• Title/Summary/Keyword: Thermodynamic parameter

Search Result 104, Processing Time 0.029 seconds

Unsteady Heat Transfer in Radiatively Active Spherical Medium (구형 복사 매질에서의 비정상 열전달 특성에 관한 연구)

  • 한상헌;백승욱;안국영
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.17 no.10
    • /
    • pp.2582-2589
    • /
    • 1993
  • Transient heat transfer characteristics of cooling of a spherical body were investigated in the radiatively active spherical medium. Initially the spherical body and the medium were maintained at their constant temperatures. Then heat transfer begins from spherical body t medium. The heat transfer mode inside the spherical body is just conduction. But heat is transferred by both conduction and radiation inside the medium. All thermodynamic properties were held constant in time. Spherical symmetry is assumed. DOM was adopted to solve RTE. The effect of characteries-tic optical thickness, conduction to radiation parameters, and solid surface emissivity has been studied.

On the drying out of bipolar membranes

  • Kedem, Ora;Ghermandi, Andrea;Messalem, Rami
    • Membrane and Water Treatment
    • /
    • v.4 no.3
    • /
    • pp.215-222
    • /
    • 2013
  • The maximum current density that can be achieved in bipolar membrane electrodialysis is limited by the sharp increase in resistance that is experienced when the water content at the membrane interface is not adequately replenished and the membranes dry out. In this paper we show how the water content near the interface depends on the properties of the membranes. A water retaining parameter is introduced, which characterizes the thermodynamic properties of the membrane material and may be used to guide the choice of polymers for mitigation of the dry-out problem.

RECURRENT PATTERNS IN DST TIME SERIES

  • Kim, Hee-Jeong;Lee, Dae-Young;Choe, Won-Gyu
    • Journal of Astronomy and Space Sciences
    • /
    • v.20 no.2
    • /
    • pp.101-108
    • /
    • 2003
  • This study reports one approach for the classification of magnetic storms into recurrent patterns. A storm event is defined as a local minimum of Dst index. The analysis of Dst index for the period of year 1957 through year 2000 has demonstrated that a large portion of the storm events can be classified into a set of recurrent patterns. In our approach, the classification is performed by seeking a categorization that minimizes thermodynamic free energy which is defined as the sum of classification errors and entropy. The error is calculated as the squared sum of the value differences between events. The classification depends on the noise parameter T that represents the strength of the intrinsic error in the observation and classification process. The classification results would be applicable in space weather forecasting.

Equations of State for Hard-Sphere Chains: Effect of Attractive Contribution

  • Kim Jae-Jun
    • Macromolecular Research
    • /
    • v.14 no.2
    • /
    • pp.220-229
    • /
    • 2006
  • Several equations of state for hard-sphere chains with various perturbation terms are reviewed. For each model, three characteristic parameters are required to represent phase equilibria of normal fluids and obtained from thermodynamic properties of pure saturated liquids. The models are then compared with computer simulation data to show the effect of attractive contribution forms employed. Calculated values of vapor-liquid equilibria (VLE) of hydrocarbons that can be reproduced for each model are also compared with experimental results. An additional parameter, ${\zeta}_{KB}$, is required to represent the VLE of pure water, which is ascertained to have a strong influence on the theoretical coexistence curve.

The Relationship Between the Permeation Rate and the Solubility Parameter for Polyethylene-n-Hexane-Benzene System in Pervaporation (폴리에틸렌-n-헥산-벤젠계에 대한 투과속도와 용해도 파라메타 사이의 관계)

  • Rhim, Ji-Won
    • Membrane Journal
    • /
    • v.3 no.3
    • /
    • pp.136-139
    • /
    • 1993
  • It is well known that the membrane permeation in pervaporation is governed by both the chemical nature of the membrane material and the physical structure of the membrane and also the separation can be achieved by differences in either solubility, size or shape. The solubility of the penerrant in the polymeric membrane can be described qualitively by applying the Hildebrand relation [1] which relates the energy of mixing of the penerrant and the polymer material. Froehling et al. have tried to predict the swelling behavior of polymers for the systems of polyvinylchloride(PVC)-toluene-methanol, PVC-trichloroethylene-nitromethane and PVC-n-butylacetate-nitromethane[2]. The former two systems which do not show the donor/acceptor interactions upon mixing showed the successful results[2]. In addition to this technique, there are several other possible approaches to predict the swelling behaviors of polymers, such as the surface thermodynamic approach[3, 4], the comparison of the membrane polarity with the solvent polarity in terms of Dimroth's solvent polarity value[5].

  • PDF

Second Law Optimization of Water-to-Water Heat Pump System

  • Kim, Kyu-Hyung;Woo, Joung-Son;Lee, Se-Kyoun
    • Journal of Mechanical Science and Technology
    • /
    • v.17 no.1
    • /
    • pp.122-128
    • /
    • 2003
  • This paper presents a thermodynamic analysis of heat pump system using water as a heat source and heat sink. The primary object in this study is the optimization of exergetic efficiency. Two different systems, 2-stream and 1-stream system, are analyzed in detail. Mass flow ratio (the ratio of mass flow rate of water through evaporator to that through condenser) is identified as the most important parameter to be optimized. It is shown that there exists an optimum mass flow ratio to maximize exergetic efficiency. The variation of optimum exergetic efficiency of 2-stream system is quite small and the value lies between 0.2∼0.23 for the range of investigation in this study. However, far better performance can be obtained from 1-stream system. This means considerable irreversibilities are generated through condenser of the 2-stream system. The effects of adiabatic efficiency of compressor-motor unit on the overall system performance are also examined in the analysis.

A Numerical Analysis of Supersonic Impinging Jet Flows on Curved Surfaces using Upwind Wavier-Stokes Method (Upwind Navier-Stokes 방법을 이용한 굴곡면에 충돌하는 초음속 제트유동의 수치 해석적 연구)

  • Seo Jeong Il;Song Dong Joo
    • Proceedings of the KSME Conference
    • /
    • 2002.08a
    • /
    • pp.229-232
    • /
    • 2002
  • For the purpose of Thermal Protection Material design problem, a numerical analysis of axisymmetric high temperature supersonic impinging jet flows of exhaust gas from combustor on curved surfaces has been accomplished. A modifed CSCM Upwind Navier-Stokes method which is able to cure the carbuncle Phenomena has been developed to study strong shock wave structure and thermodynamic wall properties such as pressure and heat transfer rate on various curved surfaces. The results show that the maximum heat transfer rate which is the most important parameter affecting thermo-chemical surface ablation on the plate did not occur at the center of jet impingement, but rather on a circle slightly away from the center of impingement and the shear stress distribution alone the wall is similar to the wall heat transfer late distribution.

  • PDF

Chemical Equilibria of Nickel Chloride in HCl Solution at 25˚C

  • Lee, Man-Seung;Nam, Sang-Ho
    • Bulletin of the Korean Chemical Society
    • /
    • v.30 no.10
    • /
    • pp.2203-2207
    • /
    • 2009
  • Chemical equilbria of nickel chloride in HCl solution at $25\;{^{\circ}C}$ were analyzed by considering chemical equilibria, mass and charge balance equations. The activity coefficients of solutes were calculated by using Bromley equation. The necessary thermodynamic properties, such as the equilibrium constant for the formation of Ni$Cl^+$ at zero ionic strength and interaction parameter, were evaluated by applying Bromley equation to the stability constant data reported in the literature. It was found that most nickel exists as $Ni^{2+}$ in HCl solution up to 5 molality HCl. The pH values of Ni$Cl_2-HCl-H_2O$ system at $25\;{^{\circ}C}$ calculated in this study agreed well with the pH values measured by employing pH meter.

Solvolysis of p-Nitrobenzyl chloride in the Ethanol-water Mixtures (Ethanol-Water 溶液內에서의 p-Nitrobenzyl Chloride의 Solvolysis)

  • Lee, Euk-Suk
    • Journal of the Korean Chemical Society
    • /
    • v.10 no.1
    • /
    • pp.11-14
    • /
    • 1966
  • The thermodynamic parameters for the solvolysis of the p-nitrobenzyl chloride which take place in the ethanol-water mixture media were determined. From the application of this data to the formula ${\delta}_M{\Delta}H^{\neq} = a'Y + b{\delta}_M{\Delta}S^{\leq}$ the following conclusion was obtained. The substrate constant a' for this reaction was not varied in the media which contain more than 50% alcohol and less than 50% alcohol. From this, it is clear that the mechanism of this reaction is the same both in the water-rich solvent and in the alcohol-rich solvent.

  • PDF

Mathematical Model for Adsorption of Berberine on Encapsulated Adsorbent (캡슬에 고정화된 흡착제에의 Berberine의 흡착에 관한 수학적 모델)

  • 최정우;조상원이원홍
    • KSBB Journal
    • /
    • v.10 no.4
    • /
    • pp.358-369
    • /
    • 1995
  • A mathematical model using local thermodynamic equilibrium isotherms for adsorption in encapsulated adsorbent is proposed in order to optimize the design parameters in situ bioproduct separation process. The model accurately follows the experimental data on the adsorption of berberine, secondary metabolite produced in Thaictrum rugosum plant cell culture. The adsorption rate on encapsulated adsorbent is compared with that on alginate-entrapped adsorbent. The result shows that the higher loading capacity in encapsulated adsorbent is mainly due to the increase in the maximum solid phase concentration. Based on the adsorption rate and loading capacity, the encapsulated adsorbent would be more useful than the entrapped adsorbent when used in situ bioproduct separation process. Design parameters in situ bioproduct separation process, such as the size of the capsule, membrane thickness, the ratio of capsule volume to bulk volume, the ratio of single capsule volume to total capsule volume and the adsorbent content in the capsule, are evaluated by using the model. The ratio of single capsule volume to total capsule volume is the most effective parameter for adsorption of berberine on encapsulated adsorbent.

  • PDF