| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 87 === This study simulated the thermal flow field of a thermal mass flow meter (TMFM) using the FIDAP''s flowsolver and conducted the thermal difference experiments to verify FIDAP''s solutions. Flow simulations emphasized on analyzing the velocity and pressure distribution in the region of the bypass and sensor tubes, and computed the flow rate ratio of the sensor tube to the TMFM and pressure drops within the TMFM. A semi-analytical solution for velocities of the sensor tube and bypass tubes was also derived in this study and compared with the simulation''s results. Reasonable agreement between the analytical and numerical predictions for the velocity and pressure solutions was obtained, although these comparisons were not good in the cases of high flow rate. Analytical prediction shows that with more bypass tubes, the flow rate ratio for the sensor tube or the bypass tube to the total flow rate of TMFM has a stronger tendency to remain constant, and doesn''t vary with the total flow rate of TMFM. As for the comparison of pressure drops, experimental data, results of the numerical simulations, and the analytical solution agreed well with one another.
This study also modeled the thermal characteristics of the heating sensor tube of the TMFM under a isothermal heating mode. Thermal simulations focused on investigating the relation between the heat flux difference between these two heaters and the variation of flow rate of the sensor tube. Experiments of gas flow-rate-sensing were conducted to verify results of the thermal simulations of the sensor tube. By comparing the experimental data and numerical results, it was found that the heat flux difference did not hold a linear relation with total flow rate of the TMFM. Besides, it was necessary to consider the heat loss from the sensor tube into the ambient environment and specify carefully the heating mode of heaters during the numerical simulations; otherwise simulation''s prediction would disagree with the experimental data.
In summary, this study analyzed flow field of the TMFM using the numerical simulation, the semi-analytical prediction and the thermal difference measurement, respectively. Though agreements among these three approaches were not well, their functions are complementary to one another. Thus, these tools were capable to provide useful data to design the TMFM.
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