• 한국지역사회생활과학회지
• /
• 제15권2호
• /
• pp.55-64
• /
• 2004

The purpose of this study was to examine the differences in skin temperature and thermal comfort of participants in a $19^\circ{C}$ room (the recommended room temperature in the winter) depending on age, sex and clothing weight. Subjects were divided into four groups (6 young males, 5 young females, 6 old males, 6 old females) and experimental trials consisted of three conditions: wearing underwear in a $19^\circ{C}$ room (19CUW), without underwear in a $19^\circ{C}$ room (19C), and without underwear in a $24^\circ{C}$ room (24C). The results indicated the following: 1) There were no significant differences in mean skin temperature based on age or sex, and the mean skin temperatures of the four groups were in the range of 32.4∼$34.0^\circ{C}$. 2) In the 19C condition, the skin temperatures of the hands and feet of old females were higher than those of the other three groups. 3) In terms of perceived thermal comfort, young females showed a tendency to feel the most uncomfortable. Both old and young groups agreed that the 24C condition was the most comfortable. 4) Relational coefficients between thermal comfort and skin temperatures were higher in the young group than in the old group. Furthermore, the perceived thermal comfort had a stronger relationship with mean skin temperatures than with local skin temperatures. 5) The mean skin temperatures of subjects who indicated they were 'comfortable' were in the range of 31∼$36^\circ{C}$ regardless of age or sex.

• 한국화재소방학회논문지
• /
• 제11권2호
• /
• pp.11-17
• /
• 1997

화재시 실내의 경계면 선정에 관한 연구를 하기 위하여 쓰레기통, 의자, 카패트 및 소파의 화재실험 을 실제건물에서 수행하였다. 경계변의 선정을 하기위해서 화재실의 온도변화가 큰 지점은 여러 곳 온 도를 측정하고, 각 측정점의 온도를 시간과 높이별로 평균온도를 구한다. 또한 기본 측정점을 기준으로 화재실 전체구역에 대한 평변의 온도분포를 구하여 용도변화가 가장 큰 지점을 경계면의 높이로 정한 다. 이결과 어느 화재의 경우나 경계면이 뚜렷이 나타났고, 경계면 높이는 1[m] 근처에서 일정한 상태 값을 유지하였다. 다만, 최대온도를 나타내는 시간에는 경계면 높이가 O.25[m]내지 O.75[m]까지도 내 려왔다.

• The Korean Journal of Ceramics
• /
• 제4권4호
• /
• pp.331-335
• /
• 1998

R-curve, of three kinds of silicon nitride-based ceramics were measured, using single edge notched beam (SENB) method at room and at elevated temperatures, up to $1200^{\circ}C$. Stable fraacture was seen on ceramic materials with SENB specimens if the machined notch is deep enough, even though the crack resistance did not increase with crack length. Hot pressed silicon nitride did not show the rising R-curve behavior at room temperature, but it showed some rising at $1000^{\circ}C$ and above. Si3N4 reinforced with SiC whiskers showed no rising behavior at room and elevated temperatures, as it has smaller grain size, compare to the monolithic specimen. Gas pressure sintered silicon nitride had very large and elongated grains, and it showed rising R-curve even at room temperature. However, it showed some creep behavior at $1200^{\circ}C$ and the calculated R-curve on this condition did not show a good result. We cannot apply this technique on this condition for obtaining the R-curve.

• 한국정밀공학회지
• /
• 제28권12호
• /
• pp.1403-1410
• /
• 2011

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polymethyl methacrylate(PMMA) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PMMA at room temperature is 85 % of tensile strength. which is higher than that of PE (75%)at room temperature. Also the creep limits decreased to nil linearly as the temperatures increased, up to $120^{\circ}C$ of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages were non-existent nor were there any rupture failure which occurred for many metals at high temperatures.

• 설비공학논문집
• /
• 제3권5호
• /
• pp.376-385
• /
• 1991

The purpose of this paper is to propose basic data on convection heat-transfer coefficients in Ondol-heated room. Surface temperatures and several temperatures around each inside surface of wall, floor and ceiling composed of heating room are measured vertically in Ondol-heated model rooms, and the vertical temperature profiles could be expressed by nonlinear equation models. Also, the convection heat transfer phenomena are analysed from the nonlinear equation models. In the results, the convection heat-transfer coefficients of Ondol heated space are suggested by the term of temperature difference between each wall surface and room air temperature and by the relationship between Nusselt number and Rayleigh number of dimensionless numbers.

• 한국축산식품학회지
• /
• 제18권4호
• /
• pp.322-331
• /
• 1998

Good temperature control in the chill chain is imperative for maintaining safety and quality of the fresh meat. Therefore, the actual state of temperature or relative humidity histories of fresh meat product from carcass chill room to retail shop and the temperatures of chill and freezing rooms at local butcher shops were monitored by means of data loggers. The relative humidity and air temperature in carcass chill room were between 86 and 98%, and -3 and 0$^{\circ}C$, respectively. The surface temperatures of boxed beef measured in winter, when the outside air temperature was measured between -2 and -5$^{\circ}C$, were recorded between 1 and 3$^{\circ}C$, although transport vehicle switched off the chilling unit during transportation, However, the inside temperatures of chill transport vehicle measured in summer, when the transport time was prolonged to maximum 8 hrs, were raised to 10 to 15$^{\circ}C$, in worst case up to 25$^{\circ}C$. In that case, however, the inside temperature of boxed beef was maintained generally lower than 5$^{circ}C$ as the loading and unloading were finished within 30 min. The storage temperatures for meat in the subfreezing room, at which the butcher shops in local market are used to set to facilitate the thin slicing of meat, were measured between -2 and -8$^{\circ}C$. Furthermore, the temperatures of storage room for vacuum packaged meat in the chilled meat retail shops were maintained generally between 0 and +2$^{\circ}C$.

• 한국정밀공학회지
• /
• 제27권9호
• /
• pp.78-85
• /
• 2010

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polycarbonate(PC) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PC at room temperature is 85 % of tensile strength. which is higher than PE (75%)at room temperature. Also the creep limits decreased exponentially as the temperatures increased, up to 50 % of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages was non-existent nor was there any rupture failure which occurred for many metals.

• Journal of Advanced Marine Engineering and Technology
• /
• 제32권2호
• /
• pp.276-283
• /
• 2008

The purpose of this study is to measure and analyze the ship's indoor thermal conditions and also to integrate experimental database of those which are supplied and controlled by marine HVAC. On this study, temperature, humidity and air volume of 6 different needs' cabin are measured like previous report on a newly-launched training ship during 25th through 27th of July, 2007. Followings are the results of this study. (1)The air supply volumes to each cabins are measured 250CMH(Recreation room), 800CMH(Conference room), 1.000CMH(Bridge), 5,100CMH(Lecture room) respectively. (2)The temperatures are maintained at $21{\sim}27^{\circ}C$ in almost cabins through measuring period, but the temperatures are fluctuated over ${\pm}4^{\circ}C$ at the bridge and conference room. (3)The relative humidities are shown between $40{\sim}60%$ known as comfort conditions, but the conference room is needed to dehumidified because of over 70% humidity. (4)From the student cabins' measurements which have different supply diffuser(s), it is clear that the design is suitable for this case. (5)Because of temperature diversities, only 32% among the measured data are satisfied with the comfort standard range proposed by ASHREA.

• 소성∙가공
• /
• 제24권6호
• /
• pp.405-410
• /
• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• 한국해양공학회지
• /
• 제14권1호
• /
• pp.23-28
• /
• 2000

The fatigue crack growth behavior of the cold-rolled STS 304 steel developed for membrane material of LNG storage tank was examined experimentally at 293K, 153K and 111K. The fatigue crack growth rate(do/dN) tends to increase as the stress ratio (R) increases over the testing temperature when compared at the same stress intensity factor range($\Delta$K). The effect of R on do/dN is more explicit at low temperatures than at room temperature. The resistance of fatigue crack growth at low temperatures is higher compared with that at room temperature which is attributed to the extent of strain-induced martensitic transformation at the crack tip. The temperature dependence of fatigue crack growth resistance is gradually vanished with an increase in $\Delta$K which correlates with a decreasing fracture toughness with decreasing temperature. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperature are mainly explained by the crack closure and the strengthening due to the martensitic transformation.