Jayranaiwachira, Nuthvipa
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Jayranaiwachira, Nuthvipa
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nuthvipa.ja@kmitl.ac.th
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Item type:Publication, Thermal performance of heat exchanger tube inserted with curved-winglet tapes(2018-01-25); ; ; The paper deals with the effect of curved-winglet (CW) inserts on thermal and flow behaviors in a constant heat-fluxed tube. A straight tape is used to support the 45° CWs mounted repeatedly on both tape sides to generate two pairs of longitudinal counter-rotating vortices along the test tube in order to assist the chaotic flow mixing and to disrupt the boundary layer leading to faster rate of heat transfer. The airflow and heat transfer behaviors in the tube are examined for Reynolds number (Re) in the range of 4150–25,400. The curved-winglet tape (CWT) parameters involved are the winglet attack angle of 45° three relative winglet heights (b/D = B<inf>R</inf> = 0.1, 0.2 and 0.3) and winglet pitches, (P/D = P<inf>R</inf> = 0.5, 1.0 and 2.0). The investigation reveals that the maximum thermal enhancement factor (TEF) of the CWT is about 1.62 at B<inf>R</inf> = 0.1 and P<inf>R</inf> = 1.0. For further improvement, the CWT at B<inf>R</inf> = 0.1 and P<inf>R</inf> = 1.0 is modified by punching the CW to be the perforated-curved-winglet tape (P-CWT) to reduce the pressure loss. The P-CWT characteristics include five different punched hole diameters (d = 1.0, 1.5, 2.0, 2.5 and 3.0 mm). The experimental results show that TEF of all the P-CWTs is higher than that of the CWT and the maximum TEF of 1.76 higher than the CWT around 9% is found for d = 1.5 mm. To understand the flow pattern and heat transfer mechanism, a three-dimensional CFD investigation is also performed and for validation, the good agreement between numerical and experimental results is found. For experimental data, empirical correlations for Nu, f and TEF for the CWT and P-CWT inserts are also determined. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Experimental and numerical heat transfer investigation in a tubular heat exchanger with delta-wing tape inserts(2016-11-01); ; Effects of insertion of a straight tape with double-sided delta wing pairs (called “delta-wing tape”, DWT) used as a longitudinal vortex generator (LVG) on forced convective heat transfer and flow friction characteristics in a uniform heat-flux heat exchanger tube are investigated experimentally and numerically in the present work. The experiment is conducted for turbulent airflow with the Reynolds number (Re) from 4200 to 25,500. The delta wings are in a forward-wing arrangement with three wing inclination angles (α = 30°, 45° and 60°) and with five ratios of wing-pitch to tube-diameter (P/D = PR = 0.5, 1.0, 1.5, 2.0 and 2.5). Influences of the DWT insert on heat transfer in terms of Nusselt number (Nu) and pressure drop in the form of friction factor (f) are examined. The results indicate that the DWT provides the increases in Nu and f up to 505% and 69 times above the plain tube, respectively and the maximum thermal enhancement factor (TEF) is at 1.49. The 60° DWT with PR = 0.5 yields the highest Nu and f but the 30° one with PR = 1.0 gives the best TEF. To understand the flow structure and heat transfer mechanism, a three dimensional CFD simulation of the inserted tube is also performed. The simulated results are validated and are in good agreement with the current measurements. A simulated heat transfer and fluid flow structure is also reported. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Thermal behaviors in a round tube equipped with quadruple perforated-delta-winglet pairs(2017-01-01); ; The article deals with an experimental investigation of enhancing convective heat transfer in a heated circular tube with pairs of perforated-delta-winglets placed repeatedly on a perforated-cross-tape (PW-XT). The perforated-delta-winglets are placed in inline array and a triangular-hole is punched on each winglet to reduce the friction loss. The aim at using the PW-XT insert is to produce streamwise-vortex flows in the tube to reduce the thickness of thermal boundary layer and to increase fluid mixing of the flow. The involved winglet parameters are composed of relative winglet height or blockage ratio, (B<inf>R</inf> = b/D = 0.1, 0.15, 0.2 and 0.25) and relative winglet pitch or pitch ratio, (P<inf>R</inf> = P/D = 0.5, 1.0, 1.5 and 2.0) and those are performed at a single delta-winglet inclination/attack angle, α = 30° and a winglet porosity ratio, A<inf>p</inf>/A<inf>w</inf> = 0.359 for Reynolds number from 4180 to 26,000. The present results of heat transfer and pressure loss displayed in terms of respective Nusselt number (Nu) and friction factor (f) show that Nu increases with increasing B<inf>R</inf>but with decreasing P<inf>R</inf>. Nu for the PW-XT insert is in a range of 1.96–5.06 times while f increases around 2.06–35.68 times above the plain tube alone. To estimate the real merits of the PW-XT, the thermal enhancement factor (TEF) is evaluated and found to be a maximum around 1.902 at B<inf>R</inf> = 0.15, P<inf>R</inf> = 1.0. In comparison, the PW-XT gives considerably higher TEF than the typical four delta-winglet pairs placed on the cross-tape (TW-XT) having the highest TEF around 1.72. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Numerical Heat Transfer Investigation in a Heat Exchanger Tube with Hexagonal Conical-ring Inserts(2016-11-01); The hexagonal conical rings (HCR) modified from the typical conical ring (CR) are used as a turbulence promoter for producing the vortex flows to enhance the heat transfer rate in a heat exchanger tube. To reduce the pressure loss, the V-shaped HCR (V-HCR) obtained by cutting both symmetric plane of the cone-tip of HCR at 30°, 45°and 60°is offered in the present work. The tube fitted with V-HCR elements having a fixed inlet and outlet diameter is numerically investigated. The computation is carried out for Reynolds number in a range of 3000 to 20,000 in a uniform heat-fluxed test tube. The numerical results show that the V-HCR insert leads to much higher heat transfer than the typical CR/HCR insert or the smooth tube alone and also provides lower friction factor. The 30°V-shaped HCR gives the highest heat transfer and thermal performance due to the lowest friction loss, indicating the promising device of the V-HCR. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Experimental and numerical heat transfer investigation in turbulent square-duct flow through oblique horseshoe baffles(2016-01-01); ; An experimental and numerical work has been carried out to study the heat transfer enhancement in a heat exchanger square-duct fitted with 30° oblique horseshoe baffles (HB). In the current work, air is passed through the HB-inserted duct having a constant surface heat-flux. The air flow and heat transfer behaviors are presented for turbulent flow region, Reynolds number ranging from 4000 to 25,000. The pertinent parameters of the 30° HB elements include three relative baffle-pitches (P<inf>R</inf>=P/H=0.5, 1 and 2) and five relative baffle heights (B<inf>R</inf>=b/H=0.05, 0.1, 0.15, 0.2 and 0.25). Influences of those parameters on heat transfer and energy loss due to friction in terms of Nusselt number and friction factor, respectively are studied. The experimental result shows that at a given B<inf>R</inf>, the smallest pitch spacing (P<inf>R</inf>=0.5) provides the highest heat transfer and friction factor. The HB at B<inf>R</inf>=0.25 and P<inf>R</inf>=0.5 yields the highest heat transfer and friction factor but the one at B<inf>R</inf>=0.2 and P<inf>R</inf>=1 gives the maximum thermal performance. In addition, the thermal performance of using the HB is much higher than that of the wire coil insert, in comparison with other turbulators. To understand the heat transfer mechanism, a numerical inserted-duct flow simulation is also conducted and the obtained numerical results are in good agreement with measurements. Numerical flow and heat transfer behaviors such as streamlines, temperature and Nusselt number contours of the duct flow model are also reported. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Heat transfer augmentation in a solar air heater channel with combined winglets and wavy grooves on absorber plate(2017-01-01); ; ; An investigation on heat transfer characteristics in a solar air heater channel using wavy grooves incorporated with pairs of trapezoidal-winglets (TW) placed on the absorber plate has been experimentally conducted. Air as the test fluid entered the test section having a constant heat-flux on the absorber plate while the Reynolds numbers obtained by controlling the airflow rate is in a range of 4500–22,000. The TW characteristics include three relative winglet-pitches (P<inf>R</inf>) and five relative winglet height or blockage ratios (B<inf>R</inf>) at a single attack angle of 45° whereas the wavy rectangular-groove parameters are three relative groove-pitch lengths (P<inf>R</inf>) similar to the TW case but at a fixed width and height. The investigation shows that the TW together with the groove provides the substantial increase in heat transfer over the smooth channel. The TW alone gives much higher heat transfer but the groove yields considerably lower pressure drop. The combined groove and TW devices at a given B<inf>R</inf>, perform the highest heat transfer and friction factor at smaller P<inf>R</inf> and also provides considerably higher thermal performance than the single device acting alone. At P<inf>R</inf> = 1, the compound device with B<inf>R</inf> = 0.28 offers the highest heat transfer and friction factor while the one with B<inf>R</inf> = 0.24 gives the maximum thermal performance. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Effect of pitch to height ratio on flow visualization, heat transfer, and thermal performance in a round tube with upstream RWVG(2014-01-01); Fully developed periodic laminar flow and heat transfer in an isothermal wall tube with 45° upstream rectangular winglet vortex generators (RWVG) with closed end are investigated numerically. The fluid flow and heat transfer characteristics are proposed for Reynolds numbers based on the diameter of the tube, Re = 100 to 2000. The RWVGs with an attack angle of 45° are mounted with in-line arrangement on both sides of a plate and the closed tip pointing upstream is inserted in the middle of the tested tube to produce longitudinal vortex flows through the tested section. Effects of different blockage ratios (b/D, BR) and pitch spacing ratios (P/D, PR) on heat transfer, pressure loss, and the thermal enhancement factor (TEF) in the round tube are studied. The results show that the longitudinal vortex flows can induce impinging flows on a tube wall leading to an extreme increase in heat transfer rate over the round tube for all cases. Additionally, the rise in the BR and the reduction of PR result in the increase of both the Nusselt number and friction factor values. The optimum TEF in the range studied is around 2.9 at BR = 0.15, PR = 1, and Re = 2000. © 2014 Withada Jedsadaratanachai and Nuthvipa Jayranaiwachira. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Computational investigation on fully developed periodic laminar flow structure in baffled circular tube with various BRThis paper presents a 3D numerical analysis of fully developed periodic laminar flow in a circular tube fitted with 45° inclined baffles with inline arrangement. The computations are based on a finite volume method, and the SIMPLE algorithm has been implemented. The characteristics of fluid flow are presented for Reynolds number, Re = 100-1000, based on the hydraulic diameter (D) of the tube. The angled baffles were repeatedly inserted at the middle of the test tube with inline arrangement to generate vortex flows over the tested tube. Effects of different Reynolds numbers and blockage ratios (b/D, BR) with a single pitch ratio of 1 on flow structure in the tested tube were emphasized. The flows in baffled tube show periodic flow at x/D ≈ 2-3, and become a fully developed periodic flow profiles at x/D ≈ 6-7, depending on Re, BR and transverse plane positions. The computational results reveal that the higher of BR and closer position of turbulators, the faster of fully developed periodic flow profiles. © 2014 Withada Jedsadaratanachai et al. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Thermal behaviors in a square duct with U-ribbed tape inserts(2014-01-01); This paper presents an experimental study on thermal characteristics in a constant heatfluxed square-duct heat exchanger with U-ribbed tape inserts. The experiments are carried out by varying airflow rate for Reynolds number ranging from 4000 to 38,000. The insertion of the Uribbed tape is performed with an axial rib-pitch set to four times duct-height (4H) at a single attack angle, α=45° and the ribbed tape is diagonally inserted in the square duct in order to generate longitudinal vortex flows. Effects of five blockage ratios (e/H=0.1, 0.15, 0.2, 0.25 and 0.3) on heat transfer and friction loss are experimentally investigated. The experimental result shows that the insertion of the U-ribbed tape at e/H=0.3 provides the highest heat transfer and friction factor values but the one at e/H=0.25 yields the highest thermal performance enhancement. © (2014) Trans Tech Publications, Switzerland. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, 3D numerical study on flow structure and heat transfer in a circular tube with V-bafflesA 3D numerical investigation has been carried out to examine periodic laminar flow and heat transfer characteristics in a circular tube with 45° V-baffles with isothermal wall. The computations are based on the finite volume method (FVM), and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers ranging from 100 to 2000. To generate main longitudinal vortex flows through the tested section, V-baffles with an attack angle of 45° are mounted in tandem and in-line arrangement on the opposite positions of the circular tube. Effects of tube blockage ratio, flow direction on heat transfer and pressure drop in the tube are studied. It is apparent that a pair of longitudinal twisted vortices (P-vortex) created by a V-baffle can induce impingement on a wall of the inter-baffle cavity and lead a drastic increase in heat transfer rate at tube wall. In addition, the larger blockage ratio results in the higher Nusselt number and friction factor values. The computational results show that the optimum thermal enhancement factor is around 3.20 at baffle height of B = 0.20 and B = 0.25 times of the tube diameter for the V-upstream and V-downstream, respectively.