Shiang-Wuu Perng, Horng Wen Wu, Yi-Ling Guo and Tao-Hsuan Liu
The purpose of this study is to value the thermal and hydraulic transport augmentation of turbulent fluid flow within the round-pipe axis fixed by a twisted-staggered…
Abstract
Purpose
The purpose of this study is to value the thermal and hydraulic transport augmentation of turbulent fluid flow within the round-pipe axis fixed by a twisted-staggered concave/convex dimples tape.
Design/methodology/approach
This study meets the report’s novel design by axis-inserting a twisted plastic tape with staggered concave/convex dimples of varying diameters (4 and 6 mm) and depths (1, 1.4 and 1.8 mm). Introducing a realizable model integrated with an improved wall function and SIMPLE solving procedure evaluates the thermo-hydraulic transport as Reynolds number is feasible as 5,000, 10,000, 15,000 and 20,000. In addition, using the findings from the present experimental work validates the numerical methodology.
Findings
This paper reveals that the staggered concave/convex dimples on the axis-fixed plastic tape can significantly improve thermo-hydraulic transport within this outer-heated tube. Furthermore, the processed dimples can cause flow disturbance, which increases turbulent kinetic energy and accelerates fluid mixing around a twisted plastic tape, resulting in enhanced thermal convection. The six kinds of twisted tapes (C1−C6) result in the thermo-hydraulic performance index (η) of 1.18–1.32 at Re = 5000. Among all the cases, the dimples using 4 mm combined with 6 mm diameter and 1.4 mm height (C4) earn the highest, around 1.40 at Re = 5,000.
Research limitations/implications
The conditions of constant hydraulic-thermal characteristics of working fluid (air), steady Newtonian fluid considered, and the ignored radiative heat transfer and gravity are the research limitations of the numerical simulation.
Practical implications
The given results can benefit from a round tube design of a thermal apparatus axis fixed by a twisted-staggered concave/convex dimples tape to augment the thermo-hydraulic transport.
Originality/value
Staggered concave/convex dimples on the surface of a twisted tape allow for impinging and swirling flow along the tape. These processed dimples can induce flow disturbance, which increases the turbulent kinetic energy and facilitates fluid mixing in a twisted tape. Furthermore, the hybrid-diameter dimples have enough flow channels for fluid separation-reattachment, and the thermo-hydraulic performance index has improved. This paper then presents a helpful passive approach for cooling a thermal device.
Details
Keywords
Shiang-Wuu Perng, Horng Wen Wu and De-An Huang
The purpose of this study is to advance turbulent thermal convection inside the constant heat-flux round tube inserted by multiple perforated twisted tapes.
Abstract
Purpose
The purpose of this study is to advance turbulent thermal convection inside the constant heat-flux round tube inserted by multiple perforated twisted tapes.
Design/methodology/approach
The novel design of this study is accomplished by inserting several twisted tapes and drilling some circular perforations near the tape edge (C1, C3, C5: solid tapes; C2, C4, C6: perforated tapes). The turbulence flow appearances and thermal convective features are examined for various Reynolds numbers (8,000–14,000) using the renormalization group (RNG)
Findings
The simulated outcomes reveal that inserting more perforated-twisted tapes into the heated round tube promotes turbulent thermal convection effectively. A swirling flow caused by the twisted tapes to produce the secondary flow jets between two reverse-spin tapes can combine with the main flow passing through the perforations at the outer edge to enhance the vortex flow. The primary factors are the quantity of twisted tapes and with/without perforations, as the perforation ratio remains at 2.5 in this numerical work. Weighing friction along the tube, C6 (four reverse-spin perforated-twisted tapes) brings the uppermost thermal-hydraulic performance of 1.23 under Re = 8,000.
Research limitations/implications
The constant thermo-hydraulic attributes of liquid water and the steady Newtonian fluid are research limitations for this simulated work.
Practical implications
The simulated outcomes will avail the inner-pipe design of a heat exchanger inserted by multiple perforated twisted tapes to enhance superior heat transfer.
Originality/value
These twisted tapes form tiny circular perforations along the tape edge to introduce the fluid flow through these bores and combine with the secondary flow induced between two reverse-spin tapes. This scheme enhances the swirling flow, turbulence intensity and fluid mixing to advance thermal convection since larger perforations cannot produce large jet velocity or the position of perforations is too far from the tape edge to generate a separated flow. Consequently, this work contributes a valuable cooling mechanism toward thermal engineering.
Details
Keywords
Shiang-Wuu Perng, Horng Wen Wu and Jun-Kuan Wu
The purpose of this study is to promote laminar heat transfer from the channel heated through a slab with slits and inclined ribs protruding across.
Abstract
Purpose
The purpose of this study is to promote laminar heat transfer from the channel heated through a slab with slits and inclined ribs protruding across.
Design/methodology/approach
The novel design of this study is performed through making the slits in the slab (C1–C3: with slits; C4–C6: without slits) and changing the vertical location of this slab (1/4, 1/2 and 3/4 channel height). The thermal fluid characteristics of all cases are analyzed for various Reynolds numbers (500, 1,000, 1,500 and 2,000) by the SIMPLE-C algorithm.
Findings
The results display that the ribbed slab effectively improves the heat transfer. The slits can modify the flow field in the vortexes around the inclined ribs and remove more heat from this zone to promote the heat transfer. As compared with C0 (without a slab), C2 (the slab with slits and inclined ribs protruding across located vertically on the 3/4 channel height) raises the averaged Nusselt number up to 27.7% at Re = 2,000. As compared with C4 (without slits), C1 (with slits) gains the maximum increase in the averaged Nusselt number by 5.07% at Re = 1,000.
Research limitations/implications
The constant thermo-physical properties of incompressible fluid and the steady flow are considered in this study.
Practical implications
The numerical results will profit the design of heated passageway using a slab with slits and inclined ribs protruding across to acquire better heat transfer promotion.
Originality/value
This slab with slits and inclined ribs protruding across can be applied to the heat transfer promotion and thus be viewed as a useful cooling mechanism in the thermal engineering.
Details
Keywords
Shiang-Wuu Perng, Horng Wen Wu, Nugroho Putra Kelana, Yi-Ling Guo and Chen-Jui Yang
The purpose of this paper, computational fluid dynamics (CFD) work, is to promote turbulent thermal convection in a heated circular tube using a passive scheme of a slotted…
Abstract
Purpose
The purpose of this paper, computational fluid dynamics (CFD) work, is to promote turbulent thermal convection in a heated circular tube using a passive scheme of a slotted twisted sheet.
Design/methodology/approach
The inventive design uses square-cut and conjugate triangular perforations to diversify the twisted tape for better thermal convection. The current novel passive scheme methodology is accomplished by carving the same square cuts and slitting various sizes of equilateral triangle perforations (side length varies between 8 and 16 mm). The re-normalisation group turbulence model and the semi-implicit method for pressure-linked equation method examine the turbulent thermal convection aspects of all simulations at different Reynolds numbers (6,000, 10,000 and 14,000).
Findings
The analyses of simulations exhibit that the placement of a twisted tape with triangle perforations and equidistant square cuts can effectually promote thermal convection in a circular tube. A larger-sized triangle perforation can increase the thermal convection enhancement and thermal performance factor, but an enlarged perforation may decrease the thermal convection enhancement and thermal performance factor. As a result, compared with the smooth circular tube, the circular tube with the slotted twisted sheet slit by a 10 mm equilateral triangle brings about the maximum improvement ratio of the mean Nusselt number of about 2.8 at Re = 6,000. Under weighing the friction through the circular tube, the tube with the slotted twisted sheet slit by a 10 mm equilateral triangle gains the best thermal performance factor of about 1.36 at Re = 6,000.
Research limitations/implications
The working fluid is water and its physical features are assumed to be constant. In addition, the fluid is considered a steady flow in this CFD work.
Practical implications
These CFD predictions will benefit the development of heat exchanger tubes equipped with a slotted twisted sheet to acquire preferable thermal convection enhancement.
Social implications
Higher thermal performance achieved by placing a slotted twisted tape in a heated tube will benefit society in lower energy consumption, machinery maintenance costs and impact on the environment.
Originality/value
This study combined triangle perforations and square cuts on the twisted sheet. This combination can induce the fluid flow across the sheet to disturb the swirling flow and then promote the fluid mixing to increase thermal convection. Therefore, this modified tape can be a profitable passive device for designing a heat exchanger.
Details
Keywords
Horng‐Wen Wu and Shiang‐Wuu Perng
To investigate the heat transfer enhancement performed by installing a rectangular plate turbulator for internal flow modification induced by vortex shedding.
Abstract
Purpose
To investigate the heat transfer enhancement performed by installing a rectangular plate turbulator for internal flow modification induced by vortex shedding.
Design/methodology/approach
The large eddy simulation (LES) and SIMPLE‐C method coupled with preconditioned conjugate gradient methods have been applied to the turbulent flow field and heat transfer enhancement of mixed convection in a block‐heated channel.
Findings
Provides information about heat transfer performance indicating that heat transfer performance can be affected by various width‐to‐height ratio of turbulator and Grasehof numbers with a constant Reynolds number. The results show that the installation of turbulator in cross‐flow above an upstream block can effectively enhance the heat transfer performance by suitable width‐to‐height ratio of turbulator and Grasehof numbers.
Research limitations/implications
It is limited to two‐dimensional mean flow for the turbulent vortex‐shedding flow past a long square cylinder.
Practical implications
A very useful source of information and favorable advice for people developing heat transfer enhancement for electronic devices.
Originality/value
The results of this study may be of interest to engineers attempting to develop thermal control of electronic devices and to researchers interested in the turbulent flow‐modification aspects of heat transfer enhancement of mixed convection in a vertical channel.
Details
Keywords
Horng‐Wen Wu, Shiang‐Wuu Perng, Sheng‐Yuan Huang and Tswen‐Chyuan Jue
To investigate the effect of transient mixed convective flow interaction between circular cylinders and channel walls on heat transfer with three circular cylinders arranged in an…
Abstract
Purpose
To investigate the effect of transient mixed convective flow interaction between circular cylinders and channel walls on heat transfer with three circular cylinders arranged in an isosceles right‐angled triangle within a horizontal channel.
Design/methodology/approach
This paper uses a semi‐implicit finite element method to solve the incompressible Navier‐Stokes equation, energy equation and continuity equation in primitive‐variable form by assuming the flow to be two‐dimensional and laminar.
Findings
Provides information indicating that the transient streamlines, isotherms, drag coefficient and time‐mean Nusselt number around the surfaces of three cylinders are affected by various gap‐to‐diameter ratio, Reynolds numbers and Grashof numbers. The results show that the maximum value of surface‐ and time‐mean Nusselt number along cylinders exists at S=0.75.
Research limitations/implications
It is limited to two‐dimensional laminar flow for the transient mixed convective flow interaction between circular cylinders and channel walls in a horizontal channel.
Practical implications
A very useful source of information and favorable advice for people is applied to heat exchangers, space heating, power generators and other thermal apparatus.
Originality/value
The results of this study may be of interest to engineers attempting to develop thermal control of thermal apparatus and to researchers interested in the flow‐modification aspects of mixed convection between circular cylinders and channel walls in a horizontal channel.
Details
Keywords
Horng‐Wen Wu and Shiang‐Wuu Perng
An axisymmetric two‐dimensional computer program employing the Large Eddy Simulation (LES) and SIMPLE‐C method coupled with preconditioned conjugate gradient methods is applied to…
Abstract
An axisymmetric two‐dimensional computer program employing the Large Eddy Simulation (LES) and SIMPLE‐C method coupled with preconditioned conjugate gradient methods is applied to the turbulent flows in the compression‐expansion strokes for various combustion chamber geometries under realistic engine conditions. The squish area percent of piston crown is changed (SQ = 0 percent for flat piston model, SQ = 46 percent for shallow bowl piston model and SQ = 76 percent for deep bowl piston model) under engine speeds (500∼1,500rpm) for the purpose of investigating the heat transfer performance. Comparison was made of present heat flux results and earlier experimental and numerical results. It is shown that the numerical method can predict the turbulence with reasonable accuracy. The results show that the configuration of piston crown for squish area percent can obviously enlarge the surface heat flux of wall boundaries in reciprocating engines.