Bejan’s Constructal Theory Analysis of Gas-Liquid Cooled Finned Modules

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Giulio Lorenzini ◽  
Simone Moretti
Keyword(s):  
Thermal Behavior ◽  
Heat Exchangers ◽  
High Performance ◽  
Numerical Study ◽  
Constructal Theory ◽  
Electronic Components ◽  
Theory Analysis ◽  
Pressure Losses ◽  
Different Types ◽  
Overall Performance

High performance heat exchangers represent nowadays the key of success to go on with the trend of miniaturizing electronic components as requested by the industry. This numerical study, based on Bejan’s Constructal theory, analyzes the thermal behavior of heat removing fin modules, comparing their performances when operating with different types of fluids. In particular, the simulations involve air and water (as representative of gases and liquids), to understand the actual benefits of employing a less heat conductive fluid involving smaller pressure losses or vice versa. The analysis parameters typical of a Constructal description (such as conductance or Overall Performance Coefficient) show that significantly improved performances may be achieved when using water, even if an unavoidable increase in pressure losses affects the liquid-refrigerated case. Considering the overall performance: if the parameter called Relevance tends to 0, air prevails; if it tends to 1, water prevails; if its value is about 0.5, water prevails in most of the case studies.

A Bejan’s Constructal Theory Approach to the Overall Optimization of Heat Exchanging Finned Modules With Air in Forced Convection and Laminar Flow Condition

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Giulio Lorenzini ◽  
Simone Moretti
Keyword(s):  
Laminar Flow ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Flow Condition ◽  
Numerical Study ◽  
The Other ◽  
Constructal Theory ◽  
Theory Approach ◽  
Overall Performance ◽  
The One

Optimizing ever smaller heat exchangers determines two opposite needs: augmenting performances, on the one hand; removing heat in excess to reduce failures, on the other. This numerical study, modeled thanks to Bejan’s Constructal theory, researches the overall optimization of finned modules, differently shaped and combined, cooled by air in laminar flow and forced convection condition: Losses of pressure, together with heat removed, contribute to the final assessment made through a novel idea of performance based on the so called overall performance coefficient.

scholarly journals Numerical Study of Flow Maldistribution in Multi-Plate Heat Exchangers Based on Robust 2D Model

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3121 ◽  
Author(s):  
Arkadiusz Brenk ◽  
Pawel Pluszka ◽  
Ziemowit Malecha
Keyword(s):  
Heat Exchangers ◽  
Numerical Study ◽  
High Heat ◽  
Pressure Balance ◽  
Plate Heat ◽  
Pressure Losses ◽  
Heat Transfer Efficiency ◽  
High Heat Transfer ◽  
Wide Range ◽  
Flow Maldistribution

Plate heat exchangers (PHE) are characterized by high heat transfer efficiency and compactness. An exploitation problem of the PHE is related to flow maldistribution, which can make part of the PHE idle, resulting in overheating and damage. Making geometrical modifications to the PHE can help reduce flow maldistribution. Modifications should be kept to a minimum, so as not to complicate the production process. There is a large number of possible geometrical modifications, which simply considers additional obstacles or stream dividers. To test all of them would be impractical and would also take a prohibitively long amount of time to obtain experimental measurements. A typical PHE is characterized by a complex system of channels. Making numerical calculations of its 3D model can be prohibitively time and resource-consuming. The present work introduces a physically consistent methodology of the transformation of a real 3D geometry to its 2D representation. Its main novelty is to assure the same pressure drop balance remains between the 3D and 2D geometries. This is achieved by a preservation of the same cumulative pressure losses in both geometries. The proposed innovative approach levels the pressure balance difference by adding properly designed local geometrical modifications. The developed methodology allowed a wide range of parameter space and various geometrical modifications to be investigated, and revealed geometrical optimizations leading to the improved performance of the PHE. To minimize the influence of other factors, an incompressible and single-phase flow was studied.

Numerical Study of Bubble Instability During Microchannel Flow Boiling

2015 ◽  
Author(s):  
Matthew Blomquist ◽  
Arman Khalighi ◽  
Abhijit Mukherjee
Keyword(s):  
Heat Exchangers ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Flow Boiling ◽  
Microchannel Flow ◽  
Electronic Components ◽  
Vapor Interface ◽  
Compact Size ◽  
Convection Cooling ◽  
Liquid Vapor

In recent years, the forced convection cooling for the heat dissipation of electronic components has become a significant area of research. Many high-end computing applications, from consumer gaming to scientific research, encounter performance limitations due to heat generation in micro-electronic components. Micro heat exchangers can offer an ideal cooling solution for these applications due to their compact size and heat dissipation characteristics. Single-phase heat exchangers are widely used in both industry and consumer applications, but are limited by operational temperature ranges as well as the working fluid’s thermo physical properties. Two-phase, convection cooling systems, however, can further increase the capabilities of micro-heat exchangers. In the present study, a model has been created to investigate bubble growth and the values of wall superheat, contact angle, and Reynolds number that cause instability at the liquid-vapor interface during microchannel flow boiling. The results show how bubble instability is caused by the transfer of heat being restricted by the liquid-vapor interface.

Numerical Study of Turbulence Nanofluid Flow to Distinguish Multiphase Flow Models for In-House Programming

2016 ◽  
Author(s):  
Anchasa Pramuanjaroenkij ◽  
Amarin Tongkratoke ◽  
Sadık Kakaç
Keyword(s):  
Mixture Model ◽  
Heat Exchangers ◽  
High Performance ◽  
Numerical Study ◽  
Experimental Studies ◽  
Working Fluid ◽  
Eulerian Model ◽  
Time Consumption ◽  
Vof Model ◽  
Multiphase Models

Fluid flow with particles are found in many engineering applications such as flows inside lab-on-a-chips and heat exchangers. In heat exchangers, nanofluids or base fluids mixed with nanoparticles are applied to be used as the working fluid instead of the traditional base fluids which have low thermal-physical properties. The nanoparticle diameters are in the range from 1 to 100 nanometers are mixed with the traditional base fluids before they are applied inside the heat exchangers and the nanofluids have been proved continually that they enhance heat transfer rates of the heat exchangers. Turbulent and laminar nanofluid flows have shown different enhancements in different conditions. This work focused on comparing different turbulent nanofluid simulations which used the computational fluid dynamics, CFD, with different multiphase models. The Realizable k-ε turbulence model coupled with three multiphase models; Volume of Fluid (VOF) model, Mixture model and Eulerian model, were considered and compared. The heat exchanger geometry in the work was rectangular as in the electrical device application and the nanofluid was a mixture between Al2O3 and water. All simulated results, then, were compared with experimental results. The comparisons showed that numerical results did not deviate from each other but their delivered-time consumptions and complications were different. If one develops his own code, Eulerian model was the most complicated while Mixture model and Eulerian model consumed longer performing times. Although the Eulerian model delivered-time consumption was long but it provided the best results, so the Eulerian model should be chosen when time consumption and errors play important roles. From this ordinary study, the first significant step of in-house program developments has started. The time consumption still indicated that the high performance computers should be selected, and properties obtained from the experimental studies should be imported to the simulation to increase the result accuracy.

Effect of housing size on the performance of a centrifugal compressor for turbocharger application: An experimental and numerical study

2021 ◽  
pp. 095440702110505
Author(s):  
Ealumalai Karunakaran ◽  
J M Mallikarjuna
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
High Performance ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Marked Change ◽  
Cross Sectional ◽  
Pressure Losses ◽  
Percentage Points ◽  
Compressor Performance

Currently, engine downsizing through turbocharging is widespread in the automotive industry to improve fuel economy and emissions. The engine downsizing demands compact and high performance centrifugal compressors for turbochargers. A compressor contains mainly an impeller and housing, which often uses a vaneless diffuser and an overhanging volute. High-speed flow from the impeller is decelerated in the diffuser and volute, to recover static pressure for boosting the engine. The volute flow characteristics and pressure recovery depend on the housing size, which determines the overall compressor performance and size. This study evaluates the effect of four different housing sizes viz., baseline, 12% scaled up, and 12% and 20% scaled-down geometrically, through experimental and numerical analysis. The experiments are conducted using different housing sizes with a given impeller to measure the compressor pressure ratio and efficiency. Also, steady-state numerical simulations are performed to examine the flow mechanisms causing pressure losses due to changes in housing size. Then, the simulation is also done for different volute surface roughness levels in each housing to establish its effect on compressor performance. From the results, it is found that there is no marked change in compressor efficiency between the baseline and 12% scaled-up housing. Whereas, the scaled-down housings (12% and 20%) showed efficiency drop of about 2–5 percentage points at near-choke flow rate. The CFD analyses of these scaled down housings with reduced cross-sectional area indicated substantial increase of meridional velocity, which results in higher swirl velocity in the volute causing more pressure losses. Besides, the increased volute surface roughness is realized to cause extra pressure loss due to higher wall shear stress. It amounts to additional efficiency reduction of 0.5–1 percentage points at the same near-choke flow.

Three-Dimensional Numerical Study of Flow and Heat Transfer Enhancement Using Vortex Generators in Fin-and-Tube Heat Exchangers

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
P. Chu ◽  
Y. L. He ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Heat Exchangers ◽  
Numerical Study ◽  
Three Dimensional ◽  
Performance Comparison ◽  
Transfer Enhancement ◽  
Local Flow ◽  
Overall Performance

In this paper, a three-dimensional numerical investigation was performed for heat transfer characteristics and flow structure of full scale fin-and-tube heat exchangers with rectangular winglet pair (RWP). For the Reynolds number ranging from 500 to 880, the baseline configuration (without RWP) is compared with three enhanced configurations (with RWP): inline-1RWP case, inline-3RWP case, and inline-7RWP case. It was found that the air-side heat transfer coefficient improved by 28.1–43.9%, 71.3–87.6%, and 98.9–131% for the three enhanced configurations, with an associated pressure drop penalty increase of 11.3–25.1%, 54.4–72%, and 88.8–121.4%, respectively. An overall performance comparison was conducted by using the London area goodness factor. It is revealed that among the three enhanced configurations, the inline-1RWP case obtains the best overall performance, and the inline-3RWP case is better than the inline-7RWP case. The numerical results were also analyzed on the basis of the field synergy principle to provide fundamental understanding of the relation between local flow structure and heat transfer augmentation. It was confirmed that the reduction in the average intersection angle between the velocity vector and the temperature gradient was one of the essential factors influencing heat transfer enhancement. The analysis also provides guidelines for where the enhancement technique is highly needed.

Co-planar two-dimensional Metal-Insulator-Semiconductor Capacitor: Numerical study of the device electrostatics.

2017 ◽  
Author(s):  
Varun Bheemireddy
Keyword(s):  
Space Charge ◽  
High Performance ◽  
Numerical Study ◽  
2D Materials ◽  
Space Charge Density ◽  
Two Dimensional ◽  
Short Channel ◽  
Metal Insulator ◽  
Metal Insulator Semiconductor ◽  
New Family

The two-dimensional(2D) materials are highly promising candidates to realise elegant and e cient transistor. In the present letter, we conjecture a novel co-planar metal-insulator-semiconductor(MIS) device(capacitor) completely based on lateral 2D materials architecture and perform numerical study of the capacitor with a particular emphasis on its di erences with the conventional 3D MIS electrostatics. The space-charge density features a long charge-tail extending into the bulk of the semiconductor as opposed to the rapid decay in 3D capacitor. Equivalently, total space-charge and semiconductor capacitance densities are atleast an order of magnitude more in 2D semiconductor. In contrast to the bulk capacitor, expansion of maximum depletion width in 2D semiconductor is observed with increasing doping concentration due to lower electrostatic screening. The heuristic approach of performance analysis(2D vs 3D) for digital-logic transistor suggest higher ON-OFF current ratio in the long-channel limit even without third dimension and considerable room to maximise the performance of short-channel transistor. The present results could potentially trigger the exploration of new family of co-planar at transistors that could play a signi significant role in the future low-power and/or high performance electronics.<br>

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