空调PTC加热器热分析与工艺参数优化

针对空调PTC加热器内部温度分布不均匀、换热性能恶化的问题,对空调PTC加热器整体结构进行热分析,提出解决温度分布不均、换热性能较弱问题的应对方法。通过对加热芯的热分析,确定了PTC片排片与空调PTC加热器内部温度分布的关系,并提出了最优排片模型。通过对散热翅片的热数值计算与仿真计算,确定了散热翅片尺寸与换热性能的关系,并以热阻最小为优化目标,进行了散热翅片的参数优化设计。最后设计实验对优化空调PTC加热器与原有空调PTC加热器进行了比对。结果表明:优化空调PTC加热器热阻比原有空调PTC加热器减小5.62%,换热性能更优。     

对流换热可控温差场分布原则

应用火积概念导出了对流换热过程的火积耗散表达式,进一步基于火积耗散极值原理讨论了换热器N股冷、热流在不同情况下参与换热的优化。研究表明,若参与换热的任何冷、热流之间的温差可以独立调控,在总换热量一定寻求火积耗散最小或在总火积耗散一定的条件下寻求换热量最大,则整个换热系统冷、热流之间的温差分布均匀时换热最优;若参与换热的任何冷、热流体之间的换热量或火积损耗可独立确定,则换热冷热流之间的温差分别保持各自的均匀温差分布时换热最优;若在任何冷、热流之间存在可能换热的情况下,无论是总换热量一定时寻求火积耗散最小,还是总火积耗散一定时寻求换热量最大,整个换热系统不同的冷热流换热的优化温差并不是同一个常数。     

火积耗散理论在平行流热管换热器性能评价中的应用

火积耗散作为传热过程可逆性判断依据,可应用于换热器优化. 分析探究了热管换热器的温差、充液率、倾角及迎面风速对火积耗散的影响,利用焓差实验室进行平行流热管换热器性能试验. 随温差增大,火积耗散增大. 随充液率增大,火积耗散先增大后减小,温差越大,火积耗散变化幅度随充液率增大而增大. 增加倾角,火积耗散比未倾斜时小. 随迎面风速增大,火积耗散减小,且减小幅度随温差增大而增大. 相同传热量,火积耗散值最小时,为系统最优工况.     

换热器及换热网络优化设计的专家系统

论述了运用所建立的换热器设计的数据库、知识库和推理机所组成的专家系统,为完成一定换热任务而设计最优组合的换热器和换热网络,且使所需换热面积为最小的设计方法。用于炼油厂换热网络技术改造优化设计,实践证明是很有效的。     

导热过程不同优化目标的优化准则

对于不同目的导热过程存在不同的优化目标。基于传递方程和火积传递方程,分别导出了以降低作功能力耗散为目标的导热过程优化准则和以降低传热能力耗散为目标的导热过程优化准则。以降低作功能力耗散为目标的导热过程优化准则表明,在总导热能力一定的条件下,相对温度梯度分布均匀导热最优;以降低传热能力耗散为目标的导热过程优化准则表明,在总导热能力一定的条件下,温度梯度分布均匀导热最优。     

环形换热翅片的理论研究及设计

换热器传热效率的大小与翅片管的排列方式和翅片的结构参数有关。运用电脑软件对换热器中环形翅片管束的实物模型进行了仿真模拟,研究了顺排管束和错排管束的换热效果,并通过固定参数法对加热器模型进行理论计算。研究结果表明,错排管束的换热效果优于顺排管束,加热器翅片的最优间距为5.5 mm,与无翅片的换热器管道相比,有翅片的换热器管道的传热效率提高了387.35%。     

换热强化及其优化设计的新途径

审视了强化换热及其优化设计换热系统的方法,无论是传统的强化换热方法还是场协同方法,都只片面地强调了强化传递强度而忽视了由于强化所引起的能量耗散的约束。在强化传递强度的层次上,给出了换热强度与流体中内场和外场的数学关系,通过协调不同驱动力之间的关系可以强化热传递强度。在优化设计换热系统的层次上,给出了优化设计的热力学判据,表明了不可逆性与推动力之间的权衡,并由此得到换热器强化的优化设计温差。     

金属丝网多孔体对斯特林机传热性能影响的研究

针对斯特林发动机光管换热加热器换热效果较差的问题,提出在加热器内部填充金属丝网多孔体,以提高加热器的传热性能。采用数值模拟的方法对有无多孔介质以及不同孔隙率下换热器内传热性能进行模拟研究。模拟结果表明:加入多孔介质后,加热器的传热量增大,传热系数明显升高;随着孔隙率的减少,加热器传热量增大,传热系数升高。与相关实验数据相比,模拟结果真实有效。     

考虑控制性能的换热网络合成研究

将换热网络的合成与控制性能有机的结合起来,针对复杂换热网络优化中存在的可操作性、计算效率及优化质量的矛盾,建立了基于智能合成法的数学模型,以满足具有可操控性的换热网络最优结构。对无分流换热网络和有分流换热网络都能达到很好的设计效果,真正实现了考虑控制要求的最优换热网络的自动合成。通过实例证明了本方法的可靠性和实用前景。     

基于拓扑和尺寸组合优化的ATV车身轻量化研究

针对车身结构在概念设计阶段出现的拓扑优化结果不连续,结构优化设计周期时间长等问题,基于optistruct优化软件,提出一种拓扑和尺寸组合优化模型.该模型可以同时进行尺寸优化和拓扑优化设计,得到车身蒙皮优化尺寸和最优的车身骨架加载路径,同时缩短了结构的概念设计阶段的设计周期.以ATV车身的结构优化设计为研究对象,对比优化前后的分析结果,在不降低结构性能的前提下优化后的结构减重105.5kg,验证了该方法的可行性.     

Distribution optimization of circulating water in air-cooled heat exchangers for a typical indirect dry cooling system on the basis of entransy dissipation

The flow and heat transfer of air-cooled heat exchangers play important roles in the performance of indirect dry cooling systems in power plants,so it is of benefit to the design and operation of a typical indirect dry cooling system to optimize the thermo-flow characteristics of air-cooled heat exchangers.The entransy dissipation method is applied to the performance optimization of air-cooled heat exchangers in this paper.Two irreversible heat transfer processes in air-cooled heat exchangers,the heat transfer between circulating water and cooling air and the mixing of circulating water,are taken into account and analyzed by means of the entransy dissipation method.The total entransy dissipation rate,which connects the geometrical parameters of air-cooled heat exchanger sectors and the heat capacity rates of the fluids to the heat flow rate in every sector,is obtained.Based on the mathematical relation and the conditional extremum method,an optimization equation group is derived,by which the air-cooled heat exchanger with known air-side parameters is optimized,showing that the entransy dissipation based optimization approach can contribute to the distribution optimization of circulating water in air-cooled heat exchangers of a typical indirect dry cooling system.     

Heat transfer performance evaluation of one-stream heat exchangers and one-stream heat exchanger networks

One-stream heat exchangers and one-stream heat exchanger networks are widely used in engineering. In this paper, the heat transfer performance evaluation of one-stream heat exchangers and one-stream heat exchanger networks is analyzed with the concepts of entropy generation rate, entropy generation number, revised entropy generation number, entropy resistance, entransy dissipation rate, entransy dissipation number and generalized thermal resistance. For the analyzed one-stream heat exchangers, our numerical results show that the extremum value of the entransy dissipation rate and the minimum values of the entropy resistance and the generalized thermal resistance always lead to the largest heat transfer rate or the lowest temperature of the cooled object,while the minimum values of the other parameters do not always. For the analyzed one-stream heat exchanger networks, the minimizations of entransy dissipation rate, entransy dissipation number and generalized thermal resistance always correspond to the lowest average temperature of the cooled objects, while the minimizations of the other parameters do not. Therefore, only the extremum entransy dissipation principle and the minimum generalized thermal resistance principle are always applicable for the heat transfer performance evaluation of the systems in this paper, while the applicability of the other parameters is conditional.     

基于理论的相变储能换热器传热性能分析

在理论成功应用于常规换热器的基础上,将传递效率、耗散数及基于耗散的换热器热阻应用于相变储能换热器的传热性能分析中。定义广义耗散率并由此推导出相变储能换热器蓄热、放热及总过程的传递效率及其瞬时值。确定耗散数及基于耗散的换热器热阻计算中换热量的取法。选取一种相变储能装置作为分析对象,通过理论分析绘制各主要部分温度变化趋势,进一步简化得到硅油、水的出口温度表达式,作为算例分析基础。结果表明, 传递效率的应用范围最广,可用于计算相变储能换热器蓄热、放热及总过程的(瞬时)不可逆热损失,且评价结果与传热性能相符,瞬时传递效率随蓄热时间的增加先增大后不变再增大,随放热时间的增加先减小后不变再减小; 耗散数在蓄热过程和总过程中的评价结果与传递效率一致,瞬时耗散数随蓄热时间的增加先减小后不变再减小,然而在放热过程中的应用受限。基于耗散的换热器热阻的部分评价结果与实际不符,应用限制较大。蓄热过程及总过程中,当蓄热量、取热量与蓄、放热阶段时长同步变化时, 传递效率、耗散数与基于耗散的换热器热阻几乎无变化;当装置传热性能提高时, 传递效率增大, 耗散数减小,基于耗散的换热器热阻减小;放热过程中,设置参数的变化不影响装置传热性能, 传递效率基本无变化。     

An entransy dissipation-based optimization principle for solar power tower plants

The entransy theory,which can be used to optimize the heat transfer network of a solar power tower system(SPTS)and improve its energy efficiency,was introduced in this paper.Firstly,the irreversibility of the heat transfer processes in a SPTS was analyzed and the total entransy dissipation equation of a SPTS was derived.Then,two types of optimization problems(reducing the total circulating flow rate or the total heat-exchanging area)of a SPTS were solved with conditional extremum model based on the formulas of total entransy dissipation.Finally,the entransy dissipation-based optimization principle was applied to a simple SPTS without re-heater and a complex SPTS with a re-heater.The results showed that under the chosen calculation conditions the minimum total thermal conductance was 19306.03 W K?1 for a SPTS without re-heater when the total heat capacity rate of heat transfer fluid(HTF)was 3200 W K?1.The minimum total thermal conductance was about 7.9%lower than the value predicted based on the typical outlet temperature of a receiver.This meant that the total heat exchange area or initial investment could be effectively reduced under the prescribed total HTF circulating flow rate.We also studied the variation trends of the two optimized results including minimum total HTF heat capacity rate and minimum total thermal conductance.The minimum total HTF heat capacity rate decreased with the given total thermal conductance,the minimum total thermal conductance decreased first and then increased with the given total HTF heat capacity rate.We also found that for a SPTS with a re-heater,the mixing temperature and the mixing position of HTF had significant effects on the two types of optimization problems.     

热声热机换热器性能的分析

热声换热器热量传递的速率与效率直接影响着热声热机的性能. 　　耗散理论能更好地揭示换热器的传热优化特性,在热声换热器研究中引入　　耗散理论,针对顺流和逆流两种情况,计算了热声换热器的　　耗散热阻,并和最小熵产原理的结果进行了对比分析. 结果表明,在一定条件下,顺流比逆流情况下的不可逆损失要大;当换热器低温端流体的热容量小于高温端流体热容量时不可逆损失较小,结果最优.     

Application of entransy dissipation based thermal resistance to design optimization of a novel finless evaporator

Entransy has been applied and studied in a broad range of heat transfer optimizations recently. Current study proposes the entransy of evaporators to conduct the optimization of heat exchangers in heating, ventilation, air conditioning and refrigeration systems. A novel finless bare tube heat exchanger was studied using a validated heat exchanger modeling tool. The capacity based optimization and entransy dissipation based thermal resistance were used and compared. The applicability of using entransy dissipation based thermal resistance in this type of heat exchanger optimization has been discussed. It has been demonstrated that minimizing entransy dissipation and maximizing capacity are equivalent to optimizing evaporators with fixed flow rates and different when optimizing evaporators with variable flow rates and the deviation is negligible when heat exchanger capacity is small (～1 kW) and more obvious as heat exchanger capacity increases. Thus entransy dissipation based thermal resistance could be used as an alternative optimization index to capacity for evaporators with fixed flow rate and small capacity evaporators with variable flow rates and should be used individually with capacity as an optimization index for evaporators with large capacity and variable flow rates.     

倾斜螺旋片强化的套管换热器数值模拟

为了减小螺旋片强化的套管换热器的摩擦阻力系数f,提出倾斜螺旋片强化的方法.基于RNG k-ε模型对倾斜螺旋片强化的套管换热器进行模拟;将雷诺数Re为2 362～16 860范围内螺旋升角α为35°,螺旋片倾斜角β为5°、10°、15°时的传热性能与光滑管以及α为35°的普通螺旋片强化管的传热性能进行对比;考察f、努塞尔数Nu和综合传热性能PEC值的变化规律;并运用火积耗散理论对传热性能进行分析.结果表明：模拟结果与实验结果吻合较好,证明模拟方法是可行的;普通螺旋片和倾斜螺旋片均有强化传热的作用,与普通螺旋片相比,倾斜螺旋片能够有效地减小f,且对f的减小程度随着β的增大呈现出先增大后减小的趋势,分别减小1.7%～3.3%、12.5%～14.5%和6.3%～7.8%;Nu随着β的增大呈现先减小后增大的趋势,但变化不大;倾斜螺旋片的PEC值均高于普通螺旋片,当β为10°时PEC值最高,相对于普通螺旋片的1.26～1.62,增大到1.38～1.71;采用倾斜螺旋片强化的火积耗散率均低于采用普通螺旋片强化的火积耗散率,当β为10°时,火积耗散率最小,与等泵功条件下所得出的结论吻合.     

Application of entransy dissipation extremum principle in radiative heat transfer optimization

The concepts of entransy flux and entransy dissipation in radiative heat transfer were introduced based on the analogy with heat conduction and heat convection processes. Entransy will be partially dissipated during the radiative heat transfer processes due to the irreversibility. The extremum principle of entransy dissipation was developed for optimizing radiative heat transfer processes. This principle states that for a fixed boundary temperature the radiative heat transfer is optimized when the entransy dissipation is maximized, while for a fixed boundary heat flux the radiative heat transfer process is optimized when the entransy dissipation is minimized. Finally, examples for the application of the entransy dissipation extremum principle are presented. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2007CB206901)