![]() The lower half had solid mounting points located near the lower ear lobe and on the inside surfaces of the neck region. The top half had 36 evenly and symmetrically spaced holes across the surface of the scalp for the placement of thermocouples. The head was split along the reference plane of a K-type headform, and as such defines the head region typically covered by a cycling helmet. This head model was scaled by a minor factor such that it fitted a typical 58 cm medium cycling helmet and this provided the surface for instrument installation. Averaged 3D models of five different heads of standard sizes were created from this data, with the 50th percentile head size being obtained by the authors. The external geometry of the headform was obtained from a survey by Zhuang and Bradtmiller that measured head and facial dimensions of 3997 subjects in conjunction to scanning 1013 of the subjects with a 3D scanner. Using a material with a high thermal conductivity, such as aluminium or copper, would result in high heat dissipation with any localized hot spots quickly dissipating over the entire head, obscuring finer cooling details. This facilitates the design and evaluation of cycling helmets, as the effectiveness of cooling vents can clearly be seen in thermal images or temperature maps. Acrylonitrile Butadiene Styrene (ABS) has a value for k close to but slightly lower than any natural human material and hence would encourage the creation of local hot spots. In order to adequately resolve the temperature distribution across the scalp, a thermal conductivity close to that of a human head was a primary factor in material choice. As a head has a relatively low thermal conductivity it does not distribute heat evenly over the scalp, rather the local temperature can vary considerably from the average temperature. The value for k for various materials used previously to construct heated headforms are presented in Table 1 alongside estimated k for human flesh. The rate of this heat transfer is the conduction heat flux q″ (Wm −2) and is given in Equation 1 where k (Wm −1 K −1) is the thermal conductivity of the material and Δ T (K) is the change in temperature. These temperature gradients are attenuated via lateral conduction across the scalp. Hence a focus in the design of this headform was for the ability to adequately replicate and observe the various hot and cold regions that a human head would experience during cycling. observed spatial differences of up to 5.5 ☌ between different areas of the head. Generally they are similar to the previously described headforms, constructed from aluminium, and incorporate varying numbers of thermocouples.Īs a cyclist’s head is cooled via airflow channeled through vents in their helmet, there can be large variations in the local head temperature depending on the location of these vents. A number of commercial helmet manufacturers have also designed their own heated heads but limited information on these is available. The temperature on the headform was recorded with 13 thermocouples and a weighting scheme was used to determine the average temperature of the whole head. The cooling effectiveness was directly compared to that of a bare sphere measured simultaneously. A different method is demonstrated by Reid and Wang who used a headform constructed from aluminium filled cast urethane that was heated at a constant power. The heater mat is heated to 56 ☌ in still air and the temperature drop is monitored for five minutes when the head is placed in a wind tunnel. attaches a heater pad and nine thermocouples externally to a fashion mannequin head. This allows greater quantification of the local heating efficiency of helmets with a clear distinction in the cooling power differentials between alternate zones. ![]() , however this newer headform is constructed from a carbon-fibre/epoxy matrix and is split into nine thermal zones. An additional headform, which functions in an analogous manner to the Brühwiler head, has also been developed and tested by Martínez et al. This headform produces sweat through pores at a computer-controlled and regulated flow rate. The subsequent input power required to maintain constant temperature conditions corresponds to the heat losses of the head. Each area is maintained at a constant temperature measured by resistance wires on the head surface. A headform constructed by Brühwiler from a polyester fashion mannequin is split into three independently heated areas, two of which are monitored for investigations. The efficacy of a helmet’s cooling ability is generally measured quantitatively through the use of a heated mannequin headform in a wind tunnel which provides convective cooling.
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