The Experts below are selected from a list of 3795 Experts worldwide ranked by ideXlab platform

Fengrui Sun - One of the best experts on this subject based on the ideXlab platform.

  • Constructal Entropy Generation Rate minimization for cylindrical pin-fin heat sinks
    International Journal of Thermal Sciences, 2017
    Co-Authors: Lingen Chen, Zhihui Xie, Aibo Yang, Fengrui Sun
    Abstract:

    Abstract Optimization of in-line cylindrical pin-fin heat sinks (PFHS) is carried out by using constructal theory and Entropy Generation minimization (EGM) theory for fixed total heat sink volume and fin-material volume. The optimal constructs of cylindrical pin-fin are obtained by taking the minimum Entropy Generation Rate (MEGR) as objective, and the influences of fin-material fraction, heat transfer load (HTL) of the heat sink and the fluid velocity on the optimization results are studied. It is shown that there exists optimal diameters makes the EGR minimized for the fixed shape of the heat sink; the MEGR decreases, the corresponding optimal diameter and number of cylindrical pin-fin increase as the fin-material fraction increases; the MEGR increases, the corresponding optimal diameter and number of cylindrical pin-fin decrease as the HTL and the fluid velocity increase, respectively; when the shape of the heat sink can be morphed freely, the MEGR increases as the aspect ratio of the heat sink increases, and the corresponding optimal geometric parameters are different, which means there is no quadratic optimal constructs for the heat sink by taking MEGR as optimal objective. That is the less MEGR can be obtained by choosing the more fin-material fraction, the lower fluid velocity and the smaller aspect ratio of the heat sink in allowed range. The results can provide theoretical support for the MEG optimization design of in-line cylindrical PFHS.

  • Constructal Entropy Generation Rate minimization for X-shaped vascular networks
    International Journal of Thermal Sciences, 2015
    Co-Authors: Huijun Feng, Lingen Chen, Zhihui Xie, Fengrui Sun
    Abstract:

    Based on constructal theory, an X-shaped vascular network model in a rectangular area is built in this paper. Subjected to the constraints of the total volume of the tubes and space occupied by the rectangular area, the model is optimized by taking the minimizations of the dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio, respectively. For the specified heat flow per unit length, the results show that there exist optimal ratios of the elemental diameters (22/3) and lengths of the tubes which lead to the minimum dimensionless Entropy Generation Rate of the X-shaped vascular network. They are obviously different from the optimal results of the H-shaped vascular network. Compared the performances of the X-shaped vascular network with those of the corresponding order of the H-shaped vascular network, the dimensionless Entropy Generation Rate and the dimensionless Entropy Generation ratio are reduced by 30.78% and 31.55% for the fixed mass flow Rate, respectively. However, these reductions are small for the fixed pumping power. Moreover, the performance of the X-shaped vascular network can further be improved by removing the perpendicular constraint of the tubes. The results obtained can provide some new guidelines for the designs of the vasculatures.

  • Constructal Entropy Generation Rate minimization for asymmetric vascular networks in a disc-shaped body
    International Journal of Heat and Mass Transfer, 2015
    Co-Authors: Huijun Feng, Lingen Chen, Zhihui Xie, Fengrui Sun
    Abstract:

    Abstract Based on constructal theory, the vascular networks with asymmetric pairing in a disc-shaped body are optimized by taking the minimizations of the dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio as optimization objectives, respectively. The results show that there exist optimal tube lengths and angles which lead to the minimum dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio of the vascular networks with two and three levels of asymmetric pairing, respectively. The optimal constructs of the vascular networks based on asymmetric and symmetric designs are different. For the specified heat flow per unit length on each tube surface, when the number of outlets N = 24 and the dimensionless mass flow Rate M 1 ∗ = 10 - 2 , the dimensionless Entropy Generation Rate with two levels of pairing based on asymmetric design is decreased by 7.80% than that based on symmetric design; when the number of outlets N = 24 and the dimensionless pumping power W 2 ∗ = 1 , the dimensionless Entropy Generation Rate with three levels of pairing based on asymmetric design is decreased by 6.78% than that based on symmetric design. Moreover, the performance improvements of the vascular networks with asymmetric design can also be found for the specified heat flux on each tube surface. The optimization results of the vascular networks based on minimum flow resistance are special cases of those based on minimum Entropy Generation Rate in this paper.

  • constructal Entropy Generation Rate minimization of line to line vascular networks with convective heat transfer
    International Journal of Thermal Sciences, 2013
    Co-Authors: Zhihui Xie, Lingen Chen, Fengrui Sun
    Abstract:

    Abstract The constructal optimization of line-to-line vascular networks (proposed by Lorente and Bejan) are carried out by taking the minimization of dimensionless overall Entropy Generation Rate (combining Entropy Generation Rates caused by heat transfer with finite temperature difference and by fluid flow with finite pressure difference) per unit load of heat transfer as the optimization objective, with the constraints of fixed total area occupied by the vasculature and fixed total volume of channels. The correlations of vasculature performance versus dimensionless mass flow Rate and dimensionless pumping power are investigated. The analytical correlations and numerical examples of the dimensionless overall Entropy Generation Rate and the dimensionless overall Entropy Generation Rate per unit load of heat transfer versus the number of assembly levels, the dimensionless mass flow Rate and the dimensionless pumping power are presented. The results based on the minimization of flow resistance are special cases of this paper. The results show that the comprehensive performance of the vasculature is improved with the increase of the number of assembly levels, but the increase of the number of assembly levels to improve the comprehensive performance of vasculature has a threshold value. The effect of the change of load on comprehensive performance of vasculature with larger number of assembly levels is a little.

  • Ecological performance analysis of an endoreversible modified Brayton cycle
    International Journal of Sustainable Energy, 2013
    Co-Authors: Junhua Wang, Lingen Chen, Fengrui Sun
    Abstract:

    An endoreversible closed modified simple Brayton cycle model with isothermal heat addition coupled to variable-temperature heat reservoirs is established using finite-time thermodynamics. Analytical expressions of dimensionless power output, thermal efficiency, dimensionless Entropy Generation Rate and dimensionless ecological function are derived. Influences of cycle thermodynamic parameters on ecological performance and optimal compressor pressure ratio, optimal power output, optimal cycle thermal efficiency and optimal Entropy Generation Rate corresponding to maximum ecological function are obtained and compared with those corresponding to maximum power output. The results show that cycle thermal efficiency improvement and Entropy Generation Rate reduction are obtained at the expense of higher compressor pressure ratio and a little sacrifice of power output at maximum ecological function. The compromises between power output and Entropy Generation Rate and between power output and cycle thermal efficie...

Lingen Chen - One of the best experts on this subject based on the ideXlab platform.

  • Minimum Entropy Generation Rate and Maximum Yield Optimization of Sulfuric Acid Decomposition Process Using NSGA-II
    Entropy (Basel Switzerland), 2020
    Co-Authors: Ming Sun, Lingen Chen, Shaojun Xia, Chao Wang, Chenqi Tang
    Abstract:

    Based on the theory of finite-time thermodynamics (FTT), the effects of three design parameters, that is, inlet temperature, inlet pressure, and inlet total mole flow Rate, of a tubular plug-flow sulfuric acid decomposition reactor on the total Entropy Generation Rate (EGR) and SO2 yield are analyzed firstly. One can find that when the three design parameters are taken as optimization variables, the minimum total EGR and the maximum SO2 yield of the reference reactor restrict each other, i.e., the two different performance objectives cannot achieve the corresponding extremum values at the same time. Then, the second-Generation non-dominated solution sequencing genetic algorithm (NSGA-II) is further used to pursue the minimum total EGR and the maximum SO2 yield of the reference reactor by taking the three parameters as optimization design variables. After the multi-objective optimization, the reference reactor can be Pareto improved, and the total EGR can be reduced by 9% and the SO2 yield can be increased by 14% compared to those of the reference reactor. The obtained results could provide certain theoretical guidance for the optimal design of actual sulfuric acid decomposition reactors.

  • Entropy Generation Rate minimization for steam methane reforming reactor heated by molten salt
    Energy Reports, 2020
    Co-Authors: Lingen Chen, Shaojun Xia, Lei Zhang, Rui Kong, Huijun Feng
    Abstract:

    Abstract Traditional steam methane reforming facilities for producing hydrogen not only consume a large amount of natural gas, but also emit a lot of greenhouse gas. Considering the utilization of clean energy, the reduction of carbon dioxide emission, and the production of chemicals, this paper establishes a model of steam methane reforming reactor heated by molten salt by utilizing finite-time thermodynamics. In order to reduce the irreversibility of this reactor, the Entropy Generation Rate minimization and some operating parameters are taken as the optimization objective and variables, respectively. The hybrid particle swarm optimization algorithm is proposed for solving this model. Afterwards, the influences of the porosity of the catalyst bed and catalyst activity on the optimal performance are analyzed. The results indicate that the total Entropy Generation Rate of the reactor is reduced by 22.08% after optimizing the inlet parameters of the molten salt and reaction mixture. Within the scope of this study, the total Entropy Generation Rate of the optimal reactor decreases with the increasing porosity of catalyst bed. When the catalyst activity decreases, the hydrogen production Rate can remain constant by adjusting the operating parameters. The obtained results are favorable to guide the optimal design of the practical reactors.

  • Entropy Generation Rate Minimization for Methanol Synthesis via a CO2 Hydrogenation Reactor.
    Entropy (Basel Switzerland), 2019
    Co-Authors: Lingen Chen, Shaojun Xia, Lei Zhang
    Abstract:

    The methanol synthesis via CO2 hydrogenation (MSCH) reaction is a useful CO2 utilization stRategy, and this synthesis path has also been widely applied commercially for many years. In this work the performance of a MSCH reactor with the minimum Entropy Generation Rate (EGR) as the objective function is optimized by using finite time thermodynamic and optimal control theory. The exterior wall temperature (EWR) is taken as the control variable, and the fixed methanol yield and conservation equations are taken as the constraints in the optimization problem. Compared with the reference reactor with a constant EWR, the total EGR of the optimal reactor decreases by 20.5%, and the EGR caused by the heat transfer decreases by 68.8%. In the optimal reactor, the total EGRs mainly distribute in the first 30% reactor length, and the EGRs caused by the chemical reaction accounts for more than 84% of the total EGRs. The selectivity of CH3OH can be enhanced by increasing the inlet molar flow Rate of CO, and the CO2 conversion Rate can be enhanced by removing H2O from the reaction system. The results obtained herein are in favor of optimal designs of practical tubular MSCH reactors.

  • Entropy Generation Rate minimization for hydrocarbon synthesis reactor from carbon dioxide and hydrogen
    International Journal of Heat and Mass Transfer, 2019
    Co-Authors: Lei Zhang, Shaojun Xia, Lingen Chen, Chao Wang, Huijun Feng
    Abstract:

    Abstract The process of hydrocarbon synthesis from carbon dioxide and hydrogen in a fixed-bed reactor, a novel approach of converting renewable and distributed energy to high-energy-density liquid hydrocarbon fuels, is designed and optimized thermodynamically in the present study. With the minimum Entropy Generation Rate (EGR) due to heat transfer, frictional flow and chemical reactions as objective function, finite time thermodynamics (or Entropy Generation minimization) and optimal control theories are applied to find the minimum EGR along with the corresponding optimal paths of the carbon dioxide hydrogenation reactor. The results show that a reduction up to 26.29% can be achieved by optimizing the profile of the heat reservoir temperature outside the tube and inlet conditions, which is mainly due to a compromised decrease in the irreversibilities of chemical reactions and heat transfer. The chemical driving forces of the FT (Fischer-Tropsch) reactions in the optimal reactors decrease considerably compared with those of the reference reactor under the operation of constant heat reservoir temperature. The results obtained in the present study can provide some theoretical guidelines for the optimal thermal design of the real-world reactor of hydrocarbon synthesis process from carbon dioxide and hydrogen.

  • Entropy Generation analysis for convective heat transfer of nanofluids in tree-shaped network flowing channels
    Thermal Science and Engineering Progress, 2018
    Co-Authors: Susu Qiu, Lingen Chen, Zhihui Xie, Aibo Yang, Junle Zhou
    Abstract:

    Abstract In this paper, convective heat transfer processes of nanofluids flowing through tree-shaped network flowing channels with prescribed heat flux on channel wall are investigated. The Entropy Generation Rate equations of nanofluids flowing through the tree-shaped network channels are deduced; the interaction between volume fractions of nanoparticles and Entropy Generation Rate is investigated. For H-shaped tree network flowing channels, the recurrence formulas of total Entropy Generation Rate and the order number of flowing channels are deduced, and the numerical examples are presented. A new dimensionless number is proposed to describe the Entropy Generation properties of nanofluids. Analytical solutions of Entropy Generation Rate distribution of any order of H-shaped construct of flowing channel using nanofluids are obtained.

Jianlin Yu - One of the best experts on this subject based on the ideXlab platform.

  • optimization design of falling film type plate fin condenser reboilers by minimizing specific Entropy Generation Rate
    Cryogenics, 2019
    Co-Authors: Yuanyuan Zhou, Jianlin Yu
    Abstract:

    Abstract This paper presents an optimization model for falling film type plate-fin condenser/reboilers based on the Entropy Generation minimization method, which considers the irreversibilities owing to both irreversible heat transfer and pressure drop. The specific Entropy Generation Rate, i.e. the Entropy Generation Rate per unit total heat transfer area, is proposed as an optimization objective function. Main geometrical parameters (i.e. fin height and fin pitch) of the evaporation channel of a falling film type plate-fin condenser/reboiler are optimized. The analytical results show that under certain fin pitch, there exist different optimal fin heights corresponding to the minimum Entropy Generation Rate and the minimum specific Entropy Generation Rate, respectively. In addition, the value of minimum specific Entropy Generation Rate decreases with the increase of the fin pitch, and the optimal value of the fin height varies little with the fin pitch. Effects of the heat transfer temperature difference, inlet mass flow Rate of liquid to be evapoRated and inlet mass flow Rate of vapor to be condensed on both the minimum specific Entropy Generation Rate and optimum values of fin parameters are also analyzed in detail.

  • Optimization of heat sink of thermoelectric cooler using Entropy Generation analysis
    International Journal of Thermal Sciences, 2017
    Co-Authors: Jianlin Yu
    Abstract:

    Abstract In the present study, an optimization model is developed for a thermoelectric cooler (TEC) based on the Entropy Generation minimization method. In the model, the total Entropy Generation Rate, the Entropy Generation number and the exergetic efficiency are proposed as optimization objective functions, respectively, while the number of transfer units of the heat sink is considered as a constraint. The heat capacity Rate of cooling fluid in the heat sink is optimized under other given conditions. The results show that a minimum total Entropy Generation Rate and a minimum Entropy Generation number can be achieved by optimally selecting the heat capacity Rate of the cooling fluid. In addition, the minimum total Entropy Generation Rate and corresponding optimal heat capacity Rate of the cooling fluid are both dominated by the number of transfer units and the electrical current. Furthermore, the effects of the heat capacity Rate of cooling fluid and the electric current in terms of the exergetic efficiency are also evaluated.

  • optimization of plate fin heat exchangers by minimizing specific Entropy Generation Rate
    International Journal of Heat and Mass Transfer, 2014
    Co-Authors: Yuanyuan Zhou, Jianlin Yu, Yanzhong Li
    Abstract:

    In the present study, an optimization model is developed for plate-fin heat exchangers (PFHEs) based on the Entropy Generation minimization method. In the modeling, the Entropy Generation Rate per unit partition plate area, i.e., specific Entropy Generation Rate is proposed as an optimization objective function and the total heat transfer area of a PFHE is considered as a constraint. The model takes into account the irreversibility due to both irreversible heat transfer and pressure drop. The analysis of optimal allocation of total heat transfer area between the hot- and cold-side for a PFHE is conducted with a case study. The results show that optimal geometric parameters of a PFHE such as the fin spacing and fin height on both the hot- and cold-sides can be achieved when the finite total heat transfer area is optimally allocated with minimizing the specific Entropy Generation Rate. In addition, the effects of total heat transfer area, heat transfer Rate, as well as the ratio of mass flow Rate between the cold- and hot-side fluid on the specific Entropy Generation Rate and optimal allocation ratio of total heat transfer area are also analyzed.

Bekir Sami Yilbas - One of the best experts on this subject based on the ideXlab platform.

  • Entropy Generation Rate in Forced Convection Flow About Inclined Surfaces in a Porous Medium
    ASME JSME 2011 8th Thermal Engineering Joint Conference, 2011
    Co-Authors: Bourhan Tashtoush, Bekir Sami Yilbas
    Abstract:

    Entropy Generation Rate has been the attraction of research, since it provides information on the thermodynamic irreversibility associated with the thermal systems. The exergy distraction in the thermal system increases Entropy Generation Rate while lowering the second law efficiency of the thermal system. The heat transferring devices, such as heat exchangers, opeRates better when temperature difference between the transferring device and the heat sink is maintained high. In addition, the use of porous material in these devices enhances the heat transfer Rates due to the achievement of high heat transfer coefficients. However, the presence of the porous material also increases the pump power because of the high pressure drop in the flow system. This increases the operational costs. Consequently, Entropy Generation Rate due to pressure drop needs to be minimized to reduce the cost; however, heat transfer Rates from the thermal system needs to be enhanced to improve the thermal performance of the heat transferring device. Therefore, a balance between the Entropy Generation Rates due to pressure drop and heat transfer needs to be attained to achieve optimum operating conditions of such devices. To investigate the optimum operating conditions, the forced convection problem about inclined surfaces (or wedges) in satuRated porous medium is considered. The flow in the porous medium is described by the Darcy-Brinkman momentum equation. An exact analytical solution of the governing equations using Kummer function is developed for the velocity, temperature, Nusselt Number, and Entropy Generation Rate for the case where the free stream velocity and wall temperature distribution of the inclined surface vary according to the same power function of distance x, along the plate. It is demonstRated that the Entropy Generation number is weakly dependent on the Brinkman-Darcy number for forced convection flow, which is particularly true near the wall region.Copyright © 2011 by ASME

  • Investigation into temperature rise and volumetric Entropy Generation Rate in fluid and porous subsystems
    Heat Transfer Research, 2010
    Co-Authors: Bekir Sami Yilbas, S. Bin Mansoor
    Abstract:

    Temperature differential occurs between the fluid phase and the solid phase in porous medium. The heat transfer in fluid and solid phases in a porous medium becomes non-equilibrium and the fluid phase as well as the solid phase in the porous medium sepaRates thermally forming two subsystems. In the present study, temperature fields in fluid and solid phases in the porous medium are predicted using the two-equation model. Entropy Generation Rates in each phase as well as Entropy Generation Rate due to thermal exchange between phases are computed. It is found that temperatures of both subsystems are different along the axial distance at the mid-plane and this difference varies with time. Volumetric Entropy Generation Rate due to thermal exchange between both phases is considerably less than that geneRated in each phase. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/htj.20298

  • Entropy Generation in flow field subjected to a porous block in a vertical channel
    Transport in Porous Media, 2008
    Co-Authors: S. Z. Shuja, Bekir Sami Yilbas, A. Jamal
    Abstract:

    Entropy Generation in the flow field subjected to a porous block situated in a vertical channel is examined. The effects of channel inlet port height (vertical height between channel inlet port and the block center), porosity, and block aspect ratio on the Entropy Generation Rate due to fluid friction and heat transfer in the fluid are examined. The governing equations of flow, heat transfer, and Entropy are solved numerically using a control volume approach. Air is used as the flowing fluid in the channel. A uniform heat flux is considered in the block and natural convection is accommodated in the analysis. It is found that Entropy Generation Rate due to fluid friction increases with increasing inlet port height, while this increase becomes gradual for Entropy Generation Rate due to heat transfer for the inlet port height exceeding 0.03 m. The porosity lowers Entropy Generation Rate due to fluid friction and heat transfer. The effect of block aspect ratio on Entropy Generation Rate is notable; in which case, Entropy Generation Rate increases for the block aspect ratio of 1:2.

  • Entropy Generation Rate during laser pulse heating: Effect of laser pulse parameters on Entropy Generation Rate
    Optics and Lasers in Engineering, 2008
    Co-Authors: Hussain Al-qahtani, Bekir Sami Yilbas
    Abstract:

    Laser pulse heating of solid surface and Entropy Generation during the heating process are considered. Time exponentially decaying pulse is accommodated in the analysis and the laser pulse parameter (β1/β2) resulting in minimum Entropy Generation Rate is computed. Analytical solutions for temperature rise are presented and volumetric Entropy Generation Rate is formulated. Two laser pulses resulting in low volumetric Entropy Generation Rate are examined in detail and volumetric Entropy Generation Rate is associated with the laser pulse parameter (β1/β2). It is found that volumetric Entropy Generation Rate attains high values in the early heating period due to large (1/T2). Moreover, the laser pulse with high-peak intensity results in lower volumetric Entropy Generation Rate than that corresponding to the low-intensity laser pulse with the same energy content.

  • Entropy Generation due to jet impingement on a surface: effect of annular nozzle outer angle
    International Journal of Numerical Methods for Heat & Fluid Flow, 2007
    Co-Authors: Shahzada Zaman Shuja, Bekir Sami Yilbas, M. O. Budair
    Abstract:

    Purpose – The purpose of this paper is to examine Entropy Generation Rate in the flow field due jet emanating from an annular nozzle and impinging on to a flat plate. Since the flow field changes with the geometric configuration of the annular nozzle, the influence of nozzle outer cone angle on the Entropy Generation Rate is considered.Design/methodology/approach – The steady flow field pertinent to jet impingement on to a flat plate is modeled with appropriate boundary conditions. A control volume approach is introduced to discretize the governing equations of flow and to simulate the physical situation numerically. Entropy Generation Rate due to heat transfer and fluid friction is formulated. The resulting Entropy equations are solved numerically.Findings – Thermodynamic irreversibility, which is quantified through Entropy Generation Rate, gives insight into the thermodynamics losses in the flow system. Entropy Generation Rate is highly affected by the nozzle outer cone angle. In this case, increasing n...

Zhihui Xie - One of the best experts on this subject based on the ideXlab platform.

  • Entropy Generation analysis for convective heat transfer of nanofluids in tree-shaped network flowing channels
    Thermal Science and Engineering Progress, 2018
    Co-Authors: Susu Qiu, Lingen Chen, Zhihui Xie, Aibo Yang, Junle Zhou
    Abstract:

    Abstract In this paper, convective heat transfer processes of nanofluids flowing through tree-shaped network flowing channels with prescribed heat flux on channel wall are investigated. The Entropy Generation Rate equations of nanofluids flowing through the tree-shaped network channels are deduced; the interaction between volume fractions of nanoparticles and Entropy Generation Rate is investigated. For H-shaped tree network flowing channels, the recurrence formulas of total Entropy Generation Rate and the order number of flowing channels are deduced, and the numerical examples are presented. A new dimensionless number is proposed to describe the Entropy Generation properties of nanofluids. Analytical solutions of Entropy Generation Rate distribution of any order of H-shaped construct of flowing channel using nanofluids are obtained.

  • Constructal Entropy Generation Rate minimization for cylindrical pin-fin heat sinks
    International Journal of Thermal Sciences, 2017
    Co-Authors: Lingen Chen, Zhihui Xie, Aibo Yang, Fengrui Sun
    Abstract:

    Abstract Optimization of in-line cylindrical pin-fin heat sinks (PFHS) is carried out by using constructal theory and Entropy Generation minimization (EGM) theory for fixed total heat sink volume and fin-material volume. The optimal constructs of cylindrical pin-fin are obtained by taking the minimum Entropy Generation Rate (MEGR) as objective, and the influences of fin-material fraction, heat transfer load (HTL) of the heat sink and the fluid velocity on the optimization results are studied. It is shown that there exists optimal diameters makes the EGR minimized for the fixed shape of the heat sink; the MEGR decreases, the corresponding optimal diameter and number of cylindrical pin-fin increase as the fin-material fraction increases; the MEGR increases, the corresponding optimal diameter and number of cylindrical pin-fin decrease as the HTL and the fluid velocity increase, respectively; when the shape of the heat sink can be morphed freely, the MEGR increases as the aspect ratio of the heat sink increases, and the corresponding optimal geometric parameters are different, which means there is no quadratic optimal constructs for the heat sink by taking MEGR as optimal objective. That is the less MEGR can be obtained by choosing the more fin-material fraction, the lower fluid velocity and the smaller aspect ratio of the heat sink in allowed range. The results can provide theoretical support for the MEG optimization design of in-line cylindrical PFHS.

  • Constructal Entropy Generation Rate minimization for X-shaped vascular networks
    International Journal of Thermal Sciences, 2015
    Co-Authors: Huijun Feng, Lingen Chen, Zhihui Xie, Fengrui Sun
    Abstract:

    Based on constructal theory, an X-shaped vascular network model in a rectangular area is built in this paper. Subjected to the constraints of the total volume of the tubes and space occupied by the rectangular area, the model is optimized by taking the minimizations of the dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio, respectively. For the specified heat flow per unit length, the results show that there exist optimal ratios of the elemental diameters (22/3) and lengths of the tubes which lead to the minimum dimensionless Entropy Generation Rate of the X-shaped vascular network. They are obviously different from the optimal results of the H-shaped vascular network. Compared the performances of the X-shaped vascular network with those of the corresponding order of the H-shaped vascular network, the dimensionless Entropy Generation Rate and the dimensionless Entropy Generation ratio are reduced by 30.78% and 31.55% for the fixed mass flow Rate, respectively. However, these reductions are small for the fixed pumping power. Moreover, the performance of the X-shaped vascular network can further be improved by removing the perpendicular constraint of the tubes. The results obtained can provide some new guidelines for the designs of the vasculatures.

  • Constructal Entropy Generation Rate minimization for asymmetric vascular networks in a disc-shaped body
    International Journal of Heat and Mass Transfer, 2015
    Co-Authors: Huijun Feng, Lingen Chen, Zhihui Xie, Fengrui Sun
    Abstract:

    Abstract Based on constructal theory, the vascular networks with asymmetric pairing in a disc-shaped body are optimized by taking the minimizations of the dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio as optimization objectives, respectively. The results show that there exist optimal tube lengths and angles which lead to the minimum dimensionless Entropy Generation Rate and dimensionless Entropy Generation ratio of the vascular networks with two and three levels of asymmetric pairing, respectively. The optimal constructs of the vascular networks based on asymmetric and symmetric designs are different. For the specified heat flow per unit length on each tube surface, when the number of outlets N = 24 and the dimensionless mass flow Rate M 1 ∗ = 10 - 2 , the dimensionless Entropy Generation Rate with two levels of pairing based on asymmetric design is decreased by 7.80% than that based on symmetric design; when the number of outlets N = 24 and the dimensionless pumping power W 2 ∗ = 1 , the dimensionless Entropy Generation Rate with three levels of pairing based on asymmetric design is decreased by 6.78% than that based on symmetric design. Moreover, the performance improvements of the vascular networks with asymmetric design can also be found for the specified heat flux on each tube surface. The optimization results of the vascular networks based on minimum flow resistance are special cases of those based on minimum Entropy Generation Rate in this paper.

  • constructal Entropy Generation Rate minimization of line to line vascular networks with convective heat transfer
    International Journal of Thermal Sciences, 2013
    Co-Authors: Zhihui Xie, Lingen Chen, Fengrui Sun
    Abstract:

    Abstract The constructal optimization of line-to-line vascular networks (proposed by Lorente and Bejan) are carried out by taking the minimization of dimensionless overall Entropy Generation Rate (combining Entropy Generation Rates caused by heat transfer with finite temperature difference and by fluid flow with finite pressure difference) per unit load of heat transfer as the optimization objective, with the constraints of fixed total area occupied by the vasculature and fixed total volume of channels. The correlations of vasculature performance versus dimensionless mass flow Rate and dimensionless pumping power are investigated. The analytical correlations and numerical examples of the dimensionless overall Entropy Generation Rate and the dimensionless overall Entropy Generation Rate per unit load of heat transfer versus the number of assembly levels, the dimensionless mass flow Rate and the dimensionless pumping power are presented. The results based on the minimization of flow resistance are special cases of this paper. The results show that the comprehensive performance of the vasculature is improved with the increase of the number of assembly levels, but the increase of the number of assembly levels to improve the comprehensive performance of vasculature has a threshold value. The effect of the change of load on comprehensive performance of vasculature with larger number of assembly levels is a little.