开式循环吸收式热泵系统变工况性能研究

开式循环吸收式热泵是用于燃气潜热及水回收的新技术.本文建立了开式循环吸收式热泵系统变工况分析模型.首先,在设计条件下,进行了系统设计及性能模拟;其次,在系统确定条件下,改变输入参数,进行了系统变工况性能的分析.结果显示,在选择参数变化范围内,系统性能变化不大,运行比较稳定,变工况性能较好.烟气温度、流量及冷却水温度、流量增加时,系统性能系数及水回收率变化相反,实际过程中可以作为互相调节的参数,简化了调节手段.输出热负荷相同条件下,烟气湿度增加时系统性能变化较小,系统变工况性能最稳定,最利于系统的稳定运行.     

三元工质氨吸收式制冷性能实验研究

通过实验研究了氨–水–溴化锂三元工质的对氨吸收式制冷系统的影响。实验测试了发生温度100～130℃,蒸发温度-16～-4℃和冷却水温度22～33℃工况下的系统性能系数,发现适用于氨吸收式制冷的最佳溴化锂浓度为15%,与氨吸收式制冷系统相比,性能系数最高提升了10%。溴化锂最为第三工质对系统的影响是整体的,使用三元工质可以降低精馏负荷与回流比,提高热能利用效率同时降低了发生压力,有利于提升性能系数;但其不利影响体现在会降低浓溶液中氨的浓度,导致系统循环倍率上升,不利于提升性能系数。合理使用氨–水–溴化锂三元工质是不增加系统复杂度提高氨吸收式制冷性能有效方式。     

1.x级溴化锂吸收式制冷循环性能分析

提出了一个适合于利用太阳能的新型1.x级溴化锂吸收式制冷循环。计算了该循环的性能。结果表明,在现有太阳能集热器所能提供的热水温度范围,1.x级循环克服了单效循环运行范围窄的缺点,其性能指标明显高于两级循环;冷却水先进入冷凝器的串联流程优于并联流程;热水、冷媒水、冷却水温度对溴冷机循环系统的性能系数、热源单耗、面积单耗等经济性指标有较大影响。     

耦合热泵换热器的原理及变工况性能研究

工业能耗占我国总能耗超过70%,而其能源利用效率不足50%,因此工业余热高效回收利用是节能减排的重要途径之一。热泵技术是提升能量品位的有效方法,但吸收式热泵需要配置三个不同温度品位的热源或热汇,而电动热泵受热力学循环、工质物性、压缩机耐温耐压限制以及避免润滑失效一般只能工作于有限温度范围(<100℃)之内,因此该研究将吸收式循环与压缩式循环进行深度耦合,用于直接回收工业余热制取高温热水,同时确保压缩机的安全稳定运行.该文首先分析耦合热泵换热器的运行原理,其次建立了耦合热泵换热器的数学模型,最后对模型进行求解分析了关键参数对耦合热泵换热器性能影响变化规律。在设计工况下,当制取133℃热水时,耦合热泵换热器COP达到3.6,压缩机排气压力为1.2 MPa,排气温度为79℃,远低于压缩机耐温耐压上限和润滑油失效温度,因此耦合热泵换热器在利用余热制取高温热水或蒸汽领域具有一定的应用潜力。     

热泵热水器变工况性能的无量纲对比态分析法

本文介绍一种热泵热水器性能的无量纲对比态分析法,该方法采用不同工况的热泵热水器性能参数与标准设计工况的参数对比的无量纲参数来描述实际工况性能。分别导出了理论和实际的描述热泵热水器变工况性能的无量纲表达式,给出了环境气温从-5～40℃,进水温度从5～30℃的无量纲性能曲线,以及两种型号的实验机的结霜温度区的实验结果无量纲对比性能。研究发现,热泵热水器的对比热水流量m_w是体现变工况性能的极为敏感和重要的参数,只有用m_w和COP相结合,才能全面反映热泵性能。     

用于废热回收的开式吸收式热泵性能研究

本文提出了一种用于回收中低温高湿空气潜热的开式吸收式热泵系统,在设计工况下系统COP可达1.632,并能产生温度高于60℃的热水。通过对系统进行理论建模,分析了水蒸气吸收量、湿空气进气温度、换热器效率以及液气比对系统性能的影响。增加水蒸气吸收量、湿空气进气温度和溶液换热器效率均能提高系统COP。最后,讨论了冷却水流向布置对系统运行的影响,提出了防止溶液结晶的系统流程。     

烟气型吸收式制冷机的变工况特性研究

基于分布式冷热电联产系统变工况运行的实际需要,建立了烟气型双效溴化锂吸收式制冷机的变工况模型。制冷机变工况模拟计算时,保持浓溶液流量及换热系数(高压发生器除外)不变,得到了烟气进口温度、烟气流量及冷却水进口温度变化时的制冷机各重要性能参数曲线,发现当烟气流量低于50%时,COP下降较快,冷却水进口温度降低时有利于制冷机运行,但是要注意防止浓溶液结晶。制冷机额定工况模拟计算时,与已有文献进行对比,验证模型的可靠性。     

双热源型复叠式高温热泵系统性能研究

设计了以热源型冷凝蒸发器为核心部件的双热源复叠式高温热泵系统,该复叠式高温热泵系统能够同时对中、低温两种热源进行复合利用。搭建了试验台,按照国家标准规定的高温热泵的额定供热工况对系统性能进行了实验研究。研究结果表明,低温热源工况不变时,随着中温热源进口温度、流量的升高,复叠式高温热泵系统性能均呈升高趋势,但与中温热源流量的升高相比,中温热源进口温度的升高对复叠式高温热泵系统性能的改善程度较大,为复叠式高温热泵技术的高效化提供了借鉴作用。     

热源塔热泵系统夏季工况优化运行实验研究

由于热源塔在冬夏季工况下的换热能力存在较大差异,按冬季工况设计的热源塔热泵系统,在夏季工况下运行时存在换热能力过剩的问题,影响系统性能。为解决上述问题,本文构建了热源塔热泵系统,实验研究了其冬夏季工况的性能差异。在此基础上,对夏季工况下的优化运行进行了实验研究,结果表明,通过调节空气和溶液流量,将热源塔的逼近度和冷幅分别控制在3.5℃和4.3℃,可使得系统性能系数由3.6提升至3.9,并对其节能机理进行了分析。     

喷淋吸收过程模型及实验研究

开式循环吸收式热泵是用于HAT循环烟气水回收的新型技术手段.本文以喷淋吸收器为对象,对应用氰化钙溶液的吸收过程进行了研究.首先通过理论建模预测了吸收过程的温度及浓度分布,并且就温度及浓度等参数的影响进行了分析;其次对喷淋吸收过程进行了实验研究并与冷却水喷淋减湿进行对照,结果表明要达到相同的吸收效果,冷却水流量要多于溶液流量5倍以上.     

PSM高压电源干式变压器的热分析计算

多绕组干式整流变压器作为托卡马克装置加热系统中高压电源的一个重要设备,其性能优良与否直接关系到高压电源的输出品质。开展变压器的功率损耗与散热分析研究,减少变压器因温度上升造成的性能影响,对保证变压器的良好工作状态是十分重要的。通过MATLAB对干空气下的比热容、传热系数等热物理性质与温度的关系进行拟合分析,得到相关的关系方程,对变压器的对流传热与热辐射进行分析计算,得到仅在空气自然对流和热辐射的情况下,不能使变压器的温度控制在满足性能的温度范围之内。在强迫空气对流的情况下,实现了变压器良好的散热。进一步利用ANSYS对变压器的温度场分布进行分析,利用温度场的分布趋势图观察强迫风冷相对于自然冷却的优点,强迫风冷降低了整体的温度,使热量更快地散发到周围大气中,减少了变压器受高温的危害。     

Coupling a two-stage absorption heat transformer with finite heat sources and sinks

The coupling among a two-stage heat transformer (TSHT) and finite heat sources and sinks is considered. A novel configuration is proposed, in which the evaporator of the second stage is fed both by the absorber of the first stage and by the external source. A lumped-parameter mathematical model is used to compute the performance of the proposed TSHT. It has been found that the range of applicability is widened, when compared with the usual configuration. Moreover, the use of a two-stage apparatus allows one to noticeably increase the performance compared with that obtainable with a simpler single-stage transformer. Thus, it is possible to increase the output heat and/or the user temperature, to reduce the discharge temperature, or to use lower quality energy sources. The results also allow one to draw some more general conclusions on the applicability of absorption heat transformers of different configurations, when different heat sources/sinks are considered.     

水蒸气超高温热泵系统的实验研究

近年来以低温室效应(GWP)的制冷剂的蒸汽压缩式高温热泵一直是余热回收领域的研究热点.为获得更高的输出温度,本课题组搭建了一台采用自然工质水作为循环冷媒的超高温热泵样机并进行了实验测试.实验结果表明蒸发温度为80℃,冷凝温度从115℃升至145℃时,热泵的COP从4.88降至1.89.在85℃蒸发,117℃冷凝时,最高...     

Water adsorption performance of UiO-66 modified by MgCl2 for heat transformation applications

UiO-66 is a potential material for adsorption heat transformation (AHT) with high specific surface area, and excellent thermal and chemical stability. However, the low water adsorption capacity of UiO-66 in the low relative pressure range ($0< P/P_0< 0.3$) limits its application in AHT. We prepare the UiO-66 modified by MgCl$_{2 }$ through using the solvothermal method and impregnation method, and study their water vapor adsorption performances and heat storage capacities. Attributed to the extremely high saturated water uptake and excellent hydrophilicity of MgCl$_{2}$, the water adsorption performance of UiO-66 is improved, although the introduction of MgCl$_{2}$ reduces its specific surface area and pore volume. The water adsorption capacity at $P/P_0=0.3$ and the saturated water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 0.57 wt%) modified by the solvothermal method are 0.27 g/g and 0.57 g/g at 298 K, respectively, which are 68.8% and 32.6% higher than the counterparts of pure UiO-66, respectively. Comparing with pure UiO-66, the water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 1.02 wt%) modified by the impregnation method is increased by 56.3% and 14.0% at the same pressure, respectively. During 20 water adsorption/desorption cycles, the above two materials show high heat storage densities ($\sim1293 $ J/g and 1378 J/g). Therein, the UiO-66 modified by the solvothermal method exhibits the excellent cyclic stability. These results suggest that the introduction of an appropriate amount of MgCl$_{2}$ makes UiO-66 more suitable for AHT applications.     

On the performance of advanced absorption heat transformers—I. The two stage configuration

High performance absorption heat transformers based on improved configurations can be proposed with the aim of widening the range of operation of the single stage heat transformer (SSHT). In this paper a two stage heat transformer arranged by coupling the absorber of the first stage to the evaporator of the second stage (TSHT) is analyzed by means of a lumped-parameter mathematical model, written with reference to the water-sulphuric acid system.The computed values of four different indexes of performance show that the proposed TSHT allows one to noticeably increase the gross temperature lift obtainable with a SSHT, while saving a large fraction of the input energy.     

Optimal choice of the performance parameters of an absorption heat transformer

The optimal performance of an absorption heat transformer, i.e. a type II absorption heat pump, is investigated by using the cyclic model with continuous flow. The effect of thermal resistances between the heat transformer and the heat reservoirs is considered in the model. A general expression related to the rate of heat-pumping, the coefficient of performance and the overall heat transfer area of the heat transformer is derived. The expression is used to optimise the main performance parameters of the heat transformer. The maximum rate of heat-pumping and the corresponding coefficient of performance are calculated. For a given overall heat transfer area of the heat transformer, the optimal relation of the heat transfer areas of the heat exchangers is obtained. The problems concerning the optimal choices of other performance parameters are discussed. The results obtained here can not only enrich the theory of finite time thermodynamics, but also provide some new theoretical bases for the optimal design and operation of real absorption heat transformers.     

Thermodynamic study of advanced absorption heat transformers—I. Single and two stage configurations with heat exchangers

A thermodynamic analysis was carried out to study the effect of heat exchanger effectiveness (EF) on the performance of single stage heat transformers (SSHT). Moreover, an analysis of three different arrangements of two stage heat transformers was performed using a mathematical model assuming water/lithium bromide as the working fluid. An increase in the solution heat exchanger effectiveness (EF) greatly improved the performance of absorption heat transformers when the absorber temperature was at least 40°C higher than the temperature of the heat supplied to the system. In two stage heat transformers (TSHT), higher absorber temperatures were obtained by coupling the absorber of the first stage to the evaporator of the second. However, higher performance coefficients were obtained in general by coupling the absorber of the first stage to the generator of the second.     

Thermodynamic study of advanced absorption heat transformers—II. Double absorption configurations

A thermodynamic analysis has been carried out to study the performance of double absorption heat transformers (DAHT) assuming water/lithium bromide as the working fluid. The performance of single (SSHT) and two stage heat transformers (TSHT) analyzed in Part I, was compared with the performance of double absorption heat transformers (DAHT) under the same operating conditions. The results showed that single stage heat transformers (SSHT) were the simplest and most efficient. Greater absorber temperatures were reached with two stage heat transformers (TSHT). However, these systems were in general less efficient than the others and technically the most complex. Double absorption heat transformers (DAHT) were technically simpler than two stage heat transformers (TSHT) and may reach absorber temperature as high as these systems.     

超声吸收体物理参数对红外热成像测量高强度聚焦超声声场的影响

超声吸收体的物理参数对利用水听器和红外热成像技术的高强度聚焦超声(High-Intensity Focused Ultrasound,HIFU)声场测量结果具有重要影响。为了探索超声吸收体的物理参数(密度、声速、衰减系数、热扩散系数、定压比热容)对测量结果的影响规律,本文根据层状模型计算出相同声源功率输出时不同物理参数对应的超声吸收体内部声场和热场,利用有限差分法计算出超声吸收体表面在辐照过程中的温度变化;利用基于水听器和红外热成像技术的聚焦声场测量方法测量出焦域内不同位置上声场特征值(轴线声强和-6 dB声束宽度),与通过理论计算得到的声源在纯水中声场特征值进行比较,分析了不同物理参数对测量结果的影响。超声吸收体的声、热学参数中除了声速外,其它物理参数的变化引起声场特征值的测量造成最大相对差异率小于15%。因为声波传播速度的改变会导致超声吸收体内部热场分布变化,使测量结果与理论计算值有较大偏差,其中-6 dB声束宽度和轴线声强最大相对差异率为95.37%和69.97%。因此在选择超声吸收体的声、热学参数时应重点关注声波在吸收体内声速的影响。超声吸收体的声学参数与水的声学参数相近时,可以在焦域内获得较好的测量结果。