KMITL

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

Browse

Search Results

Now showing 1 - 10 of 10

Some of the metrics are blocked by your
consent settings
Enhancing convective heat transfer coefficient in a circular heat exchanger tube mounted with modified V-orifice (MVO): CFD analysis and correlations
(2026-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
This study investigates the airflow dynamics and heat transfer (HT) profiles in a circular heat exchanger tube (CHET) mounted with a modified V-orifice (MVO) acting as a turbulator/vortex generator, which is a passive technique to enhance HT. A numerical modeling approach based on the finite volume method using a commercial software package was employed to provide detailed insights into the air flow profile, which is essential for the design of both the turbulator and the CHET system. The MVO is a turbulator derived from the orifice concept, an established engineering device, and has been adapted in combination with a V-shaped structure to effectively generate vortices and enhance HT. Key parameters expected to influence the flow and HT behavior were investigated. These include the ratio of the MVO thickness, b, to the CHET diameter, D (referred to as the blockage ratio, B-R), which was studied in the range of 0.05–0.30, and the ratio of the MVO spacing, P, to the CHET diameter (pitch ratio, P-R), which was considered at values of 1, 1.5, and 2. Attack angles of 30°, 45°, and 60° were examined for both + x and–x flow directions. The study covered turbulent flow conditions corresponding to Reynolds numbers in the range of 3,000–16000, representative of the operating conditions at the CHET inlet. The results indicate that MVO installation in the CHET acts as a flow obstruction, generating a pressure difference that induces vortex formation. These vortices play a key role in modifying the HT behavior, resulting in increased convective HT coefficients. The outcomes are summarized in forms of dimensionless variables. The highest observed HT enhancement reached 9.93 times that of the plain CHET, while the maximum thermal enhancement factor (TEF) was 1.92, obtained at an attack angle of 30°, P-R = 1, B-R = 0.25, in the +x fluid-flow direction at Re = 3,000.
Some of the metrics are blocked by your
consent settings
Numerical Study of Turbulent Forced Convection in a Square Duct with Discrete X-V Inducing Turbulators (DXVIT)
(2025-04-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
This research is an extension study that applies a vortex generator previously developed and tested under laminar flow conditions to investigate its performance under turbulent flow conditions, covering the operating range of various heat exchanger systems. This type of vortex generator is called the discrete X-V inducing turbulator (DXVIT), which is derived from the V-baffle, known for its high heat transfer enhancement efficiency, combined with the structure of an orifice that provides durability and stability when installed in heat exchanger systems. The DXVIT is installed to modify the primary flow structure and disrupt the thermal boundary layer (ThBL), resulting in an increase in the convective heat transfer coefficient. This study examines the effects of DXVIT size, installation spacing, flow direction, and DXVIT type on the heat transfer and flow behavior under turbulent flow conditions with Reynolds numbers ranging from 3000 to 16,000. The investigation is conducted using numerical simulation methods. The results are presented in terms of flow and heat transfer behavior, along with an analysis of thermal performance using dimensionless parameters. The findings indicate that the heat transfer rate increases up to 5.29 times, and the thermal performance factor reaches 2.65 under the same pumping power conditions.
Some of the metrics are blocked by your
consent settings
Numerical Assessments on Laminar Airflow, Thermal Characteristic, and Performance Improvement in a Round Tube Equipped With Combined Vortex Generators
(2025-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
A round tube heat exchanger (RTHE) with combined vortex generators (CVGs) is subjected to numerical assessments of its airflows and thermal characteristics. The CVGs are V-shaped ribs and rectangular winglets. The effects of CVG arrangement (A-1, A-2, and B), blockage ratio (b<inf>1</inf>/H and b<inf>2</inf>/D), and airflow direction (+x, −x) on airflow and thermal behavior are considered. To solve the numerical problem, a commercial program’s finite volume technique is chosen. Presenting streamlines, fluid temperature distributions, and local Nusselt number contours (on the tube wall) are the numerical findings obtained in the RTHE fitted with the CVG. The study presents the performance analysis of RTHE using dimensionless variables, including the thermal enhancement factor (or thermal performance factor), averaged friction factor, and averaged Nusselt number. The numerical results indicate that the general flow configuration in the RTHE is dramatically altered by the CVG. The mixing quality of the fluid seems to be enhanced. The vortex flows are found through the RTHE. As a result of the vortex flows impinging on the RTHE wall, the thermal boundary layer (T-BL) over the heat transfer surfaces changes. Enhancing the convective heat transfer coefficient, heat transfer ability, and thermal performance in the RTHE is mostly because of the reduction of the T-BL thickness. When compared to a smooth round tube, the maximum enhanced heat transfer of the RTHE fitted with the CVG is 13.83 times greater. Furthermore, at Re = 2000, type B, b<inf>1</inf>/D = 0.15, b<inf>2</inf>/D = 0.05, and V-Upstream scenario, the optimal TEF is 3.81.
Some of the metrics are blocked by your
consent settings
Potential jet-space based practical identifiability and integral backstepping sliding mode control of heat exchanger
(2025-01-01)
Sitthisuk, Nichaphat
;
Wongvanich, Napasool
This work develops the minimal modeling methodology for modeling and control of the liquid-liquid heat exchanger system. An application of the potential jet space theory is firstly presented, where the cross-convection model of the heat exchanger dynamics is prolonged onto the potential jet space to generate the input-output equations that are written in terms of integrals of the measured data. This integral based input-output equation then facilitates the parameter estimation without extensive computational loading demands. The linear potential jet space model was first applied to the measured data, and extended to capture the time delay effect in the measurement. An integral backstepping sliding mode controller was also designed. The delay model was shown to give a tracking temperature error to within 0.0004 degrees, with a mean integral absolute error (ITAE) of around 0.27, even with heavy parameter changes.
Some of the metrics are blocked by your
consent settings
Investigations of thermal behavior, flow structure, and performance in a circular tube heat exchanger fitted with diamond-shaped orifice (DSO): a CFD assessment
(2025-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
This study numerically investigates the enhancement of heat exchanger performance using a passive technique based on vortex generation. The proposed enhancement device, termed a diamond-shaped orifice (DSO), is a modified configuration that combines a conventional orifice plate with a conical ring. The DSO is inserted into a circular tube to modify the flow structure and induce strong vortices, thereby promoting convective heat transfer and improving the overall thermal performance. The effects of key geometric parameters, including the attack angle (α = 20°, 30°, and 45°), flow blockage ratio (FBR = 0.05–0.30), and pitch ratio (PRT = 1–2), are systematically examined under turbulent airflow conditions with Reynolds numbers ranging from 3,000 to 20,000. The results reveal that incorporating the DSO generates intense swirling flow, which effectively disrupts the thermal boundary layer and enhances the convective heat transfer coefficient. The maximum Nusselt number improvement reached 7.16 times that of a plain tube, while the highest thermal enhancement factor (TEF) attained was 1.77, indicating a substantial improvement in heat exchanger performance without additional active energy input.
Some of the metrics are blocked by your
consent settings
Heat transfer characteristics of a swirling impinging air jet emerging from a triple spiral-corrugated nozzle with a twisted tape installed
(2022-07-01)
Eiamsa-ard, P.
;
Wongcharee, K.
;
Kunnarak, K.
;
Kumar, M.
;
Eiamsa-ard, S.
Thermal visualization using a thermochromic liquid crystal sheet was performed to investigate and compare heat transfer behavior of a swirling impinging jet emerging from a triple spiral-corrugated nozzle with a twisted tape (SIJ with TT), a SIJ issuing through a triple spiral-corrugated nozzle, and a typical/conventional impinging jet (CIJ) emerging from a smooth straight circular nozzle. The experimental results showed that the stronger jet recirculation close to the wall due to the swirl flow created by triple spiral-corrugated nozzle and twisted tape inserts (SIJ with TT) support in reducing the value of Nusselt number between the stagnation region and surroundings. For the SIJ with TT, the average Nusselt number performed by the jets with L/d<inf>H</inf> shows that the magnitude of the heat transfer coefficient was significantly enhanced with increasing twist ratios. The maximal value Nu of the SIJ with TT was obtained at the lowest twist ratio (y/W = 2.0). This was up to 5.7 % and 35.5 % higher than those of the SIJ with TT at y/W = 4.0, and the CIJ, respectively.
Some of the metrics are blocked by your
consent settings
IMPACT OF THREE DIFFERENT DOUBLE BAFFLE DESIGNS ON THE THERMAL PERFORMANCE OF SQUARE DUCTS
(2022-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
CFD analyses of flow characteristics and heat transfer topology in a heat exchanger duct (HXD) placed with three various configurations of the double V-baffles (DVB) are reported. Parameters of interest are DVB height ratios (b/H = 0.05 – 0.25), gap spacing ratios (g = 0.05 – 0.40), flow directions (+x,-x), and DVB configurations (Type I, II and III). Laminar flow with Reynolds numbers (based on the inlet conditions) between 100 – 2000 is measured. The present problem is solved with the finite volume method (a commercial program). Fluid flow and heat transfer characteristics in the tested duct are described. Thermal assessments of the tested duct are also presented. Simulation results showed that the installation of the DVB in the HXD results in higher heat transfer rate due to the creation of the vortex flow and the disturbance of the thermal boundary layer (TBL). Different flow structures and heat transfer behavior are observed when gap spacing ratios, flow directions and DVB shapes are changed. In addition, the type II DVB provides the highest TEF of 3.55 at b/H = 0.10, g/H = 0.25 for the-x flow direction.
Some of the metrics are blocked by your
consent settings
Variations of heat transfer mechanism and flow structure in a heat exchanger tube fitted with 30° inclined ring
(2020-03-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
Flow prediction, heat transfer pattern, and thermo-hydraulic efficiency in a heat exchanger tube fitted with vortex generator are chosen for the present research. The 30° inclined ring is opted to develop the performance of the heat exchanger tube. The effects of inclined ring configuration and placement in the heat exchanger tube on the patterns of flow and heat transfer are investigated. The Reynolds number (at the entry zone of the periodic model) in the range of around 100–2000 (laminar flow region) is discussed. The heat transfer ability, pressure loss, and efficiency of the heat exchanger tube fitted with 30° inclined ring are analyzed with the numerical method (finite volume method). The SIMPLE algorithm of the commercial code is picked for the present study. The simulated results in the heat exchanger tube fitted with 30° inclined ring are offered in patterns of streamlines, temperature contour, and Nusselt number contour. From the preliminary result, it is found that the creation model of the heat exchanger tube fitted with 30° inclined ring has sufficient reliance to measure flow and heat transfer profiles. The installment of the 30° inclined ring in the heat exchanger tube leads to greater heat transfer ability and thermo-hydraulic performance because of the creation of the vortex flow and thermal boundary layer disturbance on the heat exchanger tube surface. The heat transfer ability in the heat exchanger tube fitted with 30° inclined ring is found to be around 1.00–10.56 times above the plain circular tube. In addition, the installation of the 30° inclined ring in the heat exchanger tube gives the maximum thermal enhancement factor around 3.18.
Some of the metrics are blocked by your
consent settings
Forced convective heat transfer and thermal efficiency assessment in square channel equipped with 10° wavy thin rib
(2020-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
Forced convective heat transfer and thermo-hydraulic efficiency in the heat exchanger square channel (HESC) inserted with 10° wavy thin rib (WTR) are reported numerically. The effects of rib height, pitch distance and flow velocity on flow and heat transfer profiles are considered. The rib height to the channel height; e/H or H<inf>R</inf>, is varied in the range 0.05–0.30, while the rib pitch to the channel height; P/H or P<inf>R</inf>, is varied in the range 0.50–1.25. The air velocity in the HESC inserted with the WTR is considered in terms of Reynolds number. The Reynolds numbers (Re = 100–2000) for the present investigation is analyzed at the inlet condition. The finite volume method (commercial code) with SIMPLE algorithm is picked to solve the present problem. The numerical model of the HESC inserted with the WTR is validated for both grid independence and verification of the smooth HESC. The numerical results of the HESC inserted with the WTR are printed in terms of flow and heat transfer profiles. The values of Nusselt number, friction factor and thermal efficiency factor in the HESC inserted with the WTR are also plotted. As the numerical result, it is found that the WTR in the HESC can produce the vortex flow that the reason for the enhancements of heat transfer and efficiency. The increment of the heat transfer ability in the HESC is detected when increasing rib height and Reynolds number. In addition, the greatest thermal efficiency factor in the HESC inserted with the WTR is around 3.43 at H<inf>R</inf> = 0.20, P<inf>R</inf> = 1, and Re = 2000.
Some of the metrics are blocked by your
consent settings
LAMINAR FORCED CONVECTION AND PERFORMANCE EVALUATION IN A SQUARE DUCT HEAT EXCHANGER PLACED WITH WAVY THIN RIB
(2020-01-01)
Boonloi, Amnart
;
Jedsadaratanachai, Withada
Simulated examinations on convective heat transfer and flow topology in a square duct heat exchanger placed with wavy thin rib (WTR) are presented. The influences of WTR heights, pitch distances and flow directions on flow and heat transfer characteristics are investigated for the laminar flow regime at the inlet condition (Re = 100 – 2000). The finite volume method (SIMPLE algorithm) is picked to analyze the numerical problem. The numerical validations; grid independence and verification of the smooth duct, are presented. The simulated results of the heat exchanger duct placed with WTR are reported in terms of flow and heat transfer visualizations. The relations of the Nu/Nu0, f/f0 and TEF with Re and P/H in the heat exchanger square duct inserted with WTR are also plotted. The numerical result reveals that the heat transfer and friction loss increase when augmenting the Reynolds number and WTR height. The optimum pitch spacing ratio may give the highest heat transfer rate and thermal performance.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results