THERMAL FLOWMETER

To provide a thermal flowmeter having a sub-passage of a curved folded-back shape and not of a loop-like circulating shape, in which a lack of balance in the flow velocity distribution of a gas being measured is suppressed.SOLUTION: A detour passage 113 includes a direction-changing part 113a curved or branched from an inlet passage 111 in a direction that intersects a main flow direction F, a turnaround part 113b curved so as to turn around toward an outlet passage 112, and an inner circumferential resistance part 113c provided between this turnaround part 113b and the direction-changing part 113a. The pressure loss of the inner circumferential resistance part 113c to a gas G being measured that flows on the inner circumferential side of the detour passage 113 is higher than the pressure loss to the gas G being measured that flows on the outer circumferential side of the detour passage 113. A flow rate measuring element 120 is arranged between the inner circumferential resistance part 113c of the detour passage 113 and the outlet passage 112.SELECTED DRAWING: Figure 2 【課題】ループ状の周回形状を有しない湾曲した折返し形状の副通路を有する熱式流量計において、被計測気体の流速分布の偏りを抑制する。【解決手段】迂回通路１１３は、入口通路１１１から主流れ方向Ｆに交差する方向に湾曲または分岐した方向転換部１１３ａと、出口通路１１２に向けて折り返すように湾曲した折返し部１１３ｂと、この折返し部１１３ｂと方向転換部１１３ａとの間に設けられた内周抵抗部１１３ｃとを有している。内周抵抗部１１３ｃは、迂回通路１１３の内周側を流れる被計測気体Ｇに対する圧力損失が迂回通路１１３の外周側を流れる被計測気体Ｇに対する圧力損失よりも高い。流量計測素子１２０は、迂回通路１１３の内周抵抗部１１３ｃと出口通路１１２との間に配置されている。【選択図】図２