New thin cooling fan for narrow space is fabricated. Fan performance (PQ curve) of the thin cooling fan and commercial side flow fan are measured with different upper spaces. Upper space of 3 mm or more is required for the side flow fan. When upper space is 0mm, performance of the side flow fan is significantly reduced. On the other hand, the thin cooling fan is able to operate even with upper space of 0mm. And, with upper space of 0mm, fan performance of the thin cooling fan is higher than the side flow fan. Optimizing the shape of the thin cooling fan using the Taguchi method reveals about 44% increase in maximum flow rate.
A numerical model was developed to clarify the optical characteristics of the human skin surface, i.e., the reflection and transmission characteristics. First, the bidirectional reflectance of the skin surface was measured to understand the optical characteristics, and a numerical model was developed to predict the bidirectional reflectance. Then, we developed a numerical model that simulates light behavior on the skin surface at the interface between air and the skin. We proposed two different numerical models based on geometric optics and verified their accuracy by comparing the model results with measurements. The tested models are Model A, which considers only the groove structure on the skin surface, and Model B, which considers the finer structures. By comparing the bidirectional reflectance from the measurement and the numerical analysis, it was found that Model A could not be used for predicting the bidirectional reflectance of the experimental results. However, Model B, which considers the finer structure of the surface as well as the groove structure, enabled us to predict profiles of the bidirectional reflectance, even though it showed slight discrepancies with the measurement results.
Heat and mass transfer of an evaporator of a loop heat pipe (LHP), which had a liquid-vapor interface inside a porous wick, was analyzed by a three-dimensional model. Pore network model (PNM) was used to simulate the two-phase flow in the porous structure with a distribution of pore radius. The calculation includes two behaviors of phase distribution in a wick: the wick saturated with liquid fully and unsaturated with liquid and vapor. The evaporator heat-transfer coefficient as a function of heat flux had local maximum. The relation between the heat-transfer coefficient and liquid-vapor phase distribution in the wick were discussed.
This paper describes that the characteristics of heat transfer on natural convection in inclined circular tube with heating using three-dimensional numerical analysis. The working fluid was water. The velocity, pressure and temperature distributions obtained PIMPLE method based on finite volume method. Analytical parameter were tube diameters D=0.01-0.03m at inclined angle φ=30° and φ=15-75° at D=0.03m, respectively. Result shows that the axial velocity along the flow direction increased with tube diameter and inclined angle. However, pressure drop was almost same at various tube diameters. The case of Grashof number based on tube diameter Gr was higher than 4.0×106, the flow was turbulent. The correlate equations of Reynolds number using axial average velocity of natural convection Re and Nusselt number Nu obtained the function of φ and Gr. These equations were good agreement with Re and Nu.
Subcooled flow boiling is an effective heat transfer approach and used widely in industries. In this paper, an experimental study was conducted on the bubble behaviors in subcooled flow boiling in an upward annular flow at relatively high degrees of subcooling. The bubble images during its whole lifetime were captured with high spatial and temporal resolutions by using a high speed video camera and a Cassegrain telemicroscope. The degree of subcooling in this study was above 30 K. The phenomenon of two successive bubbles was observed and analyzed. This phenomenon was caused by the severe deformation of the first bubble departing from the wall, and the second bubble grows from the remaining vapor of the first bubble after its departure from the wall. Consequently, its dynamical behaviors were strongly influenced by the first bubble. Quantitative data were also obtained to analyze the bubble behavior, such as the maximum size of the second bubble was smaller than the first one, and both the growth and condensation rates of the second bubble were slower than the first bubble.