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An experimental study was carried out to examine the antifouling effect of compound treatment with ultrasonic and magnetic fields simultaneously in convection heat transfer process. The ultrasonic was provided with a frequency of 20 kHz and powers up to 240 W, and the magnetic field was applied with field intensity of 0.25 T and 0.4 T, respectively. The results showed that the ultrasonic treatment presented a good antifouling effect in flow and heat transfer of hard water, and further the combined treatment of the ultrasonic and magnetic displayed much better performance in scale inhibition of convection heat transfer, in which the scale-inhibition efficiency got up to a maximum of 93.9%. The water treatment not only presented the good scale-inhibition effect but also had the morphology of fouling crystal changed. The crystal of calcium carbonate was mainly comprised of the dense calcite with a cubic shape for the case untreated but transformed to the slender aragonite branchlike after the treatment, and the aragonite became longer with the compound treatment. The experimental phenomenon was also discussed for understanding of the mechanism of the technical treatment, which may be referenced to the antifouling application in heat exchanger. [ABSTRACT FROM AUTHOR]

An experimental study on the antifouling performance of ultrasonic and/or electronic treatment was carried out in a convective heat transfer process by using a fouling monitor system. An ultrasonic device was used in a frequency of 28 kHz and a power of 80 W, and a low-voltage electronic processor also used with a maximum current of 0.8 A for water treatment. The experimental results showed that both of the ultrasonic and the electronic treatment, all displayed good scale-inhibition effects for hard water in convective heat transfer, and further the compound treatment of them gave much better antifouling performance at the same conditions. The fouling inhibition efficiency got up to a maximum of 100% by the treatments. The technical treatment may change not only the amount of deposition on heat transfer surface, but also the morphology of crystals formed in microscale. The fouling crystal displayed a clear type of aragonite of calcium carbonate but varied obviously with the treatments. It can be sure that the technical treatments are effective and applicable in real heat transfer application with hard water as a working fluid. [ABSTRACT FROM AUTHOR]

Based on a modification of a magnetohydrodynamic turbulence model, a numerical study was performed to investigate the effects of transverse uniform and gradient magnetic field on the turbulent flow and heat transfer characteristics of a low melting point molten salt in a stainless steel pipe. With the Hartmann number from 0 to 80, the numerical results showed that the fluid flow displayed anisotropic distributions under the magnetic field with decrease of velocity in the mainstream region, and decrease of turbulent intensity, whereas the flow velocity increased in the boundary layer near the Hartmann and Roberts wall. Especially, a velocity jet phenomenon was observed in the Roberts boundary layers at higher Hartmann number in the uniform magnetic field or the positive gradient magnetic field. Under the gradient magnetic field, the flow and heat transfer of molten salt displayed much more variations than under the uniform magnetic field. The magnetohydrodynamic calculation results proposed here might be helpful to the design of the composite heat transfer system for molten salt in actual industrial applications. • Both the uniform and non-uniform magnetic field were applied in pipe flow of molten salt for comparison. • A modified MHD turbulence model was established for turbulent flow of molten salt. • The characteristics of flow and heat transfer were numerically studied for a low melting point molten salt. • The complex influence of magnetic field to flow and heat transfer of molten salt was observed. [ABSTRACT FROM AUTHOR]

In order to investigate the heat transfer characteristics of mixed molten salt, an experimental setup for the submerged jet impingement has been established in this paper. Firstly, an experimental investigation on heat transfer of submerged jet impingement with water as working fluid was carried out to verify reliability of experimental method. A good consistence was found between experimental results and those classical correlations from references for stagnation heat transfer, which indicate the reliability and accuracy of experimental method. On the basic of ensuring the reliability of experiment, a series of studies on jet impingement experiments were carried out with new mixed molten salt. The results indicated that effect of submerged jet impingement heat transfer enhanced gradually with the increase Reynolds number and the heat transfer characteristics at the stagnation are analogous with the water in the scope of experimental investigations. Further, a correlation about quaternary mixed molten salt was proposed based on experimental data. At same Reynolds number, the Nusselt number of mixed molten salt is obviously higher than that of water at stagnation zone because of its higher Prandtl number and becomes lower than water at larger radial distance due to its higher viscosity. The results indicated that thermophysical properties of working fluid have an enormous influence on the Heat transfer performance. The experimental results in this paper provide a necessary technical guarantee for the study of heat transfer of the high temperature fluid. [ABSTRACT FROM AUTHOR]

In this paper, a prediction model for the crystallization fouling was proposed on the basis of the Kern-Seaton model for the heat transfer and fouling process in circulated cooling water. The fouling deposition and removal process were analyzed, respectively, for the fouling process, on which the coupling effects of the scale layer, temperature and ions concentration were considered. The model calculation may predict the fouling resistance variations in fouling process, which were in good agreement with experimental data from references within a range of given conditions especially for the turbulent flow, indicating the model applicability for actual process. Since the model can be used without requirement of a large amount of measured data for fitting, it gives a more convenient way for predicting fouling process of heat exchangers in industry. • A prediction model for CaCO 3 crystallization fouling in circulating cooling water was established. • The fouling deposition and removal processes were all analyzed in the model respectively. • The coupling effects of fouling layer, temperature and concentration of fouling ions were considered. • The calculation of model may provide a fouling prediction without requirement of a number of experimental data for fitting. [ABSTRACT FROM AUTHOR]

An innovative physical method to control fouling in heat transfer equipment—low voltage electrolysis anti-fouling (LVEAF) technology—is introduced. The objective of the present study is to testify the effect of LVEAF treatment in forced convective system and identify the operating mechanism. A series of fouling tests were carried out with and without LVEAF treatment. During the experiments fouling resistance was monitored, and the properties of test liquid were measured, including hardness, alkalinity, electrical conductivity, and pH. The main results were as follows: (1) The fouling was effectively restrained to form on the heat exchanger surface if the circulating water was treated with LVEAF. The scale inhibition ratios exceeded 90% in most cases. (2) The LVEAF technology is an active anti-fouling technology with lower energy consumption. The properties of treated test liquid were changed. (3) Electrochemical reactions occur near the electrode due to the low current existence in the water when the LVEAF device is working. A lot of fouling deposits formed in the test liquid near the cathode or on the inner surface of the treatment unit, but did not deposit on the heat exchanger surface. [ABSTRACT FROM AUTHOR]

• An experimental setup for free-surface jet impingement heat transfer of molten salt. • A new correlation of stagnation heat transfer with molten salt proposed. • Heat transfer characteristics of molten salt along heat transfer surface obtained. An experimental study of free-surface jet impingement was carried out with compound molten salt to understand its characteristics of heat transfer. Based on pre-experimental verification on the reliability of experimental method by water as working fluid, a compound molten salt was chosen as a new working fluid to conduct experiment of free-surface jet impingement. The heat transfer of molten salt at stagnation point was investigated in detail, and the Nusselt number of molten salt increased with increasing of the Reynolds number and the Prandtl number, and was nearly constant with increasing of nozzle-to-plate spacing at present ranges. The data was correlated by an empirical formula, which was compared with those classical correlations from references. Next, the variation of the Nusselt number of molten salt was also verified along heated surface. It was shown that the local Nusselt number decreased monotonously with increasing of lateral distances from stagnation point, and increased with increasing of the Reynolds number. The profiles of the Nusselt number were nearly unchanged for different nozzle-to-plate spacing, which can be well correlated by a normalized formula. This work focused on the heat transfer characteristics of the molten salt in free-surface jet impingement, which may be recognized as a reference for promoting the application of molten salt in heat transfer process, especially in high temperature situations. [ABSTRACT FROM AUTHOR]