Fundamentals and applications of CFD technology on analyzing falling film heat and mass exchangers: A comprehensive review

This article deals with an experimental investigation of thermal performance of mechanical draft wet cooling towers by changing various parameters such as hot water temperature, water flow rate, air mass flow rate and stage numbers of packing. In fact, this research attempts to focus on packing density influences with an emphasis on the role of stage numbers of packing. The results imply that coefficient of efficiency is in direct relation with air mass flow rate, hot water temperature and stage numbers of packing, while it diminishes by increasing the water flow rate. On the other hand, thermal images are provided for visualizing temperature distribution within the studied cooling tower. Afterward, these images are utilized so as to obtain pertinent temperature histograms and also temperature distribution along the vertical and horizontal directions for three packings. Finally, regression analysis is employed in order to derive design equations from the measured data.

Investigation of heat transfer in mechanical draft wet cooling towers using infrared thermal images: An experimental study.

Deciphering the heat and mass transfer behaviors of staggered tube bundles in a closed wet cooling tower using a 3-D VOF model

The present work deals with an experimental study of the performance of an evaporative cooling tower (ECT) with a developed fill pack. The fill pack consists of inclined-corrugated contact elements (ICCE) made of the metal plates with perforations, providing a uniform distribution of interacting phases over the ECT cross-sectional area. This study investigates the effect of fill pack design on hydraulic and thermal characteristics of the ECT. Four empirical equations were found for the pressure drop through four types of dry fill packs. The detailed analysis includes two fill packs consisting of ICCE with 6 mm holes with and without a metal grid. Hydraulic operating regimes of the ECT and empirical equations for the wetting pressure drop through the fill packs had been defined. Based on experimental data and the method of transfer units, empirical relationships of the volumetric mass transfer coefficients were determined. The comparison between the obtained results and those found in the literature for other types of proves the high performance of the developed fill packs. Besides, using the Lewis relation, the dependencies of the volumetric heat transfer coefficient on the average air velocity were analyzed. The results indicate that maximum cooling efficiency of the studied fill packs was observed at the low wetting rates according to the Merkel number. The fill pack from ICCE with 6 mm holes and without the metal grid seems to be more efficient, as it provides relatively higher values of the heat and mass transfer coefficient and lower pressure drop.

Experimental investigation of fill pack impact on thermal-hydraulic performance of evaporative cooling tower

This study was designed to experimentally investigate the intensification effect of Al2O3/water nanofluid used as the spray fluid on the thermal performance of counterflow closed wet cooling towers (CWCTs). The mass fraction of nanoparticles was 0.1–1 wt % with nanoparticle dimensions of 10, 30, and 80 nm. Meanwhile, glycerin as stabilizer was used. After that the thermophysical properties of Al2O3 nanofluids were systematically measured. It was observed that the thermal conductivity, density, and viscosity of Al2O3 nanofluids increased with the increments of mass fraction. The results revealed that the maximum mass transfer coefficient was found to be 0.16 kg·m–2 s–1 for 0.5 wt % nanofluids and spray mass flow rate of 0.278 kg·s–1. Moreover, the heat transfer capacity of the CWCT spraying 0.5 wt % Al2O3 nanofluid could reach 1.22 times that of the water case, while the water consumption reduced about 15% under the same heat transfer capacity.

Bench-Scale Experimental Study on the Heat Transfer Intensification of a Closed Wet Cooling Tower Using Aluminum Oxide Nanofluids

Deciphering the thermal and hydraulic performances of closed wet cooling towers with plain, oval and longitudinal fin tubes

This work proposes one kind of closed wet cooling tower (CWCT) equipped with longitudinal finned tubes, and develops a two-dimensional numerical model using FLUENT. The Navier-Stokes and k-e equations are applied to calculate the vapor flow and Reynolds stress. Important operational/structural parameters such as the inlet air angle and velocity are analyzed by the multi-fields synergy theory, in which the increment in synergy degree between the velocity field, temperature field and humidity field can enhance the heat and mass transfers. The results show that the increase in fin number, inlet air velocity and decrease in fin height are conducive to the distribution uniformity of vortex and air turbulence in CWCT, which improves the field synergy degree between the velocity, temperature and humidity. With the alteration of air inlet angle, the field synergy degree is optimal at the angle of 45o, in which the heat transfer coefficient and mass transfer coefficient are about 1.15 times and 1.5 times of those of 30o, respectively. Moreover, the field synergy principle revealed that near the fin where the thermal boundary layer is thin, the α of the fin tube cases were about 1.2 ~ 1.5 times.

Heat transfer enhancement for the coil zone of closed wet cooling towers through field synergy analysis

The invention discloses a water-saving fog-dispersing closed cooling tower. A fan system, a throttling and water collecting device, a spraying system, a filler part, a cooling coil and the like are arranged in a tower body of the closed cooling tower from top to bottom. The throttling and water collecting device is a throttling cooling element of a special structure and is used for lowering the temperature and humidity of air at an outlet of the closed cooling tower, so that evaporation losses spray water are reduced, and blowing losses are reduced. The closed cooling tower utilizes the throttling expansion principle, after wet air in the closed cooling tower passes through a throttling expansion element at the tower top, the wet air expands rapidly, and the temperature and humidity of the wet air are lowered at the same time. By adopting the technical scheme, the rime fog phenomenon occurring to the tower top of the closed cooling tower can be eliminated, and the using amount of the spray water of the closed cooling tower is reduced. The purposes of water conservation and fog dispersal are achieved through a throttling cooling method, and the closed cooling tower has the advantages of being good in water saving effect, capable of keeping circulating water clean, low in maintaining cost, easy to operate and the like.

Xiaocui Xie

Papers

Deciphering the heat and mass transfer behaviors of staggered tube bundles in a closed wet cooling tower using a 3-D VOF model

Deciphering the thermal and hydraulic performances of closed wet cooling towers with plain, oval and longitudinal fin tubes

Bench-Scale Experimental Study on the Heat Transfer Intensification of a Closed Wet Cooling Tower Using Aluminum Oxide Nanofluids

Heat transfer enhancement for the coil zone of closed wet cooling towers through field synergy analysis

Water-saving fog-dispersing closed cooling tower