Ekiciler, Recep; Demir, Fatih; Kalkan, Orhan

Enhancing heat transfer efficiency is crucial for improving performance and reducing the energy consumption of thermal equipment in various industrial sectors. The emergence of passive enhancement methods, such as corrugated grooves, has improved convective heat transfer cost-efficiently. To this end, this study addresses the thermal and hydraulic performance of the baffle duct with numerical analysis and multi-objective optimization methods. The study is innovative in that it places movable L-shaped baffles inside the duct, which have their own internal connections and a connection to the grooved channel. L-shaped baffles have the ability to move at alpha angles (α = 30°, 60°, 90°) with the upper wall of the duct and at beta angles (β = 60°, 90°, 120°, 150°) with their internal connection points, which affect the thermal and hydraulic performance of the duct. Air, water, mono (GO/water), and tetra hybrid (Al2O3-Au-Ag-TiO2/water) nanofluids are used as coolant fluids in the range of Re = 2500 to 3100. The coolant air and a baffle-less triangular grooved duct are used for comparison to evaluate the thermal and hydrodynamic performance in other cases. The results show that at Re = 2500, the baffled duct achieves a 65% higher Nu than the one without baffles. As α = 90° decreases to 30°, Nu increases by 12.85% and 12.11%, respectively. As β = 60° to 120° increases, Nu increases by 21.67%, while f increases by 59% from β = 90° to 120°. The highest performance evaluation criteria (PEC) is achieved at β = 90° and the lowest at β = 150°. The tetra hybrid nanofluid exhibits the highest Nu and f values across all Re ranges, demonstrating the most efficient cooling performance with a PEC value approximately 8% higher than that of water. Multi-objective optimization reveals that the combination of α = 30°, β = 35°, Re = 2500, and water is the most suitable design. Generally, thermal and hydraulic performance can be significantly improved by carefully selecting channel geometry and fluid properties.

Dalkılıç, Ahmet Selim; Celen, Ali; Erdoğan, Murat; Sakamatapan, Kittipong; Newaz, Kazi Salim; Wongwises, Somchai

In this paper, heat transfer coefficients and critical heat fluxes of the R134a fluid in two-phase flow was studied in a 27-channel, 421 μm hydraulic diameter and 40 mm long microchannel experimental set-up. Data were collected at constant mass flux of 1000 kg m−2 s−1, saturation inlet temperature range of 20–28 °C and at inlet vapor quality range of 0.01–0.20. The heat flux was initiated at 250 kW m−2 and gradually increased until reaching the critical heat flux (CHF). The effect of inlet vapor quality, saturation inlet temperature and heat flux on heat transfer coefficient and critical heat flux were investigated in detail and presented graphically. It can be observed that the CHF decreases with the increasing of saturation inlet temperature and inlet vapor quality. However, the heat transfer coefficient at the CHF point increased with the increasing of saturation temperature and the heat transfer coefficient at the CHF point was decreased with the increasing of vapor quality. The test results from the correlations, suggested in well-known articles, were compared with the experimental data, where the Kosaz et al. proposed correlation was showing well fit with the experimental data having absolute error of 9.86%. In this investigation, the new correlations for the heat transfer coefficient for the heat transfer coefficient and the critical heat flux have been proposed by taking into account the effect of the vapor quality.

Dalkılıç, Ahmet Selim; Uluç, Baran; Cellek, Mehmet Salih; Celen, Ali; Jumpholkul, Chaiwat; Newaz, Kazi Salim; Wongwises, Somchai

Heat transfer and pressure drop of turbulent fluid flow were studied numerically and experimentally in a quad-channel with twisted tapes placed in a circular tube under uniform heat flux boundary condition. All the tests were conducted with water as the working fluid where the turbulent flow range of Reynolds numbers were maintained at 4250 to 11000. Quad-channel twisted tapes (QCTT) were manufactured by 3D printer with the material PLA, the lengths of 50 mm, 100 mm, 200 mm with the twist ratio of 4.48. The tapes were identified with their tape/pipe length ratios (TPR) of 0.025, 0.05 and 0.1. Validation of the experimental data was performed by the comparison of the experimental results with the data from the well-known empirical correlations. Alteration of the friction factors and Nusselt numbers with the Reynolds numbers are presented in this paper. The results showed that the Nusselt number and the friction factor increased with the increasing of the length of QCTTs. On the other hand, the performance evaluation criteria (PEC) should be declining with the increase of the lengths of the tapes. The evaluated temperature distributions inside the tested tubes with the inserts were plotted in order to investigate the observed data. Based on the obtained experimental data, the empirical correlations for the Nusselt number within the deviation of ±2% and the friction factor within the deviation of ±5% were developed for the practical usage.

Celen, Ali; Çebi, Alican; Dalkılıç, Ahmet Selim

In this study, boiling heat transfer and pressure drop experiments are performed in order to investigate heat transfer enhancement of microfin tube comparing with smooth one. During constant heat flux (10 kW m−2) experiments, effect of mass flux (190–381 kg m−2 s−1), saturation temperature (15–22 °C) and vapor quality (0.21–0.77) on heat transfer coefficient and pressure drop are investigated. In addition, boiling heat transfer coefficient and frictional pressure drop correlations given in the literature are compared with measured ones. Moreover, the experiments revealed that experimental boiling heat transfer coefficient and total pressure drop of R134a flowing microfin tube are 1.9 and 3.0 times higher than smooth one having the same fin root diameter, respectively. Furthermore, 94 number of heat transfer and pressure drop raw experimental data belonging to the microfin tube are given for researchers to validate their theoretical models.