A heat exchanger is a piece of equipment aimed to transfer energy in the form of internal heat (enthalpy) between two or more fluids, or between a surface and a fluid, between a particle and a fluid through a thermal contact without external interactions and without external work .
The fluid can be composed of a single component or mixtures.
Typical applications are heating and cooling of a fluid of interest, the evaporation or condensation of a single or multi-component flow, the recovery or dissipation of heat from a system.
In the case of the agro-food industry, the goal can be a process of sterilization, pasteurization, fractionation, distillation, concentration, crystallization, or to simply control a process.
The simplest type of heat exchanger is in direct mixing.
The most common type of heat exchanger is instead the so-called recovery heat exchanger.
The simplest heat exchanger is the tube in a tube heat exchanger.
Depending on the warm and cold flow direction, we can define two major configurations: concurrent flow heat exchanger and countercurrent flow heat exchanger.
The simplest type of heat exchanger is in direct mixing.
The most common type of heat exchanger is instead the so-called recovery heat exchanger.
The simplest heat exchanger is the tube in a tube heat exchanger.
Depending on the warm and cold flow direction, we can define two major configurations: concurrent flow heat exchanger and countercurrent flow heat exchanger.
Concurrent Flow – In this exchange system, the two fluids flow in the same direction.
Countercurrent Flow - In this exchange system, the two fluids flow in the opposite direction.
where mH is the mass flow (kg/h), hH the specific enthalpy, cPH is the specific heat at constant pressure (kcal / kg ºC) and T the average temperature (ºC) of the fluid;
where flow positive sign applies to the concurrent ( positive slope of the temperature gradient), while negative applies to the countercurrent(negative slope of the gradient of temperature).
Equating the two expressions, we can therefore write that
We can then introduce the thermal capacity per hour (kcal/hºC) for hot fluid CH=mHCPH and CC=mCCPC for the cold one,
Assuming that these two thermal capacity allocations are constant along the whole heat exchanger, the integration of this equality is quite simple:select for the integration, the input section (characterized by temperaturesTCI and THI) and a generic section (characterized by TC and TH),we obtain
taking into account the ± in the integration process.
In the generic section the difference in temperature between hot and cold fluid, adding and subtracting the term CHTC at first member and rearranging, we obtain
and
Where at the inflow A=0 and T=TCI and at the outflow A=Atot and T=TCO, obtaining
This relation holds for any section of the HE including the outflow, where we can write
Considering that
we can write:
and rearranging
Observing that
and
it results:
Defining the log mean temperature difference (also known as LMTD)
we obtain for both concurrent and countercurrent heat exchanger
Limitations:
1. Introductory concepts about batch and continuous precess
2. Materials in use for food equipments – Part I
3. Materials in use for food equipments – Part II
4. Equipment for raw material handling: pneumatic systems - Part I
5. Equipment for raw material handling: pneumatic systems - Part ...
6. Equipment for raw material handling: pneumatic systems - Part ...
7. Equipment for raw material handling: pneumatic systems - Part I...
8. Size reduction equipment - Part I
9. Size reduction equipments - Part II
10. Extruders
12. Positive displacement pumps
14. Cold Chain Equipment - Part I
15. Cold Chain Equipment - Part II
16. Cold Chain Equipment - Part III
17. Separation equipment - Part I
18. Separation Equipments – Part II
21. Liquid Mixing