Experimental Characterization of Compact Heat Exchangers With Short Flow Lengths at Simulated Elevated Altitudes

2003 ◽  
Vol 125 (1) ◽  
pp. 171-180 ◽  
Author(s):  
J. A. Mathias ◽  
J. Cao ◽  
M. E. Ewing ◽  
R. N. Christensen
Keyword(s):  
Pressure Drop ◽  
Heat Exchangers ◽  
Reynolds Numbers ◽  
Experimental Results ◽  
Experimental Characterization ◽  
Rectangular Duct ◽  
Low Reynolds Numbers ◽  
Compact Heat Exchangers ◽  
Experimental Pressure

This paper presents experimental pressure drop and heat transfer results of compact heat exchangers made with plain rectangular fins of short flowlengths tested with air at very low Reynolds numbers. Experiments were performed at sea level and at simulated elevated altitudes up to 25,298 m (83,000 ft). From the experimental results, the additional pressure drop of the air caused by the developing boundary layers and the hydrodynamic entrance length were determined. An equation was produced that predicted the average Nusselt number of the air, which significantly decreased with nondimensional length. The experimental results varied with respect to the aspect ratio of the rectangular duct and nondimensional length, which is inversely related to the Reynolds number.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

Thermal and Hydraulic Performance of a Rectangular Duct With Multiple V-Shaped Ribs

1998 ◽  
Vol 120 (4) ◽  
pp. 1072-1077 ◽  
Author(s):  
C.-O. Olsson ◽  
B. Sunden
Keyword(s):  
Cross Sections ◽  
Heat Exchangers ◽  
Reynolds Numbers ◽  
Swirl Flow ◽  
Rectangular Duct ◽  
Transfer Enhancement ◽  
Flow Cells ◽  
Compact Heat Exchangers ◽  
Staggered Arrangement ◽  
Flow Duct

Experiments have been carried out to investigate the performance of a new swirl flow duct which is suitable for compact heat exchangers such as radiators. The ducts tested have rectangular cross sections with aspect ratio 1 to 8, and multiple V-shaped ribs are attached to the wide walls in a staggered arrangement such that square secondary flow cells are established. A previous investigation has shown that multiple V-shaped ribs may provide greater heat transfer enhancement than angled straight ribs and V-shaped ribs at Reynolds numbers below 2000. The data are presented as j and f factors for Reynolds numbers from 500 to 15,000, and correlations are obtained for the influence of rib height (0.1 < e/H < 0.2), rib pitch (3 < p/H < 7), and rib angle (15 deg < Φ < 45 deg). It was found that a rib angle of 45 deg provided the highest j/f ratio, while increasing the rib height or decreasing the rib pitch lowers the j/f ratio.

Flow Visualization of Airflow Through a Rectangular Duct With Combined Heat and Mass Transfer

2010 ◽  
Author(s):  
M. T. Fauchoux ◽  
C. J. Simonson ◽  
D. A. Torvi
Keyword(s):  
Flow Visualization ◽  
Reynolds Numbers ◽  
Porous Membrane ◽  
Experimental Facility ◽  
Rectangular Duct ◽  
Concentration Gradients ◽  
Low Reynolds Numbers ◽  
Test Conditions ◽  
Reduce Energy Consumption ◽  
Heat And Moisture

Radiant ceiling panels have been shown to provide good thermal comfort for occupants and reduce energy consumption in large buildings. A disadvantage of radiant panels however, is the inability to alter the relative humidity (RH) of a space, which can also lead to occupant discomfort. A new panel is being developed which will transfer both heat and moisture to a room, to moderate space temperature and RH simultaneously. In order to determine how this panel performs, a test panel has been created and tested in an experimental facility. The panel is situated in the top of a rectangular duct. The surface of the panel is made of a porous membrane, which allows moisture to transfer between the air and the panel. Air passes through the duct and underneath the panel, at low Reynolds numbers (Re). As heat and moisture are transferred between the panel and the air, temperature and concentration gradients form in the duct. If these gradients become large, free convection will occur. Depending on which type of convection is dominant, free or forced, the air will flow in different patterns. In order to understand the performance of the panel, flow visualization is used to determine how the airflow is affected by temperature and concentration gradients. Test conditions include heating, cooling, humidification and dehumidification.

Controllable, High Force Amplification Using Elastic Cable Capstans

2012 ◽  
Author(s):  
Gray C. Thomas ◽  
Clayton C. Gimenez ◽  
Erica D. Chin ◽  
Andrew P. Carmedelle ◽  
Aaron M. Hoover
Keyword(s):  
Dynamic Performance ◽  
Experimental Results ◽  
Rotating Drum ◽  
Experimental Characterization ◽  
Experimental Apparatus ◽  
Linear Force ◽  
Low Torque ◽  
Robotic Applications

This paper presents the design and experimental characterization of a continuously variable linear force amplifier based on the theory of capstans. In contrast to traditional capstan amplifiers, the design presented here uses an elastic cable, enabling a control actuator to not only continuously clutch output to a rotating drum but also passively declutch by releasing tension. Our experimental results demonstrate successful declutching at all force amplification ratios up to the limit of our experimental apparatus, 21 — significantly higher than previously published values. A system of distributed capstan amplifiers driven by a central torque source with cable engagement switched by lightweight, low torque actuators has potential to reduce the mass of distal actuators and enable more dynamic performance in robotic applications.

Experimental characterization of random packed spheres, cylinders and rings, and their influence on pressure drop

2020 ◽  
Vol 222 ◽  
pp. 115644 ◽  
Author(s):  
Jennie von Seckendorff ◽  
Normen Szesni ◽  
Richard Fischer ◽  
Olaf Hinrichsen
Keyword(s):  
Pressure Drop ◽  
Experimental Characterization
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