• Title/Summary/Keyword: gas transfer

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Effect of Dissolved Gases on Liquid Droplet Heat Transfer Enhancement (액적 열전달 향상에 미치는 Dissolved 가스의 영향에 관한 연구)

  • Lee, Jung-Ho;Kim, Jung-Ho;Kiger, Kenneth T.
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1491-1498
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    • 2003
  • Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. A high-speed digital video camera was used to simultaneously record images of the drop from below. The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The splat diameter was observed to increase with time just after the initial transient dies out due to the growth of the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the bubble corresponded to a sudden decrease in droplet heat transfer.

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Determination of the Proton Transfer Energies of Glycine and Alanine and the Influence of Water Molecules

  • Gwon, O Yeong;Kim, Su Yeon;No, Gyeong Tae
    • Bulletin of the Korean Chemical Society
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    • v.16 no.5
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    • pp.410-416
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    • 1995
  • The proton transfer energies of gas phase glycine and alanine and those of hydrated glycine and alanine were calculated both with Hartree-Fock and $M{\Phi}ller-Plesset$ ab initio molecular orbital (MO) calculations with 6-31G** basis set. The transition states of the proton transfer of gas phase glycine was also investigated. For zwitterions, both for glycine and alanine, the water bound to -NH3+ site stabilize the complex more compared with the water bound to -CO2-. The proton transfer energy, ΔEpt, of glycine, alanine, mono-hydrated glycine, mono-hydrated alanine, di-hydrated glycine and di-hydrated alanine were obtained as 30.78 (MP2: 22.57), 31.43, 23.99 (MP2: 17.00), 24.98, 22.87, and 25.63 kcal/mol, respectively. The activation energy for proton transfer from neutral (Nt) glycine to zwitterion (Zw) glycine, Ea, was obtained as 16.13 kcal/mol and that for reverse process, Ear, was obtained as 0.85 kcal/mol. Since the transition state of the proton transfer of gas phase glycine locate near the glycine zwitterion on the potential energy surface and the shape of the potential well of the zwitterion is shallow, the zwitterion easily changed to neutral glycine through the proton transfer.

Production of high dissolved O2/O3 with rotating wheel entraining gas method for environmental application

  • Li, Haitao;Xie, Bo;Hui, Mizhou
    • Advances in environmental research
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    • v.2 no.1
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    • pp.1-8
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    • 2013
  • There is a significant demand to make various dissolved gases in water. However, the conventional aeration method shows low gas mass transfer rate and gas utilization efficiency. In this study, a novel rotating wheel entraining gas method was developed for making high dissolved $O_2$ and $O_3$ in water. It produced higher concentration and higher transfer rate of dissolved $O_2$ and $O_3$ than conventional bubble aeration method, especially almost 100% of gas transfer efficiency was achieved for $O_3$ in enclosed reactor. For application of rotating wheel entraining gas method, aerobic bio-reactor and membrane bio-reactor (MBR) were successfully used for treatment of domestic and pharmaceutical wastewater, respectively; and vacuum ultraviolet $(VUV)/UV+O_3/O_2$ reactors were well used for sterilization in air/water, removal of dust particles and toxic gases in air, and degradation of pesticide residue and sterilization on fruits and vegetables.

Comparison Study on Empirical Correlation for Mass Transfer Coefficient with Gas Hold-up and Input Power of Aeration Process (폭기공정의 물질전달 계수와 기체 포집율 및 소요동력의 상관관계에 대한 비교연구)

  • Park, Sang Kyoo;Yang, Hei Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.6
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    • pp.415-421
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    • 2017
  • As stricter environmental regulation have led to an increase in the water treatment cost, it is necessary to quantitatively study the input power of the aeration process to improve the energy efficiency of the water treatment processes. The objective of this study is to propose the empirical correlations for the mass transfer coefficient with the gas hold-up and input power in order to investigate the mass transfer characteristics of the aeration process. It was found that as the input power increases, the mass transfer coefficient increases because of the decrease of gas hold-up and increase of Reynolds number, the penetration length, and dispersion of mixed flow. The correlations for the volumetric mass transfer coefficients with gas hold-up and input power were consistent with the experimental data, with the maximum deviation less than approximately ${\pm}10.0%$.

Numerical Analysis of Hypersonic Shock-Shock Interaction using AUSMPW+ Scheme and Gas Reaction Models (AUSMPW+ 수치기법과 반응기체 모델을 이용한 극초음속 충격파-충격파 상호작용 수치해석)

  • Lee Joon-Ho;Kim Chongam;Rho Oh-Hyun
    • 한국전산유체공학회:학술대회논문집
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    • 1999.05a
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    • pp.29-34
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    • 1999
  • A two-dimensional Navier-Stokes code based on AUSMPW+ scheme has been developed to simulate the hypersonic flowfield of hypersonic shock-shock interaction. AUSMPW+ scheme is a new hybrid flux splitting scheme, which is improved by introducing pressure-based weight functions to eliminate the typical drawbacks of AUSM-type schemes, such as non-monotone pressure solutions. To study the real gas effects, three different gas models are taken into account in this paper: perfect gas, equilibrium flow and nonequilibrium flow. It has been investigated how each gas model influences on the peak surface loading, such as wall pressure and wall heat transfer, and unsteady flowfield structure in the region of shock-shock interaction. With the results, the value of peak pressure is not sensitive to the real gas effects nor to the wall catalyticity. However, the value of peak heat transfer rates is affected by the real gas effects and the wall catalyticity. The structure of the flowfield also changes drastically in the presence of real gas effects.

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Heat Transfer Characteristics During Gas Cooling Process of Carbon Dioxide in a Horizontal Tube (수평관내 초임계 영역의 Co2 냉각 열전달 특성)

  • Son, Chang-Hyo;Lee, Dong-Gun;Oh, Koo-Kyu;Jeong, Si-Young;Kim, Young-Lyoul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.3
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    • pp.289-295
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    • 2004
  • The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flowmeter, an evaporator, and a gas cooler(test section). The main components of the water loop consist of a variable-speed pump, an isothermal tank, and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal stainless steel tube of the outer diameter of 9.53mm and of the inner diameter of 7.75mm. The length of the test section is 6m. The refrigerant mass fluxes were 200∼300kg/(m2$.$s) and the inlet pressure of the gas cooler varied from 7.5㎫ to 8.5㎫. The main results were summarized as follows : Pressure drop of CO2 increases with increasing gas cooler pressure. The friction factors of CO2 in a horizontal tube show a relatively good agreement with the correlation by Blasius. The heat transfer coefficient of CO2 in transcritical region increases with decreasing gas cooler pressure and decreasing mass flux of CO2. Most of correlations proposed in a transcritical region showed significant deviations with experimental data except for those predicted by Gnielinski.

Heat Transfer Characteristics of Supercritical $CO_2$ in Helical Coil Gas Coolers on the Change of Coil Diameters (코일직경변화에 따른 헬리컬 코일형 가스냉각기내 초임계 이산화탄소의 냉각열전달 특성)

  • Son, Chang-Hyo
    • Journal of the Korean Institute of Gas
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    • v.11 no.3
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    • pp.44-48
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    • 2007
  • The cooling heat transfer characteristics of supercritical $CO_2$ in a helical coil gas cooler on the change of coil diameters are experimentally investigated. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flow-meter, a pre-heater and a helical coil gas cooler (test section). The test sections are made of a copper tube which the inner diameter is 4.55 mm and the helical coil diameters are done of 26.75 mm and 41.35 mm. The mass fluxes of refrigerant are varied from 200 to 800 [$kg/m^2s$] and the inlet pressures of gas cooler are 7.5 to 10.0 (MPa). A gas cooler with helical coil diameter of 26.75 mm has larger heat transfer coefficient than that of 41.35 mm. Also, when compared with experimental data and published correlations avaliable, most of correlations are under-predicted, but Pitla published correlations avaliable, most of correlations are under-predicted, but Pitla et al.'s correlation shows a relatively good coincidence with the experimental data except the region of pseudo critical temperature.

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A Study of Thermal and flow Characteristics Induced by Fire in a Partial Enclosure (부분밀폐공간내에서 화재로 야기되는 열 및 유동특성에 관한 연구)

  • 박희용;한철희;박경우
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.5
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    • pp.1288-1300
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    • 1994
  • Mathematical modeling and numerical calculation on the flow and thermal characteristics induced by fire in a partial enclosure are performed. The solution procedures include the Shvab-Zeldovich approximation for the physical transport equations, low Reynolds number k-.epsilon. model for the turbulent fluid flow and Discrete Ordinate method(DOM) to calculate the radiative heat transfer. PMMA(Polymethylmethacrylate) is adopted as a solid fuel. Two different cases are considered : combustions with and without gas radiation occuring in a open cavity for variable pyrolyzing location of PMMA. When the fire source is located at the left-wall, the flow region of flame gas is limited at the left-wall and ceiling and recirculation region of inlet gas is formulated at neat the floor. In case of neglecting the radiative heat transfer, more large flame size and higher temperature is predicted. It is essential to consider the radiative heat transfer for analysis of fire phenomenon.

Experimental study on the heat flux and heat transfer coefficient in a spark ignition engine (스파크 점화기관의 열유속 및 열전달 계수에 대한 실험적 연구)

  • Han, Seong-Bin;Gwon, Yeong-Jik;Lee, Jeong-Yeol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.11
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    • pp.1466-1474
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    • 1997
  • In order to design and develop a spark ignition engine, many studies must be preceded about the characteristics of thermal flow. For measurement of transient wall temperature thin film thermocouples of Bendersky type were manufactured and these probes were fixed into the wall of combustion chamber. Surface wall temperatures were measured in experiments of various engine speeds. Transient heat fluxes were calculated from the wall temperature measurements. Pressure was measured from combustion chamber using pressure transducer and gas temperatures were calculated using the state equation of ideal gas. And instantaneous heat transfer coefficients were obtained. It will be the basic data for the formulae of instantaneous heat transfer coefficients.

Heat Transfer Analysis of Exhaust Gas into the Passenger Car Muffler (승용차 머플러에 유입되는 배기가스의 열전달 해석)

  • Lee, Chung-Seub;Shin, Jae-Ho;Lee, Hae-Jong;Suh, Jeong-Se;Chung, Han-Shik;Jeong, Hyo-Min
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.157-162
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    • 2003
  • This study is analysis on the heat transfer of exhaust gas into the muffler at passenger Car. Numerical analysis with Computational fluid Dynamics(CFD) was carried out to investigate exhaust gas flow. The STAR-CD S/W used for the three dimensional steady state CFD analysis in a muffler. The Navier-Stokes Equation is solved with the SIMPLE method in a general cartesian coordinates system. Result of numerical simulation; Inlet and outlet temperature shown about ${\Delta}T=239K$, 216K, 202K at in the muffler. Heat transfer was progressed quickly by atmospheric temperature of muffler external at in the near wall.

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