{"id":20416,"date":"2018-12-02T09:29:00","date_gmt":"2018-12-02T09:29:00","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=20416"},"modified":"2023-02-14T17:08:39","modified_gmt":"2023-02-14T17:08:39","slug":"mechanism-on-convection-characteristics","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/convection-convective-heat-transfer\/mechanism-on-convection-characteristics\/","title":{"rendered":"The mechanism on Convection – Characteristics"},"content":{"rendered":"
Conduction<\/strong> and convection<\/strong> are similar in that both mechanisms require the presence of a material medium (in comparison to thermal radiation). On the other hand, they are different in that convection requires the presence of fluid motion.<\/div><\/div>\n In thermal conduction<\/strong><\/a>, energy<\/a> is transferred as heat<\/a> either due to the migration of free electrons <\/strong>or lattice vibrational waves (phonons<\/a>).<\/strong> There is no mass movement in the direction of energy flow, and heat transfer<\/a> by conduction<\/strong> depends on the driving \u201cforce\u201d of temperature difference. Conduction<\/strong> and convection<\/strong> are similar in that both mechanisms require the presence of a material medium (in comparison to thermal radiation). On the other hand, they are different in that convection requires the presence of fluid motion.<\/p>\n <\/p>\n At the surface<\/strong>, it must be emphasized that\u00a0<\/strong>energy flow occurs\u00a0purely by conduction, <\/strong>even in conduction. There is always a thin stagnant fluid film layer<\/strong> on the heat transfer surface.<\/span><\/strong> But in the next layers, both conduction and diffusion-mass movement occur at the molecular or macroscopic levels. Due to the mass movement, the rate of energy transfer is higher. The higher the mass movement rate, the thinner the stagnant fluid film layer will be, and the higher the heat flow rate.<\/p>\n It must be noted nucleate boiling<\/strong> at the surface effectively disrupts this stagnant layer. Therefore, nucleate boiling significantly increases the ability of a surface to transfer thermal energy to the bulk fluid.<\/p>\n As was written, heat transfer through a fluid is by convection in the presence of mass movement and conduction in its absence. Therefore, thermal conduction in a fluid can be viewed as the limiting case of convection, corresponding to the case of quiescent fluid.<\/p>\n Some experts do not consider convection<\/strong><\/a> to be a fundamental mechanism of heat transfer since it is essentially heat conduction in the presence of fluid motion. They consider it a special case of thermal conduction<\/a><\/strong>, known as \u201cconduction with fluid motion<\/strong>\u201d. On the other hand, it is practical<\/strong> to recognize convection as a separate heat transfer mechanism despite the valid arguments to the contrary.<\/p>\nConvection as a Conduction with Fluid Motion<\/h2>\n