门窗开启对室内R32浓度分布的影响

新型环保制冷剂大多具有可燃性,须对其泄露的安全性进行研究。通过实验的方法,研究10~13匹多联机空调系统,在某房间泄漏时,门窗开启对R32浓度分布的影响。监测0.2、1.2、2.2m平面R32浓度随时间的变化曲线,及室内R32浓度稳定时的分布。结果表明,门开启1/3时,室内R32浓度在5%以下,不存在危险区域;比较通风窗开启1/3和门窗关闭两个工况,室内R32浓度下降了7%~8%。分析首次达到可燃下限(14.4%)的时间,在0.2、1.2m平面分别推迟了27.6、16.3min,在2.2m平面没有达到可燃下限,在可燃区间的维持时间分别缩短了144.6min(76.9%)、92.4min(60.2%)。     

活塞压缩机内制冷剂R1234yf泄漏模拟研究

基于活塞压缩机R1234yf制冷剂泄漏问题,运用Fluent模拟软件对活塞压缩机一个运动周期内制冷剂R1234yf的内部流场和泄漏趋势进行模拟,通过对不同吸气温度和吸气压力下制冷剂R1234yf的泄漏速度以及泄漏质量流量的对比分析,确定了制冷剂R1234yf在活塞压缩机内的泄漏规律,为制冷剂R1234yf的推广提供依据。     

不同制冷剂用于双回路耦合冰箱性能研究

本文对R134a、R290、R600a及R600等四种制冷剂用于双回路耦合制冷系统的性能进行模拟计算。其中R600的当量性能系数最高、单位质量制冷量最大而容积制冷量最小;R600a排气温度最低;R290循环压比最小。对由R290、R600及R600a组成的不同混合制冷剂进行模拟计算,当小端温差一定时,混合制冷剂当量性能系数高于纯质;当有效换热温差一定时,混合制冷剂R290/R600a当量性能系数与纯质R600相当,循环压比稍高于R290,最高排气温度低于所选纯质制冷剂.     

混合制冷剂泄漏试验研究与模拟分析

1研究背景目前在制冷和空调系统中，绝大多数采用混合制冷剂作为R502与HCFC－22等的替代物。但混合物的特殊问题，即在贮存、使用时因泄漏而引起的成分变化、特别是成分变化而导致制冷剂可燃性或系统性能的变化，引起了人们的普遍重视。英国I.C.I公司对R407C（HFC－32／125／134a）系统进行测试表明，由于泄漏后成分变化而引起的性能变化在10％以内。日本DAIKIN公司研究HFC－32／134a混合物时发现：其临界可燃配比为56Wt％，即HFC－32重量比超过56％时可燃；使用名义配比30／70wt％的HFC－32／134a混合物并不可燃，但发生泄漏后…     

纤维素、木质素对生物质与煤混烧特性的影响

利用热重红外分析仪着重分析了生物质中纤维素和木质素含量对混合热解及混烧特性的影响.生物质与煤的混合热解相比于纯煤的单一热解失重明显较大较快,并且纤维素含量越高,混合燃料失重越大;木质素含量较高,则混合燃料失重较慢.当燃烧温度为300～400℃之间时,混合燃料中纤维素含量越高,质量下降幅度越大;当燃烧温度为500～700℃之间时,混合燃料中则是木质素含量越高,质量下降幅度越大.     

L20在家用空调器中替代R22的理论分析北大核心

L20制冷剂是基于HFO制冷剂R1234ze(E)开发出的新型低GWP非共沸制冷剂,用于替代R22。其组成成分为R32、R152a和R1234ze(E),ODP值为0,GWP值为295。对其热物理性质、制冷循环理论计算以及替代R22时CO2减排率进行了分析。结果表明,除了有较大的滑移温度以外,L20和R22有相似的饱和蒸气压力-温度曲线,其导热系数高于R22;在空调标准工况下其单位质量制冷量为R22的115%,单位容积制冷量与R22的基本一致;压缩机排气温度比R22低2.2℃。在替代R22时,可减少86%的CO2排放量。     

L20在家用空调器中替代R22的理论分析

L20制冷剂是基于HFO制冷剂R1234ze(E)开发出的新型低GWP非共沸制冷剂,用于替代R22。其组成成分为R32、R152a和R1234ze(E),ODP值为0,GWP值为295。对其热物理性质、制冷循环理论计算以及替代R22时CO2减排率进行了分析。结果表明,除了有较大的滑移温度以外,L20和R22有相似的饱和蒸气压力-温度曲线,其导热系数高于R22;在空调标准工况下其单位质量制冷量为R22的115%,单位容积制冷量与R22的基本一致;压缩机排气温度比R22低2.2℃。在替代R22时,可减少86%的CO2排放量。     

基于白光发光二极管的室内可见光通信光源布局优化

传统基于照明的光源布局方式在室内难免会存在光照度不均匀现象,造成通信盲区效应,从而影响通信系统的可靠性。为了解决此问题,以4m×4m×3m房间为模型,在常用的室内光源布局模式下,采用光照度补偿技术,对其进行合理的布局优化,得出了一种由5个发光二极管阵列组成的光源布局方式,这种布局方式可同时降低系统功耗并提高光照度均匀性。为了兼顾可见光通信(VLC)系统的可靠性,采用室内接收平面的光照度标准差与通信中接收平面的平均误码率(BER)构建系统优化模型函数f(L,i),当f(L,i)达到最小值时可同时满足接收平面的照度要求和通信BER要求。仿真结果表明,当L=0.35m、i=0.025m时,f(L,i)取最小值,此时接收平面光照度的最小值为301.26lx,最大值为389.90lx,均匀度为93.24%,系统照度标准差为20.1,功耗为140.5 W,BER为6.39×10-7。所提系统可同时兼顾室内接收平面光照度分布的均匀性和通信的可靠性,为室内VLC光源布局提供了一种优化方法。     

HFC类二元混合制冷剂气相黏度预测

根据Vesovic-Wakeham理论,预测了10种HFC类二元混合制冷剂的气相黏度,所研究的混合制冷剂包括R32/R125、R32/R134a、R32/R143a、R32/R152a、R125/R134a、R125/R143a、R125/R152a、R134a/R143a、R134a/R152a和R143a/R152a,温度范围为298.15～423.15 K,压力范围为0.1～8.85 MPa,结果表明,黏度预测值具有较高的精度,可以满足工程应用的实际要求。     

R32/油混合物管内两相流动摩擦压降模型预测研究

R32具有很好的热物性,且GWP值相对较低,在制冷剂的替代进程中有潜力得到推广应用。在蒸汽压缩制冷系统中,润滑油难免随制冷剂混入换热部件,恶化制冷剂侧的流动特性。基于文献R32/油混合物两相流动摩擦压降实验数据,对比文献中四种模型的预测值和实验值。结果表明:在低质流密度工况下,文献模型对实验的结果预测精度较高,在高质流密度工况下,预测结果偏离了实验结果,且预测值均大于实验值,模型需进一步研究和优化。     

Point defects on graphene on metals

Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in freestanding graphene layers.     

基于Matlab分析负荷对多联机IPLV的影响

多联机有其特殊的优点,但是不同部分负荷的组合对IPLV的影响仍需进一步研究。文中建立IPLV与部分负荷的相关公式,运用MATLAB软件分析不同卸载级负荷与IPLV的关系,从而确定不同部分负荷的最优组合。     

Note on duality on polarized symplectic manifolds

In this note we use some of the results of [3] to derive a general duality theorem for the cohomologies of foliated structures on a manifold. The result is applied to the special case of a symplectic manifold M on which the foliation is given by a complex polarization F in the sense of geometric quantization. We obtain, for example, a rigorous proof of the fact that for a smooth function ƒ on M whose Hamiltonian vector field leaves F invariant, the spectrum of the corresponding prequantization operator v(ƒ) coincides with the spectrum of its transpose, under the above duality. This latter result was obtained by Simms in [12] under certain hypotheses. Proofs of the validity of those hypotheses are now available in the literature; cf. [3] and [7].     

Space-charge effects on multipactor on a dielectric

Analyzes the effects of space charge shielding on the steady state of a multipactor discharge on a dielectric. Analytic methods are used to obtain an exact function for the potential in the discharge, assuming a Maxwellian distribution of emitted electrons. An equation for the amount of power deposited on the dielectric by the multipactoring electrons, for a given saturation level, is given. A simple method for obtaining the saturation level, for a given material, is obtained     

Remarks on KdV-type flows on star-shaped curves

We study the relation between the centro-affine geometry of star-shaped planar curves and the projective geometry of parametrized maps into RP¹. We show that projectivization induces a map between differential invariants and a bi-Poisson map between Hamiltonian structures. We also show that a Hamiltonian evolution equation for closed star-shaped planar curves, discovered by Pinkall, has the Schwarzian KdV equation as its projectivization. (For both flows, the curvature evolves by the KdV equation.) Using algebro-geometric methods and the relation of group-based moving frames to AKNS-type representations, we construct examples of closed solutions of Pinkall’s flow associated with periodic finite-gap KdV potentials.