Оценка тепловых потерь на фронте детонационной волны при движении вдоль металлической пористой поверхности

oai:oai.aerospace.elpub.ru:article/39The paper considers a computational technique of the heat flow from the hot products of detonation combustion into the porous coating and estimates the efficiency of the coating layer that results in slowing the flame front down with disregard the transverse displacement of the combustion products weight of a hydrogen-air mixture.Initial thermodynamic parameters of combustion products on the porous coating surface have been estimated. A drag (stagnation) temperature of flow was determined.The statement of task was to calculate the heat flow into the long cylindrical metal fiber with radius of 15 μm. The reference values of heat capacity and heat diffusivity were used to estimate a thermal diffusivity in a wide range of temperatures. An approximation of the parameters is given for a wide range of temperatures.The calculation algorithm using an explicit four-point scheme is presented. The convergence and accuracy of the results were confirmed. The theoretical estimation using cylindrical Bessel functions was made to prove the accuracy of the results.Total heat loss was estimated using the photos of moving detonation front and hot combustion gases.Comparison of the total heat loss and the amount of energy absorbed by a single fiber allowed us to find that the porous coating thickness, resulting in attenuation of detonation wave, is efficient.Рассматривается метод расчета теплового потока от горячих продуктов детонационного горения внутрь пористого покрытия, и оценка эффективного слоя этого покрытия, приводящего к замедлению фронта пламени в пренебрежении поперечного смещения массы продуктов горения водородно-воздушной смеси.Проведена оценка начальных термодинамических параметров продуктов горения на поверхности пористого покрытия. Определена температура торможения потока.Поставлена задача расчета теплового потока внутрь цилиндрического длинного металлического волокна радиуса 15 мкм. По справочным значениям теплоемкости и теплопроводности сделана оценка температуропроводности в широком диапазоне температур. Для удобства расчета параметров приведена аппроксимационная зависимость.Приведен алгоритм расчета с использованием явной четырехточечной схемы. Обоснована сходимость и достоверность результатов. Для подтверждения достоверности результатов была сделана теоретическая оценка с использованием цилиндрических функций Бесселя.С использованием фотографий движения фронта детонации и горячих продуктов сгорания проведена суммарная оценка тепловых потерь. На основе сравнения суммарных тепловых потерь и количества энергии, поглощенной одиночным волокном сделано заключение об эффективной толщине пористого покрытия, приводящей к затуханию детонационной волны

Experimental and numerical investigation of hydrogen gas auto-ignition

ABSTRACT This paper describes hydrogen self-ignition as a result of the formation of a shock wave in front of a high-pressure hydrogen gas propagating in the tube and the semi-confined space, for which the numerical and experimental investigation was done. An increase in the temperature behind the shock wave leads to the ignition on the contact surface of the mixture of combustible gas with air. The required condition of combustible self-ignition is to maintain the high temperature in the mixture for a time long enough for inflammation to take place. Experimental technique was based on a highpressure chamber inflating with hydrogen, burst disk failure and pressurized hydrogen discharge into tube of round or rectangular cross section filled with air. A physicochemical model involving the gasdynamic transport of a viscous gas, the detailed kinetics of hydrogen oxidation, k-ω differential turbulence model, and the heat exchange was used for calculations of the self-ignition of high-pressure hydrogen. The results of our experiments and model calculations show that self-ignition in the emitted jet takes place. The stable development of self-ignition naturally depends on the orifice size and the pressure in the vessel, a decrease in which leads to the collapse of the ignition process. The critical conditions are obtained

New User-Friendly Approach to Obtain an Eisenberg Plot and Its Use as a Practical Tool in Protein Sequence Analysis

The Eisenberg plot or hydrophobic moment plot methodology is one of the most frequently used methods of bioinformatics. Bioinformatics is more and more recognized as a helpful tool in Life Sciences in general, and recent developments in approaches recognizing lipid binding regions in proteins are promising in this respect. In this study a bioinformatics approach specialized in identifying lipid binding helical regions in proteins was used to obtain an Eisenberg plot. The validity of the Heliquest generated hydrophobic moment plot was checked and exemplified. This study indicates that the Eisenberg plot methodology can be transferred to another hydrophobicity scale and renders a user-friendly approach which can be utilized in routine checks in protein–lipid interaction and in protein and peptide lipid binding characterization studies. A combined approach seems to be advantageous and results in a powerful tool in the search of helical lipid-binding regions in proteins and peptides. The strength and limitations of the Eisenberg plot approach itself are discussed as well. The presented approach not only leads to a better understanding of the nature of the protein–lipid interactions but also provides a user-friendly tool for the search of lipid-binding regions in proteins and peptides

Evaluation of Heat Losses Behind the Front of the Detonation Moving Along the Metallic Porous Surface

The paper considers a computational technique of the heat flow from the hot products of detonation combustion into the porous coating and estimates the efficiency of the coating layer that results in slowing the flame front down with disregard the transverse displacement of the combustion products weight of a hydrogen-air mixture.Initial thermodynamic parameters of combustion products on the porous coating surface have been estimated. A drag (stagnation) temperature of flow was determined.The statement of task was to calculate the heat flow into the long cylindrical metal fiber with radius of 15 μm. The reference values of heat capacity and heat diffusivity were used to estimate a thermal diffusivity in a wide range of temperatures. An approximation of the parameters is given for a wide range of temperatures.The calculation algorithm using an explicit four-point scheme is presented. The convergence and accuracy of the results were confirmed. The theoretical estimation using cylindrical Bessel functions was made to prove the accuracy of the results.Total heat loss was estimated using the photos of moving detonation front and hot combustion gases.Comparison of the total heat loss and the amount of energy absorbed by a single fiber allowed us to find that the porous coating thickness, resulting in attenuation of detonation wave, is efficient

Detonation wave parameters in a variable cross section channel in gas mixture of methane with oxygen and nitrogen

Propagation of the detonation wave in gas mixtures of methane with oxygen in a channel of variable cross section was studied experimentally. To conduct these investigations a special detonation combustion chamber comprising sections of various diameters has been designed. In the section of detonation wave formation a combustible mixture was ignited. After that, a flame front accelerated till the formation of detonation. At the exit from the combustion chamber there was an outlet conical section. In conducted experiments the toe-in angle was equal to 3 °. The combustion chamber was open-ended. So an initial pressure inside the combustion chamber prior to each experiment was equal to the atmospheric pressure. The initial temperature was ambient one of 300 K. As a diagnostics, piezoelectric sensors of pressure and photo diodes were used.Detonation initiation was accomplished by spark gap. For this pulse generator I-1 was used. Spark energy did not exceed 0.1 J and was much lower than the energy of the direct initiation of detonation.Deflagration-to-detonation transition was occurred. A composition of the mixtures was selected in such a way that the detonation cell width was several times smaller than the diameter of the channel. The mixture was composed by the partial pressures of methane, oxygen, and nitrogen and was kept in the 40 l tank within 24 hours under 5-8 atm. pressure. Возникновение де- тонации возникало вследствие перехода горения в детонацию.The aim of this study was to determine the parameters of a detonation wave in a channel of variable cross section in the methane-oxygen mixture. The influence of nitrogen impurities on the cell size and the speed and pressure of the detonation wave was investigated.The waves velocities and peak pressures at the front of the detonation wave were measured depending on composition, including the presence of nitrogen. The sizes of the detonation cells were measured using smoked foil mounted inside the channel.The effect of the interference of the shock waves in a conical section was studied.Diagrams of the shock waves, flame fronts, and detonation waves in the combustion chamber depending on the mixture composition are presented. The paper gives data on some compositions of mixtures.</p