We are gonna built an experimental setup about the flow of supercritical CO2 under constant heat flux in stainless steel circular microtube (0.5 mm diameter and 300 mm length). It will be placed lots of T-type thermocouple along the tube to measure the wall and hence the bulk temperature. I would like to take your advice about the correct inserting types of thermocouples on the tube to take the better results. Regards,
I think using thermocouples will be challenging in your case, because the tube inner diameter is very small. If your external diameter is big enough (>3mm) you could consider to drill or laser etch small holes into the tube and then inserting the thermocouples in those holes using thermal paste. Make sure that the thermocouples are electrically insulated from the tube wall to avoid erroneous measurements. But the problem with this approach is that the thermocouples itself are evasive, meaning that they will inevitably influence the local heat flux.
Did you consider other alternatives? You could for example measure the external wall temperature with an infrared camera or IR sensor. Alternatively, you could measure the electrical resistance of the tube itself (or sections of the tube) using a Wheatstone bridge. The electrical resistance is related to the average temperature of the tube by the temperature coefficient of resistivity. (This is essentially the same principle as a Pt100 sensor.)
Dear Ergin,
a measurement with contact thermometers like thermocouples will probably affect the wall temperature at the given dimensions because of different reasons.
If you place the thermocouple on the outside of the tube (e.g. laser-welded) and the thermocouple has nearly the same diameter as the tube, it will change the local heat flux in a critical way. Always keep in mind the basic rule that the sensor for temperature measurement should be small compared to the size of the object you measure.
If you drill a hole and put a mineral insulated thermocouple inside, you do not exactly know where the hot junction is located in the tip of the thermocouple. Therefore, you should always try to place the thermocouple parallel to the surface where you want to measure the temperature.
Try to consider alternatives to contact thermometers. With IR-sensors you will probably have problems finding out the right emissivity and angle. Additionally, the object you try to measure is quite small, so you have to find an apropriate IR-sensor wiht a really small spot size.
Surface temperature measurement is always challenging...
You could use a pure copper pipe and spot weld to it small constantan (0.1mm diameter) single wires so making a series of T thermocouples. Be sure they are not electrically shorted on the cold side.
The copper tube will also ensure a temperature very close to the pipe internal one.
Sir, as it is a thin in nature, embedded the grounded thermocouples (Sheath materials can be used as stainless steel or coper material) or RTDs are the best way to measure the temperatrure.
Thank you sir
Dear Ergin,
(a) Thermometers b) semiconductor Probes like a resistance probe c) Non-contact- non-contact temperature sensor category includes a wide variety of primarily optical devices(single reading devices, camera reading devices, camera system outputs, control system outputs, digital output transmitters, Ethernet devices) could be used.
Hope it help you out.
Ashish
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