高温级输气量对变频复叠制冷系统的影响

为了研究高温级输气量对R410A/R410A变频复叠制冷系统的影响,搭建了变频复叠制冷系统实验台.实验研究了高温级输气量在不同工况下对R410A单一制冷剂变频复叠制冷系统性能的影响规律.实验结果表明:冷凝温度为30℃、蒸发温度为-34～-42℃,高温级压缩机排气温度低于120℃,系统可以安全稳定运行;蒸发温度为-42℃...     

R600a/R23两级自动复叠制冷系统降温特性研究

以R600 a/R23两级自动复叠制冷系统为例,研究了不同配比条件下,制冷系统中的特征点温度在降温过程中变化特性。试验表明混合制冷剂的配比是自动复叠制冷系统关键问题,通过控制关键点的温度可以判断混合制冷剂的最佳配比。     

三级复叠式制冷系统性能的模拟研究

对R404A/R23/R14三级复叠制冷系统进行模拟,研究了三级复叠制冷循环中间温度的选取对系统制冷系数的影响,比较了R404A/R23/R14与R404A/R23在重叠温区的制冷系数以及不同制冷剂对三级复叠系统制冷系数的影响。结果表明:R404A/R23/R14复叠式制冷循环存在最佳中间温度,最佳温度下的压缩机压比大致相等;在重叠温区内,R404A/R23的制冷系数高于R404A/R23/R14;R404A/R508B/R14、R404A/R508A/R14更适用于做三级复叠制冷系统的制冷剂。     

R22、R134a在五级自动复叠制冷系统中的应用比较研究

对于多级自动复叠制冷系统,混合制冷剂的选取和组分配比具有很大的影响作用。分别采用R22/R23/R14/R740/R728和R134a/R23/R14/R740/R728两组混合制冷剂应用于五级自动复叠系统,对系统高温级制冷剂R22与R134a进行理论分析和对比实验研究,研究结果表明采用R134a更能有效控制系统排气温度,获取了更低的制冷温度。     

不同中温制冷剂的CO2复叠制冷系统性能研究

针对NH_3/CO_2复叠系统的安全风险较大,R507、R404A等中温制冷剂的CO_2复叠系统GWP高等问题,提出了R449A/CO_2复叠制冷系统,采用容量调节精准、效率高的数码涡旋技术,分析不同冷媒的低温级蒸发温度、低温级冷凝温度、中间换热温差、高温级冷凝温度等因素对系统性能的影响。结果表明:在相同低温级蒸发温度下,R449A复叠系统EER要高于R404A与R507两种制冷剂,且随着蒸发温度的升高,EER的增长幅度相对也更大;随低温级冷凝温度的升高,R449A复叠系统能效比较R404A与R507高3%左右;在相同中间换热温差下,R449A的系统EER相比于R404A复叠系统提升约2%;R449A系统在冷凝温度较低时表现出的系统性能更为优越,在冷凝温度为30℃时,系统EER与R404A、R507系统相比提升2.8%。     

R404A双级压缩载冷循环和复叠式制冷循环系统对比分析

阐述了R404A为制冷剂的两种不同形式的两级循环:R404A双级压缩CO_2载冷循环和R404A/CO_2复叠制冷循环。通过对比分析发现,两个系统都存在系统最大COP且都随着冷凝蒸发换热温差的增大而减小,随着蒸发温度的升高而增大。同时,在低温区间上复叠系统的COP较大,但是在-30℃附近,双级压缩载冷循环的系统COP和复叠式制冷系统相当,而且双级压缩载冷循环中R404A和CO_2的充灌量比复叠制冷系统少,在节约能源和系统维护方面很具有级优势。     

一种三级自动复叠制冷系统的试验研究

本文提出一种三级自动复叠的制冷系统,搭建了相应的研究装置,采用R134 a/R23/R14混合制冷剂,对试验装置和混合制冷剂组分的优化试验。并对降温过程中制冷系统中混合制冷剂合流特性进行了分析。     

R50对-100℃三级分凝循环中后期的影响

为了确定R50对-100℃温区三级自动复叠系统中后期运行状态的影响,分别以R134a/R23/R14、R134a/R23/R14/R50为混合工质在同一台实验装置上进行两次试验,其中R134a、R23、R14组分充注量相同。通过对两组工质进行实验和对比分析,发现添加R50时第二、三级分凝器蒸发温度和冷却后温度更低,但是系统压力明显更高,设备耗能增加,达到设计温度所需时间增长,因此在-100℃温区的自动复叠系统混合组分添加R50会对系统的性能不利。     

复叠式制冷系统性能的模拟分析

为提高制冷系统运行性能、优化系统结构设计,用EES软件对可实现复叠与双级压缩转换的制冷系统进行模拟分析,分析对比了复叠循环与双级压缩循环、级间容量比及高温级频率对复叠循环的影响。结果表明:蒸发温度对复叠循环和双级压缩循环系统COP的影响都很大,且蒸发温度较低工况下,应选用复叠循环以提高系统COP。对于复叠循环:蒸发温度和冷凝温度一定,随级间容量比的增加,复叠式制冷系统的中间温度降低,级间容量比与冷凝温度一定,蒸发温度每上升1℃,系统的中间温度增加1.5℃;当工况一定时,系统COP随级间容量比的增加呈现出先增大后减小的变化趋势,故对于固定工况下的复叠式制冷系统存在一个使系统COP最优的级间容量比;随高温级频率增大,系统的级间容量比减小,系统的COP先增大后缓慢减小,在达到最佳COP后,系统运行稳定。     

应用于血液冷库的双级复叠系统的实验研究

本文结合天津大学土木馆某水泥低温试验冷库工程,模拟各大血站对RH阴性血液的超低温(-80℃)保存环境,设计并搭建了一套以R508B为低温工质、R404A为高温工质的复叠式制冷系统的超低温冷库,并对R404A/R508B复叠制冷系统的循环特性进行了研究。经实验验证,本系统达到了预期的性能要求,可提供对稀有血型良好的超低温保存环境。     

一种新型近共沸混合工质的循环性能实验研究

文中开展了对一种新型近共沸混合物的整机性能实验研究,该混合物具有零ODP值和低GWP值,可作为传统工质R502甚至是R404A的长期替代物。根据国标GB/T 5773-2004搭建了第二制冷剂量热器的整机性能测试实验台。试验在蒸发温度为-40℃的商用制冷温区进行,系统研究了在不同蒸发温度、冷凝温度、过冷度、过热度等工况下的性能。实验结果与R404A进行了比较,包括压比、压缩机功耗、制冷量、COP、吸气温度。实验结果表明,该新工质COP比R404A高9.2%至14.2%。     

复叠系统低温级制冷剂的循环性能对比实验

通过实验测试,比较了不同冷凝温度和蒸发温度下复叠系统低温级常用制冷工质R13、R23、R503和RS08B的COP、压比及制冷量等循环性能,又结合各制冷工质的环境性能、热工性能,分析了现有常用复叠系统低温级制冷工质各自的优缺点,为新工质的开发及进一步的制冷性能对比实验工作提供了有益的帮助.     

Mn nuclear magnetic resonance studies in RMn2Ge2 (R = rare earths)

The ⁵⁵Mn NMR in RMn₂Ge₂ (R= La,Nd and Gd) were observed as a function of temperature. In Nd and Gd compounds the ⁵⁵Mn NMR frequencies exhibit anomalous temperature dependences owing the effects of rare earth sublattices. The ordering temperatures of the Nd and Gd sublattices are found to be 30 and 95 K, respectively.     

Decreasing iron susceptibility with temperature in quantitative susceptibility mapping: A phantom study

To clarify the temperature dependence of susceptibility estimated by quantitative susceptibility mapping (QSM) analysis, we investigated the relationship between temperature and susceptibility using a cylinder phantom with varying temperatures. Six solutions with various concentrations of superparamagnetic iron oxide (SPIO) nanoparticles were employed. These tubes were placed in a cylinder phantom and surrounded with water. The temperature of the circulated water was adjusted to change the temperature in the cylinder phantom from 25.8 °C to 42.5 °C. The cylinder phantom was scanned via a three-dimensional multiple spoiled gradient-echo sequence for R2* and QSM analyses with varying temperatures. The relationships between temperature, susceptibility, and R2* values were determined. Moreover, the temperature coefficients of susceptibility (χ-Tc) and (R2*-Tc) were calculated at each concentration and the linearities in these indices against each SPIO concentration were validated. Significant inverse correlations were found between temperature, susceptibility, and R2* values at each SPIO concentration due to the decrease in paramagnetic iron susceptibility that occurred with increasing temperature based on Curie's law. Moreover, although there were significant correlations between the susceptibility and R2* values at any temperature, the slopes of the regression lines grew in height with greater temperatures. The percentage of difference per Celsius degree in susceptibility in any SPIO concentration was lower than the corresponding finding among the R2* results. There were strong linearities between the SPIO concentration, χ-Tc (r = −0.994; p < 0.001), and R2*-Tc (r = −0.998; p < 0.001). The χ-Tc and R2*-Tc outcomes in a particular voxel varied considerably with the iron contents. Although there was an inverse correlation noted between temperature and susceptibility, the susceptibility analysis showed smaller temperature dependence relative to the R2* analysis. QSM analysis might be a more suitable option for magnetic resonance-based iron quantification in comparison with R2* relaxometry.     

R23跨临界循环最优高压侧压力分析

跨临界热泵循环在大温差加热时具有显著优势。为了寻求更高效的跨临界热泵循环,对R23跨临界热泵循环进行了理论分析,计算了压缩机排气压力对系统性能的影响。计算结果表明,R23热泵系统存在最优高压侧压力,最优高压侧压力与制冷剂气冷器出口温度、蒸发温度、过热度都有关系,其中以制冷剂气冷器出口温度对最优高压侧压力影响最大。以制冷剂气冷器出口温度为自变量,利用多项式函数对最优高压侧压力进行了拟合,拟合的最大相对误差为-3.14%,平均相对偏差为1.22%。结果可以为R23跨临界热泵系统的设计和控制提供理论参考。     

Heat treatment of human esophageal tissues: Effect on esophageal cancer detection using oxygenated hemoglobin diffuse reflectance ratio

The main objective of the present work is to study the influence of heat treatment on the esophageal cancer detection using the diffuse reflectance (DR) spectral intensity ratio R540/R575 of oxygenated hemoglobin (HbO₂) absorption bands to distinguish the epithelial tissues of normal human esophagus and moderately differentiated esophageal squamous cell carcinoma (ESCC) at different heat treatment temperature of 20, 37, 42, 50, and 60°C, respectively. The DR spectra for the epithelial tissues of the normal esophagus and ESCC in vitro at different heat-treatment temperature in the wavelength range 400–650 nm were measured with a commercial optical fiber spectrometer. The results indicate that the average DR spectral intensity overall enhancement with concomitant increase of heat-treatment temperature for the epithelial tissues of normal esophagus and ESCC, but the average DR spectral intensity for the normal esophageal epithelial tissues is relatively higher than that for ESCC epithelial tissues at the same heat-treatment temperature. The mean R540/R575 ratios of ESCC epithelial tissues were always lower than that of normal esophageal epithelial tissues at the same temperature, and the mean R540/R575 ratios of the epithelial tissues of the normal esophagus and ESCC were decreasing with the increase of different heat-treatment temperatures. The differences in the mean R540/R575 ratios between the epithelial tissues of normal esophagus and ESCC were 13.33, 13.59, 11.76, and 11.11% at different heat-treatment temperature of 20, 37, 42, and 50°C, respectively. These results also indicate that the DR intensity ratio R540/R575 of the hemoglobin bands is a useful tool for discrimination between the epithelial tissues of normal esophagus and ESCC in the temperature range from room temperature to 50°C, but it was non-effective at 60°C or over 60°C.     

Invar behaviour and in situ observation of the nitriding process in R2Fe17Nx intermetallics

Thermal expansion measurements in the high range of temperature (300–1000 K) have been performed from starting R₂Fe₁₇ intermetallics (R = Nd and Er). Large anomalies in the thermal expansion were observed during the nitriding process for increasing temperatures, which have allowed us to study the dynamics of the nitrogen absorption. From our results it is clear that this process takes place in the range of temperature 500–700 K. Large invar anomalies starting at high temperature ((733 ± 5) K for Nd and (688 ± 5) K for Er) have been also observed in the thermal expansion for decreasing temperatures, being an indication of the strong magnetovolume effect which apparently is responsible for the large increase of the Curie temperature in the R₂Fe₁₇N_x compounds.     

加压对110 K Bi-Pb-Sr-Ca-Cu-O单相样品超导电性的影响

 在静压0~1 GPa（10 kbar）范围内，80~300 K温区，用测量电阻的方法，研究了Bi-Pb-Sr-Ca-Cu-O（起始转变温度T_c^on=110 K，终止转变温度T_c^fi=106 K）的起导电性。观察到超导临界温度T_c随压力以dT_c/dp=2K/GPa的速率增高，而在不同压力下的斜率d logR/dp却保持不变。