In this study, building upon previous research on fouling, we combined ultrasonic equipment with a self-developed pool-boiling experimental setup to investigate the scale inhibition and anti-fouling effects of ultrasonic waves in high-concentration CaCO3 solutions under various process conditions. The experimental system consisted of a pool boiling device (including heating and boiling sections), an ultrasonic system, and a data acquisition system.
The pool boiling device featured a copper rod (diameter 0.07 m, height 0.1 m) enclosed in a stainless steel electric heating jacket, connected to a test copper column (diameter 0.03 m, height 0.06 m). A Teflon insulation pad was placed on the surface of the test copper column to prevent the experimental medium from seeping through the edges. The heater’s surface area was 9×10ⴠm². The experiments were conducted using silica-free distilled water, and the heat transfer coefficient was measured at a fixed heat flux. The timing began when the solution reached 100°C, and the heating power was set to 150W with an experimental temperature of 100°C.
Due to the intermittent operation of the ultrasonic waves, the heat transfer coefficient fluctuated over time. Initially, the heat transfer coefficient increased rapidly due to the growing number of bubble nucleation sites caused by rising heat flux. Overall, the application of ultrasound significantly enhanced the heat transfer coefficient. From a mechanistic perspective, power ultrasound introduces vibrational energy that alters physical, chemical, and biological properties of substances, accelerating processes. This energy weakens molecular and metal surface bonds, increasing molecular mobility and enhancing heat transfer.
From the heat transfer coefficient versus time curve, it is evident that ultrasound has notable anti-fouling capabilities. Theoretical analysis suggests that ultrasonic radiation affects liquids in three key ways: it creates shear stress at interfaces due to velocity differences, weakening molecular and metal surface bonding; it generates pressure peaks during cavitation, promoting precipitation and breaking down scale particles; and it accelerates chemical reactions in the high-temperature, high-pressure environment created by cavitation, altering scaling conditions.
The effect of fouling solution concentration on the heat transfer coefficient showed that higher concentrations generally hinder heat transfer. However, after applying ultrasound, the heat transfer improved. At both high and low concentrations, the anti-fouling performance of ultrasound was effective. When the CaCO3 concentration was 300 or 1200 mg/L, the heat transfer coefficient was higher, while at 600 and 900 mg/L, it was lower. At higher concentrations, ultrasound enhances the nucleation rate of supersaturated solutions, promoting the formation of small particles that reduce supersaturation and alleviate surface scaling. Additionally, hydrolysis produces long-lived H radicals that can peel off existing scale.
Ultrasonic waves generate numerous cavities and bubbles in the solution. When these collapse or interact, they create strong pressure peaks that break up scale layers, making them easier to remove. Higher concentrations mean more supersaturation and more scale, but ultrasound increases the nucleation rate, leading to more scale removal. At a certain critical point, the enhancement of the heat transfer coefficient by ultrasound surpasses the negative impact of scale, causing the coefficient to rise.
The effect of heat flux on the heat transfer coefficient was also studied. At a constant concentration of 1200 mg/L, increasing the heating power from 150W to 180W led to a 1.3-fold increase in the heat transfer coefficient. This is because higher heat flux increases active nucleation sites, resulting in more bubbles and better heat transfer. The effect is most significant in the early stages of heat transfer, with higher heat flux values yielding higher initial coefficients that eventually stabilize at lower levels.
Overall, regardless of whether the solution was scaled or not, the use of ultrasound significantly improved heat transfer. Increasing the heat flux boosted the coefficient, especially in the initial phase. In the pool boiling setup, ultrasound proved beneficial for both low and high concentration fouling solutions. An increase in the heat transfer coefficient means less fouling. At higher concentrations, the strong cavitation effect of ultrasound breaks down carbonate scale into fine particles, preventing adhesion to the heater surface and reducing scale buildup.
Children Wheel Chair Removeble Armrest
The Children Wheel Chair Removeble Armrest has a variety of functions, raising the armrests, close to the desk and close to the back of the chair, so that your child does not lie on the table, does not hunched over, and achieves a true upright sitting posture. The Single Piece Study Chair has a streamlined mechanical design and 3D mechanical bionic armrests, which fit closely to the child's elbow curve. The Comfortable Removeble Armrest Chair supports the arms and further relieves the pressure on the hands. With a 0-90° rotating armrest, the Adjustable Height Study Chair can meet a variety of usage scenarios, making life more convenient and easy, and can be used as a walking chair for children. The New Design Kid Study Chair has a stable structure, and Family Learning Seats For Children makes it easier for children to sit on the chair and play without tipping over easily. Children can sit at ease and study more attentively.
Comfortable Removeble Armrest Chair,Ergonomic Reading Chair,Comfortable Ergonomic Chair,Kids Study Chairs
Igrow Technology Co.,LTD , https://www.igrowdesks.com