-shaped baffle (AB) showed a significant effect on the augmented heat transfer and friction loss penalty as compared to a smooth channel. As the attached arc shaped angle (θ) increased, both Nusselt number and friction factor intensified. The Nusselt number values at θ = 90° were higher than those at θ = 20°, 40°, 60°, and 80° by up to 5.8%, 3.9%, 2.3% and 2.5%, respectively. The Nusselt number increased when the p/w was raised from 4.0 to 8.0 while the opposite trend was observed when the p/w was raised from 8.0 to 12.0. The maximum OPI of 1.43 was achieved by using the baffles with θ = 90° and pitch ratio of 8.0 at Re = 4000. For the development of ANN models for predicting the OPI, it was found that the best predictive performance was (R2) of 0.99843407 for ANN model of 3-50-50-1 with Tanh-Tanh activation function at epoch of 1200.
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Heat Transfer Augmentation in Round Tube with Diamond-shaped Baffle Inserts
(2019-04-09)
Khanoknaiyakarn, C.
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Sripattanapipat, S.
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Promvonge, P.
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Skullong, S.
Influences of diamond-shaped baffle (DSB) insertion in a heat exchanger tube on its thermal performance are experimentally presented. The DSB elements were repeatedly mounted into the tube using two straight small rods to connect the DSBs together to produce the longitudinal vortex flows inside. The experiments were carried out in a constant surface heat-fluxed tube equiped with DSBs. The DSBs were placed periodically with an attack angle of 45° and a pitch spacing of three times of tube diameter (PR=P/D=3) while four different DSB heights called blockage ratios (BR=b/D=0.1, 0.2, 0.3 and 0.4) were offered. Air was used as the test fluid flowed into the tube to yield the Reynolds number (Re) in a range of 4190-26,000. The heat transfer rate and the pressure drop of the current work were presented in terms of Nusselt number (Nu) and friction factor (f), respectively. The experimental results showed that the DSB provides the increase in the heat transfer around 3.53-4.16 times higher than the smooth tube while friction factor increases around 16.68-29.52 times. To evaluate the gain of using the DSB, the thermal performance factor (TEF) is determined in a range of 1.25-1.55 whereas the highest TEF is found at BR=0.1.
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Heat Transfer Enhancement in a Heat Exchanger Tube with 45° Rectangular-Winglet Pairs
(2019-04-09)
Tongyote, P.
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Sripattanapipat, S.
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Promvonge, P.
An experimental investigation on thermal characteristics in a heat exchanger equipped with 45° rectangular winglet pairs (RWP) is conducted using air flowing in a constant heat flux tube with Reynolds number (Re) in a range of 5,200 to 23,000. Parameters of RWP included three relative height or blockage ratios (BR = 0.06, 0.08 and 0.1) and two pitch-spacing ratios (PR = 1.0 and 2.0). The heat transfer and the pressure drop in the test tube are displayed in the form of Nusselt number (Nu) and friction factor (f), respectively. The investigation shows that Nu and f values of the tube with RWP insert are, respectively, in the range of about 1.55-3.2 and 3.76-6.44 times above the plain tube alone, depending on the operating condition. The maximum thermal performance for using the RWP is found to be 1.7 at the lowest Re.
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Drying peppercorn characteristics in fluidized bed dryer equipped with baffle vortex generators
(2018-03-26)
Chuwattanakul, V.
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Banthumporn, K.
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Promvonge, P.
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Eiamsa-Ard, S.
The paper deals with the characteristic study of drying peppercorn using fluidized-bed dryer fitted with baffle vortex generators. The experiments were operated at three different superficial air velocities of 1.2U<inf>mf</inf>, 1.4U<inf>mf</inf> and 1.6U<inf>mf</inf>. Experiments were operated from the initial to final moisture contents of around 12% (dry basis). During the experiments, peppercorns were sampling every 5 minutes, for moisture analysis. A typical fluidized-bed dryer was also tested under similar operating conditions for the assessment. The results indicate that the influence of superficial air velocity on drying peppercorn characteristic in the fluidized-bed dryer fitted with baffle vortex generators is more significant than that in the typical fluidized-bed dryer. It is observed that fluidized-bed dryer fitted with baffle vortex generators shows better performance in reducing moisture content with faster drying rate than the typical fluidized bed dryer especially at high superficial air velocity due to the strong longitudinal vortex which helps in improving the fluid mixing, heat and mass transfer rates.
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Performance improvement in a tubular heat exchanger by punched delta-winglet vortex generators
(2018-02-07)
Khanoknaiyakarn, C.
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Promvonge, P.
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Thianpong, C.
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Skullong, S.
A novel tubular heat exchanger incorporated with punched delta-winglet vortex generators (called perforated delta-winglet vortex generator, P-DWVG) is proposed for improving its thermal performance and energy saving. The P-DWVG elements are punched out from a straight tape having its width nearly equal to the tube diameter before insertion. The main aim at employing the P-DWVG insert is to produce counter-rotating vortices along the tube to promote turbulence intensity inside as well as to transport the cold fluid at the central core to the near-wall regions. The experiment was performed to study thermal behaviors in a uniform heat-fluxed tube inserted with P-DWVGs. The P-DWVGs with the attack angle of 45° were mounted periodically with three different blockage ratios (B<inf>R</inf> = 0.1, 0.2 and 0.3) and two pitch ratios (P<inf>R</inf> = 2 and 3). Air as the test fluid was varied to obtain turbulent airflow for Reynolds number (Re) in a range of 4,150-25,500. The experimental results show that the P-DWVG provides a considerable increase in the rate of heat transfer around 3.1-4.01 times whereas friction factor increases around 11.44- 34.23 times higher than the plain tube. To assess the real benefits of P-DWVGs, thermal performance factor (TEF) is examined and in the range of 1.39-1.48 where its maximum is at B<inf>R</inf> = 0.1 and P<inf>R</inf> = 2.
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Turbulent periodic flow and heat transfer in a rectangular channel with detached V-baffles
(2017-10-01)
Kaewkohkiat, Y.
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Promvonge, P.
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Eiamsa-ard, S.
This paper presents a numerical analysis of turbulent periodic flow and heat transfer in a rectangular channel with detached V-baffles. The computations are based on the finite volume method with the SIMPLE algorithm for handling the pressure–velocity coupling and using the QUICK scheme for the convection terms. Air is used as the test fluid with the air flow rate in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of different detached-clearance ratios (c/H, CR) of 0.0, 0.05, 0.1, 0.15, and 0.2, baffles-pitch to square channel-diameter ratio (pitch ratio (p/H), PR) is 1.0, baffles-height to square channel-diameter ratio (blockage ratio (b/H), BR) is 0.10, and attack angle (α) is 45◦ on heat transfer, friction factor and thermal enhancement factor are investigated numerically. It is found that a pair of counter-rotating vortices (P-vortex) caused by the baffles can induce impingement/attachment flows repeatedly on the rectangular channel walls leading to a greater increase in the heat transfer over the test channel. The maximum thermal performance and heat transfer are found to be about 1.5 and 3.3, respectively for CR = 0.05 and Re = 3000, while the highest pressure loss is about 21.5 in the case of CR = 0.2 and Re = 20,000.
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Numerical heat transfer study in a round tube with 60° V-shaped rings
(2017-06-01)
Kaewkohkiat, Y.
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Tamna, S.
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Pairoj, W.
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Promvonge, P.
Turbulent flow and heat transfer behaviors in a 3-dimensional isothermal tube mounted repeatedly with 60° V-shaped rings (V-rings) are numerically investigated. The computation based on the finite volume method was conducted for the airflow rate in terms of Reynolds number (Re) in the range of 4000 to 20,000. The ring parameters include three flow blockage ratios, (BR=e/D=0.1, 0.15 and 0.2) and a single ring pitch ratio, PR=1. The computed result shows that friction factor and Nusselt number (Nu) increase with the increment in BR and the maximum thermal enhancement factor (η) of about 1.73 with Nu/Nu<inf>0</inf> = 4.5 is found at BR=0.1 and Re=4000. For the need of maximum heat transfer enhancement (Nu/Nu<inf>0</inf>), the case of BR=0.2 V-ring is selected and modified since this case provides the highest heat transfer. The modification is made by cutting off some area of both ends of the BR=0.2 V-ring and the effect of cutting off (called end-cut ratio, ER=c/e) on thermal performance is also examined. The study reveals that for the end-cut V-ring, the friction factor is considerably decreased while the heat transfer rate reduces moderately with increasing ER. The end-cut V-ring yields the maximum η of 1.64 at ER=0.9, Re= 4000 with Nu/Nu<inf>0</inf> = 5.4. Thus, the Nu/Nu<inf>0</inf> of the end-cut one is about 20% higher than that of the BR=0.1 V-ring.
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Numerical thermal performance study in a heat exchanger tube with inclined elliptical rings
(2017-06-01)
Sodsri, W.
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Tamna, S.
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Thianpong, C.
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Promvonge, P.
The paper deals with a numerical study on the effect of inclined elliptical ring (IER) on heat transfer augmentation in a uniform heat-fluxed heat exchanger tube. In the present work, the 60° IER was mounted repeatedly in the tube with six different eccentricity ratios (E<inf>R</inf> = b/a = 1, 0.9, 0.8, 0.7, 0.6 and 0.5) at a single ring-pitch ratio P<inf>R</inf> = 1.0. Air as the test fluid flows into the tube for Reynolds number ranging from 4000 to 20,000. To find the optimum thermal performance, the effect of E<inf>R</inf> values on the heat transfer and pressure loss is investigated. The study indicates that the use of IER can induce higher turbulent intensity imparted to the flow leading to higher heat transfer in range of about 237 to 461% above the smooth tube.

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