Spray liquid film flow theory and experimental study of spray cooling of electronic devices

Title: Spray liquid film flow theory and experimental study of spray cooling of electronic devicesAuthor: Guo XianDegree-granting units: Xi'an University of Electronic Science and TechnologyKeywords: spray cooling;; separation of variables;; film model;; CHF;; nozzle trajectory;; inclined jet;; dynamic jet;; electromagnetic drive device;; pullSummary:
Existing heat flux electronic devices more and more, how to chip-level, system level for effective cooling of electronic devices for enhancing the reliability of electronic devices is an important factor. Heat transfer in the field of electronic devices as the most promising breakthrough in one of the three techniques, spray cooling (Spray Cooling) technology is being more Neodymium Magnets and more attention. Most of the current research focused on experimental research, however, due to different experimental conditions, the researchers made a variety of different and even conflicting conclusions differ, the spray cooling is relatively more a lack of theoretical research, so the spray for electronic devices cooling technology, there are theoretical and experimental studies have broad space for development.
Electronic devices based on spray cooling technology Research and research focus, the paper surface of the spray in the heat flow and the impact of film thickness model, based on the CHF (Critical Heat Flux, the critical heat flux) jet nozzle trajectory criteria tilt the nozzle optimum heat transfer from the heat source when the height of the inclined jet injection experiments as well as for dynamic electromagnetic drive device pull-studied problems in areas such as:
For axisymmetric conical spray cooling system in the spray area to be divided, based on the introduction of slip flow boundary conditions, the cone-shaped http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets spray assumptions made on the basis of the establishment of the spray droplet density area equivalent continuum the model.
Film based on flow separation of variables method for solving kinetic equations, the momentum equation to find a reasonable set of compatibility relationship, obtained by physical methods applied mathematics within the velocity field of the film series solution of separation of variables. Necking on the assumption that film exports, based on the truncated boundary conditions, boundary conditions by simultaneous other, and seek undetermined coefficient, and has been flow field and film thickness of the film for solving equations, the unknown boundary to achieve a film film flow problem solving. Simulation results show that: ① When the spray rate is uniform, the film is flat film. When the rate of non-uniform, the film centers can appear convex and concave center of both cases, the specific shape of the liquid film surface and the rate of distribution of the spray; ② thin layer near the surface of the heat within the liquid film flow rate greater than that Most of the remaining liquid film flow rate is slow; the film thinning in two ways: to increase speed and reduce spray spray density; ③ velocity slip on the film thickness and the flow field is very small and can be ignored.
Determined by analyzing the jet spray cooling in the tilt of a reasonable premise: CHF guidelines that ensure maximum utilization of coolant under the premise of the spray impact area corresponding to the largest maximum value of CHF. CHF meet the criteria for analysis of different cone angle of the cone and pyramid-shaped nozzle, respectively, for round and square spray nozzle inclined heat source in which the trajectory curve, tilting, and the impact area with spray spray spray angle changes. Spray nozzle tilted square in the analysis, the rotation of the nozzle into the tilt axis and the diagonal rotation type rotary types. The results show that the jet spray coverage on the tilt, the heat source for injection of round and / or tilt jet, the best selection of cone-shaped nozzle; of the square heat source for injection, the best choice of the appropriate square nozzle, and when the square the selection of spray nozzle tilt axis tilt-type jet (angle is not too large).
Visaria, who with the experimental data, to meet the criteria under the premise of CHF, from the theoretical analysis of the conical nozzle of the spray jet square heat source tilt angle of the impact of CHF. The results show that: spray angle has little effect on the CHF, CHF increases slightly with increasing jet inclination.
Purchase and manufacture of test equipment or necessary devices (nozzle, heat, pressure pumps and a variety of measuring instruments, etc.), set up an experimental platform. Application of the theory, consider the drag force of the impact on the establishment of experimental systems a feature-assessment, including the export rate and diameter of the droplet, the droplet rate during exercise, diameter and temperature changes, etc., and then on the jet to heat the surface of the droplet characteristics to predict.
Applications to build the experimental system, the choice of three DANFOSS nozzle exit pressure and pump pressure into the relationship between the measured results show a linear relationship between the two basic; of the nozzle spray characteristics were measured, drawn The total nozzle flow and pump pressure of the relationship: the total flow of the nozzle into the nozzle exit and ends about the opening pressure proportional to the square; the center of the nozzle flow density determination, to find most of the relatively uniform spray nozzle pressure of work .
Application of different levels of heat DANFOSS vertical nozzle jet, the nozzle away from the heat source in the surface height change under the premise of the optimal heat transfer performance in the circumstances (optimal height), resulting in H criteria: When the formation of liquid spray membranes coincided with the region round extrapolated tangent to the edge of the heat source, the system performance to achieve optimum heat transfer. Select two nozzles on the square and circular heat source for heat inclined jet experiments, the results of that research should focus on jet inclination is to solve the resulting problem of increasing the surface temperature gradient (and not too much spray angle is best), while the system heat transfer performance is a secondary issue.
According to the concept of intermittent jet and its significance, proposed the concept of dynamic injection to determine the electromagnetic drive as drive dynamic injection nozzles drive. Describes the electromagnetic properties of pull-driven device concept, Research and Analysis. Mainly for two different structural forms of electromagnetic driving device, the magnetic momentum control model based on the analysis of their quasi-static, step-step magnetic momentum and magnetic momentum-driven modulation of the pull characteristics.Degree Year: 2009