Effect of Non Uniform Flow Distribution on Single Phase Heat Transfer in Parallel Microchannels

2007 ◽  
Author(s):  
Akhilesh V. Bapat ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Single Phase ◽  
Flow Distribution ◽  
Uniform Flow ◽  
Hydrodynamic Performance ◽  
Flow Area ◽  
Cross Sectional ◽  
Uniform Flow Distribution ◽  
Parallel Microchannels

The continuum assumption has been widely accepted for single phase liquid flows in microchannels. There are however a number of publications which indicate considerable deviation in thermal and hydrodynamic performance during laminar flow in microchannels. In the present work, experiments have been performed on six parallel microchannels with varying cross-sectional dimensions. A careful assessment of friction factor and heat transfer in is carried out by properly accounting for flow area variations and the accompanying non-uniform flow distribution in individual channels. These factors seem to be responsible for the discrepancy in predicting friction factor and heat transfer using conventional theory.

Uniform Flow Control for a Multipassage Microfluidic Sensor

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Stephen A. Solovitz ◽  
Jiheng Zhao ◽  
Wei Xue ◽  
Jie Xu
Keyword(s):  
Standard Deviation ◽  
Power Law ◽  
Electronics Cooling ◽  
Flow Distribution ◽  
Uniform Flow ◽  
Individual Agent ◽  
Microparticle Image Velocimetry ◽  
Uniform Flow Distribution ◽  
Channel Space ◽  
Parallel Microchannels

Microfluidic sensors have been very effective for rapid, portable bioanalysis, such as in determining the pH of a sample. By simultaneously detecting multiple chemicals, the overall measurement performance can be greatly improved. One such method involves a series of parallel microchannels, each of which measures one individual agent. For unbiased readings, the flow rate in each channel should be approximately the same. In addition, the system needs a compact volume which reduces both the wasted channel space and the overall device cost. To achieve these conditions, a manifold was designed using a tapered power law, based on a concept derived for electronics cooling systems. This manifold features a single feed passage of varying diameter, eliminating the excess volume from multiple branch steps. The design was simulated using computational fluid dynamics (CFD), which demonstrated uniform flow performance within 2.5% standard deviation. The design was further examined with microparticle image velocimetry (PIV), and the experimental flow rates were also uniform with approximately 10% standard deviation. Hence, the tapered power law can provide a uniform flow distribution in a compact package, as is needed in both this microfluidic sensor and in electronics cooling applications.

Characteristic Analysis of the Influence of Flow Rate Distribution in Each Flat Tube of Parallel Flow Heat Exchanger to Heat Transfer

2014 ◽  
Vol 1008-1009 ◽  
pp. 927-933
Author(s):  
Hai Jiang Yang ◽  
Ming Li ◽  
Xiao Ye Xue ◽  
Yan Liu ◽  
Kui Huang
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Transfer Rate ◽  
Flow Distribution ◽  
Uniform Flow ◽  
Parallel Flow ◽  
Transfer Efficiency ◽  
Heat Transfer Efficiency ◽  
Uniform Flow Distribution ◽  
Flow Heat

In this paper, the heat transfer rate of parallel flow heat exchanger was obtained in the condition of non-uniform flow distribution by 3D numerical simulation. The maximum theoretical heat transfer rate of parallel flow heat exchanger was obtained through 1D calculation. Ultimately, the correlation of the influence of non-uniform flow distribution on heat transfer efficiency was obtained by the comparative analysis of non-uniform flow distribution and heat transfer efficiency and regression calculation. It was found that the forecasted heat transfer efficiency error of correlation was within 2%.

Influence of Radiative Heat Transfer on Variation of Cell Voltage Within a Stack

2003 ◽  
Author(s):  
A. C. Burt ◽  
I. B. Celik ◽  
R. S. Gemmen ◽  
A. V. Smirnov
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Flow Distribution ◽  
Cell Voltage ◽  
Uniform Flow ◽  
Transfer Model ◽  
Computational Performance ◽  
Uniform Flow Distribution ◽  
The Impact

In this study, a numerical investigation of cell-to-cell voltage variation by considering the impact of flow distribution and heat transfer on a stack of cells has been performed. A SOFC stack model has been previously developed to study the influence of flow distribution on stack performance (Burt, et al., 2003). In the present study the heat transfer model has been expanded to include the influence of radiative heat transfer between the PEN (positive electrode, electrolyte, negative electrode) and the neighboring separator plates. Variations in cell voltage are attributed to asymmetries in stack geometry and nonuniformity in flow rates. Simulations were done in a parallel computing environment with each cell computed in a separate (CPU) process. This natural decomposition of the fuel cell stack reduced the number of communicated variables thereby improving computational performance. The parallelization scheme implemented utilized a message passing interface (MPI) protocol where cell-to-cell communication is achieved via exchange of temperature and thermal fluxes between neighboring cells. Inclusion of radiative heat transfer resulted in more uniform temperature and voltage distribution for cases of uniform flow distribution. Non-uniform flow distribution still resulted in significant cell-to-cell voltage variations.

Experimental Study of Pressure Drop and Heat Transfer in a Single-Phase Micropin-Fin Heat Sink

2007 ◽  
Vol 129 (4) ◽  
pp. 479-487 ◽  
Author(s):  
Abel Siu-Ho ◽  
Weilin Qu ◽  
Frank Pfefferkorn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Heat Sink ◽  
Single Phase ◽  
Tip Clearance ◽  
Hydrodynamic Performance ◽  
Pin Fin ◽  
Heat Transfer Correlations

The pressure drop and heat transfer characteristics of a single-phase micropin-fin heat sink were investigated experimentally. Fabricated from 110 copper, the heat sink contained an array of 1950 staggered square micropin fins with 200×200μm2 cross section by 670μm height. The ratios of longitudinal pitch and transverse pitch to pin-fin equivalent diameter are equal to 2. De-ionized water was employed as the cooling liquid. A coolant inlet temperature of 25°C, and two heat flux levels, qeff″=50W∕cm2 and qeff″=100W∕cm2, defined relative to the platform area of the heat sink, were tested. The inlet Reynolds number ranged from 93 to 634 for qeff″=50W∕cm2, and from 127 to 634 for qeff″=100W∕cm2. The measured pressure drop and temperature distribution were used to evaluate average friction factor and local averaged heat transfer coefficient/Nusselt number. Predictions of the previous friction factor and heat transfer correlations that were developed for low Reynolds number (Re<1000) single-phase flow in short pin-fin arrays were compared to the present micropin-fin data. Moores and Joshi’s friction factor correlation (2003, “Effect of Tip Clearance on the Thermal and Hydrodynamic Performance of a Shrouded Pin Fin Array,” ASME J. Heat Transfer, 125, pp. 999–1006) was the only one that provided acceptable predictions. Predictions from the other friction factor and heat transfer correlations were significantly different from the experimental data collected in this study. These findings point to the need for further fundamental study of single-phase thermal/fluid transport process in micropin-fin arrays for electronic cooling applications.

scholarly journals Modeling of flow uniformity by installing inlet distributor within the inflow part of a pressurized module using computational fluid dynamics

2020 ◽  
Vol 25 (6) ◽  
pp. 969-976
Author(s):  
Changkyoo Choi ◽  
Chulmin Lee ◽  
In S. Kim
Keyword(s):  
Water Distribution ◽  
Flow Distribution ◽  
Uniform Flow ◽  
Membrane Module ◽  
Energy Utilization ◽  
Cross Sectional ◽  
Uniformity Coefficient ◽  
Fluid Behavior ◽  
Uniform Flow Distribution ◽  
Velocity Pressure

Uniform flow distribution is a significant parameter for designing pressurized membrane modules because non-uniform flow distribution can cause serious local flux and fouling problems within a module. Thus, this study investigated the fluid behavior with regards to the evenness of water distribution using newly designed inlet distributors in the inflow part of a pressurized membrane module. From the results of velocity and pressure at the cross-sectional and outlet planes, we confirmed that a conventional membrane module with no distributor (non-distributor) had fluid that was concentrated at the central part. Case 1, which had a cross-shaped distributor, reduced the central concentration tendency, and Case 2, which had a round-shaped distributor, displayed a relatively uniform flow based on the velocity, pressure, flux, and standard deviation data. Here, the non-uniformity coefficient (<i>N</i>) and energy utilization (<i>η</i>) for Cases 1 and 2 showed a lower non-uniformity coefficient (0.030 and 0.017, respectively) than for the Non-distributor (0.039). The energy utilization of Cases 1 and 2 were higher (1.35e-0.5 and 1.46e-05) than the Non-distributor (1.64e-05). Overall, we confirmed that the inlet distributors led to increased evenness of flow distribution within an inflow part.

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