• 대한기계학회논문집B
• /
• 제23권11호
• /
• pp.1434-1443
• /
• 1999

The turbulent fluctuations of temperature and two components of velocity have been measured with hot- and cold-wires in the Thermally Stratified Wind Tunnel(TSWT). Using the fin-tube heat exchanger type heaters and the neural network control algorithm, both stable ($dT/dz=109.4^{\circ}C$) and unstable ($dT/dz=-49.1^{\circ}C$) stratifications were realized. An ambient air jet was issued normally into the cross flow($U_{\infty}=1.0 m/s$) from a round nozzle(d = 6 mm) flushed at the bottom waII of the wind tunnel with the velocity ratio of $5.8(U_{jet}/U_{\infty})$. The characteristics of turbulent dispersion in the cross flow jet are found to change drastically depending on the thermal stratification. Especially, in the unstable condition, the vertical velocity fluctuation increases very rapidly at downstream of jet. The fluctuation velocity spectra and velocity-temperature cospectra along the jet centerline were obtained and compared. In the case of stable stratification, the heat flux cospectra changes Its sign from a certain point at the far field because of the restratification phenomenon. It is inferred that the main reason in the difference between the vertical heat fluxes is caused by the different length scales of the large eddy motions. The turbulent kinetic energy and scalar dissipation rates were estimated using partially non-isotropic and isotropic turbulent approximation. In the unstable case, the turbulent energy dissipation decreases more rapidly with the downstream distance than in the stable case.

• 대한미생물학회지
• /
• 제18권1호
• /
• pp.53-58
• /
• 1983

Enterotoxigenic E. coli is one of causative agents of the infantile diarrhea and traveler's diarrhea. A modified infant mouse assay(IMA) was developed for the detection of heat stable enterotoxin (ST) of E. coli isolated from diarrheal and control infants and assay system was established with using enterotoxin producing reference strains. The supernatant of the 24 hour-shaking culture of E. coli in Casamino Acid Yeast Extract Salt Broth(CYES-2) was ingested orally into the 2-4 day old ICR mice. After the mice were kept at $25^{\circ}C$ for 4 hours, they were sacrificed and the gut weight body weight ratio(GW/BW) was taken as the index of fluid accumulation induced by heat stable enterotoxin of E. coli. The results obtained were as follows; 1. The GW/BW responses of IMA tested with enterotoxin reference strains of E. coli(E. coli O148H28:$ST^+LT^+$, E. coli $O78H^-:ST^+LT^+$, E. coli O15H11:$ST^-LT^+$, E. coli O1H7:$ST^-LT^-$) appeared ta be ST dose-dependent, and not LT-dependent. From the dose-response curve, $25{\mu}l$ of culture supernatant was determined as test amount of the IMA. 2. Frequency distribution of IMA result from 643 strain of E. coli showed normal distribution at low GW/BW ratio and dispersed pattern at high GW/BW ratio. The GW/BW ratios of $0.056{\pm}0.004(mean{\pm}SD)$ of normal distribution which distributed from 0.044 to 0.068(P<0.01) was considered as ST negative. Thus the GW/BW ratio above 0.069 could be regarded as ST positive.

• KIEAE Journal
• /
• 제15권1호
• /
• pp.111-116
• /
• 2015

Heat loss from windows and condensation occuring on its surface due to its lower insulation value causes much discomfort to occupants. In this study, Heated glass was used to make a basic study on prevention of condensation on glass surface for its heating functionality through experimental measurement and simulation analysis of total heat flux on the interior and exterior surface of glass. Error between experimental results and three dimensional steady-state heat transfer analysis were caused firstly, beacuse in the experimental chambers, cold chamber and steady temperature and humidity chamber, air temperature setting was not constant but rather ON/OFF control, and secondly, due to error rate in heat flux meter due to heat flux direction even in stable conditions.

• Journal of Mechanical Science and Technology
• /
• 제20권12호
• /
• pp.2230-2241
• /
• 2006

This paper presents a sole application of boundary element method to the conjugate heat transfer problem of thermally developing laminar flow in a thick walled pipe when the fluid velocities are fully developed. Due to the coupled mechanism of heat conduction in the solid region and heat convection in the fluid region, two separate solutions in the solid and fluid regions are sought to match the solid-fluid interface continuity condition. In this method, the dual reciprocity boundary element method (DRBEM) with the axial direction marching scheme is used to solve the heat convection problem and the conventional boundary element method (BEM) of axisymmetric model is applied to solve the heat conduction problem. An iterative and numerically stable BEM solution algorithm is presented, which uses the coupled interface conditions explicitly instead of uncoupled conditions. Both the local convective heat transfer coefficient at solid-fluid interface and the local mean fluid temperature are initially guessed and updated as the unknown interface thermal conditions in the iterative solution procedure. Two examples imposing uniform temperature and heat flux boundary conditions are tested in thermally developing region and compared with analytic solutions where available. The benchmark test results are shown to be in good agreement with the analytic solutions for both examples with different boundary conditions.

• 설비공학논문집
• /
• 제23권5호
• /
• pp.321-326
• /
• 2011

Recently, ground source heat pump (GSHP) systems have been introduced in many modem buildings which use the annually stable characteristic of underground temperature as one of the renewable energy uses. However, all of GSHP systems cannot achieve high level of energy efficiency and energy-saving, because their performance significantly depends on thermal properties of soil, the condition of groundwater, building loads, etc. In this research, the effect of thermal properties of soil on the performance of GSHP systems has been estimated by a numerical simulation which is coupled with ground heat and water transfer model, ground heat exchanger model and surface heat balance model. The thermal conductivity of soil, the type of soil and the velocity of groundwater flow were used as the calculation parameter in the simulation. A numerical model with a ground heat exchanger was used in the calculation and, their effect on the system performance was estimated through the sensitivity analysis with the developed simulation tool. In the result of simulation, it founds that the faster groundwater flow and the higher heat conductivity the ground has, the more heat exchange rate the system in the site can achieve.

• 설비공학논문집
• /
• 제27권3호
• /
• pp.169-173
• /
• 2015

Recently, ground source heat pump (GSHP) systems have attracted much attention, according to the enhanced social demand of renewable energy. GSHP systems can achieve higher coefficient of performance than the conventional air-source heat pump systems by utilizing stable underground temperature. However, the initial cost of GSHP system is higher than that of the conventional systems, especially, in the small-size buildings. Therefore, it is necessary to develop small-size ground heat exchanger with low cost and quick installation. In this study, a unit-type ground heat exchanger was developed and heat exchange rate was calculated by the numerical simulation. As a result, 27.45 W/m of heat exchange rate was acquired in the condition of $0.5m{\times}0.2m{\times}2m$ unit.

• 설비공학논문집
• /
• 제21권11호
• /
• pp.621-628
• /
• 2009

The objectives of this study are to analyze the performance of a river water-source heat pump and to carry out economic assessment for the heat pump. The COP of the river water-source heat pump was 3-21% higher than that of the air-source heat pump because river water provides stable operating temperature compared with air temperature throughout the year. The economic analysis was carried out by comparing the initial and operating cost of the river water-source heat pump with those of the conventional air-source heat pump. The ratio of the life cycle operating cost to the life cycle cost increased with the increase of building capacity. The payback period was found to be less than 3.5 years when the capacity of the river water-source heat pump was larger than 10 RT.

• 에너지공학
• /
• 제10권4호
• /
• pp.349-356
• /
• 2001

물과 증기의 직접접촉에 의한 응축 열전달은 움직이는 증기/물 경계면에서 열 및 물질 전달이 이루어지는 현상으로서, 매우 큰 열전달계수를 수반하는 특징이 있기 때문에 이를 응용한 설계가 산업계에서 광범위하게 이루어지고 있다. 본 연구에서는 단일 수평 배관을 통해 과냉각수가 있는 응축탱크로 안정된 증기제트가 방출될 때, 증기제트 형상을 예측하는 간단한 응축해석모델을 제시하였다. 해석모델은 축대칭 좌표계에서 질량, 운동량 및 에너지 방정식과 증기/물 경계면에서 의 응축 특성을 고려한 열평형 방정식을 사용하여 유도하였다. 증기/물 경계에서의 매우 큰 열전달율은 기존의 실험을 근거로 한 유효열전도계수에 의해 반영되었다. 해석결과는 실험결과와 비교하였고, 제시된 해석 모델은 실험에서 관찰된 바와 같이 증기 질량유속과 수조 온도가 증가할수록 증기제트 크기(반경 및 길이)가 증가하는 경향을 보였다.

• 한국식품과학회지
• /
• 제32권4호
• /
• pp.822-827
• /
• 2000

새우 알러지를 감소시키기 위한 방법으로써 감마선 조사기술의 이용 가능성을 평가하였다. 새우로부터 분리한 열안정성 단백질(HSP)과 병원에서 임상진단용으로 사용하는 새우 단백질 추출액을 1, 3, 5, 7, 10 kGy의 선량으로 감마선을 조사하였다. 단백질 추출액 및 HSP의 알러지성과 항원성의 변화를 mAb와 환자의 IgE를 사용한 ELISA법과 immunoblotting법으로 측정하였고, 단백질의 구조변화는 gel permeation chromatography와 SDS-PAGE로 관찰하였다. 환자의 IgE는 감마선 조사된 단백질 추출액과 HSP용액 모두에서 감마선 조사선량이 증가함에 따라 감소하였다. GPC-HPLC와 sandwich ELISA법으로 HSP를 정량하였을 때도 역시 감마선 조사선량이 증가함에 따라 감소하였다. SDS-PAGE pattern 변화에서 HSP는 감마선 조사에 의해 변화되어 더 큰 분자량으로 전환되었다. 이러한 결과는 감마선 조사가 새우 알러지 억제에 적용 할 수 있다는 가능성을 시사하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제40권2호
• /
• pp.96-101
• /
• 2016

The thermal management of high-power LED components in an assembly structure is crucial for the stable operation and proper luminous function. This study employs numerical tools to determine the optimum thermal design in LEDs with a heat sink consisting of a crevice-type vapor-chamber heat pipe. The effects of the MCPCB are investigated in terms of the substrate thicknesses on which the LEDs are mounted. Further, different placement configurations in a system module are considered. This study found that for a confined area, a power of 40 W/LED is applicable to a high-power package. Furthermore, the thermal conductivity of dielectric layer materials should ideally be greater than 0.9 W/m.K. The temperature conditions of the vapor chamber in a heat pipe greatly affect the thermal performance of the system. At an offset distance of 9.0 mm and a $2^{\circ}C$ increase in the temperature of the heat pipe, the resulting maximum temperature increase is approximately $1.9^{\circ}C$ for each heat dissipation temperature. Finally, at a thermal conductivity of 0.3 W/m.K, it was found that the total thermal resistance changes dramatically. Above 1.2 W/m.K, the resistance change reduces exponentially.