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.

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.

Three-Dimensional Numerical Simulation on the Laminar Flow and Heat Transfer in Four Basic Fins of Plate-Fin Heat Exchangers

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
Yinhai Zhu ◽  
Yanzhong Li
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Exchangers ◽  
Flow Direction ◽  
Three Dimensional ◽  
Entry Length ◽  
Flow And Heat Transfer ◽  
F Factor ◽  
The One ◽  
Data Reduction Method

In this paper, four basic fins of the plate-fin heat exchangers, rectangular plain fin, strip offset fin, perforated fin, and wavy fin, are modeled and simulated by taking account of fin thickness, thermal entry effect, and end effect. Three-dimensional numerical simulations on the flow and heat transfer in the four fins are investigated and carried out at laminar flow regime. Validity of the modeling technique is verified by comparing computational results with both corresponding experimental data and three empirical correlations from literatures. Global average Colburn factor (j factor) and friction factor (f factor) and their local 1D streamwise-average distributions along the fins are presented by introducing data reduction method. The heat transfer behaviors in both the developing and developed regions are analyzed by examining variations of the local Nusselt number along the flow direction. It is found that the thermal entry length of the four fins might be expressed in the format of Le=c1 Rec2 Pr Dh, which has the same form as the one in a circular tube.

Thermal Boundary Conditions and Some Solutions for Laminar Duct Flow Forced Convection

1974 ◽  
Vol 96 (2) ◽  
pp. 159-165 ◽  
Author(s):  
R. K. Shah ◽  
A. L. London
Keyword(s):  
Laminar Flow ◽  
Boundary Conditions ◽  
Forced Convection ◽  
Heat Exchangers ◽  
Duct Flow ◽  
General Classification ◽  
Compact Heat Exchangers ◽  
Thermal Boundary Conditions

The importance of laminar flow forced convection theoretical solutions for the design of compact heat exchangers has been well realized. Many of these theoretical solutions published in the literature are difficult to interpret by a designer, because thermal boundary conditions used in the analysis are generally not defined clearly and consistently. The objective of this paper is to clarify this situation by a systemized presentation. Starting with a general classification, nine specific thermal boundary conditions are categorized for singly connected ducts. At the end, the most useful fully developed laminar flow solutions for some important duct geometries are summarized for the designer.

scholarly journals One-Sided and Two-Sided w-of-w Runs-Rules Schemes: An Overall Performance Perspective and the Unified Run-Length Derivations

2019 ◽  
Vol 2019 ◽  
pp. 1-20 ◽  
Author(s):  
S. C. Shongwe ◽  
J.-C. Malela-Majika ◽  
E. M. Rapoo
Keyword(s):  
Markov Chain ◽  
Steady State ◽  
Positive Integer ◽  
The Other ◽  
Unified Approach ◽  
Run Length ◽  
Runs Rules ◽  
Overall Performance ◽  
The Mean ◽  
The One

The one-sided and two-sided Shewhart w-of-w standard and improved runs-rules monitoring schemes to monitor the mean of normally distributed observations from independent and identically distributed (iid) samples are investigated from an overall performance perspective, i.e., the expected weighted run-length (EWRL), for every possible positive integer value of w. The main objective of this work is to use the Markov chain methodology to formulate a theoretical unified approach of designing and evaluating Shewhart w-of-w standard and improved runs-rules for one-sided and two-sided X- schemes in both the zero-state and steady-state modes. Consequently, the main findings of this paper are as follows: (i) the zero-state and steady-state ARL and initial probability vectors of some of the one-sided and two-sided Shewhart w-of-w standard and improved runs-rules schemes are theoretically similar in design; however, their empirical performances are different and (ii) unlike previous studies that use ARL only, we base our recommendations using the zero-state and steady-state EWRL metrics and we observe that the steady-state improved runs-rules schemes tend to yield better performance than the other considered competing schemes, separately, for one-sided and two-sided schemes. Finally, the zero-state and steady-state unified approach run-length equations derived here can easily be used to evaluate other monitoring schemes based on a variety of parametric and nonparametric distributions.

Thermal Coupling in Laminar Flow Double-Pipe Heat Exchangers

1991 ◽  
Vol 113 (3) ◽  
pp. 526-534 ◽  
Author(s):  
G. Pagliarini ◽  
G. S. Barozzi
Keyword(s):  
Laminar Flow ◽  
Heat Exchangers ◽  
Point Of View ◽  
Entropy Production Rate ◽  
Thermal Coupling ◽  
Local Entropy ◽  
Axial Conduction ◽  
Overall Performance ◽  
Double Pipe ◽  
Pipe Heat

Thermal interaction between the streams of laminar flow double-pipe heat exchangers is investigated theoretically by accounting for axial conduction along the wall separating the fluids. In a countercurrent arrangement, thermal coupling is demonstrated to have a definite influence on all the more important heat transfer parameters, such as the wall temperature, the heat flux density, the local entropy production rate, and the Nusselt number distributions. The overall performance of the device is considered under a second law point of view, and a complete parametric study is carried out.

Numerical Study of EHD-Enhanced Forced Convection Using Two-Way Coupling

2001 ◽  
Author(s):  
M. Huang ◽  
F. C. Lai
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Electric Fields ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Transfer Enhancement ◽  
Wide Range ◽  
The One

Abstract In this paper, numerical results are presented for heat transfer enhancement using electric field in forced convection in a horizontal channel. The electric field is generated by charging a wire electrode located at the center of the channel with direct current at a high voltage. The main objective of the present study is to verify the assumption that is commonly used in the numerical study of this kind of problems, which assumes the electric field can modify the flow field but not vice versa (i.e., the so-called one-way coupling). To this end, numerical solutions have been obtained for a wide range of governing parameters (Vo = 10, 12.5, 15 and 17.5 kV as well as ui = 0.0759 to 1.2144 m/s) using both one-way and two-way couplings. Using the two-way coupling approach, the possible modification of the electric field by the primary flow, which was previously neglected, is accounted for. The results obtained using these two approaches, in terms of the flow, temperature, and electric fields as well as the heat transfer enhancement, are thoroughly examined. In addition, their influence over the flow stability is investigated. Finally, the conclusion about the validity of the one-way coupling is reached at the end of the study.

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.

Note on Selection of Coordinate Systems for Geodynamics

1975 ◽  
Vol 26 ◽  
pp. 395-407
Author(s):  
S. Henriksen
Keyword(s):  
Sea Level ◽  
The Other ◽  
Coordinate Systems ◽  
Mean Sea Level ◽  
The Earth ◽  
The One ◽  
Static Systems ◽  
Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

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