Studies on the optimum Shapes of Cross-Section and Arrangement of Fin Rows of a Heat Exchanger

换热器最佳截面形状及翅片排排列的研究

• 批准号: 01550140
• 负责人: OKAJIMA Atsushi
• 金额: $ 1.41万
• 依托单位: Kanazawa University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1989
• 资助国家: 日本
• 起止时间: 1989 至 1991
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-01550140/
• 关键词: Heat exchanger; Shape and arrangement of fins; Experiment in a wind tunnel; Numerical simulation; Biased flow; Heat transfer; Rectangular cylinder row; Thermal field

A row of uniformly spaced bluff bodies with a rectangular cross-section placed perpendicularly to an approaching flow like the fin rows of a heat exchanger produces unsteady and non-uniform flow across the row, which consists In separated flow region with an unsteady cell structure. The present study consists of experiments In a wind tunnel and numerical simulations of flow by a finite difference method. Firstly, a simultaneous measurements of pressures around the circumference of a fin row and velocity distribution of a wake In a wind tunnel allow the evaluation of instantaneous drag and lift forces In each mode of two and more flow patterns which appear by unsteadiness of a biased flow formed In the gaps, and In the biased flow, we find good correspondence of pressure distributions and lift and drag forces to wake velocity profiles. It Is concluded that the biased flow is metastable and can switch Intermittently In gaps, and that the nonuniformity of gap and wake flows is significant … More in the range of the gap ratio S/H below a critical value. We find also that the uniformity of a wake velocity Is the best at the critical gap for elongated rectangular cylinders, B/H=3, 5 In rows. Next, we have developed the computer-code for computation of flows around rectangular cylinders, to gain a better Insight into the detailed characteristics of the fluld- and thermo-dynamics of bluff bodies. By a finite volume method, both laninar flow and thermal fields around bluff bodies with a rectangular cross section of various B/H ratios and an aerofoil seption haie been computed on body-fitted curvilinear coordinates at a Reynolds number of(1, 4, 7)x1O^3, and we can successfully simulate some Interesting flow and thermal phenomena whereby a flow pattern critically, changes when the B/H ratio Is about 2.5 and 6 ; that Is, a fully separated flow, an alternately reattached one and a stationarily reattached one. It is also clarified that Nusselt number distribution well corresponds with a motion of flow about the body, such as the size of a vortex-formation region and a notion of vortices shed downstream over the side walls. The present computational code Is certified to be suitable as the computed results show a good agreement with the measured results, and the computed results clearly show the effects of a shape of the bluff body on aero- and thermo-dynamic characteristics. The results reveal an interactions between a wake and separation bubbles, also. Furthermore, turbulent flows around rectangular bodies also have been computed by a standard k-epsilon turbulence model. There are, however, some discrepancies between the results from the k-epsilon, turbulence model and experiments for unsteady phenomena. We have reported the results of experiments and numerical simulations on the optimum shapes of cross-section and arrangement of a row of fins, In six papers. Less

一排等间距、矩形截面的钝体，与靠近的气流垂直放置，类似于换热器的翅片排，在该排上产生非定常和非均匀流动，它由具有非定常单元结构的分离流区组成。本研究包括风洞实验和有限差分法的数值模拟。首先，在风洞中同时测量翼排周长周围的压力和尾迹的速度分布，可以评估两种或两种以上流型的瞬时阻力和升力，这些流型是由间隙中形成的偏置流的非定常引起的，在偏置流中，我们发现压力分布、升力和阻力与尾迹速度分布有很好的对应关系。在间隙比S/H低于临界值的范围内，间隙和尾流的不均匀性是显著的。我们还发现，在B/H= 3,5排长形矩形圆柱的临界间隙处，尾流速度均匀性最好。接下来，我们开发了计算矩形圆柱体周围流动的计算机代码，以便更好地了解钝体的流体和热力学的详细特征。本文采用有限体积法，在雷诺数为（1,4,7）x10 ^3的拟体曲线坐标下，计算了具有不同B/H比和翼型吸力的矩形横截面的直流体周围的流场和热场，成功地模拟了一些有趣的流动和热现象，其中当B/H比约为2.5和6时，流型发生了严重变化；也就是说，一个完全分离的流，一个交替重新连接的流和一个固定重新连接的流。此外，还澄清了努塞尔数分布很好地与流体在物体周围的运动相对应，例如涡形成区域的大小和沿侧壁向下流动的涡的概念。计算结果与实测结果吻合较好，表明钝体形状对气动和热力特性的影响是正确的。结果还揭示了尾流和分离泡之间的相互作用。此外，还用标准k-epsilon湍流模型计算了矩形体周围的湍流。然而，k-epsilon模型、湍流模型和非定常现象的实验结果之间存在一些差异。我们已经在六篇论文中报道了关于最佳横截面形状和排鳍排列的实验和数值模拟结果。少

项目成果

小林 秀樹,岡島 厚,矢部 隆二: "角柱列を通過する非定不均一流れ" 日本機械学会・流体工学部門講演論会講演論文集. No.910ー50. 48-50 (1991)

Hideki Kobayashi、Atsushi Okajima、Ryuji Yabe：“通过棱镜阵列的未定义的非均匀流动”日本机械工程师学会流体工程分部会议记录，第 910-50 号（1991 年）。

Okajima A.: "Change of Flow about an Elongated Rectangular Cylinder in a Range of Reynolds Numbers of 200 to 0.7×10^4" Proceeding of the First ASME-JSME Fluids Engineering Conference. FED-112. 107-113 (1991)

Okajima A.：“雷诺数为 200 至 0.7×10^4 范围内细长矩形圆柱体的流动变化”第一届 ASME-JSME 流体工程会议论文集 (1991)。

岡島 厚,上野 久儀,木綿 隆弘,恵上 浩一: "並列2角柱の空力静特性におよぼす迎え角の影響" 土木学会・構造工学論文集. 38AーII. 857-864 (1992)

Atsushi Okajima、Hisagi Ueno、Takahiro Motomen、Koichi Egami：“迎角对平行双面棱镜的空气静力学特性的影响”，日本土木工程师学会结构工程学报 38A-864（1992 年）。

岡島 厚,坂井 晴久: "直接法とkーεモデルによる矩形柱まわりの流れの数値シミュレ-ション" 日本風工学会誌. 47. 79-80 (1991)

Atsushi Okajima、Haruhisa Sakai：“使用直接法和 k-ε 模型对矩形柱周围流动进行数值模拟”日本风工程学会杂志 47. 79-80 (1991)。

Okajima A.: "Numerical Simulation of Flow Around Rectangular Cylinders" J.Wind Eng.and Industrial Aerodynamics. 33. 171-180 (1990)

Okajima A.：“矩形圆柱体周围流动的数值模拟”J.Wind Eng.and Industrial Aerodynamics。