Quantification of local ventilation efficiency under bicycle helmets

Abstract

Bicycle helmets can reduce the risk for head injuries in traffic accidents where cyclists are involved. Unfortunately, bicycle helmets are often unpopular due to the thermal discomfort that they may induce. Most bicycle helmets have therefore many large vents. These large vents can give helmet wearers the perception that helmets are well ventilated, but their efficiency on local airflow between head and helmet has not yet been quantified.This research aimed at quantifying local ventilation efficiency of five bicycle helmets using a tracer gas measurement technique for 13 positions between a manikin head and a helmet. The 3D fresh air distributions that were quantified are a major parameter influencing thermal comfort of a bicycle helmet. Large variations in ventilation efficiency were seen for all helmets: from 0 × 10−3 s−1 to 16 × 10−3 s−1 or 20 × 10−3 s−1. Highly ventilated zones were observed at the front of the manikin head, while low ventilated zones were monitored at the rear for all helmets.This research suggests minimising the number of inlet vents, but to maximise the projected inlet area of each inlet vent to optimize the thermal characteristics of bicycle helmets. Furthermore, it is suggested that inlets in the front of a bicycle helmet should be connected with outlets at the rear using air channels. Vents on top of a bicycle helmet are not always useful during cycling. Relevance to industryThermal discomfort is one of the major reasons why cyclists do not like to wear a helmet. The described method allows characterizing airflow between a helmet and a manikin head for real helmets that can be used on simple prototypes as well as final models.