Tepe, Ahmet Ümit; Kuru, Muhammet Nasıf; Yilmaz, Harun

This study focuses on the multi-objective optimization of fin and tube heat exchangers to maximize the Thermal Performance Factor and minimize the Volume . A novel fin design is proposed and integrated onto the tube surfaces to enhance thermo-hydraulic performance. The numerical simulations were conducted using Computational Fluid Dynamics with the conjugate heat transfer method, while the optimization framework was established on modeFRONTIER using a Multi-Objective Genetic Algorithm (MOGA-II). The numerical model was validated against experimental data in this study and existing literature data. The optimization process investigated various fin parameters, (Dwing, Dring, αback,αfront and Gwing), alongside heat exchanger design parameters (ST and SL) and inlet velocity (Vinlet) including 0.3–10 m/s. A total of 1271 design points were evaluated, resulting in 998 feasible configurations and 24 distinct Pareto-optimal designs. The Pareto-optimal Design set yielded TPF values ranging from 1.09 to 1.66. The results highlight the typical trade-off between thermal performance and heat exchanger Volume . Higher TPF values generally correspond to larger volumes, with Design ID 1 achieving the maximum TPF (1.66) but also the largest volume. Conversely, designs with smaller volumes (Design IDs 22–24) exhibit lower TPF values (≈1.09–1.13). Even among designs with the same volume and inlet velocity, variations in fin geometry significantly affect thermal performance. Therefore, designs with higher TPF are preferable when thermal efficiency is the priority, while more compact designs are suitable when minimizing volume is the main goal.

Dogan, Ahmet; Kayaci, Nurullah; Bacak, Aykut

The research introduces an artificial neural network model that predicts temperature and assesses thermal comfort metrics for a cooling room, demonstrating how machine learning advancements can enhance thermal efficiency and cost-effectiveness in building design. The study utilized the Levenberg-Marquardt (LM) artificial neural network (ANN) approach to derive the average temperature and thermal comfort metrics collected under actual operating settings. The Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)values were measured at three distinct sites and then compared to the trial findings. The model uses a dataset of 205 observations, with 143 cases used for training and 31 examples for testing and validation. The ANN model demonstrated effective training, with negligible errors in estimated error values. The mean squared error values for average temperature and thermal comfort parameters were 0.0342, 0.0376, 0.0571, 0.0029, and 0.2296. The R values for temperature measurements are 0.9947 and 0.9923, 0.9847 and 0.9437, and 0.9737, demonstrating a highly effective engineering method. The ANN model provided precise predictions for temperature and thermal comfort metrics, such as PMV and PPD in a cooling chamber, with a tolerance of ± 15 %. The LM approach, a machine learning methodology, produced excellent outcomes, particularly at lower temperatures, with 15 % of the data exceeding this range.

Demir, Fatih; Turgut, Oguz

This study investigates the heat transfer and flow dynamics of combined impinging jets at low nozzle-plate distances. The combined jets comprise (i) circular and quadruple helical jets and (ii) circular and double helical jets. A conventional jet is generated from the only circular part of the combined jet. Experiments are conducted with a constant total flow rate (Qt = 85 LPM) and low nozzle-plate distances (H/D = 0.1, 0.2, 0.3, 0.4) for confined and unconfined jet cases. Flow rate ratios (Q*=0.176, 0.235, 0.352, 0.588, 0.823) are used for different swirl intensities. A numerical study was performed using ANSYS Fluent software. The results show that the numerical analysis is consistent with the experimental research. The combined impingement jet shows a potential to improve the low heat transfer occurring at the stagnation zone at low nozzle-plate distance in the swirl jet, leading to non-uniform heat transfer. The confined jet case at the low nozzle-plate distance reduces the heat transfer at the stagnation point and over the entire plate as regards the unconfined jet case. Increasing the H/D distance in the combined impinging jet improves the heat transfer in the confined jet case but reduces it in the unconfined case. Correlations are given for heat transfer prediction depending on H/D and Q* for unconfined and confined cases of the combined jet. Increasing the flow rate ratio and the nozzle-plate distance increases the heat transfer uniformity for the confined and unconfined jet cases. In contrast, the unconfined jet case is better regarding heat transfer uniformity. The confinement plate creates a negative pressure on the impingement plate in all conditions. In contrast, the unconfined jet case is precisely the opposite.

Kalkan, Orhan; Celen, Ali; Bakirci, Kadir; Dalkilic, Ahmet Selim

The world's tendency towards electric vehicles has accelerated and the thermal management of them are critical part of the actual studies. Liquid-based cooling is known as the most common one among other cooling techniques. However, there is still need on the use of various heat transfer enhancement techniques to reduce the maximum temperature and maintain homogenous temperatures. This study experimentally investigated thermal performance of water-cooled cold plates used in thermal management of batteries by using conventional serpentine tube and a novel mini channel designs including a lithium-ion phosphate battery under certain discharge rates from 1C to 5C. Experiments are conducted for different water flow rates from 0.1 to 1.1 L/min as the coolant with inlet temperatures from 15 to 35 °C. Experimental results show that lower coolant inlet temperature causes the largest maximum temperature difference on battery surface. The use of mini channel cold plate resulted in 5.7 °C reduction in the maximum average battery surface temperature compared to serpentine one. Battery surface temperature homogeneity is improved up to 40% for operating conditions for mini channel cold plate usage. Thus, enhancement on thermal performance of proposed new mini channel cold plate is accomplished by temperature measurements.

Kara, Yusuf Ali; Kurnuç, Aslihan

A PCM wall includes phase change material (PCM) as a heat storage medium. In the current project, the south faade of a test room was constructed using PCM walls that were made of (from inside to outside) insulation, brick, plaster (including PCMs), an air gap and a novel triple glazing unit (TGU). Although the annual behaviour of the PCM walls were investigated in the project, the current paper covers an evaluation of the performance of PCM walls in the summer only. The solar transmittance of the TGU decreased approximately 100% during summer compared to winter. There were no overheating problems observed for the PCM wall during the summer.

Bilen, Kadir; Cetin, Murat; Gul, Hasan; Balta, Tuba

An experimental study of surface heat transfer and friction characteristics of a fully developed turbulent air flow in different grooved tubes is reported. Tests were performed for Reynolds number range 10,000-38,000 and for different geometric groove shapes (circular, trapezoidal and rectangular). The ratio of tube length-to-diameter is 33. Among the grooved tubes, heat transfer enhancement is obtained up to 63% for circular groove, 58% for trapezoidal groove and 47% for rectangular groove, in comparison with the smooth tube at the highest Reynolds number (Re = 38,000). Correlations of heat transfer and friction coefficient were obtained for different grooved tubes. In evaluation of thermal performance, it is seen that the grooved tubes are thermodynamically advantageous (Ns, a < 1) up to Re = 30,000 for circular and trapezoidal grooves and up to Re = 28,000 for rectangular grooves. It is observed that there is an optimum value of the entropy generation number at about Re = 17,000 for all investigated grooves.

Çetin, Murat; Yüksel, Fikret

This paper briefly reviews the use of hazelnut oil as an alternative fuel in pre-chamber diesel engines, and compares it with diesel fuel. In order to investigate the effects of the use of hazelnut oil as a diesel engine fuel, an experimental setup was constructed. The results showed that the hazelnut oil may be employed as a possible candidate for most diesel fuel operating conditions in terms of the performance and emission parameters without any modification and preheating of the fuels.

Tandiroglu, Ahmet; Ayhan, Teoman

In this paper energy dissipation analysis was conducted to evaluate the performance of nine circular tubes with baffle plate inserts having different pitch to tube inlet diameter ratio and baffle orientation angle in the range of Reynolds number 3000 ≤ Re ≤ 20,000 for the case of constant heat flux. The characteristic parameters of the tubes are pitch to tube inlet diameter ratio H/D = 1, 2, 3 and baffle orientation angle β = 45, 90, 180°. Air having Prandtl number is 0.71 was used as working fluid, while stainless steel is considered as a pipe material. As an evaluation criteria of iE has been proposed by Sano et al., which is based on correlating the heat transfer coefficient and the dissipation energy in a fluid has been considered to evaluate transient forced convection. The data show that unsteady dissipation energy criterion for the baffled tubes is higher than smooth tube and the type of 9031 has been found as the most effective one.