• Nuclear Engineering and Technology
• /
• v.54 no.11
• /
• pp.4329-4337
• /
• 2022

Jet impinging device is designed for decay heat removal on horizontal fuel rods in a low temperature heating reactor. An experimental system with a fuel rod simulator is established and experiments are performed to evaluate water film covering capacity, within 0.0287-0.0444 kg/ms mass flow rate, 0-164.1 kW/m² heating flux and 13.8-91.4℃ feeding water temperature. An effective method to obtain the film coverage rate by infrared equipment is proposed. Water film flowing patterns are recoded and the film coverage rates at different circumference angles are measured. It is found the film coverage rate decreases with heating flux during single-phase convection, while increases after onset of nucleate boiling. Besides, film coverage rate is found affected by Marangoni effect and film accelerating effect, and surface wetting is significantly facilitated by bubble behavior. Based on the observed phenomenon and physical mechanism, dry-out depth and initial dry-out rate are proposed to evaluate film covering potential on a heating surface. A model to predict film coverage rate is proposed based on the data. The findings would have reliable guide and important implications for further evaluation and design of decay heat removal system of new reactors, and could be helpful for passive containment cooling research.

• Journal of Mechanical Science and Technology
• /
• v.16 no.6
• /
• pp.839-850
• /
• 2002

A performance simulation program for the turboprop engine (PT6A-62), which is the power plant of the first Korean indigenous basic trainer KT-1, was developed for performance prediction, development of an EHMS (Engine Health Monitoring System) and the flight simulator. Characteristics of components including compressors, turbines, power turbines and the constant speed propeller were required for the steady state and transient performance analysis with on and off design point analysis. In most cases, these were substituted for what scaled from similar engine components'characteristics with the scaling law. The developed program was evaluated with the performance data provided by the engine manufacturer and with analysis results of GASTURB program, which is well known for the performance simulation of gas turbines. Performance parameters such as mass flow rate, compressor pressure ratio, fuel flow rate, specific fuel consumption and turbine inlet temperature were discussed to evaluate validity of the developed program at various cases. The first case was the sea level static standard condition and other cases were considered with various altitudes, flight velocities and part loads with the range between idle and 105% rotational speed of the gas generator. In the transient analysis, the Continuity of Mass Flow Method was utilized under the condition that mass stored between components is ignored and the flow compatibility is satisfied, and the Modified Euler Method was used for integration of the surplus torque. The transient performance analysis for various fuel schedules was performed. When the fuel step increase was considered, the overshoot of the turbine inlet temperature occurred. However, in case of ramp increase of the fuel longer than step increase of the fuel, the overshoot of the turbine inlet temperature was effectively reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.911-916
• /
• 2012

It is important to identify dynamic characteristics of nuclear fuel components. Since the fuel always exposed to turbulent flow, the dynamic contact between grids and rods is one of the fuel failure modes. The dynamic behavior of grids in nuclear fuels is quite complex, since two pairs of spring support are placed in the limited space. The strap in a cell has single spring and double dimples and this paper focuses on investigation of the grid strap(Test Fuel Strap, TFS) vibration in one cell. To identify the grid strap vibration, modal analysis of the strap is performed using Finite Element Method (FEM). Modal testing on a $5{\times}5$ grid structure without rods is performed. The modal testing results are compared to analytic results. In addition, random test considering rod effect is performed about a $5{\times}5$ grid with rods under real contact condition in the air. Finally, the strap vibration of a $5{\times}5$ fuel bundle in INvestigation of Flow INduced vIbraTion(INFINIT) facility is measured in real fluid velocity condition without heating. It is shown that modal frequencies from the test are almost equal to those peak frequencies in the INFINIT test.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.380-384
• /
• 2004

A fuel spiking test was performed to measure the surge margin of the compressor in a gas turbine engine. During the test, fuel spiking signal was superimposed on the engine controller demand and the mixed signals were used to control a fuel line servo-valve. For the superimposition, a subsystem composed of a fuel controller and a function generator was used. During the fuel spiking test, the original scheduled fuel signals and the modified signals were compared to guarantee the consistency excluding the spiking signals. The spiking signals were carefully selected to maintain the engine speed constant. The fuel spiking effects were checked by three dynamic pressure sensors. Sensors were placed before the servo-valve, after the servo-valve, and after the compressor location, respectively. The modulations of the spiking signal duration and fuel flow rate were examined to make the- operating point approach the surge region. The real engine test was performed at the Altitude Engine Test Facility (AETF) in Korea Aerospace Research Institute (KARI). In the real engine test, fuel spiking signals with 25~50 ㎳ of spiking signal time and 17~46 % of base fuel flow rate condition were used. The dithering signal was 5~6 ㎃ at 490 Hz. The test results showed good agreement between the fuel spiking signals and the fuel line pressure signals. Also, the compressor discharge pressure signals showed fuel spiking effects and the changes of the operating point on the compressor characteristic map could be traced.

• Advances in aircraft and spacecraft science
• /
• v.1 no.3
• /
• pp.311-330
• /
• 2014

Environmental impact of aircraft emissions can be addressed in two ways. Air quality impact occurs during landings and takeoffs while in-flight impact during climbs and cruises influences climate change, ozone and UV-radiation. The aim of this paper is to investigate airports related local emissions and fuel consumption (FC). It gives flight path optimization model linked to a dispersion model as well as numerical methods. Operational factors are considered and the cost function integrates objectives taking into account FC and induced pollutant concentrations. We have compared pollutants emitted and their reduction during LTO cycles, optimized flight path and with analysis by Dopelheuer. Pollutants appearing from incomplete and complete combustion processes have been discussed. Because of calculation difficulties, no assessment has been made for the soot, $H_2O$ and $PM_{2.5}$. In addition, because of the low reliability of models quantifying pollutant emissions of the APU, an empirical evaluation has been done. This is based on Benson's fuel flow method. A new model, giving FC and predicting the in-flight emissions, has been developed. It fits with the Boeing FC model. We confirm that FC can be reduced by 3% for takeoffs and 27% for landings. This contributes to analyze the intelligent fuel gauge computing the in-flight fuel flow. Further research is needed to define the role of $NO_x$ which is emitted during the combustion process derived from the ambient air, not the fuel. Models are needed for analyzing the effects of fleet composition and engine combinations on emission factors and fuel flow assessment.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.2
• /
• pp.191-198
• /
• 2011

According to the propagation of fuel cell system, the importance of that system efficiency is being magnified. Thus, the efficiency improvement of reformer which is the important factor of fuel cell system will be required. This study has been experimentally performed to evaluated the performance of plate type STR reactor. At first, we changed fuel flow rate (2, 3 and 4 l/min) in burner, and then we measured a proportion of hydrogen in produced gas through the STR reactor by G.C for evaluating the performance of plate type STR reactor in various fuel supply conditions. And we changed S/C ratio (2 and 4) and measured a proportion of hydrogen in produced gas through the STR reactor. As a results, condition at fuel flow rate 2 and 3 l/min could not be supplied amount of heat for STR sufficiently. Condition at fuel flow rate 4 l/min could supplied a heat excessively. And condition at S/C ratio 2, reaction occurred insufficiency. But condition at S/C ratio 4 was excess. From above, we found the optimum conditions that were fuel rate 3.5 l/min and S/C ratio 3.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.7
• /
• pp.573-580
• /
• 2021

Paraffin wax is attracting many attentions for promising solid fuel of hybrid rocket because of its higher regression than other fuels. However, even with paraffin fuel combustion, unsteady low-frequency oscillation of combustion pressure is still observed. And, this is related to the formation of liquid layer and the entrainment of fuel droplets entering the axial combustion gas flow. This study investigates the effect of additional combustion of fuel droplets on the occurrence of low-frequency combustion instability. On the other hand, the formation of fuel droplets depends on Weber Number (the ratio of the inertial force to the surface tension of the liquid) and Reynolds Number of the oxidizer flow. Therefore, a laboratory-scale hybrid rocket was used to monitor the occurrence of combustion instability while changing We number. A series of combustion tests were conducted to control We number by changing the oxidizer flow rate or adding LDPE (low density polyethylene) to base fuel. In the results, it was confirmed that there is a critical We number above which the low-frequency combustion instability occurs.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.3
• /
• pp.20-27
• /
• 2003

In this paper, the fuel transport characteristics during transient condition was studied by using a Fast Response Flame Ionization Detector(FRFID). The quantitative measurement method for the inducted fuel mass into cylinder is studied. The inducted fuel mass into the cylinder was estimated by using calculated air-fuel ratio by hydrocarbon concentration of cylinder and air flow model. In order to estimate the transportation of injected fuel from the intake port into cylinder, the wall wetting fuel model was used. The two coefficient $\alpha$,$\beta$) of the wall-wetting fuel model was determined from the measured fuel mass that was inducted into the cylinder at the first cycle after injection cut-off To reduce an air/fuel ratio fluctuation during rapid throttle opening, the appropriate fuel injection rate was obtain from the wall wetting model with empirical coefficients. Result of air/fuel ratio control, air/fuel excursion was reduced.

• 한국신재생에너지학회:학술대회논문집
• /
• 2008.05a
• /
• pp.542-545
• /
• 2008

Experiments have been performed to investigate effects of pulsating cathode flow on a 10-cell proton exchange membrane fuel cell (PEMFC) stack. For all the experiments, the flow rate, temperature and relative humidity of hydrogen at the anode inlet are fixed. The effects of the pulsating frequency, amplitude and flow rate at the cathode inlet on performance of 10-cell PEMFC are examined. The polarization and power curves show that the power output and limiting current is substantially increased when the pulsating component is added to cathode flow channel. The maximum power output increases by up to 38% and enhancement of the overall performance is more pronounced at lower flow rate region.

• 한국신재생에너지학회:학술대회논문집
• /
• 2008.05a
• /
• pp.572-575
• /
• 2008

Flow-field design has much influence over the performance of proton exchange membrane fuel cell (PEMFC) because it affects the pressure magnitude and distribution of the reactant gases. To obtain the pressure magnitude and distribution of reactant gases in four kinds of flow-field designs without additional measurement equipment, computational fluid dynamics (CFD) analysis was performed. After the CFD analysis, the performance values of PEMFC according to the flow-field configurations were measured via a single cell test. As expected, the pressure differences due to different flow-field configurations were related to the PEMFC performance because the actual performance results showed the same tendency as the results of the CFD analysis. A large pressure drop resulted in high PEMFC performance. So, the single serpentine configuration gave the highest performance. On the other hand, the parallel flow-field configuration gave the lowest performance because the pressure difference between inlet and outlet was the lowest.