ﻣﻄﺎﻟﻌﻪ ﺗﺠﺮﺑﯽ دﯾﻨﺎﻣﯿﮏ رﺷﺪ و ﺟﺪاﯾﺶ ﺣﺒﺎب ﻣﻨﻔﺮد از ﻣﺠﺮاي زﯾﺮآﺑﯽ در ﺳﺘﻮن ﻣﺎﯾﻊ ﺑﻪ روش اﻧﺘﺸﺎر آواﯾﯽ ﻏﯿﺮﻓﻌﺎل

Experimental Study of a Single Bubble Growth and Detachment from a Submerged Orifice in the Liquid Column Using Passive Acoustic Emission

در ﭘﮋوﻫﺶ ﺣﺎﺿﺮ، دﯾﻨﺎﻣﯿﮏ ﻣﺮﺗﺒﻂ ﺑﺎ رﺷﺪ و ﺟﺪاﯾﺶ ﺣﺒﺎب ﻣﻨﻔﺮد ﺑﻪ ﮐﻤﮏ دو روش ﺗﺠﺮﺑﯽ اﻧﺘﺸﺎر آواﯾﯽ ﻏﯿﺮﻓﻌﺎل و ﺗﺼﻮﯾﺮﺑﺮداري ﺑﺎ ﻧﺮخ ﻓﺮﯾﻢ ﺑﺎﻻ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﻫﻤﮕﺎمﺳﺎزي ﺗﺼﻮﯾﺮﺑﺮداري ﺑﺎ دادهﺑﺮداري آﮐﻮﺳﺘﯿﮏ، ﻗﺎﺑﻠﯿﺖ ﺑﺎﻻي روشﻫﺎي ﻣﺒﺘﻨﯽ ﺑﺮ اﻧﺘﺸﺎر آواﯾﯽ را در ﻣﻄﺎﻟﻌﻪي دﯾﻨﺎﻣﯿﮏ رﺷﺪ و ﺟﺪاﯾﺶ ﺣﺒﺎب ﺑﻪ اﺛﺒﺎت رﺳﺎﻧﺪ. ﺑﺮرﺳﯽﻫﺎ ﻧﺸﺎن داد ﮐﻪ ﺑﯿﺸﯿﻨﻪي داﻣﻨﻪي ﻧﻮﺳﺎﻧﺎت در ﺳﺮي زﻣﺎﻧﯽ ﺳﯿﮕﻨﺎل اﻧﺘﺸﺎر آواﯾﯽ، اﻧﺪﮐﯽ ﻗﺒﻞ از ﻟﺤﻈﻪي ﺟﺪا ﺷﺪن ﺣﺒﺎب از ﻣﺠﺮا رخ ﻣﯽدﻫﺪ و در اﯾﻦ ﻟﺤﻈﻪ ﻧﺮخ اﻓﺰاﯾﺸﯽ ﺣﺠﻢ ﺣﺒﺎب در ﺣﺎل ﮐﻨﺪ ﺷﺪن ﻣﯽﺑﺎﺷﺪ. از روي ﻓﺮﮐﺎﻧﺲ ﻏﺎﻟﺐ ﻣﻮج اﻧﺘﺸﺎر آواﯾﯽ ﮐﻪ در ﻫﻤﯿﻦ زﻣﺎن رخ ﻣﯽدﻫﺪ، اﻧﺪازهي ﺣﺒﺎب ﺗﺨﻤﯿﻦ زده ﺷﺪه اﺳﺖ ﮐﻪ ﺑﺮاﺳﺎس راﺑﻄﻪي ﻣﯿﻨﺎﺋﺮت ﺑﺎ ﺿﺮاﺋﺐ ﺗﺼﺤﯿﺢ، ﺗﻨﻬﺎ 1/37 درﺻﺪ ﺑﺎ ﻧﺘﺎﯾﺞ ﺣﺎﺻﻞ از ﭘﺮدازش ﺗﺼﻮﯾﺮ اﺧﺘﻼف دارد. ﻣﻄﺎﺑﻖ ﺗﻮاﻟﯽ ﺗﺼﺎوﯾﺮ ﺛﺒﺖ ﺷﺪه از ﻣﺮاﺣﻞ رﺷﺪ ﺣﺒﺎب، ﻧﺴﺒﺖ ﻃﻮل ﻣﺤﻮرﻫﺎي ﻋﻤﻮدي و اﻓﻘﯽ ﺣﺒﺎب ﻫﻤﻮاره در ﻃﻮل زﻣﺎن رﺷﺪ ﺣﺒﺎب در ﺣﺎل ﺗﻐﯿﯿﺮ اﺳﺖ و ﺣﺒﺎب زﻣﺎﻧﯽ از ﻣﺠﺮا ﺟﺪا ﻣﯽﺷﻮد ﮐﻪ اﯾﻦ ﻧﺴﺒﺖ ﺑﻪ 1 ﻧﺰدﯾﮏ ﺷﻮد؛ ﻫﺮﭼﻨﺪ در اﯾﻦ ﻟﺤﻈﻪ ﺑﻪ دﻟﯿﻞ ﻧﯿﺮوﻫﺎي ﻓﺸﺎري، ﺣﺒﺎب ﺷﮑﻞ ﮐﺮوي ﻧﺪارد.

In the present study, the dynamics associated with single bubble growth and its detachment has been studied using passive acoustic emission and high frame rate imaging methods. Synchronization of imaging with acoustic data acquisition demonstrated the functionality of the acoustic emission method in studying the dynamics of bubble growth and detachment. The investigations showed that the maximum amplitude of the oscillations in the time series of the acoustic emission signal occurs shortly before the bubble detaches. Instantly the rate of bubble volume rise is decelerating. in accordance with the dominant frequency of the acoustic emission wave that arises at the same time with the jump in acoustic time series, the bubble size based on the Minnaert equation with the corrected coefficients is estimated to be only 1.37% different from the results of image processing. According to the sequence of images recorded from the bubble growth frames, the ratio of the vertical and horizontal axis lengths of the bubble is continually changing during the bubble growth period and eventually, the bubble detaches from the orifice when the ratio approaches 1. Although by detachment, the bubble does not have a spherical shape due to the pressure forces.