Theoretical and Experimental Study on the Performance of Hermetic Diaphragm Squeeze Film Dampers for Gas-Lubricated Bearings

Low damping characteristics have always been a key sticking points in the development of gas bearings.The application of squeeze film dampers can significantly improve the damping performance of gas lubricated bearings.This paper proposed a novel hermetic diaphragm squeeze film damper(HDSFD)for oil-free turbomachinery supported by gas lubricated bearings.Several types of HDSFDs with symmetrical structure were proposed for good damping performance.By considering the compressibility of the damper fluid,based on hydraulic fluid mechanics theory,a dynamic model of HDSFDs under medium is proposed,which successfully reflects the frequency dependence of force coefficients.Based on the dynamic model,the effects of damper fluid viscosity,bulk modulus of damper fluid,thickness of damper fluid film and plunger thickness on the dynamic stiffness and damping of HDSFDs were analyzed.An experimental test rig was assembled and series of experimental studies on HDSFDs were conducted.The damper fluid transverse flow is added to the existing HDSFD concept,which aims to make the dynamic force coefficients independent of frequency.Although the force coefficient is still frequency dependent,the damping coefficient at high frequency excitation with damper fluid supply twice as that without damper fluid supply.The results serve as a benchmark for the calibration of analytical tools under development.

Experimental Study and Property Analysis of Seal-filling Hydrogel Material for Hermetic Wall in Coal Mine

The effects of monomer, crosslinker, and accelerator content on the mechanical property of seal-filling hydrogel material for building hermetic wall were analyzed through a series of single-direction compression experiments. Grey predication by GM（1,1） model was also used to analyze the persistent property of hydrogel material. The results showed that the elastic modulus and strength of seal-filling hydrogel increased, and the elastic tended to reduce with the growth of monomer and crosslinker content. In comparison, the effect of accelerator content was diametrically opposed. At the same time, staggered change of elastic modulus occurred and its demarcation point generally appeared at the point of 50% of vertical deformation value. In addition, through the testing of correlation degree, the accuracy of the grey prediction model to test the persistent stability of hydrogel material can be proved. As the concentration of hydrophilic monomer in hydrogel material increased, the stability was improved. The energy originated from explosion shock wave can be absorbed by seal-filling hydrogel through deformation.

Study on the performance of silver paste sintered sealing joints for hermetic packaging

The traditional hermetic packaging methods,which require high temperatures and high voltages,would have adverse effects on electronics devices.Based on current-assisted sintering technology,we proposed a new hermetic packaging method using silver paste.Comparing the microstructure of the joints sintered with different currents,we found that with the increasing sintering current from 4.7 kA to 5.3 kA,the density of the joint increases,which improves the hermeticity and bonding strength of the joints.The results of thermal cycling tests showed that the sealing joints sintered at 4.7 kA with larger porosity are more prone to fail because pores tend to be sources of defects under thermal cycling.After 250 ℃ high thermal storage,there is the coarsening of the pores and the delamination near the Ag/Au interface,degrading the sealing performance of the sintered joint.Besides,the sealing joints sintered at 5.3 kA exhibit superior reliability when exposed to high temperatures.

AN EXACT ANALYSIS FOR FREE VIBRATION OF A COMPOSITE SHELL STRUCTURE-HERMETIC CAPSULE

An exact analytical solution was presented for free vibration of composite shell structure-hermetic capsule. The basic equations on axisymmetric vibration were based on the Love classical thin shell theory and derived for shells of revolution with arbitrary meridian shape. The conditions of the junction between the spherical and the cylindrical shell segments are given by the continuity of deformation and the equilibrium relations near the junction point. The mathematical model of problem is reduced to as an eigenvalue problem for a system of ordinary differential equations in two separate domains corresponding to the spherical and the cylindrical shell segments. By using Legendre and trigonometric functions, ex act and explicitly analytical solutions of the mode functions were constructed and the exact frequency equation were obtained. The implementation of Maple programme indicates that all calculations are simple and efficient in both the exact symbolic calculation and the numerical results of natural frequencies compare with the results using finite element methods and other numerical methods. As a benchmark, the exactly analytical solutions presented in this paper is valuable to examine the accuracy of various approximate methods.

Grain Hermetic Storage Adoption in Northern Uganda: Awareness, Use, and the Constraints to Technology Adoption

Post-harvest storage losses (PHLs) remain significant in Sub-Saharan Africa (SSA) due to several factors mainly insect pests and molds. Hermetic storage technologies (HSTs) are being promoted to address these storage losses. In Uganda, HSTs were first introduced in 2012. However, its use among farming households remains low today. Data were collected from 306 smallholder farmers from four districts of Northern Uganda using a pre-tested semi-structured questionnaire to understand their knowledge, use, and constraints to the adoption of hermetic storage. A multivariate Logit regression model was used to find the significance of the factors affecting adoption. Results showed low awareness and use of hermetic storage among smallholder farmers. Only 53.3% of the interviewed farmers were aware of the use of hermetic storage for grain storage. The SuperGrain bag was the most known form of hermetic storage (35.3%), followed by the Purdue Improved Crop Storage (PICS) bag (34.9%), metallic silo (15.5%), and plastic silo (14.4%). Hermetic storage use was even lower as only 17.6% of the surveyed farmers were using one or more forms of hermetic storage to store their grains. Insect pest management without chemical insecticides was the main reason (83.1%) for hermetic storage use. About 75.5% of those aware of hermetic storage had received training in the technology. Hermetic storage use in farming households led to improved food availability, household income, and nutrition. Lack of local availability (50.2%), high costs (37.8%), and inadequate knowledge (6.9%) were the main constraints hindering the adoption of hermetic storage in Northern Uganda. The logit regression models showed that only training in hermetic storage significantly (p = 0.002) affected farmers’ decision to adopt hermetic storage. Understanding the factors that constrain the adoption of HSTs could provide policymakers with important information to initiate and design policies and programs aimed at reducing crop storage losses.

A novel matrix topology-based analysis method of thermal circuits for reliability optimization of HSER

Hermetically Sealed Electromagnetic Relay(HSER), used in aviation and aerospace,demands high reliability due to its critical applications. Given its complex operating conditions, efficient thermal analysis is essential for optimizing reliability. The commonly used Finite Element Method(FEM) is often time-consuming and may not be efficient or adaptable for complex multi-dimensional system calculations and design processes. This paper introduces an analysis method for thermal networks based on matrix perspective technology, encompassing matrix transformation, backpropagation of the heat path model, temperature rise calculation, solution comparison, and product implementation. Using the similarity theory of heat circuits, a basic thermal unit is established. Based on the fundamental connection between key components, a thermal network for a typical HSER is designed. An experimental system is set up, and the thermal network model's accuracy is confirmed using test data. Employing the topology analysis method, the topology of the thermal network is analyzed under both coil-energized and de-energized states. Potential thermal paths are identified, leading to optimized solutions for the HSER. Utilizing these solutions, the thermal path matrix topology model is backpropagated to the thermal path for temperature rise calculations. When compared to prototype HSER test data, the efficiency and accuracy of this matrix topology-based analysis method are confirmed.

Advanced hermetic electronic packaging based on lightweight silicon/aluminum composite produced by powder metallurgy technique

Silicon/aluminum(Si/Al)composite is a kind of lightweight electronic packaging material that received a lot of attention in the past 20 years.In this paper,a series of Si/Al composites with lowered coefficient of thermal expansion(CTE)and high thermal conductivity were produced by powder metallurgy(PM).The Si/Al composites are fully dense and have fine Si particles uniquely distributed within pure Al matrix.Three 50%Si/Al composites were designed to have strength in the range of 185-290 MPa to meet different demands,while the other properties keep invariable.Fracture toughness of the composites is measured to be 9-10 MPa·m^(1/2).The composites were machined to 50%Si/Al housings and 27%Si/Al lids.Both the hermeticities of housings before and after laser-beam-welding sealing are determined.The measured leak rate of composites and sealed housings is in magnitude order of 1×10^(-10)and 1×10^(-9)Pa·m^(3)·s^(-1),respectively,suggesting high hermeticity.The good hermeticity is attributed to the full dense materials,good weldability,and extremely low weld porosity.The present Si/Al composites are expected to be extensively used in highly hermetic electronic packages.

Wafer level hermetic packaging based on Cu-Sn isothermal solidification technology

A novel wafer level bonding method based on Cu-Sn isothermal solidification technology is established. A multi-layer sealing ring and the bonding processing are designed, and the amount of solder and the bonding parameters are optimized based on both theoretical and experimental results. Verification shows that oxidation of the solder layer, voids and the scalloped-edge appearance of the Cu6Sn5 phase are successfully avoided. An average shear strength of 19.5 MPa and an excellent leak rate of around 1.9 × 10-9 atm cc/s are possible, meeting the demands of MIL-STD-883E.