一种变截面涡旋压缩机型线的构建与性能研究

针对传统变截面型线设计中因曲线类型不同和引入高次曲线而导致的设计过程复杂、加工难度大等问题,提出了一种利用加速螺旋线取代高次曲线的型线设计方法。基于该方法,构建了一种以加速螺旋线为主涡旋线的变截面型线,并建立了该型线的基本几何理论,研究了工作腔容积的变化规律,得到了轴向气体力与切向气体力随着主轴转角的动态变化历程。结果表明:采用相同类型曲线构建的变截面型线,不仅弥补了传统变截面型线的不足,而且在容积性能与力学性能方面更具优势。在相同设计参数条件下,与高次曲线构成的传统变截面型线相比,吸气容积和压缩比分别提高了39.51%和11.54%,最大轴向气体力与切向气体力分别降低了11.06%和8.58%。该研究成果对简化变截面型线设计及降低加工难度具有一定的参考作用。

冷库氨双级压缩制冷系统最佳工况研究

本文研究了氨活塞式双级压缩制冷系统的最佳中间温度、最佳高、低压级输气容积比和最大COP值随冷凝温度和蒸发温度的变化规律 ,并采用微机程序确定任意工况条件下的最佳中间状态和任意中间状态下高、低压级输气容积比与中间温度的关系 ,进一步比较了 1 2和 1

基于分析的压缩冷凝机组试验方法比较

从热力学角度考虑能量使用的完善性和合理性(效率),从经济学角度考虑最小初投资和运行费用,综合考虑以上两个因素,并将此作为容积式压缩冷凝机组性能试验方法选择的依据.对目前广泛采用的容积式压缩冷凝机组两种性能试验方法—第二制冷剂量热器法和二次流体量热器法—做了试验方法上的介绍,利用流图进行了分析比较.从热力学和经济学两个方面对容积式压缩冷凝机组性能试验方法做出综合性评价,为容积式压缩冷凝机组性能试验方法提出了基于分析的选择依据.

Nonlinear state estimation for fermentation process using cubature Kalman filter to incorporate delayed measurements

State estimation of biological process variables directly influences the performance of on-line monitoring and op- timal control for fermentation process. A novel nonlinear state estimation method for fermentation process is proposed using cubature Kalman filter （CKF） to incorporate delayed measurements. The square-root version of CI（F （SCKF） algorithm is given and the system with delayed measurements is described. On this basis, the sample-state augmentation method for the SCKF algorithm is provided and the implementation of the proposed algorithm is constructed. Then a nonlinear state space model for fermentation process is established and the SCKF algorithm incorporating delayed measurements based on fermentation process model is presented to implement the nonlinear state estimation. Finally, the proposed nonlinear state estimation methodology is applied to the state estimation for penicillin and industrial yeast fermentation processes. The simulation results show that the on-fine state estimation for fermentation process can be achieved by the proposed method with higher esti- mation accuracy and better stability.

ABNORMAL LEFT VENTRICULAR SYSTOLIC AND DIASTOLIC FUNCTIONAL RESPONSE TO ISOMETRIC EXERCISE IN IDIOPATHIC DILATED CARDIOMY-OPATHY: BENEFICIAL EFFECT OF CAPTOPRIL

In 19 patients with idiopathic dilated cardiomyopathy and symptoms of congetive heart failure, left ventricular (LV) systolic performance and diastolic velocity profiles were assessed by two- dimensional echocardiography and pulsed wave Doppler at rest and during handgrip exercise before and ninety minutes after administration of captopril (mean dose 25 +12mg; range 12. 5─50mg). Although heart rate and blood pressure increased similarly during handgrip exercise before and after captopril treatment, both were lower with handgrip exercise during captopril treatment. The results from this study indicated that acute angiotensin converting enzyme inhibition with captopril reduces preload and afterload and ameliorates handgrip exercise-induced LV systolic and diastolic filling dysfunction in patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy.

Electrochemical Behavior of Electrodeposited Sn Films： Possible Negative Electrode for Na^＋ Rechargeable Batteries

Tin films on copper substrate, obtained by electrodeposition procedure, were structural and electrochemical characterized. In particular to investigate the possibility to use such metal as possible negative electrode in Na＋ rechargeable batteries, EPS （electrochemical potential spectroscopy） and galvanostatic charge/discharge cycling of the electrodes were investigated, at room temperature in organic electrolyte. Three crystalline and one amorphous phases were identified as well as high discharge capacity （738 mAb/g） was obtained after 4 cycles. Unfortunately material fading, due to the internal stress during sodiation/desodiation process, causes poor cyclability.

What are the practical limits for the specific surface area and capacitance of bulk sp^2 carbon materials?

The possible practical limits for the specific surface area and capacitance performance of bulk sp^2 carbon materials were investigated experimentally and theoretically using a variety of carbon materials. We find the limit for the specific surface area to be 3500–3700 m^2 g^(-1), and based on this, the corresponding best capacitance was predicted for various electrolyte systems. A model using an effective ionic diameter for the electrolyte ions was proposed and used to calculate the theoretical capacitance. A linear dependence of experimental capacitance versus effective specific surface area of various sp^2 carbon materials was obtained for all studied ionic liquid, organic and aqueous electrolyte systems. Furthermore, excellent agreement between the theoretical and experimental capacitance was observed for all the tested sp^2 carbon materials in these electrolyte systems, indicating that this model can be applied widely in the evaluation of various carbon materials for supercapacitors.

One-step electrodeposition fabrication of Ni_3S_2 nanosheet arrays on Ni foam as an advanced electrode for asymmetric supercapacitors

Ni3S2 nanosheet(NS) arrays on Ni foam were fabricated by a simple one-step electrodeposition strategy, and used as a kind of electrode material for asymmetric supercapacitors. The Ni3S2 NS arrays are interconnected, which can be regarded as bridges between these individual nanoparticle units. The electrochemical performances were evaluated by cyclic voltammetry and chronopotentiometry techniques in a three-electrode system. The Ni3S2 NS arrays display a specific capacitance of 773.6 F g^-1 at 1 A g^-1, and excellent rate property of 84.3% at 10 A g^-1. The performance of the Ni3S2 NS arrays was further investigated in an asymmetric supercapacitor for potential practical application. The asymmetric supercapacitor using the Ni3S2 electrode and reduced graphene oxide electrode as positive and negative electrodes, respectively, exhibits an energy density of 41.2 W h kg^-1 at 1.6 kW kg^-1. When up to 16 kW kg^-1, it holds 25.3 W h kg^-1.These excellent electrochemical performances are attributed to the improved electronic conductivity and rich redox reaction sites from Ni3S2 NS arrays. Our results indicate that the Ni3S2 NS arrays have great potential for supercapacitors.

Facile electrodeposition of 3D concentration-gradient Ni-Co hydroxide nanostructures on nickel foam as high performance electrodes for asymmetric supercapacitors

Novel three-dimensional （3D） concentration-gradient Ni-Co hydroxide nanostructures （3DCGNC） have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three- electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g^-1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g^-1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg^-1 at a power density of 3.0 kW·kg^-1, and excellent rate capability-energy densities of about 70.4 and 26.0 Wh·kg^-1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg^-1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g^-1 was achieved, which compares very well with the traditional doublelayer supercapacitors.