Heat and Mass Transfer From Freely Falling Drops

Abstract

When a drop breaks free from a liquid film or feeding orifice and falls through an atmosphere of lower temperature it experiences a transient heat and mass transfer process involving acceleration, the development of hydrodynamic, thermal, and concentration boundary layers in the gas, oscillation of the drop shape, and the development of internal circulation within the drop. This problem, which is of importance in evaporative cooling systems, has been studied experimentally for water drops 3–6 mm in diameter falling through air. Study of a simplified set of governing equations indicates that similitude does not exist in this problem. However, it has been found that for this size range an approximate procedure based on the assumption of negligible internal thermal resistance and an empirical transient correction factor applied to the Ranz-Marshall [1] correlation could describe the data very well.

CFD Modeling Analysis of Mechanical Draft Cooling Tower

“…The calculation results show that when single droplet has 6mm diameter, the model underpredicts the data by about 18% on the average since the current model assumes spherical droplet. The experimental observations [10] clearly show that when droplet are larger than 4mm, it become non-spherical during free falling period. Test data -4mm droplet [Yao, 1976] Model predictions -4mm droplet Air temp = 22 deg C 36% Relative humidity Test data -6mm droplet [Yao, 1976] Model predictions -6mm droplet…”

“…As shown in Fig. 7, the present model was benchmarked against the test results available in the literature [10]. The calculation results show that when single droplet has 6mm diameter, the model underpredicts the data by about 18% on the average since the current model assumes spherical droplet.…”

“…Test data -3mm droplet [Yao, 1976] Droplet size = 3 mm Droplet size = 4 mm Droplet size = 6 mm Fig. 7.…”

CFD Modeling and Analysis for a-Area and H-Area Cooling Towers

“…The calculation results show that when single droplet has 6 mm diameter, the model under predicts the data by about 18% on the average since the current model assumes spherical droplet. The experimental observations [11] clearly show that when a droplet is larger than 4mm, it becomes non-spherical during free fall. Test data -4mm droplet [Yao, 1976] Model predictions -4mm droplet Air temp = 22 deg C 36% Relative humidity Test data -6mm droplet [Yao, 1976] Model predictions -6mm droplet Model predictions -3mm droplet Test data -3mm droplet [Yao, 1976] Droplet size = 3 mm …”

“…Based on the literature information [10] and SRS experimental observation, the model used the fixed droplet diameter to be 1 mm for the present analysis. Yao and Schrock [11] performed the experimental work to measure the temperature drops for 3 to 5 mm diameter ranges of water droplets falling through a 3m column containing the conditioned air. As shown in Fig.…”