Measuring the relative humidity of humid air using a hair hygrometer

Abstract

An instrument has been designed and constructed to allow direct measurement of the relative humidity of humid air. The objective of the study is to use the effect of humidity on the linear expansion of a piece of hair that is pulled with a spring or a small weight while exposed to the humid air. This can result in producing such an instrument if the hair sample is specific. For the hair used in this work, relative humidities ranging from 0 to 100 per cent result in a one-dimensional change of about 0.02m/m. As the humidity of the air is decreased or increased, the hair is shortened or lengthened and turns the pointer connected to its end. The pointer detects the relative humidity of humid air on a calibrated plate. A series of experimental data are extracted in different environments using this instrument. The data are in good agreement with the results obtained from the psychrometric chart and mass transfer calculations.