Hyung Ju Lee

An unsteady conduction and two-phase radiation in a 2-D rectangular enclosure with gas and particles

A problem of combined conductive and two-phase radiative heat transfer in a two-dimensional rectangular enclosure with two-phase (gas-particles) media is analyzed. A two-phase radiative transfer equation (RTE) considering radiation by both gas and particles is studied. Its nonlinear integrodifferential RTE is solved using the discrete ordinates method (DOM, or so-called S N method). To validate the program, we compare the solution in a two-dimensional rectangular black enclosure with others. The DOM is then applied to the unsteady thermal development in two-phase media contained in a rectangular enclosure. A parametric study is performed by changing the gas and particle absorption coefficients, particle number density, particle emissivity, wall emissivity, and aspect ratio of the enclosure. The results confirm a significant effect of the two-phase radiation on the thermal development in the geometry. However, it is found that the conduction is predominant near the hot wall.

ANALYSIS OF TWO-PHASE RADIATION IN THERMALLY DEVELOPING POISEUILLE FLOW

Combined conductive and radiative heat transfer in a thermally developing two-phase Poiseuille flow in a cylindrical duct is studied here. A two-phase radiative transfer equation (RTE) considering radiation by both gas and particles is taken into account. A complexform of nonlinear integrodifferential RTE is solved by the discrete ordinates method (DOM, or so called SN method) in axisymmetric geometry. After such validation, namely, the solution in a two-dimensional channel flow between two flat plates is compared with that solved by the zone method, the program is then applied to fully developed gas-particle two-phase flow in a cylindrical duct. A parametric study is performed for gas and particle absorption coefficients, particle number density, particle emissivity, and wall emissivity. The results show a significant effect of two-phase radiation on the thermal characteristics. However, in all cases, it was found that conduction is predominant near the wall.

A Study on Injection Characteristics of High Temperature Fuel through Orifice Injectors

An experimental study was conducted to study fuel injection characteristics through plain orifice injectors when the fuel was heated to the temperature higher than its boiling point. Three injectors with different orifice diameters were used to measure the flow coefficient (α) for the injection pressure ranges of 3, 5, and 10 bar and the fuel temperature ranges between 50 and 270°C. The study showed that α decreases gradually with the fuel temperature below 180°C while it drops abruptly when the temperature goes beyond 187°C, the boiling temperature of the fuel. The slope of α bifurcated at the boiling temperature for different injection pressures, and α decreased faster for the lower injection pressure due to the more active boiling in the injector. In addition, the larger orifice diameter had the higher α value, and α jumped at moderate temperature ranges when the injection pressure was low, implying the turbulent-laminar transition phenomena. The measured α was plotted against the cavitation number(Kc), and the characteristics were independent of the applied pressure for small injectors when the fuel was evaporated before it was injected.

A Study on High-Temperature Fuel Injection Characteristics through Swirl Injectors

An experimental study was conducted to investigate fuel injection characteristics through swirl injectors when the fuel was heated to very high temperature conditions. Three swirl injectors with different orifice diameters and swirler geometries were used to measure the flow coefficient () for the injection pressure ranges between 3 and 10 bar and the fuel temperature from 50 to . The results showed that the variation characteristics of with respect to cavitation number () were highly dependent on both the orifice diameter and the swirler geometry. In addition, the characteristics of variation with respect to AR, the area ratio of the flow through the swirler and the orifice, has revealed that the effect of boiling is retarded but the slope of decreasing after the boiling effect is present tumbles as AR increases.

A Study on the Effect of Fuel Boiling Point on Injection Characteristics at High Fuel Temperature Conditions

ABSTRACT An experiment was conducted to study fuel injection characteristics of high boiling point test fuels (HBPTF), which are newly developed with higher boiling points than conventional aviation fuels, for various injection pressures when the fuel was heated to the temperature higher than their boiling points. The injection characteristics with elevating fuel temperature were quantified by the flow coefficient (α) and the cavitation number (K c ), and it was found that the trends between α and K c for various fuels were very similar with each other. In addition, compared with a conventional fuel, HBPTFs not only have higher fuel temperatures at which the effect of fuel boiling on the injection initiates, but also are less affected by the fuel boiling inside the injectors at temperatures over the boiling point.초 록 기존 항공유보다 비등점을 높인 고비등점 연료에 대하여 다양한 분사 압력 조건에서 비등점 이상의 온도까지 연료를 가열하는 경우의 분사특성을 실험적으로 연구하였다. 연료 온도 상승에 따른 인젝터의 특성은 유량계수(α)와 캐비테이션 수(K c )를 파라미터로 나타내었는데, 고온에서의 각 연료별 α 특성을 K