The issue of measuring fluid temperature
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I would like to ask the experts: is there any difference between the temperature measured using a \"glass mercury thermometer\" on the outer wall of steel pipes in the white steel processing process and the actual temperature of the fluid inside the pipes? If there is such a difference, will it be more than 10 degrees Celsius? (assuming the effect of ambient temperature is ignored)
No, but the insertion length needs to be sufficient
It won’t exceed that much; the difference isn’t significant. If environmental factors are taken into account when measuring steam, it’s possible
What’s the point? Measuring the temperature of the medium is not the same as measuring the temperature of the tube wall. Generally, it’s the temperature of the medium inside the tube that is measured; it’s rare to measure the temperature of the tube wall. Unless the temperature is very high. Use a mercury thermometer to measure it? It seems that this is not allowed in the chemical industry. 10 degrees short, haha, not necessarily. Is the poster going to do an experiment?
Using a mercury thermometer is likely not very effective; it seems unable to measure very high temperatures. Even when used with a mercury thermometer, there will be discrepancies, as the temperature at the center of the tube is the highest while it’s lower near the walls. However, the temperature difference shouldn’t be that great. It’s best to use an infrared thermometer, as it is simple, convenient, practical, and offers minimal errors.
The temperature measured with a \"glass mercury thermometer\" on the outer wall of the stainless steel process pipeline is determined through heat transfer; I think the error of 10 degrees Celsius is quite low.
What is the purpose of the poster? Mercury thermometers are still used in industry; if they are indeed used, then must the pipes be insulated? If there is no insulation layer, then there’s nothing to say about it – it’s definitely not allowed, not even at 10°
Mercury thermometers are quite inaccurate; the error increases as the temperature rises. At 20 degrees Celsius, for example, the error is already 0.5 degrees. Also, why is it necessary to measure the temperature at the wall of the tube? Glass thermometers have a red line that indicates the proper insertion point – it’s important to follow this guide in order to ensure accuracy. If high precision is required, it’s better not to use glass thermometers; they can only provide an approximate reading.:lol
Also, since you need to measure fluids, you need to pay attention to the insertion direction when installing it; generally, it should be in counterflow or at an angle of 45 degrees. Instrument installers are constantly inserting things, haha!
There is definitely a significant difference between the temperature measured outside the pipe and the actual temperature of the fluid inside it. Moreover, mercury thermometers are not capable of measuring high temperatures. If the pipe can be opened, it is recommended to use bimetallic thermometers; although their accuracy is lower (with grades of 1, 1.5, or 2.5), the temperatures they measure are much more accurate than those obtained with mercury thermometers, and they are also not expensive.
Add a sleeve, or use a thermistor for measurement
I’ve never heard of a method for measuring the temperature of the medium inside pipes like this. To accurately measure temperature with a mercury thermometer, it is essential to ensure that the mercury bulb at its bottom is completely submerged in the medium being measured. The error in the measurement method mentioned by the original poster cannot be quantitatively calculated. This is itself an incorrect method of measurement; how can one then calculate its error? If local temperature indication is required, a bimetallic thermometer is a good choice. It has much less error compared to the measurement methods you mentioned, and the price is not high either. Buy an armored bimetallic thermometer, along with a sleeve that can be connected via flanges or threads.
There is a difference. The contact area between the measuring surface of the mercury thermometer and the steel tube is too small; as a result, the error between the temperature measured and the temperature of the fluid inside the tube could be more than 10 degrees
A surface thermometer or infrared thermometer can be used.