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The understanding of the transient behavior of natural convection boundary layer (NCBL) on a heated vertical solid surface under various heating conditions is of fundamental significance and application importance. In this study, scalings for the parameters representing the behavior of unsteady NCBL flow of a linearly-stratified Pr > 1 fluid on a semi-infinite vertical solid surface heated with a time-varying sinusoidal temperature at different development stages are developed with a scaling analysis, in terms of Ra, Pr, s, and fn, which are the Rayleigh number, Prandtl number, stratification number, and frequency of the sinusoidal temperature, respectively. These scalings are validated and quantified with a series of numerical simulations over wide ranges of Ra, Pr, s, and fn. The frequency of the fluctuations experienced by the NCBL behavior at the transitional stage, due to the stratification of the ambient fluid, is also analyzed, and it is shown that the previously obtained scaling for the unsteady NCBL case with the constant heat flux heating condition is basically applicable for the current case, Ra and fn have additional effects as well due to the time-varying nature of the applied temperature. [ABSTRACT FROM AUTHOR]

A common heat exchange method used for most new designs is the use of heat sinks such as short pin fins. This experimental study investigated the static pressure characteristics developed in a short pin fin. Different fin array arrangements, fin longitudinal and transverse spacing ratios and individual slot heights in the fin were investigated. It was found that the row removed arrangement has superior flow efficiency, but to enhance heat transfer the staggered array is a better choice; the greater the fin spacing and slot height in each fin are, the less the pressure loss was experienced in the array. [ABSTRACT FROM AUTHOR]

A "fountain filling box" flow produced by discharging a weak laminar plane fountain in a confined open channel is studied numerically. Two‐dimensional direct numerical simulations were performed for weak plane fountains. The development of the fountain flow experiences five stages; the initial upflow and the subsequent downflow after the fountain penetrates to the maximum height, followed by the outward movement of the intrusion of the fallen fountain fluid on the channel bottom, and then the wall fountain formed by the impingement of the intrusion on the vertical sidewall, which results in the reversed flow, and finally the gradual stratification of the fluid. The behavior of the intrusion can be approximately described with the plane gravity current theory. The period for the intrusion to reach the bounded side wall increases with increasing Re or decreasing Fr. Three regimes are found for the wall fountain behavior; "no‐falling," "slumping down," and "rolling down" behavior. Convection, mixing, conduction, and filling all contribute to the formation and development of stratification, but their effects vary at different stages. For the initial stages, convection and mixing play a key role, resulting in an increasing bulk entrainment rate, while conduction and filling are dominant after quasi‐steady stratification is created, presenting a decreasing bulk entrainment rate. [ABSTRACT FROM AUTHOR]

The understanding of the transient behavior of the natural convection boundary layer on a heated vertical solid surface is crucial for numerous applications. In this study, scaling analysis is performed to derive the scaling laws for the major parameters that characterize the transient behavior of natural convection boundary layer of a Prandtl number larger than 1 fluid on a vertical solid surface subject to a sinusoidal heating flux in a linearly stratified ambient. It is found that the developed scaling laws are in good agreement with the direct numerical simulation results over wide ranges of Prandtl number, stratification parameter, and frequency of the sinusoidal heat flux. [ABSTRACT FROM AUTHOR]