Discharge characteristics of different lightning air terminals under composite voltages

Different types of lightning air terminals have been designed over the years.Concern regarding the effect of different types of air terminals,especially the early streamer emission(ESE)-type,remains controversial.This paper describes the discharge characteristics of different types of air terminals,two of which are quite similar to the ESE-type dynasphere,and concludes that the tested non-standard air terminals have discharge characteristics similar to those of Franklin rods and that their lightning protection performance should be similar.

Application of jet main region specification model in CFD simulation for room air movement analysis

This paper analyzes the applications of four air terminal device（ATD）models（i.e.,the basic model,the box model,the N-point momentum model,the jet main region specification model）in computational fluid dynamics（CFD）simulation and their performance in case study.A full-scale experiment is performed in an environment chamber,and the measured air velocity and temperature fields are compared with the simulation results by using four ATD models.The velocity and temperature fields are measured by an omni-directional thermo-anemometer system.It demonstrates that the basic model and the box model are not applicable to complicated air terminal devices.At the occupant area,the relative errors between simulated and measured air velocities are less than 20% based on the N-point momentum model and the jet main region specification model.Around the ATD zone,the relative error between the numerical and measured air velocity based on the jet main region specification model is less than 15%.The jet main region specification model is proved to be an applicable approach and a more accurate way to study the airflow pattern around the ATD with complicated geometry.

Comparison study of thermal comfort and energy saving under eight different ventilation modes for space heating

The relative location of inlets and outlets plays an important role in thermal comfort and energy conservation under ventilation modes for the building non-uniform indoor environment.Hence,a comparison study of thermal comfort and energy efficiency of eight widely-used ventilation modes for space heating was conducted in this study.Both subjective experiments and verified computational fluid dynamics(CFD)models were carried out.In the subjective experiments,the vote of local thermal sensation(LTS),overall thermal sensation(OTS)and draft sensation were collected.In the CFD simulations,RNG κ-ε model was applied to compare and analyze the air temperature field,turbulence intensity,ventilation effectiveness and air diffusion performance index(ADPI).The thermal comfort results showed that the air inlets are better located at the mid-height level of a wall,and the outlets are located at the same or higher height.While the results of the energy efficiency suggested that the inlets are better installed at the lower level of a wall,and the outlets should be placed far from the inlets.Since the results were conflict,the economic-comfort ratio was introduced to calculate and compare the thermal comfort and energy efficiency simultaneously.The final results concluded that it can achieve excellent thermal comfort performance without sacrificing energy efficiency when the inlets are at the height of 1.2 m of the front wall,and the outlets are at 1.2 m height of the back wall.Hence it is the best choice for the winter air distribution in northern China.This study can offer a guideline for the air terminal arrangements in non-uniform ventilation under heating mode.