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In oil refineries and petrochemical industries, a containment seal (CS) can be applied to a flashing hydrocarbon pump as a sealing device to prevent environmental pollution. It is extremely difficult to design a CS to ensure the contradictory functions of fluid-tight sealing and sealing-surface wear resistance, which are required under both conditions of dry running in gas and wet running in liquid. In this study, a new CS design concept, “CSAM” (Containment Seal by Additive Manufacturing), for the sealing surface and internal structure of a sealing ring was developed by additive manufacturing. A lubrication film formed on the sealing surfaces of mechanical seals is maintained by the opening force (OF) with fluid pressure and the closing force (CF) with fluid pressure and spring load. To obtain the desired OF, the CSAM controls the pressure distribution across the sealing surfaces by introducing outside pressure through slots on the sealing surfaces, and an annular cavity is formed within the sealing ring. Based on a series of numerical analyses and static tests, it has been found that the difference between OF and CF can be properly controlled using slot design parameters. The results suggest the possibility of achieving the contradictory functions of sealing and wear resistance under both the gas and liquid conditions required for CSs.

Mechanical seals are composed of two annular flat rings in contact and relative motion to ensure sealing of a rotating shaft. Because of friction in the sealing interface, a significant temperature rise can be experienced in the contact. Two decades ago, it has been shown that creating a network of shallow dimples on one sealing surface can help to create a lubricant film in the interface and thus reduce friction. Since then, many research works have been carried out on the so-called surface texturing, showing the interest of surface modification for mechanical seals. In the present work, several surface patterns, defined by numerical simulations and machined by plasma etching on stainless steel rings were tested. The rings were mounted on a test bench in which they slide against a sapphire disk counter face. This disk is transparent to infrared radiation and allows interface temperature measurements by infrared thermography. It is shown that all the tested surface texture patterns exhibit a temperature rise at least 2 times lower than with flat smooth surfaces. A slight difference between the different dimple shapes is obtained indicating that the temperature and friction are more controlled by texture area and surface roughness rather than by the texture pattern.

The purpose of this study is to find out the effects of hematocrit of the sealed blood on the leakage characteristics of blood cell components and plasma components in a mechanical seal, which separates blood from cooling water. The hematocrit was controlled to 0, 10, 20, 30 and 40%. Each component leakage was obtained by measuring the increase in the potassium ion concentration and the sodium ion concentration in the cooling water. It was revealed that each component leakage became larger with the increase of the hematocrit in the three-hour measurement. When changing the hematocrit from 20% to 30%, the volume percentage of the blood cell component leakage remarkably increased by 7.7 times. The friction characteristics of the mechanical seal under blood sealing and the hemolytic properties of the sealed blood were also studied. There is a typical trend under the mixed lubrication condition where the friction torque decreased with each of the sealed blood as the rotational speed increased. The hemolytic index of the sealed blood after the measurement experiments of the blood leakage increased with the increase of the hematocrit.

The present paper describes a two-phase flow model used to study backward pumping of the low pressure fluid in the sealing interface of a mechanical seal. The Reynolds equation for a homogeneous mixture is solved as well as a transport equation used to determine the ratio of both fluids at each point. Several examples are presented to show that the second function of a seal (prevent the contamination of the process fluid by the operating environment) is not always insured because of possible reverse flows. The behavior of the seal can be greatly affected when it is partially lubricated by the low pressure fluid.

TThe friction characteristics of a mechanical seal for rotary blood pumps were investigated to evaluate the volume percentage of blood in the sealing face. These mechanical seals separate blood and cooling water, so the fluid film in the sealing face is composed of two different solutions. Therefore, the volume percentage of each solution is not known. In the experiments, various viscosities of an ethylene glycol solution were used as a substitution for blood, and the friction characteristics were compared for different Ra values for the seat rings: 0.009 and 0.088 μm. These friction characteristics were investigated based on the two different assumptions: a completely mixed state and a completely separated state. As a result, the volume percentage of the sealed fluid in the completely mixed state was larger than that in the completely separated state. In fact, it was considered reasonable that the practical state in the sealing face was between two states. For example, the volume percentage of the sealed fluid showed 65-73% at a viscosity of the sealed fluid of 3.53 mPa·s and at a rotational speed of 3000 min-1. Additionally, it was found that smaller volume percentage of the sealed fluid was evaluated for 0.088 μmRa than for 0.009 μmRa.

Liquid hydrogen (LH2) is excellent in extensive storage and transportation systems, such as being used as fuel in highly efficient liquid-rocket engines. To consider the use of LH2 required for future hydrogen-energy systems, this paper presents a topical review of previous cryogenic tribology studies on the research and development of the bearings and shaft seals for LH2 turbopumps. Cryogenic tribology studies were conducted for the LE-5/LE-7 rocket engines of the Japanese H-2 rocket as well as for an advanced ultra-high-speed LH2 turbopump. The tribo-chemical formation of CaF2/FeF2 film due to the reduction power of LH2 showed excellent self-lubrication, resulting in a sound wear condition within the turbopump bearing. A new hybrid ceramic bearing with Si3N4 balls, which bearing had a single-guided retainer, tested excellently at an ultra-high speed of 120,000 rpm (3 million DN) in LH2. Seal performance for the floating-ring seals using Ag-plated metal seal-rings at ultra-high speeds was also tested.

It is considered that cavitation plays an important role in maintaining the sealing performance of mechanical seals. However, there are not any studies that demonstrated how to control cavitation regions and take advantage of them to improve the sealing performance of mechanical seals. In this study, we have tried to demonstrate that the cavitation rings could be formed and maintained by taking advantage of the laser-textured surface. Furthermore, the effects of the cavitation rings on the frictional characteristics were also investigated. As a result, it was found that the sharp edge of the laser-textured surface could act as the geometric barrier to prevent the gas-liquid interface migration. Eventually, the gas-liquid interface maintained the steady fluid flow along the rows of dimples as the cavitation rings. Furthermore, it was also found that the friction coefficient of the textured surface fluctuated less than that of the plain surface.