Impact of Micropillar Density Distribution on the Capillary Limit of Heat Pipes

This paper shows the performance enhancement of heat pipes by tailoring the density distribution of micropillar wicks to minimize viscous pressure loss while maintaining sufficient capillary pumping. In a heat pipe, capillarity and permeability are linked, since small pores create higher capillary pumping while unfortunately inducing more pressure drop along the heat pipe. This pressure loss accumulates along the heat pipe, leading to a non-uniform pressure difference between the liquid and vapor. Therefore, we do not need a uniform capillary pressure to withstand this difference. This provides the opportunity to spatially tailor the wick structure, aiming for a high capillarity to pump the liquid, but a low permeability to induce less pressure loss. Our study offers a compromise between capillarity and permeability by designing the density distribution of the pillar wick structure. This density distribution, which was not studied before, will be shown to enhance the heat pipe performance. The theoretical models show that a tailored density distribution can enhance the heat pipe performance by a factor of 1.5. To support this result, ‘rate of rise’ measurements along a pillar array demonstrate that the liquid pressure loss in a tailored density array are less compared to a constant pillar density.

Self-Lubricanting Slippery Surface with Wettability Gradients for Anti-Sticking of Electrosurgical Scalpel

Soft tissue sticking on electrosurgical scalpels in minimally invasive surgery can increase the difficulty of operation and easily lead to medical malpractice. It is significant to develop new methods for anti-sticking of soft tissue on electrosurgical scalpels. Based on the characteristics of biomimetic ultra-slippery surface, a self-lubricating slippery surface with wettability gradients on electrosurgical scalpel was designed and fabricated. Non-uniformly distributed cylindrical micro pillars, which constitute the wettability gradients, were prepared by an electrolytic etching process and the theoretic of the spontaneous liquid spreading process was analyzed. The silicophilic property of wettability gradients surface was modified by octadecyltrichlorosilane (OTS) self-assembling coat with biocompatible liquid lubricant dimethyl silicone oil. The contact angle of gradient’s surface at different temperatures was measured. The transportation behaviors of both water and dimethyl silicone oil on the wettability gradient’s surface were investigated; the results illustrate that the wettability gradient’s slippery surface can successfully self-lubricate from regions with low pillar density to regions with high pillar density, ascribed to the unbalanced Young’s force. The anti-sticking capability of the electrosurgical scalpel with self-lubricating slippery surface was tested. Both the adhesion force and adhesion mass under different cycles were calculated. The results suggest that the as-prepared slippery surface has excellent anti-sticking ability associated with better durability.

Pillar Density Modulation in a Semi-packed MEMS Column

Gas chromatography is a technology that is constantly moving forward. The current trend for this field is moving towards miniaturizing the columns towards achieving high-speed separations. Groups are constantly researching different geometries, topographies, and stationary phases in order to make these separations more efficient. In order to achieve this goal of increased efficiency, we have taken two ideas from previous works, namely being width modulated channels as well as semi-packed columns, and tried to use the redeeming qualities that exist in both and combine them to achieve something that shares their positive points. Semi-packed columns have been shown to increase the plate height for a column. However, the pressure drop that occurs in these types is a significant drawback that makes high-speed separations very difficult to achieve with lower inlet pressures. Width modulation of the column channel can be used to change the overall velocity of the gas as it travels throughout the column resulting in a lower overall pressure drop. The method that was used to combine these two ideas was to change the density of the pillars in the semi-packed column along the length of the channel to achieve the same effect of the width modulation. This was achieved by changing the number of pillars across in the channel as well as the pitch distance between sets of pillars. Controls were also fabricated so the results could be compared to the two extreme designs. After extensive testing, the results indicated that between the minimum and maximum density, the maximum density allowed only ~50% of the total flow that the minimum density design showed at the same inlet pressure. In comparison, the design that changed pillar density throughout the channel allowed ~89% of the flow the minimum density design. This is a significant increase in flow and allows for much more to pass through the chip in a given time span increasing the efficiency of high-speed separations. The other factor that was tested for was the number of theoretical plates for each of the designs. It was shown through testing with a constant sample that the minimum density column behaves very similarly to an open column without pillars whereas the density modulated column has plate numbers between those of the minimum density and the maximum density. This is even further data that supports the use of a pillar density modulated chip for high-speed separations.

Synthesis and properties of aluminapillared fluorine micas having cation exchangeability

Alumina-pillared fluorine micas were prepared from synthetic highly layer-charged expandable fluorine mica and polyhydroxoaluminium solutions under different solution loadings (Al mmol in solutions per 1.0 g mica) in order to clarify the effects of solution loading on thermal durability and microporous properties. The intercalated Al content of the pillared micas increased with increased solution loading. The intercalated Al content (i.e. the pillar density) of the pillared micas influenced both the thermal durability and specific surface areas of the pillared micas. The pillared micas obtained from the high solution loadings showed better thermal durability than those obtained from the low solution loadings. Through micropore formation upon heating, the pillared micas exhibit cation exchangeability due to the liberation of residual Na+ ions from steric hindrance in the interlayer pillaring space. The amount of the exchangeable ions depends on the heating temperature of the pillared micas.