Shukla Digvijay, Panigarhi Pradipta K
Appl Opt. 2020 Jul 1;59(19):5851-5863. doi: 10.1364/AO.394874.
The current study investigates evaporation of liquid hydrocarbons from a circular well cavity of small depth. Gravimetric analysis is performed to measure the evaporation rate and digital holographic interferometry is used for the measurement of normalized mole fraction profile inside the vapor cloud above the well. Phase unwrapping has been implemented to obtain continuous phase distribution in the image plane. The Fourier-Hankel tomographic inversion algorithm is implemented to obtain the refractive index change distribution inside the object plane, i.e., vapor cloud. Four liquid hydrocarbons, i.e., pentane, hexane, cyclohexane, and heptane, are studied. The radius of circular well cavities is varied in the range of 1.5 to 12.5 mm. Results using a quasi-steady, diffusion-controlled model are compared with the experimental evaporation rate. Measured evaporation rates are higher than the diffusion-limited model calculation for all working fluids and well sizes. This difference is attributed to natural convection occurring inside the vapor cloud due to the density difference between the gas-vapor mixture and the surrounding air. Holographic analysis confirms the presence of natural convection by revealing the formation of a flat disk-shaped vapor cloud above the well surface. Experimentally obtained vapor cloud shape is different from the hemispherical vapor cloud obtained using the pure diffusion-limited evaporation model. The gradient of vapor mole fraction at the liquid-vapor interface is higher compared to that of the diffusion-limited model because of the additional transport mechanism due to natural convection. Transient analysis of the vapor cloud reveals time invariant overall shape of the vapor cloud with a reduction in average magnitude of vapor concentration inside the vapor cloud during evaporation. The existing correlation for sessile droplet cannot successfully predict the evaporation rate from a liquid well. A new correlation is proposed for evaporation rate prediction, which can predict the evaporation rate within a root mean square error of 5.6% for a broad size range of well cavity.
当前的研究调查了浅圆形井穴中液态烃的蒸发情况。进行了重量分析以测量蒸发速率，并使用数字全息干涉测量法来测量井穴上方蒸汽云中归一化摩尔分数分布。已实施相位展开以获得图像平面中的连续相位分布。采用傅里叶 - 汉克尔层析反演算法来获得物平面（即蒸汽云）内的折射率变化分布。研究了四种液态烃，即戊烷、己烷、环己烷和庚烷。圆形井穴的半径在1.5至12.5毫米范围内变化。将使用准稳态扩散控制模型得到的结果与实验蒸发速率进行了比较。对于所有工作流体和井穴尺寸，测得的蒸发速率均高于扩散受限模型的计算值。这种差异归因于蒸汽云内部由于气 - 汽混合物与周围空气之间的密度差而发生的自然对流。全息分析通过揭示井穴表面上方扁平盘状蒸汽云的形成证实了自然对流的存在。实验获得的蒸汽云形状与使用纯扩散受限蒸发模型得到的半球形蒸汽云不同。由于自然对流产生的额外传输机制，液 - 汽界面处蒸汽摩尔分数的梯度比扩散受限模型的更高。蒸汽云的瞬态分析表明，蒸汽云的整体形状随时间不变，且在蒸发过程中蒸汽云内蒸汽浓度的平均大小有所降低。现有的关于固着液滴的关联式无法成功预测液井的蒸发速率。提出了一种新的蒸发速率预测关联式，对于宽尺寸范围的井穴，该关联式能在均方根误差为5.6%的范围内预测蒸发速率。
