The three isentropic exponents of dry steam

The isentropic change of an ideal gas is described by the well known relations pv^k=const, Tv^(k−1) =const and p^(1−k)T^k=const, where the exponent k is defined as the ratio of the constant pressure to the constant volume specific heat, k=c_p/c_v. The same relations are also used for real gases if small or differential isentropic changes are considered. A better examination of the differential isentropic change shows that for p, v, T systems, there are three different isentropic exponents corresponding to each pair formed out of the variables p, v, T. These three exponents noted k_T,p, k_T,v, k_p,v after the corresponding pair of variables used, are interconnected by one relation, and accordingly only two out of the three are independent. The analysis of the present paper leads to the conclusion that calculations encountered in real gas isentropic change, with the exponent k taken as the ratio of the local specific heat values may lead to incorrect results. The numerical values of these exponents for steam, have been calculated and are presented. It can be seen that the deviations obtained, in comparison to the use of conventional k=c_p/c_v values are considerable.     

The normal shock waves of real gases and the generalized isentropic exponents

When a supersonic gas flow is choked or otherwise disturbed, a shock wave appears. When this shock wave is perpendicular to the direction of the one-dimensional flow, a normal shock wave transforms the flow to a subsonic one. The thermodynamic variables involved are five, i.e. the pressure, the specific volume, the temperature, the enthalpy and the velocity of the flow. To determine their values after the normal Shock, five relations are used namely the equation of state, the enthalpy equation, the laws of conservation of impulse and energy, and the continuity of mass. For the simple case of a perfect gas, these relations are explicit and allow a straightforward solution of the system of the five equations. In the case of a real gas flow the system is solved numerically. The present work considers two other possibilities, i.e. the use of perfect gas like equations describing the phenomenon or the use of the Redlich-Kwong equation of state. Perfect gas like equations may be used now, to describe the phenomenon, after it has been shown that there exist three isentropic exponents, instead of the one used until now, and after it has been observed that the mathematical form of the perfect gas equations fit the real gas isentropic expansion when suitable numerical values of the corresponding constants and exponents are used. The other possibility, the use of the Redlich-Kwong equation of state, allows the calculation of the state variables after the normal shock when only the two constants of this equation and the specific heat of the corresponding perfect gas state (pressure approaching zero) are available. Both methods presented here require the numerical solution of a onevariable equation. In the first method the variable is the Mach number while in the second the specific volume.     

Relaxation properties of non-equilibrium wet steam flows

Internal relaxation processes in wet steam flows through channels and nozzles are analysed basing on derived general equations describing non-equilibrium wet steam processes. Characteristic relaxation distances for single-deviation processes are determined and their application is discussed. As a synthetic intensity measure of complex multi-parameter processes a concept of entropy relaxation distance is introduced. Calculation methods of wet steam relaxation processes and thermodynamic loss determination are presented.     

Isentropic exponent and characteristic quantities of wet steam

Wet steam thermal processes with maintained saturation (equilibrium) conditions are analyzed with account taken of the qualitative and quantitative influence of capillary effects. General expressions for the determination of the isentropic exponent, specific heat and latent heat and enthalpy of evaporation are derived and calculation results of these quantities are presented.     

Electrical measurement of droplet sizes in fast-flowing wet steam

A new method has been developed for determining droplet sizes that extends the range of the Wicks-Dukler method. Experimental results are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 5, pp. 841–846, May, 1979.     

The normal and oblique impact of three types of wet granules

Impact tests against a hardened steel plate have been carried out to obtain the coefficient of restitution of three types of spherical granules. The dominant elastic γ-Al₂O₃, the elastic-plastic zeolite 4A and the dominant plastic sodium benzoate have been chosen as granule samples. An electromagnetic canon has been constructed to accelerate the granules and to measure the normal coefficient of restitution. The moisture content of the granules has been varied so that the pore saturation ranges between of S = 0–1. Thereby, the influence of the moisture content on the normal coefficient of restitution could be determined. A free fall apparatus, on which the impact angle is changeable in the range of Θ_A = 0–80°, has been used to investigate the tangential coefficient of restitution. A high speed digital camera has been used to record the events of impact and rebound. The record frequency of the camera has been varied between 4,000 and 8,000 frames per second.     

Liquid film and droplet stability consideration as applied to wet steam flow

The state of art and ongoing research concerning the flow of wet steam in large steam turbines is reviewed, particularly from the viewpoint of the behavior of the liquid film deposited upon the stationary blading. New experimental results concerning the non-steady behavior of the film and the resultant wavelet formation patterns under the action of high-velocity low-pressure steam flow are presented. These results are then correlated as a flow regime “map” showing various flow regions in terms of steam velocity (or relative steam-film velocity since film velocity is relatively very small) vs. film flow rate per unit transverse distance. The distribution of liquid droplets shed from the blade trailing edge in the wake are studied as a function of distance downstream, steam velocity, and liquid film flow rate. In addition the droplet size is correlated in terms of critical droplet Weber number and compared with results of previous investigators. High-speed photographs of droplet distortions in a high-velocity air stream are also included.     

Using the isentropic index to calculate the parameters of two-phase flow

A method of determining the volume vapor content in two-phase mixture is proposed, on the basis of the relation between the isentropic index of the mixture and the frozen sound velocity there.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 5, pp. 756–762, November, 1989.     

Air-side performance evaluation of three types of heat exchangers in dry,wet and periodic frosting conditions

The performances of three types of heat exchangers that use the louver fin geometry: (1) parallel flow parallel fin with extruded flat tubes heat exchanger (PF²), (2) parallel flow serpentine fin with extruded flat tubes heat exchanger (PFSF) and (3) round tube wave plate fin heat exchanger (RTPF) have been experimentally studied under dry, wet and frost conditions and results are presented. The parameters quantified include air-side pressure drop, water retention on the surface of the heat exchanger, capacity and overall heat transfer coefficient for air face velocity 0.9, 2 and 3 m/s, air humidity 70% and 80% and different orientations. The performances of three types of heat exchanger are compared and the results obtained are presented. The condensate drainage behavior of the air-side surface of these three heat exchanger types was studied using both the dip testing method and wind tunnel experiment.     

Lyapunov exponents and the evolution of normals

Differential equations are derived which determine the smallest Lyapunov exponents. These o.d.e. arise from relationships describing the evolution of normal tensors associated with the subspaces of an n-dimensional Euclidean phase space. The derived equations are an expression in E_n of relationships in E₃ arising in continuum kinematics. Numerical studies indicate their utility.     

Recent theoretical estimates of the critical exponents

It is shown that the latest estimates of the critical exponents obtained by different methods can be represented as fractions: =1/32 and v=17/27. New formulas are given which reproduce the values of the critical exponents for systems with various dimensionalities and numbers of order parameters.Translated from Inzhe-nerno-Fizicheskii Zhurnal, Vol. 51, No. 5, pp. 758–764, November, 1986.     

PAN原丝性能对比及对碳纤维性能的影响研究

对采用不同的纺丝方法即湿法和干湿法纺制的原丝及碳纤维的性能结构进行对比,结果表明,由干湿法纺制的原丝以及最终生成的碳纤维的性能要优于由湿法纺制的原丝以及碳纤维的性能。     

Ideal gas relations for the description of the real gas isentropic changes

Using the best available relations describing the thermal and caloric behaviour of the media H₂O, air, NH₃ and of the refrigerants R12 and R22, numerous isentropic expansions starting at different initial points, have been computed. The results obtained were approximated by explicit relations having mathematical forms similar to those of the ideal gas but with different constants and exponents. The obtained accuracy is remarkable, being for the most cases better than 0.5% and in any case better than 3%. In this way the isentropic change, of the above mentioned media, can be computed by simple explicit relations having as independent variable the Mach number. Considering all the above media, the following general rules can be traced. The specific volume, reduced by the corresponding value of the stagnation point, up to a Mach number of less than 0.7, follows a parabolic law common to all gases considered. The reduced pressure, in the transonic region 0.7≦M≦1.3, has a nearly linear decrease, having a slope, common to all media, and equal to about ?0.605. The reduced nozzle cross-sectional area, for M≦1,2 has a common form given by the relation F^*/F=?0.034+M(2.04?M). The values of the constants and exponents used in the relations cannot be derived from the k _id =C_p/C_v values since they are all the three different isentropic exponents k_p,v, k_T,v and k_p,T involved and further since the true sound velocity α is given by the relation α=(zk_p,v RT)^1/2 and is not approximated by the ideal gas sound velocityα _id=(k _id RT)^1/2.     

变面积孔板流量计在蒸汽计量中的应用

变面积孔板是一种新型差压式流量计,范围度宽,可测范围100：1,测量准确度高,精确度±1％,尤其适合蒸汽计量使用。     

稠油油藏蒸汽驱阶段汽窜的研究

本文分析了稠油油藏蒸汽驱汽窜情况及其成因，研究了一些防汽窜的措施，提出了在蒸汽驱阶段利用循环转注方式生产有望延缓汽窜的发生并提高蒸汽总体波及体积和最终采收率。     

湿法纺丝条件对临界凝固时间的影响

以聚丙烯腈-二甲基亚砜-水体系为研究对象,通过建立数学模型,对聚丙烯腈湿法纺丝凝固的初期阶段进行研究。借助MATLAB软件,采用有限元法对数学模型进行求解。利用数学模型考察纺丝条件对纺丝液临界凝固时间的影响。结果表明:(1)凝固浴浓度在一定程度上决定凝固进程;纺丝液临界凝固时间随凝固浴浓度升高而增加,且增加的趋势是越来越快,当浓度大于60%尤为明显;(2)纺丝液临界凝固时间随纺丝液中水含量的增加而减小,使纺丝液凝固时发生瞬时相分离的趋势增大;(3)随着喷丝孔直径的增加,纺丝液临界凝固时间会延长。