• 대한기계학회논문집
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• 제15권6호
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• pp.2132-2146
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• 1991

본 연구에서는 기존 유속계에 의한 측정이 어려운 점을 감안하여 나프탈렌 승 화법을 이용하여 열교환기 시스템의 한 모델인 원봉에 유한한 길이의 환상핀이 부착된 경우 환상핀과 원봉이 만나는 부분에서 와류들 특히 V2, V3등 구석와류가 물질전달을 증가시키는 구조에 대해 고찰한다. 이는 원봉 주위의 환상핀에 의한 대류 물질전달 에 영향을 줄수 있는 레이놀즈수, 환상핀의 크기에 따른 형상비, 그리고 경계층 두께, 배제 두께 등의 유동변수를 변화시켜 가며 물질전달률과의 관계를 규명하여 열교환기 설계의 기본자료를 제공한다. 또한 환상핀 사이의 원봉표면에 대한 전체물질전달률 을 측정하며, 환상핀에 인접한 곳에서 구석와류에 대한 환상핀의 끝 벽면 영향을 알아 보고 이를 근거로 하여 말굽와류의 3차원 박리 유동구조를 정성적으로 규명하고자 한 다.

• 대한기계학회논문집B
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• 제36권3호
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• pp.259-268
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• 2012

엇갈리게 배열된 두 개의 수평관의 수직 이격거리($P_v$/D)와 수평 이격거리($P_h$/D)를 변화시키며 자연대류 열전달을 실험적으로 측정하였다. 열/물질전달의 상사성을 이용하여 물질전달 실험을 수행하였고 난류영역까지 확장하였다. Pr 수 2,014, RaD 수 $1.5{\times}10^8\sim2.5{\times}10^{10}$, $P_v$/D는 1.02~5, $P_h$/D는 0~2 범위에서 수행하였다. 하단 수평관의 물질전달은 단일 수평관 상관식의 예측치와 일치하였다. 상단 수평관의 물질전달은 $P_v$/D가 작을 때, 하단 수평관에서 상승하는 플룸의 예열영향(Preheating effect)으로 인해 감소하였고, $P_h$/D가 증가하면 급격히 상승하였다. 그러나 $P_v$/D가 클 때, 상단 수평관의 물질전달은 하단 수평관의 플룸 속도영향으로 인하여 단일 수평관보다 컸고, $P_h$/D가 증가함에 따라 완만하게 감소하였다. $P_h$/D가 매우 증가하여도 굴뚝효과(Chimney effect)와 측면유동효과(Side flow effect) 인하여 상단 수평관의 열전달이 하단 수평관의 열전달보다 크게 나타났다.

• 한국환경과학회지
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• 제23권1호
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• pp.53-60
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• 2014

Adsorption of phenol on activated carbon in a fixed bed was studied. The effects of fixed-bed length, superficial velocity (flow rate) and particle size of adsorbent on fixed-bed performance were investigated. Some characteristic parameters such as the breakthrough time ($t_{0.05}$), saturation time ($t_{0.95}$), length of mass transfer zone ($L_{MTZ}$), adsorptive capacity (W), and adsorption rate constant ($K_a$) were derived from the breakthrough curves. Adsorbent particle sizes significantly affected the shape of the breakthrough curve. Larger particle sizes resulted in an earlier breakthrough, a longer $L_{MTZ}$ and a lower adsorption rate. Superficial velocity was a critical factor for the external mass transfer during fixed-bed adsorption process. The external mass transfer resistance was dominant as increasing superficial velocity.

• 상하수도학회지
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• 제25권4호
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• pp.503-510
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• 2011

Ammonia in water which is toxic to human, its concentration is regulated below 0.5 mg/L in drinking water. Current study aimed to develop appropriate models for ammonia stripping using hollow fiber membrane contactor. Two different models were developed during the study. Model 1 was assumed only free ammonia ($NH_3$) transfer in stripping process, whereas the Model 2 was assumed with total ammonia ($NH_3+{NH_4}^+$) transfer. Ammonium chloride ($NH_4CI$), sodium hydroxide(NaOH) were used to make ammonia solution, which was concentration of 25 mg as N/L at a pH of 10.5. The experimental conditions were such that, the liquid flow was in tube-side in upward direction and t he gas flow was on shell-side in downward direction a t room temperature. The experimental and modeling results showed that marginal difference were observed at low gas flux. However the difference between the both models and experimental value were increased when the gas flux was increased. The study concludes that the Model 1 with free ammonia is more appropriate when both models were compared and useful in ammonia stripping process at low gas flux.

• 에너지공학
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• 제23권2호
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• pp.21-27
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• 2014

수직평판의 거칠기에 따른 자연대류 열전달의 변화를 실험적으로 측정하였다. 열전달 실험을 대신하여 유사성에 기초한 물질전달로 모사하여 실험을 수행하였다. 또한 국부적인 열전달률을 알기위해 Piecewise electrode를 채택하였다. Pr수는 2,014 그리고 높이(L)는 0.154m로 고정하고 매끈한 수직평판에 대해 실험을 수행한 결과 Le Fevre의 수직평판 상관식과 거의 일치하였다. 거칠기 정도를 $0.5R_z{\mu}m{\sim}14.1R_z{\mu}m$로 변화시켰을 때 $Nu_L$수는 거칠기 정도가 커지면서 증가하는 경향을 나타내었다. 실험결과는 간단한 상관식으로 정리하였다.

• 한국위험물학회지
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• 제6권2호
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• pp.95-104
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• 2018

Gas-liquid bubble column reactors are extensively used in industrial processes. A detailed knowledge of bubble size distribution is needed for determining the mass transfer in gas-liquid film. Experimental data on bubble size distribution and liquid-side mass transfer coefficient($k_L$) were used to calculate the estimated time to saturation in bubble column reactor. Also, the gas flux was evaluated to the liquid-side mass transfer coefficient($k_L$) and solubility data for hydrogen sulfide($H_2S$) and chlorine($Cl_2$) absorption into water. Simulation results show that $H_2S$ absorption time to 50 % of saturation concentrations are 611 sec and 1,329 sec when bubble diameters are 0.5 mm and 4.5 mm, while absorbing 1 % $H_2S$ gas. In case of $Cl_2$, absorption time range 657 to 1,400 sec when bubble size range 0.5 mm to 4.5 mm, while absorbing 1 % $Cl_2$ gas. Calculated simulation results can be used in the design of emergency relief bubble reactors.

• 소음진동
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• 제10권5호
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• pp.769-774
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• 2000

The purpose of the work is to present successful applications of a modified wavelet shrinkage method for the accurate and fast estimation of a transfer function. Although the experimental process of determining a transfer function introduces not only Gaussian but also non-Gaussian noises, most existing estimation methods are based only on a Gaussian noise model. To overcome this limitation, we propose to employ a modified wavelet shrinkage method in which L1 -based median filtering and L2 -based wavelet shrinkage are applied repeatedly. The underlying theory behind this approach is briefly explained and the superior performance of this modified wavelet shrinkage technique is demonstrated by a numerical example.

• 오토저널
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• 제2권1호
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• pp.21-31
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• 1980

Two phase boundary layer equations of laminar filmwise condensation are solved by an approximate integral method under the following condition; saturated vapour flows vertically downward over a cooled surface of uniform temperature, the condensate film is so thin that the inertia and convection terms are neglected. The following conclusions are drawn under the above assumptions. 1. free convection In case of the linear temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$=4/3,(G $r_{l}$ /4.H)$^{1}$4/ and in case of the quadratic profile, numerical results may be expressed as N $u_{m}$=2/1.682,(G $r_{l}$ /H)$^{1}$4/. 2. Forced convection When the temperature profile is assumed to be linear in a liquid film, numerical results fir the average heat transfer coefficients may be expressed as N $u_{m}$=(A, R $e_{l}$ /H)$^{1}$2/. This expression is compared with the experimental results hitherto reported; For theoretical Nusselt number (N $u_{m}$)$_{th}$<2*10$^{4}$, the experimental Nusselt number (N $u_{m}$)$_{exp}$ is on the average larger than theoretical Nusselt number (N $u_{m}$)$_{th}$ by 30%. For (N $u_{m}$)$_{th}$>2*10$^{4}$, experimental Nusselt number (N $u_{m}$)$_{exp}$ is about 1.6 times as large as theoretical Nusselt number (N $u_{m}$)$_{th}$. These large deviation may be caused by the presence of turbulence in the liquid film. In case of the quadratic temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$'=(2,A,Re/H)$^{1}$2/. This formular shows that theoretical Nusselt number (N $u_{m}$)$_{th}$ is larger than experimental Nusselt number (N $u_{m}$)$_{exp}$ by 60%. It is speculated that when the temperature difference between cooled surface and saturated vapour is small, temperature profile in a liquid film is quadratic.quadratic.. quadratic.quadratic..atic..

• 한국분무공학회지
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• 제19권1호
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• pp.15-18
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• 2014

In the present study, experiment on the evaporation of pure water droplet on heated surface was conducted, and the evaporative heat transfer coefficients were calculated from experimental results. The pure water droplet of about $10{\mu}l$ was applied onto the heat transfer surface, then the shape of the droplet was analyzed during the evaporation. In addition, the effect of surface roughness on the evaporative heat transfer was also investigated. Experimental results showed that the evaporative heat transfer coefficients increased rapidly along with the increase of surface temperature and the heat transfer coefficients increased with the increase of surface roughness.

• 한국수정란이식학회지
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• 제6권2호
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• pp.37-46
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• 1991

A field trial was performed to evaluate the effects of hormone treatment on estrus induction, ovulation, embryo transfer and reproductive performance in post-weaning sows. This trial involved 61 mixed breed sows of varying parity on a commercial pig farm. Sows were allocated to one of five trials: control group involved 25 sows that were treated with a single intramuscular injection of 5 ml physiological saline, 6 sows received 1,500 IU PMSG on the day of weanning and 500 IU HCG at the onset of estrus in trial I, 7 sows received 750 IU PMSG on the day of weanning and 500 IU HCG at the onset of estrus in trial II, 5 sows were treated with the same as trial II on day 28 after weanning in trial III. and 18 sows were treated with 10 mg PGF$_2$$\alpha$ plus 2 mg estradiol benzoate on day 31 after weanning in trial IV. Ovarian responses were checked by laparotomy and ova were recovered by oviducal flushing between 40 and l00hrs after mating. Fertilized ova were transferred into the oviduts of recipient sows synchroni- zed. The results obtained were summarized as follows: 1. Percentages of sows detected in standing estrus following treatment were 86~100% among trial groups. The interval from treatment to standing estrus(6l.7$\pm$0.5lhrs) in lOmg PGF$_2$$\alpha$ and 2mg estradial henzoate treated group was significantly earlier than in other trial groups(P<0.05). 2. Average number of ovulations was 11.5~37.8 among trial groups. The ovulation rate in 1,500 IU PMSG and 500 IU RCG treated group (37.8$\pm$ 19.87) was significantly different from other trial groups(P<0.05). 3. Ova were recovered by oviducal flushing between 40~ l00hrs after mating and recovery rates of ova wore 91.4% between 40~59hrs. 4. Fertilized ova were transferred into the oviducts of 8 recipient sows synchronized with 7 to 17 ova per animal. Three of the recipients were pregnant and delivered 25 piglets. 5. Four of the donor sows in those embryo collection was not successful were pregnant following oviducal flushing and delivered 23 piglets. 6. Recurrence of estrus and farrowing performance of experimental sows were observed following the experiment was no difference among trial groups, respectively.