Experimental study of the effect of twisted-tape inserts on flow boiling heat transfer enhancement and pressure drop penalty

This study presents experimental results of heat transfer coefficient and pressure drop during two-phase flow of R134a in a horizontal tube containing twisted-tape inserts. The test section is a 2 m long copper tube of 15.9 mm inner diameter. The experiments were performed for tapes with twist ratios of 9 and 14 and a tube without insert. The mass velocity ranged from 75 to 200 kg m−2 s−1 and the vapor quality from 5 to 95%, for adiabatic condition and for constant heat flux of 10 kW m−2. Experimental pressure drop and heat transfer coefficient results are presented, and also an analysis of overall enhancement due to the inserts. The use of twisted-tape inserts is suitable if applied to the high vapor quality region of the evaporator and under high mass velocities.

► Flow boiling in horizontal tubes without twisted-tape insert.
► Twisted-tape inserts and its effect on pressure drop and heat transfer enhancement during flow boiling in horizontal tubes.
► Overall performance of the heat transfer enhancement technique.