基于R410A制冷剂的空气源燃气热泵系统制冷特性

该文搭建了使用R410A制冷剂涡旋式压缩机的高能效空气源燃气热泵实验平台。在实验台上进行不同进水温度t_w,in(8.8～18.8℃)、发动机转速N_eng(1400～2400 r/min)、环境温度T_amb(24～43℃)、进水流量G_w(9.16～18.32 m³/h)影响下的制冷特性研究，得到制冷量(Q·_c)、耗气功率(P_gas)、压缩机功率(P_comp)、一次能源利用率(R_PER)、总一次能源利用率(R_PER,all)及性能系数(R_COP)的变化规律。结果表明，R_PER受R_COP与发动机热效率η_eng的双重影响，制冷运行时R_PER、R_PER,all与η_eng分别处于0.935～1.224、1.388～1.720与27...     

基于多元回归模型的燃气热泵系统制热性能分析

基于实测数据构建燃气热泵系统中天然气发动机的多元回归模型和开式涡旋压缩机的计算模型,采用EES软件对燃气热泵系统进行性能计算,分析出口水温(t_out)、发动机转速(N_eng)、环境温度(t_amb)及余热回收量对系统制热性能系数COP与一次能源利用率PER的影响。模拟研究表明：在同等条件下,不开启余热回收系统时,COP与PER随t_out增加线性降低,模拟值与实测值的最大误差分别为1.62%与3.06%;同时,t_amb对COP的影响较大,当N_eng为1 500 r/min时,随着t_amb从-15℃变化到24℃时,COP上升了225.87%,PER上升了217.26%;开启余热回收系统后,同等条件下的COP与PER分别提升了24.65%和24.67%,且COP,PER变化的趋势发生了明显变化。     

GHP系统发动机余热回收探讨

GHP系统实现了能量的梯级利用,系统中的余热回收是实现低品位热能回收的主要措施,是提高系统一次能源利用率的有效途径,余热回收的效果影响着GHP系统的效率及经济性。因此,余热回收对于GHP系统有着比较重要的意义。余热回收系统的形式根据排烟余热回收换热器和发动机缸体余热回收换热器的连接形式可分为简单串联、简单并联、旁通串联。讨论了发动机余热回收系统的形式以及余热回收换热器的种类,并对此给出了建议。     

基于水蒸气工质新型压缩-吸收式热泵循环性能分析

针对常规热泵在工业余热利用领域应用温度范围受限的技术难题,该文对一种压缩-吸收式耦合热泵系统在大温升工况下制取约130 ℃热水或蒸汽开展研究。首先介绍耦合热泵循环的运行原理,构建耦合热泵的完整热力学模型,通过EES软件最优化函数计算发现吸收侧压力越低,循环性能系数（COP）越好,同时在溶液热交换器出口浓溶液温度高于结晶温度10 ℃及溶液放汽范围为5.0%~5.5%的约束条件下,以某工业余热回收工况为设计工况,其中余热热水进/出口温度为90/75 ℃,余热水流量为30 kg/s,高温热水进/出口温度为100/125 ℃,吸收与发生侧最优压力值分别为40和2.2 kPa,对应耦合热泵的COP为9.8。同理分析了不同余热热水出口温度及高温热水出口温度变化工况下系统的循环性能,验证了该循环在高制热温度下仍具有较好的性能系数。     

对一种具有余热回收系统的LNG联合循环电站分析

提出了一种深度回收以液化天然气为燃料的联合循环电站中的蒸汽轮机排汽潜热和余热锅炉排烟中水蒸气潜热的系统.热力学分析表明,相对于240 MW的常规联合循环,所提系统的净电效率和火用效率分别提高1.6%和2.84%,其燃料利用率达62.88%;相对于传统联合循环,所提系统从每千克排烟中可多回收86.27 kJ/s的热量.可从低压省煤器出口抽取质量流率大约为46.1 kg/s,温度为167.45℃,压力为0.84 MPa 的热水送入余热利用子系统;经济性生分析显示,回收余热所增加投资的回收期为0.117年.这些特征对新建和已有LNG联合循环电站的改造具有很强的吸引力.     

基于燃机余热和地热能的联合发电系统优化设计及热力性能分析

设计了一种超临界二氧化碳(S-CO₂)再压缩系统与地热双闪蒸系统相结合的新型燃机余热利用联合发电系统。基于所建联合系统参数优化模型,应用遗传算法计算分析了联合系统内部参数和边界参数对最大输出功和燃机余热利用率的影响。结果表明：通过系统参数优化,联合系统实现了余热在2个子系统中的合理分配,加深了燃机余热的进一步利用;当一级闪蒸压力取99.89 kPa、二级闪蒸压力取29.4 kPa、S-CO₂质量流量取22.68 kg/s、分流比取0.308 5时,联合系统最大净输出功达到6.402 MW,对应余热效率为67.9%;当一级闪蒸压力在90～115 kPa、二级闪蒸压力在25～35 kPa时,联合系统均可实现较高的净输出功,与最佳值的相对偏差在0.8%以内;随着S-CO₂流量或分流比逐渐增大,联合系统的净输出功均呈现先增大后减小的规律;联合系统的最大净输出功随S-CO₂透平进口压力的增大而增加,随S-CO₂透平出口压力和预冷器出口温度的增大而减小。     

高进水温度下CO_2空气源热泵热水系统变频运行性能

构建CO_2空气源热泵热水系统变频运行实验装置,测试分析高环境温度、高进水温度下变频运行对CO_2空气源热泵热水系统气体冷却器压力、制热功率及性能系数(COP)的影响。实验结果表明,CO_2空气源热泵压缩机降频运行能有效避免压缩机过载、抑制气体冷却器压力过高等问题。随压缩机频率的减小,气体冷却器压力持续减小,COP先增大后减小,存在最优压缩机频率值。在高环境温度和高进水温度工况下,CO_2空气源热泵热水系统压缩机最优运行频率区间为35～45 Hz。     

燃气-超临界CO2联合循环发电系统

  [目的]  燃气轮机排气温度高,可增加底循环,利用排气的余热发电,从而提高燃料总的能量利用率。鉴于超临界CO₂循环热效率高,并且具有系统简单、结构紧凑、运行灵活等潜在优势,可与燃气轮机组成新型的燃气-超临界CO₂联合循环。  [方法]  为了充分利用燃气轮机排气余热,提出在简单回热超临界CO₂循环的基础上,再嵌套一个简单回热循环的布置方式,并以PG9351(FA)型燃气轮机为例,对其热效率进行了计算分析。同时,在系统中增加余热利用装置,可将剩余热量用于供热、转换为冷量或发电。  [结果]  结果表明:对于选定的燃气轮机,超临界CO₂循环最高温度可达约600 ℃,循环发电效率约32%,获得余热温度为170 ℃以上,余热热量占燃气轮机排气热量9%,联合循环发电效率约54%。  [结论]  燃气-超临界CO₂联合循环发电系统具有较高的热效率,并且保留部分较高品位的余热,可进一步用于电厂运行。     

燃煤电站烟气余热回收系统构型在线调整与运行参数优化

烟气余热回收是提高燃煤电站运行效率的有效手段。本文建立了某600 MW机组烟气余热回收系统的变工况计算模型,获得了环境温度、设计参数和运行参数对系统变工况运行特性的影响规律,提出了运行参数优化与构型在线调整相结合的优化策略：在环境温度较高时采用系统构型自适应策略,在环境温度较低时采用系统构型自适应结合参数调控策略。研究结果表明：优化后,系统在运行范围内的平均节煤率达到了2.72 g/(kW·h),相比原系统平均节煤率仅降低了0.3 g/(kW·h),安全运行的环境温度下限由24℃扩展至-10℃。     

余热发电两级能量转换系统的研究

为提高余热发电的经济性,提出余热热水发电的两级能量转换系统,并建立了该系统的两级闪蒸和两级双工质循环的热力计算的数学模型;对电站的功率和效率进行了计算,以此对单级及两级能量转换系统进行了比较。结果表明:在计算所给的热水温度(100～200℃)和冷凝温度下,两级闪蒸比单级闪蒸的发电量多24.8%～31.2%;两级双工质循环比单级双工质循环的发电量多14.5%～24.0%;两级闪蒸比两级双工质循环的发电量多7.2%～67.5%。     

General energy decay rates for a weakly damped Timoshenko system

In this paper, we consider the following Timoshenko-type system:

Rolling of manifolds without spinning

The control model of rolling of a Riemannian manifold (M; g) onto another one $ \left( {\hat{M},\hat{g}} \right) $ consists of a state space Q of relative orientations (isometric linear maps) between their tangent spaces equipped with a so-called rolling distribution $ {\mathcal D} $ _R, which models the natural constraints of no-spinning and no-slipping of the rolling motion. It turns out that the distribution $ {\mathcal D} $ _R can be built as a sub-distribution of a so-called no-spinning distribution $ {{\mathcal{D}}_{\overline{\nabla}}} $ on Q that models only the no-spinning constraint of the rolling motion. One is thus motivated to study the control problem associated to $ {{\mathcal{D}}_{\overline{\nabla}}} $ and, in particular, the geometry of $ {{\mathcal{D}}_{\overline{\nabla}}} $ -orbits. Moreover, the definition of $ {{\mathcal{D}}_{\overline{\nabla}}} $ (contrary to the definition of $ {\mathcal D} $ _R) makes sense in the general context of vector bundles equipped with linear connections. The purpose of this paper is to study the distribution $ {{\mathcal{D}}_{\overline{\nabla}}} $ determined by the product connection $ \nabla \times \hat{\nabla} $ on a tensor bundle $ {E^{*}}\otimes \hat{E}\to M\times \hat{M} $ induced by linear connections ?, $ \hat{\nabla} $ on vector bundles $ E\to M,\,\,\,\hat{E}\to \hat{M} $ . We describe completely the orbit structure of $ {{\mathcal{D}}_{\overline{\nabla}}} $ in terms of the holonomy groups of ?, $ \hat{\nabla} $ and characterize the integral manifolds of it. Moreover, we describe the general formulas for the Lie brackets of vector elds in $ {E^{*}}\otimes \hat{E} $ in terms of $ {{\mathcal{D}}_{\overline{\nabla}}} $ and the vertical tangent distribution of $ {E^{*}}\otimes \hat{E}\to M\times \hat{M} $ . In the particular case of tangent bundles $ TM\to M,\,\,\,T\hat{M}\to \hat{M} $ and Levi-Civita connections, we describe in more detail how $ {{\mathcal{D}}_{\overline{\nabla}}} $ is related to the above mentioned rolling model, where these Lie brackets formulas provide an important tool for the study of controllability of the related control system.     

The Deligne–Simpson Problem and the Connectedness of some Varieties

The Deligne–Simpson problem is formulated as follows: give necessary and sufficient conditions for the choice of the conjugacy classes or so that there exist irreducible (p+1)-tuples of matrices M _j ∈ C _j or A _j ∈ c _j satisfying the equality M ₁ ⋯ M _p+1 = I or A ₁ + ⋯ + A _p+1 = 0. The matrices M _j and A _j are interpreted as monodromy operators of regular linear systems and as matrices-residues of Fuchsian ones on the Riemann sphere. We prove that in the so-called simple case the subset or of the variety or consisting of all irreducible (p+1)-tuples (if nonempty) is connected. “Simple” means that the greatest common divisor of all quantities of Jordan blocks of a given size, of a given matrix M _j or A _j , and with a given eigenvalue is 1. To the memory of my mother     

Regions Where the Exponential Map at Regular Points of Sub-Riemannian Manifolds is a Local Diffeomorphism

For a k-step sub-Riemannian manifold which admits a bracket generating vector at a point, we describe a region near the point where the exponential map is a local diffeomorphism. This is proved by taking the Taylor series of the exponential map and calculating the first nonzero term, which has order , where n is the topological dimension and is the Hausdorff dimension of the metric space associated to the sub-Riemannian manifold.      

Foliation Admitting Recurrent Leaves of Infinite Depth on Compact Two-Manifolds

Let be a foliation on a two-manifold M. Denote the topology closure of each leaf L of by . A sequence of proper inclusions , where each L _i is a recurrent leaf of , is called a nest of length k. The maximal length of various nests is known as the depth of the foliations . It is well known that if is orientable and M is compact, the depth of is at most one. In this paper, we show that on any orientable, compact two-manifold, there exist nonorientable foliations of infinite depth. This work negatively answers the Aranson conjecture [1]. This work was partially supported by FAPESP-Proj. Tematico No. 03/03107-9.     

An Estimate for the Entropy of Hamiltonian Flows

In this paper, we present a generalization to Hamiltonian flows on symplectic manifolds of the estimate proved by Ballmann and Wojtkovski in [4] for the dynamical entropy of the geodesic flow on a compact Riemannian manifold of nonpositive sectional curvature. Given such a Riemannian manifold M, Ballmann and Wojtkovski proved that the dynamical entropy h _μ of the geodesic flow on M satisfies the inequalitywhere v is a unit vector in T _p M if p is a point in M, SM is the unit tangent bundle on M, K(v) is defined as , where is the Riemannian curvature of M, and μ is the normalized Liouville measure on SM. We consider a symplectic manifold M of dimension 2n, and a compact submanifold N of M, given by the regular level set of a Hamiltonian function on M; moreover, we consider a smooth Lagrangian distribution on N, and we assume that the reduced curvature of the Hamiltonian vector field with respect to the distribution is non-positive. Then we prove that under these assumptions, the dynamical entropy h _μ of the Hamiltonian flow with respect to the normalized Liouville measure on N satisfies      

Controllability of control systems on complex simple lie groups and the topology of flag manifolds

Let S be a subsemigroup with nonempty interior of a connected complex simple Lie group G. It is proved that S = G if S contains a subgroup G(α) ≈ Sl (2, $ \mathbb{C} $ ) generated by the exp $ {{\mathfrak{g}}_{{\pm \alpha }}} $ , where $ {{\mathfrak{g}}_{\alpha }} $ is the root space of the root α. The proof uses the fact, proved before, that the invariant control set of S is contractible in some flag manifold if S is proper, and exploits the fact that several orbits of G(α) are 2-spheres not null homotopic. The result is applied to revisit a controllability theorem and get some improvements.     

Multiple positive solutions of singular dirichlet second-order boundary-value problems with derivative dependence

The existence of multiple positive solutions for the singular Dirichlet boundary-value problem

Limit Cycles for a Class of Three-Dimensional Polynomial Differential Systems

Perturbing the system inside the family of polynomial differential systems of degree n in , we obtain at most n ² limit cycles using the first-order averaging theory. Moreover, there exist such perturbed systems having at least n ² limit cycles.      

On Topological Equivalence of Linear Lows with Applications to Bilinear Control Systems

This paper classifies continuous linear flows using concepts and techniques from topological dynamics. Specifically, the concepts of equivalence and conjugacy are adapted to flows on vector bundles, and the Lyapunov decomposition is characterized using the induced flows on the Grassmann and the flag bundles. These results are then applied to bilinear control systems, for which their behavior in , on the projective space , and on the Grassmannians is characterized. This research was partially supported by Proyecto FONDECYT No. 1060981 and Proyecto FONDECYT de Incentivo a la Cooperación Internacional No. 7020439.