• 제목/요약/키워드: low-shear viscosity

검색결과 154건 처리시간 0.029초

천이영역의 희박기체 압축성 경계층 해석 (Analysis of rarefied compressible boundary layers in transition regime)

  • 최서원
    • 대한기계학회논문집B
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    • 제21권4호
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    • pp.509-517
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    • 1997
  • Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

Thermotropic Liquid Crystal Polymer and PBT Blend

  • Lim, Sung-Tack;Kim, Seong-Hun
    • 한국섬유공학회:학술대회논문집
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    • 한국섬유공학회 1998년도 봄 학술발표회 논문집
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    • pp.14-19
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    • 1998
  • Increasing demand for high modulus high strength polymeric materials have drawn considerable interest in industry. Thermotropic liquid crystal polymers (TLCP), differing from lyotropic liquid crystal polymers, have excellent melt processability and mechanical property resulting from the high degree of molecular orientation under a shear flow field in the molten state with relatively low viscosity$\^$1,2/.(omitted)

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Polymer blends with a liquid crystalline polymer dispersed phase

  • Lee, Heon-Sang;Morton M. Denn
    • Korea-Australia Rheology Journal
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    • 제11권4호
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    • pp.269-273
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    • 1999
  • Immiscible polymer blends containing a liquid crystalline polymer dispersed phase can be described by existing blend theories when the dispersed-phase droplets are large relative to the orientation correlation length ("domain size") of the LCP. There does not appear to be an interfacial contribution to the linear viscoelastic properties of the blend from droplets smaller than the correlation length. Polyester blends, where interfacial interactions occur between the LCP and the matrix, exhibit a reduction in viscosity to below the viscosity of either component at low shear rates, where the droplet morphology is spherical. These anomalies cannot be explained in the context of existing theory.ng theory.

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키토산으로 처리한 직물의 태의 변화에 관한 연구(제 4보) (A Study on the Change of Hand of Chitosan-treated Fabrics(Part IV))

  • 서한경;김종준
    • 한국의류학회지
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    • 제22권8호
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    • pp.1079-1089
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    • 1998
  • Various fabrics, including natural fibers, regenerated cellulosic fibers, synthetic fibers, blend yarn, and mixture fabrics, were treated with the solutions of high purity chitosan in 1% acetic acid, having high viscosity of 930cps or low viscosity of 8cps. Physical/ mechanical properties of the treated fabrics samples were measured using Kawabata Evaluation System and drape tester. From these, hand values and total hand values of the fabric samples were calculated using Kawabata-Niwa translation equations. KOSHI, SHARI, HARI values have increased for the treated samples, while FUKURAMI values have decreased in general.

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Si3N4의 슬립물성과 Slip Cast Si3N4의 미세구조에 관한 연구 (Rheological Properties of Si3N4 Suspension and Microstructure of Slip Cast Si3N4)

  • 박정현;김진숙;박한수
    • 한국세라믹학회지
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    • 제25권6호
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    • pp.615-622
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    • 1988
  • To develope good slip and microstructure of Si3N4 the knowledge of the interaction of particles in liquid systems is required. In this work polyethyleneimines was tested as a stabilizer for Si3N4-water system. The stability of slip dispersed with polyethyleneimines was good over a wide range of pH and concentrated slips with low viscosity could be cast. This work comprises a systematic investigation including determination of electrical mobility in order to estimate the particle surface charge, determination of sedimentation rate, as well as measurements of the viscosity as a function of dispersants, pH and shear rates. The influence of deflocculation on the microstructure of slip cast Si3N4 was discussed.

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숙성기간에 따른 재래 고추장의 유동성 변화 (Flow Properties of Traditional Kochujang : Effect of Fermentation Time)

  • 유병승;최원석;류영기
    • 한국식품영양과학회지
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    • 제28권3호
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    • pp.554-558
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    • 1999
  • Flow properties of traditional kochujang at various fermentation times(0~12 weeks) were determined with rotational cylindrical(RC) and serrated plate plate(PP) viscometer. Magnitudes of consistency index(K) of power law model and Cassson parameters(yield stress and viscosity) measured by PP viscometer were higher than those using RC viscometer. All kochujang samples during fermentation were much shear thinning with values of flow behavior index(n) as low as 0.2~0.34. K value and Casson yield stress measured by PP viscometer had good correlations(r=0.94; r=0.91) with fermentation time. No significant changes in flow model parameters measured by RC viscometer were observed for kochu jang during fermentation. Magnitudes of flow model parameters measured by PP viscometer more closely correlated with fermantation times of kochujang than did RC viscometer.

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Performance of Urea-Formaldehyde Resins Synthesized at Two Different Low Molar Ratios with Different Numbers of Urea Addition

  • Jeong, Bora;Park, Byung-Dae
    • Journal of the Korean Wood Science and Technology
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    • 제47권2호
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    • pp.221-228
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    • 2019
  • This study reports the performance of urea-formaldehyde (UF) resins prepared at two different low formaldehyde/urea (F/U) mole ratios with different numbers of urea addition during synthesis. The second or third urea was added during the synthesis of UF resins to obtain two different low molar ratios of 0.7 and 1.0, respectively. The molecular weights, cure kinetics, and adhesion performance of these resins were characterized by the gel permeation chromatography, differential scanning calorimetry, and tensile shear strength of plywood, respectively. When the number of urea additions and F/U molar ratio increased, the gelation time decreased, whereas the viscosity and molecular weight increased. Further, the UF resins prepared with the second urea and 1.0 molar ratio resulted in greater activation energy than those with third urea and 0.7 molar ratio. Tensile shear strength and formaldehyde emission (FE) of the plywood that bonded with these resins increased when the number of urea additions and molar ratio increased. These results suggest that the UF resins prepared with 0.7 molar ratio and third urea addition provide lower adhesion performance and FE than those resins with 1.0 mole ratio and the second urea addition.

Evaluation of physicochemical and textural properties of myofibrillar protein gels and low-fat model sausage containing various levels of curdlan

  • Lee, Chang Hoon;Chin, Koo Bok
    • Asian-Australasian Journal of Animal Sciences
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    • 제32권1호
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    • pp.144-151
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    • 2019
  • Objective: Curdlan has been widely used as a gelling agent in various food systems. This study was performed to evaluate the rheological properties of pork myofibrillar protein (MP) with different levels of curdlan (0.5% to 1.5%) and its application to low-fat model sausages (LFS). Methods: MP mixtures were prepared with 0.5%, 1.0%, and 1.5% of curdlan. Cooking loss (%), gel strength (gf), shear stress (Pa), and scanning electron microscopy were measured. Physicochemical and textural properties of LFS containing different levels of curdlan were measured. Results: The shear stress of MP mixtures increased with increasing levels of curdlan. MP gels with increased levels of curdlan decreased cooking loss and increased gel strength (p<0.05). The MPs with 1.0% and 1.5% of curdlan were observed more compact three-dimensional structure than those with 0.5% curdlan. Increased curdlan level in LFS affected redness ($a^{\star}$) and yellowness ($b^{\star}$) values. Although expressible moisture of LFS did not differ among curdlan levels, LFSs with various levels of curdlan decreased cooking loss as compared to control sausages. Hardness values (2,251 to 2,311 gf) of LFS with 0.5% and 1.0% curdlan was increased and differ from those (1,901 gf) of control sausages. Conclusion: The addition of 1.0% curdlan improved the functional and textural properties of LFS.

Effect of addition of methanol on rheological properties of silk formic acid solution

  • Bae, Yu Jeong;Um, In Chul
    • International Journal of Industrial Entomology and Biomaterials
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    • 제40권1호
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    • pp.28-32
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    • 2020
  • Recently, many studies have been undertaken on the wet spinning and electrospinning of silk because wet-spun fibers and electrospun webs of silk can be applied in the biomedical and cosmetic fields owing to the good biocompatibility of silk. The rheological properties of silk solution are important because they strongly affect the spinning performance of the silk solution and the structures of resultant fibrous materials. Therefore, as a preliminary study on the effect of solvent composition on the rheological properties of silk fibroin (SF) solution and structure of the resultant film, in the reported work, methanol was added to the SF formic acid solution. A small amount of methanol (i.e. 2%) added to the SF formic acid solution significantly altered the rheological properties of the solution: its shear viscosity increased by 10 folds at low shear and decreased on increasing the shear rate, demonstrating shear thinning behavior of the SF solution. Dynamic tests for the SF solution indicated that the addition of 2% methanol altered the viscous state of the SF formic acid solution to elastic. However, the molecular conformation (i.e. β-sheet conformation) of the regenerated SF film cast from formic acid remained unchanged on the addition of 2% methanol.

난류 파이프 유동에서의 레이놀즈 수 영향: Part I. 평균 유동장 및 저차 난류통계치 (REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART I. MEAN FLOW FIELD AND LOW-ORDER STATISTICS)

  • 강창우;양경수
    • 한국전산유체공학회지
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    • 제16권4호
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    • pp.28-38
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.