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The purpose of this paper is to present a novel approach on the process zone characterization for direct feedback regarding the state of vapour, in order to assure a better monitoring, control and understanding of the process.

Different pressure sensors were applied in an experimental vapour phase soldering (VPS) station, where the hardware setup was dedicated to the current experiments. Static and dynamic pressure values were analyzed and correlated with additional thermal measurements.

The results reveal the dynamics of the vapour blanket generation. The correlated measurements show different stages of the process initialization, highlighting better accuracy than sole temperature measurements of saturated vapour identification. It is possible to trace the height of the available saturated vapour blanket with static pressure measurements.

The VPS process may benefit from the more precise saturation detection, giving better control on the heat transfer, enabling more efficient production with the reduction of idle time, and resulting in better soldering quality.

Reducing the idle time of the VPS stations may result in better efficiency and smaller power consumption, reducing the environmental impact of the method.

The presented methods provide a completely novel approach from the aspect of process zone state variables and parameters characterization, focusing on pressure measurements.

To clarify the principles and mechanisms of water vapour transfer by diffusion in waterproof breathable fabrics for clothing, experiments using a simple glass dish were carried out under steady state conditions with and without a temperature gradient in the climatic chamber. It was found that both vapour pressure and natural convection within the air gap affect water vapour transfer. The rates of water vapour transfer are ranked microfibre fabrics, cotton ventiles, PTFE‐laminated fabrics, poromeric polyurethane laminated fabrics, hydrophilic laminated fabrics, and polyurethane‐coated fabrics. In the presence of a temperature gradient, condensation was also found to be a major factor, especially at air temperatures below 0°C. Condensation occurred the least on the inner surface of PTFE‐laminated fabrics followed by cotton ventiles, microfibre fabrics, hydrophilic‐laminated fabrics, poromeric polyurethane‐laminated fabrics, and polyurethane coated fabrics.

At the present time, green cutting has become the focus of attention in ecological and environmental protection. Water vapor is cheap, pollution‐free and eco‐friendly. Therefore, it is a good and economical coolant and lubricant. To find the discipline of nozzle diameter, the parameters of water vapor jet flow and cooling distance influence on its lubricating action effect, experiments were carried out in which YT15 (P10 type in ISO) tool was used in cutting C45 steel.

The vapor generator and vapor feed system are manufactured. The temperature and velocity distribution of water vapor jet flow influences the velocity such that water vapor fills up the capillaries and forms the boundary lubricating film layer in the cutting zone, and the temperature and velocity distribution of the vapor jet flow section contains the effective area for the lubricating effect. Through the temperature distribution measured, the empirical formula of temperature distribution is obtained and simulated by Matlab. The turning experiment was carried out according to quantity in cutting υ_c=45, 60, 75, 90, 105, 120 mm/min, f=0.1 ∼ 0.3 mm/rev, a_p=1, 2, 3, 3.5 mm and the jet flow parameters were changed, respectively.

It was found that: significant decrease of cutting force can be realized with reduced nozzle diameter, increased the sett pressure and shortened the cooling distance. However, reduced to a certain extent it will lead to the increase of the cutting force. The optimal nozzle diameter is 2 mm for the best lubricating effect. The effect on cutting force of the cooling distance is much better than the setting pressure. Significant decrease of friction coefficient of tool‐chip can be realized with reduced nozzle diameter. However, reduced to a certain extent it will lead to the increase of friction coefficient. Significant thinness of chips can be realized by reducing nozzle diameter. But if the diameter is reduced to a certain degree, chips will be thickened. Increased set pressure and shortened cooling distance can both reduce chip thickness, resulting in reduction of chip deformation coefficient. Since water vapor has the advantage of being cheap, pollution‐free and harmless, and there is no need for disposal and recycling, it is ideal for cooling and lubricating technology in green cutting.

The paper establishes the discipline of nozzle diameter, the parameters of water vapor jet flow and cooling distance influence on its lubricating action effect.

The first part of this article dealing with Degrees of Vacuum, Pump Design, Use of Cold Traps, etc., appeared in our October issue.

This paper focuses on the fluid-structure interaction (FSI) analysis of moisture induced stress for the flip chip ball grid array (FCBGA) package with hydrophobic and hydrophilic materials during the reflow soldering process. The purpose of this paper is to analyze the influence of moisture concentration and FCBGA with hydrophobic material on induced pressure and stress in the package at varies times.

The present study analyzed the warpage deformation during the reflow process via visual inspection machine (complied to Joint Electron Device Engineering Council standard) and FSI simulation by using ANSYS/FLUENT package. The direct concentration approach is used to model moisture diffusion and ANSYS is used to predict the Von-Misses stress. Models of Test Vehicle 1 (similar to Xie et al., 2009b) and Test Vehicle 2 (FCBGA package) with the combination of hydrophobic and hydrophilic materials are performed. The simulation for different moisture concentrations with reflows process time has been conducted.

The results from the mechanical reliability study indicate that the FSI analysis is found to be in good agreement with the published study and acceptable agreement with the experimental result. The maximum Von-Misses stress induced by the moisture significantly increased on FCBGA with hydrophobic material compared to FCBGA with a hydrophilic material. The presence of hydrophobic material that hinders the moisture desorption process. The analysis also illustrated the moisture could very possibly reside in electronic packaging and developed beyond saturated vapor into superheated vapor or compressed liquid, which exposed electronic packaging to higher stresses.

The findings provide valuable guidelines and references to engineers and packaging designers during the reflow soldering process in the microelectronics industry.

Studies on the influence of moisture concentration and hydrophobic material are still limited and studies on FCBGA package warpage under reflow process involving the effect of hydrophobic and hydrophilic materials are rarely reported. Thus, this study is important to effectively bridge the research gap and yield appropriate guidelines in the microelectronics industry.

FUEL quality not only has a very great influence on engine operation and maintenance, but it is also one of the most important factors controlling engine development. Gasolines used as internal‐combustion engine fuels possess many physical characteristics, each of which has some practical influence upon the operation and running of engines. The selection of the most suitable fuels for aircraft engines demands a knowledge of these fuel characteristics, which are discussed below.

This paper aims to gain a clear understanding of the ventilated cavity evolution around an NACA0015 hydrofoil by using both experimental and numerical investigation.

The bubble evolution around an NACA0015 hydrofoil with or without air injection was observed in a water tunnel, and the simulation was conducted using a modified turbulence model and homogeneous cavitation model.

The present simulation method can successfully predict the bubble evolutions around the NACA0015 hydrofoil with or without air injection. Air injection can alleviate the nature cavitation oscillation, and the suppression effect on nature cavitation depends on the air-entrant coefficient. It is confirmed that the air and vapor cavity have the same shedding frequency. It is seen that the air sheet closely attaches to the hydrofoil surface and is surrounded by the vapor sheet. Thus, the injected air promotes vapor growth and results in an increase in the cavity shedding frequency. Further, with a large air-entrant coefficient, the pressure fluctuation is suppressed completely.

The new simulation method is adopted to explore the mechanism of ventilated cavitation. The bubble evolutions with and without air injection have been comprehensively studied by experimental and numerical investigation. The effects of air injection on natural cavity oscillations and pressure fluctuations have been revealed in the present study.

The purpose of this paper is to accurately predict the cavitation performance of a cryogenic pump and reveal the influence of the inlet pressure, the surface roughness and the flow rate on the cavitation performance.

Firstly, the Zwart cavitation model was modified by considering the thermodynamic effect. Secondly, the feasibility of the modified model was validated by the cavitation test of a hydrofoil. Thirdly, the effects of the inlet pressure, the surface roughness and the flow rate on cavitation flow in the cryogenic pump were studied by using the modified cavitation model.

The modified cavitation model can predict the cavitation performance of the cryogenic pump more accurately than the Zwart cavitation model. The thermodynamic effect inhibits cavitation development to a certain extent. The higher the vapor volume fraction, the lower the pressure and the lower the temperature. At the initial stage of the cavitation, the head increases first and then decreases with the increase of the roughness. When the cavitation develops to a certain degree, the head decreases with the increase of the roughness. With the decrease of the flow rate, the hydraulic loss increases and the cavitation at the impeller intensifies.

A cavitation model considering the thermodynamic effect is proposed. The mechanism of the influence of the roughness on the performance of the cryogenic pump is revealed from two aspects. Taking the hydraulic loss as a bridge, the relationships among flow rates, vapor volume fractions, streamlines, temperatures and pressures are established.

As a result of the revisions at present being made to the science syllabus for schools, a large number of teachers in grammar and secondary modern schools are finding themselves involved for the first time in the mysteries of high vacuum. This article is intended as a guide to the practical aspects of obtaining and demonstrating high vacuum in schools. It contains a brief description of the workings of modern high vacuum pumps and gauges, together with some elementary ‘dos and don'ts’ of vacuum technique.

Rotary high‐vacuum pumps are oil‐lubricated. The lubricating oil acts as a seal against atmospheric pressure, and to enable it to do this the pump is normally submerged, or virtually submerged, in the oil. In the course of operation of the pump, the oil inevitably becomes contaminated with substances extracted from the system under evacuation. This complicates the questions involved in selection of the oil and has given rise to a number of remarkable devices to limit the accretion of contaminants.