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.

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.

Recuperators in Gas Turbine Systems

1998 ◽  
Author(s):  
Esa Utriainen ◽  
Bengt Sundén
Keyword(s):  
Research And Development ◽  
Gas Turbine ◽  
Cross Sections ◽  
Heat Exchangers ◽  
Power Plants ◽  
Pressure Ratio ◽  
Compact Heat Exchangers ◽  
Thermodynamic Cycles ◽  
Large Pressure ◽  
Gas Turbine Cycle

The application of recuperators in advanced thermodynamic cycles is growing due to stronger demands of low emissions of pollutants and the necessity of improving the cycle efficiency of power plants to reduce the fuel consumption. This paper covers applications and types of heat exchangers used in gas turbine units. The trends of research and development are brought up and the future need for research and development is discussed. Material aspects are covered to some extent. Attempts to achieve compact heat exchangers for these applications are also discussed. With the increasing pressure ratio in the gas turbine cycle, large pressure differences between the hot and cold sides exist. This has to be accounted for. The applicability of CFD (Computational Fluid Dynamics) is discussed and a CFD–approach is presented for a specific recuperator. This recuperator has narrow wavy ducts with complex cross-sections and the hydraulic diameter is so small that laminar flow prevails. The thermal-hydraulic performance is of major concern.

Single-Phase Heat Transfer Enhancement Techniques in Microchannel and Minichannel Flows

2004 ◽  
Author(s):  
Mark E. Steinke ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Electric Fields ◽  
Single Phase ◽  
Flow Boiling ◽  
Swirl Flow ◽  
Flow Transition ◽  
Transfer Enhancement ◽  
Compact Heat Exchangers ◽  
Chip Cooling

The single-phase heat transfer enhancement techniques are well established for conventional channels and compact heat exchangers. The major techniques include flow transition, breakup of boundary layer, entrance region, vibration, electric fields, swirl flow, secondary flow and mixers. In the present paper, the applicability of these techniques for single-phase flows in microchannels and minichannels is evaluated. The microchannel and minichannel single-phase heat transfer enhancement devices will extend the applicability of single-phase cooling for critical applications, such as chip cooling, before more aggressive cooling techniques, such as flow boiling, are considered.

scholarly journals Heat Transfer Enhancement by Perforated and Louvred Fin Heat Exchangers

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 400
Author(s):  
Miftah Altwieb ◽  
Rakesh Mishra ◽  
Aliyu M. Aliyu ◽  
Krzysztof J. Kubiak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Flow Rates ◽  
Pressure Drops ◽  
Fin Design

Multi-tube multi-fin heat exchangers are extensively used in various industries. In the current work, detailed experimental investigations were carried out to establish the flow/heat transfer characteristics in three distinct heat exchanger geometries. A novel perforated plain fin design was developed, and its performance was evaluated against standard plain and louvred fins designs. Experimental setups were designed, and the tests were carefully carried out which enabled quantification of the heat transfer and pressure drop characteristics. In the experiments the average velocity of air was varied in the range of 0.7 m/s to 4 m/s corresponding to Reynolds numbers of 600 to 2650. The water side flow rates in the tubes were kept at 0.12, 0.18, 0.24, 0.3, and 0.36 m3/h corresponding to Reynolds numbers between 6000 and 30,000. It was found that the louvred fins produced the highest heat transfer rate due to the availability of higher surface area, but it also produced the highest pressure drops. Conversely, while the new perforated design produced a slightly higher pressure drop than the plain fin design, it gave a higher value of heat transfer rate than the plain fin especially at the lower liquid flow rates. Specifically, the louvred fin gave consistently high pressure drops, up to 3 to 4 times more than the plain and perforated models at 4 m/s air flow, however, the heat transfer enhancement was only about 11% and 13% over the perforated and plain fin models, respectively. The mean heat transfer rate and pressure drops were used to calculate the Colburn and Fanning friction factors. Two novel semiempirical relationships were derived for the heat exchanger’s Fanning and Colburn factors as functions of the non-dimensional fin surface area and the Reynolds number. It was demonstrated that the Colburn and Fanning factors were predicted by the new correlations to within ±15% of the experiments.

Experimental Comparison of Heat Transfer Enhancement Methods in Heat Exchangers

2003 ◽  
Vol 31 (2) ◽  
pp. 160-167 ◽  
Author(s):  
Hosni I. Abu-Mulaweh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Engineering Students ◽  
Swirl Flow ◽  
Experimental Comparison ◽  
Transfer Enhancement ◽  
Acquisition Device ◽  
Extended Surfaces ◽  
Almost All

This paper presents an experimental comparison of four different types of heat transfer enhancement techniques or methods in heat exchangers: two insert devices (a displacement device and a swirl flow device), extended surfaces, and obstruction devices. The objective of these experiments is to assist undergraduate mechanical engineering students in understanding the basic heat transfer processes and the methods and devices that can be implemented to enhance the heat transfer. The experimental setup and apparatus required to carry out these experiments are relatively simple. The apparatus includes five tube-within-a-tube heat exchangers with three thermocouples at each end, two rotameters, a heating element, a water pump, and a data acquisition device. Four of the five heat exchangers are modified by one type of the above-mentioned heat transfer enhancement techniques. The equipment is relatively inexpensive and available in almost all undergraduate heat transfer laboratories.

EHD Enhanced Convective Boiling of R-134a in Grooved Channels—Application to Subcompact Heat Exchangers

1997 ◽  
Vol 119 (4) ◽  
pp. 805-809 ◽  
Author(s):  
M. Salehi ◽  
M. M. Ohadi ◽  
S. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Flow Direction ◽  
Reynolds Numbers ◽  
Convective Boiling ◽  
Field Polarity ◽  
Electrical Field Strength ◽  
Compact Heat Exchangers ◽  
R 134A

Electrohydrodynamically (EHD) enhanced flow boiling of refrigerant R-134a inside grooved channels of approximately 1-mm hydraulic diameter was investigated with the objective of addressing the applicability of the EHD technique in highly compact heat exchangers. Two sets of experiments were performed. The first set included experiments in a channel with a smooth heat transfer wall, whereas in the second set a corrugated (enhanced) surface was used. In each case experiments were conducted as a function of the applied electrical field strength, electric field polarity, flow Reynolds number, inlet test section vapor quality, and flow direction (upward, downward, or horizontal). It is demonstrated that in all cases the EHD effect can substantially increase the heat transfer coefficient particularly at low Reynolds numbers and when applied over the enhanced heat transfer wall.

Air-Side Heat Transfer Enhancement and Pumping Power Penalty in Air-Cooled Heat Exchangers With Dimpled Fins

2017 ◽  
Author(s):  
Tung X. Vu ◽  
Lokanath Mohanta ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Fold Increase ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Power Penalty ◽  
Flat Tubes

In this work, we focus exclusively on heat transfer enhancement techniques for the air-side heat transfer in air-cooled heat exchangers/condensers. An innovative dimpled fin configuration is explored. Experiments, in which both heat transfer and drag are measured, are conducted with flat tubes in three configurations: without fins, with plain fins and with dimpled fins. Reynolds numbers based on the hydraulic diameter of the finned passages are varied between 600 and 7000. Results indicate that fins are more advantageous at lower Reynolds numbers since the increase in drag at higher Reynolds numbers quickly erases any advantage due to an increase in heat transfer rate. As an example, for the plain fins versus a bare tube at a Reynolds number of 600, there is a 7 fold increase in heat transfer with only a 5 fold increase in drag. However, at a Reynolds number of 7000, both heat transfer and drag increase by approximately 6 times, indicating that the increase in drag has caught up with the heat transfer enhancement. Similarly, while dimpled fins do result in higher heat transfer compared with the plain fins, the advantage is also more prominent at lower Reynolds numbers where heat transfer enhancement is higher than the associated increase in pumping power.

Sign in / Sign up

Export Citation Format

Share Document