Underwater gas self-transportation along the femtosecond laser-written open superhydrophobic surface microchannels (< 100 µm) for bubble/gas manipulation

Underwater transportation of bubbles and gases has essential applications in manipulating and using gas, but there is still a great challenge to achieve this function at the microscopic level. Here, we report a strategy to self-transport gas along the laser-induced open superhydrophobic microchannel with a width less than 100 µm in water. The femtosecond laser can directly write superhydrophobic and underwater superaerophilic microgrooves on the polytetrafluoroethylene (PTFE) surface. In water, the single laser-induced microgroove and water medium generate a hollow microchannel. When the microchannel connects two superhydrophobic regions in water, the gas can be spontaneously transported from the small region to the large area along this hollow microchannel. The gas self-transportation can be extended to the laser-drilled microholes through a thin PTFE sheet. Anti-buoyancy unidirectional penetration is even achieved. The gas can overcome the buoyance of the bubble and spontaneously transport downward. The Laplace pressure difference drives the processes of spontaneous gas transportation and unidirectional bubble passage. We believe the property of gas self-transportation in the femtosecond laser-structured open superhydrophobic and underwater superaerophilic microgrooves/microholes has significant potential applications related to manipulating underwater gas.

New Developments in PTFE Sheet Gaskets With Engineered Surface Profile

This paper presents laboratory performance testing of new technology utilizing a textured raised pattern on filled restructured PTFE (R-PTFE) sheet gasketing. The technology published in PVP2018-84039 and PVP2018-84040 and presented in Prague1,2 examined the load retention attributes of filled PTFE sheet gaskets with hexagonal/honeycomb surface texture in a miniaturized and standard raised face flange joints. This paper will show performance characteristics and comparisons to flat traditional R-PTFE gaskets. Data is presented on leak performance based on DIN-3535-4/6 and EN 13555, deflection under compressive load, bolt load retention and ASTM F36 compression and recovery. The paper gives a summary of results from a study of PTFE gasket users expressing their needs and desires for gasket performance. Examples of current field cases from chemical processors are also be presented.

Review of Mechanical and Sealing Performance Aspects of Commercially Available PTFE Based Gasket Materials

Gaskets incorporating polytetrafluoroethylene (PTFE) are one of the most common in use today where soft sealing material is needed in bolted joints. Over the years, various types of gaskets have been developed including those using skived, expanded, filled, or molded PTFE sheet. Still other PTFE gaskets have been fabricated, incorporating some type of metal insert. Although many of the key benefits (e.g., chemical resistance, application in a broad range of flange types, higher maximum temperature and stress levels than most elastomers, indefinite shelf life, etc.) remain, the performance of the gasket will vary significantly according to the type of PTFE gasket employed. These variations in accordance with PTFE gasket styles are presented and discussed with an emphasis on such criteria as relaxation, gasket tightness / leak rate, and safe reserve operating temperature. For estimating tightness and predicted leak rates, the previously reported “Fugitive Emissions Calculator” (FEC) model has been used which employs Room Temperature Testing (ROTT) data and an ASME / PVRC draft empirical equations set. Published test data have also been compiled to support conclusions concerning relative capabilities for selected PTFE gasket categories. The differences in analytical and leak rate performance criteria have been used to suggest appropriate applications for various subtypes of PTFE gaskets.

Behavior of Bolt Force Changes of Flanged Connections Under Thermal Loading

When flanged connections are used at a high temperature, one of the issues is the reduction of bolt forces, especially in the cases where PTFE-based gaskets are employed. Bolt forces significantly reduce when flanged connections are heated and re-torque is necessary in many cases. It is important to estimate the residual bolt forces under thermal loading to ensure the integrity of flanged connections. In this paper, the behavior of bolt force changes under thermal loading was experimentally examined using a flanged connection with expanded PTFE sheet gaskets. The flanged connection was heated and then cooled in an electric oven and the changes of the bolt forces were measured. It is found that the bolt forces reduce at the first thermal loading due to the gasket flow. Once the gasket is settled, the bolt force changes depend on the difference of thermal coefficients of the bolts and the gasket. It is also clarified that thinner gaskets and spiral wound gaskets are effective for elevated temperature applications.