Thermal resistance indication issue
Thread Content
For thermoresistors, the displayed value is lower due to insufficient insertion depth. Are there any empirical data indicating by how much the temperature changes in a regular manner when the insertion depth is too low?
This is related to factors such as the heat transfer coefficient of the medium, flow velocity, size of the container, temperature level, and so on; therefore, it is uncertain.........
It can’t possibly go through the pipe. . .
In the case of process pipes or containers, the insertion depth must reach 1/2 of the inner diameter of the pipe or container. In other cases, at least contact with the medium must be ensured.
The insertion depth of the thermometer used to be required by standards to be at 1/3 to 2/3 of the length, but this is difficult to achieve in some cases; when the flow rate in the pipe is high, the strength calculations for the sleeve do not hold up, and sometimes even using a thicker sleeve does not solve the problem. On high-pressure pipelines, the temperature outlet had a DN40 size, and an outer diameter of the sleeve of 38 mm was not acceptable. Therefore, the current \"Specifications for the Selection and Design of Automated Instrumentation\" (HG/T20507-2014) stipulate the following requirements regarding thermometers: 1. Calculation requirements for temperature-resistant sleeves have been added; the vibration frequency should be ≤80% of the natural frequency, and there is no need to calculate the strength of thermometers installed within the equipment. 2. Pipe thermometers (applicable only to process pipes; when equipment such as heating furnaces has no impact on the strength of the casing, the insertion depth is designed according to actual needs): There are common problems in calculating the vibration frequency when the pipe diameter is too large. Specification: The end of the temperature sensing element should be submerged in the inner wall of the pipe by a length of not less than 50 mm, and not more than 125 mm (it is no longer required to be inserted to the center of the pipe). For non-full pipes, the thermometer should be installed on the side or at the bottom. (ASME PDC 19.3)
It is complex to explore this issue; different fluids, different pipe diameters, and different flow speeds all have varying effects； Install it as perpendicular to the flow as much as possible, with its length ideally at the center point. The temperature gradient is also related to the surrounding heat dissipation environment, so it is not easy to discuss