A Study on the Characteristics of an Oscillating Fluidic Atomizer

Kim, K.H.,Kiger, K.,Lee, W. The Institute for Liquid Atomization and Spray Sys 2006 한국액체미립화학회지 Vol.11 No.2

A unique feature of fluidic atomizers is that the nozzle geometry produces a thin capillary Jet which is forced to oscillate on a 2-dimensional plane through the use of a passive feedback mechanism. The objective of the current work is to characterize the influence of the stagnation pressure at the nozzle exit, jet oscillation and stretching on the breakup properties of the capillary ligament. To achieve this, shadow graph technique is used to measure size, shape, velocity and the number density of the droplets as a function of the position within the spray fan. The breakup length, defined as the radial distance from the breakup point, is analyzed as a function of the non-dimensional parameters. Finally, a kinematic model is developed to simulate the breakup of the oscillating jets at low stagnation pressures. Using the existing jet breakup theories, the model is used to predict the size and diameter distribution of the droplets after primary atomization.

A Study on the Characteristics of an Oscillating Fluidic Atomizer

( K. H. Kim ),( K. Kiger ),( W. Lee ) 한국분무공학회 2006 한국액체미립화학회지 Vol.11 No.2

A Study on the Characteristics of an Oscillating Fluidic Atomizer

( K. H. Kim ),( W. Lee ),( K. Kiger ),( S. Y. Jeung ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-

A unique feature of fluidic atomizer is that the nozzle geometry produces a thin capillary jet which is forced to oscillate in a 2-dimensional plane through the use of a passive feedback mechanism. The objective of the current work is to characterize the influence of the stagnation pressure at the nozzle exit, jet oscillation and stretching on the breakup properties of the capillary ligament. To achieve this, PIV, PDA and shadowgraph techniques are used to measure size, shape, velocity and the number density of the droplets as a function of the position within the spray fan. The breakup length, defined as the radial distance of the breakup point, is analyzed as a function of the non-dimensional parameters. Finally, a kinematic model is developed to simulate the breakup of the oscillating jets at low stagnation pressures. Using the existing jet breakup theories, the model is used to predict the size and diameter distribution of the droplets after primary atomization.

액적 열전달 향상에 미치는 Dissolved 가스의 영향에 관한 연구

이정호(Jungho Lee),Jungho Kim,Kenneth T. Kiger 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4

Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin<br/> liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing<br/> this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow<br/> and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved<br/> heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated.<br/> The local wall heat flux and temperature measurements were provided by a novel experimental technique<br/> in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the<br/> surface. A high-speed digital video camera was used to simultaneously record images of the drop from below.<br/> The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The<br/> splat diameter was observed to increase with time just after the initial transient dies out due to the growth of<br/> the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the<br/> bubble corresponded to a sudden decrease in droplet heat transfer.

Field dependence of the <i>n</i>-value and its relation with the critical current of Nb₃Sn strands

Oh, Sangjun,Lee, Chulhee,Cho, K W,Kim, Keeman,Uglietti, D,Flü,kiger, R IOP Publishing Ltd 2007 Superconductor science & technology Vol.20 No.8

<P>We find a simple expression for the field dependences of the <I>n</I>-value for Nb<SUB>3</SUB>Sn strands which gives reasonable fits to empirical data. It is also found that a relationship between the <I>n</I>-value and the critical current, which is obtained from an assumed reduction of the flux line lattice shearing pinning force due to thermal activation, can describe the field dependence of the critical current. Using the relation between the <I>n</I>-value and the critical current, we propose a scaling law which we have called the Kramer model including thermal activation. It is shown that the proposed scaling law can explain the critical current data at 4.2 K, even at high field near the upper critical field. It is also compared with Ekin’s strain scaling law.</P>

Growth, structure and physical properties of single crystals of pure and Pb-doped Bi-based high Tc superconductors

E. Giannini,R. Gladyshevskii,N. Clayton,N. Musolino,V. Garnier,A. Piriou,R. Flu¨kiger 한국물리학회 2008 Current Applied Physics Vol.8 No.2

Single crystals of (Bi1xPbx)2Sr2Ca2Cu3O10+d (x = 0 and 0.16) (sizes up to 3 · 2 · 0.1 mm3) have been grown by means of a newly developed ‘‘vapour-assisted travelling solvent floating zone’’ technique (VA-TSFZ). Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 C) was applied to enhance Tc (up to 111 K) and improve the homogeneity of the crystals (DTc 6 1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7)A ˚ , and a = 5.395(1), b = 5.413(1) and c = 37.042(11)A ˚ , for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q 0.21 a*), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) A ˚ ). With respect to the ‘‘non-modulated’’ structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be 50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy. Single crystals of (Bi1xPbx)2Sr2Ca2Cu3O10+d (x = 0 and 0.16) (sizes up to 3 · 2 · 0.1 mm3) have been grown by means of a newly developed ‘‘vapour-assisted travelling solvent floating zone’’ technique (VA-TSFZ). Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 C) was applied to enhance Tc (up to 111 K) and improve the homogeneity of the crystals (DTc 6 1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7)A ˚ , and a = 5.395(1), b = 5.413(1) and c = 37.042(11)A ˚ , for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q 0.21 a*), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) A ˚ ). With respect to the ‘‘non-modulated’’ structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be 50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.