An Inverse Study For Optimizing The Geometric Parameters Of A 2D Rib-Roughed Rectangular Channel For Heat Transfer Enhancement

Mounting ribs in the channel is a common method for heat transfer enhancement,which has been widely used in electronic devices,cooling passages,solar air heater et al.The ribs enhanced the heat transfer of heated surface by breaking the thermal layer and creating local turbulence.Therefore,an inverse method was adopted to optimize the rib pitch in a two-dimensional channel.The channel mounted with equal-spaced ribs was studied by the method of direct problem first.The result showed that the Nusselt number of the channel increased and then decreased as the rib pitch increased.And the Nusselt number increased again when the rib pitch got approach to the maximum value.As a result,a maximum value existed,and the corresponding optimal rib pitch shows great dependence of the vortex structure between the successive ribs.Then the friction factor and performance evaluation factor respect to the rib pitch was studied.The result showed that the optimal rib pitch obtained when the performance evaluation factor was chosen as the objective function was proximate with that when the Nusselt number was chosen.Therefore,the heat transfer performance was chosen as the object for further study.Finally,the Nusselt number changing respect to the Reynolds number in different rib pitch was studied.It showed that the optimal rib pitch is proper for a big range of Reynolds number.Thus a constant Reynolds number(Re = 8000)was adopted in the inverse study.As for the inverse study,the dynamic method of the Fluent code combined with user-defined functions(UDFs)was adopted to optimize the pitch ratio of the equal-spaced ribs mounted in the channel with simplified conjugate gradient method(SCGM).It showed that the inverse results showed good agreement with the direct result.The value of the search step was also considered,which showed that a value of 0.0002 is proper to the inverse study.The objective function changing vs.number of updates showed an oscillating tendency as a result of the dynamic mesh which would cause error when the mesh updated.Therefore,the dynamic mesh method was not adopted when optimizing the rib pitch of non-uniform mounted ribs.All mesh generates when the model updates.Then the rib pitch of non-uniform mounted ribs was optimized by an inverse method.The result showed that an identical result can be obtained and the objective function showed similar tendency with different initial values.Besides,for n > 3,the optimal rib pitch showed that the pitch ratio on the both sides are bigger than the middle pitch.It is because that the inlet and outlet part have an effect on the flow structure and heat transfer between the successive ribs.