An apparatus with a horizontal capillary tube intended for measurement of the surface tension of supercooled liquids

Abstract

Abstract. New experimental apparatus for measurement of the surface tension of liquids under the metastable supercooled state has been designed and assembled in the study. The measuring technique is similar to the method employed by P.T. Hacker [NACA TN 2510] in 1951. A short liquid thread of the liquid sample was sucked inside a horizontal capillary tube partly placed in a temperature-controlled glass chamber. One end of the capillary tube was connected to a setup with inert gas which allowed for precise tuning of the gas overpressure in order of hundreds of Pa. The open end of the capillary tube was precisely grinded and polished before the measurement in order to assure planarity and perpendicularity of the outer surface. The liquid meniscus at the open end was illuminated by a laser beam and observed by a digital camera. Application of an increasing overpressure of the inert gas at the inner meniscus of the liquid thread caused variation of the outer meniscus such that it gradually changed from concave to flat and subsequently convex shape. The surface tension at the temperature of the inner meniscus could be evaluated from the overpressure corresponding to exactly planar outer meniscus. Detailed description of the new setup together with results of the preliminary tests is provided in the study.

Improvements of the experimental apparatus for measurement of the surface tension of supercooled liquids using horizontal capillary tube

“…Preliminary measurements performed in the previous study [1] proved the functionality of main components of the new experimental apparatus with the horizontal capillary tube. However, only relatively low degree of supercooling of -7 °C was achieved and the data for the surface tension of water were quite scattered.…”

“…The analysis of uncertainties of measurements performed in the previous study [1] showed that the measurement of counterpressure p ' had the major influence on the uncertainty budget of measured surface tension. Therefore, new pressure transducer Omega PX 653 with a pressure range of 1245 Pa and accuracy 0.25% FS was additionally installed inside the helium distribution setup described in section 2.2 in the previous work [1].…”

“…The outer meniscus at the open end is kept at an ambient temperature. Knowing the inner diameter of capillary tube, the temperature of inner meniscus, and the counterpressure of gas corresponding to the planar meniscus at the open end, the surface tension can be determined from equation (1). A constant contact angle ș = 3° [11] can be considered for the water and the fused silica capillary tube at temperatures below 200 °C [12].…”

“…metastable liquids at temperatures below the equilibrium freezing point, using a horizontal capillary tube was introduced in the previous study [1]. The apparatus is based on a measuring technique developed by Ferguson and Kennedy [2] in 1932.…”

“…In this study, the experimental apparatus with the horizontal capillary tube introduced in the previous work [1] was further modified in order to improve the reproducibility and the accuracy of measured surface tension of supercooled water. The improved setup will allow achieving higher degrees of supercooling of up to 20 °C.…”