Numerical flow simulation in the humidity of external auditory canal

Abstract

Objective To determine the influence of environmental factors on the external auditory canal humidity through the characteristics of external auditory canal flow calculated via computational fluid dynamics (CFD) , and to provide the preliminary theoretical basis for the physiological and pathological phenomena of the external auditory canal. Methods A study case was selected by review of history, and findings of otoscopy, ear endoscopy, acoustic immittance measurement and CT scanning. CFD method was used to calculate the temperature, velocity and humidity characteristics of the external auditory canal in steady state. The effects of environmental factors (such as airflow velocity, temperature and humidity) on the external auditory canal airflow humidity were analyzed. Results The average temperature of the external auditory canal was 34.01 ℃ when the rate of water vapor released from the external auditory canal was 1.557×10-6 kg/m2s, the ambient temperature was 20 ℃, the ambient humidity was 5.991 g/m3 and the ambient wind speed was 0.25 m/s. The average airflow velocity in the external auditory canal area was 4.6×10-4 m/s; the average humidity in the external auditory canal region was 18.963 g/m3. The humidity presented a gradient-reducing feature from inside to the outside. Reduced ambient temperature (and thereby an increase in the temperature difference) led to decreased external auditory canal humidity. The external auditory canal humidity showed only minimal change when the ambient wind speed was less than 0.5 m/s, and then decreased rapidly along with increasing ambient airflow velocity. The external auditory canal humidity increasedsynchronously with the ambient humidity. Conclusions The external auditory canal is a relatively occluded area with a very low-speed airflow, a temperature close to the human body temperature, and a humidity decreasing from the inside to the outside. The external auditory canal humidity decreases with the increase in the ambient wind speed. The ambient temperature affects the humidity of the external auditory canal by a change in the airflow, but the effect may be minimal. The external auditory canal humidity increased with the ambient humidity. Key words: Ear canal; Microfluidic analytical techniques; Humidity