基于熵产理论的三维涡激振动低速水流能俘能分析

以刚性圆柱作为俘能结构,通过强流固耦合数值方法模拟俘能结构在低速水流环境下的三维涡激振动,对共振约化速度(U_r=2～12)范围内进行俘能结构的俘能大小及俘能效率分析。为获得俘能结构三维尾流对俘能大小的影响,采用熵产理论并结合尾流特性以捕捉俘能结构尾涡的能量损失来源及分布,获得不同振动分支下俘能大小与尾流耗散间的关系。结果表明,基于熵产理论的能量损失分析可准确捕捉到俘能结构的能量耗散趋势。黏性熵产主要发生在圆柱表面,湍流熵发生在耗散率较大的尾流区。随着约化速度的增加,上端分支内,当U_r=6时俘能结构的俘能效率最大达到30.5%,俘能结构俘获的水动能增加,圆柱表面的黏性熵损耗和圆柱周围及尾流区湍流熵产损失也增加,俘能结构表面的黏性熵产损失和尾流区湍流熵产损失增大成为俘能效率下降的主要原因。     

Numerical analysis reliability control for a double‐pipe heat exchanger with virtual entropy generation method

There are two primary laws including the first and second laws of thermodynamics that should be used to assess a process. Generally, only the first law of thermodynamics is investigated in numerical solutions, so it is possible to exist some numerical results that do not satisfy the second law of thermodynamics because of numerical errors. To achieve reliable numerical outcomes, it is better to apply two indexes of HEAT BALANCE ERROR and VIRTUAL ENTROPY GENERATION, which come from the second law of thermodynamics. In other words, an approach to develop computational fluid dynamics investigations is to take second law of thermodynamics into consideration. In this study, two different models including counterflow double‐pipe heat exchanger and single‐pipe with constant wall temperature are simulated in various cases with different efficiencies and temperature ratios. It is found that 46 cases of total 523 double‐pipe models and 24 cases of total 402 simulations of single‐pipe models had unacceptable results regarding to two mentioned criteria. The results revealed that it is less likely to gain unreliable results in smaller efficiency and lower inlet temperature for double‐pipe heat exchanger and single‐pipe respectively.     

Analysis of Entropy Generation of Combined Heat and Mass Transfer in Internal and External Flows with the Assumption of Local Thermodynamic Equilibrium

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MHD conjugate heat transfer and entropy generation analysis of MWCNT/water nanofluid in a partially heated divided medium

The aim of this article is to conduct the lattice Boltzmann simulation of the magnetohydrodynamic (MHD) natural conjugate heat transfer in an apportioned cavity loaded with a multiwalled carbon nanotube/water nanofluid. The divided cavity is, to some extent, heated and cooled at the upright walls, whereas the horizontal walls are adiabatic. The nanofluid properties are evaluated on the basis of experimental correlations. The parameters ranges in the study are as follows: nanoparticles' volume fraction (%): 0 ≤ ? ≤ 0.5, temperature (°C): T = 27, Rayleigh number (Ra): 10³ ≤ Ra ≤ 10⁵, Hartmann number (Ha): 0 ≤ Ha ≤ 90, and the magnetic field inclination angle (γ): 0 ≤ γ ≤ π/2. The current outcomes are observed to be in great concurrence with the numerical results introduced in the literature. The impacts of the aforesaid parameters on local and average heat transfer, entropy generation, and Bejan number (Be) are explored and discussed. Indeed, the transfer of heat increases linearly with ? for a low Ra. As Ra increases, the average Nusselt number decreases for a high value of ?. The increase of nanoparticles' volume fraction leads to a reduction in the entropy generation and an increase in the Bejan number for a high Ra, but at low Ra, these functions remain constant. As the Ha increases, the transfer of heat and the entropy generation decreases, whereas there is an increase in Be. The transfer of heat, total entropy generation, and the Be depends strongly on the direction of the magnetic field. The increase of heater and cooler size has a great influence on the transfer of heat, entropy generation, and Be.     

H形对流传热脉管的熵产率最小构形优化

针对H形对流传热脉管,以脉管区域面积和通道总表面积为约束,在线热流密度恒定时,基于熵产生最小化进行了构形优化,给出了无量纲总熵产量和无量纲单位传热负荷的总熵产率与脉管组合级数、无量纲质量流量和无量纲泵功率的完整解析关系式及优化算例.结果表明:给定通道总表面积与文献中给定通道总体积约束的优化结果是不同的;无量纲单位传热负...     

Influence of conjugate heat transfer on the minimization of entropy generation for forced convective flow through parallel plate channel filled with porous material

A fluid–solid conjugate heat transfer model is developed to analyze the characteristics of entropy generation for forced convective steady hydrodynamically fully developed laminar flow of a Newtonian fluid through a parallel plate channel filled with porous material by modulating the following parameters: substrate thickness, the ratio of thermal conductivity of wall to fluid, Biot number, the axial temperature gradient in the fluid, and Peclet number. The exteriors of both the walls are subjected to the thermal boundary conditions of the third kind. The mass and Brinkman momentum conservation equations in the fluidic domain and the coupled energy conservation in both the solid and fluidic domain are solved analytically using the local thermodynamic equilibrium model, so as to derive closed-form expressions for the velocity in the fluid and the temperature both in the fluid and solid walls in terms of relevant parameters. Suitable combinations of influencing factors, namely the geometric parameters of the system, fluid, flow, and substrate properties are identified for which global entropy generation rate is minimized. The findings may be helpful in the design of thermal systems frequently used in diverse engineering applications having heat transfer in the solid wall being a crucial parameter.     

地源热泵空调系统的经济性分析

介绍了地源热泵系统的概念和在我国的发展概况 ,并对地源热泵系统与几种常用空调系统的经济性进行了对比分析     

Energy analysis of a solar-ground source heat pump system with vertical closed-loop for heating applications

A heat pump system is the ideal way to extend the heat supply of existing oil or gas fired heating system. Consumption costs are lowered through the use of free energy from the environment, and the dependence on fossils fuels simultaneously reduces. In order to investigate the performance of the solar-ground source heat pump system in the province of Erzurum having cold climate, an experimental set-up was constructed. The experimental apparatus consisted of solar collectors, a ground heat exchanger (GHE), a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. In this study, the performance of the system was experimentally investigated. The experimental results were obtained from October to May of 2008-2009. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP) and the system performance (COPS). The coefficient of performance of the heat pump and system were found to be in the range of 3.0-3.4 and 2.7-3.0, respectively. This study also shows that this system could be used for residential heating in the province of Erzurum being a cold climate region of Turkey.     

Statistical analysis of stagnation-point heat flow in Williamson fluid with viscous dissipation and exponential heat source effects

This analysis explores the effect of the novel exponential space-dependent heat generation factor on the stagnation-point Williamson fluid flow over a stretchable surface. The heat transport phenomenon is carried out by the addition of viscous and Ohmic dissipations. Similarity transformations are applied to the nonlinear system of partial differential expressions that arise by the flow. The nonlinear ordinary differential system hence obtained is solved to visualize the role of different constraints graphically. Statistical methods such as correlation, probable error, and regression are utilized. The probable error is evaluated to calculate the reliability of the computed correlation factors. The study reveals that the velocity phenomenon is reduced by incrementing the Weissenberg parameter. The velocity of the hydromagnetic liquid is lesser than the velocity of magnetohydrodynamic fluid flow. Also, the higher heat generation factor gives a boost to the temperature of the flowing material.     

风能辅助供暖的地源热泵系统经济性分析

以热负荷为主的北方地区,冬季土壤温度较低,若完全采用地源热泵来供暖,则地热换热器和机组的初投资均比较高,连续运行的效率也较低.提出利用风力发电机产生的电能构成风能集热器作为地源热泵供暖的辅助能源的构想.白天完全依靠地源热泵供暖,夜间利用风能集热器辅助加热,使地热换热器与风能集热器串联运行.通过分析比较,该方案比完全用地...     

太阳能辅助供暖的地源热泵经济性分析

在冬季土壤温度较低，而且以热负荷为主的北方地区，若完全采用地源热泵来供暖，则地热换热器和机组的初投资均比较高，连续运行的效率也较低，因此，可利用太阳能集热器作为辅助能源。白天完全依靠地源热泵供暖，夜间利用太阳能集热器蓄存的热量，使地热换热器与太阳能集热器串联运行，通过分析比较，该方案比完全用地源热泵供暖更经济。