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本研究では，重力場および微小重力場の加振及び無加振状態における立方体容器内部の水の対流を考え，一面加熱，対面冷却，側面完全熱伝導を境界条件とし，プラントル数Pr=7.1として，ブシネスク近似を用いて有限差分法による数値解析を行う．本研究では特に，層流定常状態において新たに発見した構造について述べる．この流れ構造は一対となる三叉の上昇流と下降流とで構成される流れ構造である．この構造は，地上重力場無加振定常状態・微小重力場/地上重力場での強制加振状態の三つの場合で安定的に生じる．, We numerically investigate thermal convection in a cubic cavity. Thermal convection in a cube is induced heating from one wall and chilling from its opposite wall in the terrestrial-gravity and zerogravity fields with and without a sinusoidal modulation. The gravity and its modulation are parallel to the temperature gradient. An incompressible fluid with Prandtl number Pr = 7.1 (water) is considered and hence the Boussinesq approximation is used. We have reported a new flow structure which consists of a pair of trident currents. This previously-unidentified flow is not so weakly-stable but rather durable, and can be observed not only in a stationary cube under the terrestrial gravity, but also in an oscillating cube under the terrestrial gravity and zero gravity.

陸面大気相互作用によって形成される農耕地の熱環境は，作物の生育や収量を左右するなど農業上の重要な役割を果たしている．群落微気象モデルの農業における利用例として，イネの生育に影響を及ぼす水田水温のシミュレーションについて解説した．水田水温を推定する既存モデルをレビューするとともに，田面と群落の熱収支に基づいたモデルを紹介し，田面における熱交換係数の特性を論じた．これをもとに，水田の水深や灌漑時刻など水管理方法によって水田水温がどのように変化するのかシミュレーションを行った．その結果から，水管理方法が水田群落の熱環境に強く影響を及ぼしている可能性を示した．, The thermal environment of the agricultural land formed by the interaction between the land surface and the atmosphere plays an important role in agriculture to affect growth and yield of crops. As an application example of micro-meteorological model in agriculture, a water temperature simulation of rice paddies was described. In addition to reviewing existing models estimating paddy water temperature, a model based on the energy budgets of the ground and the plant canopy was explained in detail, and the characteristics of the heat exchange coefficient on the paddy ground surface was also discussed. Based on these knowledge, it was simulated how the paddy water temperature is changed by water management such as water depth and irrigation time in paddy fields. It was suggested from the result that the water management strongly affects the thermal environment in paddy fields.

農耕地と大気間における運動量や熱・水蒸気等の輸送過程を理解することは，作物生育に適した環境の保全や，周辺の微気候に与える影響を予測する上で大変重要である．本解説では農耕地に焦点を当て，大気陸面間で交換される運動量や熱・水蒸気等を定量的に評価するために欠かせない交換係数について，定義や特性，導出方法を含めて紹介する．交換係数の決定要素は，地表面の粗度とゼロ面変位，そして大気の安定度である．農耕地において，地表面の粗度とゼロ面変位は植生高と葉面積指数の関数として表すことが可能である．ただし，水面のように滑らかな地表面や微風時の交換係数の扱いには注意が必要である．, Understanding the transport processes of momentum, heat and water vapor between the agricultural land surface and the atmosphere is highly important for controlling cultivation environments and predicting surrounding microclimate. I introduce the exchange coefficients of momentum, heat and water vapor between the agricultural land surface and the atmosphere, including their definitions, characteristics and derivation methods. The determinant factors of the exchange coefficients are roughness lengths, zero-plane displacement height, and stability of the atmosphere. In the case of agricultural land surface, the roughness lengths and the zero-plane displacement height can be expressed as a function of vegetation height and leaf area index. It must be noted that the exchange coefficients of smooth surface and/or under natural convective conditions have characteristics different from other conditions.

本研究では，微小重力場において一面加熱かつ対面冷却，側面完全熱伝導の壁面を有する三次元正方形容器を強制加振し内部の水（[Pr] = 7.1）に関して周波数応答を調べている．加振方向は，温度勾配と平行方向である．支配パラメータである無次元加振周波数ωと振動レイリ―数Ra[η]について，今回の解析範囲では五つの対流構造S2とS4, S5, S6, Sαを確認している．Sαは，一組の三又流れにより特徴づけられる対流構造である．得られた解析結果から，ω < 5.0×10[2] では，もし熱伝導状態でなく熱対流状態であるならば，各加振周期毎に対流はいつもS4から始まることを明らかにしている．また，各Ra[η]で空間平均運動エネルギーが最大のピーク値をとる時の周波数を，最適周波数と定義している．この時，常にS4の対流構造を取ることから，最適周波数とS4に相関関係があることを示している．さらに，全ての解析結果をω-Ra[η] 平面上の安定領域図としてまとめ，準定常近似は，定量的にはω ≲ 10[0]で有効となることを示している．, To investigate the forced-oscillation-frequency responses on the three-dimensional thermal convection inside a cube heated from one wall and chilled from its opposite wall in the non-gravitational field, the authors conduct computations at Prandtl number [Pr] = 7.1 (water). The direction of the forced sinusoidal oscillation is parallel to the temperature gradient inside the cube. As a result, five kinds of flow structures S2, S4, S5, S6 and Sα appear in the tested ranges of vibrational Rayleigh number Ra[η] and non-dimensional forced-oscillation frequency ω. The Sα consists of a pair of trident currents. Whenever it is not conductive but convective for ω < 5.0×10[2], convective motion always starts with the S4 from the rest at each forcing cycle. The authors find out the optimum frequency where the amplitude of a spatially-averaged kinetic energy attains the maximum at each Ra[η]. At the optimum frequency, flow structure is always characterised by the S4. So, the optimum frequency can be related with the S4. In addition, the authors show the occurrence condition for convection as a function of Ra[η] and ω, and the boundary for the quasi-steady approximation which is permissible at ω ≲ 10[0]., 抄録中の[2][0] は上付き文字、[η]は下付き文字、[Pr]は斜体文字

In the present study. we report on the effect of double diffusive convection associated with solute discharge in the early stage of unidirectional solidification from above. Two-dimensional miincrical simulations have beeti conducted to clarify the concentration, lemperatLire and heat flux on the solid-liquid interface under a constant solid layer growth rate. The moving boundar due to solid layer growth was formulated according to the boundary tracking method. l'he simulations were conducted by vaing the initial conditions: concentration, solid layer growth rate and heating temperature at the bottom. The effects of thermal and solutal Rayleigh number on the concentration and the convective heat flux at the solid-liquid boundary crc discussed, and the associated correlations to predict those values as functions of the initial thermal and solutal Rayleigh tiumbers as well as the speeds of solidification were derived. © 2012 The Japan Society of Mechanical Engineers.

We apply the immersed boundary method to the thermal lattice Boltzmann methodto simulate natural convection. The thermal lattice Boltzmann method neglects thecompression work done by the pressure and the viscous heat dissipation in the evolution equation for the temperature. We utilize the direct forcing method that does not need to determine free parameters. In the numerical calculation of heat transfer between two horizontal concentric cylinders, the deviation between the analytical and numerical results strongly depends on the relaxation parameter. The numerical results of streamlines, isotherms and Nusselt numbers in natural convection show good agreement with those of the previous studies. We demonstrate that the IB-LBM with the adequate relaxation times gives reasonable results for the simulation of flows with heat transfer.

In this paper, the seamless virtual boundary method is applied to the incompressible flow analysis with heat transfer. In the seamless virtual boundary method, the forcing term is added not only on the grid points near the boundary but also on the grid points inside the boundary, in order to satisfy the velocity conditions on the virtual boundary points. Then, the smooth physical quantities can be obtained. For the heat transfer, the forcing term satisfied the temperature condition has to be added to the energy equation. First, we validate the present approach for the natural convection in square cavity. The results show that the present solutions are in good agreement with reference solution. Next, we try to apply the present approach to the flow around a heated circular cylinder. Then it is concluded that the present seamless virtual boundary method is applicable to the incompressible flow analysis with heat transfer successfully.

3D numerical simulation for penetrative convection of water with density inversion in a rectangular enclosure was performed by the numerical scheme with the combination of finite volume method and SIMPLE method and the results were compared with experimental ones. The inspection of numerical techniques revealed that it is important to obtain rational result that to solve the liner system for pressure correction factor in SIMPLE method accurately. The comparison between numerical results and experimental ones under the same conditions shows that the discrepancy between them becomes remarkable with increasing of hot wall temperature

Transient melting of ice layer placed vertically in the air under condition of natural convection was analyzed and compared with experimental results. First， the heat transfer coefficient on the falling film surface was investigated experimentally， where the natural convection and the vapor condensation of the humid air occur simultaneously. In the data analysis， the Lewis relation was used between the heat transfer coefficient and the mass transfer coefficient. Then， applying the obtained heat transfer coefficient on the falling film surface， the transient melting of ice was calculated. Lastly， a melting experiment was conducted using vertically placed ice layers and ice cylinders. The calculated results agreed well with experimental results.

Transient melting of ice layer placed vertically in the air under condition of natural convection was analyzed and compared with experimental results. First， the heat transfer coefficient on the falling film surface was investigated experimentally， where the natural convection and the vapor condensation of the humid air occur simultaneously. In the data analysis， the Lewis relation was used between the heat transfer coefficient and the mass transfer coefficient. Then， applying the obtained heat transfer coefficient on the falling film surface， the transient melting of ice was calculated. Lastly， a melting experiment was conducted using vertically placed ice layers and ice cylinders. The calculated results agreed well with experimental results.

In the authors’ previous report the numerical analysis was presented on the effect of plate thickness on natural convection around an isothermal horizontal plate. There is no report that has discussed the effect of plate temperature on natural convection around an isothermal horizontal plate. This report presents the numerical results by CFD analysis on the velocity and temperature fields and the local and average Nusselt numbers for the case with a higher plate temperature than that of the previous report.

In the authors’ previous report the numerical analysis was presented on natural convection from an isothermal horizontal plate. This report presents the numerical results by CFD analysis for the velocity and temperature fields and the local and average Nusselt numbers for natural convection from an isothermal vertical cylinder with horizontal bottom surface. The effects of the cylinder height, cylinder temperature and Prandtle number on the velocity and temperature fields and heat transfer are discussed., 長崎大学工学部研究報告Vol.37(68) p.26-40, 2007

In the authors’ previous report the numerical analysis was presented around an isothermal horizontal thin plate. There is no report that discusses the effect of plate thickness on the fluid flow and heat transfer due to natural convection around an isothermal horizontal plate. In this report the numerical results by CFD code for the velocity and temperature fields and the local and average Nusselt numbers are presented and discussed for various thick plates., 長崎大学工学部研究報告Vol.37(68) p.1-13, 2007

[Abstract] An enhancement technique is developed for natural convection heat transfer from a vertical heated plate with inclined fins, which are attached on the vertical heated plate to isolate a hot air flow from a cold air flow. Experiments are performed in air for inclination angles of the inclined fins in the range of 30 to 90 degrees measured from a horizontal plane, for height of 25 to 50mm, and for fin pitch of 20 to 60mm. The convective heat transfer rate for the vertical heated plate with inclined fins at the inclination angle of 60 degree is found to be 19% higher than that for the vertical heated plate with vertical fins. A dimensionless equation on the natural convection heat transfer of the vertical heated plate with inclined fins is presented., Copyright (c) 2007, 一般社団法人日本機械学会, rights: 本文データは学協会の許諾に基づきCiNiiから複製したものである, relation: isVersionOf: http://ci.nii.ac.jp/naid/110006165280/

For horizontal concentric double rectangular duct with cooled outer duct and heated inner duct, two-dimensional numerical calculations were analyzed. Numerical calculation used repeat calculation tool of "Excel" were carried in a range of Prandtl number Pr=0.7, aspect ratio γ=1.0～3.5 and Rayleigh number Ra≦4060. It was illustrated streamlines of natural convection, isotherms and average Nusselt number. The flow patterns of natural convention consist of a pair of the "L-type" circulation in side-bottom space and small vortices in upper space. Those flow velocity increases when Ra increases. When γ is growing larger, the vortices number increases. It was shown that 1, 2, 3 and 4 pair of the vortices appeared for γ=1.0, 1.5, 2.5 and 3.5, respectively. When γ is growing larger, pattern of isotherm is complicated. The average Nusselt number at the bottom surface decreases with increasing aspect ratio.

In the authors’ previous reports, the numerical results on natural convection from a downward-facing isothermal plate were compared with the experiments by Aihara et al. The numerical analysis using a CFD code showed a good agreement with the actual flow and thermal fields obtained in the experiments. However, the analysis was limited to the fluid flow and heat transfer from a downward-facing surface of the isothermal plate as no information has given on the flow and thermal fields from the upward-facing and sideward-facing surfaces in the Aihara et al.’s experiment. In this report, the flow and thermal fields on the entire surfaces of the horizontal isothermal plate are numerically simulated using a CFD code and the numerical results are presented.

In the third report are presented the numerical simulations by CFD under a downward-facing isothermal surface with an insulated upward-facing surface. The effects of the heat transfer from an upward-facing surface on the fluid flow and heat transfer under the downward-facing surface are discussed. It is shown that the velocity and temperature fields are hardly affected by the heat transfer from an upward-facing surface.

A lot of studies on natural convection from a horizontal plate have been carried out, so far, experimentally and/or analytically. However, experimental results, particularly, flow behaviors below the downward-facing heated surface, have not been well demonstrated analytically or numerically. In this and the following reports are presented the numerical simulations by CFD analysis on natural convection below an isothermal horizontal plate facing downwards. The numerical results obtained in this report are compared with the experiments by Aihara et al. and the numerical analysis by Nakano et al. The present analysis by CFD shows good agreement with the experimental data.

In the second report are presented the numerical simulations by CFD under the different computational domain and boundary condition from those in the first report. The numerical results are compared with those of the first report. It is shown that the numerical results on the velocity and temperature profiles are considerably affected by the computational domain and boundary condition.

Thermal energy applied to a pure fluid near its critical point immediately makes a strong expansion. This causes an adiabatic compression in the front of the expansion and a large density difference is formed there. The difference with adiabatic energy is transported as an acoustic wave. This rapid heat transportation is called 'Piston Effect'. In our study, an ultra-sensitive and high-speed density measurement system was developed to conduct a quantitative measurement of the 'Piston Effect'. By using the system, we succeeded to directly observe the elementary process of 'Piston Effect'. To demonstrate the performance of the system, the measurement of sound velocity in a critical fluid was conducted. Using the FFT method to the experimental results, the sound velocity could be precisely evaluated. The velocity profile versus temperature from the experimental results shows a good agreement with the simulation results and theoretical prediction, that is, the profile should have the scale universality. However, the profile from the experimental results obeys another scale universality if T-T(sub c) is less than 0.1 K. These indicate that our experimental system enables us to quantitatively discuss the critical phenomena., 資料番号: AA0049057017, レポート番号: JAXA-SP-05-011

This paper deals with the exchange flow under the unstably stratified field. The author developed the effective measurement system as well as the numerical analysis program. The system and the program are applied to the helium-air exchange flow in a rectangular channel with inclination. Following main features of the exchange flow were discussed based on the calculated results.(1) Time required for establishing a quasi-steady state exchange flow.(2) The relationship between the inclination angle and the flow patterns of the exchange flow.(3) The relationship between the concentration profile and the inclination angle.(4) The relationship between the net in-flow rate and the inclination angle.(5) The comparison of the computed velocity profile and the net in-flow rate with experimental data.A good agreement was obtained between the calculation results and the experimental results.

A numerical analysis was made on natural convection from a downward-facing heated plate. Basic equations for mass, momentum and energy were discretized by finite difference method and numerically solved by the HSMAC method. The computation domain with many grids was arranged to allow for the edge effect of the plate and its suitable size was decided from the viewpoint of better agreement with experimental results. The numerical solutions of fluid flow and thermal fields were obtained and their characteristics were investigated in terms of Rayleigh number. Correlations of Nusselt number were compared with experimental and numerical results.

Three dimensional linear stability analysis for onset of natural convection flow in a cubic cavity is performed by using the spectral element method. The cubic cavity is placed horizontally and is heated from the bottom surface and cooled from the upper one. The lateral boundaries are assumed to be rigid and in a thermally medium state between conducting and insulating wihch can be established by introducing Biot number. The fluid is in a motionless state if the Rayleight number is small. On the other hand, natural convection occurs if the Rayleigh number exceed a critical value. The critical Rayleigh numbers for the onset of the natural convection are evaluated numerically for various Biot numbers by constituting eigenvalue problem using linear stability theory. In addition, the velocity and temperature field at the critical state are obtained and discussed., ・rights：一般社団法人日本機械学会, ・出版社版：https://www.jstage.jst.go.jp/article/kikaib1979/70/690/70_690_482/_article/-char/ja/

This paper has dealt with the Heat storage characteristics of the microcapsule slurry composed of phase change material (PCM) as a latent heat storage material and water. A rectangular cavity with a heating vertical wall, which was filled with the microcapsule slurry, was selected as the present research model. The heating wall temperature, the width of the cavity and the PCM concentration were set as parameters. It was clarified that the transportation of latent heat evolved by melting of the PCM in the slurry exerted on a remarkable influence on the natural convection heat transfer. In addition, it was found that the heat transfer coefficient reached a local maximum value with an increase in initial temperature difference between heating wall and PCM. The heat storage completion time also have a local maximum value with an increase in heating wall temperature due to the latent heat by melting the PCM in the slurry., 内壁面のうちの一側面を加熱熱源とする短形蓄熱槽は、工業的な応用が多い基礎的な形態であり、従来から多くの研究がなされている。Eftekharらはパラフィンワックスを充填した垂直フィンを有する短形蓄熱槽の下面を加熱した場合における固駅境界線の移動を詳細に検討し、熱移動に関する実験整理式の提案を行っている。平田らは氷およびパラフィンを充填した短形蓄熱槽の下面を加熱した場合において、蓄熱材固相が固定されて移動しない場合と固相が浮力により移動し加熱面と接触する場合を比較することで接触融解の効果について検討を行っている。斉藤らも分割フィンを有する短形蓄熱槽を用いた蓄熱において接触融解の効果を検討している。これらの短形蓄熱槽の潜熱蓄熱に関する既往の研究は全て固液相変化を伴う水、パラフィン、低融点の金属などの物質を蓄熱材とするものであり、その蓄熱過程における熱源から蓄熱材への熱伝達特性や蓄熱完了時間、蓄熱材の移動といった蓄熱挙動は、蓄熱材の相状態、すなわち流動可能な液相であるか、流動しない古相であるかに強く依存している。一方、本件で対象とする潜熱マイクロカプセルスラリーはマイクロカプセル芯物質がその融点温度以下で凝固した状態においても、分散媒により流動性は維持され、蓄熱材スラリーを巨視的に観察した場合には固相蓄熱材の壁面への固着も発生せず、固液境界も存在しない性質を有している。融解・凝固の際の固液境界は個々のマイクロカプセル内に存在するのみである。このため蓄熱挙動を支配する要因は前述のような潜熱蓄熱に関する従来の研究とは大きく異なり、マイクロカプセル芯物質の相状態や潜熱マイクロカプセルスラリーの温度および潜熱マイクロカプセルの質量濃度による物性と僭熱量の変化が現象を支配する要因となる。このような潜熱マイクロカプセルスラリーの蓄熱材として用いた場合の非安定な蓄熱挙動を解明するため、潜熱マイクロカプセル質量濃度、蓄熱槽寸法、蓄熱熱源となる加熱壁面の温度などを操作パラメータとし、それらが蓄熱過程における加熱面から蓄熱材への熱伝達特性、蓄熱量および蓄熱材融解割合の経時変化、蓄熱完了時間などに与える影響を本研究において数値解析により検討した。

This paper has dealt with the natural convection heat transfer of the microcapsule slurry composed of phase change material (PCM) as a latent heat storage substance. A rectangular cavity with two opposing heating and cooling vertical walls was selected as the present research model. The temperature difference between heating and cooling walls, the width of the cavity and the PCM concentration were set as parameters of natural convection heat transfer. The heat transfer coefficient of heating and cooling wall, the flow velocity profile and the temperature distribution of the microcapsule slurry were calculated by numerical computation. It was clarified that the transportation of latent heat evolved by melting and solidifying of the PCM in the slurry exerted on a strong influence on the natural convection heat transfer. Moreover, it was found that the heat transfer coefficient reached at the local maximal value with an increase in temperature difference between heating and cooling walls. In addition, Nusselt number was influenced by the transportation effect of latent heat that was caused by melting and solidifying of the PCM. The numerical results revealed quantitatively that the natural convection heat transfer depended on the PCM concentration, temperature difference between heating and cooling walls, and width of the rectangular cavity., 近年、熱エネルギー有効利用を目的とした潜熱蓄熱システムに注目が集まっており、さまざまな蓄熱材が開発されている。中でも、潜熱体融点温度以下の状態においても、常に流動性を維持する潜熱マイクロカプセルスラリーや潜熱マイクロエマルジョンといった潜熱物質を含有する機能性熱媒体が蓄・放熱特性において有利であり有望視されている。このような潜熱体を分散媒中に分散混合させた機能性熱流体を蓄熱材として利用する場合には、加熱及び冷却時における自然対流挙動および熱伝達特性を把握しておくことが必要不可欠である。本研究は自然対流の基本的な形態の一つである垂直対抗加熱・冷却壁を有する矩形密閉容器に潜熱マイクロカプセルスラリーを充填した場合の自然対流挙動や熱伝達特性に影響を及ぼすスラリーの熱物性、潜熱量、そして容器寸法などの影響について数値解析により検討するものである。

Quantitative investigation of the gravity effect was performed for acetone and kerosene pool fires. A centrifuge was used to examine the gravity effect. Small-scale pool fires were observed under various high gravity fields. Regions of stable flame, puffing flame and irregular oscillatory flame were mapped with the gravity level and pool diameter. Flame height decreased and oscillatory frequency increased with an increase in the gravity level. Behavior of the flame height was agreed quantitatively with the scaling prediction presented by Orloff and Heskestad. Puffing phenomena observed under various gravity fields were summarized with the Strouhal number and Froude number. As the result, we could obtain an empirical equation of St=0.517Fr^. From this equation, puffing frequency could be estimated for a flame of various pool diameter varying from 0.01 to 50 meters.

The characteristics of ice melting heat transfer in a horizontal elliptical tube in water were studied experimentally and numerically. This phenomenon is caused by a combination of the natural convection heat transfer of water around a tube and the ice melting heat transfer inside a tube. Large number of studies on melting heat transfer in a simple shape capsule has been done ; however, study of melting heat transfer in a horizontal elliptical tube is less. Results are presented as ice melting characteristics, temperature distributions, flow patterns and melting rate.

This paper describes quantitative 3-D measurement method for flow field of a rotating Rayleigh-Benard convection in a cylindrical cell heated below and cooled above. A correlation method for 2-D measurement is well advanced to a spatio-temporal correlation method. Erroneous vectors, often appeared in the correlation method, is successfully removed using Hopfield network. As a result, calculated 3-D velocity vector distribution well corresponds to the temperature distribution.

application/pdf, 学術雑誌論文, The natural convection with large temperature difference is computed numerically using the Low-Mach-Number approximation with temperature dependent viscosity and thermal conductivity. In this study staggered grid system is used in order to hold down the numerical oscillation. Firstly, steady laminar natural convection above a horizontal heat source is simulated in order to validate the simulation method. The result is in good agreement with the analytical solution. Secondly, two dimentional flow field driven by two parallel heat sources is computed. This boundary condition may be regarded as a model situation of the big fire covering both sides of a wide straight road. At the same time, it is interesting to investigate interactions between two thermal plumes. The numerical results disclosed different flow behavior when the imposed temperature of the heat sources is changed and the rest of the governing system parameters are varied.

This study was researched by a numerical analysis and experiment, on a natural convection heat transfer in a oriented horizontal elliptical annuli between heated outer tube and cooled inner tube. The outer tube was elliptical tube, and inner tube was cylindrical tube. It was experimented with the outer tube oriented to vertical side, slant upper side 45 degrees, horizontal side, respectively. The numerical analyses were performed by changing the elliptical ratio, inner tube radius, oriented angle, and Rayleigh number as parameters. Results obtained for different conditions are presented as temperature profiles, flow patterns, local Nusselt number, and total heat transfer. It was presented that the heat transfer enhancement effect or heat transfer obstruction effect for the total heat transfer by oriented angle.

This study was researched by a numerical analysis and experiment, on a natural convection heat transfer in a horizontal cylindrical eccentric annuli, which heated outer tube and cooled inner tube. The inner tube shifted to vertical upper side, slant upper side 45 degrees, horizontal side, slant lower side 45 degrees and vertical lower side, respectively. The numerical analysis was performed by changing the shift direction, eccentricity and Rayleigh number as parameters. Results obtained for different conditions are presented as temperature profiles, flow patterns, local Nusselt number and total heat transfer. It was presented that the heat transfer enhancement effect or heat transfer obstruction effect on the total heat transfer were affected by shift direction and eccentricity.

This paper deals with the heat transfer characteristics of a liquid-liquid direct contact operation in which a Perfluorocarbon (PFC) liquid is released in a hot water stream, a low-grade heat source such as urban sewage, for the purpose of heat recovery from it. The paper reports on a set of experiments in which a PFC liquid (1800 kg/m^3 at 20℃) was continuously injected from a single, downward-facing nozzle into a slow, upward flow of hot water to be disintegrated into droplets descending in, and thereby heated from the water flow. The results of the experiments show how the size distribution and the translational motions of the droplets affect the overall coefficient for the water-flow-to-droplets heat transfer and also the temperature effectiveness for the droplets., 近年、未利用エネルギー活用の観点から、工場や家庭温排水などを熱源として利用する廃熱回収用熱交換器の開発が急務となっている。従来のシェルアンドチューブなどの隔壁型交換器では、伝熱面に排水中のごみやスケールが堆積し、その伝熱効率が著しく低下する等の問題点があった。この問題解決として、このような汚濁排水中に、非水溶性熱媒体を噴射・注入し、直接接触熱交換により、熱抽出が可能となる。このような直接接触熱交換法は、個体壁伝熱面の汚れによる伝熱効率低下の問題がなくなり、廃熱回収用熱交換方式として極めて有効である。さらに、この熱交換法は、個体壁を介さないために高い熱通過率が得られ、小温度差での熱交換に有効である。また、液－液の直接接触する界面が、そのまま伝熱面に相当するため、単位体積当たりの伝熱面積が増加する利点を有する。本研究は、下水等の汚れた熱水源より効率的な熱回収をする手段として液液直接熱交換法に注目したものであり、熱回収媒体としてフッ素系不活性液体を熱源水へ噴射し、形成したフッ素系不活性液滴群と熱源水の直接接触による、流動及び熱伝達特性を検討するものである。すなわち、円形単孔ノズルから高密度のフッ素系不活性液体を熱源である温水槽へ上部より噴射し、その液滴群形成過程の観察及び液滴群の流れの特性の解明を通じて、熱水源からの直接熱交換法による熱抽出に関する基礎特性を明らかにすることを目的とする。最終的に、この種の熱源水よりの熱回収媒体としてフッ素系不活性液体を用いた場合における実用に寄与する無次元熱伝達率等に関する実験整理式の検討をも行うものである。