An analytical method for detecting blown-out shots in coal mines

Abstract

Permanent Magnet Flow Meter (PMFM) made with ALNICO-5 magnet is presently used for measuring flow in sodium circuits. These flowmeters are heavy, bulky and occupies more space in the plant mainly because of the large size of the magnet assembly. Rare earth permanent magnet material like Samarium Cobalt (SmCo) is having higher coercivity and energy product than ALNICO-5. A PMFM suitable for 20 NB pipe was designed and manufactured using SmCo magnet assembly. The magnetic flux density obtained at the center of air gap was 60% higher than the flux density of ALNICO-5 assembly of nearly same size. The 20 NB size PMFM with SmCo magnet assembly was calibrated in sodium against a reference PMFM in 500 kW sodium loop. Calibration runs were conducted at different temperatures of 300 C, 400 C and 500 C and at different flow rates. Sensitivity of the SmCo PMFM was found to be 3.4 mV/m3/h compared to 2.1 mV/m3/h as that of ALNICO-5 PMFM. Two SmCo magnet assemblies from the same lot were used for stability testing of the magnet. Long term stability of the magnet assembly at operating temperature was tested by keeping the magnet assembly in the furnace at 100 °C for 5000 hours and was observed that flux density remains steady. Accelerated long term stability test at 200 °C for 5000 hours was also completed and found that no significant reduction in flux density. The results shows that stability of the magnet with time and temperature is found to be good. Hence the feasibility of manufacturing PM flowmeters suitable for high temperature sodium flow measurement with SmCo magnet assembly was demonstrated. These types of flow meters will be compact compared to ALNICO-5 flowmeters if designed for same sensitivity and can be deployed in future Fast reactors. This paper gives the details of Samarium cobalt flowmeter, sensitivity estimate, stability testing and sodium test results.