Heat transfer enhancement (HTE) techniques refer to the improvement of thermohydraulic performance of heat exchangers. Since the past decade, the heat transfer enhancement techniques have been extensively applied in heat exchangers. Inserting a swirl/vortex generator into a heat exchanger tube is one of the most popular HTE techniques [1-12]. The technique has been applied in several thermal systems such as shell and tube heat exchanger, solar water heater, air conditioning and refrigeration systems, and chemical reactors, etc. Inserting twisted tape causes swirling flow as a secondary in bulk fluid. The swirling flow promotes the fluid mixing between core and wall regions, disturbs the thermal boundary layer and thus enhances heat transfer coefficient in existing system. Several attempts have been made to modify twisted tapes in order to improve heat transfer rate and/or to reduce pressure loss depending on application requirements. Ghadirijafarbeigloo et al. [8] used louvered twisted-tape inserts in a receiver tube of solar parabolic trough concentrator. The thermal performance factor of the tube with a louvered twisted-tape was enhanced up to 26 % as compared with that of the one with a classical twisted tape. Nanan et al. [11] compared heat transfer enhancement by a common helical twistedtape and perforated helical twisted-tape inserts and found that perforated helical twisted-tapes caused lower friction loss at similar operating conditions. Piriyarungrod et al. [13] reported the effect of the tapered twisted tapes on heat transfer enhancement characteristics in a circular tube. Their results indicated that heat transfer enhancement increased with decreasing taper angle and twist ratio. Chokphoemphun et al. [14] studied the heat transfer and pressure loss characteristics in tubes with multiple twisted-tape inserts (Double, triple and quadruple tapes) in co and counter arrangements (Co/counter clockwise). Among the studied inserts, the quadruple countertwisted tape insert provided the maximum thermal performance. Recently, Tamna et al. [15] employed double twisted tapes in common with 30° V-shape ribs in a round tube. V-shape ribs with different relative rib heights were employed. Their results showed that the heat transfer and pressure drop increased with increasing rib height. Yongsiri et al. [16] studied the heat transfer and friction factor and thermal performance characteristic in a uniform heat flux tubes containing helically twisted tapes with alternate axes. Tapes with different tape pitch to tube diameter ratios (P/D = 1.0, 1.5 and 2.0) and alternate length to pitch length ratios (l/P = 1.0, 1.5 and 2.0) were utilized. As compared to a common helically twisted tape, the helically twisted tapes with alternate axes gave higher heat transfer rate and thermal performance factor. Singh et al. [17] reported the heat transfer rate and friction factor behaviors of roughened tubes with twisted tape inserts. Under constant pumping power criterion, the thermal performance of the roughened tube fitted with twisted tape was as high as 1.61 times of those of a plain tube. Khatua et al. [18] examined the heat transfer in horizontal tubes inserted with perforated twisted tapes in a condensation process of pure R245fa vapor. They could observe that the use of perforated twisted tapes resulted in heat transfer enhancement up to 37.5 % over those of a plain. Eiamsa-ard et al. [19] investigated the heat transfer enhancement in a three-start spirally twisted tube inserted with triple-channel twisted tape at different tape width ratios (w/D = 0.1, 0.25, 0.34 and 0.5) and tube/tape arrangements (Belly-to-belly and belly-to-neck arrangements).