• 설비공학논문집
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• 제14권6호
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• pp.477-484
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• 2002

A numerical investigation of the performance of the plate heat exchanger with rectangular winglet is conducted to examine the combined effect of vortex generator and louver fins. Velocity and temperature fields and spanwise averaged Nu and friction factor are presented. Enhancement of heat transfer and flow loss penalty is evident. A Parametric study of three factors (Re, angle of attack and louver angle) with levels of 5 (Re= 300, 500, 700, 900, 1100), 4($\alpha=15^{\circ}, 30^{\circ}, 45^{\circ}, 90^{\circ},$), and 4($\beta=0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}$), respectively, indicates the performance defined by the ratio of heat transfer enhancement to flow loss penalty shows monotonic behavior for each parameter alone but the interactions between parameters is found to be considerable effect on the performance of heat exchanger and should be considered in design. The effect of stamping is also examined.

• 한국자기학회지
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• 제11권1호
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• pp.14-20
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• 2001

The structure, shape, size, and magnetic properties of Ni$_{0.5}$Cu$_{0.1}$Zn$_{0.4}$Fe$_2$O$_4$ have been investigated as a function of annealing temperatures. In order to control the microwave absorbing properties of ferrite-rubber composite and the complex losses (magnetic loss and conduction loss), the effect of carbon addition was also studied. It was found that the coercive force decreased with increasing heat-treatment temperatures. Relative complex permeability and reflection loss were measured by the network analyzer. As a result, the natural resonance occurred in the low frequency tinge, and the matching frequency of the ferrite-rubber composite prepared at 130$0^{\circ}C$ was found to be lower. As heat-treatment temperatures were increased, the magnetic loss ($\mu$$_{r}$", $\mu$$_{r}$′) and the dielectric loss ($\varepsilon$$_{r}$"/$\varepsilon$$_{r}$′) were increased. It was caused that the absorption characteristics of the absorber were improved. The conduction loss and magnetic loss were expected to be occurred together because two matching frequencies were shown with carbon addition. It was confirmed that the matching frequency of the microwave absorber could be controlled by controlling heat-treatment temperatures and carbon additions.ons.tions.

• 에너지공학
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• 제23권2호
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• pp.35-41
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• 2014

본 연구는 냉장고의 냉장실과 냉동실 사이에 있는 멀리언부의 가스켓 주위의 열전달 해석을 수행하여 이 부분에서 열손실을 크게 하는 구조물인 구조보강용 철구조물 유무에 따른 전산해석을 통한 열전달 해석과 이의 결과에 대한 검증을 위해 냉장고 내부 벽면의 온도를 측정하여 열손실 분석을 통한 냉장고 열손실을 개선하는 것을 목적으로 하였다. 본 연구를 통해 철구조물이 있는 경우에 이를 통하여 고온의 Hotline과 외부 공기의 열이 잘 전달되어서 냉장고의 열손실에 크게 영향을 미치는 것을 알 수 있었으며 이를 제거하면 냉장고 열손실이 24.8% 감소하여 철구조물을 제거하는 것이 냉장고 열손실 설계 개선을 크게 향상시킴을 알 수 있었다.

• 대한기계학회논문집B
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• 제29권12호
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• pp.1352-1359
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• 2005

Unsteady simulations were performed to investigate the flame structure and the dynamic behavior of a premixed flame exposed to the wall heat loss. A 3-step global reaction mechanism was adopted in this study. Simulations were performed for two tube combustors with inner diameters($d_i$) of 1mm and 4mm. The material of tube combustor was assumed to be a Silicon Nitride($Si_{3}N_4$). The heat loss from the outer tube wall was controlled by adjusting the amount of convective and radiative heat loss. A conical premixed flame could be stabilized inside a tube of $d_i=4mm$. The flame stability inside a tube of $d_i=4mm$ combustor was not much sensitive to the amount of heat loss. In case of a tube of $d_i=1mm$, an oscillating flame was observed in very low heat loss condition and a flame could not be sustained in realistic heat loss condition.

• 산업기술연구
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• 제22권B호
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• pp.21-26
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• 2002

The non-dimensional heat loss from a thermally asymmetric triangular fin is investigated as a function of a ratio of upper and lower surface Biot numbers (Bi2/Bi1), the non-dimensional fin length and tip surface Biot number using the two-dimensional separation of variables method. The effect of fin tip surface Biot number on the variation of the non-dimensional temperature along the sloped upper and lower surfaces for the thermally asymmetric condition is presented. The relationship between the non-dimensional fin length and the fin tip surface Biot number for equal amount of heat loss is also discussed as well as the relationship between upper surface Biot number and tip surface Biot number for equal amount of heat loss.

• 에너지공학
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• 제22권2호
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• pp.105-111
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• 2013

본 연구는 빌트인 냉장고 내부를 가열하여 냉장고의 열손실 특성을 파악하는 역열손실 방법을 이용하여 냉장고의 열손실이 큰 부분이 어느 영역인지를 분석함으로써 이를 개선하는 것에 목적을 두고 있다. 이를 위해서 적외선 열화상 카메라를 이용하여 냉장고 외부 표면 온도를 측정함으로써 열손실을 분석하였으며 이를 통하여 상대적으로 열손실이 큰 부분인 얼음배출구에서의 열손실 개선을 시도하였다. 또한, 이에 관한 열전달 전산해석을 수행하여 열손실 구조를 규명하였으며 적용 가능한 열손실 개선 방안인 모서리 부분의 곡면반경을 증가하여 열손실이 개선되는 특성을 살펴보았다. 본 연구의 결과로 부터 얼음배출구 모서리 부분의 곡면 반경을 30mm로 하면 모서리 부분의 열손실이 최적으로 개선되는 것을 알 수 있었다.

• 한국임상수의학회지
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• 제37권5호
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• pp.235-241
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• 2020

We aimed to determine the effect of timed artificial insemination (TAI) protocols on the pregnancy rate per insemination and pregnancy loss compared with AI performed at detected estrus in dairy cows and Korean Hanwoo cattle under heat stress. In dairy cattle, 1,250 sets of data that underwent AI during heat stress (temperature-humidity index ≥ 72) were categorized according to their TAI protocols or as controls: 1) PGF_2α-36 h-estradiol benzoate (EB)-36 h-TAI (PG-EB group, n = 113); 2) GnRH-7 days-PGF_2α-56 h-GnRH-16 h-TAI (Ovsynch group, n = 455); or 3) GnRH-6 days-Ovsynch (G6G group, n = 136). The remaining cows underwent AI at detected estrus (AIDE group, n = 546). The probability of pregnancy per AI 45 days after AI was higher (P < 0.01) in the PG-EB (odds ratio [OR]: 1.68), Ovsynch (OR: 1.48), and G6G (OR: 1.79) groups than in the AIDE group. However, the prevalence of pregnancy loss between 30 and 45 days after AI did not differ among the groups. In Hanwoo cattle, 617 sets of data inseminated artificially under heat stress were categorized into AIDE (n = 281), PG-EB (n = 194), and combined Ovsynch or G6G (n = 142) groups. The probability of pregnancy per AI 45 days after AI and the prevalence of pregnancy loss between 30 and 45 days after AI did not differ among the groups. Thus, implementation of a TAI protocol (PG-EB, Ovsynch, or G6G) in dairy cows under heat stress improves the pregnancy rate per AI versus AIDE, whereas there is no beneficial effect of TAI on the pregnancy rate of Hanwoo cattle under heat stress.

• 설비공학논문집
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• 제11권2호
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• pp.215-223
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• 1999

Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

• 대한기계학회논문집
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• 제13권2호
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• pp.257-264
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• 1989

본 연구에서는 높은 열확산의 재료까지도 수용할 수 있도록 시편의 전면 전체를 가열하는 기존의 방법으로부터, 가열하는 시편 전면의 면적을 그 중심으로 부터 임의로 조절하여 축 및 반경방향의 열흐름을 강화시켜, 반경방향의 온도를 측정한 후 이를 이용하여 열확산계수를 구할 수 있는 방정식을 제시하였다. 방정식에서는 시편의 전.후면은 물론 열원의 방사시간도 함께 다루었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.788-789
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• 2011

A comprehensive thermo-electromagnetic model has been developed to estimate temperature and electromagnetic distribution in an three-phase induction motor under steady state operation. Electromagnetic modeling enables us to predict thermal dissipation rates by eddy-current loss and copper loss in induction motors. Non-uniform temperature distributions are investigated to account for the strong effect of local temperature build-up on the motor performance and expected life-span. For more accurate thermal modeling purpose, Heat loss mapping method, which is matched up with electromagnetic losses and volumetric heat source, is developed and performed analysis. Heat loss mapping method can be greatly used as a design or diagnostic tool for three-phase induction motors with complex structural electromagnetic fields.