بررسي عددي اثر ميدان الكتريكي بر ديناميك حباب و انتقال گرما در جوشش هسته اي

چكيده انگليسي :

Numerical Simulation of Bubble Dynamics and Heat Transfer under Electrical Field in Nucleate Boiling Maryam Aliakbary Mianmahale m aliakbarymianmahale@ce iut ac ir Date of Submission 2013 01 24 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Arjomand Mehrabani Zeinabad Arjomand@cc iut ac ir Mohsen Davazdaemami Mohsen@cc iut ac ir Abstract Boiling heat transfer is one of the most efficient modes of heat transfer The most widely used regime is perhaps the nucleate boiling In nucleate boiling very high wall heat fluxes can be achieved at low superheats The heat transfer duty of heat exchangers can be improved by heat transfer enhancement techniques In general these techniques divided into two groups of active and passive techniques Applying electrical field have been introduced as one of the type of active heat transfer enhancement techniques In this study a two dimensional axisymmetric model on growth and departure of a single bubble have been presented To validate the present model the simulation results in absence of electric field including the bubble departure diameter and departure time were compared with the experiment and numerical data Then the effects of electric field on bubble characteristics were studied The phase field method was employed to track the interface between the gas liquid two phases The phase field method has been adopted to capture the vapor liquid interface By solving the coupling problems of fluid flow thermal and electric filed along with the phase field equation the effect of an applied electric field on heat transfer and flows of a vapor bubble surrounded by saturated water were studied and simulated numerically A vapor bubble nucleus initially attached to a superheated wall and grew with two different contact angle of 50 and 90 at superheats of 7 8 5 and 10 C The bubble growing size and bubble departure time were increased and decreased with increasing in the wall superheat respectively Also increase in contact angle has changed the velocity field and temperature field around the base of bubble and increase the departure diameter and departure time The predicted errors in the case with contact angle 50 compared to experimental data were 16 for departure time and 8 for departure diameter In addition for contact angle of 90 results were consistent with the available numerical data in literatures with error less than 10 Then effect of applied electric field on bubble characteristics such as velocity field growth time waiting time departure frequency and departure diameter were discussed The bubble growth time and waiting time were decreased as the electric field strength increase Consequently the bubble departure frequency was increased by increasing the applied voltage In contact angle of 50 and wall superheat of 7 C bubble was detached from heated wall after 50 4ms with diameter of 2 91mm But upon applying the 4000V voltage departure time and departure diameter were decreased to 23 2ms and 1mm respectively Application of electric field resulted in raising the number of detached bubbles from the superheated wall in a certain time interval and decreasing of the bubbles departure size and elongates bubbles were resulted in a change in the temperature field over the domain and enhancing the rate of heat flux A non linear relation was existed between the applied voltage and the heat flux For example application of imposed electrical voltage of 4kV resulted in decreasing of the thickness of thermal boundary layer at the right end of computational domain in presence of 60 and increasing of the heat flux up to 85 Keywords Nucleate boiling enhanced heat transfer phase field method electrohydrodynamic PDF created with pdfFactory trial version www pdffactory com

علي اكبري ميان محله، مريم

بررسي عددي اثر ميدان الكتريكي بر ديناميك حباب و انتقال گرما در جوشش هسته اي

تقويت انتقال گرما , روش ميدان فاز , الكتروهيدروديناميك