Development of exposed rapid thermocouple for internal fluid temperature testing under pressure

•A novel exposed thermocouple with multi-bended channels is designed for transient internal fluid temperature tests and can avoid the leakage of the internal fluid under 2 MPa, 200 °C.•The thermocouple has the ability to detect transient temperature change with extremely fast response time of 1.74 ms.•The model shows that the heat conduction error △Ts could be neglected in this case. The thermal inertia error △Td caused by lag was the main error of thermal error caused by a thermocouple placed in a flow field.•The average error of the whole exposed thermocouple was 0.32 K, which was 36 % lower than that in the referred literature.