著者

Shigenao MARUYAMA Takeshi NAGAYAMA Hiroki GONOME Junnosuke OKAJIMA

出版者

The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan

雑誌

Journal of Thermal Science and Technology (ISSN:18805566)

巻号頁・発行日

vol.10, no.2, pp.JTST0022, 2015 (Released:2015-09-02)

参考文献数

38

被引用文献数

2 2

---

Global warming is one of the most serious problems faced by humans. One method to decrease the Earth's temperature is to reduce solar irradiation by dispersing nanoparticles in the atmosphere. Submicron-diameter particles or aerosols scatter solar irradiation, whereas they are transparent to long-wavelength infrared radiation emitted by the Earth. This phenomenon has received attention in the discussions of the nuclear winter, which is an uncontrolled cooling of the global temperature. The objective of the present work is to examine the first-order approximation of the feasibility of controlling the global temperature without reducing the emission of greenhouse gases. We propose the controlled dispersion of nanoparticles into the stratosphere at an altitude of 30 km. A precise analysis of the radiative properties of particles in the solar spectrum and IR regions is conducted, and radiative transfer through the stratosphere-dispersed nanoparticles is approximated using a one-dimensional single-scattering model. Several types of nanoparticles are considered. The optimum size of the nanoparticles determined using the model is 350-450 nm. The dispersion of nanoparticles with a total mass of 3×107 tons into the stratosphere will reduce 3% of the solar irradiation. The blockage can be maintained by launching 10-ton projectiles 19 times per day from 100 launch sites.

著者

Soumyadeep PAUL Wei-Lun HSU Mirco MAGNINI Lachlan R. MASON Yusuke ITO Ya-Lun HO Omar K. MATAR Hirofumi DAIGUJI

出版者

The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan

雑誌

Journal of Thermal Science and Technology (ISSN:18805566)

巻号頁・発行日

vol.16, no.1, pp.JTST0007, 2021 (Released:2021-01-01)

参考文献数

42

被引用文献数

4

---

The increasing demands of computational power have accelerated the development of 3D circuits in the semiconductor industry. To resolve the accompanying thermal issues, two-phase microchannel heat exchangers using have emerged as one of the promising solutions for cooling purposes. However, the direct boiling in microchannels and rapid bubble growth give rise to highly unstable heat flux on the channel walls. In this regard, it is hence desired to control the supply of vapor bubbles for the elimination of the instability. In this research, we investigate a controllable bubble generation technique, which is capable of periodically producing bubble seeds at the sub-micron scale. These nanobubbles were generated in a solid-state nanopore filled with a highly concentrated electrolyte solution. As an external electric field was applied, the localized Joule heating inside the nanopore initiated the homogeneous bubble nucleation. The bubble dynamics was analyzed by measuring the ionic current variation through the nanopore during the bubble nucleation and growth. Meanwhile, we theoretically examined the bubble growth and collapse inside the nanopore by a moving boundary model. In both approaches, we demonstrated that by altering the pore size, the available sensible heat for the bubble growth can be manipulated, thereby offering the controllability of the bubble size. This unique characteristic renders nanopores suitable as a nanobubble emitter for microchannel heat exchangers, paving the way for the next generation microelectronic cooling applications.

著者

Hiroto SHIBUYA Nobuhiro NAGUMO Kio KUMAGAI Atsushi SAKURAI

出版者

The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan

雑誌

Journal of Thermal Science and Technology (ISSN:18805566)

巻号頁・発行日

vol.17, no.2, pp.22-00051, 2022 (Released:2022-05-18)

参考文献数

20

被引用文献数

1

---

Spacecraft use photovoltaics as power-generation systems. Although photovoltaics have advantages such as no requirement of fossil fuel or moving parts, a disadvantage is that generating power without sunlight is impossible. Spacecraft require new power-generation systems that do not depend on sunlight to make power generation possible in deep space where sunlight cannot reach. In this study, a thermoradiative (TR) system was investigated. The TR system generates power by thermal radiation from the TR cells to the surrounding environment. The possibility that the TR system would be most effective in spacecraft for which the surrounding temperature is 3 K was considered. Because the power generation of the TR system depends on the amount of radiation from the TR cells, the ideal state was simulated by assuming that the TR cell emits blackbody radiation to obtain the upper limit of the power generation. Furthermore, the effects of output voltage, cell bandgap, and TR cell temperature on the power generation were investigated numerically by using a HgCdTe photodiode, and the results were compared with those for blackbody radiation.

著者

Alejandro DATAS Daisuke HIRASHIMA Katsunori HANAMURA

出版者

The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan

雑誌

Journal of Thermal Science and Technology (ISSN:18805566)

巻号頁・発行日

vol.8, no.1, pp.91-105, 2013 (Released:2013-03-19)

参考文献数

42

被引用文献数

12 21

---

We present the numerical simulation, using the finite difference time domain (FDTD) method, of the radiative heat transfer between two thin SiC slabs. We aim to explore the ability of the FDTD method to reproduce the analytical results for the Surface Phonon Polariton (SPhP) assisted near field radiative energy transfer between two SiC slabs separated by a nano/micro-metric vacuum gap. In this regard, we describe the key challenges that must be addressed for simulating general near-field radiative energy transfer problems using the FDTD method. FDTD is a powerful technique for simulating the near-field radiative energy transfer because it allows simulating arbitrary shaped nano-structured bodies, like photonic crystals, for which an analytical solution is not readily obtained.

著者

Jingying WANG Pengfei JU Li LEI

出版者

The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan

雑誌

Journal of Thermal Science and Technology (ISSN:18805566)

巻号頁・発行日

vol.14, no.1, pp.JTST0004, 2019 (Released:2019-02-18)

参考文献数

17

被引用文献数

1

---

A two-dimensional finite volume method (FVM) based on structured grids is developed to solve the axisymmetric radiative heat transfer with absorbing, emitting and anisotropically scattering media. The present scheme is not derived by discretizing axisymmetric radiative transfer equation (RTE), but by taking the axisymmetric limit of general 3D radiation FVM, which can save the computation workloads greatly and avoid the singularity of the axisymmetric RTE when r→0. Because of sharing same philosophy and meshes, it has very strong potentials of being coupled with popular computational fluid dynamics (CFD) solvers. This method is also fully validated by three benchmark cases: the cylindrical enclosure, truncated conical enclosure, and rocket nozzle, and performs excellently both in prediction accuracy and geometric flexibility.