• Membrane and Water Treatment
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• 제6권6호
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• pp.451-476
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• 2015

Membrane distillation (MD), which can utilize low-grade thermal energy, has been extensively studied for desalination. By incorporating solar thermal energy, the solar membrane distillation desalination system (SMDDS) is a potential technology for resolving the energy and water resource problems. Small-scale SMDDS (s-SMDDS) is an attractive and viable option for the production of fresh water for small communities in remote arid areas. The minimum-cost design and operation of s-SMDDS are determined by a systematic method, which involves a pseudo steady state approach for equipment sizing and the dynamic optimization using overall system mathematical models. The s-SMDDS employing three MD configurations, including the air gap (AGMD), direct contact (DCMD) and vacuum (VMD) types, are optimized. The membrane area of each system is $11.5m^2$. The AGMD system operated for 500 kg/day water production rate gives the lowest unit cost of $5.92/m^3$. The performance ratio and recovery ratio are 0.85 and 4.07%, respectively. For the commercial membrane employed in this study, the increase of membrane mass transfer coefficient up to two times is beneficial for cost reduction and the reduction of membrane heat transfer coefficient only affects the cost of the DCMD system.

• Nuclear Engineering and Technology
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• 제31권5호
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• pp.465-475
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• 1999

The objective of the present work is to assess the analysis capability of two wall film condensation models, the default and the alternative models, of RELAP5/MOD3.2 on condensation experiments in the presence of noncondensable gas in a vertical tube of PCCS of CP-1300. In the calculation of a base case the default model of RELAP5/MOD3.2 under-predicts the heat transfer coefficients, and Its alternative model over-predicts them throughout the condensing tube, Also, both models over-predict the void fractions. The nodalization study shows that the variation of the node number does not change both modeling results of RELAP5/MOD3.2 Sensitivity study for varying input parameters shows that the inlet steam-air mixture flow rate, the inlet air mass fraction, and the inlet saturated steam temperature give significant changes of their heat transfer coefficients Run statistics show that the grind time of the default model is always higher than that of the alternative model by about 23%.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.213-217
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• 2017

액체로켓엔진 고장에서 시동과정이 30% 이상을 차지하며 특히, 우주왕복선 주 엔진(Space Shuttel Main Engine, SSME)은 2%의 밸브위치 오차 또는 0.1초의 시간오차와 같은 작은 변화에도 급격하게 변화하는 매우 민감한 시스템으로 시동과정의 모델링이 중요하다. 하지만, 시동과정에서 비선형 질량 유량과 열전달 특성 때문에 많은 어려움이 발생한다. 본 논문에서는 이를 해결하기 위하여 부분적인 전산유체해석(Computational Fluid Dynamics, CFD) 방법을 사용하였으며 본 논문에서는 구성품의 모델링을 수행하여 정상상태에서 확인을 하였다.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.624-635
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• 2024

In two-fluid simulations of flow boiling, the modeling of the mean bubble diameter is a key parameter in the closure relations governing the intefacial transfer of mass, momentum, and energy. Monodispersed approach proved to be insufficient to describe the significant variation in bubble size during flow boiling in a heated pipe. A population balance model (PBM) has been employed to address these shortcomings. During nucleate boiling, vapor bubbles of a certain size are formed on the heated wall, detach and migrate into the bulk flow. These bubbles then grow, shrink or disintegrate by evaporation, condensation, breakage and aggregation. In this study, a parametric analysis of the PBM aggregation and breakage models has been performed to investigate their effect on the radial distribution of the mean bubble diameter and vapor volume fraction. The simulation results are compared with the DEBORA experiments (Garnier et al., 2001). In addition, the influence of PBM parameters on the local distribution of individual bubble size groups was also studied. The results have shown that the modeling of aggregation process has the largest influence on the results and is mainly dictated by the collisions due to flow turbulence.

• 방사성폐기물학회지
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• 제5권1호
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• pp.29-37
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• 2007

특정 구획으로 유입된 오염물질이 해당 구획 내부에 순간적으로 균일하게 분포한다는 구획모델에 대한 기본가정의 한계로 인해, 전통적인 단일구획모델로는 불포화대에서 오염물질의 이동현상을 적절하게 예측할 수 없다. 한편 물리적으로 동일한 불포화대를 여러 개의 구획으로 구분한 다중구획모델링 기법은 실제 불포화대에서의 오염물질 이동 지연효과를 적절하게 설명할 수 있으나, 지금까지 일반적인 해석해가 보고된 바 없으며 고려하는 구획의 개수가 증가할수록 모델링에 많은 시간이 소요되는 등의 한계가 있다. 이러한 문제점을 해결하기 위하여, 이류가 지배적인 조건 하에서 불포화대의 오염물질 이동현상에 대한 다중구획모델을 수립하고 이를 해석적인 방법으로 계산할 수 있는 일반해를 유도한 후, 다중구획모델을 단일구획모델로 근사할 수 있는 수학적 제약조건을 도출하였다. 단순화된 근사방법론의 유효성은 가상적인 조건 하에서 간단한 수치해석적 방법을 통해 검증하였다. 물리적으로 동일한 특성을 갖는 불포화대를 단일 구획으로 가정할 경우, 불포화대로부터 포화대로 유입되는 오염물질의 전이율은 상수가 아닌 시간 종속적인 명목전이율로 표현할 수 있음을 증명하였다. 또한 명목전이율은 불포화대 구획간 전이율에 민감하며 오염층으로부터의 전이율에 대한 민감도는 미미한 것으로 나타났다. 이 연구에서 개발된 단순화된 근사방법론은 많은 시간이 요구되는 다중구획 모델링을 통하지 않고 불포화대 오염물질 이동현상을 신속하고 합리적으로 예측하기 위한 목적으로 활용될 수 있을 것으로 기대된다.

• 설비공학논문집
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• 제4권4호
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• pp.306-315
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• 1992

This paper addresses performance analysis of a reciprocating compressor. A computer simulation model has been developed to predict and estimate the compressor performance. Instead of using ideal gas equations, real gas equations are used in describing the state of gas. The compressor simulation model consists of a cylinder control volume, suction system and discharge system. Conservation laws of mass and energy are applied to the cylinder section only, The suction and discharge system are described by the Helmholtz resonator modeling. Some of input data required for the simulation have been obtained from experiments. These experimentally obtained input data are effective flow area, effective force area and dynamic characteristics of valves. Simulation results of real gas equations have been compared with those of ideal gas equations. It has been found that the simulation with real gas equations yields lower cylinder temperature and heat transfer compared with those of ideal gas equations. Differences in pressure, mass flowrates, valve motions and gas pulsations are found quite small.

• 설비공학논문집
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• 제20권7호
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• pp.486-491
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• 2008

The performance of a microturbine CHP system equipped with an absorption chiller was analyzed by modeling it. The microturbine with recuperator was simulated with the Brayton cycle model. The mass flow rate and available heat energy of the exhaust gas from the microturbine were simulated. These results were utilized as input values for the generator of the absorption chiller. The absorption chiller is a single-effect air cooled type with a solution heat exchanger. The heat input into the generator was proportional to the heat transfer rate and the UA values of the heat exchangers of the absorption chiller. Furthermore, the COP of the absorption chiller increased with respect to an increase of the heat input into the generator, under the sufficient evaporator capacity condition. When the capacity of the CHP system increased from 30 to 60 kW, the mass flow rate of the LiBr for the absorption chiller doubled, and the UA values for evaporator and condenser increased by factors of x3.9 and x3.4, respectively, under the same COP condition.

• 대한금속재료학회지
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• 제47권5호
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• pp.304-310
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• 2009

Recently, manganese nodule has been focused on alternative resources because of its high grade of noble metallic elements such as Co, Ni, and Cu etc. From the viewpoint of an optimization the operating variables for energy efficiency of smelting reduction process, thermodynamic model for smelting reduction process of Manganese nodule was developed by using energy and material balance concept. This model provided that specific consumption of pure oxygen and coke was strongly depended on post combustion ratio (PCR) and heat transfer efficiency (HTE). The dressing and dehydrating process of low grade manganese can be proposed an essential process to minimize the specific energy consumption with decreasing slag volume. The effect of electricity coal base smelting reduction process was also discussed from the energy optimizing point of view.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.78.2-78.2
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• 2010

Effect of temperature elevation of inlet air on performance of a membrane humidifier for PEMFC vehicle application was investigated both experimentally and numerically. A shell-and-tube typed gas-to-gas humidifier with Nafion membrane was tested. The experimental result showed that water transfer varies nonlinearly with the temperature elevation. Numerical analysis based on detailed modeling is also conducted on a single tube geometry to explain this nonlinear behavior. The simulation revealed that the local water flux varies nolineary and dramatically along the tube. Analysis is based on competing role of temperature increase and relative humidity decrease, both of which seriously affect water conductivity of the membrane.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1042-1048
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• 2007

This work analytically investigated the radiated noise of a helical gear-housing system due to the excitation of helical gears. The helical gears were modeled as a 12-degree of freedom mass-spring-damper system; the shaft was modeled as a rod, a beam, and a torsional shaft; and the gear housing was modeled as a clamped circular plate with viscous damping. The modeling of this system used transfer matrices for helical gears, shafts, and bearings. Damping for both the bearings and the plate were obtained by modal testing. For the evaluation of noise, sound pressure from the plate due to the force and the moment in both radial and tangential directions was analytically derived by the Rayleigh integral. The analytical derivation and parameters from the experiment were applied to an analysis of noise for the two sets of helical gears with differing gear ratios. The analysis showed that the moment excitation in both helical gears contributed more to the noise of the plate than axial force excitation.