Research Of The Acoustic Levitation Device And Its Application In Studying The Supercooling Degree Of Nanofluids

Acoustic levitation as one of a kind of important levitation technology, can obtainsteady microgravity environment, can be applied to the areas of study on phase changeof material properties and fluid property measurement. Its advantage is noelectromagnetism requirements for levitation samples, and does not produce significantthermal effects, can deal with low temperature phase change materials. Nanofluids asemerging phase change storage material are attracting widespread attentions. The studyof phase transformation characteristics of nanofluids has also become an importantdirection. A set of ultrasonic levitation device has been designed and optimized byanalysis of acoustic levitation theory in the article, and a set of refrigeration system hasbeen made for the suspended droplets freeze. The supercooling characteristics ofnanofluids have been analyzed by experiment data, and the specific results are asfollows:The basic parameters, such as the frequency of acoustic levitation device and typeof transducer have been determined based on analysis of acoustic levitation principle.Temperature change will affect the stability of the samples in the experimental range,but the influence is less. In order to increase performance suspension of acousticlevitation, the curvature of reflector, sample add method and height adjustment devicehave been optimized by analysis of ultrasonic levitation performance influence factors.As a debugging, the tuning method has been stated and the stable suspension hasobtained, droplet with diameter6-8mm can be suspended stably for a long time.Through modulation, also can make the suspended droplets produce periodic oscillation,provides conditions for studying the characteristics of the surface of the suspendeddroplets.Refrigeration system has been formed for the analysis of supercoolingcharacteristics of graphene oxide nanofluids. Acoustic levitation device is placed on thelow temperature constant temperature box, constant temperature environmenteffectively avoids the droplet jitter or instability caused by uneven temperature field.Temperature and image signal acquisition are placed in the box, which reduces thedisturbance introduced from outside. In supercooling test process, affecting factors suchas ultrasonic dispersing time, concentration of graphene oxide nanoparticles, metastabledisturbance power ultrasound and suspended state have been analyzed, the experimental results show that the mass fraction of50mg/100ml of graphene oxide nanofluid inultrasonic dispersing150min, phase change is the shortest time and supercoolingdegree is lowest; applying different power ultrasound disturbance, supercooling degreeand phase transformation time of samples are greatly reduced, the ultrasonic disturbancepower is90w, phase change time is the shortest and supercooling degree is lowest;ultrasonic disturbance with90w applies on the concentration0~50mg/100ml, thephase change is the shortest, the supercooling degree is minimum when the nanofluidconcentration is50mg/100ml; the supercooling degree of nanofluids under the stateof suspension is larger than the containerized condition, the supercooling degree ofdeionizer water and50mg/100ml of graphene oxide nanofluid increase0.8℃and1.5℃respectively, gains14.2%and50%, comparison of supercooling degree underdifferent cooling rate, cooling rate is small, super-cooling degree is low, but the phasetransformation time is increased.