The heat transfer characteristics of double-pipe spiral heat exchanger were investigated by various curvature sizes, experimentally. The three different sizes of heat exchanger were made and tested with water as a working fluid to analyze the heat transfer characteristics. The heat transfer rates, overall heat transfer coefficient and pressure drop were analyzed with various heat exchanger sizes (i.e., curvature ratios). As result, the heat transfer rate increased with increasing the size of the heat exchanger as the flow rate increased due to increasing the area size of heat transfer. However, the overall heat transfer coefficient and pressure drop increased with decreasing the heat exchanger size (i.e., increased curvature ratio) due to the enhanced centrifugal force and inertia.
The characteristics of pollutant emission for non-premixed flames with LCG 8000 and LCG 6000 represented as low calorific gases were investigated by numerical simulation. Commercial software (ANSYS 16.2 - FLUENT) is used to predict 2-D pollutant emission with GRI 3.0 detailed reaction mechanism. In addition, the addition of hydrogen to LCG 6000 was also considered. As result, the flame length and temperature of LHVGs were decreased with decreasing calorific value at the same condition. In addition, NO concentration was decreased as temperature decreased. However, CO concentration for LCG 8000 predicted to be slightly higher than that for methane due to the high propane concentration. In the case of LCG 6000 with added hydrogen, the flame length was the shortest and NO concentration was the highest due to the highest flame temperature, but CO concentration decreased rapidly due to the addition of the carbon-free fuel.
In this study, the combustion characteristics of low calorific gas (LCG) fuels are investigated by numerical simulation. PREMIXED code is used to predict the flame structure and NO emission with two mechanisms, which are GRI 3.0 and USC II chemical reaction mechanisms for CH4 and LCG 8000 and LCG 6000, respectively. Also, elementary reactions related with production and destruction for OH radical are studied because OH radical is dominant for burning velocity and NO emission. As results, the production and the destruction of OH radical for CH4 and LCG 8000 using GRI 3.0 are dominated by reactions of No. 4, No. 2 and No. 3 and by No. 5, No. 3 and No. 7, respectively. For LCG 6000 using USC II, reactions of No. 3, No. 4 and No. 11 and of No. 7, No. 8 and No. 12 dominates to the production and the destruction, respectively. In addition, NO emissions for LCG gas fuel are generated by thermal NO because the flame temperatures are over 1800 K.
In this study, the effect of thermal grease and heat sink material of cooler on CPU temperature was measured and compared with LinX(v0.9.6) and HWMonitor.When the computer is booted without thermal grease applied, the CPU temperature rises rapidly, and the CPU temperature reaches 100℃ after 60 seconds for aluminum heat sink and 140 seconds for copper heat sink. The CPU temperature is lower as the thermal conductivity coefficient of thermal grease is higher, and the CPU temperature is lower when the thermal conductivity coefficient of the cooler is higher. In addition, when using a thermal grease and a heat sink with a high coefficient of thermal conductivity, the cooler rpm can be lowered, which is considered to be advantageous in terms of system stability and energy saving.
In this study, the laminar burning velocity of low calorific gas fuels are verified through the comparison and examination of experimental and predicted results. The bunsen burner which has contraction nozzle is used to measure the laminar burning velocity with the cone angle method. In addition, PREMIXED code combined with two mechanism, i.e., the GRI 3.0, and USC II reaction mechanisms is used to predict the laminar burning velocity. As heating value decrease, the laminar burning velocity correspondingly decreases due to inert gases in the fuels. Through the comparison and analysis of the experimental results and the predicted results, it is confirmed that LCF 9000 and LCF 8000 with the GRI 3.0 reaction mechanism and LCF 7000 and 6000 with the USC II reaction mechanism have a similar distribution of laminar burning velocity between the experimental result and the predicted result. This similarity is due to a large amount of propane, which is not suitable for the GRI 3.0 reaction mechanism in LCF 7000 and 6000.
To understand the effect of high pressure on nitrogen oxides (NOx) formation in water added methane flames, opposed nonpremixed Water-methane/air (H2O-CH4/air) flames are numerically studied with high initial pressure. With GRI 3.0 detailed kinetic mechanism, NOx emissions are predicted for various strain rates. Due to high pressure, the chemical species are distributed in a narrow region, which means the thickness of the flame is thin. This can be clearly seen with high strain rate. Elevated pressure increases maximum temperature of flames which results in increased NOx emission. Even with elevated initial pressure, NOx emissions for H2O added methane flames are significantly decreased compare to pure methane flame. In addition, increased strain rate is also significant factor for decreasing NOx emission. With detailed rate of production analysis, in case of high pressure, it is confirmed that NO2 pathway is the most dominant reaction pathway than any other pathways.
The purpose of this study was investigated heat flow and heat transfer coefficient characteristics of around tube when changing the tube arrangement type and heat transfer area. When ≒1∼4, convective heat transfer coefficient of staggered and aligned arrangement was increased. Growth rate of the heat transfer coefficient becomes smaller in case of ≒5∼8 because a change in the turbulence was very small. At the staggered arrangement, all tubes were always arranged in front of the open passage between the back of the tube. Then, the entire surface area of the tube was exposed to the main flow. Thus growth rate of heat transfer coefficient appear larger than aligned arrangement.