Hydrodynamic Characteristics of Crossflow over MEMS-Based Pillars

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Ali Koşar ◽  
Brandon Schneider ◽  
Yoav Peles
Keyword(s):  
Friction Factor ◽  
Hydrodynamic Characteristics ◽  
Flow Conditions ◽  
Pin Fin ◽  
Aspect Ratios ◽  
Friction Factors ◽  
Wide Range ◽  
Hydrodynamic Processes ◽  
Factor Data ◽  
Key Parameter

A parametric study was performed to reveal the hydrodynamic processes controlling crossflow over MEMS-based micro pin fin devices. Pressure drop experiments were conducted and used to obtain friction factors on a wide range of micro pin fin devices for various flow conditions and geometrical configurations, including pin fin height-to-diameter aspect ratios, spacings, and shapes. The acquired data suggests that the device geometry is the key parameter dictating friction factor trends and magnitude along with the Reynolds number. Additionally, friction factor data has shown that correlations based on experimental results performed on conventional scale tube bundles do not accurately predict the trends under working conditions pertaining to microfluidic systems.

scholarly journals Friction-Factor Data for Flat-Plate Tests of Smooth and Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 722-729 ◽  
Author(s):  
T. W. Ha ◽  
Dara W. Childs
Keyword(s):  
Flat Plate ◽  
Friction Factor ◽  
Smooth Surface ◽  
Factor Model ◽  
Test Apparatus ◽  
Cell Width ◽  
Plate Test ◽  
Friction Factors ◽  
Line Flow ◽  
Factor Data

Friction-factors for honeycomb surfaces are measured with a flat plate tester. The flat plate test apparatus is described and a method is discussed for determining the friction-factor experimentally. The friction-factor model is developed for the flat plate test based on the Fanno Line Flow. The comparisons of the friction-factor are plotted for smooth surface and twelve-honeycomb surfaces with three-clearances, 6.9 bar to 17.9 bar range of inlet pressure, and 5,000 to 130,000 range of the Reynolds number. The optimum geometries for the maximum friction-factor are found as a function of cell width to cell depth and clearance to cell width ratios.

scholarly journals Effect of Pin Diameter Degressive Gradient on Heat Transfer in a Microreactor with Non-Uniform Pin-Fin Array under Low Reynolds Number Conditions

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2702
Author(s):  
Miao Qian ◽  
Jie Li ◽  
Zhong Xiang ◽  
Chao Yan ◽  
Xudong Hu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Low Reynolds Number ◽  
Hydrodynamic Characteristics ◽  
Pin Fin ◽  
Low Reynolds ◽  
Pin Fin Array

To improve the efficiency of hydrogen-producing microreactors with non-uniform pin-fin array, the influence of the pin diameter degressive gradient of the non-uniform pin-fin array (NPFA) on heat transfer and pressure drop characteristics is analyzed in this study via numerical simulation under low Reynolds number conditions. Because correlations in prior studies cannot be used to predict the Nusselt number and pressure drop in the NPFA, new heat transfer and friction factor correlations are developed in this paper to account for the effect of the pin diameter degressive gradient, providing a method for the optimized design of the pin diameter degressive gradient for a microreactor with NPFA. The results show that the Nusselt number and friction factor under a low Reynolds number are quite sensitive to the pin diameter degressive gradient. Based on the new correlations, the exponents of the pin diameter degressive gradient for the friction factor and Nusselt number were 6.9 and 2.1, respectively, indicating the significant influence of the pin diameter degressive gradient on the thermal and hydrodynamic characteristics in the NPFA structure.

Test Results for Liquid “Damper” Seals Using a Round-Hole Roughness Pattern for the Stators

1999 ◽  
Vol 121 (1) ◽  
pp. 42-49 ◽  
Author(s):  
Dara W. Childs ◽  
Patrice Fayolle
Keyword(s):  
Friction Factor ◽  
Round Hole ◽  
Test Results ◽  
Partial Explanation ◽  
Rotordynamic Coefficients ◽  
Stiffness Coefficients ◽  
Friction Factors ◽  
Direct Stiffness ◽  
Factor Data ◽  
Pressure Driven Flow

Test results are reviewed for two annular liquid seals (L = 34.9 mm; D = 76.5 mm) at two clearances (.1 and .12 mm). The seal stators use hole-pattern-roughened stators that are identical except for hole depths of .28 and 2.0 mm. Tests are conducted at three speeds out to 24,600 rpm and three pressures out to 68 bars. Test data consist of leakage rates and rotordynamic coefficients at centered and eccentric positions with static eccentricity ratios out to 0.5. Test results are consistent with expectations in regard to the reduction of cross-coupled stiffness coefficients due to stator roughness. However, the measured direct stiffness coefficients were unexpectedly low. A partial explanation for these results is provided by measured friction factor data which show an increase in the friction factors for pressure-driven flow with an increase in clearance. A prediction model for rotordynamic coefficients, incorporating the friction-factor data, predicted a substantial loss in direct stiffness but could not explain the very low (or negative) values that were measured. The model did explain the measured drop in cross coupled stiffness (k) and provides an alternative explanation to observed reductions in k values; specifically, an increase in the friction factor with increasing clearance causes a reduction in k irrespective of any parallel reduction in the average circumferential velocity.

Modeling the Dynamic Lateral Buckling Response of Subsea Pipelines Using Rate-Dependent Seabed Friction

2014 ◽  
Author(s):  
Zack Westgate ◽  
Kin Yin Chee ◽  
Alastair Walker
Keyword(s):  
Slow Rate ◽  
Low Friction ◽  
Lateral Buckling ◽  
Dynamic Finite Element ◽  
Rate Dependent ◽  
Friction Factors ◽  
Wide Range ◽  
Element Approach ◽  
Subsea Pipelines ◽  
Key Parameter

As subsea pipeline installation methods become increasingly sophisticated through use of increased vessel power and advanced stability and positioning controls, pipelines are likely to exhibit lower levels of horizontal out-of-straightness on the seabed than currently considered to occur during the lay process. This has resulted in an increased tendency for the problematic phenomenon of snap-buckling to occur as part of the controlled lateral buckling design. A key parameter affecting the pipeline response during lateral buckling is the friction between the pipeline and the seabed, which is strongly influenced by the rate of pipe displacement. Under stable buckle formation, the relatively slow rate of pipe displacement is more predictable and leads to acceptable strains in the pipeline. During the formation of less stable snap-through buckles, the rate of pipe displacement can mobilize a wide range in friction factors that can cause high strains in the pipeline. Quasi-static methods cannot model the dynamic transition between a high friction (drained) response and a low friction (undrained) response. To circumvent this problem in design, a fully dynamic finite element approach is required which captures the rate-dependent frictional response. This paper presents the results of a series of FE analyses that illustrate how the changing seabed friction affects the lateral buckling response of typical subsea pipelines. A contractile seabed is modeled, chosen to capture the general case where high values of slow drained friction are followed by low values of fast undrained friction, leading to changes in the buckle shapes compared to those obtained from static buckle modeling. The results are used to examine the conditions under which dynamic buckle analysis should be used and the effects of dynamic pipeline response on the levels of strain and deformation induced in buckles.

Experimental Investigations on Friction Factors of Gaseous Flow Through a Micro-Tube With Smooth Surface

2017 ◽  
Author(s):  
Takayuki Shigeishi ◽  
Chungpyo Hong ◽  
Yutaka Asako
Keyword(s):  
Friction Factor ◽  
Smooth Surface ◽  
Gas Flow ◽  
Experimental Investigations ◽  
Adiabatic Wall ◽  
Choked Flow ◽  
Friction Factors ◽  
Wide Range ◽  
Flow Through ◽  
Local Pressures

The purpose of the present study is to experimentally investigate flow characteristics on semi-local friction factors of nitrogen gas flow through a micro-tube with a smooth surface. The experiments were performed using a glass micro-tube with 266 μm in diameter and 120 mm in length. Three static pressure holes are drilled on the wall near the micro-tube outlet at intervals of 5 mm, and the local pressures were measured with the outlet discharged into the atmosphere. The local values of Mach number, temperature and friction factor were obtained from the measured local pressures. The result in the wide range of Reynolds number was also obtained, including the choked flow. Darcy friction factor and Fanning friction factor obtained under the assumptions of both a Fanno flow (adiabatic wall) and an Isothermal flow were compared with empirical correlations in the literature and numerical results.

Experimental Measurements and Computations of Heat Transfer and Flow Friction Factor in a Staggered Pin Fin Array

2001 ◽  
Author(s):  
Forrest E. Ames ◽  
Christopher S. Solberg ◽  
Michael D. Goman ◽  
Daniel J. Curtis ◽  
Bradley T. Steinbrecker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Experimental Measurements ◽  
Wall Region ◽  
Number Range ◽  
Flow Friction ◽  
Pin Fin ◽  
Factor Data ◽  
Pin Fin Array

Abstract This paper presents experimental measurements and CFD calculations for heat transfer and flow friction factor in a staggered pin fin array. The heat transfer and flow friction factor data are taken in a constant temperature facility and are acquired over a Reynolds number range of 1500 to 31,000. The array is comprised of eight rows of pins spaced at 2.5 diameters in the streamwise and spanwise directions with a pin height of two diameters. The heat transfer data are presented in terms of both average array data and row resolved data. The data accurately match the recent pin fin correlation of Chyu et at. [1] and extend its range to lower Reynolds numbers. The flow friction factor data accurately match the low and high Reynolds number data of Metzger et al. [2]. The steady state computations for a 2D and 3D representation of the geometry are performed and compared with archival correlations and the present data. The calculations are performed using a general purpose commercial solver (FLUENT 5.3 [3]) and apply the realizable k-ε model of Shih et al. [4] along with a two layer model which solves the k equation in the near wall region. Generally, the calculations perform relatively well with the 2D calculations matching the literature correlations slightly better than the 3D calculations.

Measurement and Prediction of Rough Wall Effects on Friction Factor—Uniform Roughness Results

1988 ◽  
Vol 110 (4) ◽  
pp. 385-391 ◽  
Author(s):  
W. F. Scaggs ◽  
R. P. Taylor ◽  
H. W. Coleman
Keyword(s):  
Friction Factor ◽  
Roughness Element ◽  
Discrete Element ◽  
Turbulent Pipe Flow ◽  
Number Range ◽  
Flow Friction ◽  
Friction Factors ◽  
Roughness Model ◽  
Factor Data ◽  
Good Agreement

The results of an experimental investigation of the effects of surface roughness on turbulent pipe flow friction factors are presented and compared with predictions from a previously published discrete element roughness model. Friction factor data were acquired over a pipe Reynolds number range from 10,000 to 600,000 for nine different uniformly rough surfaces. These surfaces covered a range of roughness element sizes, spacings and shapes. Predictions from the discrete element roughness model were in very good agreement with the data.

Multijet Impingement on Pin Fin Heat Sink With Different Crossflow Schemes

2011 ◽  
Author(s):  
Nagesh K. Chougule ◽  
Gajanan V. Parishwad ◽  
Sachin Pagnis ◽  
Prashant R. Gore
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Sink ◽  
Cross Flow ◽  
Flow Conditions ◽  
Maximum Heat ◽  
Pin Fin ◽  
Flow Scheme ◽  
Air Jet ◽  
Wide Range

The fluid flow and heat transfer characteristics of multi air jet array impinging on a 4×4 pin fin heat sink with 3×3 nozzle arrays are investigated both numerically and experimentally. The results for multi jet impingement with wide range of parameters are not readily available in the literature. Different exit flow conditions such as minimum, semi and maximum cross flow conditions are simulated using shear stress transport (SST) k-ω turbulence model to study the combined effects of Reynolds number (Re) and spacing between nozzle exit and target surface (Z/d) on heat transfer coefficient (havg). The jet Reynolds number is varied from 7000 to 50000 and Z/d is varied from 6 to 10. For Re ≤ 18000, it is noticed that the minimum cross flow scheme gives maximum heat transfer, than semi cross flow and the maximum cross flow schemes at all Z/d considered here. Semi cross flow scheme works better for Re ≥ 18000. At Re = 11000 the minimum cross flow scheme indicates that Nua decreases from 50.1 to 36.41 with increase in Z/d from 6 to 10. It is also observed that the symmetry of the heat transfer patterns occur in the minimum and semi cross flow schemes as the sidewalls restrict the flow in opposite direction. However, in the maximum cross flow scheme, the stagnation peaks shifted and reduced in the stream wise direction by the strong cross flow degradation.

Friction-Factor Characteristics for Narrow Channels With Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 714-721 ◽  
Author(s):  
T. W. Ha ◽  
G. L. Morrison ◽  
D. W. Childs
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Narrow Channel ◽  
Test Results ◽  
Jump Phenomenon ◽  
Narrow Channels ◽  
Friction Factors ◽  
Factor Data

The experimental determination of friction-factors for the flow of air in a narrow channel lined with various honeycomb geometries has been carried out. Test results show that, generally, the friction-factor is nearly constant or slightly decreases as the Reynolds number increases, a characteristic common to turbulent flow in pipes. However, in some test geometries this trend is remarkably different. The friction factor dramatically drops and then rises as the Reynolds number increases. This phenomenon can be characterized as a “friction-factor jump.” Further investigations of the acoustic spectrum and friction-factor measurements for a broad range of Reynolds numbers indicate that the “friction-factor jump” phenomenon is accompanied by an onset of a normal mode resonance excited coherent flow fluctuation structure, which occurs at Reynolds number of the order of 104. The purpose of this paper is not to present the friction-factor data but to explain the friction-factor-jump phenomenon and friction-factor characteristics.

EFFECTS OF PIN FIN CONFIGURATIONS ON HEAT TRANSFER AND FRICTION FACTOR IN AN IMPROVED LAMILLOY COOLING STRUCTURE

2017 ◽  
Vol 48 (7) ◽  
pp. 657-679 ◽  
Author(s):  
Lei Luo ◽  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sunden ◽  
Songtao Wang
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Pin Fin
Sign in / Sign up

Export Citation Format

Share Document