Study On Factors Affecting Of Contact Gas Alarm's Hysteresis

Contact type gas alarm is a kind of security equipment to detect gas leakage.It can issue the warning that reduces the incidence of accidents caused by gas leak fire,explosion,poisoning when the gas leaks.It is widely used in the kitchen and dining halls,shopping malls,factories and other places.The gas is spread to the inner of the alarm contacting with the sensor through the orifices of the alarm.However,the outer shell of the alarm can obstruct the gas diffusion,so the contact gas alarm itself has the phenomenon of alarm lag.However,the outer shell of the alarm device will impede the gas diffusion,so the alarm has a warning lag.Because of long-term cooking activities,there are a lot of cooking fumes in the kitchen.Some fumes will be attached to the alarm,the breathing holes will be blocked that causing alarm lag.This study uses the CFD to imitates the contact type domestic and business gas alarm in the normal condition and oil fume contamination condition.We can come to the conclusion that the alarm time and the lag time.In this paper the mathematical model which was solved by the finite volume method was established based on continuity equation,momentum equation,energy equation,and combining with boundary conditions an initial conditions.The gas diffusion situation of the contact type domestic and commercial gas alarm is simulated under normal condition.At the beginning,the external of gas alarm is the homogeneous mixture of natural natural gas and air,the concentration is 40%LEL(volume fraction is 2%),and the inside of the contact gas alarm is air.through simulation,Through simulation,it can be obtained that it needs 150.6s and 105.7s when the volume fraction of domestic and commercial gas alarm reach 1%.When the breathing hole of a gas alarm is blocked by oil,the more serious the breathing hole is,the longer the alarm time is.Through the numerical simulation,it is concluded that the time required for the internal sensing element to reach the alarm concentration is needed when the inlets of domestic and commercial gas alarm are reduced by 20%,40%,60% and 80%.Based on the models of contact domestic and commercial gas alarm,the size of breathing holes is enlarged,and the appropriate size of breathing holes is obtained through simulation study.The effective anti smoke methods are put forward for the gas alarm.In the dailyapplication of contact gas alarm,there will appear false alarm because of improper maintenance.In this paper,suggestions are made for routine maintenance of contact gas alarm,which can make users more safe and more scientific use of gas alarm.In this paper,suggestions are made for routine maintenance of contact gas alarm,which can make users more safe and more scientific use the gas alarm.