Qualitative Analysis of the LiCl-Hygrometer

Abstract

   A mathematical model is introduced to clarify the characteristics of the LiCl-hygrometer. From the past experiments the vapour pressure of the wicking of the LiCl-hygrometer is proved to be a function of temperature and liquid water content, and by using this relation the behaviour of the LiCl-hygrometer may be explained qualitatively. The main results are as follows. (1) The hygrometer system can be described by second order derivative equations, whose coefficients are functions of the operating conditions, i.e., heater voltage, ventilation wind speed and temperature of the ambient air. (2) The dynamic response to the step change of one parameter is equivalent to that of an ordinary second order system when both step and delta functions are applied. (3) Under fixed vapour pressure of the ambient air, the change of the operating conditions reducing the initial net heat loss of the wicking causes the equilibrium temperature to rise and the equilibrium liquid water content to diminish, and vice versa. (4) When the operating conditions are fixed, the increase of the vapour pressure of the ambient air raises the equilibrium liquid water content, so that the vapour pressure-temperature curve of the LiCl-hygrometer has steeper inclination than that of the saturated bulk LiCl solution.