Доступ предоставлен для: Guest

ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

CONVECTIVE HEAT TRANSFER MEASUREMENTS IN TUBES WITH EQUALLY SPACED BAFFLES UNDER STEADY AND OSCILLATORY FLOW

Get access (open in a dialog) DOI: 10.1615/IHTC16.hte.023268
pages 5307-5314

Аннотация

An experimental study of the heat transfer characteristics in tubes with equally-spaced annular baffles working with steady-state net flow and with superimposed oscillatory flow is presented. Using propylene-glycol as working fluid, a range of Prandtl numbers between 280 and 680 and net flow Reynolds numbers 10 < Ren < 1000 are reproduced in an experimental facility where temperature and mass flow rates are modified using a frequency-controlled pump and an adjustable secondary-cooling circuit. A crank and connecting-rod mechanism, electrically driven through a gear reducer, is employed to activate an hydraulic piston that generates flow oscillations with a fixed amplitude x0=0.5D and frequencies between 0.5 and 2 Hz, covering a range of oscillatory flow Reynolds number 10 < Reosc < 230. Using Joule effect heating in the tube wall, uniform heat flux measurements were conducted in order to obtain local and pitch-averaged Nusselt number in a region where spatial-periodicity applies. When the device operates without flow oscillation, three different regimes are identified: a laminar flow region (Ren < 80), a transitional region (80 < Ren < 200) and a turbulent region (Ren > 200). Experimental results with a superimposed oscillatory flow demonstrate that a three-fold increase in heat transfer can be achieved in the studied range. The results also show the significant effect of the Prandtl number when there is an oscillatory flow superimposed. Other effects that have been detected are the flow stratification in the laminar region and how the local Nusselt number distribution clearly changes depending on the flow regime.