Faculty Profiles - Hong, Chungpyo

Papers - Hong, Chungpyo

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Hong C., Asako Y., Morini G.L., Faghri M. . Variations in gas temperature and average velocity during laminar-turbulent transition in high-speed gas flow through microtubes . Experimental Thermal and Fluid Science155 2024.6Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：Experimental Thermal and Fluid Science

The primary objective of this study is to investigate variations in gas temperature and average velocity during the laminar-turbulent transition of compressible flow. This investigation encompasses an exploration of the effect of Mach number on transitional Reynolds number. Experiments were conducted utilizing a pair of adiabatic stainless steel microtubes with a diameter (D) of 131.6 μm. The first microtube was dedicated to measuring local pressure to obtain friction factor, local Mach number, and bulk temperature. The second microtube was employed for measuring local wall temperature. Additionally, a stainless steel microtube with a diameter (D) of 124 μm and a rectangular microchannel with a hydraulic diameter (Dh) of 99.36 μm were incorporated in the study. Friction factor, Mach number, and bulk temperature were determined by measuring mass flow rate and local pressure near the outlet. The measured mass flow rate exhibited a slight increase that plateaued during the laminar-turbulent transition as the Reynolds number increased. In laminar flow, an increase in the Reynolds number resulted in an increase of the Mach number and a reduction in bulk temperature. Conversely, during the laminar-turbulent transition, the Mach number either remained constant or decreased, and the bulk temperature increased due to the conversion of kinetic energy to thermal energy. Experimental validation of this phenomenon was achieved by measuring the wall temperature of an adiabatic microtube.

DOI： 10.1016/j.expthermflusci.2024.111196

Scopus

Asako Y., Hong C., Tan L.K., Faghri M. . Performance evaluation criteria based on the first and second laws of thermodynamics . International Communications in Heat and Mass Transfer154 2024.5Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：International Communications in Heat and Mass Transfer

Numerical simulations were conducted to investigate the correlation between assessments based on the total entropy generation rate criterion and the thermal resistance criterion in the context of evaluating heat transfer performance. This study focused on a parallel plate channel heat sink with the lower wall subjected to a constant heat flux, under various flow constraints. The flow was assumed to be laminar and fully developed. The energy equation was discretized using the control volume-based power law scheme, and the resulting algebraic equations were solved by the line-by-line method. Optimal channel heights which lead to minimize irreversibility and temperature difference between heated wall and inlet fluid temperatures were determined by both the total entropy generation rate and thermal resistance criteria under four distinct flow constraints: identical mass flow rate, identical inlet velocity, identical pumping power, and identical pressure drop. The investigation revealed a lack of significant correlation between the optimal channel heights derived from assessments based on the total entropy generation rate and thermal resistance. Consequently, the utilization of the total entropy generation rate criterion for evaluating heat transfer performance, based in the second law of thermodynamics, instead of the thermal resistance criterion, based in the first law of thermodynamics, was deemed inappropriate. The total entropy generation rate criterion was based on the minimization of the irreversibility and served as an indicator of heat transfer quality. As a recommendation, it is suggested that results obtained from both the total entropy generation rate and thermal resistance criteria for assessing heat transfer performance be presented separately for each specific application.

DOI： 10.1016/j.icheatmasstransfer.2024.107437

Scopus

Asako Y., Hong C., Yamaguchi Y., Faghri M., Tan L.K., Sidik N.A.C. . Physically Realistic Inlet-Velocity Profiles in Duct Flows . Heat Transfer Engineering 2024Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：Heat Transfer Engineering

A uniform inlet velocity profile is widely used in the numerical simulations of fluid flow and heat transfer in ducts for both incompressible and compressible flows. In incompressible flows, the calculated fluid pressure at the inlet edge is extremely high and affects the calculation of the average pressure. In compressible flows, the fluctuation of pressure in the flow direction results in the fluctuation in the velocity. This has motivated this study to numerically investigate a physically realistic velocity profile at the inlet of a pipe rather than using a uniform velocity profile. The numerical simulations were based on the control volume-based power law scheme and the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The continuity and momentum equations for a flow in a pipe with the rounded inlet corner were solved to obtain a physically realistic inlet velocity profile. The obtained inlet velocity profile was expressed by a simple expression in the range of Reynolds number from 100 to 2000. Using this velocity profile, both the incompressible and compressible flows in a pipe were numerically investigated. The results resolved the previously observed inconsistencies in the pressure that were previously observed in the numerical simulations with uniform inlet velocity profiles.

DOI： 10.1080/01457632.2024.2308355

Scopus

Hong C., Katanoda H., Asako Y., Faghri M. . Temperature recovery factor for gaseous nitrogen flow in a microtube . International Journal of Heat and Mass Transfer202 2023.3Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Heat and Mass Transfer

For gas flow over a flat plate, the temperature recovery factor is defined as a fraction of free-stream total temperature rise recovered at the wall or is the ratio of the actual temperature rise at the wall to the maximum possible temperature rise in the free-stream. Its value depends on Prandtl number and is independent of Mach number. The gas velocity and temperature are determined by the temperature recovery factor using the adiabatic wall temperature. It is an important parameter to be used to evaluate the gas velocity and temperature indirectly. In the present study, for internal flow, a methodology was introduced to estimate the temperature recovery factor numerically based on the total and bulk temperature for both laminar and turbulent flow regions in a microtube. The numerical simulations are based on the arbitrary Lagrangian-Eulerian method. The compressible momentum and energy equations for an ideal gas were solved to obtain the temperature recovery factor. To further validate the temperature recovery factor from numerical results, experiments were conducted using stainless steel microtubes. Although it is not a direct comparison, the gas bulk temperature and Mach number that were determined by the temperature recovery factor were compared with the experimental results and they were in good agreement.

DOI： 10.1016/j.ijheatmasstransfer.2022.123688

Scopus

Mohd Tamam M.Q., Omi M.R.T., Yahya W.J., Ithnin A.M., Abdul Rahman H., Rahman M.M., Abd Kadir H., Noge H., Koga T., Hong C., Otaka T., Kinoshita E. . Engine performance and emissions evaluation of surfactant-free B30 biodiesel–diesel/water emulsion as alternative fuel . Scientific Reports13 ( 1 ) 10599 2023.12Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

Malaysia is one of the top exporters of palm oil, and although currently facing fierce resistance towards palm oil imports in some parts of the globe, one of the ways to utilize this commodity is by increasing palm biodiesel content in local commercial diesel. However, due to the oxygen-rich nature of biodiesel, its utilization suffers from increased nitrogen oxides (NOx) emission compared to conventional diesel. To mitigate this issue and improve diesel engine performance and emissions using biodiesel–diesel blends, this study attempted to investigate implementation of a real-time non-surfactant emulsion fuel supply system (RTES) which produces water-in-diesel emulsion as fuel without surfactants. NOx reducing capability of water-in-diesel produced by RTES has been well documented. Therefore, in this study, 30% biodiesel–diesel (B30) was used as the base fuel while B30-derived emulsions consisting of 10 wt%, 15 wt% and 20 wt% water content were supplied into a 100 kVA, 5.9-L common rail turbocharged diesel engine electric generator. Fuel consumption and exhaust emissions were measured and compared with commercially available Malaysian low grade diesel fuel (D2M). Evidence suggested that emulsified B30 biodiesel–diesel produced by RTES was able to increase brake thermal efficiency (BTE) up to a maximum of 36% and reduce brake specific fuel consumption (BSFC) up to 8.70%. Furthermore, B30 biodiesel–diesel emulsions produced significantly less NOx, carbon monoxide and smoke at high engine load. In conclusion, B30 biodiesel–diesel emulsions can be readily utilized in current diesel engines without compromising on performance and emissions.

DOI： 10.1038/s41598-023-37662-4

Scopus

PubMed

Abdul Rahman H., Rahman M.M., Yahya W.J., Kaonain T.E., Abd Kadir H., Tamam M.Q.M., Ithnin A.M., Ahmad F., Abdullah M.F.E., Noge H., Hong C., Otaka T., Kinoshita E. . Implementation of a Non-Surfactant Water-in-Diesel Emulsion Fuel in a Common Rail Direct Injection Diesel Vehicle . International Journal of Automotive Technology24 ( 5 ) 1349 - 1358 2023.10Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Automotive Technology

Water-in-diesel emulsion fuel has become a popular alternative fuel for diesel engines. The main limitation is related to its stability, whereby it relies heavily on surfactants to remain homogeneous, therefore causing production costs to rise. This paper highlights the application of real-time non-surfactant emulsion fuel supply system (RTES), a water/diesel emulsifying device without surfactants, to produce water-in-diesel emulsion fuel in a common rail direct injection diesel engine powered vehicle. In this study, RTES was installed near to the diesel fuel pump to ensure water-in-diesel emulsions were continuously fed to the engine. The test vehicle was set up on a roller dynamometer and operated following a modified West Virginia University (WVU) 5-Peak cycle. Fuel consumption and exhaust emissions were measured to determine the optimum water percentage of emulsion fuel and suitable timing for emulsion fuel to be introduced into the fuelling system based on the vehicle speed. The results revealed that the optimum water percentage of the emulsion fuel for the test vehicle is 10 wt%, as it was capable to reduce fuel consumption as well as nitrogen oxides and smoke emissions of a common rail direct injection diesel engine powered vehicle.

DOI： 10.1007/s12239-023-0109-3

Scopus

Lam B.C., Asako Y., Hong C., Tan L.K., Sidik N.A.C. . Validity of Performance Factors used in Recent Studies on Heat Transfer Enhancement by Surface Modification or Insert Devices: Constant Heat Flux Case . Journal of Advanced Research in Numerical Heat Transfer11 ( 1 ) 1 - 4 2022.9Reviewed International coauthorship International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Advanced Research in Numerical Heat Transfer

Heat transfer enhancement had been widely applied in developing a more compact heat exchanger which can save a lot of energies, materials and costs. Based on our literature review, the performance factors that proposed previously had been widely used in various papers to evaluate the heat transfer enhancement. However, no validation had been conducted before to validate the performance factors. Recently, the performance factors had been studied for the heat transfer enhancement of a circular duct with periodic annular baffle plates which is heated by constant wall temperature, and the result shown that the performance factors are not valid for evaluating the heat transfer. Whereas this study is examined the validity of the performance factors by comparing the heat transfer rate in a fully periodic developed region of a circular duct to a modifies duct with periodic annular baffle plates, which are heated by constant heat flux. The heat transfer rates are obtained numerically. Validity of the performance factors is examined by comparing the average temperature difference between wall temperature and bulk temperature. It was found that the performance factors used in previous papers except for equation (2) defined below are not valid to evaluate the heat transfer enhancement.

Scopus

Yusof S.N.A. . Validity of performance factors used in recent studies on heat transfer enhancement by surface modification or insert devices . International Journal of Heat and Mass Transfer186 2022.5Reviewed International coauthorship International journal

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Journal of Heat and Mass Transfer

Based on literature survey, the performance factors were used in 62 articles which have been published in 2021 in International Journal of Heat and Mass Transfer, International communications in Heat and Mass Transfer, International Journal of Thermal Sciences and Applied Thermal Engineering, to evaluate the heat transfer enhancement by geometry modification or insertion of tapes, wires or turbulence promoters under identical pumping power. However, the validity of the performance factors was not examined yet. The heat transfer rate in a periodic fully developed region of a circular duct with periodic annular baffle plates was numerically obtained. Comparing the heat transfer rate with that of a circular smooth duct, the validity of the performance factors used in previous studies was examined. It was found that the performance factors used in the previous studies are not valid for the evaluation of heat transfer enhancement. Furthermore, this paper shows that the direct comparison of heat transfer rates without the assumptions of equal surface area and the equal temperature difference is suitable for the evaluation of heat transfer enhancement.

DOI： 10.1016/j.ijheatmasstransfer.2021.122431

Scopus

Hong C. . Heat Transfer of Turbulent Gaseous Flow in Microtubes with Constant Wall Temperature . Journal of Heat Transfer144 ( 4 ) 2022.4Reviewed International coauthorship International journal

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Heat Transfer

In this paper, we report on experimental results to measure the total temperature of nitrogen gas at the inlet and outlet of microtubes with constant wall temperature and to quantitatively determine the heat transfer rates. Experiments were conducted with nitrogen gas flowing in a stainless steel microtube with a diameter of 524 μm and a copper microtube with a diameter of 537 μm. The temperature differences between the inlet and the wall were maintained at 3, 5, and 10 K by circulating water around the inlet and the wall. The stagnation pressures were also controlled so that the flow, with atmospheric back pressure, could reach Reynolds numbers as high as 26,000. To measure the total temperature, a polystyrene tube with a thermally insulated exterior wall containing six plastic baffles was attached to the outlet. Heat transfer rates were obtained from the gas enthalpy difference by using the pressures and the total temperatures measured at the inlet and outlet. Heat transfer rates were also compared with those obtained from the ideal gas enthalpy using the measured total temperatures and from the Nusselt number of incompressible flows. It was found that the measured total temperature at the microtube outlet was higher than the wall temperature. Also, the heat transfer rates calculated from the total temperature difference were higher than the values obtained from the incompressible flow theory.

DOI： 10.1115/1.4053215

Scopus

D. Rehman, D. Barattini, C. Hong, G. L. Morini . Effect of aspect ratio and inlet manifold shape on the laminar-to-turbulent transition of gas flow in rectangular microchannels . Experiments in Fluids62 ( 52 ) 1 - 19 2021.3Reviewed International coauthorship International journal

TANIGUCHI Tomohiro, YAMASHITA Satoshi, YAMAGUCHI Ryu, HONG Chungpyo, ASAKO Yutaka . Mach number correlation for microchannel gas flow considering temperature decrease . The Proceedings of Conference of Kyushu Branch2021.74 ( 0 ) A16 2021

TANOWAKI Yusuke, KASHIWAGI Ryo, HONG Chungpyo, ASAKO Yutaka . Prediction of flow characteristics for micro-tube gas flow by temperature recovery factor . The Proceedings of Conference of Kyushu Branch2021.74 ( 0 ) B15 2021

SEI Tomoki, KIM Minsung, HONG Chungpyo, ASAKO Yutaka . Local friction factors of microchannel gas flow by means of adiabatic wall temperatures . The Proceedings of Conference of Kyushu Branch2021.74 ( 0 ) B14 2021

D. Kang, C. Hong, D. Rehman, G. L. Morini, Y. Asako, M. Faghri . Average Friction Factors of Choked Gas Flow in Microtubes . Journal of Physics: Conference Series1599 ( 1 ) 1 - 9 2020.9Reviewed International coauthorship

R. Kashiwagi, C. Hong, Y. Asako, G. L. Morini, M. Faghri . Identification of Gas Flow Regimes in Adiabatic Microtubes by means of Wall Temperature Measurements . Journal of Physics: Conference Series1599 ( 1 ) 1 - 8 2020.9Reviewed International coauthorship

C. Hong, T. Shigeishi, Y. Asako, M. Faghri . Experimental investigations of local friction factors of laminar and turbulent gas flows in smooth micro-tubes . International Journal of Heat and Mass Transfer158 1 - 9 2020.9Reviewed International coauthorship

C. Hong, Y. Asako, M. Faghri, D. Rehman, G. L. Morini . Experiments on measurement of heat transfer rate of gas flow through microchannel with constant wall temperature . Journal of Advanced Research in Fluid Mechanics and Thermal Sciences70 ( 1 ) 28 - 36 2020.6Reviewed International coauthorship

Chungpyo Hong, Yutaka Asako, Mohammad Faghri, Gian Luca Morini . Average Friction Factor for Laminar Gas Flow in Microtubes . CFD Letters12 ( 3 ) 22 - 30 2020.3Reviewed

C. Hong, Y. Asako, M. Faghri, D. Rehman, G. L. Morini . Experiments on Measurement of Heat Transfer Rate Of Gas Flow Through Microchannel With Constant Wall Temperature . Proceedings of the 4th International Symposium on Fluid Mechanics and Thermal Sciences 2019.12Reviewed

R. Yamaguchi, C. Hong, Y. Asako, G. L. Morini . Effects of flow transition on heat transfer of gas flow in micro-tube with constant wall temperature . Proceedings of the International Symposium on Thermal Effects in Gas flows In Microscale 2019.10Reviewed

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Papers - Hong, Chungpyo