• 설비공학논문집
• /
• 제26권2호
• /
• pp.61-66
• /
• 2014

Exhaust heat recovery ventilation systems conserve energy through enthalpy recovery between air intake and exhaust, and they are being increasingly used. An exhaust heat recovery ventilation system can be installed in the ceiling of a balcony or emergency evacuation space. However, in the case of fire, the emergency evacuation space has to by law remain as empty space, and therefore, a ventilation system can't be installed in an emergency evacuation space. Therefore, the need for a proper installation space for a ventilation system is emphasized. In this study, to install a heat recovery ventilation system in a lightweight wall, a heat exchanger was assembled of thickness below 140 mm. The efficiency of heat recovery was analyzed through performance experiment, in the case of the cooling and heating mode. The heat recovery efficiency increases when the surface area is increased, by using closer channel spacing in the heat exchanger, or by increasing the size of the heat exchanger.

• 한국태양에너지학회 논문집
• /
• 제28권2호
• /
• pp.10-18
• /
• 2008

This study aims to figure out typical meteorological data according to Korean time in order to evaluate building energy performance. Various methods of calculating typical meteorological data were compared and examined to improve accuracy and reliability of this study. This study analyzed and examined such methodologies as typical meteorological data for HASP/ACLD-8001, UK CIBSE TRY developed by CIBSE and prEN ISO 15927-4, (=ISO TRY) an international standard to evaluate annual energy demand of cooling and heating devices. In addition, actual data of KMA corresponding to Seoul in $1985{\sim}2005$ were statistically analyzed according to calculation methodology. The calculated typical meteorological data were compared te actual data using MBE, RMSE and t-Statistic. As a result, According to the comparison between average annual for HASP/ACLD-8001 and ISO TRY standard year, the average annual for HASP/ACLD-8001 is closer to actual measurement, showing that the use of typical meteorological data for HASP/ACLD-8001 is preferred. However, since the input format requested by current simulation is the same international standard as TRY. Therefore, it is necessary to improve accuracy of TRY calculation methodology and accordingly figure out Korean typical meteorological data based on average year.

• 대한금속재료학회지
• /
• 제46권6호
• /
• pp.377-381
• /
• 2008

Prism sheet of LCD BLU which depends on supply from Japan and U.S.A was studied by using Si anisotropic etching and injection molding technologies. First, the prism sheet was patterned on Si wafer through photolithography, and the best conditions of Si etching were determined through etching Si wafer with TMAH to obtain straight optimized zigzag patterns, and a cross pattern to provide light diffusion and concurrent focusing. The etch rate of TMAH was concluded to be constant for $25wt%-70^{\circ}C$ condition. Ni stamp of prism sheet was made by electrodeposition using patterned Si wafer, normal or fast H/C(Heating/Cooling) injections were carried out to fabricate prism sheet. It was known that fast H/C injection could fabricate prism sheet more accurately than normal injection. Zigzag patterns and the cross pattern showed higher transmissivity than the straight patterns because of light diffusion through diagonal direction. The fast H/C injection for zigzag patterns showed lower transmissivity than normal injection because there occurred more light diffusion through precise injection patterns, but the fast H/C injection for straight patterns showed only refraction without diffusion, causing lower transmissivity than normal injection.

• 설비공학논문집
• /
• 제12권3호
• /
• pp.258-266
• /
• 2000

Experimental investigation and cycle simulation of a capacity modulation of a heat pump system using a hydrofluorocarbon (HFC) refrigerant mixture, R32/134a as an alternative to R22, have been done. In the cycle simulation, the refrigeration system was operated by assigning the temperatures of the external heat transfer fluids with the heat exchangers generalized by an average effective temperature difference. Heating capacity, cooling capacity, and coefficient of performance (COP) of the system were investigated at several operating conditions. Experimental apparatus which had a refrigeration part and a composition changing part was built, and the performance of the heat pump system filled with R32/134a mixture was investigated. A gas-liquid separator was used in the experiment to change the composition by collecting the vapor and the liquid Phase separately, The mass fraction of the charged refrigerant in the heat pump system was 40/60 and 70/30 by weight percentage. The composition of the refrigerant with initial composition of 40/60 varied from 29/71 to 41/59 in the refrigeration cycle. For the refrigerant with initial composition of 70/30, the composition varied from 65/35 to 75/25.

• Smart Structures and Systems
• /
• 제24권1호
• /
• pp.111-125
• /
• 2019

Metallic shape memory alloys present fascinating physical properties such as their super-elastic behavior in austenite phase, which can be exploited for providing a structure with both a self-centering capability and an increased ductility. More or less accurate numerical models have been introduced to model their behavior along the last 25 years. This is the reason for which the literature is rich of suggestions/proposals on how to implement this material in devices for passive and semi-active control. Nevertheless, the thermo-mechanical coupling characterizing the first-order martensite phase transformation process results in several macroscopic features affecting the alloy performance. In particular, the effects of day-night and winter-summer temperature excursions require special attention. This aspect might imply that the deployment of some devices should be restricted to indoor solutions. A further aspect is the dependence of the behavior from the geometry one adopts. Two fundamental lacks of symmetry should also be carefully considered when implementing a SMA-based application: the behavior in tension is different from that in compression, and the heating is easy and fast whereas the cooling is not. This manuscript focuses on the passive devices recently proposed in the literature for civil engineering applications. Based on the challenges above identified, their actual feasibility is investigated in detail and their long term performance is discussed with reference to their fatigue life. A few available semi-active solutions are also considered.

• 한국지열·수열에너지학회논문집
• /
• 제14권4호
• /
• pp.1-6
• /
• 2018

In this study, the energy consumption of the typical floor was compared by the total energy comsumption of the building in highrise building. In gerneral, many researchers are studying on the typical floor in highrise buildings for avoiding complexity in energy simulation. But few papers are studied on energy consumption along the floors. In the model bulding, the energy consumption data were acquired by BEMS system in 2011. According the data, the total net energy consumption was $193.99kWh/m^2$ for all area and the total net energy consumption was $247.61kWh/m^2$ for HVACR area. The total electricity and gas energy are used 47.7% for heating and cooling, 33.5% for lighting and plug, 12.9% for conveyance power and 5.9% for restaurant. In comparison of only ground floor, amount of energy consumption in the lobby is 10%, and 90% of total energy consumption is used in the typical floor. For this result, energy simulation on the typical floor is acceptable for calculating the total energy consumption in the highrise building.

• 천문학회보
• /
• 제44권1호
• /
• pp.48.4-48.4
• /
• 2019

Small-scale shear flows are ubiquitous in the universe, and astrophysical plasmas are often magnetized. We study the thermal condensation instability in magnetized plasmas with shear flows in relation to filamentary structure formation in cool structures in the universe, representatively solar prominences and supernova remnants. A linear stability analysis is extensively performed in the framework of magnetohydrodynamics (MHD) with radiative cooling, plasma heating and anisotropic thermal conduction to find the eigenfrequencies and eigenfunctions for the unstable modes. For a shear velocity less than the Alfven velocity of the background plasma, the eigenvalue with the maximum growth rate is found to correspond to a thermal condensation mode, for which the density and temperature variations are anti-phased (of opposite signs). Only when the shear velocity in the k-direction is near zero, the eigenfunctions for the condensation mode are of smooth sinusoidal forms. Otherwise each eigenfunction for density and temperature is singular and of a discrete form like delta functions. Our results indicate that any non-uniform velocity field with a magnitude larger than a millionth of the Alfven velocity can generate discrete eigenfunctions of the condensation mode. We therefore suggest that condensation at discrete layers or threads should be quite a natural and universal process whenever a thermal instability arises in magnetized plasmas.

• 대한금속재료학회지
• /
• 제49권1호
• /
• pp.9-16
• /
• 2011

To develop a 6061 aluminum alloy with low residual stress and high tensile strength, a cryogenic treatment process was investigated. Compared to the conventional heat treatment process for precipitation hardening with artificial aging, the cryogenic treatment process has two additional steps. The first step is cryogenic quenching of the sample into liquid nitrogen, the second step is up-hill quenching of the sample into boiling water. The residual stress for the sample was measured by the $sin^2{\psi}$ method with X-ray diffraction. The 6061 aluminum alloy sample showed 67% relief in stress at the cryogenic treatment process with artificial aging at $175^{\circ}C$. From this study, it was found that the optimum cryogenic treatment process for a sample with low residual stress and high tensile strength is relatively low cooling speed in the cryogenic quenching step and a very high heating speed in the up-hill quenching step.

• 한국기계가공학회지
• /
• 제20권3호
• /
• pp.113-121
• /
• 2021

In this study, the thermal characteristics of cold and hot water mattress units equipped with thermoelectric modules were investigated via numerical analyses. Cold and hot water mattress products that are currently in existence use manual methods requiring refrigerants to be added to the hot water boiler. However, the cold and hot water mattress units using thermoelectric modules can provide improved efficiency via energy savings and actively resolving environmental pollution problems. To determine the efficiency of the thermoelectric module, the mattress was modeled and its efficiency was analyzed for the cooling and heating processes using two 100-W-class and one 200-W-class thermoelectric modules, respectively. From the results of this study, it was confirmed that when two 100-W-class modules were used, the application area was larger than when a single 200-W-class module was used, with uniform temperature distribution and improved performance compared to existing products in terms of electrical energy.

• Nuclear Engineering and Technology
• /
• 제54권6호
• /
• pp.2188-2197
• /
• 2022

To ensure the safety margin of a reactor pressure vessel (RPV) under normal operating conditions, it is regulated through the pressure-temperature (P-T) limit curve. The stress intensity factor (SIF) obtained by the internal pressure and thermal load should be obtained through crack analysis of the nozzle corner crack in advance to generate the P-T limit curve for the nozzle. In the ASME code Section XI, Appendix G, the SIF via the internal pressure for the nozzle corner crack is expressed as a function of the cooling or heating rate, and the wall thickness, however, the SIF via the thermal load is presented as a polynomial format based on the stress linearization analysis results. Inevitably, the SIF can only be obtained through finite element (FE) analysis. In this paper, simple prediction equations of the SIF via the thermal load under, cool-down and heat-up conditions are presented. For the Korean standard nuclear power plant, three geometric variables were set and 72 cases of RPV models were made, and then the heat transfer analysis and thermal stress analysis were performed sequentially. Based on the FE results, simple engineering solutions predicting the value of thermal SIF under cool-down and heat-up conditions are suggested.