An Experimental Study on Cryogenic Spray Quenching of a Circular Metal Disk II. Chilldown Efficiency and Effects of Coating and Flow Pulsing

This is the second part of a two-part series that presents the results of liquid nitrogen spray quenching of a Stainless Steel disc. The results of continuous-flow spray chilldown of a bare surface disc are summarized first that serves as the baseline information for evaluating the effects of disc surface coating and pulse flow. We found that for continuous-flow spray chilldown of a bare surface disc, the chilldown efficiency is mainly a function of the average mass flow rate with the trend of decreasing efficiency with increasing mass flow rate. Additional experiments were performed to evaluate the enhancement of cryogenic spray quenching by three techniques: 1. Using intermittent pulse sprays on SS bare surface, 2. Coating the SS surface with a layer of low thermal conductivity Teflon film, and 3. Spraying liquid nitrogen intermittently on the coated SS surface. In general, the results indicate that all three methods effectively produced higher spray thermal efficiencies and reduced liquid nitrogen mass consumption. However, it was also found that the Teflon coating was more effective than the flow pulsing due to that the Teflon coating induced a large surface temperature drop at the beginning of the chilldown that allowed the quenching to move quickly from poor heat transfer film boiling to efficient heat transfer transition and nucleate boiling regimes. This quick transition shortens the film boiling period, thus facilitates the switch to much higher heat transfer transition boiling and nucleate boiling periods earlier to complete the chilldown process faster.

Experimental Study on CaCO3 Fouling Characteristics during Falling Film Evaporation

Falling film evaporation is widely used in solar desalination systems. Fouling is an important problem to be addressed in many applications involving heat transfer including processes involving the utilization of solar energy in desalination applications. In the research upon which this paper partly reports, an experimental investigation was carried out on a vertical tube in falling film evaporation to determine the effects of temperature, velocity, the use of a porous-sintered tube, and the use of Teflon coating on calcium carbonate deposition characteristics. During the fouling experiments, the pressure inside the test tubes was maintained constant at 101.3kPa, and the inlet temperature was maintained at 373K, while allowing the water mass velocity to vary from 0.42-1.05kg m−1s−1. Results show that the fouling in the test tube becomes more serious as the temperature increases and the flow rate decreases. Compared with stainless steel tubes, porous-sintered tubes can significantly reduce fouling resistance, but at the same time they bring about a decrease in the heat transfer coefficient. The Teflon coating also has anti-fouling performance, but does not affect the heat transfer coefficient in stainless steel tubes. Through the weighing of local fouling deposits, it has been found that the mass of the fouling deposits in the lower part of the tested tubes is greater than that in the upper part.

A Nanoengineered Stainless Steel Surface to Combat Bacterial Attachment and Biofilm Formation

Nanopatterning and anti-biofilm characterization of self-cleanable surfaces on stainless steel substrates were demonstrated in the current study. Electrochemical etching in diluted aqua regia solution consisting of 3.6% hydrogen chloride and 1.2% nitric acid was conducted at 10 V for 5, 10, and 15 min to fabricate nanoporous structures on the stainless steel. Variations in the etching rates and surface morphologic characteristics were caused by differences in treatment durations; the specimens treated at 10 V for 10 min showed that the nanoscale pores are needed to enhance the self-cleanability. Under static and realistic flow environments, the populations of Escherichia coli O157:H7 and Salmonella Typhimurium on the developed features were significantly reduced by 2.1–3.0 log colony-forming unit (CFU)/cm2 as compared to bare stainless steel (p < 0.05). The successful fabrication of electrochemically etched stainless steel surfaces with Teflon coating could be useful in the food industry and biomedical fields to hinder biofilm formation in order to improve food safety.

Coating Cutting Blades with Thin-Film Metallic Glass to Enhance Sharpness

In this study, we sought to enhance the cutting properties of the various blades by coating them with Zr- and Fe-based thin film metallic glasses (TFMGs) to a thickness of 234–255 nm via sputter deposition. In oil-repellency/sliding tests on kitchen blades, the sliding angle and friction forces were as follows: bare blades (31.6°) and (35 µN), Ti-coated blades (20.3°) and (23.7 µN), and Z-TFMG coated blades (16.2°) and (19.2 µN). Comparisons were conducted with bare blades and those with a Teflon coating (a low-friction material commonly used for the coating of microtome blades). We also found that the Teflon coating reduced the cutting forces of an uncoated microtome blade by ~80%, whereas the proposed Z-TFMG achieved a ~51% reduction. The Z-TFMG presented no indications of delamination after being used 30 times for cutting; however, the Teflon coating proved highly susceptible to peeling and the bare blade was affected by surface staining. These results demonstrate the efficacy of the TFMG coating in terms of low friction, non-stick performance, and substrate adhesion. The performance of Z-TFMG and F-TFMG was also evaluated in split-thickness skin graft surgery using dermatome blades aimed at elucidating the influence of TFMG coatings on the healing of surgical incisions. When tested repeatedly on hairless skin, the surface roughness of uncoated blades increased by approximately 70%, whereas the surface roughness of TFMG-coated blades increases by only 8.6%. In the presence of hair, the surface roughness of uncoated blades increased by approximately ~108%, whereas the surface roughness of TFMG-coated blades increases by only ~23%. By Day 7, the wounds produced using TFMG-coated blades were noticeably smaller than those produced using uncoated blades, and these effects were particularly evident in hairy samples. This is a clear demonstration of the efficacy of TFMG surface coatings in preserving the cutting quality of surgical instruments.

Hybrid guidewires: Analysis and comparison of the mechanical properties and safety profiles

Introduction: Hybrid guidewires are commonly used in urology due to the advantage of an atraumatic hydrophilic tip, which facilitates negotiating tight areas, coupled with an unkinkable nitinol core shaft that is easy to work over due to the Teflon coating. Our aim was to compare the physical and mechanical properties of five commercially available hybrid guidewires to assess their characteristics and functionality. Methods: In vitro testing was performed on the following straighttipped 0.035 inch guidewires: Sensor™ (Boston Scientific), Solo™ Plus (Bard), UltraTrack (Olympus), Rio Tracer™ (Rocamed), and Motion™ (Cook). We evaluated characteristics impacting function (tip flexibility, shaft stiffness, lubricity) and safety (perforation force). Measurements included tip flexibility, lubricity, shaft buckling, and force required to perforate a sheet of aluminum foil. Results: The Motion had the highest tip-bending force (p<0.00001). The Rio Tracer had the stiffest shaft (p<0.00001), followed by the Solo Plus and the Motion, which were significantly stiffer than the Sensor and UltraTrack (p<0.00001). The Solo Plus and UltraTrack had the greatest perforation force (p=0.00023), and the Rio Tracer had the lowest perforation force (p=0.016) when compared to the Sensor. There was no significant difference in frictional force between the five guidewires (p=0.1516). Conclusions: The Solo Plus and UltraTrack required the greatest force to perforate, which conveys a higher safety margin. The RioTracer is the stiffest guidewire, which may be beneficial for instrument insertion with the tradeoff of having a lower perforation force. The clinical significance of higher tip-bending forces (unfavourable) and higher shaft-bending forces (favourable) deserve further investigation.

Changes of Microstructure and Grainsize of Martensitic Stainless Steel during the Processes of Hot Reversed Extrusion, Broaching and Heat Treating

The field of high pressure steel cylinders (HPSC) used for the variety of applications, such as storage of technical gases, compressed natural gas (CNG), medical gases and special applications like scuba diving cylinders is still significantly expanding. With increasing safety requirements, the need of new techniques applied in field of HPSC structural and materials innovations comes into place.Speaking mainly about the field of scuba diving cylinders, the need of corrosion protection of inner surface comes in place due to the possible risk of valve blockage by metal corroded particles of inner surface. Even such a risk occurs in extremely rare occasions, there was until now no generally applied solution (such as inner wet, powder or Teflon coating, etc.) due to significantly high costs of such additional inner surface protection. Another problem that occurs so far are significant visual imperfections of scuba diving cylinders caused by the rough treating by scuba divers during the use and manipulation that causes chipping of outer surface painting and subsequent corroded areas.The breakthrough solution is the scuba diving cylinder made of a stainless steel by the processes of reversed extrusion and broaching from billet without any need of an additional coating. No such a product was made so far by these methods of production and no evidence of an evolution of the microstructure and grainsize changes during such manufacturing with subsequent heat treating was ever documented and analysed.

Technical Means for Safe Management of Radioactive Waste Containing Tritium

The paper considers the possibility for separate safe storage of radioactive waste containing tritium using passive protection of concrete, clay, silica gel and additional engineering barrier in the form of container made of polymeric materials. It describes some physical properties of the container made of two polymeric materials for storage of tritium radionuclides separated from other radionuclides. The experts calculated the thickness of the container walls taking into account the ability of tritium diffusion as the main physical-chemical characteristics of tritium. The use of Teflon coating protects the plastic container in case of fire.