Abstract
The article presents an experimental investigation, performed to evaluate the hydrodynamics and heat transfer characteristics in tandem arranged heated rows packed inside cylindrical channel, which use air as well as air/water mist flows as operational medium. The average surface temperature has been recorded under various air main flow, water mist rate, surface heat flux and constant pitch ratio ( y / d = constant). The heat transfer rate was found to increase with the water mist rate and decrease with the surface temperature. Heat transfer rate was enhanced over that for the single-phase air flow as a result of water mist evaporation and direct heat conduction by the water film generated on the heated surfaces. Overall, the heat transfer coefficient was enhanced by about 140%, 42%, and 10% respectively for the upper, middle and lower heated rows by suspending (111.68 kg m –2 hr –1 ) water mist rate. The frictional resistance for air/water mist flow is found to exceed that in the single-phase air flow. Compared to each water mist rate over the investigated range, the percentage enhancement in the overall heat transfer performance factor of around 116%, 35%, and 10% respectively for all the heated rows under the highest water mist rate. New experimental results obtained can be used in the development of heat exchanger modules design processes.
Highlights
In air/water mist cooling process, the water mist carried by the main air flow hits the first row of heating surface located upstream
These results suggest that suspending water mist in the main air flow is a very efficient thermal management means
The average surface temperature on the first heated row decreased extremely along with the increase in the water mist rate (j) due to the thin water film wetting that occurred in high water mist rate and Reynolds number (Re > 17 500)
Summary
In air/water mist cooling process, the water mist carried by the main air flow hits the first row of heating surface located upstream. For mist-cooled heat exchanger, Yang et al [8], Treble [9], Song et al [10] and Deshmukh et al [11] have carried out experimental studies to get the fundamental data for an enhanced mist-cooled heat exchanger These studies have largely improved the understanding of the air/water mist flow heat transfer enhancement mechanism. They failed to estimate the sufficient relation between the heat transfer rate and a range of relevant parameters of the heated surface located in downstream rows of heat exchange devices
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