Experimental investigation of various turbulator inserts in gas-heated channels

This experimental research was focused on the investigation of the heat transfer augmentation by various turbulator inserts in gas-heated channels. The work was conducted directly in a convective part of a two fire-tube boiler. The flue ducts were positioned vertically and horizontally for various design applications. Twisted-tape insert (with the twist ratio y=4.12), the straight-tape insert, and the combined turbulator insert (the internal twisted tape with the twist ratio of 180° y=2.16 and an external tape, which spirally winded on an internal tape, with longitudinal pitch H_360°=110 mm and the relative height of a tape (rib) e/D₀=0.098;0.2) were investigated. The working fluids were the combustion products of light oil fuel and wood pellets. In addition, the experiments were conducted in the two fire-tube boiler without any inserts. Despite of relatively large data scattering obtained in these experiments some qualitative and quantitative conclusions were drawn.     

扰流元诱发的二次流及其在强化传热中的应用

1前言通常所谓“茶杯效应”的二次流（即茶叶在搅拌的杯中聚集在杯中心）是一种常见的流动现象。在对流热传递过程中，常可激励传热的增强。在传热表面布置扰流结构是对流换热的无源强化技术经常采用的方式。传统的展向二维连续肋扰流元通过破坏边界层发展，减小粘性底层厚度，从而减小传热热阻。这种扰流结构所诱发的扰动是二维的，其传热强化的程度有限并且在助前、后缘附近出现回流区。流体的滞留明显消弱了回流区内的传热速率，甚至导致壁面出现局部“热点”。进一步研究发现将连续肋倾斜布置以引入展向二次流可使扰流元对流体产生三维…     

Experimental and Numerical Investigation of the Effect of Turbulator on Heat Transfer in a Concentric-type Heat Exchanger

This article experimentally and numerically analyzes the effect of turbulators with different geometries (Type I, Type II, Type III, and Type IV) located at the inlet of the inner pipe in a concentric-type heat exchanger. Experiments were performed at parallel-flow conditions in the same and opposite directions to investigate the impact of manufactured turbulators on heat transfer and pressure drop. In the numerical study, ANSYS 12.0 Fluent code program was used, and basic protection equations were solved in the steady-state, three-dimensional, and turbulence-flow conditions. Results were obtained from numerical analysis conducted at different flow values of air (7, 8, 9, 10, 11, and 12 m³/h). The distribution of temperature, velocity, and pressure was demonstrated as a result of numerical analyses. Experimental and numerical results were compared, and it was observed that they were in conformity with each other. When the data obtained from the analyses were examined, the highest heat transfer, pressure drop, and friction factor increase were detected to be in the Type IV turbulator.