• Journal of the Korean Society of Propulsion Engineers
• /
• v.1 no.2
• /
• pp.91-102
• /
• 1997

In order to evaluate the effects of aging on the ignition performance, pyrotechnic igniters were separated from twelve-year-old, fifteen-year-old, and sixteen-year-old live rocket motors. The characteristic values of the ignition material were measured, and the firing tests of the igniters were performed. The moisture content, the outer dimension, the crush strength, the thermal decomposition characteristics, and the heat of formation the B/$KNO_3$ ignition pellet were measured. The crush strength was increased and the heat of formation was reduced as aged, but no change was detected for other characteristic values. The burning test results of the igniter pellet in the closed bomb and the inert motor showed that the burning rate of the ignition pellet was increased by 10%, and the integration of pressure $P_t$ of the p-t curve was reduced by 15% for aged samples. It was inferred that the burning rate was increased as the crack was appeared in the pellet and $P_t$ could be proportionally decreased with the heat of explosion.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.5
• /
• pp.405-411
• /
• 2012

Inside a rotorcraft fuel cell, pipes and components are located for fuel storage and fuel supply into the engine. Utility helicopters, operated in battle fields, fly at lower altitude compared to fixed-wing aircraft and hence are more likely to be exposed to gunfire. Since internal pressure of fluid increases when hit, the effect on LRU due to increase in pressure must taken into account when designing the aircraft for survivability. However, it is costly and time consuming to manufacture a fuel cell for gunfire test, and due to constraints from usage of live ammunition, related data gathered through numerical simulation is needed. In this study, numerical simulation on rotorcraft fuel cell exposed to gunfire was carried out using Autodyn to analyze bullet movement inside the fuel cell after hit, and internal pressure of fluid and equivalent stress on fuel cell assessed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.3
• /
• pp.24-30
• /
• 2016

Vertical and standing column well ground heat exchangers have mostly been installed for ground source heat pump systems (GSHP) and thermal response tests (TRT) have been applied to evaluate the thermal characteristics for these heat exchangers. In this paper, the TRT coupled with a line source method was applied to evaluate the thermal characteristics of the horizontal ground heat exchanger (HGHX). Load tests of a HGHX were also performed to examine the daily variations of the ground and fluid temperatures associated with the daily intermittent operation of GSHP. For this test, the straight HGHX (depth 2 m, length 50 m, 8 line) was installed in Ansan city. The results showed that the variations of ground thermal conductivity of HGHX during one year were relatively small with the range of $1.43{\sim}1.64W/m{\cdot}K$, and the maximum and minimum values appeared in December and May, respectively. Load tests with heat injection rate of 6.0 kW for 10 hours per day to HGHX during twelve days were performed in June, September and December, and resulted in a ground initial temperature rise of $4.31^{\circ}C$, $3.14^{\circ}C$, and $1.21^{\circ}C$ during these days, respectively.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.12
• /
• pp.5-15
• /
• 2012

In this study, a series of CFD (Computational Fluid Dynamics) numerical analyses were performed in order to evaluate the thermal performance of six full-scale closed-loop vertical ground heat exchangers constructed in a test bed located in Wonju. The circulation HDPE pipe, borehole and surrounding ground formation were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the system. Two user-defined functions (UDFs) accounting for the difference in the temperatures of the circulating inflow and outflow fluid and the variation of the surrounding ground temperature with depth were adopted in the FLUENT model. The relevant thermal properties of materials measured in laboratory were used in the numerical analyses to compare the thermal efficiency of various types of the heat exchangers installed in the test bed. The simulation results provide a verification for the in-situ thermal response test (TRT) data. The CFD numerical back-analysis with the ground thermal conductivity of 4 W/mK yielded better agreement with the in-situ thermal response tests than with the ground thermal conductivity of 3 W/mK.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.1
• /
• pp.409-414
• /
• 2021

Tightness performance that blocks compartments is important for surface ships to achieve superior mission performance and survivability in combat environments. To meet the above requirements, airtightness of the structural elements and the appropriate strength to specific areas are checked during a test run after ship construction. In particular, air tests of compartments adjacent to the water surface are performed. In an air test, air is injected into the compartment up to the test pressure of the test memo. The pressure drop value is checked after 10 minutes to determine if the requirements of the corresponding area are satisfied. In summer, however, when the influence of the outside temperature is large, a phenomenon in which the internal pressure increases during the air test was identified. This phenomenon reduces the reliability of the test result. Therefore, a system was designed to compensate for temperature changes in the compartments through this study. The developed system calculates the amount of pressure change caused by a temperature change in the compartment and outputs a correction value. The pressure change was calculated using the ideal gas equation, reflecting the maintenance, increase, and decrease in temperature during the test process. A comparison of the calculated pressure correction value with the database of NIST REFPROP revealed a difference of 0.126% to a maximum of 0.253%.

• The Journal of Engineering Geology
• /
• v.28 no.3
• /
• pp.475-488
• /
• 2018

This study evaluates geothermal system efficiency in terms of input power and heat exchange volume on the heat-source and load sides, by applying a combined open-closed type loop system comprising a geothermal system and a groundwater well to a cultivation site. In addition, this study analyzes the effects of heating and cooling for a complex geothermal system, by evaluating the temperatures of an external site and a cultivation site during operation. During cooling operations the heat exchange volume on the heat source side, average 90.0kW/h for an open type system with an input of 235L/minute groundwater, and 40.1kW/h for a closed type system with an input of 85L/minute circulating water, for a total average heat exchange volume of 130.1kW/h. The actual heat exchange volume delivered on the load side averages 110.4kW/h. The average EER by analysis of the geothermal system's cooling efficiency is 5.63. During heating operation analysis, the heat exchange volume on the heat source side, average 60.4kW/h in an open type system with an input of 266L/minute groundwater, and 22.4kW/h in closed type system with an input of 86L/minute circulating water, for a total average heat exchange volume of 82.9kW/h. The actual heat exchange volume delivered on the load side averages 112.0kW/h in our analysis. The average COP determined by analysis of the geothermal system's heating efficiency is 3.92. Aa a result of the tradeoff between the outside temperature and the inside temperature of the production facility and comparing the facility design with a combined well and open-closed loops geothermal(CWG) system, we determine that the 30RT-volume CWG system temperature are lower by $3.4^{\circ}C$, $6.8^{\circ}C$, $10.1^{\circ}C$ and $13.4^{\circ}C$ for ouside temperature is of $20^{\circ}C$, $25^{\circ}C$, $30^{\circ}C$ and $35^{\circ}C$, respectively. Based on these results, a summer cooling effect of about $10^{\circ}C$ is expected relative to a facility without a CWG system as the outside temperature is generally ${\geq}30^{\circ}C$. Our results suggest that a complex geothermal system provides improvement under a variety of conditions even when heating conditions in winter are considered. Thus It is expected that the heating-cooling tradeoffs of complex geothermal system are improved by using water screen.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.7
• /
• pp.93-106
• /
• 2010

In performing a series of in-situ thermal response tests, the effective thermal conductivities of six vertical closed-loop ground heat exchangers were experimentally evaluated and compared one another, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than bentonite grouting, and the efficiency of graphite better performs than silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance. Based on the results from the in-situ thermal response tests, a series of economic analyses have been made to show the applicability of the new addictives and 3 pipe-type heat exchanger.

• Journal of Energy Engineering
• /
• v.5 no.2
• /
• pp.203-208
• /
• 1996

An experimental study was conducted on the natural convection heat transfer with a heat source (heater) in a top-vented cylindrical enclosure. Using an Air Controlled Oxidizer (ACO) for treatment of depleted uranium chips, the heat transfer characteristics of the ACO was studied with various heat generation. Heat flux, Nusselt number, Grashof number and Rayleigh number were obtained and the relation between Nusselt number and Rayleigh number was derived.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.22 no.3
• /
• pp.130-138
• /
• 2010

The thermal reliability of the closed-type BLDC motor for the high speed axial fans is analyzed by a numerical method in this paper. Since the module and the motor part are combined in a closed case, the heat generated from a rotor in the motor and the electronic components in the PCB module can not be effectively removed to the outside. Therefore the module will easily fail by high temperature. The accelerated-life testing was accomplished to formulate the life equation and numerical method is used to predict the inside temperature of the PCB module, which is one of the life equation parameter according to the environment. When the environment temperature of BLDC motor is 21, 35 and 50 $^{\circ}C$, the temperature in the PCB space is predicted as 73.4, 87.5 and 102.4 $^{\circ}C$. Then the life time with the temperature are calculated as 2,239, 863 and 328 hours.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.03a
• /
• pp.229-239
• /
• 2010

Performing a series of in-situ thermal response tests, the effective thermal conductivity of six vertical closed-loop ground heat exchangers was experimentally evaluated and compared each other, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than that of bentonite grouting, and the efficiency of graphite better performs over silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance.