Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Heat Transfer in Thin, Compact Heat Exchangers With Circular, Rectangular, or Pin-Fin Flow Passages

1992 ◽  
Vol 114 (2) ◽  
pp. 373-382 ◽  
Author(s):  
D. A. Olson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Rectangular Channel ◽  
Fluid Temperature ◽  
Compact Heat Exchangers ◽  
Pin Fin

We have measured heat transfer and pressure drop of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/cm2. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.

Effect of Entrance Condition on Frictional Losses and Transition to Turbulence in Minichannel Flows

2004 ◽  
Author(s):  
Levi A. Campbell ◽  
Satish Kandlikar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Second Step ◽  
Flow And Heat Transfer ◽  
Small Channels

In studying the fluid flow and heat transfer in microchannels and minichannels, various claims have been made regarding transition at Reynolds numbers significantly below 2300. As a first step in identifying the reasons for such reports on early transition, the effect of entrance geometry on the pressure drop and transition to turbulence was studied in a conventional channel of 19 mm inside diameter (Kandlikar and Campbell [1]). As a second step, the effect of entrance condition on pressure drop and transition to turbulence is studied in small channels with diameters of 1.067 mm and 0.457 mm. The two entrance conditions employed for both channels are re-entrant and smooth. The experimental results show the effect of entrance condition on local friction factor, transition Reynolds number, and Hagenbach’s factor.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

scholarly journals Experimental Pressure Drop and Heat Transfer in a Rectangular Channel With a Sinusoidal Porous Screen

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Gazi I. Mahmood ◽  
Carey J. Simonson ◽  
Robert W. Besant
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Air Temperature ◽  
Rectangular Cross Section ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Heated Wall ◽  
Mean Flow

Experiments are conducted to investigate turbulence enhancing effects of a porous mesh-screen with a sinusoidal shape normal to the flow direction inside a rectangular cross section air channel at low Reynolds numbers (i.e., Re = 1360–3800). The baseline measurements are obtained at the same channel and Reynolds numbers without the screen present. The surface of the screen pores are oriented parallel to the mean flow. Data are presented for the total and wall-static pressure drop along the channel, Nusselt number distributions on the heated wall at several constant heat rates, and air temperature distributions at the channel exit with and without (baseline cases) the screen. The heat transfer measurements are obtained with one wall heated as well as two parallel walls heated to simulate different applications for air channels in the flat plate heat exchangers. The results indicate that the ratio of screen channel to baseline Nusselt number (Nu/Nu0) and the ratio of screen channel to baseline friction factor (f/f0) increase with the Reynolds number (Re). The fully developed Nu/Nu0 is 2.0–2.5 as the fully developed f/f0 is 4.4 at 3100 < Re ≤ 3800. However, the screen channel heat convection performance index, (Nu/Nu0)/(f/f0)1/3 is only greater than 1.0 when Re > 2500 which is the design objective of reducing the pumping power and heat transfer area in the channel. Nonetheless, the screen insert is only beneficial to augment the convective heat transfer in the channel over the range of transition Reynolds number tested. The average total pressure drop across the channel and average exit air temperature suggest that the screen insert promotes good mixing of fluid across the channel for the Reynolds numbers tested.

Effect of Entrance Condition on Frictional Losses and Transition to Turbulence

2002 ◽  
Author(s):  
Satish G. Kandlikar ◽  
Levi A. Campbell
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Friction Factor ◽  
Closed Loop ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Flow And Heat Transfer ◽  
Inner Diameter

In studying the fluid flow and heat transfer in microchannels, various claims have been made regarding transition at Reynolds numbers significantly below 2300. As a first step in identifying the reasons for such early transition, the effect of entrance geometry on the pressure drop and transition to turbulence is studied experimentally in a conventional channel of 1.9 cm inner diameter. Four types of entrance conditions have been studied with flow of oil in a closed loop. The experimental results show the effect of entrance conditions on local friction factor, hydrodynamic developing length, and transition Reynolds number. The study will be extended to microchannels in the future.

scholarly journals Heat Transfer Enhancement inside Rectangular Channel by Means of Vortex Generated by Perforated Concave Rectangular Winglets

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 43
Author(s):  
Syaiful ◽  
Monica Pranita Hendraswari ◽  
M.S.K. Tony S.U. ◽  
Maria F. Soetanto
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Rectangular Channel ◽  
Vortex Generators ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Enhance Heat Transfer ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Study Results

Passive methods using vortex generators (VGs) to enhance heat transfer have been a concern of researchers in recent decades. This study is intended to investigate the strength of the vortex generated by VGs by trying to reduce the pressure drop in the flow. The present work also takes into account the influence of the vortex intensity on the improvement of heat transfer, which can be indicated by the low value of the synergy angle. Experiments were carried out in the current investigation to validate the results of the numerical simulations in the Reynolds number range of 3102 to 16,132. The study results indicate that the observed heat transfer coefficients from the experimental and simulation results have a similar tendency with relatively small errors. A reduction in pressure drop is observed with the use of perforated concave rectangular winglets (PCRWs) against the nonperforated ones although there was a slight decrease in heat transfer improvements.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

scholarly journals Experimental and Numerical Analysis of Additively Manufactured Inconel 718 Coupons With Lattice Structure

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Sarwesh Parbat ◽  
Zheng Min ◽  
Li Yang ◽  
Minking Chyu
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Pressure Drop ◽  
Inconel 718 ◽  
Lattice Structure ◽  
Unit Cell ◽  
Common Vertex ◽  
Constant Wall Temperature ◽  
Near Surface ◽  
Smooth Channel

Abstract In the present paper, two lattice geometries suitable for near surface and double wall cooling were developed and tested. The first type of unit cell consisted of six ligaments of 0.5 mm diameter joined at a common vertex near the middle. The second type of unit cell was derived from the first type by adding four mutually perpendicular ligaments in the middle plane. Two lattice configurations, referred to as L1 and L2, respectively, were obtained by repeating the corresponding unit cell in streamwise and spanwise directions in an inline fashion. Test coupons consisting of these lattice geometries embedded inside rectangular cooling channel with dimensions of 2.54 mm height, 38.07 mm width, and 38.1 mm in length were fabricated using Inconel 718 powder and selective laser sintering (SLS) process. The heat transfer and pressure drop performance was then evaluated using steady-state tests with constant wall temperature boundary condition and for channel Reynolds number ranging from 2800 to 15,000. The lattices depicted a higher heat transfer compared with a smooth channel and both the heat transfer and pressure drop increased with a decrease in the porosity from L1 to L2. Steady-state conjugate numerical results revealed formation of prominent vortical structures in the inter-unit cell spaces, which diverted the flow toward the top end wall and created an asymmetric heat transfer between the two end walls. In conclusion, these lattice structures provided an augmented heat transfer while favorably redistributing the coolant within channel.

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