Optimization of Pin-Fins for a Heat Exchanger by Entropy Generation Minimization and Constructal Law

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Gongnan Xie ◽  
Yidan Song ◽  
Masoud Asadi ◽  
Giulio Lorenzini
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Thermal Energy ◽  
Pin Fin ◽  
Entropy Generation Minimization ◽  
Flow And Heat Transfer ◽  
Constructal Law ◽  
Pin Fins ◽  
Computational Fluid Dynamics Cfd

Pin-fins are considered as one of the best elements for heat transfer enhancement in heat exchangers. In this study, the topology of pin-fins (length, diameter, and shape) is optimized based on the entropy generation minimization (EGM) theory coupled with the constructal law (CL). Such pin-fins are employed in a heat exchanger in a sensible thermal energy storage (TES) system so as to enhance the rate of heat transfer. First, the EGM method is used to obtain the optimal length of pin-fins, and then the CL is applied to get the optimal diameter and shape of pin-fins. Reliable computational fluid dynamics (CFD) simulations of various constructal pin-fin models are performed, and detailed flow and heat transfer characteristics are presented. The results show that by using the proposed system with optimized pin-fin heat exchanger the stored thermal energy can be increased by 10.2%.

Effect of Pin Density on Heat-Mass Transfer and Fluid Flow at Low Reynolds Numbers in Minichannels

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
N. K. C. Selvarasu ◽  
Danesh K. Tafti ◽  
Neal E. Blackwell
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Entropy Generation ◽  
Plane Channel ◽  
Performance Measure ◽  
Tip Clearance ◽  
Turbulent Regime ◽  
Pin Fin ◽  
Pin Fins ◽  
Optimal Spacing

Previous investigations on the performance of straight pins, pins with tip clearance, and profiled fins showed that closely packed cylindrical pin fins are very competitive with the modified pins. Therefore, the objective of this paper is to investigate the effect of pin density on performance. Steady/time-dependent calculations are performed to investigate the effect of pin density on friction and heat transfer. Pins packed at distances of SD=1.1, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, and 3 pin diameters (D) are investigated for 10≤ReD≤600. Two performance measures are used to compare the different pin fin densities. The first measure is to maximize heat transfer capacity for a given pumping power compared with a plane channel. The second measure used is based on entropy generation minimization (EGM), where the objective is to reduce the total irreversibility of the pin fin array to obtain an optimal spacing. Based on the performance measure of maximizing heat capacity, it is shown that for plain channels operating in the laminar range using denser pin packing has distinct advantages with SD=1.1 providing the best augmentation. However, the augmentation in heat capacity becomes relatively independent of the pin density for a channel operating in the turbulent regime. Based on the EGM method, at ReD>200, SD=1.3, 1.4, and 1.5 are the most suitable, with the least entropy generation observed at SD=1.4. At ReD<200, SD=1.1, 1.2, and 1.3 are also suitable for keeping entropy generation low.

Parametrical Study of the Flat-Tube and Pin Fin Heat Exchangers

2007 ◽  
Author(s):  
Maria Pascu ◽  
Naser Sahiti ◽  
Franz Durst
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Automobile Industry ◽  
Heat Exchangers ◽  
Unit Area ◽  
Pin Fin ◽  
Flow Length ◽  
Louvered Fin ◽  
Pin Fins ◽  
Constant Versus

The main objective of the present work was the derivation of heat transfer and pressure drop characteristics for pin fins which could be applied in heat exchangers used in the automobile industry. For this, 34 models of pin fin heat exchangers, characterized by a pin diameter of 0.35 mm, with both inline and staggered arrangements, were numerically investigated. The numerical results were validated through various comparison and validation procedures. The best performing pin fin configuration was determined by employing the performance plot: heat transfer per unit volume (or per unit area, if the pin height is constant) versus the energy input reduced to the same parameter as the heat transfer (volume or area). The heat exchanger performance plot showed that, for the investigated flow length, the staggered pin fin configuration performs better when compared to the inline arrangement. In order to prove the industrial applicability of these results, a louvered fin heat exchanger, commonly used as a car radiator, was experimentally investigated. A comparison of the best performing pin fin heat exchanger with the louvered fin model revealed an enhancement in the heat transfer of the pin fin model of 35%.

Effects of Pin-Fin Height on Flow and Heat Transfer in a Rectangular Duct

2011 ◽  
Author(s):  
X. Chi ◽  
T. I.-P. Shih ◽  
K. M. Bryden ◽  
S. Siw ◽  
M. K. Chyu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Wall Region ◽  
Rectangular Duct ◽  
Opposite Wall ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Inlet Conditions ◽  
D Values

CFD simulations were performed to study the flow and heat transfer in a rectangular duct (Wd × Hd, where Wd/Hd = 3) with a staggered array of circular pin fins (D = Hd/4) mounted on the two opposite walls separated by Hd. For this array of pin fins, five different pin-fin height (H) combinations were examined, and they are (1) H = Hd = 4D (i.e., all pin fins extended from wall to wall), (2) H = 3D on both walls, (3) H = 2D on both walls, (4) H = 4D on one wall and H = 2D on the opposite wall, and (5) H = 3D on one wall and H = 2D on the opposite wall. The H values studied give H/D values of 2, 3, and 4 and C/D values of 2, 1, and 0, where C is the distance between the pin-fin tip and the opposite wall. For all cases, the duct wall and pin-fin surface temperatures were maintained at Tw = 313.15 K; the temperature and the speed of the air at the duct inlet were uniform at Tinlet = 343.15 K and U = 8.24 m/s; the pressure at the duct exit was fixed at Pb = 1 atm; and the Reynolds number based on the duct hydraulic diameter and duct inlet conditions was Re = 15,000. This CFD study is based on 3-D steady RANS, where the ensemble averaged continuity, compressible Navier-Stokes, and energy equations are closed by the thermally perfect equation of state and the two-equation realizable k-ε turbulence model with wall functions and with the low-Reynolds number model of Chen and Patel in the near-wall region. The usefulness of this CFD study was assessed by comparing predicted heat-transfer coefficient and friction factor with available experimental data. Results are presented to show how the flow induced by arrays of pin fins of different heights affects temperature distribution, surface heat transfer, and pressure loss.

The Second Law Analysis of Thermodynamics for the Plate–Fin Surface Performance in a Cross Flow Heat Exchanger

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Mansour Nasiri Khalaji ◽  
Isak Kotcioglu ◽  
Sinan Caliskan ◽  
Ahmet Cansiz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Fluid Velocity ◽  
Cross Flow ◽  
Design Parameters ◽  
Second Law ◽  
Transfer Unit ◽  
Pin Fins

In this paper, a particular heat exchanger is designed and analyzed by using second law of thermodynamics. The heat exchanger operates with the cross flow forced convection having cylindrical, square, and hexagonal pin fins (tubular router) placed in the rectangular duct. The pin fins are installed periodically at the top and bottom plates of the duct perpendicular to the flow direction, structured in-line, and staggered sheet layouts. The entropy generation in the flow domain of the channels is calculated to demonstrate the rate of irreversibilities. To obtain the efficiencies, irreversibility, thermal performance factor, and entropy generation number (EGN), the heat exchanger is operated at different temperatures and flow rates by using hot and cold fluids. Optimization of the design parameters and winglet geometry associated with the performance are determined by entropy generation minimization. The variation of the EGN with Reynolds number for various tubular routers is presented. The Reynolds number is determined according to the experimental plan and the performance is analyzed with the method of effectiveness—number of transfer unit (NTU). Based on particular designs, it was determined that the increment in fluid velocity enhances the heat transfer rate, which in turn decreases the heat transfer irreversibility.

Optimization of Pin-Fin Heat Sinks in Bypass Flow Using Entropy Generation Minimization Method

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
W. A. Khan ◽  
J. R. Culham ◽  
M. M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Entropy Generation ◽  
Heat Sink ◽  
Heat Sinks ◽  
Entropy Generation Rate ◽  
Bypass Flow ◽  
Minimization Method ◽  
Pin Fin ◽  
Entropy Generation Minimization

An entropy generation minimization method is applied to study the thermodynamic losses caused by heat transfer and pressure drop for the fluid in a cylindrical pin-fin heat sink and bypass flow regions. A general expression for the entropy generation rate is obtained by considering control volumes around the heat sink and bypass regions. The conservation equations for mass and energy with the entropy balance are applied in both regions. Inside the heat sink, analytical/empirical correlations are used for heat transfer coefficients and friction factors, where the reference velocity used in the Reynolds number and the pressure drop is based on the minimum free area available for the fluid flow. In bypass regions theoretical models, based on laws of conservation of mass, momentum, and energy, are used to predict flow velocity and pressure drop. Both in-line and staggered arrangements are studied and their relative performance is compared to the same thermal and hydraulic conditions. A parametric study is also performed to show the effects of bypass on the overall performance of heat sinks.

Numerical Investigation on the Flow and Heat Transfer Characteristics of the Superheated Steam in the Wedge Duct With Pin-Fins

2013 ◽  
Author(s):  
Gaoliang Liao ◽  
Xinjun Wang ◽  
Xiaowei Bai ◽  
Ding Zhu ◽  
Jinling Yao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Three Dimensional ◽  
Heat Transfer Characteristics ◽  
Pin Fin ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Steam Superheat

By using the CFX software, the three-dimensional flow and heat transfer characteristics in the cooling duct with pin-fin in the blade trailing edge were numerically simulated. The effects of pin-fin arrangements, Reynolds number, steam superheat degrees, streamwise pin density and convergence angle of the wedge duct on the flow and heat transfer characteristics were analysed. The results show that the Nusselt number on the endwall and pin-fin surfaces as well as the pin-fin row averaged Nusselt number increase with the increasing of Reynolds number, while it decreased with the with the increasing of X/D. The pressure drop increases with the increasing of Reynolds number while decreases with the increasing of X/D in the wedge duct. The degree of superheat has little effect on the pressure loss in the wedge duct. A comprehensive analysis and comparison show that the highest thermal performance is reached in the wedge duct when the value of X/D is 1.5.

scholarly journals Miller Cycle Analysis Using EGM

2005 ◽  
Author(s):  
Bernardo Ribeiro ◽  
Jorge Martins
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Compression Ratio ◽  
Internal Combustion Engines ◽  
Combustion Engines ◽  
Miller Cycle ◽  
Valve Timing ◽  
Entropy Generation Minimization ◽  
Flow And Heat Transfer ◽  
Variable Valve

The Entropy Generation Minimization (EGM) method is based on the analysis by three sciences (thermodynamics, fluid flow and heat transfer) of the different processes that may occur in a system or in an equipment. Herein the EGM method is applied to internal combustion engines to determine the entropy generation caused by different processes. A model incorporating entropy generation calculations is used to assess various engines configurations. Otto cycle was tested and Variable Valve Timing (VVT) and Variable Compression Ratio (VCR) were applied so thermodynamic benefits could be tested and evaluated. With the referred model, the Miller cycle variables are analyzed in order to establish the best working conditions of an engine under a certain load. The intake and exhaust valve timing, combustion start, compression ratio adjustment and heat transfer are the variables for which a best working condition is determined based on the minimization of the entropy generation of the several engine processes.

Numerical Study on Flow and Heat Transfer Characteristics of Pin-Fins With Different Shapes

2019 ◽  
Author(s):  
Wei Jin ◽  
Ning Jia ◽  
Junmei Wu ◽  
Jiang Lei ◽  
Lin Liu
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Study ◽  
Heated Surface ◽  
Transfer Effect ◽  
Enhancement Effect ◽  
Trailing Edge ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Pin Fins

Abstract Equipping pin-fins in the blade trailing edge is an significant method for enhancing heat transfer. In order to obtain a geometry of pin-fins with good heat transfer effect and small friction factor, six pin-fins (circular, elliptic, oblong, teardrop, lancet and NACA) are selected. The flow and heat transfer features of the rectangular channel with the staggered pin-fins were numerically studied through FLUENT software. The channels with different pin-fins have the same relative spanwise pitch (S/D = 2.5) and streamwise pitch (X/D = 2.5), and the range of Reynolds number is 5×103 to 3×104. The applicability and accuracy of five turbulence models (Standard k-ε, Realizable k-ε, RNG k-ε, Standard k-ω and SST k-ω) are checked by comparing the numerically predicted results with the experimental from literature. It is found that the Realizable k-ε model is better at capturing the microstructure of flow field and has higher precision in predicting the averaged Nusselt number on the heated surface. For the six pin-fins, the leading edge is surrounded by a “U-shaped” strong heat exchange zone, but the vortex systems in the trailing edge are different from each other. Compared to the circular pin-fin, the oblong pin-fin has the best heat transfer enhancement effect, but the friction factor of channel is also larger. While the NACA pin-fin has the lowest friction factor, and the heat transfer effect is second only to the oblong. NACA pin-fin may be applied in blade trailing edge cooling by further optimizing the relative position of the pin-fins in the channel.

Entropy generation minimization of a double-pipe pin fin heat exchanger

2008 ◽  
Vol 28 (17-18) ◽  
pp. 2337-2344 ◽  
Author(s):  
N. Sahiti ◽  
F. Krasniqi ◽  
Xh. Fejzullahu ◽  
J. Bunjaku ◽  
A. Muriqi
Keyword(s):  
Heat Exchanger ◽  
Entropy Generation ◽  
Pin Fin ◽  
Entropy Generation Minimization ◽  
Double Pipe
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