• Asian-Australasian Journal of Animal Sciences
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• 제3권3호
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• pp.225-229
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• 1990

Sixteen mature sheep were fed chaffed orchardgrass hay once a day. Jaw movement of the sheep was recorded for 24 hours before slaughter. Four sheep were slaughtered either prior to eating, 2, 8 or 16 hours after the commencement of eating to measure digesta pool size and particle size distribution in the reticulo-rumen. Eating time was restricted to 120 minutes. Rumination time and actual chewing time during rumination increased with time after the meal. Mean dry matter (DM) pool size before and 2 hours after the meal were 1.36 and 2.45 times of DM intake, respectively. The proportion of large particle (>1.18 mm; LP) in the DM ingested during the meal was caculated to be about 70%. The mean DM and LP pool sizes per DM intake and the mean proportion of LP in the DM pool decreased with time after the meal. There were close negative relationships between either DM or LP pool sizes per DM intake and the chewing activities either expressed as time spent rumination, actual chewing time during rumination or total actual chewing time(total of eating time and actual chewing time during rumination). The difference between DM intake and LP pool size were assumed to be LP degradation in the present experiment, and correlated positively with the chewing activities. A large proportion of the digesta load was comprised of small particles, in excess of the daily intake.

• Asian-Australasian Journal of Animal Sciences
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• 제3권3호
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• pp.243-246
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• 1990

Sixteen mature sheep were fed chaffed orchardgrass hay once a day for 7 days. In 7th day, four sheep were slaughtered either prior to eating, 2, 8 or 16 hours after the commencement of eating to measure digesta pool size and particle size distribution in the reticulo-rumen. One sheep slaughtered at 8 hours after feeding had absesses at the cardia and in the lungs and could not ruminate normally. Time spent eating and rumination in the sheep on the day before slaughtering were 85 and 29 (pseudo-rumination 227) minutes a day, compared to those were 112 and 277 minutes in the other animals, respectively. Total actual chewing time in the sheep with absesses and the other animals were 98 and $373{\pm}132$ minutes, respectively. Dry matter(DM) intake in the sheep was $2.9g/kgBW^{0.75}$ which was only about 17% of that in the other animals. The pool sizes of reticulo-rumen DM and neutral detergent fiber (NDF) were somewhat smaller in the sheep than the others. The pool sizes of large particle (>1.18mm) DM and NDF in the animal were similar with those in the other animals. Mean DM retention time in the sheep was 207.4 hours which was about 4.2 times longer than that in the other animals.

• Nuclear Engineering and Technology
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• 제52권5호
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• pp.925-936
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• 2020

To ascertain the characteristics of pool sloshing behavior that might be encountered during a core disruptive accident of sodium-cooled fast reactors, in our earlier work several series of experiments were conducted under various scenarios including the condition with mono-sized solid particles. It is found that under the particle-bed condition, three typical flow regimes (namely the bubble-impulsion dominant regime, the transitional regime and the bed-inertia dominant regime) could be identified and a flow-regime model (base model) has been even successfully established to estimate the regime transition. In this study, aimed to further understand this behavior at more realistic particle-bed conditions, a series of simulated experiments is newly carried out using mixed-size particles. Through analyses, it is verified that for present scenario, by applying the area mean diameter, our previously-developed base model can provide the most appropriate predictive results among the various effective diameters. To predict the regime transition with a form of extension scheme, a correction factor which is based on the volume-mean diameter and the degree of convergence in particle-size distribution is suggested and validated. The conducted analyses in this work also indicate that under certain conditions, the potential separation between different particle components might exist during the sloshing process.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.125-130
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• 2006

The characteristics of boiling heat transfer and critical heat flux (CHF) behavior of nano-fluids were studied by using various sized silver and alumina nanoparticles. The diameter of nanoparticles was from 2 nm to 250 nm for silver and from 20nm to 40nm for alumina. Pool boiling characteristics and CHF enhancement of nano-fluids with different sized nanoparticles were compared with those of pure water and each nano-fluids. The experiment was performed at atmospheric pressure and the temperature of the pool was maintained constantly by using a flat immersed heater. The concentration of nano-fluids was uniform in all experiments as 0.01g/liter. The results showed that the measured boiling curves were shifted to the right. It demonstrated that the occurrence of nucleate boiling regime in nano-fluids retarded, compared with that of pure water. Also, in nano-fluids, the boiling curves showed that CHF of nano-fluids is significantly enhanced and represented the effect of particle size on boiling characteristics.

• Asian-Australasian Journal of Animal Sciences
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• 제8권3호
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• pp.267-273
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• 1995

The differences in rumen particle pool size, passage rate and rumen degradability in sheep receiving three varieties of orchardgrass hay harvested at pre-heading (H1), early-bloom (H2) and late-bloom (H3) were investigated using four ruminal-cannulated wethers (68 kg) fed 1,300 g of the hay once a day. Representative samples of whole rumen contents were collected at different times after feeding and the quantities of rumen particle pools [large particle pool (LPP), retained on a $1,180{\mu}m$ sieve; small particle pool (SPP), retained on a 47 but passed a $1,180{\mu}m$ sieve; and soluble fraction (SOL), passed a $47{\mu}m$ sieve (SOL)] were determined by a wet-sieving technique. The fullowing results were obtained: 1) The dry weight of whole rumen contents were significantly lower (p < 0.05) for HI than for H2 or H3. The reduction rate of whole rumen contents was slightly but significantly greater for HI that, the other hay varieties. 2) The LPP disappearance rates were 26.2, 25.3 and 21.7 g DM/h for H1, H2 and H3, respectively, and no statistical differences were found among the hay varieties. Appreciable changes were not observed with SPP and SOL throughout measurements for all hay varieties; however the SPP was markedly greater (p <0.05) for H2 and ill than for HI, while SOL did not differ among hay varieties. 3) The SPP passage rate (g DM/h) and effective rumen degradability (%) for HI, H2 and ill were, respectively, 9.7, 56.6; 16.9, 42.3; and 18.0, 28.9. The ruminal tum-over rate for SPP appeared to be higher for HI than for the other hay varieties.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.73-83
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• 2019

It is important to clarify the mechanisms of molten-fuel-pool sloshing behavior that might be encountered during a core disruptive accident of sodium-cooled fast reactors. In this study, motivated by acquiring some evidence for understanding the characteristics of this behavior at more realistic conditions, a number of experiments are newly performed by injecting nitrogen gas into a water pool with the accumulation of solid particles. To achieve comprehensive understanding, various parameters including particle bed height, particle size, density, shape, gas pressure along with the gas-injection duration, were employed. It is found that due to the different interaction mechanisms between solid particles and the gas bubble injected, three kinds of regimes, termed respectively as the bubble-impulsion dominant regime, the transitional regime and the bed-inertia dominant regime, could be identified. The performed analyses also suggest that under present conditions, all our experimental parameters employed can have noticeable impact on the regime transition and resultant sloshing intensity (e.g. maximum elevation of water level at pool peripheries). Knowledge and fundamental data from this work will be used for the future verifications of fast reactor severe accident codes in China.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.932-940
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• 2016

Pool boiling heat transfer of water saturated at atmospheric pressure was investigated experimentally on Cu surfaces with high-temperature, thermally-conductive, microporous coatings (HTCMC). The coatings were created by sintering Cu powders on Cu surfaces in a nitrogen gas environment. A parametric study of the effects of particle size and coating thickness was conducted using three average particle sizes (APSs) of $10{\mu}m$, $25{\mu}m$, and $67{\mu}m$ and various coating thicknesses. It was found that nucleate boiling heat transfer (NBHT) and critical heat flux (CHF) were enhanced significantly for sintered microporous coatings. This is believed to have resulted from the random porous structures that appear to include reentrant type cavities. The maximum NBHT coefficient was measured to be approximately $400kW/m^2k$ with APS $67{\mu}m$ and $296{\mu}m$ coating thicknesses. This value is approximately eight times higher than that of a plain Cu surface. The maximum CHF observed was $2.1MW/m^2$ at APS $67{\mu}m$ and $428{\mu}m$ coating thicknesses, which is approximately double the CHF of a plain Cu surface. The enhancement of NBHT and CHF appeared to increase as the particle size increased in the tested range. However, two larger particle sizes ($25{\mu}m$ and $67{\mu}m$) showed a similar level of enhancement.

• Korean Journal of Hydrosciences
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• 제6권
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• pp.1-11
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• 1995

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threaten the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new sour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variable, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on movable bed made of large spherical particles.

• 한국입자에어로졸학회지
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• 제13권1호
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• pp.1-10
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• 2017

본 총설에서는 액체층을 통과하는 기포의 크기, 형상, 상승속도를 결정하기 위한 이론들을 살펴보았다. 액체의 물리적 특성과 기포의 유량으로부터 기포의 크기, 형상, 상승속도를 체계적으로 계산하는 여러 가지 이론식 및 모수식들을 살펴보고, 각각의 장단점을 정리하였다. 이 분야에서 발표된 초기 저작들에서는 주로 반복계산을 통해 기포의 형상과 상승속도를 결정하는 기법들이 사용되었으나, 최근에 발표된 논문들에서는 간단한 모수식을 통해 기포의 형상과 상승속도를 반복계산 없이 쉽게 구하는 기법들이 제시되고 있다. 이러한 기법들은 매우 다양한 물리적 특성을 가지는 실험결과들과의 비교에서도 우수성을 보여주고 있어, 관련 분야의 연구에 매우 유용한 도구로 사용할 수 있을 것으로 보인다.

• 한국안전학회지
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• 제20권3호
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• pp.105-111
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• 2005

An experimental study is performed for extinguishing of n-heptane pool fire by water mist containing potassium acetate as a fire suppression additive. Water mist was generated by a single pressure nozzle in a small-scale chamber. The drop size distribution of water mist was measured using laser diffraction(Malvern particle sizer). The flame temperature, oxygen concentration and carbon monoxide concentration were measured. In case of using additives, the fire extinguishing time was shorter than that of pure water at a given discharge pressure and it was because the momentum of a water droplet containing additives was increased. And also dissociated metal atoms, potassium, were reacted as a scavenger of the major radical species OH, H which were generated for combustion process. Moreover, at a high pressure of 4MPa, the fire was extinguished through blowing effect as well as primary extinguishing mechanisms.