ABSTRACT
Drag force, corrosion, and biofouling have always been issues that disrupt the reliable operation of systems dealing with fluid flow. Inspired by nature, liquid- or solid-infused surfaces are brand-new surfaces that can address these problems. The present study examines nine comprehensive yet affordable samples with different surface structures, from the nanoscale to the microscale on the aluminum substrate. These surface structures, modified with stearic acid or octadecyltrichlorosilane, are infiltrated with various lubricants. The wetting test shows the magnificent slippery properties of fabricated surfaces with a contact angle hysteresis lower than 10°. The conducted polarization test reveals that the surface structures comprised of aluminum oxide or boehmite have good anti-corrosion properties. Moreover, the higher the viscosity of the lubricant, the better the anti-corrosion abilities. In the anti-bacterial tests, the surfaces possessing a liquid lubricant perform better than those containing solid ones; among them, those with lower viscosities are preferable. The frictional drag test carried out in an aquarium shows that for viscous working fluids, the layered-double hydroxide (LHD) surface containing silicone oil with a viscosity of 5 mPa s could provide a maximum drag reduction of 18%. By increasing the velocity of the surface, the drag reduction ability of LIS reduces. For more viscous lubricants and also solid ones, no appreciable drag reduction is achieved. For less viscous working fluid, however, the anodized surface filled with the same lubricant shows the best results with a maximum drag reduction of 15%. The surface based on LDH also shows good durability in the conducted stability tests.
ABSTRACT
We numerically investigate the pressure drop reduction (PDR) performance of microchannels equipped with liquid-infused surfaces, along with determining the shape of the interface between the working fluid and lubricant within the microgrooves. The effects of different parameters, such as the Reynolds number of working fluid, density and viscosity ratios between the lubricant and working fluid, the ratio of the thickness of the lubricant layer over the ridges to the depth of the groove, and the Ohnesorge number as a representative of the interfacial tension, on the PDR and interfacial meniscus within the microgrooves are comprehensively studied. The results reveal that the density ratio and Ohnesorge number do not significantly affect the PDR. On the other hand, the viscosity ratio considerably affects the PDR, and a maximum PDR of 62% compared to a smooth non-lubricated microchannel is achieved for a viscosity ratio of 0.01. Interestingly, the higher the Reynolds number of the working fluid, the higher the PDR. The meniscus shape within the microgrooves is strongly affected by the Reynolds number of the working fluid. Despite the insignificant effect of interfacial tension on the PDR, the interface shape within the microgrooves is appreciably influenced by this parameter.
ABSTRACT
In this study an expression for soot absorption coefficient is introduced to extend the weighted-sum-of-gray gases data to the furnace medium containing gas-soot mixture in a utility boiler 150 MWe. Heat transfer and temperature distribution of walls and within the furnace space are predicted by zone method technique. Analyses have been done considering both cases of presence and absence of soot particles at 100% load. To validate the proposed soot absorption coefficient, the expression is coupled with the Taylor and Foster's data as well as Truelove's data for CO2-H2O mixture and the total emissivities are calculated and compared with the Truelove's parameters for 3-term and 4-term gray gases plus two soot absorption coefficients. In addition, some experiments were conducted at 100% and 75% loads to measure furnace exit gas temperature as well as the rate of steam production. The predicted results show good agreement with the measured data at the power plant site.
