Frigosystem offers its customers a wide range of thermoregulation control units, which allow to regulate the temperature of the working fluids of process in a wide range of temperatures, ranging from 20°C up to 300°C. Depending on the required working temperature, working fluids can be of different types. Generally the most used fluids are: water, demineralized water, glycol water, diathermic oils, silicone oils.
The thermoregulation of the fluids inside the control units is achieved through the combination of a cooling system (direct or indirect) and a heating system with electrical resistances. These have the purpose of increasing the working fluid temperature that will be used as heating vector for the customer’s industrial process.
The electrical resistances must be carefully designed and selected so as not to damage the fluid that they heat. Each fluid, in fact, has its own critical temperature that must never be exceeded to avoid damaging the properties and the physical composition of the fluid itself.
The parameter to monitor and pay attention is the skin temperature, i.e. the temperature of the surface in contact between the resistance and the fluid. This depends on:
As regards to diathermic oil, this parameter must be much lower than that of the water, because cracking phenomena in the fluid itself can be triggered. The cracking phenomenon consist in the carbonization of the oil, which gives rise to the formation of encrustations of the deteriorated oil on the surface of the resistance. It is easy to understand that this phenomenon reduces the efficiency of the resistance to transfer heat to the fluid (due to the increase of the surface thermal resistance) and, consequently, causes the resistor itself to burn.
To avoid these problems, Frigosystem designs its resistances in order to have a specific load (measured in W/cm2) suitable for the working fluid. Moreover, the resistances are equipped with systems for limiting the maximum temperature of the fluid, in order to prevent damage.
With the same electrical power, the resistances with low surface load values require larger exchange surfaces. This means that we have a higher plant cost, as initial investment cost. Despite this, these measures allows us to have two big benefits: the lengthening of the useful life of the resistance (and of the control unit) and the reduction of unit downtime due to the breaking of the resistor.
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