Numerical Study on Transient Heat Characteristics of a Rectangular Latent Heat Storage Vessel

Transient characteristics of the rectangular latent heat storage vessel packed with shape-stabilized phase change (solid-liquid) material (PCM) are investigated numerically by solving the governing equations of both the PCM and the heat transfer medium(water) simultaneously as a conjugate problem with the finite difference technique. It's found that the heat storage characteristics are greatly affected by the flow direction of the heat transfer medium since the natural and forced convection coexists in the heat storage vessel. That is, it is classified that the effectively thermal efficiency of the latent heat storage system is obtained by the downflow along vertical PCM for heat storage process and the upflow for heat release process. The effect of the inlet velocity of heat transfer medium(water) on transient heat characteristics of the latent heat storage system is also revealed in the present study

Anatomy of the magnetic catalysis by renormalization-group method

We first examine the scaling argument for a renormalization-group (RG) analysis applied to a system subject to the dimensional reduction in strong magnetic fields, and discuss the fact that a four-Fermi operator of the low-energy excitations is marginal irrespective of the strength of the coupling constant in underlying theories. We then construct a scale-dependent effective four-Fermi interaction as a result of screened photon exchanges at weak coupling, and establish the RG method appropriately including the screening effect, in which the RG evolution from ultraviolet to infrared scales is separated into two stages by the screening-mass scale. Based on a precise agreement between the dynamical mass gaps obtained from the solutions of the RG and Schwinger-Dyson equations, we discuss an equivalence between these two approaches. Focusing on QED and Nambu--Jona-Lasinio model, we clarify how the properties of the interactions manifest themselves in the mass gap, and point out an importance of respecting the intrinsic energy-scale dependences in underlying theories for the determination of the mass gap. These studies are expected to be useful for a diagnosis of the magnetic catalysis in QCD.Comment: 8 pages, 3 figures, version published in PL

Unified description of dry and fluid frictions by subloading-overstress friction model

The subloading-overstress friction model is formulated for the unified description of the dry and the fluid frictions which exhibit the negative and the positive rate dependences, i.e. the decrease and the increase, respectively, of friction resistance. The validity of this model will be verified by the comparisons with test data in this article

Numerical Analysis of Heat Storage Characteristics of a Small Heat Storage Vessel Packed with Phase-Change Material Encapsulated into Spherical Hollow

We numerically investigate heat storage characteristics of a small heat storage vessel packed with phase-change material (PCM) encapsulated into a spherical hollow. The heat storage vessel is dealt with as a porous medium, and the flow of the working fluid is analyzed two-dimensionally using the modified Darcian momentum equation which takes into account both the buoyancy effect and the channeling effect. The heat transfer in the encapsulated PCM is analyzed using a one-dimensional heat conduction model. It is clarified that the completion of the heat storage process is delayed by natural convection, since the incoming hot working fluid flows mainly near the upper part of the vessel. It is also found that the nonhomogeneity near the boundary walls prolongs the heat storage process since it decreases the flow resistance near the walls and promotes a bypass flow near the upper wall due to the natural convection. A nondimensional equation is derived for the time taken to complete heat storage, where the Fourier number is expressed as a function of the modified Stefan number, the modified Reynolds number and the modified Grashof number.近年、エネルギの有効利用の観点より、蓄熱技術に関する研究・開発が盛んに行われており、大型のビル空調等の比較的大規模なシステムにおいて、実用化が進んでいる。しかしながら、一般家庭用の蓄熱装置に関しては、電気温水器の普及は見られるものの、その普及率は非常に小さい現状にある。これは、既存の顕熱蓄熱型蓄熱槽は設備が大きいため、空間的余裕のないマンションやアパート等への設置が困難なことが主な原因であり、蓄熱槽の小型化・高性能化が重要な課題となっている。著者らは、前報で、比較的大きな球カプセル化潜熱蓄熱体を充填した小型の円筒状蓄熱槽の蓄熱特性に及ぼす熱媒体流速及び熱媒体流入温度の影響を、球カプセル直径及び蓄熱材物性値の異なる二種類の球カプセルか潜熱蓄体について実験的に検討した。その結果、熱媒体流速の小さい条件において生じる、蓄熱槽内の低温の熱媒体と高温の流入熱媒体との密度差による自然対流や、比較的大きな球カプセルによる蓄熱槽内壁近傍のチャンネリング流れにより、熱媒体が蓄熱槽内を複雑に流動することや、蓄熱特性が流れ状態の影響を受け複雑に変化することを明らかにした。従って、様々なパラメータの影響を受け、複雑に変化する、熱媒体の流動や蓄熱体の融解挙動を詳細に検討するための手段として、数値解析の必要性に迫られている。球カプセル状潜熱蓄熱体の充填された蓄熱槽に関する数値解析法については、従来より検討がなされているが、そのほとんどにおいては、壁面近傍における熱媒体流れの不均質性が無視し得る、蓄熱体寸法が蓄熱槽に比べて小さい場合が対象とされている。一方、秋山らは、壁面近傍不均質領域の影響を考慮した流動解析を試みているが、彼らの採用したモデルでは、壁面近傍の蓄熱体充填率を実際よりも小さく見積もるため、比較的大きな粒子状蓄熱体を用いた場合には、蓄熱量を過少に評価することになる。さらに、球状潜熱蓄熱体を用いた蓄熱槽に関しては、熱媒体の自然対流を考慮した解析は行われていない現状にある。本報では、壁面近傍での蓄熱体充填率を過少に評価することなく流動抵抗現象の表現が可能な、球状粒子充填層に関する著者らの流動モデルに浮力の項を付加した運動量の式を用い、壁近傍の不均質性と自然対流の双方を考慮した数値解析法の提案を試みる。円筒容器内の共存対流問題の解析には厳密には三次元モデルが必要であるが、蓄熱体内部の解析にはさらに次元が必要なため、莫大な計算機容量と計算時間が必要となる。そこで本研究では、前報の円筒状蓄熱槽を、主要寸法の等しい矩形蓄熱槽に置き換えることで二次元モデルを用いた解析を行う。なお、本報においては、前報で用いた球カプセル直径及び蓄熱材物性値の異なる二種類の球カプセル化潜熱蓄熱体を対象に解析を行い、提案する解析法の妥当性を種々の条件について検討すると共に、種々の熱媒体流入温度及び熱媒体流速条件についても解析を行い、熱媒体の流動挙動に及ぼす自然対流の影響やこれに伴う蓄熱挙動の変化についても詳細な検討を行う。さらに、壁面近傍における不均質性や自然対流の影響を無視した解析も行い、これらの排除による蓄熱特性の変化についても検討を行う

Strong-Field Physics in QED and QCD: From Fundamentals to Applications

We provide a pedagogical review article on fundamentals and applications of the quantum dynamics in strong electromagnetic fields in QED and QCD. The fundamentals include the basic picture of the Landau quantization and the resummation techniques applied to the class of higher-order diagrams that are enhanced by large magnitudes of the external fields. We then discuss observable effects of the vacuum fluctuations in the presence of the strong fields, which consist of the interdisciplinary research field of nonlinear QED. We also discuss extensions of the Heisenberg-Euler effective theory to finite temperature/density and to non-Abelian theories with some applications. Next, we proceed to the paradigm of the dimensional reduction emerging in the low-energy dynamics in the strong magnetic fields. The mechanisms of superconductivity, the magnetic catalysis of the chiral symmetry breaking, and the Kondo effect are addressed from a unified point of view in terms of the renormalization-group method. We provide an up-to-date summary of the lattice QCD simulations in magnetic fields for the chiral symmetry breaking and the related topics as of the end of 2022. Finally, we discuss novel transport phenomena induced by chiral anomaly and the axial-charge dynamics. Those discussions are supported by a number of appendices.Comment: Prepared for an invited review article; Published versio