Turbulent Transition Control Using Porous Surfaces in Hypersonic Boundary Layer

임지섭,김민우,배하준,Ray-Sing Lin,지솔근 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.4

Hypersonic boundary layer on porous surfaces is simulated to investigate the effect of porous surfaces on the transition process. The fundamental breakdown involving the Mack second mode is computed using the direct numerical simulation (DNS) solver of Lim et al. (Comput Fluids 240:105437, 2022). Because it is computationally challenge to resolve numerous pores, the impedance boundary condition of a porous surface is pursued in this study to model the absorptive characteristics of a porous surface. The impedance boundary condition for a porous surface is implemented in the DNS solver and validated against relevant literature data. The stabilization of the Mack second mode on porous surfaces is well resolved in the current computations. Based on the validated numerical setup, 3D DNS computations of the hypersonic boundary layer over a porous surface are conducted. The current porous surface is optimized to absorb the Mack second mode. In this study, it is clearly shown that the turbulent transition involving the Mack second mode can be effectively delayed on the porous surface.

Experimental Study on the Hydrophilic Porous Film Coating for Evaporative Cooling Enhancement

Lee, Dae-Young,Lee, Jae-Wan,Kang, Byung-Ha The Society of Air-Conditioning and Refrigerating 2005 International Journal Of Air-Conditioning and Refr Vol.13 No.2

Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface to form a thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this respect, hydrophilic treatment of the surface has been tried to improve the surface wettability by decreasing the contact angle between the liquid and the surface. However, the hydrophilic treatment was found not very effective to increase the surface wettedness of inclined surfaces, since the liquid flow forms rivulet patterns instead of a thin film as it flows down the inclined surface and accelerates gradually by the gravity. In this work, a novel method is suggested to improve the surface wettedness enormously. In this work, the surface is treated to have a thin hydrophilic porous layer on the surface. With this treatment, the liquid can spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of inclined surfaces has been conducted to verify the effectiveness of the surface treatment. It is measured that the latent heat transfer increases almost by $80\%$ at the hydrophilic porous layer coated surface as compared with the untreated surface.

다공물질 표면처리가 경사판의 증발냉각에 미치는 영향에 관한 실험적 연구

이대영,이재완,강병하 대한설비공학회 2005 설비공학 논문집 Vol.17 No.1

Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface forming thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this work, the surface is treated to have thin porous layer on the surface. With this treatment, the liquid can be spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of an inclined surface has been conducted to verify the effectiveness of the surface treatment. It is measured that the evaporative heat transfer increases about 50% by the porous layer treatment as compared with that from orignal bare surfaces.

알칼리 표면개질을 통한 다공성 알루미늄 합금의 하이브리드 기공구조 형성

서영익,김영문,이영중,김대건,이규환,김영도,Seo, Young-Ik,Kim, Young-Moon,Lee, Young-Jung,Kim, Dae-Gun,Lee, Kyu-Hwan,Kim, Young-Do 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.1

To improve the filtration efficiency of porous materials used in filters, an extensive specific surface area is required to serve as a site for adsorption of impurities. In this paper, a method for creating a hybridized porous alloy using a powder metallurgical technique to build macropores in an Al-4 wt.% Cu alloy and subsequent surface modification for a microporous surface with a considerably increased specific surface area is suggested. The macropore structure was controlled by granulation, compacting pressure, and sintering; the micropore structure was obtained by a surface modification using a dilute NaOH solution. The specific surface area of surface-modified specimen increased about 10 times compare to as-sintered specimen that comprised of the macropore structure. Also, the surface-modified specimens showed a remarkable increase in micropores larger than 10 nm. Such a hybridized porous structure has potential for application in water and air purification filters, as well as membrane pre-treatment and catalysis.

표면변화에 따른 티타늄합금에의 골유착

원중희,서중배 충북대학교 의과대학 충북대학교 의학연구소 1996 忠北醫大學術誌 Vol.6 No.2

미세공표면을 갖는 순수 티타늄 fiber-metal로 둘러싸인 막대봉(porous coated)과 거친표면처리한 티타늄봉(rough-blasted)을 토끼의 원위대퇴골 골수강내에 삽입하여 시간경과에 따른 골유착의 유무 및 정도를 관찰하였다. 총 30마리의 토끼가 사용되었고, 15마리에는 Porous coated 삽입물을 삽입하였으며 15마리에는 rough-blasted 삽입물을 삽입하였다. 토끼는 각각 3마리씩 1, 2, 4, 6, 12 주에 희생되어 삽입물의 정중위부를 절편하여 조직학적으로 검사하였다. 전체삽입물주위에 골이 직접 닿은 부위의 비율을 측정한 결과 rough-blasted 티타늄봉과 porous-coated 티타늄봉 주위에 상당한정도의 골유착이 있었으며 전체군의 평균을 볼 때 rough-blasted 군은 36.5%, porous-coated군은 19.2% 에서 골유착이 있었다. 삽입물주위의 골형성 및 골유착은 삽입후 1주부터 관찰할 수 있었고, 4주 이후에는 골유착면적의 커다란 증가가 보이지 않았다. 임상적 의의 : 인공관절치환시 골시멘트를 사용하지 않는 경우 삽입물의 견고한 고정을 위해 삽입물 표면을 미세공처리하는 것이 필수적이며 보편적인 것으로 알려져 있다. 또한 보다 신속하고 확실한 고정을 위해 hydroxyapatite의 표면처리도 주장되고 있다. 하지만 유럽지역에서 시작된 비미세공처리한 티타늄합금의 인공관절 사용은 10년 이상 사용되고, 우수한 임상적, 방사선학적 결과를 보여주고 있다. 토끼에서 보이는 rough-blasted 티타늄봉에의 골유착이 미세골표면을 갖는 삽입물보다 우수하거나 비슷한 소견을 보여준 이 연구는 임상적, 방사선학적 우수성의 배경을 갖고있는 rough-blasted 티타늄합금의 인공관절 삽입물 사용의 이론적 근거를 보다 확실하게 하고 있다. 미세공표면 처리나 hydroxyapatite의 사용은 처리과정의 복잡성과 경제적인 비용, 또한 내재적인 단점이 많다. 따라서 특별한 적응증이 있는 경우가 아니라면 인공 관절치환술에서 rough-blasted 표면을 갖는 티타늄합금의 사용이 좋을 것으로 생각된다 The Purpose of this study was to see the host-bone response to pure titanium fiber-metal surrounding titanium alloy core and rough-blasted titanium alloy(Ti-6Al-4V) implants placed in the medullary cavity of distal femur of rabbit. Each rod was implnated into medullary cavity of tight distal femur through the knee. A total of thirty New Zealand rabbits were used. Fifteen were for fiber-metal rods and another fifteen were for rough blasted rods. The rabbits were killed at one, two, four, six, and twelve weeks after operation and studied histologically and histomorphometrically. Percentage implant perimeter surface length in contact with new bone were measured. Histomorphometry revealed excellent, comparable osseointegration onto rough-blasted titanium compared with fiber-metal titanium rod. When whole group means were compared, it was found that 36.5 percent of perimeter of the rough blasted implants was covered with bone compared with 19.2 percent of the perimeter of the fiber-metal coated implants. Peripheral bone formation and osseointegration was evident at one week, and quantitative plateau was reached at four weeks. Clinical relevance : Implantation with or without bone cement huts been a controversy among orthopaedic surgeons. Biological fixation was an alternative method introduced into the alrhroplasty field, but prerequisite was porous coated material or hydroxyapatite coated surface. However many Europian scientist suggested that a porous-coated surface is not necessary for osseointegration. Our study proved that nonporous-coated rough blasted titanium surface was enough for osseointegration not inferior to fiber-metal titanium surface. We have radiographic and clinical evidence that hip prostheses with rough-blasted titanium surface show osseointegration. The cost of manufacturing porous-coated prosthesis is high and the adverse effects of it are many. The use of rough-blasted surface may help to improve the functional outcome of total joint replacements and reduce the cost of arthroplasty.

다공성 지르코니아 표면에서 Capillary wicking 으로 인한 물의 Leidenfrost 억제 현상

이기철(Gi Cheol Lee),강준영(Jun-young Kang),박현선(Hyun Sun Park),백종원(Jong Won Baek),김동균(Tong Kyun Kim),Kiyofumi Moriyama,김무환(Moo Hwan Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

A significant increase in the Leidenfrost point temperature was observed on a porous zirconia surface compared with non-porous surface. Two samples (Non-porous, Porous surface) were fabricated by sintering. The porosity of each surface was calculated 0.8% and 30.9% from sample and particle densities. The Leidenfrost phenomenon was not observed on the porous surface for surface temperature up to 500 ℃ compared to the Leidenfrost point on non-porous surface 410 ℃. The key phenomenon determining Leidenfrost phenomenon is the rebound process of droplet during a few milliseconds following the impact on the surface. On the porous surface, due to the capillary wicking phenoenon, the rebound was disturbed.

염산티트라싸이클린의 적용시간에 따른 다공성 임프란트 표면 미세구조의 변화

정재욱,허익,권영혁,박준봉,정종혁,Jeong, Jae-Wook,Herr, Yeek,Kwon, Young-Hyuk,Park, Joon-Bong,Chung, Jong-Hyuk 대한치주과학회 2006 Journal of Periodontal & Implant Science Vol.36 No.2

Mechanical and chemical methods are the two ways to treat the implant surfaces. By using mechanical method, it is difficult to eliminate bacteria and by-products from the rough implant surface and it can also cause the structural change to the implant surface. Therefore, chemical method is widely used in order to preserve and detoxicate the implant surface more effectively. The purpose of this study is to evaluate the effect of tetracylcline-hydrochloride(TC-HCI) on the change of implant surface microstructure according to application time. Implants with pure titanium machined surface, SLA surface and porous surface were used in this study. Implant surface was rubbed with sponge soaked in 50mg/ml TC-HCI solution for $\frac{1}{2}$ min., 1 min., $1\frac{1}{2}$ min., 2 min., and $2\frac{1}{2}$ min. respectively in the test group and with no treatment in the control group. Then, specimens were processed for scanning electron microscopic observation. 1. Both test and control group showed a few shallow grooves and ridges in pure titanium machined surface implants. There were not significant differences between two groups. 2. In the SLA surfaces, the control specimen showed that the macro roughness was achieved by large-grit sandblasting. Subsequently, the acid-etching process created the micro roughness, which thus was superimposed on the macro roughness. Irrespective of the application time of 50mg/ml TC-HCI solution, in general, test specimens were similar to control. 3. In the porous surfaces, the control specimen showed spherical particles of titanium alloy and its surface have a few shallow ridges. The roughness of surfaces conditioned with tetracycline-HCI was lessened and seen crater-like irregular surfaces relative to the application time. In conclusion, pure titanium machined surfaces and SLA surfaces weren't changed irrespective of the application time of tetracycline-HCI solution. But the porous surfaces conditioned with tetracycline-HCI solution began to be slightly changed from 2 min. This results are expected to be applied to the regenerative procedures for peri-implantitis treatment.

WETTABILITY AND DRUG DELIVERY OF FUNCTIONALLY GRADED NANO-MICRO POROUS TITANIUM SURFACE

Yun, Kwi-Dug,Vang, Mong-Sook,Yang, Hong-So,Park, Sang-Won,Park, Ha-Ok,Lim, Hyun-Pil The Korean Academy of Prosthodonitics 2008 대한치과보철학회지 Vol.46 No.3

STATEMENT OF PROBLEM: It is known that an anodic oxidation technique, one of the methods for the implant surface treatment, remarkably increased surface area, enhanced wettability and accelerated the initial bone healing. Purpose: This study was performed to evaluate the wettability of anodized titanium surface which has a nanotubular structure, to assess osseointegration after the placement of implant with nano-size tubes on tibia of rats and to analyze quantitatively transferable rhBMP-2 on each surface. MATERIAL AND METHOD: Four different kinds of surface-treated titanium discs (polished (machined surface) group, micro (blasting surface) group, nano (anodizedmachined surface) group, and nano-micro (anodized-blasting surface) group) were fabricated (n=10). Three different media were chosen to measure the surface contact angles; distilled water, plasma and rhBMP-2 solution. After a single drop (0.025 $m{\ell}$) of solution, the picture was taken with the image camera, and contact angle was measured by using image analysis system. For the test of osseointegration, 2 kinds of anodized surface (anodized-machined surface, anodized-blasting surface) implants having 2.0 mm in diameter and 5.0 mm in length inserted into the tibia of Wistar rats. After 3 weeks, tibia were harvested and the specimens were stained with hematoxylin and eosin for histological analysis. To test the possibility of drug delivery, after soaking sample groups in the concentration of 250 ng/$m{\ell}$l of rhBMP-2 for 48 hours, the excess solution of rhBMP-2 were removed. After that, they were lyophilized for 24 hours, and then the rhBMP-2 on the surface of titanium was resolved for 72 hours in PBS. All the extracted solution was analyzed by ELISA. One-way analysis of variance (ANOVA) was performed on the data. RESULTS: The wettability is improved by anodic oxidation. The best wettability was shown on the nano-micro group, and it was followed by nano group, micro group, and polished group. In the histological findings, all implants showed good healing and the new bone formation were observed along the implant surface. After 3 days, nano-micro group delivered the most amount of rhBMP-2, followed by nano group, micro group, and polished group. CONCLUSION: It indicated that anodic oxidation on blasting surface produce functionally graded nano-micro porous structure and enhance hydrophilicity of the surface and osseointegration. The findings suggest that the nano-micro porous structure could be a useful carrier of osteogenic molecules like rhBMP-2.

Characterization and Surface-Derivatization of Porous Silicon

Lee, Bo-Yeon,Hwang, Min-Woo,Cho, Hyun,Kim, Hee-Chol,Jang, Seunghyun The Basic Science Institute Chosun University 2011 조선자연과학논문집 Vol.4 No.3

Chemical modification of porous silicon surface has been investigated to have different physical surface properties. Porous silicon modified with dodecyl functionality exhibits hydrophobic feature, however the oxidation of porous silicon to modify with hydroxyl group displays hydrophilic properties. Surface characterization for both dodecyl and hydroxyl derivatized porous silicon was investigated by FT-IR spectroscopy. To determine the surface coverage, the amine functionalized surface was reduced by dithiothreitol (DTT) and the released 2-thiopyridone was quantified by UV/vis spectroscopy.

Characterization and Surface-Derivatization of Porous Silicon

이보연,황민우,조현,김희철,장승현 조선대학교 기초과학연구원 2011 조선자연과학논문집 Vol.4 No.3

Chemical modification of porous silicon surface has been investigated to have different physical surface properties. Porous silicon modified with dodecyl functionality exhibits hydrophobic feature, however the oxidation of porous silicon to modify with hydroxyl group displays hydrophilic properties. Surface characterization for both dodecyl and hydroxyl derivatized porous silicon was investigated by FT-IR spectroscopy. To determine the surface coverage, the amine functionalized surface was reduced by dithiothreitol (DTT) and the released 2-thiopyridone was quantified by UV/vis spectroscopy.