Thermal conductivity detector in gas analyser - is preceded by heat exchanger to stabilise temp. of incoming gas to that of detector casing

摘要

A measuring device for gas analysis equipment used in the determination of thermal conductivity of gases comprises a detector unit (11) containing a measuring sensor bore (12), measuring sensor (13) and gas inlet and outlet ducts (18,19). The entire casing of the detector block is thermostatically heated and externally insulated. Upstream of the detector block (11) the gas inlet duct (18) passes through a heat exchanger (22) which is maintained at the same temperature as the detector block casing itself. Pref. this heat exchanger is in good thermally conducting contact with the heated casing of the detector block. The heat exchanger may comprise a helical tube (23) in good thermal contact with a hollow cylindrical core (notshown). This core is in good thermal conduct with the detector casing. . Used as a measuring device in gas chromatography where the compsn. may be determined from the thermal conductivity. The result of the readings is affected not merely by the compsn. however, but also by the flow velocity of the gas and its inlet temperature. Previous devices have partly overcome this problem but suffer from fluctuation inlet temp. of the gas leading to unstable conditions. By incorporating a heat exchanger upstream of the detector, the inlet gas is already brought to the temperature of the detector casing. Consequently the stability of the device is improved and its sensitivity is increased while at the same time constants are reduced.