The mean condensate heat resistance of dropwise condensation with flowing inert gases

The quantification of the condensate heat resistance is\ud studied for dropwise condensation from flowing air-steam\ud mixtures. Flows are essentially laminar and stable with gas\ud Reynolds numbers around 900 and 2000. The condensate shaping\ud up as hemispheres on a plastic plane wall and the presence\ud of inert gases make it possible that thermocapillary convection\ud occurs making the resistance less than the mean condensate\ud thickness (ca. 0.185 mm) divided by the heat conduction coefficient.\ud The analysis of experiments shows that the effective\ud mean condensate resistance might indeed be less, by a factor of\ud 0.8+0.2. The analysis takes account of the sensible heat transfer\ud which may be as large as 35% of the total heat transfer if inlet\ud vapor concentration, cin, is low (ca. 0.07). A method is presented\ud to determine the gas-condensate interface temperature,\ud ti, that is needed in the analysis of the heat resistance. The\ud highest temperature differences (t i- tw), t w being the mean\ud temperature of the condenser plate at the gas side, have been\ud found to occur for relatively high values of Cin (ca. 0.3)

Heat transfer, condensation and fog formation in crossflow plastic heat exchangers

In this paper heat transfer of air-water-vapour mixtures in plastic crossflow heat exchangers is studied theoretically and experimentally. First, a model for heat transfer without condensation is derived, resulting in a set of classical differential equations. Subsequently, heat transfer with wall condensation and fog formation are considered in some detail. Separate attention is paid to the heat transfer and condensation of pure steam in the heat exchanger. Finally, the experiments performed are reported and the results compared with the models presented. From this comparison it can be learnt that the models are well able to predict the rate of heat transfer and phenomena such as condensation and fog formation

The effect of phase transitions on the droplet size distribution in homogeneous isotropic turbulence

We investigate the dynamics of an ensemble of discrete aerosol droplets in a homogeneous, isotropic turbulent flow. Our focus is on the stationary distribution of droplet sizes that develops as a result of evaporation and condensation effects. For this purpose we simulate turbulence in a domain with periodic boundary conditions using pseudo-spectral discretization. We solve in addition equations for the temperature and for a scalar field, which represents the background humidity against which the size of the droplets evolves. We apply large-scale forcing of the velocity field to reach a statistically steady state. The droplets are transported by the turbulent field while exchanging heat and mass with the evolving temperature and humidity fields. In this Euler-Lagrange framework, we assume the droplets volume fraction to be sufficiently low to allow one-way coupling of the droplets and turbulence dynamics. The motion of the droplets is time-accurately tracked. The Stokes drag force is included in the equation of motion of the individual droplets. The responsiveness of the droplets to small turbulent scales is directly related to the size of the individual spherical droplets. We perform direct numerical simulation to ultimately obtain the probability density function of the evolving radius of the droplets at different points in time with characteristic heat and mass transfer parameters. We determine the gradual convergence of the distribution function to its statistically stationary state for forced homogeneous, isotropic turbulence

Forces on a boiling bubble in a developing boundary layer, in microgravity with g-jitter and in terrestrial conditions

Terrestrial and microgravity flow boiling experiments were carried out with the same test rig, comprising a locally heated artificial cavity in the center of a channel near the frontal edge of an intrusive glass bubble generator. Bubble shapes were in microgravity generally not far from those of truncated spheres,which permitted the computation of inertial lift and drag from potential flow theory for truncated spheres approximating the actual shape. For these bubbles, inertial lift is counteracted by drag and both forces are of the same order of magnitude as g-jitter. A generalization of the Laplace equation is found which applies to a deforming bubble attached to a plane wall and yields the pressure difference between the hydrostatic pressures in the bubble and at the wall, p. A fully independent way to determine the overpressure p is given by a second Euler-Lagrange equation. Relative differences have been found to be about 5% for both terrestrial and microgravity bubbles. A way is found to determine the sum of the two counteracting major force contributions on a bubble in the direction normal to the wall from a single directly measurable quantity. Good agreement with expectation values for terrestrial bubbles was obtained with the difference in radii of curvature averaged over the liquid-vapor interface, (1/R2 − 1/R1), multiplied with the surface tension coefficient, σ. The new analysis methods of force components presented also permit the accounting for a surface tension gradient along the liquid-vapor interface. No such gradients were found for the present measurements

Optical-thermal mathematical model for endovenous laser ablation of varicose veins

Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45 % of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95°C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104°C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures

Topological vs. lexical determination in English particle verbs (PVs)

Autor/s Renata GeldUniversity of Zagreb, Croatia   ABSTRACT The central aim of this work is to describe semantic determination, i.e., topological vs. lexical determination, by investigating aspects of construal (Langacker 1987) in English PVs with in and out. The paper focuses on L2 processing related to what we might call strategic thinking about linguistic meaning. More specifically, it attempts to demonstrate the following: a) how the nature of verbs affects the overall semantic determination of particle verb constructions, and b) if/how the users of English make sense of particle verbs, and how much they rely on topological/grammatical components in the process of constructing meaning. The results suggest that the nature of verbs does affect the users’ strategic meaning construal – it differs in terms of their tendency towards one of the following types of semantic determination: a) topological, b) lexical, and, c) compositional.Author/s Renata GeldUniversity of Zagreb, Croatia   ABSTRACT The central aim of this work is to describe semantic determination, i.e., topological vs. lexical determination, by investigating aspects of construal (Langacker 1987) in English PVs with in and out. The paper focuses on L2 processing related to what we might call strategic thinking about linguistic meaning. More specifically, it attempts to demonstrate the following: a) how the nature of verbs affects the overall semantic determination of particle verb constructions, and b) if/how the users of English make sense of particle verbs, and how much they rely on topological/grammatical components in the process of constructing meaning. The results suggest that the nature of verbs does affect the users’ strategic meaning construal – it differs in terms of their tendency towards one of the following types of semantic determination: a) topological, b) lexical, and, c) compositional.Autor/es Renata GeldUniversity of Zagreb, Croatia   ABSTRACT The central aim of this work is to describe semantic determination, i.e., topological vs. lexical determination, by investigating aspects of construal (Langacker 1987) in English PVs with in and out. The paper focuses on L2 processing related to what we might call strategic thinking about linguistic meaning. More specifically, it attempts to demonstrate the following: a) how the nature of verbs affects the overall semantic determination of particle verb constructions, and b) if/how the users of English make sense of particle verbs, and how much they rely on topological/grammatical components in the process of constructing meaning. The results suggest that the nature of verbs does affect the users’ strategic meaning construal – it differs in terms of their tendency towards one of the following types of semantic determination: a) topological, b) lexical, and, c) compositional

The Nature and Role of Cognitive Agility

Cognitive agility is an underresearched, formative cognitive construct that is believed to include other cognitive constructs, namely, cognitive flexibility, focused attention, and openness to experience. In this article, the construct of cognitive agility is explored through the lenses of its formativity, as well as potentially overlooked elements of the construct that are yet to be researched in the future. We also discuss other cognitive constructs, such as cognitive adaptability, whose cognitive structure and characteristics are like those of cognitive agility, yet they are defined and described as separate constructs. Furthermore, we propose an in-depth investigation of the role of personal experience in the context of one’s cognitive agility development. Finally, since the construct itself belongs to the domains of human performance and development, we discuss practical uses of cognitive agility training. The paper addresses past research results applied in a military setting in the context of establishing training and development programs for cognitive agility as well as possibilities of such developments in other areas of human activity, such as professional motorsport