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Reduction of Spreading Thermal Resistance Using Vapor Chamber Heat Pipe
You-Seop Lee(이유섭),Jongseok Kim(김종석) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
This paper studies heat spreading aspect of a vapor chamber for chip cooling application. The vapor chamber is a flat-plate heat pipe which can be embedded in the base of a heat sink to reduce the spreading thermal resistance. The thermal behavior of the vapor chamber with acetone as working fluid and micro grooves for wick structure has been experimentally investigated. The employment of the vapor chamber could make the junction temperature of the chip decrease up to 10 K with a reduction of spreading thermal resistance of 0.4 K/W. Such a thermal spreading effect depends on the area ratio of the vapor chamber and heating element. A spreading thermal resistance analysis is performed using Lee's closed form correlation to estimate the spreading capability of the vapor chamber. The thermal behavior of the vapor chamber is also numerically studied using in a good agreement with the junction temperature measurement results.
이유섭(You-Seop Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
This paper presents numerical studies of electrostatically-driven free surface flows using the COMSOL Multiphysics. Electrostatic forces are calculated by a weak formulation of the Maxwell stress tensor. Fluid interfaces are tracked with the Level Set Method. The numerical method is first validated with the leaky-dielectric model of Melcher and Taylor on the electro-capillary cellular flow. Second, the Taylor cone formation is simulated to investigate drop ejection phenomena for an electrostatic inkjet head. It is found that hydrophobic surface wetting conditions are beneficial for a better and earlier drop ejection. It is suggested that Marangoni flow can be used to control the electro-capillary flow and vice versa.
이유섭(You-Seop Lee),국건(Keon Kuk) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Crosstalk between adjacent channels is well known in thermal inkjet print heads. Excessive crosstalk can cause drop velocity and volume variations that result in poor printing quality. Thus, inkjet heads should be designed to minimize the crosstalk effects between adjacent channels. This paper presents lumped modeling and numerical studies of crosstalk characteristics within thermally driven inkjet print heads. The inter-channel crosstalk of the thermal inkjet head is investigated using the lumped R-L network model and numerical simulation. It is found that reducing restrictor width can reduce the jet crosstalk by viscous damping. The degree of crosstalk has been quantified using the value of cross-correlation between velocities of ink at the actuated channel and neighboring one. Critical dimensions of the restrictor for acceptable crosstalk have been determined by using the lumped model in a good agreement with the numerical simulation results. The present modeling and simulation can be used for a better design of thermal inkjet print heads to minimize crosstalk effects.
피에조 잉크젯 헤드 내 유체의 음향파 거동의 수치 해석
이유섭(You-Seop Lee),위상권(Sang Kwon Wee),오세영(Se Young Oh),정재우(Jae Woo Chung) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
This paper presents numerical and theoretical studies of acoustic wave interactions in slightly compressible liquids within piezoelectrically driven inkjet printheads. The interconnected flow channels may cause jet crosstalk, resulting in poor printing quality. Thus, it should be reduced by modifying the channel structure considering the acoustic wave interactions. Compressible gas flow driven by the sudden movement of a top wall in the channel is calculated using Flow3D and is validated with the result obtained by using the narrow gap theory. For the calculation of pressure waves in the ink flow, a limited compressibility model of the Flow3D is used. It is found that reducing the restrictor width can damp out the jet cross-talk by inhibiting the pressure wave propagation. This finding is verified by drop visualization experiments using silicon-micromachined piezo inkjet printheads that are designed and fabricated by our group.
Numerical Simulation on the Drop Formation of Viscoelastic Ink Ejected from a Nozzle
이유섭(You-Seop Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
This paper presents numerical studies of viscoelastic inkjet drop formation using the COMSOL Multiphysics. Pigment-based inks are usually used to improve the color durability of an inkjet printout. The pigment inks are usually viscoelastic. The Oldroyd-B and PIT viscoelastic fluid models have been applied as the constitutive equation. Fluid interfaces are tracked with the Level Set Method. This study investigates the effect of elasticity on the on-demand drop formation for low viscosity inks ranging from 1.8 to 4.5 cP. It will be shown that increased elasticity can decrease the drop ejection velocity for the piezo type inkjet. In contrast, the drop velocity is slightly increased. for the thermal bubble inkjet, with the increasing relaxation time. Such effects of elasticity on the drop formation become less dominant as the ratio of the polymer viscosity to the ink viscosity decreases.