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Among lattice configurations of densely packed hard ellipses, Monte Carlo simulations are used to identify the so-called parallel and diagonal lattices as the two favorable states. The free energies of these two states are computed for several system sizes employing the Einstein crystal method. An accurate calculation of the free energy difference between the two states reveals the parallel lattice as the state with the lowest free energy. The origin of the entropic difference between the two states is further elucidated by assessing the roles of the translational and rotational degrees of freedom. [ABSTRACT FROM AUTHOR]

The increase in heat generated by electronic components requires a need to expand the range of two-phase heat exchangers for thermal stabilization of the components. The efficiency of the two-phase systems (heat pipes, steam chambers) can be improved by using metal-fiber capillary-porous structures. Experimental studies for the conditions close to the operating conditions of heat pipes and vapor chambers described in known publications are rather incomplete. The aim of this study is to determine the boundary heat fluxes for water boiling on porous structures under capillary soaking, to investigate the influence of saturation pressure and structural parameters on the boundary heat fluxes, and to determine the optimal structural parameters of porous samples, i.e. such parameters that would allow the highest possible values of critical heat fluxes under given conditions. The authors investigate 0.3 and 0.5 mm thick capillary structure samples made of copper fibers with a diameter of 10 to 50 μm and a porosity range of 65—85%. The study has found that reducing the saturation pressure from 0.1 to 0.012 MPa leads to a decrease in the boundary heat flux values by 15—40%, depending on the effective pore diameters. The study allowed establishing that the maximum heat flux values are achieved for the samples with an effective pore diameter of 60 to 80 μm. It was also found that for the 0.5 mm thick samples, the boundary heat fluxes are 5—20% higher than for the 0.3 mm thick samples. The decrease in saturation pressure has been found to lead to a decrease in the range of two-phase heat exchange systems. For a number of samples, the authors have obtained the optimal effective pore diameters ensuring the highest critical heat flux values in the studied range.

Currently, thermosyphons are used to cool such devices as power amplifiers of radio frequency systems, data center hardware, LED light sources, etc. One of the important factors affecting the efficiency of such cooling systems is the orientation of the thermosyphons in space. This paper is dedicated to research and visualization of vaporization events in two-phase thermosyphons, primarily focusing on investigating and visualizing the influence of orientation in space on vaporization. The studies were performed for100% fill ratio. Vaporization was video recorded at 240 frames per second, whereupon the obtained footage was converted into image sequence. The analysis of the obtained materials has shown that at intensive boiling for tilt angle range of 5—45°, a part of the working fluid is always outside the evaporator. When the angle is decreased, the portion of the working fluid outside the evaporator increases. Moreover, for the 5° tilt angle, the evaporator can be completely drained at certain time intervals. It is proposed that the thermal resistance at low heat flux values for smaller tilt angles can be lower than for vertical orientation because of thin liquid films. Evaporation is more effective in thin liquid films than in large volumes. This prompts the conclusion that smaller angles will allow obtaining lower thermal resistance for the same filling ratio. On the other hand, maximum heat transfer ability decreases dramatically for the angle range of 0—10°. The obtained results can be used in further studies to analyze and explain the aspects of heat transfer in two-phase thermosyphons with a short evaporator.

The paper presents the experimental results on the permeability of metal felt capillary-porous structures with a fiber diameter of 10—50 μm at porosity values from 57% to 90% when the fluid filtration occurs along the felt plane. It is determined that the permeability depends on the geometric parameters of the capillary structure (fiber diameter), porosity and direction of fluid filtration. In previous permeability studies, no attention was paid to the direction of fluid movement in the capillary structure. It was believed that the metal felt structure is isotropic and the permeability was studied for cross-fiber filtration. In reality, unlike regular capillary structures (powder), metal felt structures are anisotropic and their characteristics depend on the direction of fluid filtration. In heat pipes, the capillary structure fibers are mostly positioned parallel to the axis of the pipe, and thus the fluid moves from the condensation zone to the evaporation zone along the fibers. It was shown that at a porosity of 55—70%, the value of permeability does not depend on the direction of filtration. In the porosity range from 70% to 90%, error can exceed 50%. In this porosity range, the permeability value at cross-fiber filtration significantly exceeds the permeability value at longitudinal filtration. This proves that the calculation relations for determining the permeability coefficients of metal felt capillary-porous structures obtained for cross-fiber filtration cannot be used to calculate heat pipes. Analyzing the results and processing the obtained experimental data allowed proposing an empirical dependence that generalizes the data with an error of up to 20% in the whole range of the studied porosity values. The research results can be used to design heat pipes with maximum heat transfer characteristics for cooling electronics.

In an effort to illuminate the general principles governing the critical behavior of model fluids, we investigate in this study how the shape and the (attractive) interaction range of the molecule affect the gas–liquid equilibrium and the critical behavior of the system. A combination of Monte Carlo simulations and analytical theory is employed to compute critical properties, i.e., temperature and density, of a system of hard-core ellipses with an attractive square-well potential in two-dimensional space. The critical temperature is found to decrease monotonically as the asphericity of the molecule is increased. This trend can be successfully explained in terms of the strength of the effective attraction acting between molecules measured, for instance, by the second virial coefficient. The critical density shows a complex dependence on both the range of attraction and the asphericity of the molecule. We find that the properties of particle clusters formed in near-critical states reproduce some of the most important features of the critical density, including multiple minima and maxima. It is shown that a model based on the extent of the overlap between attractive shells surrounding the ellipses captures the variation of the size of the clusters. Based on the obtained results, we discuss implications of varying the shape of the attraction potential for critical density. [ABSTRACT FROM AUTHOR]

The paper describes features of the design and manufacturing technology of a volumetric detachable heat flow imitator designed for the study of thermal characteristics and for carrying out thermal tests of heat pipes of cooling systems for electronic equipment. The authors use thin alumina ceramic plates with deposited with diamond-like films as heating elements of the imitator. Experimental results are presented on the surface temperature of heating elements and the temperature drop between the heating elements and the heat pipe in the region of the input heat flux values from 5 to 25 W. The use of the proposed heat flow imitator allows speeding up the process of research and testing of heat pipes.

Aluminium and copper heat pipes with grooved and metal fibrous capillary structure are high effective heat transfer devices. They are used in different cooling systems of electronic equipment like a LED modules, microprocessors, receive-transmit modules and so on. However thus heat pipes have heat transfer limitations. There are few types of this limitations: hydraulic limitation, boiling limitation, liquid entrainment by vapor flow and sonic limitation. There is necessity to know which one of these limitations is determinant for heat pipe due to design process. At a present article calculations of maximum heat transfer ability represented. All these calculations were made for LED cooling by using heat pipes with grooved and metal fibrous capillary structures. Pentane, acetone, isobutane and water were used as a coolants. It was shown that the main operation limit for axial grooved heat pipe, which determinate maximum heat transfer ability due to inclination angle for location of cooling zone higher than evaporation zone case, is entrainment limit for pentane and acetone coolants. Nevertheless, for isobutane coolant the main limitation is a boiling limit. However, for heat pipes with metal fibrous capillary structure the main limitation is a capillary limit. This limitation was a determinant for all calculated coolants: water, pentane and acetone. For high porosity range of capillary structure, capillary limit transfer to sonic limit for heat pipes with water, that means that the vapor velocity increases to sonic velocity and can't grow any more. Due to this, coolant cant in a needed quantity infill condensation zone and the last one drained. For heat pipes with acetone and pentane, capillary limit transfer to boiling limit. All calculations were made for vapor temperature equal to 50°C, and for porosity range from 30% to 90%.

In this study, Boltzmann inversion is applied in conjunction with molecular dynamics simulations to derive inter-molecular potential for protein lysozyme in aqueous solution directly from experimental static structure factor. The potential has a soft repulsion at short distances and an attraction well at intermediate distances that give rise to the liquid-liquid phase separation. Moreover, Gibbs ensemble Monte Carlo simulations demonstrate that a non-spherical description of lysozyme is better suited to correctly reproduce the experimentally observed properties of such a phase separation. Our findings shed new light on the common problem in molecular and cell biology: "How to model proteins in their natural aqueous environments?". [ABSTRACT FROM AUTHOR]

Based on the quantum-chemical method of molecular orbitals, implemented in the Gaussian 09w software package, a method of modelling nanocomplexes for creation of antitumour and anti-inflammatory medicines is developed. The object of study is a complex of C60 fullerene and antitumour agent 1-(4-C1-benzyl)-3-C1-4-(CF3-phenylamino)-1H-pyrrole-2,5-dione (abbreviated as MI-1). Each detached part, C60 and MI-1, has a therapeutic effect. The main antitumour and anti-inflammatory action relies on MI-1 compound. It is found that the nanocomplex of C60 fullerene with MI-1 is stable at human-body temperature. The nanocomplex is able to serve as a vehicle of medicines to the tumour tissue and dissociate in the tumour due to its low pH (higher acidity) compared to healthy tissue and exhibit therapeutic properties of individual components. [ABSTRACT FROM AUTHOR]

Using the density functional theory to quantum-mechanical calculations in the Gaussian 09w software package, antitumor drug of target action on the basis of titanium dioxide and pyrrole derivative 1-(4-Cl-benzyl)-3-Cl-4-(CF3 - fenylamino)-1H-pyrrol-2.5-dione (chemical compound MI-1) is simulated. MI1 compound has high therapeutic potential as an antitumor agent. Titanium dioxide is insoluble in the stomach and used as a filler and sheath of medicines. There is reason to use TiO2 to transport MI-1 to the site of the affected tissue for targeted effect on colorectal tumours. Computational tools of the software package reveal that titanium dioxide TiO2 together with MI-1 forms a stable nanocomplex. Upon penetration into the tumour tissue, due to the low pH in comparison with healthy tissue, a significant proportion of these nanocomplexes will be dissociate with the separation titanium dioxide and MI-1 compound that will be have a therapeutic effect on damage tissue. [ABSTRACT FROM AUTHOR]