Flow Boiling Heat Transfer Characteristics Of Parallel Rectangular Microchannels

In the heat exchanger equipment,most of them are parallel manifold.Due to the flow pattern alternating and the uneven distribution of each branch in the flow process in the parallel pipe,the unequal flow distribution in the microchannel parallel pipe makes the heat exchanger part of the heat exchanger too high,which will affect the safe operation of the micro heat exchanger,which makes the micro channel flow flow.It is necessary to study the mechanism of dynamic and heat transfer.At present,most studies only focus on the influence of some macro factors.The key micro scale mechanism is still at the primary stage.But the importance of its application in engineering has been widely concerned.Up to now,although many scholars have done a lot of research on the characteristics of heat transfer,flow and pressure drop in microchannel,there is still a lot of research on the influence mechanism of flow distribution,and the flow distribution in the boiling process of the refrigerant in the microchannel and the change of pressure drop and heat transfer characteristic under different distribution conditions are less.See.In this paper,the flow boiling characteristics and heat transfer mechanism of R141 b refrigerant in a rectangular microchannel parallel tube with 1 x 0.5mm and three 0.5 x 0.5mm branches are studied.A visual experimental system is designed and constructed.The flow pattern and flow distribution in the flow boiling process are analyzed,and the mass flow,heat flow density,dry degree and the flow rate are also analyzed.The influence of flow pattern and flow distribution on heat transfer coefficient and pressure drop is analyzed.In the study of convective type,bubbly flow,elastic flow,disturbance flow and annular flow can be observed in the main channel in front of the distribution point through a visual system under the microscope.With the increase of the dry degree in the tube,the flow pattern changes in turn.Because the length of the channel before the distribution point is short,the fog flow will not appear.According to the change of flow pattern before the distribution point,we draw the flow pattern for mass flow and heat flux.In the study of flow distribution,the effects of heat flux and mass flow on the flow distribution of three branches were studied,and the flow distribution mechanism was studied by combining the flow pattern of the distribution point with the bubble dynamics.In the study of the pressure drop characteristics,the average pressure drop in the channel is investigated according to the heat flux and the change of the mass flow.The pressure drop changes in each branch are analyzed in combination with the flow distribution.Finally,a comparison is made with the pressure drop established in the literature,and the pressure drop model established by Kim and Mudawar is corrected.In the study of heat transfer characteristics,the influence of the mass flow,heat flux and dry degree on the heat transfer characteristics of the microchannel parallel tube under different working conditions is explored,and the heat transfer characteristics in each branch pipe are analyzed by the flow distribution.Finally,the heat transfer models established in the six literatures are summarized and compared with experimental data.