共查询到20条相似文献,搜索用时 62 毫秒
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《工程热物理学报》2020,(7)
迎面风速和喷淋密度会影响蒸发式冷凝器的传热传质效率。本文搭建了R404A制冷系统实验台,测试了不同的迎面风速和喷淋密度下系统的冷凝压力、制冷量和能效比,并对数据进行了分析。结果表明:对于蒸发式冷凝器制冷机组,喷淋密度的控制较迎面风速更为重要;机组存在最佳迎面风速(3.1~3.3 m·s-1),在迎面风速增加到最佳值之前,风速每增加1 m·s~(-1),EER增加0.3~0.37,当迎面风速超过最佳值后,管外水膜将遭到破坏,蒸发式冷凝器的换热性能趋于稳定,因此冷凝压力和制冷量趋于稳定;最佳喷淋密度为0.057 kg·m~(-1)·s~(-1),在喷淋密度增加到最佳值之前,喷淋密度每增加0.01 kg·m~(-1).s~(-1),EER增加0.27~0.31,当喷淋密度超过最佳值后,管外水膜变厚,水膜热阻增加,蒸发式冷凝器的换热性能减弱,因此冷凝压力升高明显,制冷量下降明显。 相似文献
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水蒸气在低能表面相变形态的热力学分析 总被引:6,自引:1,他引:5
1前言滴状冷凝具有很高的传热速率,其冷凝传热系数是膜状冷凝的几至几十倍。而现行的冷凝器一般采用界面能较高的金属材料制成,所以膜状冷凝是现行冷凝器中的普遍现象。为在金属壁面上实现滴状冷凝,必须在最大限度上降低其界面能。对此,前人进行长期大量的工作,提出了很多方法,但是均未达到工业应用的要求[‘-’]。本文对应用低能复合股作为表面处理技术,改善在该膜表面水蒸气相变形态,以实现冷凝器中的滴状冷凝、改善热泵一空调装置中的蒸发器的传热性能和通风阻力,以及制冷装置中的抑制蒸发器结霜而进行热力学分析。所谓低能… 相似文献
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以直接膨胀式冷库制冷系统为对象,通过改变风冷冷凝器风机频率,对不同库温下的制冷系统性能进行了实验研究。研究发现,在相同的库温下,随着冷凝器风机频率的降低,系统制冷量减小,压缩机功率增大,系统总功率减小;当库温高于-18℃时,制冷系统COP随冷凝器风机频率的降低而减小,但当库温降至-18℃时,制冷系统COP反而增大。在相同的冷凝器风机频率下,随着库温的降低,系统制冷量减小,压缩机功率减小,系统总功率减小,制冷系统COP减小。当库温为-18℃时,冷凝器风机频率变化对制冷量影响较小,制冷系统COP主要受系统总功率的影响;库温高于-18℃时,冷凝器风机频率变化对系统总功率和制冷量均有影响,但制冷量变化对制冷系统COP影响更大。因此,在厦门地区冬季运行时,冷凝器风机在变频运行方式下,冷库制冷系统节能与否须结合库温工况确定。 相似文献
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基于质量守恒、能量守恒方程,耦合环路热管各关键节点处压力、温度及传热传质关系,通过计算冷凝器中汽液界面位置,将环路热管内压力损失分为蒸汽侧压损和液相侧压损,并构建了从局部到整体的稳态运行数学物理模型,重点分析了冷凝界面位置和蒸发器热泄漏对环路热管稳态运行的影响规律。发现,低热流密度下,冷凝界面越靠近蒸汽出口越有利于提高环路热管的传热性能,但随着热流密度增加,冷凝位置对环路热管稳态性能的影响程度越来越小;抑制热泄漏或增加流入补偿室内的冷量,均可增大毛细芯两侧温度梯度,降低运行温度,进而提高环路热管的传热性能。 相似文献
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以低温下的液态氨为例,从热力学角度探讨了冷凝过程的发生机制,给出了提高冷凝速率防止冷凝器壁面结霜的有效途径。 相似文献
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A. N. Elsukov 《Russian Physics Journal》1965,8(4):39-42
A rigorous solution is given for modes of TMnmo type. The complex resonant frequency n is expressed via a transcendental characteristic equation. Some particular cases are discussed.Read at the Third All-Union Conference on Ferrites, Leningrad, 23 October 1963. 相似文献
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Yu. D. Chernichenko 《Physics of Atomic Nuclei》2004,67(2):414-423
Within the relativistic quasipotential approach to quantum field theory, a method is developed for solving a finite-difference quasipotential equation for the case where a total quasipotential describing the interaction of two relativistic spinless particles of unequal masses is a superposition of a nonlocal separable and a local quasipotential. The cases are investigated where the local component of the total interaction—it is assumed to be known—either admits or does not admit the existence of bound states. This makes it possible to obtain an exact expression for the increment of the phase shift, to determine the conditions of the existence of bound states, and to give a generalization of the Levinson theorem. 相似文献
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T. Ouisse 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):415-420
The tunnelling lifetime of an electron lying in a p-type orbital localised at a given distance from a semiconductor or a metal is calculated by using Bardeen's method. It is
then shown that even in the absence of broad bands, the hole injection process from semiconductors and metals into polymers
should follow a Fowler-Nordheim dependence, provided that the current is not bulk-limited. In the semiconductor case, the
current can be expressed by a fully analytical formula, and by an approximate one in the case of a metal. It is demonstrated
that the effective Fowler-Nordheim barrier is not the mere difference between the metal work function or the semiconductor
electron affinity and the HOMO level of the polymer, but a simple function of both levels.
Received 6 April 2001 and Received in final form 29 May 2001 相似文献
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The existence of surface polaritons in a dielectric at a boundary with an ideal metal or superconductor in a static electric
field is predicted. The frequency regions in which polaritons exist are substantially different for opposite orientations
of the electric field, so that a change in the direction of the field signifies “switching on” or “switching off” of surface
polaritons with a fixed frequency.
Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 876–880 (25 December 1998) 相似文献
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V. P. Glashchenko 《Technical Physics》2014,59(5):754-761
The conditions under which the nonuniform compensating field of the reflector of the mass-reflectron can be generated with an acceptable accuracy at the symmetry axis of the reflector and extrapolated to the radial neighborhood of the axial line are determined. The plots that illustrate the distribution of the calculated nonuniform field of the reflector, the possibilities for implementation, and errors of focusing with respect to time of flight in the radial neighborhood are presented. Analytical expressions for the calculation of the time of flight of ions in the reflector in which the field distribution is described using a power series and analytical expressions for the calculation of the field distribution in the reflector in which the time of flight is determined using a power series are derived. A method for the analytical calculation of the compensating nonuniform field of the reflector based on the given dependence of the time of flight in the absence of such a field is proposed using a solution to the Abel integral equation. The solution to this equation yields analytical expressions for the calculation of the compensating field of the reflector in mass-reflectrons that contain the zero-field drift space and regions of acceleration (deceleration) of ions with a uniform field. 相似文献
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V. I. Bukreev 《Doklady Physics》2002,47(12):880-882
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Molecular-dynamics was used to investigate the structural changes occurring in a three-dimensional solid when the solid is
transferred from an amorphous into a crystalline state. Crystal cells of a new type — pentadecahedrons with five square lateral
faces and ten regular triangular faces at the vertices of a cell — were found for the first time in a computer experiment.
It is shown that a bistructure consisting of crystal cells of different types, including cells with five-fold symmetry axes,
are stable in the solid.
Fiz. Tverd. Tela (St. Petersburg) 40, 1919–1924 (October 1998) 相似文献