Heating and cooling

Heating and cooling are fundamental thermal process steps in process engineering. They serve to specifically change the temperature of bulk materials, liquids or pastes in order to achieve certain product qualities, storage stability or reaction conditions. In amixon® mixers, heat transfer can take place during heating (e.g. drying, reaction) or during cooling (e.g. product stabilisation, agglomerate consolidation).

The amount of heat supplied or removed is described by the heat capacity. A simple basic equation for heating or cooling a body is:

Q = m · c_p · (T_2 − T_1)

• Q: Amount of heat [J]
• m: Mass [kg]
• c_p: specific heat capacity [J/(kg·K)]
• T₁: Initial temperature [°C or K]
• T₂: Final temperature [°C or K]

Heat flows are used in continuous processes. For steady states, the following can be written:

Q_(dot) = m_(dot) · c_p · (T_(out) − T_(in))

• Q_(dot): Heat output [W]
• m_(dot): Mass flow [kg/s]
• T_(in): inlet temperature
• T_(out): Outlet temperature

Heating and cooling are technically implemented using heat transfer surfaces. Typical examples include double-walled containers, jacket heaters, internal heating or cooling coils, and temperature-controlled tools. A simple heat transfer balance is as follows:

Q_(dot) = U · A · (T_(medium) − T_(Produkt_mittel))

• U: overall heat transfer coefficient [W/(m²·K)]
• A: effective heat transfer area [m²]
• T_(medium): Temperature of the heating or cooling medium

• T_(product average): average product temperature

   

In mixers, the movement of the product has a significant influence on heat transfer. Intensive, three-dimensional mixing reduces temperature gradients and produces a narrow product temperature distribution. At the same time, it increases the convective portion of heat transfer at the wall. This allows bulk materials, pastes or suspension systems to be heated or cooled efficiently and gently.

Controlled temperature management is important for temperature-sensitive products. These include:

• Moderate temperature differences between medium and product
• short dwell times at critical temperatures
• even distribution of heat inputs in the batch

amixon® mixers can be equipped with heated or cooled mixing chamber walls and, if necessary, temperature-controlled tools. This allows heating or cooling to be elegantly combined with the mixing process. This saves process steps, reduces energy losses and ensures reproducible temperature profiles throughout the entire product volume.