The Flow And Heat Transfer Characteristics For Low Flow Rate Flow Under Rolling Motion Conditions

Experimental and numerical studies of low flow rate instantaneous flow and heat transfercharacteristics in a vertical narrow rectangular channel under rolling motion were conductedin this paper.The flow loop employed in this experiment is fixed on a rolling device and with deionizedwater as the test fluid. The testing narrow rectangular channel is made of transparent organicglass with the cross section of40.23×2.75mm~2. Experimental results show that whether theflow rate fluctuates depends on the relationship of the additional inertial force, driving forceand loop friction coefficient. The flow with a larger driving force and loop friction coefficientand smaller inertial force tends to be more stable. The flow rate fluctuation boundary wasobtained by combining the experiment and theoretical studies. When the driving force is50times larger than the additional inertial force, the relative amplitude of flow rate fluctuation isless than1%and the flow can be treated as steady flow. Two definitions for the instantaneousfriction coefficient were raised up and the time average friction coefficients were acquired,the different variation tendency indicated by different definitions in laminar flow can berelated to “the time average viscous dissipation” and “time average frictional pressure drop”.Correlations for the instantaneous friction coefficient are obtained by fitting lots ofexperimental data, and the correlations will become the one under steady conditions when therolling frequency or rolling amplitude tends to zero.A thermal loop is occupied to study the convective heat transfer characteristics in rollingmotion. The test fluid is deionized water and the nominal cross section of the narrowrectangular channel used is40×2mm~2. The experimental results show that the time averageheat transfer coefficient of the narrow rectangular channel in rolling motion is the same asthat under steady condition, and the heat transfer is not enhanced by rolling motion. Theinstantaneous heat transfer coefficient fluctuates periodically with its fluctuation periodequals to rolling period. A correlation of the heat transfer coefficient in rolling motion isacquired, and the value of this correlation will become the one calculated by the classicalcorrelations such as Shah&London and Gnielinski correlation when the rolling frequency orrolling amplitude tends to zero. Numerical investigations of the pulsating flow and heat transfer characteristics in anarrow rectangular channel under rolling motion condition were performed. The crosssection of the narrow rectangular channel is40×3mm~2. Stresses were put upon the velocitydistributions of the cross section and the variations of the friction coefficient and heattransfer coefficient affected by the transverse additional inertial force. Calculations showthat the transverse additional inertial force causes the distributions of the vortexes for thecross section of the narrow rectangular channel. The intensity of the second flow in the crosssection changes periodically, and the value of the second flow in rolling motion is alwayslarger than that in the pulsating flow without the transverse additional inertial force. Underthe under the most severe situation that ocean renders, the boundary layer is not affected bythe transverse additional inertial force, therefore, the flow friction and heat transfercoefficient of the narrow rectangular channel under rolling motion will not be changed.