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Enhancing Solid Fuel Properties of Sawdust Torrefaction using a Rotary Drum Reactor
(2026-07-01)
Sripha, Yutthana
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Phengpom, Tinnapob
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Kaewpengkrow, Prangtip Rittichote
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Thianpong, Chinaruk
This study investigated the physicochemical properties of torrefied sawdust obtained from the industry using a rotary drum reactor. Sawdust samples were torrefied at 220, 250, and 280 °C for 15, 30, and 45 min under a nitrogen atmosphere. Proximate analysis was conducted to determine the moisture, volatile, fixed carbon, and ash contents. The volatile content of the torrefied sawdust ranged from 69.05 to 88.06 wt.%. The results suggested that the chemical energies of solid fuels are stored in volatile matter and fixed carbon, both of which have a higher reactivity during carbonization. Characterization of functional groups was conducted using an FTIR spectrophotometer, and the higher heating value (HHV) of the torrefied sawdust was also investigated. The HHV increased from 15.36 MJ/kg to 21.13 MJ/kg, with the highest HHV achieved at 280°C for 45 min. Moreover, the torrefaction at 250 °C for 30 min gave a biofuel with more than 80% energy density, which allowed us to classify this biofuel as lignite. Therefore, torrefaction is a promising pretreatment technique that can improve the energy quality and combustion properties.
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Thermal performance enhancement of a circular tube fitted with inclined perforated disk inserts
(2026-03-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Thianpong, Chinaruk
Heat exchangers are crucial devices in industries, and enhancing their thermal performance while controlling pressure losses remains a significant challenge. This paper examines the idea that inclined perforated disk (IPD) inserts can be effectively used to improve heat transfer in circular tubes with constant heat flux conditions at acceptable levels of hydraulic penalties. Turbulent airflow with Reynolds numbers (Re) ranging from 5000 to 21,000 was examined in experiments, and three perforation indices (PI = 0.21, 0.24, and 0.27) were tested to determine the effects of hole density on thermal and hydraulic performance. Evidence showed that the Nusselt number (Nu) had been improved by over 86 % compared to plain tubes, with the thermal enhancement factor (TEF) reaching as high as 1.53 at PI = 0.27 and Re = 5000. Particle swarm optimization (PSO) and neural network modelling multi-objective optimization were used to test the results of the experiment and determine the best operating conditions at PI = 0.21. The paper has demonstrated that inclined perforated disk inserts can form a viable passive method for enhancing the efficiency of heat exchangers, as the swirl and jet flow patterns created by the perforations effectively break the thermal boundary layer, thereby increasing the rate of convective heat transfer.
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Thermodynamic performance analysis of a round tube fitted with gradient quadruple twisted tapes
(2026-03-01)
Samruaisin, Prachya
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Liengsirikul, Sathaporn
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Chamoli, Sunil
Air-cooled heat exchangers employing twisted-tape passive inserts exist in many forms; however, designing tapes that are practical to manufacture while enhancing heat transfer without incurring excessive pressure drop remains challenging. This study therefore introduces gradient quadruple twisted tapes (GQTT), which gradually vary the pitch across four tapes to control swirl and mix along the tube. In addition, the turn count changes in steps along the four tapes, which triggers extra turbulence near each change and keeps the flow well mixed downstream. This simple and manufacturable pattern aims to boost heat transfer while keeping the added friction under control. Our objective is to evaluate whether GQTT can improve overall performance while keeping the pressure drop within a practical range, in comparison with a plain tube and a constant-turn tape. A realizable k-ε turbulence model, rigorously validated against benchmark data, was applied to eight GQTT variants and benchmarked against a plain tube and a constant-turn tape for Reynolds numbers (Re) between 5000 and 19,000. Spatial second-order schemes, grid-independence testing, and strict residual criteria ensured solution accuracy. Among the candidates, the descending-opposite-pitch configuration (Ds-OPSD) consistently delivered the highest performance. First-law analysis reveals a peak thermal performance factor (TPF) of 1.42 at Re = 5000, equating to a 42 % gain in overall thermo-hydraulic efficiency over the plain tube, with the Nusselt number (Nu) climbing from 57.5 to 100 across the examined Re window. Second-law metrics corroborate this superiority. At the same Re of peak TPF, the Ds-OPSD cuts exergy destruction from 291.4 to 62 W (≈79 % reduction versus the plain tube and ≈22 % versus the constant-turn tape). Total entropy generation remains minimal and nearly constant (S<inf>total</inf> ≈ 0.206–0.212), while the Bejan number stays high (≈0.999–0.971), indicating that the enhancement is achieved without excessive frictional penalties.
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Evaluation of heat transfer performance of a channel mounted with square-wing perforated V-type baffles
(2025-01-01)
Eiamsa-Ard, Smith
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Phila, Arnut
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Maruyama, Naoki
The current study examines the aerothermal performance behaviors of a rectangular-channel with square-wing perforated V-type baffles (SW-PVBs). The SW-PVBs were attached to lower channel walls at five attack angles, θ = 0° (solid V-type baffle), 22.5°, 45°, 67.5° and 90°. The heat transfer and pressure drop results of a channel without SW-PVBs were performed to normalize the results of the SW-PVBs and evaluate thermal performance factors (TPFs). It can be observed that as the attack angles decreased, the heat transfer and pressure loss rose. Among the SW-PVBs that were tested, those characterized by θ = 22.5° exhibited the most significant improvement in heat transfer, whereas SW-PVBs with θ = 45° gave the highest thermal performance factors. Additionally, the SW-PVBs with θ = 45° offered the highest TPF, as high as 1.93.
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Effect of trapezoidal louvered winglets on increased heat transfer and exergy in tubular heat exchanger
(2024-10-01)
Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
The effect of inserting a trapezoidal louvered winglet tape (TLWT) into a uniformly heat-fluxed tube on its thermal effectiveness was studied experimentally. The exergy and entropy analyses for turbulent flows, as well as frictional loss and thermal features, were highlighted as key aspects of the experimental finding for the Reynolds number which measured between about 4700 and 30,000. Because fixing baffles to the curved shape of tube wall presented a challenge, the baffles were consequently positioned on double surfaces of a flat tape. Six values of the louver angle (θ<inf>1</inf> = 0°, 25°, 30°, 45°, 60°, and 90°) and three values of the relative pitch of winglet (P<inf>R</inf> = 1.0, 1.5, and 2.0) were employed in the arrangement of TLWTs, with the V-apex oriented upstream (V-up). Each of these had only a fixed height (B<inf>R</inf> = 0.25) and angle of attack (α = 30°). The winglets were utilized to induce streamwise vortices which can hinder the boundary layer formation, while the louvered openings were adopted to lessen pressure drop without significantly impacting the primary vortices. The experiment results disclosed that the smallest θ<inf>1</inf> and P<inf>R</inf> produced the largest relative friction factor (f<inf>R</inf>) and Nu<inf>R</inf>, which were about 13.57 and 4.04 times higher, while P<inf>R</inf> = 1 and θ<inf>1</inf> = 45° provide the greatest TEF of about 2.27. The greatest exergy efficiency (η<inf>Ex</inf>) resulting from the TLWT was reached at θ<inf>1</inf> = 0°, but the generation of entropy (S˙<inf>g</inf>′) dropped with lowering θ<inf>1</inf> and Re. A further examination, however, showed that the best scenario with α = 60° and staggered arrays is more desirable since it yields the largest TEF of 2.45 at θ<inf>1</inf> = 45° and P<inf>R</inf> = 1. For the range of parameters under consideration, the Nu and f correlations were additionally established.
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Enhanced thermal effectiveness of square duct with V-type double-baffles: Numerical study
(2024-09-01)
Promvonge, Pongjet
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Sripattanapipat, Somchai
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Thianpong, Chinaruk
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Skullong, Sompol
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Promthaisong, Pitak
The article puts forward three-dimensional computational research on heat transmission augmentation within a square channel containing 45o V-type double-baffles positioned on the lower and top parts at regular intervals in the turbulence zone for Reynolds numbers (Re) that vary from 3000 to 20,000. The primary goal of this research is to increase the thermal effectiveness and relative Nusselt number (Nu/Nu<inf>0</inf>), in order to conserve energy and reduce the size of the heating or cooling system. The simulations utilize a finite volume approach in common with the SIMPLE algorithm, whereas the turbulent model used is the realizable k–ε. The baffles are designed to be separated vertically for reducing pressure loss. Both single V-baffles and double V-baffles have four relative pitches (PR = 0.4, 0.5, 0.6, and 1.0) and height/blockage ratios (BR = 0.05, 0.1, 0.15, and 0.2), with a fixed attack angle (α) of 45o. The computational findings show that both V-baffles are capable of producing the primary vortices, but only the double V-baffles have the ability to provide the impinging streams onto the wall, cooling the region behind the baffles. This suggests that the double V-baffles not only boost heat transmission but also reduce frictional loss. When compared to a single V-baffle, the double ones enhance heat transfer by an average of 1.04–9.94% while decreasing frictional loss by an average of 9.88–31.73%. The thermal effectiveness factor (TEF) of the double V-baffles ranges from 1.03 to 3.21, and its peak value of around 3.21 is for PR = 0.4, BR = 0.05, at lower Re.
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Evaluation of aerothermal performance of a round tube with regularly-spaced multi-channel twisted tape elements installed
(2024-06-01)
Phila, Arnut
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Chuwattanakul, Varesa
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Thianpong, Chinaruk
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Bhattacharyya, Suvanjan
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Naphon, Paisarn
This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%.
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Numerical heat transfer study of square duct equipped with novel flapped V-baffles
(2024-03-01)
Thianpong, Chinaruk
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Promvonge, Pongjet
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Skullong, Sompol
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
The paper describes a computational study of heat transfer enhancement inside a square duct with V-shaped flapped baffles located repeatedly on the bottom and top walls for fluid flowing with Reynolds numbers (Re) from 3000 to 21,000. The basic goal of this work is to attain the largest relative Nusselt number (Nu/Nu<inf>0</inf>) whilst maintaining the highest thermal performance to improve energy savings. A finite volume method was used in the computations, along with the Realizable k‒ε turbulent model. The variable baffle parameters considered first in the current simulation were the relative height/blockade ratio (B<inf>R</inf> = 0.05−0.2) and the flap angle of the baffle hole (β = 0° − 90°), while the fixed parameters included the attack angle (α = 60°), hole diameter ratio (d<inf>R</inf> = 0.5), and pitch ratio (P<inf>R</inf> = 0.5). To accomplish this goal, the previously mentioned parameters providing the best thermal performance were investigated further by extending the values of B<inf>R</inf> to 0.25−0.3, d<inf>R</inf> to 0.8 and α to 45°−30°. The simulation results indicate that the jet flowing from the flapped hole, as well as the vortices created by the baffle, can boost heat transfer and friction loss in comparison to the plain duct. In comparison, using a flapped baffle with β > 0° results in less friction loss, a greater thermal enhancement factor (TEF), and a higher Nusselt number than using a baffle with no flap. The first investigation disclosed that for B<inf>R</inf> = 0.2 and β = 20°, the greatest TEF of 2.19 with Nu/Nu<inf>0</inf> of 7.9 times are obtained. The extended study, on the other hand, showed that the highest TEF of roughly 2.49 with Nu/Nu<inf>0</inf> of 8.4 times are seen for α = 45°, d<inf>R</inf> = 0.8, B<inf>R</inf> = 0.25 and β = 20° at lowest Re. Thus, the flapped baffle provides a significant increase in Nu/Nu<inf>0</inf> and TEF over the baffle alone.
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COMPUTATIONAL ANALYSIS OF FLOW CHARACTERISTICS AROUND A TWIN-SPLINED CYLINDER WITHIN A 2-D CHANNEL
(2024-01-01)
Chamoli, Sunil
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Sahi, Samarth
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Jaiswal, Shivam
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Negi, Anant
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Pant, Pawan Kumar
In the present research work, external flow-induced stresses on a circular cylinder with double-splined surfaces are investigated at a Reynolds number Re of 100. Opposite sides of the cylinder have splined surfaces. The splines are positioned between 0° and 90° from the cylinder's front and rear stagnation points. It is demonstrated that the spline on the cylinder's leading edge modifies the vortex dynamics and causes considerable changes in flow-induced forces. At Re = 100, when a spline is placed on a cylinder's surface, noticeable reduction is observed in the coefficients of lift and drag compared to a smooth cylinder. When the inclination angle is increased to a maximum of 60°, the stagnation point moves to the windward side. Additionally, the spline in the front and back side of the cylinder significantly strengthens the vortex flow. At inclinations of 90° and 0°, maximal and minimal vorticities are obtained. Furthermore, the present work's double-spline cylinder demonstrates the advantage of reduced drag over many previously reported bluff bodies.
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Enhanced heat transfer performance in channel with delta-wing perforated V-type baffles
(2023-10-01)
Eiamsa-ard, Smith
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Phila, Arnut
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Maruyama, Naoki
The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0o (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000.

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