scholarly journals Thermal and Flow Characteristics of Discrete Double Inclined Ribs at Low Curvature Coil for GSHP Application

2020 ◽  
Vol 3 (1) ◽  
pp. 10-20
Author(s):  
Teguh Hady Ariwibowo ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Characteristics ◽  
Working Fluid ◽  
Straight Tube ◽  
Transfer Enhancement ◽  
Particle Path ◽  
Ground Heat Exchangers ◽  
Condition Effect ◽  
Inclination Angles

In this study, the thermal and hydraulic characteristics in low curvature coil with Discrete Double Inclined Ribs (DDIR) were investigated. Water is selected as a working fluid, and flowrate range from 1 to 5 L/min, which is a low flowrate condition. Effect of geometry parameters such as distance between ribs, curvature ribs, and ribs inclination angles was observed. Results obtained by numerical simulations show that the heat transfer in DDIR-coil is 7.7 to 29.11% greater than that in plain coil, while the pressure drop was approximately 12.7 to 89.5% larger than that of plain-coil. A COP improvement factor that is calculated based on energy loss by pressure drop and energy saving by heat transfer enhancement was found to vary between 0.25 and 5.29. Flow visualization shows that there are two vortexes in cross-section at the downstream, and local vortexes arise around the ribs of DDIR-coil, which shows similar pattern and strength to DDIR-straight tube. The vortex makes a long fluid particle path and strengthens the turbulent mixing between the wall and the core flow of the coil. Based on these findings, DDIR-coil is recommended for applications in Slinky Ground Heat Exchangers, especially at low flowrates.

Heat Transfer Enhancement in a Microchannel Heat Sink with Trapezoidal Cavities on the Side Walls

2016 ◽  
Vol 819 ◽  
pp. 127-131
Author(s):  
Navin Raja Kuppusamy ◽  
N.N.N. Ghazali ◽  
Saidur Rahman ◽  
M.A. Omar Awang ◽  
Hussein A. Mohammed
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Fluid Mixing ◽  
Microchannel Heat Sink ◽  
Transfer Enhancement ◽  
Side Walls

The present study focuses on the numerical study of thermal and flow characteristics in a microchannel heat sink with alternating trapezoidal cavities in sidewall (MTCS). The effects of flow rate and heat flux on friction factor and Nusselt are presented. The results showed considerable improvement heat transfer performance micro channel heat sink with alternating trapezoidal cavities in sidewall with an acceptable pressure drop. The heat transfer rate has improved in the cavity area due the greater fluid mixing in fluid vortices and thermal boundary layer disruption. The slipping over the reentrant cavities and pressure gain reduces pressure drop appears as the reason behind of only minor pressure drop due to the cavities.

Effect of Protuberances in the Heat Transfer Enhancement in Mini-Channels

2021 ◽  
Author(s):  
Ariel Cruz Diaz ◽  
Gerardo Carbajal
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Heat Removal ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Mini Channels

Abstract This study presents the effects of adding an array of protrusions in a microchannel for heat transfer enhancement. The presence of mini-channels increases the overall heat transfer area and boosts the mixing development near the solid-fluid interaction; therefore, it can remove more heat than conventional mini-channels without protuberances. A numerical study proved that protuberances in a mini-channel increase the heat transfer performance by disturbing the relative fluid motion near the solid wall. The numerical simulation was performed with three different protuberances arrays: aligned, staggered, and angular. Each array consists of a thin flat plate with a hemispherical shape; the working fluid and the solid materials were water and copper. The study also includes the effect of different Reynolds numbers: 1,000, 1,500, and 2,000. Three heat inputs were applied in the numerical simulation; these were 1W, 3W, and 5W. The study was compared with a simple microchannel with non-protuberances to analyze the microchannel performance regarding heat removal and pressure drop. For heat transfer performance, the best array was the staggering array with a maximum heat removal increase of 5.26 percent. In terms of pressure drop performance, the best array was the aligned array, with a maximum increase of 34.73 percent.

Experimental Investigations on Heat Transfer Enhancement in a Horizontal Tube Using Converging and Diverging Conical Strip Inserts

2014 ◽  
Vol 592-594 ◽  
pp. 1590-1595 ◽  
Author(s):  
Naga Sarada Somanchi ◽  
Sri Rama R. Devi ◽  
Ravi Gugulothu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Working Fluid ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Enhancement Of Heat Transfer

The present work deals with the results of the experimental investigations carried out on augmentation of turbulent flow heat transfer in a horizontal circular tube by means of tube inserts, with air as working fluid. Experiments were carried out initially for the plain tube (without tube inserts). The Nusselt number and friction factor obtained experimentally were validated against those obtained from theoretical correlations. Secondly experimental investigations using three kinds of tube inserts namely Rectangular bar with diverging conical strips, Rectangular bar with converging conical strips, Rectangular bar with alternate converging diverging conical strips were carried out to estimate the enhancement of heat transfer rate for air in the presence of inserts. The Reynolds number ranged from 8000 to 19000. In the presence of inserts, Nusselt number and pressure drop increased, overall enhancement ratio is calculated to determine the optimum geometry of the tube insert. Based on experimental investigations, it is observed that, the enhancement of heat transfer using Rectangular bar with converging and diverging conical strips is more effective compared to other inserts. Key words: Heat transfer, enhancement, turbulent flow, conical strip inserts, friction factor, pressure drop.

Effects of Channel Length and Chevron Angle on Pressure Drop in the Entrance Region of Corrugated Rib Channels

2019 ◽  
Author(s):  
M. A. Hamoda ◽  
K. Pope ◽  
Y. S. Muzychka
Keyword(s):  
Pressure Drop ◽  
Friction Factor ◽  
Channel Length ◽  
Experimental Results ◽  
Working Fluid ◽  
Transfer Enhancement ◽  
Test Fixture ◽  
Inclination Angles ◽  
Formed Channel ◽  
Channel Lengths

Abstract Plates with corrugated walls are used in plate heat exchangers for heat transfer enhancement usually at the expense of the fluid friction. In this paper, the effects of varying channel lengths and corrugation angles on the pressure drop in corrugated rib channels are examined. Water was used as the working fluid and the Reynolds number varied over the range 400 ≤ ReDe ≤ 2,500. The test fixture is constructed from aluminum and the plates core were machined with the same corrugation depth, 1.14 mm, but with different lengths, 10.16 cm and 20.32 cm and different corrugation inclination angles, 30°, 45°, and 60°. The hydraulic diameter of the formed channel is about 2.0 mm. Experimental results show that the friction factor for the short ribbed plates is significantly higher than those of the longer ribbed plates. In addition, the pressure drop increases with an increase of the corrugation angle for all ribbed plates tested. Based on the experimental results, correlations for predicting friction factor are proposed.

Inclination Angle Optimization for “Inclined Projected Winglet Pair” Vortex Generator

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohammad Oneissi ◽  
Charbel Habchi ◽  
Serge Russeil ◽  
Daniel Bougeard ◽  
Thierry Lemenand
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Inclination Angle ◽  
Heat Exchangers ◽  
Vortex Generator ◽  
Working Fluid ◽  
Static Mixers ◽  
Thermal Enhancement ◽  
Laminar And Turbulent Flow ◽  
Inclination Angles

Abstract Vortex generators (VG) are widely used in multifunctional heat exchangers/reactors for augmenting the heat transfer from fin plates to the working fluid. In this study, numerical simulations for longitudinal VGs are performed for both laminar and turbulent flow regimes. The shear-stress transport (SST) κ–ω model is used for modeling turbulence. Inclination angle for a new streamlined VG configuration called inclined projected winglet pair (IPWP) was varied to study the effect of this angle on the heat transfer enhancement and pressure drop. Response surface methodology (RSM) was used to deduce the inclination angle effects on heat transfer, pressure drop, and vorticity from both local and global points of view. Such study highlights the optimization for this VG configuration for better heat transfer intensification, based on thermal enhancement factor (TEF). Finally, it is found that the VG with inclination angle ranging from 30 deg to 35 deg exhibits the best global performance compared to other inclination angles. This type of studies is important for the enhancement of the thermal performance of heat exchangers and static mixers in various engineering applications.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Experimental Study on Flow Behavior and Heat Transfer Enhancement with Distinct Dimpled Gas Turbine Blade Internal Cooling Channel

2021 ◽  
pp. 1-28
Author(s):  
Farah Nazifa Nourin ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Thermal Performance ◽  
Diameter Ratio ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement

Abstract The study presents the investigation on heat transfer distribution along a gas turbine blade internal cooling channel. Six different cases were considered in this study, using the smooth surface channel as a baseline. Three different dimples depth-to-diameter ratios with 0.1, 0.25, and 0.50 were considered. Different combinations of partial spherical and leaf dimples were also studied with the Reynolds numbers of 6,000, 20,000, 30,000, 40,000, and 50,000. In addition to the experimental investigation, the numerical study was conducted using Large Eddy Simulation (LES) to validate the data. It was found that the highest depth-to-diameter ratio showed the highest heat transfer rate. However, there is a penalty for increased pressure drop. The highest pressure drop affects the overall thermal performance of the cooling channel. The results showed that the leaf dimpled surface is the best cooling channel based on the highest Reynolds number's heat transfer enhancement and friction factor. However, at the lowest Reynolds number, partial spherical dimples with a 0.25 depth to diameter ratio showed the highest thermal performance.

Optimal Position of Rectangular Vortex Generator for Heat Transfer Enhancement in a Flat-Plate Channel

2017 ◽  
Author(s):  
Tariq Amin Khan ◽  
Wei Li ◽  
Zhengjiang Zhang ◽  
Jincai Du ◽  
Sadiq Amin Khan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Numerical Simulations ◽  
Flat Plate ◽  
Heat Transfer Enhancement ◽  
Angle Of Attack ◽  
Vortex Generator ◽  
Transfer Enhancement ◽  
Optimal Position ◽  
Plate Channel

Heat transfer is a naturally occurring phenomenon which can be greatly enhanced by introducing longitudinal vortex generators (VGs). As the longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty, VGs are widely used to enhance the heat transfer of flat-plate type heat exchangers. However, there are few researches which deal with its thermal optimization. Three dimensional numerical simulations are performed to study the effect of angle of attack and attach angle (angle between VG and wall) of vortex generator on the fluid flow and heat transfer characteristics of a flat-plate channel. The flow is assumed as steady state, incompressible and laminar within the range of studied Reynolds numbers (Re = 380, 760, 1140). In the present work, the average and local Nusselt number and pressure drop are investigated for Rectangular vortex generator (RVG) with varying angle of attack and attach angle. The numerical results indicate that the heat transfer and pressure drop increases with increasing the angle of attack to a certain range and then decreases with increasing angle of attack. Moreover, the attach angle also plays an importance role; a 90° attach angle is not necessary for enhancing the heat transfer. Usually, heat transfer enhancement is achieved at the expense of pressure drop penalty. To find the optimal position of vortex generator to obtain maximum heat transfer and minimum pressure drop, the data obtained from numerical simulations are used to train a BRANN (Bayesian-regularized artificial neural network). This in turn is used to drive multi-objective genetic algorithm (MOGA) to find the optimal parameters of VGs in the form of Pareto front. The optimal values of these parameters are finally presented.

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