KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 10 of 29

Some of the metrics are blocked by your
consent settings
Characterization of Heat Transfer Enhancement and Flow Topology in a Three-Start Spirally Corrugated Tube
(2025-12-01)
Du, Yuexiang
;
Phila, Arnut
;
Promthaisong, Pitak
;
Chuwattanakul, Varesa
;
Eiamsa-ard, Smith
The article provides a numerical analysis of the heat transfer characteristics and laminar periodic flow in a three-dimensional 3-start spirally corrugated tube. The working fluid is air, with a flow rate in terms of Reynolds numbers (Re) that ranges from 200 to 2,000. The investigation is conducted at six different pitch ratios (PR = 0.75, 1.0, 1.25, 1.5, 2.0, and 2.5) and five different depth ratios (DR = 0.02, 0.04, 0.06, 0.08, and 0.10). The results indicated that the spiral flow along the tube length was generated by the 3-start spirally corrugated tube. The swirl flow is divided into two components: the primary swirl flow, which is visible at the core, and the secondary swirl flow, which is visible at the near wall. These components contribute to the enhancement of fluid mixing, boundary layer disruption, and heat transfer on the tube wall. The Nusselt number (Nu) and friction factor (f) were increased as a result of the decrease in PR and the increase in Re and DR. The range of the Nu/Nu₀, f/f₀, and thermal performance factor (TPF) in a range analysis is 1.02 - 15.90, 0.97 - 5.52, and 0.73 - 2.33, respectively. At Re = 2,000, the corrugated tube with DR = 0.10 exhibited the greatest TPF of 2.33. Additionally, the results indicate that the 3-start spirally corrugated tube significantly improves heat transfer compared to the corresponding straight tube. The findings suggest that the structural characteristics of the flow path within the tube can be changed by a suitable PR and DR to optimize the overall heat transfer rate and thermal performance factor.
Some of the metrics are blocked by your
consent settings
Evaluation of aerothermal performance of a round tube with regularly-spaced multi-channel twisted tape elements installed
(2024-06-01)
Phila, Arnut
;
Chuwattanakul, Varesa
;
Thianpong, Chinaruk
;
Bhattacharyya, Suvanjan
;
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%.
Some of the metrics are blocked by your
consent settings
Influence of sawtooth twisted tape on thermal enhancement of heat exchanger tube
(2023-03-01)
Samutpraphut, Boonsong
;
Eiamsa-ard, Smith
;
Chuwattanakul, Varesa
;
Thianpong, Chinaruk
;
Maruyama, Naoki
This article employs sawtooth twisted tapes to generate swirling flow and interrupted flowing disturbance in order to increase the level of heat transfer rate. The influences of the sawtooth twisted tape (S-TT) on enhanced heat transfer rate, friction factor and aerothermal performance index (API) behaviors are analyzed. The sawtooth twisted tapes (S-TTs) possessing constant pitch/twist ratio (y//W) of 3.0 and six sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° are assessed. Considering turbulent flow using air as the testing fluid, experiments were investigated at 6,000 < Re < 20,000 under boundary conditions of constant heat flux. According to the experimental findings, sawtooth twisted tape (S-TT) improves heat transfer rate and raises pressure loss with varying rates based on sawtooth angles (α). With the sawtooth twisted tape (S-TT) and 70° sawtooth angles, the optimum API of 1.33 is attained, while Nusselt number and friction factor are 32 and 0.135 at Re = 6,000. The recommended sawtooth twisted tape (S-TT) yields a highest Nusselt number of 78, which is 1.6 times greater than the typical twisted tape (TT) and 1.1 times greater than the plain tube. The combination of the TT and sawtooth patterns can be beneficial in terms of boosting heat transfer rate and API relating coupling of swirling flow and interrupted flowing disruption effects since the sawtooth twisted tape (S-TT) offers superior performance than the TT. Additionally, the heat exchanger tubes fitted with sawtooth twisted tape (S-TT) at sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° gain greater Nusselt number than the plain tube up to 158.3%, 162.2%, 166.1%, 171.7%, 179.7% and 186.2%, respectively.
Some of the metrics are blocked by your
consent settings
Heat transfer visualization of swirling impinging jets using nozzle with centrally hollow helical-tape
(2020-05-01)
Eiamsa-Ard, Smith
;
Kunnarak, Kengkla
;
Wongcharee, Khwanchit
;
Chuwattanakul, Varesa
The present research was conducted to determine the heat transfer visualization of swirling impinging jets (SIJs) induced by nozzle with centrally hollow helical-tape using a thermochromic liquid crystal (TLC) sheet. The effects of jet-to-plate spacing ratios (L/D= 2.0, 4.0, 6.0 and 8.0) and Reynolds numbers (10,000 Re 20,000) on the radial uniformity and intensity of convective heat transfer were investigated. The experimental results of SIJs were compared with those of conventional impinging jets (CIJs). The formation of swirl flow of swirling impinging jet (SIJs) helped in improving the uniformity of local heat transfer or Nusselt number (Nu) and also average Nusselt number, as compared to those of conventional impinging jets (CIJs). Furthermore, the average Nusselt number (Nu) increased as jet-to-plate spacing ratio (L/D) decreased while Reynolds number (Re) increased for both conventional impinging jets (CIJs) and swirling impinging jets (SIJs). The highest Nusselt number (Nu) of swirling impinging jet (SIJ) was obtained at the jet-to-plate spacing ratio (L/D) of 4.0 and Reynolds number (Re) of 20,000. The maximum Nusselt number (Nu) of swirling impinging jet (SIJ) was higher than that of conventional impinging jets (CIJs) at similar conditions by around 5.3%.
Some of the metrics are blocked by your
consent settings
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.
;
Kumar, Manoj
;
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).
Some of the metrics are blocked by your
consent settings
Hydrodynamics investigation of pepper drying in a swirling fluidized bed dryer with multiple-group twisted tape swirl generators
(2019-03-01)
Chuwattanakul, V.
;
Eiamsa-Ard, S.
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/U <inf>mf</inf> = 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/U <inf>mf</inf> = 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.
Some of the metrics are blocked by your
consent settings
Effect of geometrical parameters on turbulent flow and heat transfer behaviors in triple-start corrugated tubes
(2018-01-01)
Promthaisong, Pitak
;
Jedsadaratanachai, Withada
;
Eiamsa-Ard, Smith
Computational results of flow structure, pressure loss and heat transfer characteristics in triple-start corrugated tubes are reported. The influences of the depth ratio (DR = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) and pitch ratio (PR = 0.5, 0.65, 0.75, 1.0, 1.5 and 2.0) were investigated in turbulent flow regime, Re = 5000 to 20,000. The computational results indicated that the triple-start corrugated tubes generate main swirl flow and helical swirl flow which helps to reduce the thermal boundary layer thickness and enhance the heat transfer rate. The flow and heat transfer become under fully developed periodic condition around x/D = 6.0. The friction factor monotonically increases with the rise of DR values and decrease PR values while maximum heat transfer rate is found at DR = 0.08 and PR = 0.75. Nusselt numbers and friction factors of triple-start corrugated tubes in the investigated range are found to be 0.8 to 2.31 and 1.0 to 17.14 times over those of the straight circular smooth tube, respectively. For the range studied, the triple-start corrugated tube with DR = 0.06 and PR = 0.75 offers the maximum thermal enhancement factor of 1.21 at Re = 5000.
Some of the metrics are blocked by your
consent settings
Heat transfer enhancement by tapered twisted tape inserts
(2015-10-01)
Piriyarungrod, N.
;
Eiamsa-ard, S.
;
Thianpong, C.
;
Pimsarn, M.
;
Nanan, K.
The effects of inserted tapered twisted tapes, their taper angle and twist ratio on heat transfer rate, pressure drop and thermal performance factor characteristics have been reported. The experiments were carried out by using the tapered twisted tapes with 4 different taper angles which θ= 0.0° (typical twisted tape), 0.3°, 0.6° and 0.9°. At each taper angle, the tapered twisted tapes were twisted at three different twist ratios (y/W) of 3.5, 4.0 and 4.5. All tapes were tested under turbulent flow regime for Reynolds numbers between 6000 and 20,000. A twist ratio is defined as the ratio of twist length (y) to twisted tape width at the large end (W). The plain tube was also tested for comparison. Heat transfer enhancement and friction loss increased with decreasing taper angle and twist ratio. Thermal performance factor tended to increase with increasing taper angle and decreasing tape twist ratio. For the present range, the tube with the tape with taper angle (θ) of 0.9° and twist ratio (y/W) of 3.5 yielded the maximum thermal performance factor of 1.05 at Reynolds number (Re) of 6000.
Some of the metrics are blocked by your
consent settings
Thermal performance evaluation of micro-fin tube with twisted tape inserts
(2015-01-01)
Eiamsa-Ard, Smith
;
Kunlabud, Suttisak
;
Wongcharee, Khwanchit
;
Pimsarn, Monsak
;
Eiamsa-Ard, Petpices
The heat transfer coefficient and pressure drop characteristics of turbulent flow through micro-fin tubes fitted with twisted tape in co/counter-arrangement have been studied. In the experiments, water as the tested fluid is passed in a Reynolds number range of 7800 to 17,650. The results reveal that, the Nusselt numbers in the system with a micro-fin tube and twisted tape are considerably higher than those in the system without tape. Evidently, the tape with the smaller twist ratio gives higher heat transfer rate, friction factor as well as thermal performance factor than the one with larger twist ratio as a result of a larger contact surface area, and stronger turbulence intensity and thus better fluid mixing which leads to a thinner thermal boundary layer. The result reveals that for using the micro-fin tube with twisted tape, the increases in the mean Nusselt number and friction factor are, respectively, up to 181% and 3.86 times of the plain tube and the maximum thermal performance factor is 1.52. It is also obvious that the heat transfer and friction factor obtained from the micro-fin tube with twisted tape in counter-arrangement is higher than that from the micro-fin tube with twisted tape in co-arrangement.
Some of the metrics are blocked by your
consent settings
Turbulent heat transfer enhancement in round tubes by inserting triple twisted-tapes
(2015-01-01)
Eiamsaard, S.
;
Promthaisong, P.
;
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.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results