不可逆四热源吸收式热变换器的最优性能

在恒温内可逆四热源吸收式热变换器循环模型的基础上,建立了线性(牛顿)传热定律下考虑泵热空间向环境的热漏、工质的内部牦散以及工质与外部热源间的热阻损失的不可逆四热源吸收式热变换器循环模型。导出了在总换热面积一定的条件下,循环泵热率和泵热系数的基本优化关系、最大泵热率和相应的泵热系数、最大泵热系数和相应的泵热率以及最佳工质工怍温度和最佳换热面积分配关系。     

Optimal analysis of primary performance parameters for an endoreversible absorption heat pump

The cycle model of a heat-engine-driven heat pump is used to study the performance of an absorption heat pump affected by heat resistances. The coefficient of performance of the absorption heat pump is adopted to be the objective function for optimization. The optimal regions of the coefficient of performance and the specific heating load are determined. The optimal relations between the heat transfer areas of the four heat exchangers involved and the coefficient of performance, or the specific heating load of an absorption heat pump, are obtained. Problems concerning the optimal design of an absorption heat pump are also discussed.     

四热源吸收式制冷机的传热面积优化

本文提出了一种不可逆的四热源四温度位吸收式制冷机模型，研究其最佳制冷率，性能系数和传热面积之间的优化关系，并进行了讨论，获得了一些有意义的新结论；可以为四热源吸收式制冷机的优化设计和最佳运行工况的选择提供理论指导．     

Ecological optimization for an irreversible magnetic Ericsson refrigeration cycle

An irreversible Ericsson refrigeration cycle model is established, in which multi-irreversibilities such as finite-rate heat transfer, regenerative loss, heat leakage, and the efficiency of the regenerator are taken into account. Expressions for several important performance parameters, such as the cooling rate, coefficient of performance （COP）, power input, exergy output rate, entropy generation rate, and ecological function are derived. The influences of the heat leakage and the time of the regenerative processes on the ecological performance of the refrigerator are analyzed. The optimal regions of the ecological function, cooling rate, and COP are determined and evaluated. Furthermore, some important parameter relations of the refrigerator are revealed and discussed in detail. The results obtained here have general significance and will be helpful in gaining a deep understanding of the magnetic Ericsson refrigeration cycle.     

Parametric optimum analysis of an irreversible Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas

An irreversible model of an Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas is established, which is composed of two isothermal and two isobaric processes. The influence of both the quantum degeneracy and the finite-rate heat transfer between the working fluid and the heat reservoirs on the performance of the cycle is investigated, based on the theory of statistical mechanics and thermodynamic properties of an ideal Fermi gas. The inherent regeneration losses of the cycle are analyzed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. Especially, the optimal performance of the cycle in the strong and weak gas degeneracy cases and the high temperature limit is discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Ericsson refrigeration cycles working with the Fermi and classical gases are revealed.      

立式升温型溴化锂吸收式热泵的设计与变工况研究

本文对立式升温型溴化锂吸收式热泵循环和各部件建立了数学模型,并设计了85℃热水驱动产110℃热水的立式降膜升温型溴化锂吸收式热泵,吸收器输出功率为50 kW。然后对其在热源热水温度和流量变化、冷却水入口温度和流量改变等非设计工况下的工作特性进行了计算与分析研究,得到变工况对于机组性能系数,效率和机组负荷的影响关系图。发现在我们的研究范围内,热源水参数的变化对机组性能的影响要大于冷却水。并且在热源水参数变化过程中,机组性能存在性能急剧变化的拐点,实际运行中应当避免。     

Thermodynamic assessment of an absorption heat transformer with TFE-Pyr as the working pair

An absorption heat transformer using the working pair trifluoroethanol-pyrrolidone (TFE-Pyr) is described. Trifluoroethanol is used as the working fluid and pyrrolidone is used as the absorbent. A computer simulation model is developed for the thermodynamic analysis of the heat transformer. By the verification of a group of experimental measurements, the model is used to investigate the influences of various operating conditions, design parameters and component dimensions on the performance of the heat transformer. Conclusions on the heat transformer are made according to the results of the thermodynamic assessment.     

Optimal Heat Exchanger Area Distribution and Low-Temperature Heat Sink Temperature for Power Optimization of an Endoreversible Space Carnot Cycle

Using finite-time thermodynamics, a model of an endoreversible Carnot cycle for a space power plant is established in this paper. The expressions of the cycle power output and thermal efficiency are derived. Using numerical calculations and taking the cycle power output as the optimization objective, the surface area distributions of three heat exchangers are optimized, and the maximum power output is obtained when the total heat transfer area of the three heat exchangers of the whole plant is fixed. Furthermore, the double-maximum power output is obtained by optimizing the temperature of a low-temperature heat sink. Finally, the influences of fixed plant parameters on the maximum power output performance are analyzed. The results show that there is an optimal temperature of the low-temperature heat sink and a couple of optimal area distributions that allow one to obtain the double-maximum power output. The results obtained have some guidelines for the design and optimization of actual space power plants.     

矩形肋片热沉(火积)耗散率最小与最大热阻最小构形优化的比较研究

针对矩形肋片热沉, 分别以最大热阻最小化和基于(火积)耗散定义的当量热阻最小化为优化目标, 采用二维传热模型并结合有限元数值仿真对其进行构形优化, 比较了两种目标下的热沉最优构形, 并分析了全局参数(综合了对流换热系数、肋片占据的总面积及其热导率的函数)和材料占比对两种目标(最大热阻、当量热阻)及其对应最优构形的影响. 结果表明: 热沉外形固定时, 两种目标下均不存在最优的肋片厚度; 热沉外形自由变化时, 两种目标下的最优构形存在一定的差异. 此外, 全局参数对两种目标下的最优构形均没有影响, 而材料占比对两种目标下的最优构形均有较大影响. 提高全局参数和材料占比均可以减小最大热阻最小值和当量热阻最小值, 但对两种目标的减小程度不同. 总体上, 调节热沉结构参数使当量热阻最小, 可以同时获得很好的局部极限性能; 而调节热沉结构参数使最大热阻最小, 获得的整体平均散热性能却较差. 因此, 对本文热沉模型进行优化时, 以当量热阻最小化为优化目标更合理.     

Experimental investigation on thermal-hydraulic characteristics of a tube equipped with modified vortex-generator inserts

The heat transfer, pressure drop, and overall performance specification of a straight circular tube fitted with vortex-generator inserts are investigated experimentally. To modify the thermal-hydraulic performance, the longitudinal spacing of winglets is varied along the flow direction. The experiments are performed in the turbulent regime (7,470 ≤ Re ≤ 18,670). Good agreement is obtained when the results are compared and validated with previous correlations proposed for the plain tube. The results show that the use of vortex-generator inserts inside the tube yields a higher heat transfer coefficient and pressure drop than the plain tube, and these parameters augment with increasing the number of winglets. The effect of variation of longitudinal spacing of winglets along the vortex-generator inserts on the heat transfer coefficient is higher that the pressure drop. It is also detected that the variation of this parameter affects each arrangement of winglets exclusively.     

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.     

Thermodynamic performance characteristics of a three-terminal quantum dot hybrid thermoelectric heat engine

We propose a new model of the three-terminal quantum dot hybrid thermoelectric heat engine in which the electrons transfer between two electronic terminals at different temperatures and chemical potentials through two coupled single-level quantum dots. Based on master equation we derive the expressions for the output power and the efficiency. The working region of the hybrid heat engine is determined according to the first and second law of thermodynamics. The performance characteristic curves are plotted and the optimal performance parameters are obtained. Finally, the influence of the non-radiative effect on the optimal performance parameters is discussed in detail.     

An Experimental and Theoretical Investigation into the Thermal Performance Characteristics of a Staggered Vertical Pin Fin Array Heat Sink with Assisting Mixed Convection in External and In-Duct Flow Configurations

A theoretical and experimental study was carried out on the thermal performance of a pin fin array heat sink. A theoretical model was utilized based on the success of prior research that has the capability of predicting the influence of various geometrical, thermal, and flow parameters on the effective thermal resistance of the heat sink. An experimental investigation was carried out for measuring the thermal performance of the heat sink, and the overall convective heat transfer coefficient for the fin bundle, including the thermal and flow bundle effect. Utilizing the new empirical correlations, theoretical predictions were made and experimentally validated for a wide range of parameters for combined forced and natural convection in the assisting flow configuration. Both the theoretical model and experimental data indicated the existence of optimal fin spacing.     

Q-Switched Intracavity Frequency-Doubled Solid State Lasers: Influence of ETU Effect, Repetition Rate and ESA Effect

Our theoretical analysis showed that the overall intracavity frequency-doubled actively Q-switched solid state laser performance is affected by both pulse repetition rate and energy transfer up-conversion effect. The energy transfer up-conversion effect increased greatly and seriously degraded the laser performance especially when operating at high pumping power and low pulse repetition rate. The curves generated by numerical computation of the presented model can be used to predict the laser performance. We concluded that the pulse lengthening effect also appears with the influence of energy transfer up-conversion and is not related to the repetition rate. From the analysis, we found that the frequency doubling coefficient that Liu and Kim chose in their experiment was just the optimized value. Considering the effect of excited state absorption of saturable absorber into passively Q-switched intracavity frequency doubled solid state laser, the second threshold condition for this model is derived. A simple and very clear formula is obtained.     

基于固有光学量的高光谱数据反演城市河网水质

水体辐射传输模型是水体光谱特性分析的理论基础,水体固有光学量由水体组成决定,与水体表面光场无关。基于统计的半经验算法虽然能获取指定区域水质参数反演结果,但是缺乏物理意义;基于生物光学模型的分析算法,针对城市河网内陆Ⅱ类水体光学特性复杂、空间分布异质性强、水体细小、流动性大等特点,利用高光谱数据,研究基于固有光学量的城市河网水质参数反演模型,对内陆城市浑浊水体光谱特性研究具有重大意义。提出了适用于内陆城市河网水体的改进QAA算法,以获取水体固有光学量,改进包括后向散射估计模型调整和参考波段优化两个方面;计算参考波段总吸收系数、颗粒物后向散射系数等固有光学量,得到浮游植物吸收系数和剔除纯水吸收系数;对浮游植物吸收系数最优波段比值与叶绿素a浓度进行线性回归分析,构建叶绿素a水质浓度反演模型,对剔除纯水吸收系数最优波段比值与悬浮物浓度线性回归分析,构建悬浮物水质浓度反演模型。针对内陆河网Ⅱ类水体,以典型的河网城市嘉兴市为研究区域,获取了研究区域航空高光谱数据,以及水质采样化验数据和水面以上光谱数据等地面准同步测量数据;利用QAA算法和IIMIW算法对实测水面以上光谱进行固有光学量反演,对比分析两个算法并结合城市河网水体特点,提出改进QAA算法;利用改进的QAA算法实现了研究区域水体的固有光学量反演,基于反演的水体固有光学量建立了叶绿素a浓度和悬浮物浓度两项水色参数定量反演模型,反演模型决定系数R2分别为0.64和0.71;并用航空高光谱数据同步区域的4个地面样点实测数据,对反演结果进行验证分析。通过水质参数浓度反演值与实测值的对比,叶绿素a和悬浮物水质浓度反演的平均相对误差分别为9.2%和9.4%,反演得到的叶绿素a和悬浮物浓度分布图,也与城市河网的特点和实际情况相符,为城市河网水质监测提供方法和模型参考。     

On the performance of advanced absorption heat transformers—II. The double absorption configuration

An innovative heat transformer can be derived from the TSHT discussed in Part I. Its configuration is essentially based on a serial arrangement of the two absorbers (“double absorption heat transformer”, DAHT) and allows a drastic reduction of the number of items necessary for the TSHT.The performance of a DAHT operated with the water-sulphuric acid system was computed by means of a lumped-parameter mathematical model and expressed in terms of the four indexes of performance previously used for the TSHT examined in Part I. The results show that the DAHT reaches its optimum performance at values of gross temperature lift intermediate between those optimal for the SSHT and the TSHT, respectively.     

吸收式热变换器的生态学优化性能

1引言热变换器是一种有效节能装置，可直接利用中、低温余热。这已引起许多先进工业国家的重视。近年来，有些学者应用有限时间热力学新理论对其进行优化分析，取得一些比经典热力学理论更为有用的新结论［‘－’］。发现在热变换器的合理工作区域中，供热率越大时拥损率也越大，两者应得到合理的兼顾和折衷，以便使能量得到更有效的利用。一些研究表明，以“生态学准则”研究热力循环的优化性能，可使热力循环的功能率（如热机的功率、热泵的供热率等）与功能率耗散达到最佳的折衷［‘－’］。本文应用此准则对不可逆吸收式热变换器进行优…     

Thermal Performance of Laser Diode Array under Constant Convective Heat Transfer Boundary Condition

Three-dimensional heat transfer model of laser diode array under constant convective heat transfer coefficient boundary condition is established and analytical temperature profiles within its heat sink are obtained by separation of variables. The influences on thermal resistance and maximum temperature variation among emitters from heat sink structure parameters and convective heat transfer coefficient are brought forward. The derived formula enables the thermal optimization of laser diode array.     

液幕式吸收塔中传质模型研究

对液幕式吸收塔脱硫性能进行了实验研究,研究了烟气流量、循环浆液量、浆液浓度,喷嘴阵列形式等参数对脱硫性能的影响,合理选择装置结构和运行参数时,脱硫效率可达90%以上;提出了液幕式吸收塔中当量传质面积的计算方法,建立了液幕式吸收塔的传质模型,得到了液幕式吸收塔的传质系数关于气相和液相雷诺数及喷嘴阵列的经验关系式。     

Numerical simulation of tissue freezing by liquid nitrogen based cryoprobe

A model is presented to simulate the cooling processes during tumor cryosurgery with different kinds of flows through the cryoprobe. The heat flux between the cryoprobe wall and the tumor, the heat transfer coefficient under different inflow conditions are obtained numerically. The impact of the inlet mass flow rate, gas volume fraction on these parameters is investigated. It is found that the heat transfer coefficient decreased significantly when inflow changed from two-phase annular flow to droplet flow, and to gas flow. The inlet gas volume fraction and flow velocity only significantly affect the freezing ability of the probe when the inflow is gas or in droplet phase. Simulation of the tumor temperature profiles under different flow conditions show that the heat transfer coefficient is a crucial parameter in temperature prediction during cryosurgery. Results indicate that when the cryoprobe wall is assumed at a constant temperature conventionally, the cooling effect could be overestimated. It would be more reasonable to use the constant wall heat transfer coefficient to simulate the cooling progress under a specific flow.