Dissertation > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Industrial thermal equipment > Heat Transfer Equipment

Numerical Study of Heat Exchangers with Different Geometric Parameters

Author YangGang
Tutor YinJiXiang
School Taiyuan University of Technology
Course Thermal Power Engineering
Keywords corrugated plate heat exchangers numerical simulation geometric parameters turbulence
Type Master's thesis
Year 2012
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Heat Transfer Enhancement Technology what were used in Engineering Practice will not only save energy and protect environment, but also a substantial savings on investment costs. The development and application of the heat exchanger is one of technology to enhance heat transfer. The heat transfer was widely used in the field of energy, chemical industry, metallurgy, petroleum, its enhanced heat transfer have get much attention. Corrugated ducts are basic channel geometry in plate heat transfer exchangers and plate-fin heat exchangers because the heat transfer rate of the heat transfer devices tends to increase. There are various forms of the corrugated surfaces, such as triangular, sinusoidal, arc-shaped, rounded corners similar to triangular and trapezoidal. Among these different types of corrugated surface geometries available, the triangular and sinusoidal profile geometry is more commonly used in heat exchanger devices.Modeling software Gambit2.0is used to established reasonable grid for two-dimensional triangular channel and three-dimensional sinusoidal channel. The paper simulates the air flow and heat transfer in turbulence condition by Fluent6.3. Under a constant wall temperature, analysis of different geometric parameters that including spacing ratio, severity and duct cross-section aspect ratio effect on the flow and heat transfer performances. The paper comparing the streamline distribution, temperature distribution, shearing stress distribution, friction coefficient and Nusselt numbers with different geometric parameters, and the area goodness factor are used to assessing the thermal-hydraulic performance enhancement of the corrugated channels with different geometric parameters.Trough numerical research, The analysis results about triangle corrugated channels with in-phase shifts surface:when the severity value remain unchanged, the vortex which located at the entrance of the upper wall, at wavy trough and at the wavy peak of the lower wall become larger with the increase of spacing ratio; As Reynolds number increases, the fluid inertia action increased gradually and the vortex intensity enhanced, vortex size enlarged. When the spacing ratio value remain unchanged, the streamline in the small severity channel parallel to each other and there are no vortex in the channel. This is because the corrugation amplitude is relatively low, viscous force take up the leading role while the effect of inertia force is smaller. With the increased of severity, the streamline at the entrance of the channels distortion, different degrees of vortex are found at the entrance of the upper wall, at wavy trough and at the wavy peak of the lower wall. The analysis results about triangle corrugated channels with anti-phase shifts surface, When Reynolds number is certain, with the spacing ratio increases, vortex shape changed gradually from long and narrow to circle. At the same time, the scope of the vortex gradually extended to the center of the channel. When the spacing ratio remain unchanged, with the increased of Reynolds number, the fluid inertia action increased gradually and the vortex intensity enhanced, vortex size enlarged. While the severity is smaller (y=0.125), streamline and the channel perpendicular center line almost symmetry, and no vortex appeared that flow form is very close to the parallel channel.Trough numerical research, The analysis results about sinusoidal corrugated channels:flow cross-section aspect ratio(a) had no significant effect on the friction factor, but have different degrees impact on the average Nusselt number. When the spacing ratio is smaller, the area goodness factor(j/f)of in-phase shifts surface is better than the anti-phase. With the increased of the spacing ratio, the area goodness factor(j/f)of anti-phase shifts surface is better than the in-phase. Phase difference effects on flow and heat transfer due to different channel spacing ratio:an optimum goodness is attained on the in-phase channel with the smallest spacing ratio and the smallest severity while with the biggest spacing ratio and the smallest severity for the anti-phase. Finally, both in-phase and anti-phase channels have the maximum performance factor were selected to fit formula of friction factor and Nusselt number to provide reference for engineering calculation. The flow and heat transfer performances for air in periodical two-dimensional sinusoidal channels was calculated using a unsteady numerical methods, the results support that when Re=1400, the flow in the channels became unsteady. In the steady flow, the average Nusselt numbers for the corrugated channel was only moderately larger than those for a parallel-plate channel. While, in the unsteady flow, the Nusselt numbers was much larger than parallel-plate channel.

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