Kalkan, Orhan

Recently, studies on the use of MCHS applied to chips to benefit from the high thermal conductivity of liquid metals have been increasing. This study came up with an optimum choice for MCHS geometric parameters, MCHS material, Gallium-based liquid metal coolant type, and coolant inlet velocity. Total thermal resistance (Rtot), initial investment cost (Ci), pressure drop (ΔP), and maximum operating temperature (Tmax) are selected as performance parameters. I-optimality algorithm used for generation of the Design of Experiment (DoE) based on the Response Surface Method. The optimization parameters and their levels are determined by performing a parametric study. The derived mathematical models for selected performance parameters Rtot, Ci, Tmax, and ΔP, which are also objective functions, are tested by ANOVA with prediction accuracy of 0.983%, 0.997%, 0.886%, and 0.996%, respectively. As a result, the determined optimum values of the channel width, channel height, half of fin width, fin slope angle, and inlet velocity, are 1.16 mm, 3.00 mm, 0.24 mm, 5.96°, and 0.4 m s−1, respectively. In addition, a hybrid structure in which the base of the designed MCHS is aluminum, and the fins are copper, and the GaIn compound for the coolant are calculated as the optimum material options.

Kirkar, Safak Metin; Gönül, Alişan; Celen, Ali; Dalkilic, Ahmet Selim

In this study, the use of corrugated surfaces as one of the passive heat transfer improvement methods on straight tubes is numerically investigated related to the determination of Nusselt number, friction factor, and performance evaluation criteria. With the same diameter of 5.75 mm and length of 390 mm, 9 corrugated tubes having corrugation pitches of 6, 12 and 18 mm, and depths of 0.6, 0.8 and 1.0 mm are considered for the parametric studies. Water is employed as a operating fluid with Reynolds number values from 480 to 6100 covering different flow regimes. Sensitivity analyses by Genetic Aggregation Response Surface Methodology and multi-objective optimization analyses by NSGA-II are performed in order to maximize heat transfer and minimize pressure drops. It is determined that the thermal-flow augmentation created by the use of corrugated surfaces in laminar flow conditions is quite higher than those in the turbulent region of the smooth tube. According to the obtained optimum parameters and flow conditions, the maximum value of the performance evaluation criteria is 2.48 in comparison to the use of equivalent smooth and corrugated tubes. In addition, Nusselt number and friction factor equations are suggested by using 220 data points within deviation bands of ±10% and ±15%, respectively.

Firat, Ilker; Karagoz, Sendogan; Yildirim, Orhan; Sonmez, Fatin

In this study, we experimentally investigated the heat transmission and friction effects of finned turbulators with different angles in a circular pipe for single-phase flows. Experiments were conducted to see how turbulators affected the friction factor and Nusselt number. The Nusselt numbers of the finned turbulators with 30°, 20° and 10° angles rose by 121.66%, 109.05% and 81.30%, respectively, in comparison to the plain pipe, according to experiments using Reynolds numbers in the range of 10043-14386. The overall heat transfer improvement of all turbulator types appears to be more than one. Due to the increase in blade angle, the highest Nu number was obtained from the experiment with a 30° angle fin turbulator, but the greatest heat transfer improvement was obtained as 1.476 in a 20° angle blade turbulator for Re = 10043 number. The thermal improvement factors of 20° and 30° angle fin turbulators were found to be 1.1 and 1.07 times more than, respectively, compared to the turbulator with a 10° angle. In addition, it has been shown that the 20° angle fin turbulator's thermal improvement factor is 1.03 times higher than the 30° angle turbulator's.

Tepe, Ahmet Ümit; Yilmaz, Harun

In this study, heat transfer performance of circular-slice-shaped-winglet (CSSW) for tube bank heat exchanger (TBHE) was numerically investigated. Circular-slice angle (α = 5°, 10° and 20°), layer gap (h/d = 0.08, 0.14, and 0.20) and winglet diameter (D/d = 1.60, 1.76 and 1.92) were analyzed as geometric parameters to obtain optimal design. Comprehensive numerical simulations were conducted under both laminar and turbulent flow (1100 ≤ Re ≤ 8500) conditions. Navier Stokes Equations were solved by using RNG k-ε turbulence model (with enhanced wall treatment). Colburn-j factor (j), friction factor (f), modified London area goodness factor (j/f1/3) and performance evaluation criterion (PEC) were investigated quantitatively. Flow characteristics were also analyzed to elucidate the underlying physics of the effects of CSSW on thermal-hydraulic performance for TBHE. Results were compared with the data related to bare tube heat exchanger, and showed that the highest modified London area goodness factor is 26.34% with α = 10°, h/d = 0.20 and D/d = 1.92 CSSW winglet design. Additionally, numerical calculations revealed that PEC increased to 1.356 with these CSSW design parameters, which corresponds to reduction of the required total heat transfer area by 36.60% compared to the bare tube heat exchanger for the same heat duty at a fixed pumping power.