采用超声波特性参量研究PBX炸药的热处理

对压制成型Φ20mm×10mm高聚物粘结炸药PBX03试样进行了50℃条件下累积9天的热处理试验,采用超声波特性参量检测了热处理试样,获得了PBX03试样热处理作用及机理的新认识:PBX03试样的超声波增益和声速值在热处理过程中均呈现出趋同的特征;适当的热处理有助于改善PBX03压制件内部质量的一致性;PBX03中TATB的不可逆长大可能是前述结果的主要致因。     

Effect of cathode separator structure on performance characteristics of free-breathing PEMFCs

The performance of free-breathing polymer electrolyte membrane fuel cells (PEMFCs) was studied experimentally and the effect of the cathode separator structure on the cell performance was investigated. Two types of cathode separators were used for a cell with an 18 cm² active area: an open type with parallel rectangular open-slits and a channel type with straight vertical channels with open ends. The polarization curves, cell impedance, and contact pressure distribution of the separators were measured with each type of cathode structure. The result showed that it is difficult to realize a uniform contact pressure across the cell layers for the open type separator, and this results in higher contact resistance and poorer cell performance than the channel type separator. The channel type separator can maintain a low contact resistance, and the cell performance is strongly affected by the natural convection inside the channel. Optimization of the channel design of the channel type separator achieves good performance and this type of separator is superior for a free-breathing PEMFC. A computational three-dimensional analysis for the free-breathing channel type PEMFC with the different channel depths was performed, and it identified the influence of natural convection.     

Energy savings in retrofitted dwellings: economically viable?

Attempts to improve the energy performance in the residential sector mainly pay attention to new buildings. However, a decrease in energy consumption and greenhouse gas emissions will never occur if nothing is done to improve the existing energy devouring housing stock. This paper discusses economically feasible ways and means to choose between insulation measures, better glazing, installation measures and renewable energy systems such as solar collectors and PV cells. Finally a logical hierarchy of energy-saving measures is deduced from the results.     

Transient boiling crisis of cryogenic liquids

This paper introduces a new physical model of boiling crisis under rapid increase of power on the heated surface. The calculation of the time interval of the transition to film boiling in cryogenic liquids was carried out depending on heat flux and pressure. The obtained results are in good agreement with known experimental data.     

Transient thermal analysis of semitransparent composite layer with an opaque boundary

Transient coupled radiative and conductive heat transfer in a two-layer, absorbing, emitting, and isotropically scattering non-gray slab is investigated by the ray tracing method in combination with Hottel's zonal method. One outer boundary is opaque, and another is semitransparent. The radiative energy transfer process in a semitransparent composite is divided into two sub-processes, one of which considers scattering, the other does not. The radiative transfer coefficients of the composite are deduced under specular and diffuse reflection and combined specular and diffuse reflection, respectively. The radiative heat source term is calculated by the radiative transfer coefficients. Temperature and heat flux are obtained by using the full implicit control-volume method in combination with the spectral band model. The method presented here needs only to disperse the space position, instead of the solid angle. A comparison with previous results shows that the results are more accurate.     

Error in the numerical solution to the heat conduction problem with a nonlinear boundary condition

Concerning the heat conduction problem with a nonlinear boundary condition, as in the case of a boiling process, the effect of the time interval in the numerical solution scheme on the error of the solution is analyzed here.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.22, No. 5, pp. 894–898, May, 1972.     

Effect of hydrothermal treatment of coal on the oxidation susceptibility and electrical resistivity of HTT coke

The influence of hydrothermal treatment of coal prior to carbonization, on the oxidation susceptibility of resultant coke/char, calcined at 1350, 1800 and 2200 °C has been investigated. The non-isothermal thermogravimetric analysis technique has been employed, and parameters such as onset, DTG peak temperatures, and cumulative oxidation loss (wt.%) at different temperatures have been utilized to compare proneness to oxidation with respective untreated samples apart from electrical resistivity. Data suggest that all the cokes/chars samples produced from hydrothermally treated coals are less reactive and more electrically conductive (less resistive) than their respective untreated counterparts. But the extent of improvement of oxidation resistance and electrical conductivity appears to be coal-specific. The kinetic parameters obtained by non-linear regression analysis on multi-curve reveal that the n^th order reaction model (where ‘n’ was found to vary from 0.9 to 1.3) is the best-fitted model. The higher activation energy values observed for hydrothermally treated coke samples are in agreement with the observation of TG analysis data. Overall results indicate the importance of introducing a hydrothermal treatment step for the improvement of oxidation resistance as well as electrical conductivity of the coke samples.     

A new method for the measurement of solar collector time constant

A new test method about the time constant of the solar collector has been presented in this paper. It is simple and has been validated through experiments. With the new method it is not necessary to adjust the inlet temperature of the transfer fluid as closely as possible to the ambient air temperature. Also, it is not necessary to know the characteristic parameters of the collector in advance. The model used in the paper is a first order system model, as in most cases. The experimental data obtained from the test of solar collector time constant shows that the solar collector is not a strictly first order system. A criterion is proposed to decide whether the system is a first order system or not and the resemblance of the system to the first order system.     

Calculation of air-film cooling of a rotating disk

An analysis and generalization is made of experimental data on the effectiveness of film-cooling of a rotating disk.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 5, pp. 862–869, November, 1968.