under pressure since this behavior can also generate pressure transient effects of sufficient magnitude to cause false alarms the disk can be annular with a hole in the middle to allow electrolyte ions to pass through the partition between the upper and lower compartments of the cell thereby facilitating normal operation of the cell alternatively the single central hole in the disk could be replaced with a plurality of smaller holes each also capable of allowing electrolyte transport across the disk to the electrode from the main body of the cell the function of the micro porous membrane is to prevent the bulk transport of gas usually in the form of bubbles through the cell it relies on the fact that liquid is held in the pores of the membrane by surface tension and capillary action and that pressure must be applied to overcome these forces before bubbles air are able to cross the membrane the minimum pressure bubble point pressure required to force the liquid out of the membrane pores is related to the membrane capillary geometry according to the following equation p 4k cos u03b8 u03c3 d where p is the bubble point pressure d is the pore diameter k is a geometry correction factor u03b8 is the liquid solid contact angle and u03c3 is the surface tension therefore if a membrane material is chosen with pores of sufficiently small diameter the pressure required for gas to cross the membrane will exceed that created by environmental temperature changes thereby eliminating the temperature transient effect an estimate of the pressure difference that the membrane needs to withstand to eliminate the problem can be calculated from the gas law pv nrt where p v t and.