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Development of a High-Performance Heat Exchanger Using Fine Tube and a Couple of Turbulence Promoters

使用细管和一对湍流促进器开发高性能热交换器

基本信息

批准号：
01850046
负责人：
ECHIGO Ryozo
金额：
$ 11.2万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research
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/en/grant/KAKENHI-PROJECT-01850046/
关键词：
Compact Heat Exchangeer Heat-Transfer Enhancement a Couple of Turbulence Promoters Fine Tube 連成乱流促進体凝縮器

项目摘要

(1) A new-type compact heat exchanger has been suggested, and the fundamental heat transfer performance has been studied. The design concept is based on the new principles for heat transfer enhancement, namely, "reducing the size of heat transfer surfaces" and "arranging a couple of turbulence promoters to cause drastic change in turbulence structure". To satisfy such requirements, the heat exchanger consists of fine tubes(o. d. =1mm)and woven threads(d. =O. 3mm). The maximum heat transfer coefficient obtained in the experiment is fourteenfold larger than that around a cylinder without threads. The heat transfer coefficient per unit projected area is about 5x1O^3W/(m^2K), and that per unit volume reaches 3x1O^6W/(m^3K).(2) Heat-transfer mechanism of the fine-tube heat exchanger has been studied on the basis of the flow and heat-transfer experiiients. To clarify the effect of the woven threads on turbulence promotion, a test section scaled up 30 times as large as the actual heat-transfer element was made of transparent Pyrex glass, and the flow field around fine tubes was measured by laser Doppler velocimeter using castor oil as a working fluid. On the other hand, the distributions of Nusselt number around the fine tube were measured using silicon oil. The heat-transfer enhancement and its mechanism were discussed in the light of the turbulence behavior which was highly augmented by the threads.(3) Using steam as a working fluid, heat-transfer characteristics of the fine-tube condenser have been measured at atmospheric pressure. Since the threads intensify the vapor shear and act as fins, heat transfer is enhanced markedly ; the maxinuin heat transfer coefficient reaches 2OOkW/(m^2K) (the maximum heat flux is 2000 kW/m^3).

(1)提出了一种新型紧凑式换热器，并对其基本传热性能进行了研究。该设计概念基于新的强化传热原理，即“减小传热表面尺寸”和“布置一对湍流促进器，引起湍流结构的剧烈变化”。为了满足这些要求，热交换器由细管（o. D. = 1 mm）和编织线（d. =O. 3mm）。实验得到的最大换热系数是无螺纹圆柱的14倍。单位投影面积的传热系数约为5 × 10^3W/（m^2K），单位体积的传热系数可达3 × 10^6W/（m^3K）。(2)本文在流动和传热实验的基础上，对细管换热器的传热机理进行了研究。为了弄清编织线对湍流促进的影响，用透明Pyrex玻璃制作了一个比实际传热元件大30倍的试验段，用激光多普勒测速仪测量了以蓖麻油为工质的细圆管周围的流场。另一方面，用硅油测量了细管周围的努塞尔数分布。从强化湍流特性的角度探讨了螺纹的强化传热作用及其机理。(3)以水蒸汽为工质，在常压下对细管冷凝器的传热特性进行了测量。由于螺纹强化了蒸汽剪切并起到了肋片的作用，传热得到了显著的强化，最大传热系数达到200 kW/（m^2K）（最大热流密度为2000 kW/m^3）。