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九州大学大学院 工学研究院 機械工学部門 熱流体物理研究室 Thermofluid Physics Laboratory
High-pressure hydrogen research facility
(top) High-pressure hydrogen research facility
(bottom-left) Experimental setup
(bottom-right) 100MPa high-pressure vessel

Background: Data of hydrogen measured at high pressures and high temperatures are limited.

Objective: Measure hydrogen at high pressure up to 100MPa and at high temperature up to 500°C
As a part of NEDO project, we believe that this research will play a significant role in the thermophysical properties of hydrogen area in the world.

Conventional hydrofluorocarbon (HFC)-type refrigerants, which are widely used for refrigeration and air-conditioning, have a strong contribution to global warming. Hence, many researchers seek for new refrigerants with almost zero ozone depletion potential (ODP), a small global warming potential (GWP), and low flammability. Although hydrofluoroolefin (HFO)-type refrigerants have recently been proposed as an alternative, most are still flammable.

In our laboratory, we target R1123, R1234yf and R32, which have a lower boiling point among HFC-type refrigerants, and their for the suppression of the flammability and dismutation. Specifically we measure the vapor-liquid equilibrium for these binary/ternary refrigerants with an aim to modify the equation of state for refrigerant mixtures.

This work is carried out as a part of the national project by the New Energy and Industrial Technology Development Organization (NEDO).

Experimental setup Laboratory (I2CNER)
Experimental setup Laboratory (I2CNER)

Steel has been a key material for our daily life and industry over the centuries. The production of high-quality steels with specific characteristics is required for today's diverse applications. Hence, spray cooling used in steel rolling process is paramount to control temperature distribution of the material which realizes the desired properties. Especially, the reduction of the residual stress, which leads to defects of the products such as deformation and cracks, relies on the cooling process with uniform temperature distribution with in the material.

Aim of our work, therefore, is to investigate the influence of spray conditions e.g. flow rate, drop size, surface roughness, wettability etc. on entire cooling process. We have designed experimental apparatus which allows individual parameterization of these factors. We currently attempt to link fundamental processes including wetting and phase change involved in a small droplet impinging onto a hot surface to the cooling performance at the industrial scale.

Experimental apparatus
Experimental apparatus
Nucleate boiling on biphilic surfaces
Nucleate boiling on biphilic surfaces
High-speed imaging
High-speed imaging of bubble behavior
Numerical simulation
Numerical simulation results compared with experimental observations

Boiling, a phenomenon frequently encountered in daily life, plays a critical role in thermal management of a wide range of industrial applications such as fossil fuel/nuclear power plants, electronics cooling, and refrigeration/heat pumps. It is thus of great importance to enhance the efficiency of boiling heat transfer as part of the global endeavor to combat global warming and reduce CO2 emissions. However, due to its extremely complex multiphase and multiscale nature that involves various influences including fluid properties, pressure, surface structure and wettability, boiling heat transfer lacks a complete description. It calls upon us to develop a physically more rigorous understanding of boiling processes, which will inspire next-generation designs of highly efficient boiling surfaces.

In our group, the research focuses on the effect of surface wettability (both hydrophobicity and hydrophilicity) on controlled boiling. Based on a combination of experimental and theoretical approaches, we aim at elucidating the physical mechanisms underlying the evolving boiling behavior at different pressure levels. Moreover, we strive to employ the findings with regard to the fundamental mechanics of boiling heat transfer in real-world applications. For example, work is underway to optimize the evaporator design in a loop heat pipe using wettability-patterned boiling surfaces for greater heat transfer performance.
Our projects are conducted in collaboration with the University of Tokyo and KTH Royal Institute of Technology (Sweden).

Recent publications
Yamada et al., Int. J. Heat Mass Transfer, 115, 753-762 (2017)
He et al., Appl. Therm. Eng., 123, 1245-1254 (2017)
Shen et al., Sci. Rep., 7, 2036 (2017)
Shen et al., Appl. Therm. Eng., 88, 230-236 (2015)
Takata et al., Heat Transfer Eng., 27 (8), 25-30 (2006)
Takata et al., Energy, 30 (2-4), 209-220 (2005)

ESEM observation of condensation
ESEM experimental observations on
micropillared surfaces with different spacing
ESEM video 01ESEM video 02
ESEM experimental observations on
patterned wettability micropillars
Jumping droplets
Coalescence-induced droplet-jumping on
micro- and/or nano-structured surfaces

Condensation phase change is present in many industrial and everyday applications such as air conditioning, refrigeration, electricity generation, and distillation, amongst others. Due to the wide spread presence of condensation, improving its performance can lead to vast energy savings with the consequent reductions in CO2 emissions.

At the Thermofluids Physics Laboratory at Kyushu University we carry out fundamental and basic science aiming for the complete understanding of condensation phase change and fog harvesting phenomena. More specifically we are investigating the effect of wettability and surface structure underneath the condensing droplets during condensation, as well as the presence and absence of non-condensable gases. Micropillared surfaces with different wettabilities (hydrophilic, hydrophobic and patterned wettability), micro- and/or nano-structured superhydrophobic surfaces, and bioinspired surfaces have been characterized and studied by means of Environmental Scanning Electron Microscopy (ESEM), Optical Microscopy and Macroscopic observations.

We are currently collaborating with the Waterloo Institute for Technology (University of Waterloo, Canada), Shanghai Jiao Tong University (China), the University of Illinois at Urbana-Champaign (US), the Indian Institute of Technology Mandi (India), Iowa State University (US), and Mistubishi Heavy Industries, Ltd. (Japan).

Recent publications
Sharma et al., ACS Sustain. Chem. Eng., 6 (5), 6981-6993 (2018)
Lv et al., Int. J. Heat Mass Transf., 115, 725-736 (2017)
Orejon et al., Int. J. Heat Mass Transf., 114, 187-197 (2017)
Zhang et al., ACS Appl. Matter. Interfaces, 9 (40), 35391-35403 (2017)
Zhang et al., Int. J. Heat Mass Transf., 109, 1229-1238 (2017)
Chavan et al., Langmuir, 32 (31), 7774-7787 (2016)
Orejon et al., RSC Advances, 6 (43), 36698-36704 (2016)

Physics of a sessile drop
Phenomena involved in a sessile drop/droplet.
IR images depicting hydrothermal waves
in evaporating ethanol drops.
Marangoni IRMarangoni CCD
Marangoni flows in pure water induced via localized heating

Liquid drops/droplets are ubiquitous and play an important role in sveral industrial applications such as device cooling, inkjet printing, and Lab-on-a-chip to name a few. Wettability, structure and thermal conductivity of the surface, type of fluid as well as the composition of the surroundings have a strong influence on the mass diffusion, heat and mass convection within the drop and on the heat transfer. Hence, the complete understanding of the difference coupling mechanisms taking place during drop/droplet phase change and wetting is paramount for the development and optimization of cooling and inkjet printing devices, amongst others.

Surface wettability, temperature and relative humidity, as well as external forces applied, i.e., laser heating, during the phase change of water and organic fluids have been studied by means of high-speed imaging, drop-shape analysis, and infrared (IR) thermography. We have found such parameters to have a strong influence on the thermal/fluid instabilities, i.e., Hydrothermal Waves (HTWs) and on the heat transfer performance.

Our projects are conducted in collaboration with the University of Maryland, College Park (US) and the University of Edinburgh (UK).

Recent publications
Kita et al., PCCP, 20 (29), 19430-19440 (2018)
Askounis et al., Langmuir, 33 (23), 5666-5674 (2017)
Kita et al., Appl. Phys. Lett., 109 (17), 171602 (2016)
Orejon et al., Langmuir, 32 (23), 5812-5820 (2016)
Fukatani et al., Phys. Rev. E, 93 (4), 043103 (2016)
Orejon et al., Phys. Rev. E, 90 (5), 053012 (2014)
Sefiane et al., Langmuir, 29 (31), 9750-9760 (2013)