Numerical and Experimental Investigations of Micro Thermal Performance in a Tube with Delta Winglet Pairs

• Main Authors: Jiangbo Wang, Ting Fu, Liangcai Zeng, Guang Chen, Fue-sang Lien
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Micromachines
• Subjects: new vortex generators; heat transfer enhancement; multi-longitudinal vortices
• Online Access: https://www.mdpi.com/2072-666X/12/7/786

In this research, a novel vortex generator (VG) is presented. The experimental and numerical investigations were carried out to study the micro thermal-hydraulic performance in a heated tube. The numerical results showed that the fluid in the core flow region and the near-wall region was fully mixed because of the longitudinal vortices created by the vortex generators. In addition, the experimental results showed that the heat transfer coefficient (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>h</mi></semantics></math></inline-formula>) decreased with the increasing pitch ratio (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mi>R</mi></mrow></semantics></math></inline-formula>) value, while the friction coefficient exhibited the opposite trend. With the increasing ration angle (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><mi>A</mi></mrow></semantics></math></inline-formula>) numbers, the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>h</mi></semantics></math></inline-formula> values decreased while the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>f</mi></semantics></math></inline-formula> numbers increased. In addition, the maximum and minimum values of the fraction ratio were 1.66 and 4.27, while these values of the Nusselt number ratio were 1.24 and 1.83. The maximum thermal enhancement factor (TEF) was 1.21 when <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mi>R</mi><mo> </mo></mrow></semantics></math></inline-formula>= 0.5, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><mi>A</mi><mo> </mo></mrow></semantics></math></inline-formula>= 0° and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><mi>e</mi><mo> </mo></mrow></semantics></math></inline-formula>= 9090. The heat transfer enhancement mechanism of the vortex generator is explained from the microscopic point of view.