UDC 532.5.013.4
V. I. BukreevThis paper gives results of two experiments in which warmer water in the form of a vertical plane jet was let into colder water. In one experiment, the temperature of inflowing and initially quiescent water exceeded 4 • C and warm water propagated only along the free surface. In the other experiment, the temperature of inflowing water was above 4 • C and that of quiescent water was below 4 • C. In this case, two jets -surface and bottom -first formed, and then the inflowing liquid was entirely concentrated in the bottom jet.Key words: temperature of maximum density water, Rayleigh-Taylor instability, surface jet, bottom jet.At atmospheric pressure, the density of distilled water is maximal at a temperature T * of about 4 • C, and at a temperature of 0 • C it is approximately 0.07% lower. When water masses at temperatures T 1 > T * and T 2 < T * come in contact, heat transfer results in the formation of a maximum density layer, which is unstable by the Rayleigh-Taylor mechanism. Below, the hydrodynamic processes due to the nonmonotonic temperature dependence of water density will be called for brevity anomalous effects. Conditions for the occurrence of such effects are produced in fresh water pools as a result of ice melting, fluvial runoff, rainfall and snowfall, and household and process water discharges. The difference in temperature between the shallow-and deep-water parts of a pool leads to the formation of vernal and autumnal thermal bars [1][2][3]. Under laboratory conditions, the anomalous effects have been studied in the cases of propagation of plane and circular horizontal jets [4-6]. The present paper gives results of experiments shown schematically in Fig. 1. A tank 3.8 m long and 20 cm wide was divided into two parts by a vertical partition with a slot below. In the initial state, the slot was covered with a shield. The left (in the diagram) part of the tank was filled with a weak aqueous solution colored with ink at temperature T 1 > T * . Water in the right part at temperature T 2 < T 1 was clear. Below, we give results of two experiments. In experiment No. 1, T 1 = 20.7 • C and T 2 = 10.7 • C. Both these values are larger than T * ; therefore, contact of colored and clear water produced no anomalous effects. In experiment No. 2, T 1 = 19.7 • C and T 2 = 0.2 • C, so that conditions for the occurrence of anomalous effects were available. In both experiments, the initial density difference on the left and right of the partition was identical -0.159% of the maximum water density. The processes were recorded by a video camera with a frequency 25 frames/sec and were analyzed on a computer.Between the right and left parts of the tank, an initial level difference was produced, so that after the lift of the shield, lighter water in the form of a plane jet flowed into heavier water. The vertical barrier (see Fig. 1) deflected the jet upward. The jet rise was also facilitated by the initial, upward directed, buoyancy force (the difference between the gravity and Archimedean force)...
