Effect of tip clearance on the heat transfer and pressure drop performance in the micro-reactor with micro-pin–fin arrays at low Reynolds number

2014 ◽  
Vol 70 ◽  
pp. 709-718 ◽  
Author(s):  
Deqing Mei ◽  
Xinyang Lou ◽  
Miao Qian ◽  
Zhehe Yao ◽  
Lingwei Liang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Low Reynolds Number ◽  
Tip Clearance ◽  
Pin Fin ◽  
Low Reynolds ◽  
Pin Fin Arrays ◽  
Micro Reactor

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.

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 Heat Transfer and Pressure Drop for Short Pin-Fin Arrays With Pin-Endwall Fillet

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Circular Cylinders ◽  
Significant Finding ◽  
Turbine Cooling ◽  
Array Configuration ◽  
Pin Fin ◽  
Pin Fin Arrays

The effects of array configuration and pin-endwall fillet on the heat transfer and pressure drop of short pin-fin arrays are investigated experimentally. The pin-fin element with endwall-fillet, typical in actual turbine cooling applications is modeled by a spool-like cylinder. The arrays studied include an in-line and a staggered array, each having 7 rows of 5 pins. These arrays have the same geometric parameters, i.e. H/D = 1, S/D = X/D = 2.5, and the Reynolds number ranging from 5 × 103 to 3 × 10. One of the present results shows that the staggered array always has a higher array-averaged mass transfer coefficient than its in-line counterpart. However, the pressure drop for the staggered array is higher compared to the in-line configuration. These trends are unaffected by the existence of the pin-endwall fillet. Another significant finding is that an array with pin-endwall fillet generally produces lower heat transfer coefficient and higher pressure drop than that without endwall-fillet. This leads to the conclusion that pin-endwall fillet is undesirable for heat transfer augmentation. In addition, naive use of the heat transfer results obtained with perfectly circular cylinders tends to overestimate the pin-fin cooling capability in the actual turbine. The effects of endwall-fillet on the array heat transfer and pressure drop are much more pronounced for the staggered array than for the in-line array; however, they diminish as the Reynolds number increases.

Heat Transfer and Pressure Drop for Short Pin-Fin Arrays With Pin-Endwall Fillet

1990 ◽  
Vol 112 (4) ◽  
pp. 926-932 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Circular Cylinders ◽  
Significant Finding ◽  
Array Configuration ◽  
Pin Fin ◽  
Pin Fin Arrays

The effects of array configuration and pin-endwall fillet on the heat transfer and pressure drop of short pin-fin arrays are investigated experimentally. The pin-fin element with endwall fillet, typical in actual turbine cooling applications, is modeled by a spool-like cylinder. The arrays studied include an in-line and a staggered array, each having seven rows of five pins. These arrays have the same geometric parameters, i.e., H/D = 1, S/D = X/D = 2.5, and the Reynolds number ranging from 5 × 103 to 3 × 104. One of the present results shows that the staggered array always has a higher array-averaged heat transfer coefficient than its in-line counterpart. However, the pressure drop for the staggered array is higher compared to the in-line configuration. These trends are unaffected by the existence of the pin-endwall fillet. Another significant finding is that an array with pin-endwall fillet generally produces lower heat transfer coefficient and higher pressure drop than that without endwall fillet. This leads to the conclusion that pin-endwall fillet is undesirable for heat transfer augmentation. In addition, nai¨ve use of the heat transfer results obtained with perfectly circular cylinders tends to overestimate the pin-fin cooling capability in the actual turbine. The effects of endwall fillet on the array heat transfer and pressure drop are much more pronounced for the staggered array than for the inline array; however, they diminish as the Reynolds number increases.

3D Numerical Analysis of Heat Transfer in a Low Reynolds Number Microturbine Cascade

2012 ◽  
Author(s):  
M. Omri ◽  
S. Moreau ◽  
L. G. Fréchette
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Waste Heat ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Distributed Power Generation ◽  
Low Reynolds

This paper presents the conjugate heat transfer in a submillimeter scale microturbine characterized by laminar yet highly three-dimensional flows. Such a miniature turbine is part of a MEMS (microelectromechanical system) power plant-on-a-chip currently under development for distributed power generation from waste heat. Adiabatic subsonic flows in the turbine have previously been studied numerically and are characterized by low Reynolds number laminar flow (Re < 2500) but with complex vortical structures. The present work addresses the influence of these flow structures on heat transfer, including the effect of the horseshoe and tip vortices. Calculations were done for tip clearance gaps equal to 0%, 5% and 10% blade height. Three different scenarios were considered: adiabatic walls, the hub and casing temperature of 573K or the hub at 573K and the casing at 450K, for incoming flow at 600K. The heat transfer is more variable in the suction side since dominant vortices are adjacent to this blade side. The heat flux even changes its sign where the vortices begin to separate from the suction side, indicating that gas cooled in the hub and casing boundary layers is transported on the blades by the horseshoe vortices. The tip vortex prevents the top passage vortex from interacting with the suction side, which eliminates the negative heat transfer in this region. Due to the dominant vortices, the Nusselt number is found to be a function of the thermal boundary conditions and cannot be predicted with traditional boundary layer correlations.

Effect of Pin Tip Clearance on Flow and Heat Transfer at Low Reynolds Numbers

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Ali Rozati ◽  
Danesh K. Tafti ◽  
Neal E. Blackwell
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Tip Clearance ◽  
Number Range ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Low Reynolds ◽  
Flow Effects ◽  
High Reynolds

Cylindrical pin fins with tip clearances are investigated in the low Reynolds number range 5<ReD<400 in a plane minichannel. Five tip gaps are investigated ranging from a full pin fin (t*=0.0) to a clearance of t*=0.4D*, where D* is the pin diameter. It is established that unlike high Reynolds number flows, the flow and heat transfer are quite sensitive to tip clearance. A number of unique flow effects, which increase the heat transfer performance, are identified. The tip gap affects the heat transfer coefficient by eliminating viscosity dominated end wall effects on the pin, by eliminating the pin wake shadow on the end walls, by inducing accelerated flow in the clearance, by reducing or impeding the development of recirculating wakes, and by redistributing the flow along the height of the channel. In addition, tip gaps also reduce form losses and friction factor. A clearance of t*=0.3D* was found to provide the best performance at ReD<100; however, for ReD>100, both t*=0.2D* and 0.3D* were comparable in performance.

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