GB174338A - Improved apparatus for measuring the flow-velocity of gases in the flues of furnaces and the like - Google Patents

Abstract

174,338. Siemens & Halske Akt.-Ges Jan. 20, 1921, [Convention date]. Gas meters.-In apparatus for measuring the draught in the flues of boiler furnaces, and alsc for measuring the carbonic acid content of flue gases, use is made of the variation in the resis. tance of an electrically-heated wire which is exposed to the cooling effect of air or gases induced by the flue draught or drawn from the flue. In the apparatus two points of the furnace flue in which the draught is to be measured are connected by pipes 5, 6 to chambers 1, 2 respectively open to the atmosphere at 7, 8. The chambers 1, 2 contain electrically heated measuring-wires 3, 4 arranged as two arms of a wheatstone bridge, the other two arms of the bridge being indicated by the resistances 10, 11. According to the difference of pressure at the two points of the furnace flue, air flows at different velocities through the pipes 5, 6 and cools the electrically heated wires to different degrees. The temperature difference of the wires is a measure of the pressure difference in the flue, and theerfore a measure of the velocity of the draught. The temperature difference of the wires 3, 4 is measured by determining their resistance difference by the galvanometer 9. In some cases it is sufficient to determine the partial vacuum at one point only in the flue. In such a case one of the chambers 1, 2 is shut off so that it contains air only, air being drawn by the flue through the other chamber. When it is desired to measure the carbonic-acid content of flue gases, one of the chambers 1, 2 is filled with air and closed while the flue gases are drawn through the other. Owing to the lower conductivitv of carbonic acid a greater heating effect of the wire over which it flows is produced, and the temperature of the wire thus constitutes a measure of the carbonic acid content.