Ultrasonic Cleaning Machine in the field of Plate Cleaning

Plate heat exchanger, with its excellent disassembility and high heat transfer rate, is widely applied to many areas. Especially in recent years, our country practiced cogeneration generally and district heating departments mostly make heat transfer by plate heat exchangers. But due to reasons such as water quality, the plates’ surface of the plate heat exchangers are easy to scale, which will reduce the heat transfer performance to cause energy waste. It is important to clean regularly. At present the heating industry commonly use artificial scrub or pickling to plate heat exchanger plates in our country. The artificial scrub has the characteristic of intensive labor, low efficiency, poor quality, pickling mostly with hydrochloric acid to reach a certain cleaning effect, but this way could inflict severe damage on the stainless steel plate material, which can reduce the service life of plates, more importantly, and pickling waste liquor is not conducive to environmental protection. Now in the cleaning industry of our country is implementing cleaning work of eliminating ODS (fluorine chlorine hydrocarbons), therefore it is imperative to use new technology, new equipment for plate heat exchanger cleaning instead of traditional cleaning materials. In order to seek appropriate cleaning method and means, the way of combining ultrasound technology with water-based cleaning agent to simulate industrial test, has received a good cleaning effect.

1. The characteristics of ultrasonic cleaning

Ultrasonic cleaning dirt is mainly done by cavitation effect, which means to transfer high frequency current produced by the ultrasonic generator into the same frequency mechanical wave, and propagate them into the cleaning fluid in the form of ultrasonic and form tens of thousands of tiny air bubbles in the cleaning fluid, and thus to become the approximate vacuum tiny holes. Under the action of ultrasonic, the dense bubbles burst quickly, instantly become instantaneous high pressure and high temperature over thousands of atmospheres. The cleaning surfaces are bombard constantly by the strong shock wave, and the attachments from the object surface are peeled off quickly with cleaning agent to achieve the goal of removing dirt quickly. For some irregular surfaces such as groove, porous, slit and so on, it is more effective by the ultrasonic cleaning method.

2. The effects of ultrasonic cleaning are mainly concerned with the following factors:

(1) Ultrasonic power density. The higher the power density of the ultrasonic，the stronger cavitation, and the more the better cleaning effect. The ultrasonic power density is set at 0.5-1 w/cm2.

(2) The frequency of the ultrasonic. The lower the frequency of the ultrasonic is, the stronger the cleaning effect is. Based on smudgy degree, now the common frequency is 20 to 50 KHZ.

(3) Cleaning temperature. To Ultrasonic, its strongest cavitation is happened in 30-40 ℃. As the temperature rise, the bubble produced in cleaning fluid could break sound waves, make the ultrasonic wave abate. At this moment that the suitable temperature of water-based cleaning fluid is 60 ℃, the cavitation is most active. The ordinary cleaning fluid temperature is set in 50-60 ℃.

(4) The dirt ingredients of plate heat exchanger plates. Because of the difference of working conditions, the dirt components on the plate surface are very complex. Through qualitative analysis for typical dirt samples, we found that dirt ingredient is mainly carbonate, followed by silicate, sulfate, ash content, etc.

3. The determination of cleaning agents, according to the characteristics of ultrasonic cleaning, the dirt compositions and plate materials, etc., After many experimental evaluation and selection, we choose nonionic surfactant agent as the main reagent, compounded with low foam water-based cleaning agent with other surfactants and additives of to cooperate with the ultrasonic cleaning. 

4. Ultrasonic simulation cleaning experiment

(1) Experiment condition: We choose KWT - 1012 type single slot ultrasonic cleaning machine. The power density is 0.5 W/cm2, and the ultrasonic frequency 28 KHZ. Compound the low foam water-based cleaning agent to the concentration with the mass fraction 2%, and heat to 60 ℃, then add them to the internal channel of the ultrasonic cleaning machine. Make the stainless steel plates (dirt) to 12 pieces of 24 x 12 cm samples, and then hang them in slot ultrasonic cleaning machine.

(2) Cleaning procedures: ultrasonic cleaning 3 min – rinse them, dry naturally.

5. Experimental results and conclusion: the surfaces of the stainless steel plates after cleaning dirt are completely clean. People can see stainless steel surface texture clear, no residues in groove, slit by using microscope. Compared with by using 1% dilute hydrochloric acid cleaning, the former way makes plates bright and clean as before, no mechanical damage; but the latter looks grey and the surface is rough. The experiment shows that the ultrasonic cleaning cooperated with low foam water-based cleaning agent technology can replace the traditional cleaning methods. Compared with the manual cleaning, time limit for this project is reduced 60%, it can save 30% costs. The characteristic of good cleaning effects and easy to rinse avoids the environmental pollution and the harm for the operators. It is easy to operate because there are four holes to hang easily. For some large central heating water system, large industrial circulating cooling water, heating system, this method is an effective and economic method for cleaning.

read original by Crystal Zhai PHE Overseas Manager-Hofmann