Thermohydrodynamics

In spite of the progress described above, certain fundamental problems in flow and heat transfer are still unclear. This leads to difficulties in understanding the essence of micro-thermohydrodynamic phenomena. 

For a while now, the problem of flow and heat transfer in heated capillaries has attracted attention from a number of research groups, with several applications to engineering. The knowledge of the thermohydrodynamic characteristics of capillary flow with evaporative meniscus allows one to elucidate the mechanism of heat and mass transfer in porous media, to evaluate the efficiency of cooling system of electronic devices with high power density, as well as to optimize MEMS. 

As already mentioned, the system ofEqs. (8.1-8.5) is supplemented by the Clausius-Clapeyron equation, as well as by the correlation that determines the dependence of enthalpy on temperature and describes the thermohydrodynamical characteristics of flow in a heated capillary. It is advantageous to analyze parameters of such flow to transform the system of governing equations to the form that is convenient for significant simplification of the problem. 

Morris SJS (2003) The evaporating meniscus in the channel. J Fluid Mech 494 297-317 Peles YP, Yarin LP, Hetsroni G (2000) Thermohydrodynamic characteristics of two-phase flow in a heated capillary. Int J Multiphase Flow 26 1063-1093 Peles YP, Yarin LP, Hetsroni G (2001) Steady and unsteady flow in a heated capfllary. Int J Multiphase Flow 27 577-598... 

Two-phase flows in micro-channels with an evaporating meniscus, which separates the liquid and vapor regions, have been considered by Khrustalev and Faghri (1996) and Peles et al. (1998, 2000). In the latter a quasi-one-dimensional model was used to analyze the thermohydrodynamic characteristics of the flow in a heated capillary, with a distinct interface. This model takes into account the multi-stage character of the process, as well as the effect of capillary, friction and gravity forces on the flow development. The theoretical and experimental studies of the steady forced flow in a micro-channel with evaporating meniscus were carried out by Peles et al. (2001). These studies revealed the effect of a number of dimensionless parameters such as the Peclet and Jacob numbers, dimensionless heat transfer flux, etc., on the velocity, temperature and pressure distributions in the liquid and vapor regions. The structure of flow in heated micro-channels is determined by a number of factors the physical properties of fluid, its velocity, heat flux on... 

The thermohydrodynamic characteristics of the flow in the heated micro-channels depend on the following factors the heat flux on the wall, which determines the intensity of the vaporization, the location of the meniscus, the difference between the inlet and outlet pressures, the capillary, and mass and friction forces which act on the liquid and vapor. 

In this section we present the system of quasi-one-dimensional equations, describing the unsteady flow in the heated capillary tube. They are valid for flows with weakly curved meniscus when the ratio of its depth to curvature radius is sufficiently small. The detailed description of a quasi-one-dimensional model of capillary flow with distinct meniscus, as well as the estimation conditions of its application for calculation of thermohydrodynamic characteristics of two-phase flow in a heated capillary are presented in the works by Peles et al. (2000,2001) and Yarin et al. (2002). In this model the set of equations including the mass, momentum and energy balances is ... 

The flow and heat transfer in heated micro-channels are accompanied by a number of thermohydrodynamic processes, such as liquid heating and vaporization, boiling, formation of two-phase mixtures with a very complicated inner structure, etc., which affect significantly the hydrodynamic and thermal characteristics of the cooling systems. 

Safety concerns about such thermohydrodynamic instabilities were raised after a rather unexpected occurrence of oscillations in the core of the LaSalle County Nuclear Station in 1988 (Phillips, 1990), following recirculation pump trips. Quite a large relative amplitude of oscillations was reached during that event, and the reactor was finally tripped from a high flux signal (Yadigaroglu, 1993). The safety... 

Vernier, P, and J. M. Delhaye, 1968, General Two-Phase Flow Equations Applied to the Thermohydrodynamics of BWR s, Centre d Etudes Nucleaires de Grenoble, Service des Transports Thermiques Also see Energie Prmtaire 4( ). (3)... 

If all detonations were "ideal , their mechanisms would be the same as described in hydrothermodynamic theory of detonation. This mechanism is described by Cook (1958) in Chapter 4 entitled Thermohydrodynamic Theory and Mechanism of Detonation , pp 61-90. He also described the mechanism of detonation in University of Utah Technical Report No XLl, Nov 15, 1954... 

The streak camera viewed the chge upward thru a periscope in which the line of sight was reflected to a horizontal direction by a front surface mirror. Measurements of the peak pressures by the aquarium technique were found to be the C-J or detonation pressures of the thermohydrodynamic theory... 

Detonation Processes Properties of Explosive Affecting Them. This is a very broad subject and might include Chapman-Jouguet parameters (See Table under "Detonation, Chapman-Jouguet Parameters in ), thermohydrodynamic properties, brisance, density, power or strength, pressure of detonation, temperature of detonation, sensitivity to impact, sensitivity to initiation and detonation velocity... 

Schweikert s theory differs radically from the conventional thermohydrodynamic Chapman-Jouguet theory in that it provides for a continuous transition from burning to deton. In Section I entitled "Introduction , the author criticizes the validity of the C-J theory for condensed expls. In Section II the burning rate constants of a colloidal propint are related to fundamental parameters such.as specific surface vol of the powd, the most probable molecular vel, and the collision efficiency c. Schweikert arrives in Section III at the conclusion that burning deton differ primarily in the magnitude of c i.e. c l in a deton and is a much. smaller value in a burning process A surprisingly simple relation is derived in Section IV for the upper boundary of the deton vel Dm of a condensed expl ... 

Hydrothermodynamic (or Thermohydrodynamic) Theory of Detonation. See further in this Section and in Refs 32, 39 (pp 87-8), 55a 93... 

Hydrodynamic theory, strictly speaking, considers only fluid motion, whereas hydrothermodynamic (called thermohydrodynamic by Cook) Theory considers also heat effects. One might say that the hydrodynamic theory is based on the laws enumerated in treaties on fluid mechanics , or hydrodynamics , such as in the books 1) R.H. Sabersky A.J. Acosta,... 

Tables of thermodynamic data necessary to apply equations listed by Cook are given in Appendix II of his book. The complete solution of the thermohydrodynamic theory for condensed explosives may then be effected in principle by a simultaneous solution of eqs...

Definition of deton, expln de-flgrn) 44-8 (Ideal deton) 48-50 (Nonideal deton) 50-7 (Transient and unstable deton waves) 57-60 (The jumping deton) 61-90 (Thermohydrodynamic theory of deton) 61-6 (Equation of state in deton of condensed expls) 66-8 (The Chapman-Jouguet postulate) 68-75 (The deton reaction zone in gases) 75-7 (Reaction zone in nonideal deton in gases) 77-9 (Reaction zone in condensed expls) 79-87... 

The velocity of ideal deton is completely determined by the thermohydrodynamics of the explosive, with.the independent variables being the original density p of the expl and its chem compn, all quantities being calculable, at least in principle, thru the thermohydrodynamic theory and an apppropriate equation of state. For each given ideal explosive, velocity. is a function only of the original density, i.e., D=D(p ), but three fundamentally different types of D(p ) relations have been found in ideal deton. The most common is the linear D(p ) relation characteristic of solid C-H-N-0 expls at densities... 

As already mentioned, thermohydrodynamics, the ideal gas law, and Eqns (2) or (4) can be used to compute vj for condensed expls at very low packing densities. Examples of this as computed by the writer from the results of Stesik Shvedova (Ref 5) are shown in Table 2... 

Of great importance to the thermohydrodynamic interpretation of detonation phenomena (see Refs 11,15 18) is the equilibrium sound velocity, c. For a perfect gas ... 

Thermohydrodynamic Theory of Detonation. See under Hydrodynamic and Hydrothermo-dynamic Theories of Detonation in Vol 4, D610-L to D619-L sulfuric acid with mixed acid (2 vols of 90—95% nitric acid to 1 vol of coned sulfuric acid) at 0-5° Refs 1) Beil 27,15, [9 207] 2) H.v. Bobo B. Prijs, Helv 33, 306-13 (1950) CA 44, 5872 (1950) 3) S. Vicon A. Taurius, CanJ-... 

TG = thermogravimetry 98 TG = Trotil-Gheksogen = TNT/RDX mixtures (russian) theorie hydrodynamique de la detonation = thermohydrodynamic theory of detonation 80 ff. thermic differential analysis 98 thermische Sensibilitat = heat sensitivity 165 thermites 315... 

Arastoopour, H., and Gidaspow, D. Analysis of IGT pneumatic conveying data and fast fluidization using a thermohydrodynamic model, Powder Technology 22, 77 (1979). 

Such a simplification is possible through the introduction of a continuum mathematical description of the gas-solid flow processes where this continuum description is based upon spatial averaging techniques. With this methodology, point variables, describing thermohydrodynamic processes on the scale of the particle size, are replaced by averaged variables which describe these processes on a scale large compared to the particle size but small compared to the size of the reactor. There is an extensive literature of such derivations of continuum equations for multiphase systems (17, 18, 19). In the present study, we have developed (17, ) a system of equations for... 

We begin by positing a thermohydrodynamical equation for the lubricating layer, based on Penny et al. The primary hydrodynamic modelling assumption is the existence of a lubricating melt layer of thickness, / , below the skate blade. We create a time-dependent numerical model by solving the lubrication equation using finite-differences. 

In [300-302], thermohydrodynamic problems for non-Newtonian fluids were studied under the assumption that temperature varies along the walls of the tube (or channel) in this case, convective heat transfer plays an important role. It was assumed that the dependence of the apparent viscosity of the medium on temperature is exponential or power-law dissipative heat release was neglected. In one-dimensional steady-state flows of this type, the pressure gradient varies along the tube. It was shown that in some cases a situation typical of thermal explosion may arise. In this situation, heat supply due to fluid convection exceeds heat withdrawal through the walls. It was also discovered that there exists another mechanism for crisis phenomena to arise. If there is a constant heat withdrawal from the tube walls and the fluid velocity is sufficiently small, then the intensive cooling of the fluid may result in an accelerated increase of the fluid viscosity, which, in turn, results in flow choking. 

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