• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.10
• /
• pp.1412-1419
• /
• 2003

Heat regenerator occupied by regenerative materials improves thermal efficiency of combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerator with spherical particles, was numerically analyzed to evaluate the heat transfer and pressure losses and to derive the design parameter for heat regenerator. It is confirmed that the computational results, such as air preheat temperature, exhausted gases outlet temperature, and pressure losses, agreed well with the experimental data. The thermal flow in heat regenerator varies with porosity, configuration of regenerator and diameter of regenerative particle. As the gas velocity increases with decreasing the cross-sectional area of the regenerator, the heat transfer between gas and particle enhances and pressure losses decrease. As particle diameter decreases, the air is preheated higher and the exhaust gases are cooled lower with the increase of pressure losses. Assuming a given exhaust gases temperature at the regenerator outlet, the regenerator need to be linearly lengthened with inlet Reynolds number of exhaust gases, which is defined as a regenerator design parameter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.10
• /
• pp.711-717
• /
• 2012

A heat pump dryer for the frozen food needs to preheat the air to a certain temperature where condensation can efficiently occur. In this study, an analysis of a heat pump dryer performance with operating conditions, an analysis of supplying heat with internal and external evaporators and a warm-up experiment with the evaporators have been performed. The results showed that the external evaporator can significantly accelerate the warm-up time of the dryer, so that it can reduce power consumption greatly. The use of the external evaporator is more efficient for higher ambient temperature. In addition, it was found that COP decreases and the range of evaporating pressure for the evaporator becomes narrower as the condensing temperature of the condenser increases.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 2004.05a
• /
• pp.171-176
• /
• 2004

Heat regenerator attached in small-scale regenerative radiant tube burner was designed using the theoretical computation code and was confirmed the performance of waste heat recovery ratio. From the computation, when ceramic ball of 4-5kg was used, temperature efficiency and available waste heat recovery ratio were predicted 80% and 70%, respectively. Similar efficiencies were obtained from the experiments using LPG. However, since exhaust gas temperature entered into regenerator was below 85$0^{\circ}C$ which was much lower than that we expected, preheat air temperature was lowered below 80$0^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.5
• /
• pp.1330-1336
• /
• 1990

The factors to act on atomization of liquid fuel are viscosity, geometric shape of nozzle, atomizing pressure, etc. Most of high viscous liquid fuels show decrease in viscosity by raising the preheat temperature, but the viscosity of liquid fuel like CWM does not readily change with fuel temperature. As an experimental study to investigate the atomizing characteristics of CWM, CWM fuel is atomizing with a twin-fluid atomizer, and the effects of the geometric shape of spray nozzle on atomization are investigated by measuring the Sauter`s Mean Diameter (SMD) of CWM. The summarized results obtained in this study are as follows ; (1) As the ratio of the mass flows of atomizing air to that of fuel (W$_{a}$ /W$_{1}$) increases, 능 decreases when fuel temperature is constant. (2) At the ratio (t/d) 4 of thickness (t) of spray nozzle hole to the diameter (d) of the hole, there is the best atomization. And SMD decreases when t/d is between 1 to 4 and increases when t/d > 4.

• KEPCO Journal on Electric Power and Energy
• /
• v.2 no.1
• /
• pp.89-96
• /
• 2016

The mechanism for laminar dust flame propagation can only be elucidated from a comprehensive mathematical model which incorporates conduction and radiation, as well as the chemical kinetics of particle devolatilization and gas phase and char reaction. The mathematical model for a flat, laminar, premixed coal-air flame is applied to the atmospheric coal-air mixtures studied by Smoot and co-workers, and comparisons are made with their measurements and predictions. Here the principal parameter for comparison is the laminar burning velocity. The studies of Smoot and co-workers are first reviewed and compared with those predicted by the present model. The effects of inlet temperature and devolatilization rate constants on the burning velocities are studied with the present model, and compared with their measurements and predictions. Their measured burning velocities are approximately predicted with the present model at relatively high coal concentrations, with a somewhat increased inlet temperature. From the comparisons, their model might over-estimate particle temperature and rates of devolatilization. This would enable coal-air mixtures to be burned without any form of preheat and would tend to increase their computed values of burning velocity.

• Advances in aircraft and spacecraft science
• /
• v.3 no.1
• /
• pp.29-43
• /
• 2016

Composite materials are rapidly gaining popularity as an alternative to metals for structural and load bearing applications in the aerospace, automotive, alternate energy and consumer industries. With the advent of thermoplastic composites and advances in recycling technologies, fully recyclable composites are gaining ground over traditional thermoset composites. Stamp forming as an alternative processing technique for sheet products has proven to be effective in allowing the fast manufacturing rates required for mass production of components. This study investigates the feasibility of using the stamp forming technique for the processing of thermoplastic, recyclable composite materials. The material system used in this study is a self-reinforced polypropylene composite material (Curv$^{(R)}$). The investigation includes a detailed experimental study based on strain measurements using a non-contact optical measurement system in conjunction with stamping equipment to record and measure the formability of the thermoplastic composites in real time. A Design of Experiments (DOE) methodology was adopted to elucidate the effect of process parameters that included blank holder force, pre heat temperature and feed rate on stamp forming. DOE analyses indicate that feed rate had negligible influence on the strain evolution during stamp forming and blank holder force and preheat temperature had significant effect on strain evolution during forming.

• Korean Journal of Food Science and Technology
• /
• v.22 no.6
• /
• pp.659-667
• /
• 1990

Starch acetates were prepared by conventional method, preheat treatment, and extrusion process through acetylation of corn starch with acetic anhydride and their physicochemical properties were investigated. The optimal conditions of the acetylation of starch by conventional method(CSA) was found that starch concentration was 30%, reaction temperature $35^{\circ}C$ and pH 8.5. With increasing the molar ratio of acetic anhydride to anhydrous glucose unit from 0.03 to 0.20, DS(Degree of substitution) value of corn starch acetate prepared at the optimum condition was increased from 0.019 to 0.080, while the acetylation efficiency was decreased from 31.6% to 20.5%. In the case of the preheated (gelatinized), then acetylated starch(PSA), DS value was increased from 0.027 to 0.04 at the fixed molar ratio of the acetic anhydride with increasing preheating temperature from $60^{\circ}C\;to\;90^{\circ}C$. The DS was low as 0.02 in the case of starch acetate prepared by extrusion process(WESA). The CSA and PSA showed lowering gelatinization temperature and enthalpy than raw corn starch with increasing DS. All of starch acetates showed the increased degree of transparency, the decreased lightness and the increased yellowness as compared to the raw corn starch. WESA showed lower apparent viscosity and more close to the characteristic of the Newtonian fluid than CSA and PSA. Intrinsic viscosity was reduced in CSA and WESA, although PSA has a slightly higher one than raw corn starch. The rate of retrogradation of the gels was retarded in all starch acetates.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1493-1498
• /
• 2007

Silicon Nitride ($Si_3N_4$), which is widely used in a variety of applications, is hard-to-machine due to its high hardness. At high temperature (e.g. above $1000^{\circ}C$), however, the machinability can be greatly improved. In this work, we used a $CO_2$ laser with a high absorptivity to $Si_3N_4$ of 0.9 to preheat the surface of a rothting $Si_3N_4$ rod. Preheating and turning of $Si_3N_4$ was executed at the same time. The result of machining was MRR of $8.0mm^3/s$ that is four times faster than normal grinding. Continuous chip formation was observed by a microscope.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.72-77
• /
• 2003

In order to develop ASTM A302 grade C type steel plate with excellent weldability, several steels with different chemistry have been manufactured and evaluated their mechanical properties and weldability. Trial A302-C steels have revealed tensile strength in the range of $61-67kg/mm^2$ and elongation in the range of $27{\sim}32%$, depending on chemical compositions within the ASTM specification range. In case of impact toughness, trial steels showed in the range of 58-70J at $0^{\circ}C$. From the weldability test, the minimum preheat temperature was found to be about $150^{\circ}C$, and automatic welding condition satisfied the requirements of both ASTM specification and users.

• Journal of the Korean Academy of Esthetic Dentistry
• /
• v.23 no.2
• /
• pp.77-79
• /
• 2014

There are several factors affected fractures of full contour zirconia (FCZ) dental prosthesis in laboratory process. First, residual moisture can cause zirconia cracks. Complete dry is requisite before zirconia sintering to prevent zirconia cracks. Second, slow cooling rate is essential to prevent cracks during zirconia sintering process. Cracks in bridge pontic area, thick dental implant prosthesis can be prevented by slow cooling rate such as 3 degree Celsius per minute during zirconia sintering. Third, slow heating rate and slow cooling rate during staining and glazing procedure is necessary to inhibit thermal shock of sintered dental zirconia. Lower preheat temperature of porcelain furnace is recommended. Finally, using diamond disc to open embrasure can lead cracks.