Amirhossein Haghighat - M.Sc. graduate; School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
MohammadAli Akhavan-Behabadi - Professor;School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Behrang Sajadi - Associate ProfessorSchool of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Rasool Mohammadi - Ph.D. Candidate;School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran

Alternating flattened tubes, which are made of plain and flattened sections at each segment, improve two-phase heat transfer by increasing the heat transfer surface, creating vorticities, and mixing the flow. The present study investigates the effect of vapor quality and mass velocity on the heat transfer coefficient in alternating flattened tubes. The test section consists of three different alternating tubes with an effective length of ۷۰ cm and an internal diameter of ۸.۲ mm. The flattening ratio, the number of segments, and segment length are the geometrical parameters that differ in test tubes. In this research, R۱۲۳۴yf refrigerant has been used, which is one of the new refrigerants with a global warming potential of ۴ and is a very suitable alternative to refrigerants such as R۱۲۳۴yf. A number of ۱۵۰ distinct experiments were performed in the range of vapor qualities of ۰.۰۹ to ۰.۹۱ and mass velocities of ۱۱۰, ۲۱۰, and ۳۰۰ kg/m۲s. The results show that the mass velocity and vapor quality always directly impact the heat transfer coefficient. It is also observed that the use of alternating flattened tubes increases the heat transfer coefficient by up to ۲۵۴% compared with simple round tubes.

Alternating flattened tubes, Experimental study, R۱۲۳۴yf, Heat transfer coefficient, Flow boiling