A new approach to the analysis of heat and mass transfer characteristics for laminar air flow inside vertical plate channels with falling water film evaporation

Ren, Chong; Wan, Yangda

doi:10.1016/j.ijheatmasstransfer.2016.07.109

Cited by 23 publications

(9 citation statements)

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“…Pauken [38] proposed an empirical correlation between the convective mass transfer coefficients and the mean air velocity ( ∞ ) as ℎ = + ∞ (a > 0, b > 0) (13) With an assumption of saturated vapor condition at the liquid-air interface, , can be determined from the surface temperature of liquid film. ,∞ is taken as a constant in this research, as the temperature and relative humidity of the inlet air are 21 ± 1 ºC and 55 ± 3 %, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Experimental and numerical studies have been performed to investigate the factors related to the evaporation rates. These include (a) flow conditions: natural [12], laminar [13], and turbulent convection [14]; (b) geometries, such as vertical channel [15], inclined planes [7], and tube bundles [16]; and (c) coolants, such as water, R134a [17], and ammonia-water mixtures [18].…”

Section: Introductionmentioning

confidence: 99%

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Sweating-boosted air cooling using nanoscale CuO wick structures

Wang

Dawas

Alwazzan

et al. 2017

International Journal of Heat and Mass Transfer

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Low heat transfer coefficient (HTC) in air/fin-side is the bottleneck of dry cooling strategies for thermal power plants. Inspired by the phase change heat transfer during the perspiration of mammals, a sweating-boosted air cooling strategy with on-demand water dripping is proposed. The testing samples are featured with macroscale grooves for global liquid delivery, and with nanoscale hydrophilic copper oxide (CuO) wick structures for local liquid spreading. The experiments of sweating-boosted air cooling are conducted in a wind tunnel system. There are three wetting conditions with increasing dripping rates: dry, partially wetted, and flooded conditions. In the partially wetted conditions, the surface temperatures reduce and HTCs increase with increasing dripping rates. For a given dripping rate of water, HTCs are enhanced and surface temperatures are reduced with increasing air velocities. High air velocity and low surface temperature have a trade-off effect on the evaporation process. This effect results in almost constant saturated dripping rates for a given thermal load. A linear relationship between the saturated dripping rates and the thermal loads confirms that the evaporation dominates the heat transfer process of sweating-boosted air cooling. Complete surface wetting is obtained on the designed surfaces, but no obvious effect of groove width on HTCs is observed. Sweating-boosted air cooling can significantly increase air-fin side HTC in air cooled condenser (ACC), and dramatically reduce the water consumption compared to current water evaporative

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sweating-boosted air cooling using nanoscale CuO wick structures

Wang

Dawas

Alwazzan

et al. 2017

International Journal of Heat and Mass Transfer

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“…Recently, new approaches for analyzing heat and mass transfer in laminar moist air flow inside vertical plate channels with falling water film are demonstrated [14]. Moreover, this has been shown for direct air cooling of forced convection [15], as well.…”

Section: Introductionmentioning

confidence: 99%

The numerical model for direct evaporative cooler

Kovačević

Sourbron

2017

Applied Thermal Engineering

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This paper presents a numerical model for a compact direct-contact cross-flow air/water heat exchanger where evaporating water cools down an air stream, and where an innovatively designed metallic direct evaporative pad enhances air-water interaction. The numerical model implements energy and mass conservation equations of humid air and water in a one-dimensional geometry by applying correlations for heat and mass transfer coefficients. The system of ordinary differential equations is solved by central-finite discretisation using Matlab. The effective hydraulic diameter is isolated as the only unknown model parameter, and is determined by a parameter estimation using experimental data available from a producer of such a direct evaporative pad. The numerical model is able to predict the air outlet temperature, with an maximal error of 1.33 % compared to experimental data for different inlet temperature and humidity values. Humid air properties inside and at the outlet of the direct evaporative pad, the pad effectiveness and the water consumption can be evaluated by the presented model. The use of the numerical model is demonstrated with examples analysing the impact on heat exchanger effectiveness of a changed geometry (design analysis) and of varying air inlet conditions for a given geometry (operational analysis).

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“…Recently, the evaporation process gained great interest in numerical research due to its significant impact on cooling efficiency. Heat and mass transfer characteristics for laminar air flow inside vertical plate channels during cooling process with falling water film evaporation were studied using finite volume method [13,14], where empirical correlations were derived to calculate the Nusselt and Sherwood numbers taking into consideration the effects of several parameters [14]. On the other hand, the mathematical Trefftz method was employed to examine the heat transfer coefficient for Inconel during spray cooling [15].…”

Section: Introductionmentioning

confidence: 99%