Aiming at the scale problem in heat-transfer equipments, experimental investigation on antiscale and scale removal by ultrasonic cavitation is performed. By means of microscopic magnifying photography system, the sedimentary phenomenon can be observed. The experimental research reveals the influencing rule of acoustic intensity, cavitational distance, liquid temperature and solution concentration. The experimental results indicate that liquid temperature has different effects on antiscale and scale removal. Different experimental liquids are used for antiscale and scale removal experiments. The results show that every liquid has a respective cavitational active temperature. When ultrasonic is used for antiscale, the smaller acoustic intensity is, the better effect is. But, when ultrasonic is used for scale removal, acoustic intensity has a reverse influence. In addition, biggish solution concentration is propitious to antiscale for long-time running. Distance of test sample to ultrasonic transducer also has certain influence on antiscale and scale removal. The smaller the distance to ultrasonic transducer is, the better effects antiscale and scale removal have.
Monitoring and control of combustion flames in utility boilers are required in order to optimize combustion conditions. This paper presents an instrumentation system for the concurrent measurement of the temperature distribution and soot concentration of flames developed on the two-color principle. This system consists of an endoscope, an optical assembly with optical filters, a CCD camera, a frame grabber and associated image processing software. Experiments are performed on a methane-air combustor and the temperature fields and the soot concentrations corresponding to the flame images are obtained. The results have demonstrated that the system is capable of performing on-line measurement of flame and temperature distribution, providing temporal and spatial characterization of the combustion process. In addition, the combination of advanced optical sensing and digital image processing technique can help to define the threshold by the analysis of the background noise. Furthermore, the utilization of the filter technique can enhance the image presentation effect to an extent.
Molecular dynamics simulation is carried out for the bubble nucleation of water and liquid nitrogen in explosive boiling. The heat is transferred into the simulation system by rescaling the velocity of the molecules. When heat is added into the molecular cluster, liquid initial equilibrium temperature and molecular cluster size can affect the energy conversion in the process of bubble nucleation. The potential energy of the system violently varies at the beginning of the bubble nucleation, and then varies around a fixed value. At the end of the bubble nucleation, the potential energy of the system slowly increases. In the process of bubble nucleation of explosive boiling, the lower initial equilibrium temperature leads to the bigger size of the molecular cluster. With more heat added into the system of the simulation cell, the potential energy varies in a larger range. The primary potential of water molecules includes Lennard-Jones potential energy and Columbic force caused by static charges of oxygen and hydrogen atoms. This is the reason why the bubble nucleation of water is different from that of liquid nitrogen. Pressure controlling is applied in the simulation of water, which makes the bubble more fully extended than that of liquid nitrogen.
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