Distribution of the Deposition Rates in an Industrial-Size PECVD Reactor Using HMDSO Precursor

The deposition rates of protective coatings resembling polydimethylsiloxane (PDMS) were measured with numerous sensors placed at different positions on the walls of a plasma-enhanced chemical vapor deposition (PECVD) reactor with a volume of approximately 5 m3. The plasma was maintained by an asymmetric capacitively coupled radiofrequency (RF) discharge using a generator with a frequency 40 kHz and an adjustable power of up to 8 kW. Hexamethyldisiloxane (HMDSO) was leaked into the reactor at 130 sccm with continuous pumping using roots pumps with a nominal pumping speed of 8800 m3 h−1 backed by rotary pumps with a nominal pumping speed of 1260 m3 h−1. Deposition rates were measured versus the discharge power in an empty reactor and a reactor loaded with samples. The highest deposition rate of approximately 15 nm min–1 was observed in an empty reactor close to the powered electrodes and the lowest of approximately 1 nm min–1 was observed close to the precursor inlet. The deposition rate was about an order of magnitude lower if the reactor was fully loaded with the samples, and the ratio between deposition rates in an empty reactor and loaded reactor was the largest far from the powered electrodes. The results were explained by the loss of plasma radicals on the surfaces of the materials facing the plasma and by the peculiarities of the gas-phase reactions typical for asymmetric RF discharges.

MODELLING THE OPERATION OF ROTARY PUMPS

The article considers the operation of a three-bladed rotary pump, the blade profile of which consists of several conjugate circles. It is shown that the size of the gap between the rotors is an important pa-rameter that affects the quality of pumps. When designing using CAD systems, it is possible to identify gross errors, for example, the intersection of surfaces, to determine the amount of gap between the rotors at a fixed position of the mechanism. However, it is not possible to determine the size of the gap in the dynamics of the given software, it is necessary to develop a digital model of the mechanism. The model of interaction of two rotors considered in the article, implemented in the Mathcad program, allows determining the size and nature of the gap change during the operation of the mechanism.

Hydraulic transport in small livestock farms

The article highlights the advantages and benefits of pipeline transport of liquid feed mixtures on small pig farms, the device and the principle of operation and technical characteristics of the improved rotor pump developed by the authors of the article. Methods of experimental research to determine the concentration of feed mixtures, the influence of the shape of the separator on the performance characteristics, the required power and the flow of an improved pump are presented. The results of the experiments showed that one of the bottlenecks limiting the operation of rotary pumps on feed mixtures of increased concentration is the low suction capacity of the pump, that is, the design of the suction pipe of the pump, where an increase in resistance with an increase in the concentration of feed mixtures causes a breakdown of the operating mode and cavitation. To resolve this issue, we used a screw feeder installed in front of the pump suction nozzles. It was found that if the screw feeder provides excess pressure within (about, 0.25 ... 0.3) 105 Pa per suction cavity, the pump operates stably and reliably.

PREDICTION OF OIL FILM THICKNESS IN TROCHOIDAL PUMP

A model for predicting the oil film thickness between the contact surfaces of the gerotor pump teeth is given in this paper. Gerotor pumps are rotary pumps with inner trochoidal gearing. The working process of the pump is followed by mechanical losses due to friction that occurs between the coupled surfaces. In order to reduce these losses and avoid wearing of the teeth’s active surfaces, it is necessary to provide a minimum thickness of the oil film between the contact surfaces. The minimum thickness of the oil film depends on a large number of different factors, but in this paper for its determination, the Hamrock and Dowson empirical equation is used. Previously, the mathematical model that follows the change of relative velocities in contact, sliding velocity, rolling velocity and contact force at the contact points of the coupled teeth profiles is developed. The influence of different parameters on the lubrication regime has been analyzed, and it has been shown that the trohydraulic pump operates most with the limit EHD lubrication regime. The most unfavorable period occurs when the resulting rolling velocity decreases significantly, and this period dominates during coupling. The results of this research provide guidelines for the design of the tooth profile’s shape and the choice of operating parameters of the pump with high reliability.

Biocompatible materials of pulsatile and rotary blood pumps: A brief review

The biomedical materials that have been used in the structure of heart pumps are classified as biocompatible, and these can be metals, polymers, ceramics, and composites. Their positions in the pump vary according to the part’s function. Whereas various materials have different properties, all biomaterials chosen for cardiovascular applications should have excellent blood biocompatibility to reduce the likelihood of hemolysis and thrombosis. There are two major categories of the heart pumps; pulsatile and rotary blood pumps (axial and centrifugal) and the features of some of these materials allow them to be used in both. Rotary and pulsatile blood pump devices have to be fabricated from materials that do not result in adverse biological responses. The purpose of this review is to study the available biocompatible materials for the pulsatile and rotary blood pumps as clinically-approved materials and prototype heart pump materials. The current state of bio-compatible materials of rotary and pulsatile blood pump construction is presented. Some recent applications of surface amendment technology on the materials for heart assist devices were also reviewed for better understanding. The limitations of heart assist devices, and the future direction of artificial heart elements have been considered. This review will be considered as a comprehensive reference to rapidly understanding the necessary research in the field of biocompatible materials of pulsatile and blood rotary pumps.

Review and reflections about pulsatile ventricular assist devices from history to future: concerning safety and low haemolysis—still needed

Since the first use of a ventricular assist device in 1963 many extracorporeal and implantable pulsatile blood pumps have been developed. After the invention of continuous flow blood pumps the implantable pulsatile pumps are not available anymore. The new rotary pumps spend a better quality of life because many of the patients can go home. Nevertheless, the extracorporeal pulsatile pumps have some advantages. They are low-cost systems, produce less haemolysis and heart-recovery can be tested easily. Pump failure is easy to realize because the pumps can be observed visually. Pump exchange can be done easily without any chirurgic surgery. As volume displacement pumps they can produce high blood pressure, so they are the only ones suitable for pediatric patients. Therefore, they are indispensable for clinical use today and in the future. In this work, nearly all pulsatile blood pumps used in clinical life are described.

Deposition Kinetics of Thin Silica-Like Coatings in a Large Plasma Reactor

An industrial size plasma reactor of 5 m3 volume was used to study the deposition of silica-like coatings by the plasma-enhanced chemical vapor deposition (PECVD) method. The plasma was sustained by an asymmetrical capacitively coupled radio-frequency discharge at a frequency of 40 kHz and power up to 7 kW. Hexamethyldisilioxane (HMDSO) was introduced continuously at different flows of up to 200 sccm upon pumping with a combination of roots and rotary pumps at an effective pumping speed between 25 and 70 L/s to enable suitable gas residence time in the plasma reactor. The deposition rate and ion density were measured continuously during the plasma process. Both parameters were almost perfectly constant with time, and the deposition rate increased linearly in the range of HMDSO flows from 25 to 160 sccm. The plasma density was of the order of 1014 m−3, indicating an extremely low ionization fraction which decreased with increasing flow from approximately 2 × 10−7 to 6 × 10−8. The correlations between the processing parameters and the properties of deposited films are drawn and discussed.