Man Yeong Ha

• Pusan National University

Bubble-induced turbulence and mixing has been identified as a prominent passive approach in enhancing heat and mass transfer associated with engineering applications. This study numerically analyzes buoyancy-driven interactions between initially eccentric bubble pairs in a quiescent liquid column. The effects of fluid parameters and initial eccentr...

The tundish plays a crucial role in the production of high-quality steel by removing impurities and preventing defects caused by inclusions during the continuous-casting process. Thus, one approach to enhancing the product quality is to increase the residence time of molten steel inside the tundish. In this study, a 1:6 scale water model was used t...

The decrease in ejector efficiency under off-design conditions poses a significant challenge in ejector design. This study proposes a novel approach incorporating aerodynamic cavities into the mixing chamber of a supersonic ejector to enhance its performance, particularly under high back pressure conditions. A numerical parametric study was perform...

Lattice frame materials (LFMs) are considered potential candidates for developing multifunctional heat exchangers/sinks owing to superior strength-to-weight ratios and excellent structural characteristics compared with stochastic open-cellular metal foams. This research numerically studied the flow and heat transfer characteristics of fluid passing...

This work presents the development and validation of a rapid prediction tool for the pseudo steady-state (PSS) temperature of bottom-heated pulsating heat pipes (PHPs). Based on known mass flow rates and intake circumstances, the tool uses lumped parameter modeling to balance heat flows across the coolant, condenser, evaporator, and fluid flow side...

In the present work, laminar flow over one-dimensional bi-textured thin plates is numerically studied, focusing on the skin friction coefficient and its role in drag reduction for bio-mimetic, energy-efficient surfaces. Using the Finite Volume Method, the methodology is benchmarked against the Blasius solution and analyzes flow over anisotropic pat...

This paper for the first time conducted numerical simulations for the mixed convective flow and heat transfer with a viscoelastic fluid within a square enclosure containing a rotating cylinder. The flow regime was considered laminar, two-dimensional, and transient, and the Phan-Thien-Tanner (PTT) model, recognized as one of the most accurate nonlin...

A higher turbine inlet temperature is crucial for enhancing efficiency in gas turbines. However, this increase can reduce the lifetime of turbine blades due to thermal deformation in the solid material. To address this challenge, this study numerically explores the use of lattice-structured ribs within the internal cooling channels of gas turbine b...

The determination of flow-induced equilibrium positions in pressure-driven flows in microchannels is of great practical importance in particle manipulation. In the computational analysis presented in this paper, the inertial ordering of neutrally buoyant rigid spheres in shear-thinning fluid flow through a hydrophobic microchannel is investigated....

With the current advancements in artificial intelligence and machine learning, data has become a powerful tool for major improvements in various fields. In the field of aerodynamic design, most algorithms utilize an iterative method to reach their target function or geometry due to their robustness. Deep learning models enable us to exploit the dat...

This study proposes a numerical model of the cake-baking process, including its heat and mass transfer processes and the phase change process of water, using the enthalpy-porosity method. The specific heat and thermal conductivity of the cake dough were measured as functions of temperature using a differential scanning calorimeter and the hot plate...

A well-ventilated room is essential to reduce the risk of airborne transmission. As such, the scientific community sets minimum limits on ventilation with the idea that increased ventilation reduces pathogen concentration and thus reduces the risk of transmission. In contrast, the upper limit on ventilation is usually determined by human comfort an...

This study conducted molecular dynamics simulations to estimate the behavior of water and oil droplets on the same surface and to investigate how oil droplets respond to varying surface conditions. The surfaces were considered from a flat plate to pillared surfaces with varying heights. Additionally, three surface conditions were examined by alteri...

The geometric shape of an ejector’s walls plays an important role in the efficiency of the ejector. Depending on the outlet-to-throat area ratio of the primary nozzle, the flow exiting the primary nozzle of a supersonic ejector is categorized as under-expanded, isentropic, or over-expanded. Due to differences in the flow structures exiting the prim...

This study presents a comprehensive 2D numerical investigation into the heat transfer mechanisms and melting time estimation for a phase change material melting process in latent heat thermal energy storage systems. The energy storage system of interest employs an elliptic tube configuration within a cylindrical shell. This study primarily aims to...

This paper presents an upgrade to the Elastic Surface Algorithm (ESA), an iterative inverse design method for external flows, to accommodate variable angle of attack during the inverse design of 2D airfoils. The developed method was validated through the inverse design of NACA0012 and FX63-137 airfoils operating within the viscous flow regime. The...

A decrease in the computational cost of inverse design methods, especially in more complex flows and geometries, has been interested by many researchers. On the other hand, the determination of the target pressure distribution and its accuracy and optimality has always been a questionable spot in inverse design algorithms. In this work, the data ge...

Helmholtz Resonators are extensively used in various engineering applications to control acoustic phenomena, but their impact on gas mixing has not been studied yet. In this research, numerical flow simulations within a channel in the presence of Helmholtz resonators were conducted to model the gas mixing process inside the channel and investigate...

In this numerical investigation, the inertial migration of neutrally buoyant, rigid spherical particles in a shear-thinning fluid flow is examined. The pressure-driven non-Newtonian (power-law) fluid passes through a hydrophobic microchannel and the combined effect of viscosity index and fluid slippage on lateral focusing is studied in detail. The...

In a fluidic medium, ascending bubbles display complex interactions with surrounding media, including the formation of minor vortices at their trailing ends. This study aims to elucidate the effects of initial conditions on the likelihood of bubble coalescence in a still water column, particularly under off-center conditions. Utilizing the Finite V...

This study numerically investigated the ultrafine particle collection characteristics in the two-stage electrostatic precipitator with the dielectric plate according to the shape of the dielectric separator and air inlet velocity. This study developed a multi-physics model which analyzes the electrostatic characteristics and particle motion of the...

Flow and heat transfer problems in non-Newtonian fluids are considerably more complicated compared to Newtonian fluids due to their non-linear behavior and complex properties. This paper numerically studied the flow and heat transfer of a viscoelastic fluid around a hot rotating cylinder in a square enclosure. The Phan-Thien–Tanner (PTT) model, one...

We conducted numerical simulations to investigate the influence of the horizontal fin arrangement on the thermal performance of a phase change material (PCM)-filled heat sink. Six horizontal fin positions were considered to compare and analyze heat transfer features and variations in the base temperature of the heat sink. The enthalpy–porosity meth...

In this study, an artificial neural network (ANN) model was applied to predict the thermo-hydraulic performance of the offset-strip fin heat exchanger. The ANN model was used for predicting the thermo-hydraulic performance to improve the prediction accuracy and extend the applicable range compared to the results of using the empirical equations rep...

In this study, the unknown boundary heat fluxes in a square enclosure containing a cylinder were estimated by an inverse technique. A series of computations was conducted for the two-dimensional, steady-state, and buoyancy-driven heat transfer in a square section containing a cylinder with variable heat fluxes and at a Rayleigh number (Ra) of 106 a...

A numerical study estimated the mixed convection around a sinusoidal cylinder inside a rectangular cavity. The key parameters for sinusoidal circular cylinders were the wavelength and Reynolds number (Re = 100, 500, and 1000) with a fixed Prandtl number of 0.7. The flow regimes were greatly affected by these parameters. The unsteadiness of the flow...

The unique thermal properties and flexible design of pulsating heat pipes (PHP) offer opportunities for relatively lightweight, low-cost, and reliable phase-change thermal solutions. Nevertheless, the performance of PHP is affected by multiple factors making mathematical predictions of their performance difficult. So, costly experiments in restrict...

Few studies have considered using artificial neural networks to predict the temperature distribution inside a room with a heat source, even though such an approach is potentially much faster than numerical analysis. In this study, a multilayer perceptron (MLP) model was developed and applied to predicting the temperature distribution in a room with...

Owing to the spread of COVID-19, the need for an inspection center that can quickly determine whether travelers using the airport are infected has emerged. For rapid determination, not only polymerase chain reaction tests but also antigen–antibody tests and on-site analysis systems are required. However, because it is time- and cost-intensive to co...

The Cooled Cooling Air (CCA) heat exchanger is a precooler that cools the bleed air from the compressor stages and is located inside the bypass duct of the aeroengine. Nonuniform flows enter the core of the heat exchanger because the cold side is the off-take from the fan flow, compromising its aerothermal performance. These aspects has been disreg...

Despite recent advances in the area of industrial electrostatic precipitators (ESPs), their residential use remains uncertain owing to the concern about ozone emissions when the removal efficiency of fine and ultrafine particles is increased. In this study, we propose a comprehensive numerical simulation of a full-scale two-stage ESP equipped with...

A numerical study was carried out to analyze the condensation phenomena in a vertical channel between two flat plates. To solve the three-dimensional governing equations including conservation of the mass, momentum, and energy, the Volume of Fluid model was adopted. For the phase change phenomena, the Lee model was used. The tuning for the model pa...

The thermal and flow characteristics of carboxymethyl cellulose (CMC) were investigated by experimental and numerical means, in order to assess the shear-thinning behaviour of a non-Newtonian fluid inside a differentially heated square cavity. A novel particle image velocimetry technique was used to analyse natural convective flow in a non-Newtonia...

The present study reports the numerical investigation on the flow characteristics and heat transfer enhancement of the rib-dimpled channels. Two geometric variables were considered: the rib angle, θ, and the length between the rib center and the dimple rim, l. Nine cases were investigated by combining three different rib angles with three different...

In a numerical investigation of the thermal energy storage performance of a latent heat thermal energy storage system with three angled fins, the enthalpy-porosity model was used to simulate the phase-change process. To analyze the effect of the angle of inclination of the fin (θf) on the heat transfer characteristics and energy storage performance...

For a reliable design of a thermal system with oil, which shows drastic change of material properties under low temperature condition, an improved prediction model is necessary because conventional correlations have limited applicability. In this paper, a numerical study on a single and concentric pipes was conducted with i) hydrodynamically fully...

Micro-channel heat exchangers are widely used due to their superior performance compared to the existing fin and tube heat exchangers, but are limited to condensers due to refrigerant non-uniformity problems in evaporator operating conditions. Although many studies have been made to solve the refrigerant non-uniformity of the microchannel heat exch...

The inherent two-phase heat transport of heat pipes (HPs) is progressively being examined for potential uses. These thermal devices are affected by many operating factors, prompting this study to investigate the effects of different types of wicks and working conditions on the time-dependent thermal behavior. Primarily, the effects of different wic...

Recently, many studies have examined conventional heat pipes (CHP) for thermal solutions with higher dissipation rates and improved thermal management. However, several previous studies considered CHP with constant geometrical ratios. Therefore, this study experimentally investigated the time-based transient behaviors of sintered-based CHP with var...

The effect of variations in the aspect ratio (AR) of an inner cylinder on 3D mixed convection is examined by numerical means. Three Reynolds numbers are considered, Re = 100, 500, and 1000, with a fixed Grashof number of 10⁵ and a Prandtl number of 0.7. The flow patterns formed inside the enclosure are categorized as spanwise, streamwise, and clock...

The present study investigates the flow and thermal fields of Rayleigh-Bénard convection (RBC) in a rectangular channel with an internal circular cylinder. The parameters considered are Rayleigh number (10⁴≤Ra≤10⁶), Prandtl number (Pr = 0.7), and irreversibility distribution ratio (φ = 1). The vertical distance (δ) in the range of -0.2 ≤ δ ≤ 0.2 is...

The investigations on natural convection in enclosures filled with non-Newtonian fluids are of great importance due to many engineering and industrial applications. The flow and heat transfer characteristics of such phenomenon are not fully investigated in both shear-thickening and shear-thinning regimes. The applications of natural convection are...

Numerical simulations were conducted to study the flow and heat transfer characteristics of the dimpled channel with a protrusion. The protrusion was located upstream of the dimple to enhance the flow mixing inside the dimpled channel. The height of the protrusion, h, and the diameter of the protrusion, d, are the variables considered in the presen...

This study numerically investigated the melting phenomena of a phase change material (PCM) in a latent heat thermal storage system with a finned elliptical inner cylinder. The enthalpy–porosity model was used to simulate the phase change process of the PCM. A parametric study was performed by varying the length of the fin in the range of 5, 6.5, an...

A numerical investigation of a design modification of a two-dimensional supersonic gas ejector was undertaken via an adjoint method, with a focus on enhancing the performance of the ejector. Maximization of the secondary mass flow rate was used as an objective function. The entrance geometry and throat height of the primary nozzle were fixed, but t...

The objective of present study is to carry out an unsteady numerical analysis to investigate the buoyancy-driven flows in a square enclosure containing an inner circular cylinder. The square enclosure is filled with dilatant fluids commonly known as shear thickening fluids. The inner circular cylinder is placed at the center of the square enclosure...

Temperature and pressure ratios in gas turbines have grown over time to increase the performance and efficiency of the engine. This, in turn, has required improvements to the effectiveness of the secondary air system to enhance the cooling performance of critical components. Analysis of pressure losses in the secondary systems of aero gas turbines...

Natural and mixed convections around heat sinks with inclined-pin fins had been studied for various design parameters, showing that careful trade-off studies were necessary depending on operating conditions. Previous studies, however, assumed heat sinks in an open space or limited channel heights. In this study, the mixed convection around inclined...

An improved internal structure of a liquid-cooled heat sink has been proposed numerically and experimentally. The initial motivation is based on the results of thermal and fluid-flow topology optimization, which tends to produce a porous region despite suppression through the numerical scheme. The topology optimization was conducted using a Finite-...

The fuel-cooled oil cooler (FCOC) in the lubrication circuit plays a critical role in the aero gas-turbine engine's aerothermal management. However, the low temperature of the operating environment can congeal the oil and reduce the FCOC efficiency. The oil bypass valve (OBV) installed on the FCOC prevents pressure loss. Its failure may cause overh...

This study carried out a three-dimensional, unsteady, numerical simulation to investigate the effects of the cylinder radius, Reynolds number, three-dimensionality and unsteadiness on the mixed convection in a rectangular enclosure containing a cold circular cylinder. The variations in the cylinder radius in the range of 0.1 to 0.3 times the length...

A three-dimensional direct simulation was carried out to examine the natural convective fluid flow and heat transfer characteristics in a long enclosure with a twisted cylinder. The effects of the Rayleigh number, dimensionless mean radius, and wavelength (or wavenumber) for a twisted cylinder were investigated. In addition to the heat transfer cha...

The electrostatic precipitator has been widely utilized to control particulate pollutants in industry. It is important to optimize the configurations of the discharge and collecting electrode in order to increase the efficiency of electrostatic precipitators. The purpose of this paper is to investigate the influence of wavy collecting plates in a s...

Pulsating heat pipes (PHPs) are multiphase devices with relatively well known properties. Like other heat pipes, PHPs provide high heat transfer rates over long distances due to the fluid phase changes that take place within them. Several studies focused on improving our understanding of the processes driving PHPs, but limited advances have been ma...

Given the highly complex thermo-hydrodynamic features in heat pipes (HPs) but the inevitable need for efficient thermal solutions, this study investigated the effects of various wick types on the time-dependent thermal behavior of HPs. The results revealed that varying the cooling conditions and wick types in parallel is necessary for peak performa...

The thermal and flow characteristics at Ra = 107 were evaluated in a square cavity containing a circular cylinder in different places along the diagonal and horizontal center-lines. The enclosure contained non-Newtonian fluids of pseudoplastic and dilatant natures. The power-law index was varied in the range of 0.6–1.6 with an interval of 0.2 and a...

A numerical simulation was carried out to investigate the cooling performance and thermal comfort of a 4-way cassette air conditioner when its vanes are positioned at constant angles of 30°, 40°, 50° and 60° and swinging with a constant angular velocity. The indoor airflow characteristics and thermal comfort were evaluated. The average room tempera...

Here, a distinct procedure was adopted to optimize the shape of the NACA 0012 airfoil profile for Reynolds number, Mach number, and angle of attack equal to 2e6, 0.15, and 10.24 deg, respectively. The airfoil shape was appropriately parameterized, and mesh morphing tools were used to bypass the remeshing process. Computational fluid dynamic (CFD) s...

To maintain efficiency in advanced aero-engines, it is crucial to set high limits for the Operating Pressure Ratio (OPR) and Turbine Entry temperature (TET). This can be achieved using a Cooled Cooling Air (CCA) heat exchanger, which precools the compressed air with the bypass stream before the compressed air enters the turbine to cool the blades....

Experimental and numerical investigations were performed to improve the temperature uniformity in a top-freezer refrigerator system with an evaporator and a multi-duct system. In order to accurately predict the temperature uniformity as well as the distribution of the complex flow and temperature fields in the whole top-freezer refrigerator system,...

In the present study, an improved heat exchanger model is proposed to efficiently analyze the cold oil removal process inside a fuel-cooled oil cooler. When exposed to low temperature condition, oil within a heat exchanger begins to congeal, preventing oil flow and causing loss of cooling. The conventional heat exchanger models, however, shows limi...

Heat pipes, HP, are phase change devices with high conductivities compared to existing technologies of the same dimensions. However, for HP with multi-layer wicks, the layers and location of the dense wicks significantly affect the thermo-fluidics of the device. The influence of these factors on the overall performance of HP is presented for a stan...

The present study investigated the dynamic behavior of a nanosized water droplet on a flat and stepped surface using molecular dynamics simulations. The effects of a wetting gradient associated with the surface and the step height of a stepped surface on the dynamic behavior of the water droplet were considered in this study. The dynamic behaviors...

A Pulsating Heat Pipe (PHP) is a specific type of heat pipe that does not require a wick or other porous medium. The operations are achieved through a mix of capillary action and local force instabilities, which drive the mixed phase flow along the serpentine body. The main method for evaluating and analyzing PHP has been, until recently, experimen...

Fuel Cooled Oil Coolers, FCOC, may fail to provide enough lubrication cooling due to the congealing of oil in the FCOC at low-temperatures. An experimental study was carried out at design/off-design conditions: � To understand the transient decongealing process of the aero FCOC � To investigate the impact of normal and failed bypass valve, BV, on t...

Fuel Cooled Oil Coolers, FCOC, may fail to provide enough lubrication cooling due to the congealing of oil in the FCOC at low-temperatures. An experimental study was carried out at design/off-design conditions: 1. To understand the transient decongealing process of the aero FCOC 2. To investigate the impact of normal and failed bypass valve, BV, on...

This study numerically investigates the effect of the number and arrangement of tubes on the melting performance of a phase change material (PCM) in a multi-tube shell-and-tube latent heat thermal energy storage (LHTES) system. An enthalpy-porosity model was used to simulate the phase change process. Eight arrangements of tubes were examined. The m...

A finite-volume-based topology optimization procedure for application to problems in aero-thermal systems has been studied. A simplified sensitivity analysis procedure was proposed and examined by neglecting the exact adjoint approach. Two types of conventional interpolation schemes for inverse porosity with a penalized polynomial form and its grad...

Aviation faces several challenges to maintain growth while adapting to an environmentally viable footprint. Increasing efficiency, which in the past induced a steady rise in the turbine entry temperatures, requires successful cooling of critical components to relieve the combined effects of higher temperatures and pressures. Starting with a concept...

The mixed-convective heat transfer of slanted-pin fins on an inclined hot surface was studied numerically under the laminar flow condition. The computational model was constructed using the periodic boundary conditions in the lateral direction of fins. Adopting the Boussinesq approximation, the three-dimensional governing equations for fluid flow a...

The Pulsating Heat Pipe (PHP) is a promising device in the family of heat pipes. With no need for a wick, they exhibit a high heat transfer to weight ratio. Moreover, the wickless design removes limits commonly associated with conventional heat pipes, increasing the maximum power transfer per single heat pipe. These peculiarities make it an ideal c...