• Solar Energy
• /
• v.6 no.2
• /
• pp.62-69
• /
• 1986

An analysis is made of the fully developed laminar flow and heat transfer in a parallel flat plate with heated rectangular block arrays to investigated the influence of bouyancy force. The shrouds is considered as adiabatic, while the heated block surface transmit a uniform rate of heat flux per unit axial length. The governing equations for velocity and temperature are solved by SIMPLE(Semi-Implicit Method Pressure Linked Equation) algorithm. Detailed velocity and temperature fields and overall heat transfer on wide range of Rayleigh number and various aspect ratios of heated rectangular blocks are computed. The result show that bouyancy leads to a significient enhancement in heat transfer along with a smaller increase in pressure drop, with the great enhancement found when the aspect ratio is 3.0.

• Nuclear Engineering and Technology
• /
• v.39 no.1
• /
• pp.21-30
• /
• 2007

Current high-temperature gas-cooled reactors (HTGRs) are based on a closed Brayton cycle with helium gas as the working fluid. Thermodynamic performance of the axial-flow helium gas turbines is of critical concern as it considerably affects the overall cycle efficiency. Helium gas turbines pose some design challenges compared to steam or air turbomachinery because of the physical properties of helium and the uniqueness of the operating conditions at high pressure with low pressure ratio. This report present a review of the helium Brayton cycle experiences in Germany and in Japan. The design and availability of helium gas turbines for HTGR are also presented in this study. We have developed a new throughflow calculation code to calculate the design-point performance of helium gas turbines. Use of the method has been illustrated by applying it to the GTHTR300 reference.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.24 no.3
• /
• pp.358-364
• /
• 2016

The combustion and exhaust emission characteristics in a spark ignition (SI) engine with various test fuels (bioethanol - gasoline blends) and air-fuel ratio were investigated in this research. To investigate the influence of the excess air ratio and ethanol blends on the combustion characteristics such as the cylinder pressure, rate of heat release (ROHR), and fuel consumption rate were analyzed. In addition, the reduction effects of exhaust emissions such as carbon monoxide (CO), unburned hydrocarbon (HC), and oxides of nitrogen (NOx) were compared with those of neat gasoline fuel under the various excess-air ratios. The results showed that the peak combustion pressures and the ROHR of bioethanol fuel cases were slightly higher than those of gasoline fuel at all test ranges and fuel ratio. As compared with gasoline fuel (G100) at each given excess air ratio, BSFC of bio-ethanol was increased. The CO, HC, NOx emissions of bio-ethanol blends were lower than those of gasoline fuel under overall experimental conditions.

• Journal of the Korean Institute of Telematics and Electronics T
• /
• v.35T no.1
• /
• pp.75-81
• /
• 1998

This paper is to optimize single-element piezoresistor shear stress strain gauge related to aspect ratio of rectangular diaphragm. The shear stress distribution on diaphragm has been simulated by finite-element method(FEM). As simulation results, the maximum sensitivity for strain gauge was appeared at the center of diaphragm with aspect ratio 3, and in along to long edge with the ratio 2. The diaphragm with ratio 2 is not acceptable due to the yield of mask alignment in IC process technology. The optimum condition of diaphragm with respect to good sensitivity was realized in the case of ratio 3. In this case, the area by gauge was 8% of overall size of rectangular diaphragm.

• Journal of the East Asian Society of Dietary Life
• /
• v.23 no.3
• /
• pp.282-296
• /
• 2013

The study classified 83 obese adults by constitution and had them follow a strict diet according to their constitution in order to see if the Yin-Yang method would be effective on the metabolic syndrome, which is one of the main causes of death in Korea. Overall, the application of both Yin and Yang methods improved the following factors: weight, body fat percentage, systolic blood pressure, diastolic pressure, neutral fats and total cholesterol. In particular, the Yin constitution group of men showed more improvements than the Yang constitution group. Furthermore, waist circumference and the prevalence rate of systolic blood pressure, diastolic pressure, total cholesterol and metabolic syndrome were decreased noticeably. Total energy intake was increased in both men and women after the constitutional diet, along with the increase of nutrient intake, such as dietary fiber, vitamins and minerals, among others. Among various nutrients, vitamin A, vitamin C, thiamine, vitamin B6, folic acid, calcium, phosphorus, potassium, magnesium and iron intake were increased noticeably after the constitutional diet. In addition, subjects' intake of all nutrients, except for magnesium, satisfied the nutrition intake standards. Further, the nutrients adequacy ratio (NAR) and the mean adequacy ratio (MAR) improved for both men and women. The intake of potatoes, starch, greens and mushrooms increased noticeably, whereas the intake of meat, dairy, drinks and alcohol decreased after the constitutional diet. For the Yin constitution, the intake of Yin foods noticeably decreased, where as the intake of Yang foods decreased for the Yang constitution. In conclusion, the constitutional diet effectively improves the metabolic syndrome. Among many nutrients, the intake of dietary fiber, vitamins A, C and E, potassium and magnesium is positively associated with the improvement of metabolic syndrome biomarkers.

• Journal of Advanced Marine Engineering and Technology
• /
• v.30 no.4
• /
• pp.463-473
• /
• 2006

The effect of tube diameter on heat and mass transfer characteristics of absorber in absorption chiller/heater using LiBr solution as a working fluid has been investigated by both of numerical and experimental study to develop a high performance and compact absorber. The diameter of the heat exchanger tube inside absorber was changed from 15.88mm to 12.70mm and 9.52mm. In numerical study a model of vapor pressure drop inside tube absorber based on a commercial 20RT absorption chiller/heater was performed. The effect of tube diameter, longitudinal pitch, vapor Reynolds number, longitudinal pitch to diameter ratio on vapor pressure drop across the heat exchanger tube banks inside absorber have been investigated and found that vapor pressure drop decreases as tube diameter increases, longitudinal pitch increases, vapor Reynolds number decreases and longitudinal pitch to diameter ratio increases. In experimental study, a system includes a tube absorber, a generator, solution distribution system and cooling water system was set up. The experimental results shown that the overall heat transfer coefficient, mass transfer coefficient. Nusselt number and Sherwood number increase as solution flow rate increases. In both of study cases, the heat and mass transfer performance increases as tube diameter decreases. Among three different tube diameters the smallest tube diameter 9.52mm has highest heat and mass transfer performance.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.10 no.3
• /
• pp.53-59
• /
• 2011

In this study, a two-phase closed loop cooling system is desinged and tested for a laptop computer using a FC-72. The cooling system is characterized by a parametric study which determines the effects of existence of a boiling enhancement microstructure, initial system pressure, volume fill ratio of coolant and inclination angle of condenser on the thermal performance of the closed loop. Experimental data show the optium condition when the volume ratio of working fluid is 70%, the pump flowing is 6ml/min, and the inclination angle of condenser is $0^{\circ}$. This research shows the maximum values which can dissipate 33W of chip power with a chip temperature maintained at $95^{\circ}C$.

• 한국기계연구소 소보
• /
• s.18
• /
• pp.21-27
• /
• 1988

In this study, a series of experiments and analyses are performed to estimate the static characteristics of hydrostatic journal bearing such as load capacity, pressure change in each recess, eccentricity of spindle, etc. The experiments are carried out for a multi-recess type journal bearing with capillary restrictor. The Finite Element Method(FEM) is used for the analyses. The predicted load capacity under the condition of stationary or eccentric ratio of bellow 0.2 of the spindle shows excellent agreement with the measured. But, with an increase of the eccentric ratio when the spindle is rotating, the predicted load capacity is largely estimated than the measured. It seems that the difference is mainly caused among others from the fact that the effect of oil-viscosity variation due to the temperature change in the bearing is not introduced into the analyses. The analysis method proposed to estimate the static characteristics of hydrostatic journal bearing is considered to be very reliable since the predicted results are overall in good agreement with the measured.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2544-2547
• /
• 2008

A micro channel heat sink has been studied and optimized for mixed pressure driven and electroosmotic flows through three-dimensional numerical analysis. The effects of ionic concentration represented by zeta potential and Debye thickness are studied with the various steps of externally applied electric potential. Optimization of the micro channel heat sink has been performed considering two design variables related to the micro channel width, depth and fin width. The surrogate-based optimization is performed using a search algorithm taking overall thermal resistance as objective function. The thermal resistance is found to be more sensitive to channel width-to-depth ratio than fin width-to-depth of channel ratio.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.4
• /
• pp.739-752
• /
• 1989

The temperature distribution and heat flux of the inner wall of the cylinder of turbocharged gasoline engine were calculated by the 3-dimensional heat conduction analysis employing boundary element method. Overall mean effective heat transfer coefficient and thermal resistance ratio and equivalent thickness of the cylinder wall were calculated. the numerical results were discussed with respect to the engine speed, equivalence ratio, spark and boost pressure.