Study Of Heat Transfer Characteristics In A Narrow Channel Under Rolling Condition

This experimental study investigates the factors affecting the single-phase forcedconvective and subcooled flow boiling heat transfer characteristics in a narrow rectangularchannel under rolling motion.The result showed that different flow regulation ways have different influences on massflow rate under rolling motion. Whether the mass flow rate decreases or not depends on theratio of additional pressure drop to pump head. The rolling motion could enhance heat transferin laminar and turbulent flow when change the bump head to change the flow speed, and themore vigorous the rolling, the larger heat transfer enhancement. The rolling motion could onlyenhance heat transfer in laminar flow when use the valve to change the flow speed. Pressurehas nearly no effect on single-phase heat transfer. The single-phase heat transfer characteristicincreases with the increase of heat flux and mass flow. The transition to fully developedturbulent regime occurred early in narrow rectangular channel, it is fully developed turbulentregime when Re>4000, which could seem as a reason to enhancement of heat transfer. Theexperimental Nu values agree well with theoretical value in laminar region. And the deviationof the experimental values and predicted values by Gnielinski formula within20%in fullydeveloped turbulent flow, so this formula can be used as a predictor formula. Because thecommonly used predictor formula in transition zone is not applied to this channel, a newformula was obtained whose deviation is±30%.The result of subcooled flow boiling experiments showed heat concentration phenomenaoccurred easily with the increase of pressure, and the superheat of the wall become lower. Thesmaller the mass flow, the lower the degree of superheat and heat flux of ONB. Rollingmotion has no effect on ONB. The smaller the inlet subcooling, the lower the degree ofsuperheat and heat flux of ONB. In order to be suitable for this experiment, added acorrelation factor about mass flow to the Bergles-Rohsenow formula, the deviation within±30%compared with the experiment result. The heat transfer coefficient increases with theincrease of the mass flow, pressure, and inlet sub cooling. And the rolling motion has nearlyno effect on heat coefficient of subcooled flow boiling.