• Title/Summary/Keyword: Capillary performance

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Durability of self compacted concrete containing slag in hot climate

  • Yahiaoui, Walid;Kenai, Said;Menadi, Belkacem;Kadri, El-Hadj
    • Advances in concrete construction
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    • v.5 no.3
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    • pp.271-288
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    • 2017
  • This paper aims to investigate the effects of replacing cement with ground granulated blast furnace slag (GGBFS) in self compacting concrete in the fresh and hardened state. The performance of SCC in moderate climate is well investigated but few studies are available on the effect of hot environment. In this paper, the effect of initial water-curing period and curing conditions on the performance of SCC is reported. Cement was substituted by GGBFS by weight at two different levels of substitution (15% and 25%). Concrete specimens were stored either in a standard environment (T=$20^{\circ}C$, RH=100%) or in the open air in North Africa during the summer period (T=35 to $40^{\circ}C$; R.H=50 to 60%) after an initial humid curing period of 0, 3, 7 or 28 days. Compressive strength at 28 and 90 days, capillary absorption, sorptivity, water permeability, porosity and chloride ion penetration were investigated. The results show that the viscosity and yield stress are decreased with increasing dosage of GGBFS. The importance of humid curing in hot climates in particular when GGBFS is used is also proved. The substitution of cement by GGBFS improves SCC durability at long term. The best performances were observed in concrete specimens with 25% GGBFS and for 28 days water curing.

Design of air-cooled waste heat removal system with string type direct contact heat exchanger and investigation of oil film instability

  • Moon, Jangsik;Jeong, Yong Hoon;Addad, Yacine
    • Nuclear Engineering and Technology
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    • v.52 no.4
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    • pp.734-741
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    • 2020
  • A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.

The role of extensional rheology in polymer processing

  • Baird, Donald G.
    • Korea-Australia Rheology Journal
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    • v.11 no.4
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    • pp.305-311
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    • 1999
  • The shear behavior of polymers obtained by means of devices such as capillary and cone-and-plate rheo-meters is commonly used to assess their processing performance and as a characterization tool. However, the number of instances when two polymers have the same shear properties but perform differently during certain types of processing operations (e.g. film blowing and sheet extrusion) indicate that shear properties alone may not be sufficient to characterize polymeric fluids. We begin by defining the kinematics of shear-free or extensional flow and the associated material functions. The extensional and shear behavior of three different types of polyethylene (PE) are then compared to illustrate the points that one cannot ascertain the extensional properties of polymer melts from their shear properties and, furthermore, there may not be a simple relation between properties obtained from one type of extensional flow and those of another type. The kinematics of most processing flows are extensional rather than shear in nature, and , hence, the performance of polymers during processes such as fiber spinning, film casting, film blowing, thermoforming, blow molding, and even extrusion is more readily accounted for through extensional viscosity measurements. Methods for carrying out extensional flow measurements are then reviewed including approximate methods. To illustrate the sensitivity of extensional viscosity measurements to subtle changes in the molecular architecture of PEs, results are presented for samples with a narrow molecular weight distribution but with varying numbers of long chain branches. Finally, constitutive equations which allow one to separate shear and extensional flow behavior are discussed as any attempts to simulate the subtle processing differences between two polymers will require constitutive equations of this nature.

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Experimental Characterization of Hydrodynamic Bearing Spindle Motor for High Performance Hard Disk Drive (고성능 하드 디스크 드라이브 개발을 위한 유체베어링 스핀들 모터의 특성분석(현장개발사례: SAMSUNG HDD ′SPINPOINT POLARIS SERIES′))

  • Son, Young;Hwang, Tae-Yeon;Han, Tun-Sik;Kang, Seong-Woo;Morris, Frank
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.930-935
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    • 2001
  • The experimental characterization of hydrodynamic bearing spindle motor is performed for the practical implementation of high-performance hard disk drive system. Firstly, the design concept of hydrodynamic bearing for the disk drive system is addressed including the herringbone grooved journal bearing, the spiral grooved thrust bearing, capillary seal design, and the viscous pumping of fluid. Secondly, the experimental evaluation is performed for the disk drive system in which the hydrodynamic bearing spindle motor is implemented and its dynamic performances are compared with conventional ball-bearing spindle motor. The key parameters include NRRO(Non Repeatable Run-Out), disk dynamics, acoustics, and resultant PES (Position Error Signal). Finally, the external gyro-exciting test results including 200k CSS(Continuous Start-Stop) on three angular attitudes(0,90, 180 degree) are presented in order to verify the practical reliability of disk drive system subject to the gyro-motion of hydrodynamic bearing spindle motor.

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Waste Isolation Pilot Plant Performance Assessment: Radionuclide Release Sensitivity to Diminished Brine and Gas Flows to/from Transuranic Waste Disposal Areas

  • Day, Brad A.;Camphouse, R.C.;Zeitler, Todd R.
    • Nuclear Engineering and Technology
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    • v.49 no.2
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    • pp.450-457
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    • 2017
  • Waste Isolation Pilot Plant repository releases are evaluated through the application of modified parameters to simulate accelerated creep closure, include capillary pressure effects on relative permeability, and increase brine and gas saturation in the operations and experimental (OPS/EXP) areas. The modifications to the repository model result in increased pressures and decreased brine saturations in waste areas and increased pressures and brine saturations in the OPS/EXP areas. Brine flows up the borehole during a hypothetical drilling intrusion are nearly identical and brine flows up the shaft are decreased. The modified parameters essentially halt the flow of gas from the southern waste areas to the northern nonwaste areas, except as transported through the marker beds and anhydrite layers. The combination of slightly increased waste region pressures and very slightly decreased brine saturations result in a modest increase in spallings and no significant effect on direct brine releases, with total releases from the Culebra and cutting and caving releases unaffected. Overall, the effects on total high-probability mean releases from the repository are insignificant, with total low-probability mean releases minimally increased. It is concluded that the modified OPS/EXP area parameters have an insignificant effect on the prediction of total releases.

Performance Characteristics of a Loop Thermosyphon for Heat Source Cooling (열원 냉각용 루프 써모사이폰의 작동 특성)

  • Choi, Du-Sung;Song, Tae-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.12
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    • pp.1475-1483
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    • 2004
  • Loop thermosyphon(LTS) has many good characteristics such as low thermal resistance, no power consumption, noiseless operation and small size. To investigate the overall performance of LTS, we have performed various experiments varying three parameters: input power of the heater, working fluid(water, ethanol, FC3283) and filling ratio of the working fluid. At a combination of these parameters, temperature measurements are made at many locations of the LTS. The temperature difference between the evaporator and the condenser is used to obtain the thermal resistance. In addition, flow visualization using a high speed camera is carried out. The thermal resistance is not constant. It is lower at higher input power, which is one of the distinct merits of LTS. Flow instabilities are frequently observed when changing the working fluid, the input power and the filling ratio. The results show that the LTS can be readily put into practical use. Future practical application in electronic cooling is recommended.

End Use Tactile Property of the Split-type Nylon/PET Microfiber Fabrics (마찰과 세탁에 의한 극세섬유 직물의 표면과 촉감변화에 관한 연구)

  • 오경화;윤재희
    • Journal of the Korean Society of Clothing and Textiles
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    • v.28 no.3_4
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    • pp.539-545
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    • 2004
  • In this study, the effect of washing, bleaching, and abrasion on tactile and the water absorption properties of the split-type Nylon/Polyester (N/P) microfiber pile-knit was investigated under various enduse conditions. We examined the water absorption and surface properties of PET microfiber which will be very useful in the future. We also studied the variations of their performance during usage caused by friction and repeated washing, regard to all kinds of physical, chemical changes which will appear while using those textiles. Progress in further splitting of PET microfiber fabric is observed with increases in the number of washing and bleaching cycles, and treatment temperature. Initial water absorption (%) was increased with progress in splitting, which provided efficient capillary channel. Surface properties were varied with additional splitting by washing and abrasion. Formation of pilling and splitting by abrasion increase surface roughness, diminishing tactile property, and reduced water absorption property. The current results from this study is expected to provide the appropriate washing management guide to consumers, and to inform end-use performance of product to a producer for improving product quality.

Development of Powder Injection Molding Process for a Piezoelectric PAN-PZT Ceramics

  • Han, Jun Sae;Park, Dong Yong;Lin, Dongguo;Chung, Kwang Hyun;Bollina, Ravi;Park, Seong Jin
    • Journal of Powder Materials
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    • v.23 no.2
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    • pp.112-119
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    • 2016
  • A powder injection molding process is developed and optimized for piezoelectric PAN-PZT ceramics. Torque rheometer experiments are conducted to determine the optimal solids loading, and the rheological property of the feedstock is evaluated using a capillary rheometer. Appropriate debinding conditions are chosen using a thermal gravity analyzer, and the debound specimens are sintered using sintering conditions determined in a preliminary investigation. Piezoelectric performance measures, including the piezoelectric charge constant and dielectric constant, are measured to verify the developed process. The average values of the measured piezoelectric charge constant and dielectric constant are 455 pC/N and 1904, respectively. Powder injection molded piezoelectric ceramics produced by the optimized process show adequate piezoelectric performance compared to press-sintered piezoelectric ceramics.

Effects of Accumulator Heat Exchangers on the Performance of a Refrigeration System (열교환기 내장형 어큐물레이터가 냉동시스템의 성능에 마치는 영향에 관한 연구)

  • Kang, Hoon;Choi, Kwang-Min;Park, Cha-Sik;Kim, Yong-Chan
    • Proceedings of the SAREK Conference
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    • 2005.11a
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    • pp.433-438
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    • 2005
  • An AHX(Accumulator Heat eXchanger) consists of a commercial accumulator and an inner heat exchanger located inside of the accumulator. The AHX is used in multi air-conditioners to assure the liquid-phase refrigerant entering into the expansion device. This purpose is achieved by heat transfer between the refrigerant leaving the evaporator and the refrigerant leaving the condenser. In this study, the effects of AHX on the performance of a refrigeration system using H-22 were measured and the test results were analyzed. The operating characteristics of the refrigeration system with the installation of AHX were quite different from those without the installation of AHX. Therefore, it is required to find an optimum refrigerant charging amount and optimum operating conditions, when AHX is installed in the refrigeration system with an fixed area expansion device such as a capillary tube.

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Performance Analysis of Hybrid Heat Pump System of the Air-to-Air/Air-to-Water with the Ambient Temperature (외기온 변화에 따른 공기-공기/공기-물 형태로 된 복합형 열펌프 시스템의 성능 특성 분석)

  • 송현갑
    • Journal of Biosystems Engineering
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    • v.25 no.4
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    • pp.273-278
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    • 2000
  • The hybrid heat pump system of the air to air and / or air to water was composed and its COP was analyzed with the ambient temperature on the opened and closed loop system respectively. The results be indicated by the equation(7) that the COP(Coefficient of Performance) of air-source(air to air and / or air-water) heat pump is effected with the ambient air temperature and AVACTHE.(Automatic Variable Area Capillary Type Heat Exchanger) 2. The COP of air-to-water heat pump without AVACTHE decreased in accordance with the ambient temperature decrease, however in case of the heat pump with AVACTHE the COP was maintained at 2.8∼3.0 level when the ambient temperature decrease from -$5^{\circ}C$ to $-11^{\circ}C$. 3. The COP of the air-to-water heat pump operated on the open loop was higher 40∼58% than that of the heat pump operated on the close loop. 4. The lower ambient temperature air effect on the COP of the air-to-air heat pump operated on the semi closed loop could be controlled using the AVACTHE, and at the high ambient air temperature the COP increased using the Bypass circuit.

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