• Title/Summary/Keyword: specific heat coefficient

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Development of 3-D Flow Analysis Code Using Unstructured Grid System (I) - Numerical Method - (비정렬격자계를 사용하는 3차원 유동해석코드 개발 (I) - 수치해석방법 -)

  • Kim, Jong-Tae;Myong, Hyon-Kook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.9 s.240
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    • pp.1049-1056
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    • 2005
  • A conservative pressure-based finite-volume numerical method has been developed for computing flow and heat transfer by using an unstructured grid system. The method admits arbitrary convex polyhedra. Care is taken in the discretization and solution procedures to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are found by a novel second-order accurate spatial discretization. Momentum interpolation is used to prevent pressure checkerboarding and the SIMPLE algorithm is used for pressure-velocity coupling. The resulting set of coupled nonlinear algebraic equations is solved by employing a segregated approach, leading to a decoupled set of linear algebraic equations fer each dependent variable, with a sparse diagonally dominant coefficient matrix. These equations are solved by an iterative preconditioned conjugate gradient solver which retains the sparsity of the coefficient matrix, thus achieving a very efficient use of computer resources.

A Study on the Frictional Abrasion Properties of MMC (금속기 복합재료의 마찰ㆍ마모 특성에 관한 연구)

  • 이광영;박원조;허선철
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.6
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    • pp.171-177
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    • 2002
  • Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties, it was also highlighted as the material of frontier industry because strength, heat-resistant, corrosion-resistant and wear-resistant were superiored. In recent years, the study of metal matrix composite has increased by aluminum alloy. The study is based on the tribological properties of AC4CH that is a part of the mechanical property of metal matrix composites. Metal matrix composite that is produced from matrix material AC4CH and reinforcement SiO$_2$, Al$_2$O$_3$ and TiO$_2$ are added to the metal matrix composite fur strength so binding among the whisker can take place. Each metal matrix composite is produced using the squeeze casting method. To test for tribe a pin-on-disk machine and lubricant is used without paraffine 8.2CST at room temperature which is 40$\^{C}$. As the results of this study, the tribological properties of each specimen are more improved than AC4CH. The variation of coefficient resistance is more stable at the AC4CH and TiO$_2$, but the variation rates are higher at the inanimate binder.

Performance Analysis of The KALIMER Breakeven Core Driver Fuel Pin Based on Conceptual Design Parameters

  • Lee Dong Uk;Lee Byoung Oon;Kim Young Gyun;Lee Ki Bog;Jang Jin Wook
    • Nuclear Engineering and Technology
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    • v.35 no.4
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    • pp.356-368
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    • 2003
  • Material properties such as coolant specific heat, film heat transfer coefficient, cladding thermal conductivity, surface diffusion coefficient of the multi-bubble are improved in MACSIS-Mod1. The axial power and flux profile module was also incorporated with irradiation history. The performance and feasibility of the updated driver fuel pin have been analyzed for nominal parameters based on the conceptual design for the KALIMER breakeven core by MACSIS-MOD1 code. The fuel slug centerline temperature takes the maximum at 700mm from the bottom of the slug in spite of the nearly symmetric axial power distribution. The cladding mid-wall and coolant temperatures take the maximum at the top of the pin. Temperature of the fuel slug surface over the entire irradiation life is much lower than the fuel-clad eutectic reaction temperature. The fission gas release of the driver fuel pin at the end of life is predicted to be $68.61\%$ and plenum pressure is too low to cause cladding yielding. The probability that the fuel pin would fail is estimated to be much less than that allowed in the design criteria. The maximum radial deformation of the fuel pin is $1.93\%$, satisfying the preliminary design criterion ($3\%$) for fuel pin deformation. Therefore the conceptual design parameters of the driver fuel pin for the KALIMER breakeven core are expected to satisfy the preliminary criteria on temperature, fluence limit, deformation limit etc.

Estimation Methods for Turbine Nozzle Throat Area Reduction of A LOx/Kerosene Gas Generator Cycle Liquid Propellant Rocket Engine (액체산소/케로신 가스발생기 사이클 액체로켓엔진 터빈 노즐목 면적 변화 추정 방법)

  • Nam, Chang-Ho;Moon, Yoonwan;Park, Soon Young;Kim, Jinhan
    • Journal of the Korean Society of Propulsion Engineers
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    • v.23 no.5
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    • pp.101-106
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    • 2019
  • Carbon deposition on the turbine nozzle throat of a LOx/kerosene gas generator cycle(open cycle) engine causes performance reduction of the engine. Estimation methods for a turbine nozzle throat area are proposed. The discharge coefficient of the turbine nozzle was estimated with the turbine gas properties such as gas constant, specific heat ratio, and temperatures. The pressure ratio and temperature ratio of the turbine nozzle throat, was utilized to estimate the discharge coefficient also. Estimated discharge coefficient of turbine nozzle throat of KSLV-II 1st stage engine shows the carbon deposition effects on the turbine nozzle throat of a LOx/kerosene open cycle engine.

Fundamental Study for Reformation of Safety Standard about Portable Butane Gas Range (이동식 부탄 연소기의 안전기준 개정을 위한 기초 연구)

  • Kim, Sooik;Keum, Kuk Bin;Yu, Byeonghun;Lee, Chang-Eon;Kim, Young-Gu
    • Journal of the Korean Society of Combustion
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    • v.19 no.4
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    • pp.35-41
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    • 2014
  • The experiment was conducted to measure temperature and pressure around operating portable butane gas ranges with oversized cookwares. In this experiment, portable butane gas range with different safety equipment and two kinds of oversized cookware, each of which is made of aluminum alloy and rock, was used. As a result, temperature of the bottom of the butane and the pressure of butane barrel tend to aligned with each other. Through this result, it is reasonable that a safety criteria can be decided based on the temperature of the bottom of butane. Especially, portable butane gas ranges are safely conducted under the condition of the temperature is under 50 degree and pressure is under 500 kPa, respectively, at the bottom of the butane barrel.

An Experimental Study on the Bed Combustion Phenomena in MSW(Municipal Solid Waste) Incinerator (폐기물 소각로 베드에서의 연소현상 관찰을 위한 실험적 연구)

  • Min, Jee Hyun;Shin, Donghoon;Choi, Sangmin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.2
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    • pp.159-165
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    • 1999
  • Experimental studies have been performed to observe the basic phenomena of waste bed combustion in MSW incinerator. A reduced scale apparatus was utilized to simulate the combustion behavior in real plant with 1-dimensional transient behavior at the experimental setup, which uses wet cubic wood with ash content as simulated waste. LHV (lower heating value) of solid fuel, fuel particle size and flow rate of combustion air were taken as important parameters of the bed combustion. For the quantitative analysis, FPR (flame propagation rate), TBT (total burn-out time) and PBT (particle burn-out time) was defined. LHV represent the capability of heat release of the fuel, so that a higher LHV results in faster reaction rate of the fuel bed, which is shown by higher FPR. Fuel particle size is related with surface area per unit mass as well as heat and mass transfer coefficient. As the particle size increases the FPR decreases owing to decreasing specific surface area. Air injection supplies oxygen to the reaction zone. However oversupply of combustion air increases convection cooling of the bed and possibly extinguishes the flame.

High temperature Friction and Wear of Friction Material; The Effect of the Relative Amount of Graphite and Zirconium Silicate (ZrSiO$_4$) (흑연과 지르콘의 상대적 함량에 따른 마찰재의 고온 마찰 및 마모특성)

  • Kim, Seong-Jin;Jang, Ho
    • Tribology and Lubricants
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    • v.16 no.5
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    • pp.365-372
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    • 2000
  • Tribological behavior of novolac resin-based friction materials with three different relative amounts of graphite and zirconium silicate was investigated by using a pad-on-disk type friction tester. The goal of this paper is to examine the effects of the relative amount of a lubricant and an abrasive in the automotive friction material on friction and wear characteristics at elevated temperature. Friction and wear of friction materials were affected by the existence of transfer film(3$\^$rd/ body layer) at friction interface and the composition of friction material, especially lubricant amount. The friction material with higher content of graphite indicated homogenized and durable transfer film, and resulted in stable friction coefficient regardless of the increase in friction heat. The experimental result also showed that the higher concentration of ZrSiO$_4$ in friction material aggravated friction stability and wear resistance due to the higher friction heat generated at fiction interface during high temperature friction test.

An Experimental Study for Characteristics Evaluation of Cement Mortar Using Infrared Thermography Technique (적외선 화상기법을 이용한 시멘트 모르타르 특성의 실험적 평가)

  • Kwon, Seung-Jun;Maria, Q. Feng
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.1A
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    • pp.53-59
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    • 2010
  • Recently, NDTs (Non-Destructive Techniques) using infrared camera are widely studied for detection of damage and void in RC (reinforced concrete) structures and they are also considered as an effective techniques for maintenance of infrastructures. The temperature on concrete surface depends on material and thermal properties such as specific heat, thermal conductivity, and thermal diffusion coefficient. Different porosity on cement mortar due to different mixture proportions can show different heat behavior in cooling stage. The porosity can affect physical and durability properties like strength and chloride diffusion coefficient as well. In this paper, active thermography which uses flash for heat induction is utilized and thermal characteristics on surface are evaluated. Samples of cement mortar with W/C (water to cement ratio) of 0.55 and 0.65 are prepared and physical properties like porosity, compressive strength, and chloride diffusion coefficient are evaluated. Then infrared thermography technique is carried out in a constant room condition (temperature $20{\sim}22^{\circ}C$ and relative humidity 55-60%). The mortar samples with higher porosity shows higher residual temperature at the cooling stage and also shows reduced critical time which shows constant temperature due to back wall effect. Furthermore, simple equation for critical time of back wall effect is suggested with porosity and experimental constants. These characteristics indicate the applicability of infrared thermography as an NDT for quality assessment of cement based composite like concrete. Physical properties and thermal behavior in cement mortar with different porosity are analyzed in discussed in this paper.

Thermodynamic Properties of R-32(Difluoromethane) and Initial Evaluation of Thermodynamic Perfomance as A R-22 Alternative Refrigerant (대체냉매 R-32(Difluoromethane)의 열역학적 물성과 R-22 대체냉매로서 열역학적 성능의 초기 평가)

  • Park, Y.M.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.2
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    • pp.141-155
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    • 1993
  • Thermodynamic properties of R-32 are calculated and its refrigeration performance is evaluated for the purpose the feasibility study of replacing R-22 with R-32. (1) Refrigeration effect of R-32 is superior to that of R-22 because heat of evaporation of R 32 is about 50% higher than that of R-22. However, COP of R-32 system is 10-30% lower than that of R-22 system. It is mainly attributed to the vapor pressore of R-32 being about 62% higher than R-22. (2) Since the pressure ratio and the specific heat ratio of R-32 system is higher than those of R -22, compressor discharging temperature rises as high as to $130-150^{\circ}C$. It may cause mechanical failure of compressor due to the breakdown of lubricant. Compressor should be improved to lower the temperature if R-32 is to replace R-22. (3) Averaged two-phase heat transfer coefficient of R-32 is about 10-20% higher than that of R-22. It may assume better heat exchanger effectiveness but not guarantee the better COP of R-32 system than R-22. (4) The high vapor pressure is the first reason to drop R-32 out of the line of R-22 alternative refrigerant. So, refrigerant mixtures based on R-32 are recommended to adjust the vapor pressure first and keep superior volumetric capacity of R-32.

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Thermal Characteristics of Cement Concrete Mixed with Wasted Vinyl Aggregates (폐비닐 골재가 혼합된 시멘트 콘크리트의 열 특성)

  • Yeom, Woo Seong;An, Gi Hong;Liu, Ju Ho;Jeong, Jin Hoon
    • International Journal of Highway Engineering
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    • v.16 no.6
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    • pp.79-86
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    • 2014
  • PURPOSES : In this study, wasted vinyl aggregate, which possesses better thermal properties than natural aggregate, was used in cement concrete mixture to develop more economical concrete with thermal insulation and freeze prevention effects. METHODS : Slump and air content of the fresh concrete, which substituted its 0%, 5%, and 10% of coarse aggregate with wasted vinyl aggregate, were measured. Compressive strength, Poisson's ratio, elastic modulus, and splitting tensile strength of hardened concrete were measured by laboratory tests. Thermal properties of concrete such as coefficient of thermal expansion, thermal conductivity, and specific heat were also measured according to replacement ratio of wasted vinyl aggregate. Finally, the thermal insulation and freeze prevention effectiveness of the concrete mixed with wasted vinyl aggregate was confirmed through finite element analysis of road pavement crossing above concrete box culvert made from wasted vinyl aggregate. RESULTS : Even though the physical properties of wasted-vinyl-aggregate concrete such as compressive strength, Poisson°Øs ratio, elastic modulus, and splitting tensile strength were inferior to those of ordinary concrete, they met requirements for structural concrete. The thermal properties of concrete were improved by wasted vinyl aggregate because it decreased thermal conductivity and increased specific heat of the concrete. According to the result of finite element analysis, temperature variation in pavement subgrade was mitigated by box culvert made from wasted-vinyl-aggregate concrete. CONCLUSIONS : Through the laboratory test and finite element analysis of this study, it was concluded that the concrete structures made from wasted vinyl aggregate showed thermal insulation and freeze prevention effects.