Heating is the precondition for degassing. If the oil temperature does not come up, the atomisation is poor and the degassing efficiency falls with it. The heating method commonly used on the machine is far-infrared carbon fibre heating, which works on a different heat transfer principle from the electric heating rod that many people are familiar with. Understanding the difference helps to explain why the temperature control readings can be trusted, and also why the warm-up phase is worth watching on its own.
Two ways of transferring heat: contact and non-contact
In the conductive method the heating rod is in direct contact with the oil, and the heat passes from the metal surface into the oil by way of the temperature difference and the contact area. The arrangement is simple, but because a metal lies between the rod and the oil, the wall temperature of the rod is always higher than the oil temperature, and the efficiency of the transfer is also affected by the thickness of the metal and the condition of its surface. The deposit on the wall of the rod is the main source of thermal resistance: the thicker the deposit, the more slowly the oil temperature rises under the same heating conditions.
The radiant method does not require the heating surface to touch the oil. The far-infrared carbon fibre element emits infrared radiation, the oil layer absorbs the radiation directly and converts it into heat, and the conductive step through the metal tube is eliminated. For the user the difference shows up in two points: first, the heating surface does not touch the oil, so oil passing over it cannot scorch locally through local overheating; second, the temperature difference between the tank wall and the oil is reduced, so the temperature reading at the surface of the tank is closer to the actual oil temperature inside.
What the 45–80 °C temperature control range means under radiant heating
The temperature control range of the TYA series is 45–80 °C, with the upper limit pulled down to 70 °C for oil with a high water content. The range is not arbitrary: the lower limit has to guarantee that the oil is still a flowing spray after it leaves the nozzle, because below that temperature the atomised droplets are coarse and the dissolved gas cannot get out; the upper limit keeps margin below the flash point and avoids heavy foaming inside the tank. Oil with a high water content foams more easily, and as the temperature rises further the foam in the tank increases, which raises the frequency of the infrared foam detection and of the automatic defoaming action.
Under radiant heating the temperature reading is closer to the temperature of the oil itself, so the temperature control setting has a more direct meaning: the set value is the oil temperature that is wanted. When the ambient temperature varies between -20–45 °C the set value stays the same but the warm-up time does not, so more margin has to be allowed for the warm-up phase when the machine is started in winter.
| Stage | Setting or limit | What happens if it is not handled this way |
|---|---|---|
| Temperature control range | 45–80 °C | Below the lower limit atomisation is incomplete, above the upper limit the foam increases |
| Upper limit for oil with a high water content | 70 °C | Foam forms in the tank and the defoaming duty becomes heavier |
| Ambient temperature range | -20–45 °C | In low ambient conditions the warm-up time becomes clearly longer |
| Heating method | Far-infrared carbon fibre heating | Deposit on the heat transfer surface slows the warm-up |
The readings worth watching during the warm-up phase
Three things have to be watched together during the warm-up: whether the temperature is going up, whether the rate of rise has clearly slowed, and whether the pumping speed of the vacuum system has been affected. If the temperature does not come up, first confirm that the heating elements have been switched in, then check whether the oil charge is on the large side: the more oil the same machine holds, the greater the thermal capacity and the longer the warm-up. If the rate of rise slows in the middle, consider the possibility of deposit on the heat transfer surface. If the vacuum reading becomes shallower while the machine is heating, this is usually the result of more gas being released as the temperature inside the tank rises, and is normal, but the extent has to be recorded together with the set value.
Once the temperature has stabilised, the difference in the readings at different positions inside the tank is worth looking at once. The oil is circulating, so the temperature close to the oil inlet and close to the oil outlet is not exactly the same. Keep the measuring point fixed in the same position, otherwise later records cannot be compared.
- After the machine is started, look at the temperature curve before judging the machine; the data from the warm-up phase is more diagnostically useful than the data after it has stabilised.
- If the temperature does not come up over a long period, check first whether the heating has been switched in and how much oil is charged; do not go straight to suspecting the vacuum system.
- After a set value has been changed, record a fresh stabilised curve; do not compare against a curve taken before the change.
- For batches with a high water content the upper limit is pulled down to 70 °C; the margin saved here should not be spent casually.
- Confirm the correspondence between the temperature probe and the display once on the same tank of oil; pay particular attention when the season changes and the ambient temperature swings widely.
Temperature is the entry condition for degassing. If the entry condition is not met, every reading that follows is only a symptom.
