Ahmet Selim Dalkilic

• Assoc.Prof.Dr.
• Professor (Associate) at Yıldız Technical University

Advanced prediction tools are essential for assessing suitability of regenerative evaporative cooling systems, significantly reducing the time and effort required for extensive testing. Smart algorithms enable optimizing operating conditions and system performance, making the implementation of artificial intelligence tools crucial. This work aims t...

The study of condensation and evaporation in plain pipes is a significant area of engineering and scientific inquiry, as it has relevance for enhancing and developing various industrial procedures. This study utilized a Bayesian artificial intelligence method to determine the pressure drop in a vertically oriented plain copper pipe during R134a's a...

The current work examines the effect of forced convection on thermal comfort in a space, including radiant wall cooling and an innovative floor-level diffuser system. It examines the impact of various vane angles on thermal comfort in room air conditioning at 15°, 30°, 45°, 60°, and 75°, and employs experimental data to confirm a hybrid 3D computat...

This study reveals the effect of optimization on two-state piezoelectric materials for energy harvesting. The application of two-state piezoelectric materials enables effective energy extraction from vibrations and motion. The formulation originates from a two-state energy harvesting concept, which can be concluded that it is dimensionless due to i...

Optimizing controllable parameters is crucial to milli-channel cooling system design. This study investigates the heat transfer and hydrodynamic properties of a novel annular flow boiling process of water in milli-channels with better pulsation that passes through a rectangular cross section at a constant temperature. By optimizing system operating...

Gyroid structures exhibit significant potential in the fields of lightweight structural design, heat transfer, energy absorption, and biological applications. The use of gyroid for implants in dentistry is currently not sufficiently widespread. The research encompasses design, compression testing, cellular investigation using a digital microscope,...

Thermal comfort is crucial for indoor environmental quality, impacting occupant well-being and intellectual productivity. Despite the widespread use of HVAC technologies in residential and commercial buildings, there is growing awareness of thermal comfort, leading to more studies on this issue. According to international publication indexes nearly...

The estimation of heat transfer coefficients (HTC) and pressure drop (ΔP) in flow boiling processes is essential for the effective design and operation of refrigeration systems. In this study, the artificial neural network (ANN), locally weighted regression (LWR), and gradient boosted machine (GBM) methods are employed to predict the boiling heat t...

Considering stricter emission norms, different emission reduction strategies have been studied by researchers. In this work, experimentation has been performed to analyze the influence of goat urine emulsified diesel on the combustion, emission, and performance characteristics of the single cylinder engine fuel and their comparison with conventiona...

According to review of the literature, the influence of nanoparticle diameter with irregular shapes on viscosity requires further research since there is no relation between particle size and nanofluid stability. In this study, SiO2/EG–water-based nanofluid samples were prepared, and their viscosities were experimentally determined. SiO2 nanopartic...

In both centralized and decentralized air-conditioning systems, the performance, sustainability, and efficiency of the systems in delivering thermal comfort within a specific area are assessed as part of the air thermal management platform evaluation process. The evaluation of air thermal management platforms entails a thorough examination of numer...

Electrical equipment extensively uses Microchannels (MCs) for cooling. Due to their complexity, it is challenging to evaluate the features of the fluid flow and heat transfer processes in MC pin-fin heat sinks. Numerical approaches have been frequently employed in MC design to enhance efficiency. Machine learning methods have recently enabled the a...

In this study, the stability and viscosity of four different nanoparticles are discussed in conjunction with the physical properties of these nanoparticles. The aim is to provide guidance for nanoparticle selection in future nanofluid applications. Additionally, our goal is to examine hybrid nanofluids in comparison to single nanofluids, exploring...

The research examines the complex correlation between discharge valve properties in severe temperature circumstances, ranging from 54.4°C to -23.3°C, in accordance with ASHRAE operational guidelines. The design parameters include examining valve thicknesses of 0.127 mm, 0.152 mm, 0.178 mm, and 0.2 mm, together with lengths of 14.722 mm, 16.222 mm,...

The present investigation utilized a machine learning structure to ascertain the pressure drop in vertically positioned, corrugated copper tubes during the evaporation process of R134a. The evaporator was a counter-flow heat exchanger, in which R134a flowed in the inner corrugated tube and hot water flowed in the smooth annulus. Different evaporati...

Power transformers submerged in oil are universally acknowledged as very useful elements in electrical power networks. A fraction of the electrical energy involved in the conversion from high to low voltages is lost as thermal energy, which is produced inside the transformer's windings and core. The effective dissipation of heat is of paramount sig...

This study examines discharge line energy losses using advanced fluid-structure interaction methods to show how valve design parameters—length, thickness, and height—improve compressor performance. An innovative 3D fluid-structure Interaction model represents a self-acting hermetic reciprocating compressor's discharge valve as a beam element. The R...

In thermal engineering implementations, heat exchangers need to have improved thermal capabilities and be smaller to save energy. Surface adjustments on tube heat exchanger walls may improve heat transfer using new manufacturing technologies. Since quantifying enhanced tube features is quite difficult due to the intricacy of fluid flow and heat tra...

The efficiency of the compressor's thermodynamic, mechanical, and electric motors can be increased by minimizing their losses. Based on the design characteristics of the compressor, the current study proposes an artificial neural network (ANN) model to forecast the mass flow rate, cooling capacity, compression power, and discharge line loss of the...

Due to their durability and efficiency, hermetic reciprocating compressors (HRCs) are used in refrigeration and air conditioning. Compressor performance and reliability concerns reduce system efficiency and raise maintenance costs. Machine learning (ML) is being used to improve hermetic reciprocating compressor performance, reliability, and energy...

Triple concentric-tube heat exchangers are often used in a variety of industries, including HVAC, food and beverage manufacturing, and chemical processing. They may also be utilized in applications requiring thermal homogeneity, such as food and pharmaceutical production. They are appropriate for a number of applications since they may be construct...

Triple concentric-tube heat exchangers are used widely in refrigeration, drying, energy storage, chemical systems, and the food industry. To handle excessive temperature differences, the heat transfer area, as an option, the heat exchanger’s length, is necessary to be increased. Triple tubes have a significant advantage in this regard in comparison...

This study is about the fog on the windshields of passenger buses because it makes it hard for drivers to see, which is dangerous. The goal of the research is to come up with an effective way to spread the produced mist. According to the study, the air duct design, which is connected to the car’s defroster and defrosting system by Kraft hoses, has...

Bu çalışmada, Yapay Sinir Ağları kullanılarak İstanbul Asya yakası ve Avrupa yakası için günlük ve saatlik doğal gaz talep tahmin modelleri oluşturulmuştur. Doğal gaz kullanımını etkileyen parametreler; tüketici sayısı, ortalama günlük sıcaklık, minimum günlük sıcaklık, resmî tatiller, ısıtma derece gün sayısı olarak belirlenmiştir. 2008'den 2018'i...

As the demand for energy-efficient air conditioning systems enabling thermal comfort criteria increases, the research into innovative systems that combine displacement ventilation and radiant heating is being more up-to-date. This work discusses local mixed convection heat transfer coefficients over a radiant heated wall in an experimental room cou...

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 pitche...

One of the most effective ways to save energy for cooling and heating applications is thermal insulation. Because of this, determining the ideal insulation thickness is a popular topic for publications. The purpose of this study is to determine the appropriate insulation thickness needed for a submarine’s external construction while it is cruising...

The most popular approach to determine compressor losses is to generate compressor pressure-volume indication diagrams. The pressure-volume indication diagram of a novel hermetic reciprocating compressor for household refrigerators operating with R600a was experimentally obtained under American Society of Heating, Refrigerating and Air-Conditioning...

In the current work, the impacts of convector factors of a panel radiator regarding heat output and total weight have been investigated using a machine learning algorithm. An artificial neural network model, widely evaluated by machine learning algorithms, has been created to determine the heat output and total weight values of panel radiators. The...

The current work presents the flow and structural analysis of the application design in un-manned aerial vehicles (UAVs) as well as indicates a case of the modeling and simulation study with the ANSYS Fluent and Mechanical programs. This research reveals the unmanned aerial vehicle’s structural and mechanical design, structure configurations, energ...

Because of the prompt improvements in Micro-Electro-Mechanical Systems, thermal management necessities have altered paying attention to the compactness and high energy consumption of actual electronic devices in industry. In this study, 625 data sets obtained numerically according to the change of five different geometric parameters and Reynolds nu...

Shell and helically coiled tube heat exchangers (SHCTHEXs) are heat exchangers that only take up a small space and enable greater heat transfer area compared to traditional models. Information on 21 different SHCTHEXs obtained from catalog was considered for the modeling. Two other artificial neural network structures have been created to forecast...

The difficulty of the production stages of panel radiators used for heating purposes reveals the importance of determining the heat transfer performance and panel radiator weight values, which are determined depending on the design parameters. In the present work, an artificial neural network model is proposed for predicting the heat transfer and w...

The average flow velocity in heat exchangers is considered less often and thus needs further and detailed investigation because of its crucial influence on the overall thermal performance of the application. The use of nanofluids has similar influences to finned tube designs. Considering the rise in heat transfer and pressure drop, uncertainties in...

This study presented a novel liquid-cooled heat sink based on constructal theory. An experiment was conducted to investigate the influence of boundary conditions, such as the mass flow rate (ṁ), on heat transfer rate (Qin) and pressure drop. Five cylinder heater cartridges were used in the experiment for 11 different mass flow rates (0.008292 < ṁ (...

There is a rising necessity concerning low energy consumption and thermal comfort, thus, new systems combining displacement ventilation and radiant heating are becoming common as a research topic. The current paper covers free, mixed, and forced convection in an experimental chamber consisting of a radiant wall heating system and a baseboard level...

In this study, the usability of the machine learning method in predicting the discharge performance of experimentally tested sorption heat storage materials was investigated. Experimental data was obtained from a lab scale fixed-bed thermochemical heat storage unit. 9 candidate composites were tested under different inlet conditions. Based on the e...

Radiant wall applications have been favored compared to floor and ceiling ones owing to their advantages. In the current work, the heat transfer characteristics of a radiant cooled wall, which are heat fluxes, and heat transfer coefficients, have been experimentally investigated by altering supplied water temperatures and using proper reference tem...

Typically, success in the estimation of machine learning is expected to rise with increasing input parameters, whereas the noise issue may rarely arise owing to redundant input factors undesirably influencing the learning algorithm. The parameters such as overall heat transfer coefficient, pressure drop, and overall cost have been determined by two...

The present study investigates the flow pattern and thermal behavior of constructal theory-based pore-scale porous media (CTPSPM) using computational fluid dynamics (CFD) and machine learning. Due to the increasing complexity of the geometry, as the number of pairs (Np) and clusters (Nc) increase, the CFD approach is unable to present the precise r...

In this study, helically coiled tubes are used in a shell, and the effects of tube diameter, coil diameter, Reynolds number, Dean number and flow rate on heat transfer and pressure drop during laminar single-phase flows of pure and nanofluid are investigated. Performance evaluation criteria and effectiveness analyses are performed considering tube...

In the current work, the pressure drop of the refrigerant flow in smooth and micro-fin pipes has been modeled with artificial neural networks as one of the powerful machine learning algorithms. Experimental analyses have been evaluated in two groups for the numerical model such as operation parameters/physical properties and dimensionless numbers u...

The accurate calculation of pressure drop of evaporators/condensers are crucial and related with the pumping power, performance coefficient and energy consumption in a refrigeration equipment. This work aligns frictional pressure drop models/correlations with the experimental outcomes of boiling pressure drop of R134a in horizontal smooth and micro...

An increasing demand on energy efficiency and indoor air quality exists, therefore displacement ventilation and radiant surface cooling applications are taking more attention as an investigation subject. This article presents an experimental study of mixed convection in a test chamber equipped with both radiant wall cooling and air-conditioning sys...

In the current experimental investigation, the radiators’ heat transfer performances are evaluated experimentally and validation is done using the analytical ε-NTU method. In this experimental study composition of the cooling fluid is 50:50 water/EG. The pressure and temperature values are fixed for air and water/ethylene glycol sides. The velocity...

Serrated welded spiral fin-and-tube heat exchangers (SWSFTHXs) are experimentally investigated. The work primarily focuses on the effects of the segmented fin height (hs) with various fin pitches (fp) on the air-side performance (ASP). Experimental results show that SWSFTHXs provide a higher air-side heat-transfer coefficient than the plain welded...

Mixed convection phenomenon over radiant cooled surfaces with displacement ventilation in living environments is becoming a popular issue due to the airborne viruses and energy economy. Artificial neural networks are one of the machine learning methods that are widely evaluated as an engineering tool. In the current study, heat transfer coefficient...

In this study, radiators equipped with conventional pipes and newly proposed double-U grooved and brazed pipes are compared with each other under similar operating conditions. The radiators’ heat transfer performances have been evaluated experimentally and validation is done using the analytical Number of Transfer Unit Method. The cooling fluid has...

We studied the effect of fin patterns on the air-side performance of a novel type of heat exchanger, namely louver spiral fin-and-tube heat exchangers (LSFTHXs). We investigated three types of fin patterns—radial, curved, and mixed-louver spiral fins—and compared their characteristics with plain spiral fin. We fabricated heat exchangers with a crim...

In this study, delta winglet-type vortex generators, widely used in conventional macro channels and proven to be effective, are used in microchannels to increase their heat transfer capacities. The effects of vortex generators on heat transfer and pressure loss characteristics are studied numerically for different angles of attack, vortex generator...

The aim of this review is to present a summary of the published papers of the heat transfer and pressure drop characteristics for single-phase flow in helically coiled tubes. The effect of geometrical parameters such as curvature ratio, coil pitch and working conditions such as Reynolds number, Dean number, flow rate and flow arrangement on heat tr...

Since liquid-based thermal management systems are usually preferred methods for battery electric vehicles and cold plates are generally preferred to circulate the coolant, studies on their design are becoming increasingly essential. Besides, it seems useful to work artificial intelligence approaches to evaluate different battery thermal management...

Objective: In the present investigation, thermal conductivity and viscosity properties of water-based SiO2-ND hybrid nanofluid were measured, experimentally. Methods: Nanofluids were prepared by using a two-step method and with three different (0.5%, 0.75%, and 1%) concentrations. Every concentration had three different SiO2-ND mixtures (50% SiO2...

Preparing and defining of thermal properties of new type hybrid nanofluids are essential to understand the fluidity mechanism of hybrid nanofluids and select suitable nanofluids in terms of application. This research aims to provide an alternative fluid for different applications and complete the new type of nanofluid necessity in the literature th...

This paper presents the air-side performance (ASP) of embedded and welded spiral fin and tube heat exchangers (SFTHXs). Six heat exchangers were tested to investigate the effect of fin-base connections and fin pitch. Test sections were fabricated from steel tubes, with two rows of tubing and a Z-shaped water flow arrangement, and an aluminum fin wi...

This paper presents a review on heat transfer coefficient and pressure drop during condensation and boiling in helically coiled tubes. The geometric parameters such as coil diameter, coil pitch and operating parameters containing saturation temperature, system pressure, mass flux, heat flux and vapor quality have significant effects on the heat tra...

In this study, a brief review of the studies in the literature conducted for boiling in double-pipe heat exchangers at horizontal, vertical and different angles of inclination is presented. There are lots of studies in the literature for optimum heat transfer performance in double-pipe heat exchangers. Although there are many theoretical and experi...

The performance of crimped spiral fin-and-tube heat exchangers (CSFTHXs) with a small tube diameter at a Reynolds number of 1500-6400 based on the tube's outer diameter is experimentally investigated. An important factor in this study is the small-diameter tubing, with an outer diameter of 9.53 mm. Copper tubes and aluminum fins are assembled as CS...

Hydronic radiant heating systems are widely being run particularly in association with low temperature heat sources. These thermal units are capable of providing high energy saving potential as well as improvement in thermal comfort. Thus, focus on such systems have considerably ascended recently. In this context, augmentation methods have been emp...

Flow behavior and heat transfer characteristics of air flow inside the plate pin fin heat sinks (PPFHS) are presented. The effects of pin fin shape, pin fin orientation, and ratio of distance between pin and plate fin center to pin fin size (S/Dp or S/Wp) on the flow pattern and heat transfer coefficient (HTC), pressure drop (ΔP) and thermal perfor...

This study analyzes six different refrigerants with different characteristics using the same rooftop air conditioner considering the environmental effects unlike other studies. All evaluations are drafted in two different scenarios, thanks to the equal refrigerant charge amount and equal energy consumption to make the performance review more accura...

Analytical solutions may not always be applicable in the calculation of the turbulent flow convective heat transfer rate, unlike the radiative and the conductive ones. Therefore, experimental correlations on convective heat transfer coefficient have been developed in enclosures. Convective heat transfer in a cavity is classified as natural, forced,...

An investigation was experimentally performed to explore the influence of geometrical parameters on the evaporative heat transfer coefficient and pressure drop of R-134a in dimpled tubes. The test sections were the counter-flow tube-in-tube heat exchanger, where the refrigerant was evaporated in the inner tube and hot water flows in the annulus. Se...

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...

This paper presents a comprehensive review of research works on condensation and boiling heat transfer characteristics in horizontal, vertical and inclined tubes both smooth and enhanced. Although there are many studies examining two-phase flows inside tubes, it is almost impossible to find such a comprehensive study for two-phase flow in tubes. Mo...

This study examined a room with a surface of 1.8 × 1.8 × 2.85 (m) and a well-insulated floor (adiabatic condition) and examined the heat exchange from the side surfaces and ceiling. In this closed room, the heat transfer effects with radiation were investigated while bringing them to comfort conditions ranging from 30 (°C) air temperature to 20–24...

Radiant heating/cooling systems are being popular thanks to their ability of regulating the living-environment with the use of low temperature heating and high temperature cooling. In this work, an artificial neural network investigation is carried out to predict heat transfer characteristics over a heated radiant ceiling. Experimental tests consis...

Current environmental concerns on nitrogen oxides (NOx) and particulate matter (PM) emissions caused by diesel engines have led researchers to be interested in investigating vehicles with alternative power sources. Because of this reason, vehicle models with SI engine were adopted in the conducted study. Firstly, as an initial step, 1-D SI engine m...

A small plate heat exchanger filled with copper foam which can be applied for small scale electronic cooling is presented. The heat transfer coefficient and pressure drop of water flow inside a plate heat exchanger filled with copper foam (PHECF) are experimentally studied. The effect of copper foam pore density and water velocity on the optimum th...

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 1100...

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...

New experimental data were presented on the effect of heat exchanger plate surface roughness, mass flux, average quality, heat flux, and temperature on the evaporative heat transfer coefficient (HTC) and frictional pressure gradient (FPG) of R-134 flowing in a plate heat exchanger (PHE). Three different plate surface roughness of 0.594 μm, 1.816 μm...

The affiliation of the sixth author

The air side thermal performance of wavy fins with rectangular winglets are studied using experimental and numerical methods. The following parameters are selected for investigation: the attack angle, placed location, span and length of the rectangular winglet. The results show that all parameters affect the thermal performance of the air side. The...

In this study, heat transfer characteristics pertaining to a heated radiant floor are investigated experimentally. In order to achieve this aim, experiments have been conducted within extended supply water temperature ranging from 30 oC to 55 oC, and mass flow rate ranging from 0.056 kg/s to 0.125 kg/s according to experimental condition ranges in...

We report the experimental investigations of two-phase flow boiling heat transfer characteristics of a refrigerant in a microfluidic channel at a high mass flux (more than 1000 kg/m² s). We investigate the heat transfer coefficients at a heat flux range of 7.63 kW/m²–49.46 kW/m², mass flux range of 600 kg/m² s–1400 kg/m² s (high mass flux), and sat...

Professor Somchai Wongwises is one of the well-known names in the fields of two-phase flow, and heat transfer enhancement. Professor Somchai Wongwises was born on the 3rd October 1959 in Bangkok, Thailand. He received his B.Sc. in Bachelor of Engineering (with honors) in Mechanical Engineering, Faculty of Engineering, King Mongkut’s University of T...

The heat transfer and pressure drop characteristics of SiO2/water nanofluids flowing through a horizontal circular stainless steel tube equipped with free rotating swirl generators (FRSGs) at the entrance of a test tube are reported in this article. The experimental studies were performed with a Reynolds number ranging from 3500 to 13,000; volume c...

The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost. Increasing fin dimensions increases the annulus hydraulic diameters. Even though the total volume of the heat exchanger remains unchanged between the finned and bare designs, the heat duty increases...

In this study, convective heat transfer performance of a nanofluids containing graphite is studied in an industrial microchannel. In the experiments, initially, to prepare nanofluids at the volume fraction values of 0.5, 1, 1.5, 2%, distilled water has been employed as the base liquid. To provide sedimentation and stabilization of nanofluids in dis...

The heat transfer and pressure drop characteristics of R-134a during evaporation in smooth and dimpled tubes are experimentally examined. All test sections used in this study are double-tube heat exchangers, where the hot water in an annulus transfers its heat to R-134a in the inner tube. The experiments are conducted in a mass flux range of 300–50...

Background Researchers working in the field of nanofluid have done many studies on the thermophysical properties of nanofluids. Among these studies, the number of studies on specific heat are rather limited. In the study of the heat transfer performance of nanofluids, it is necessary to increase the number of specific heat studies, whose subject is...