WO2025181617A1

WO2025181617A1 - Process for operating on a working fluid according to a thermodynamic refrigeration cycle

Info

Publication number: WO2025181617A1
Application number: PCT/IB2025/051709
Authority: WO
Inventors: Flavio MANENTI
Original assignee: Politecnico di Milano
Current assignee: Politecnico di Milano
Priority date: 2024-02-26
Filing date: 2025-02-18
Publication date: 2025-09-04
Anticipated expiration: 2026-08-26

Abstract

Process for operating on a working fluid according to a thermodynamic refrigeration cycle comprising the cyclic steps of: a) evaporating a working fluid in the liquid state in an evaporation unit (10) by generating a vapour stream; the working fluid having initial temperature and pressure conditions; b) compressing at least a portion of the vapour flow from step a) into a compression unit (20) by increasing temperature and pressure of the vapour flow; c) condensing, by giving off heat to an external environment, at least a portion of the compressed vapour fluid from step b) by means of a condensation unit (30) generating a condensate flow; d) laminating at least a portion of the condensate flow from step c) by means of a lamination unit (40) by lowering the temperature and pressure of the condensate flow to obtain the working fluid substantially at the initial temperature and pressure conditions; e) sending the working fluid from step d) to step a); step a) involves overheating the vapour flow by at least partial dissolution of at least one non-volatile solute in the working fluid and by heating the resulting solution until the boiling temperature of the solution is reached and consequently producing overheated vapour consisting essentially of the working fluid, said solution having a boiling temperature higher than the boiling temperature of the working fluid.

Description

“Process for operating on a working fluid according to a thermodynamic refrigeration cycle”

DESCRIPTION

Field of the invention

The present invention relates to a process for operating on a working fluid by means of a thermodynamic refrigeration cycle that allows it to operate inversely to the second principle of thermodynamics by recovering enthalpy from the cold zone and discharging it to the hot zone by applying a certain amount of work. The present invention also relates to a system for operating on a working fluid according to the thermodynamic refrigeration cycle such as heat pumps and refrigeration systems/machines. Preferably, the thermodynamic refrigeration cycle is a two-phase vapour thermodynamic refrigeration cycle.

State of the art

As is well known, heat pumps and refrigeration systems are machines that transfer enthalpy from a cold zone to a hot zone by applying work. If the zone of interest is the cold utility, then we talk about refrigerators (refrigeration systems) or cooling/air-conditioning cycles, whereas if the zone of interest is hot, then we talk about heat pumps.

Heat pumps and refrigeration systems (hereinafter, just heat pumps for simplicity) employing a thermodynamic refrigeration cycle are characterised by vapour compression, high-pressure condensation, lamination and low-pressure boiling inside a boiler. In order to preserve the compressor, it is useful to overheat the saturated vapour coming out of the boiler, and an additional heat exchange operation is therefore necessary.

It should be noted that heat pumps can be gas or vapour depending on the type of fluid used and the operating conditions. The exploitation of phase changes (evaporation and condensation) makes the heat pump more efficient and compact for the same capacity.

A vapour heat pump is presented according to Figures 1-2. The saturated vapour leaving the boiler evaporator 1 is sent to the compressor 2. In compression, in addition to an increase in pressure, there is also an increase in temperature. The compressed vapour is sent to the condenser 3, which is located inside the heat pump’s hot utility. The vapour gives off sensible and latent heat until complete condensation. On leaving the condenser 3, the liquid passes through a lamination valve 4, decreasing in pressure and temperature. When the desired temperature is reached, the fluid is able to exchange with the cold (or external) utility of the heat pump, thus vaporising in the evaporator 1. In the lamination valve 4, some vapour is already formed. In the case of refrigeration systems, this implies a reduction in the recovery efficiency of refrigeration. Total evaporation is completed in the boiler 1. The cycle has a saturated vapour supply to the compressor 2, which can lead to the formation of small drops of condensate in the first part of the compression.

In modern heat pumps, to overcome the problem, according to Figures 3-4, additional equipment is used in the form of an energy recovery unit or a gas/liquid heat exchanger 5. The low-pressure vapour leaving the boiler 1 is at a lower temperature than the condensed liquid leaving the condenser 4. It is therefore possible to add a gas/liquid heat exchanger (recovery unit) 5 which allows heat exchange between the aforesaid flows. The effect of the heat exchanger 5 is twofold: overheating of the saturated vapour to overcome the problem on the compression side; sub-cooling of the liquid at the inlet of the lamination valve to reduce vapour formation before the boiler.

However, the overheater involves the introduction of an additional critical unit that complicates the heat pump or refrigeration system by increasing its size and reducing the efficiency of the process. Summary of the invention

In order to overcome the aforementioned problems, a process and related system was devised to operate on a working fluid producing overheated vapour without the use of additional critical units or intermediate phases to reduce the system footprint and improve process efficiency.

Thus, the subject matter of the present invention is a process for operating on a working fluid according to a thermodynamic refrigeration cycle comprising the cyclic steps of: a) evaporating a working fluid in the liquid state in an evaporation unit 10 by generating a vapour stream; the working fluid having initial temperature and pressure conditions; b) compressing at least a portion of the vapour flow from step a) into a compression unit 20 by increasing temperature and pressure of the vapour flow; c) condensing, by giving off heat to an external environment, at least a portion of the compressed vapour fluid from step b) by means of a condensation unit 30 generating a condensate flow; d) laminating at least a portion of the condensate flow from step c) by means of a lamination unit 40 by lowering the temperature and pressure of the condensate flow to obtain the working fluid substantially at the initial temperature and pressure conditions; e) sending the working fluid from step d) to step a); characterized in that step a) involves overheating the vapour flow by at least partial dissolution of at least one non-volatile solute in the working fluid and by heating the resulting solution until the boiling temperature of the solution is reached and consequently producing overheated vapour consisting essentially of the working fluid, said solution having a boiling temperature higher than the boiling temperature of the working fluid.

Advantageously, the process and system of the present invention make it possible to improve the efficiency of heat exchange in the cycle and to reduce the total volume of the apparatus for the same power compared to the prior art.

Advantageously, the process and system of the present invention allow refrigeration cycle machines and heat pumps to be simplified by removing one or more critical units.

Advantageously, the process and system of the present invention for the respective apparatus on which the process is implemented also allow a:

• Reduction in investment costs

• Reduction in operating costs

• Reduction in maintenance costs

• Reduction in monitoring and control costs

LIST OF FIGURES

Figure 1: Block diagram representing a heat pump according to the prior art;

Figure 2: Representation of the T-s diagram of the refrigeration cycle in accordance with the heat pump in Figure 1 ;

Figure 3: Block diagram representing a heat pump according to the prior art;

Figure 4: Representation of the T-s diagram of the refrigeration cycle in accordance with the heat pump in Figure 3, indicating with the solid line the T-s variations of the refrigeration cycle in accordance with the heat pump in Figure 3 and with the dashed line the T-s variations of the refrigeration cycle in accordance with the heat pump in Figure 1 at the same pressure in the evaporation unit; Figure 5: Schematic block representation of a system according to an embodiment of the present invention;

Figure 6: Representation of the T-s diagram of the refrigeration cycle in accordance with the system in Figure 5, indicating with the solid line the T-s variations of the refrigeration cycle in accordance with the apparatus in Figure 5 and with the dashed line the T-s variations of the refrigeration cycle in accordance with the heat pump in Figure 1 at the same pressure in the evaporation unit;

Figure 7: Representation of the T-s diagram of the refrigeration cycle in accordance with the system in Figure 5, indicating with the solid line the T-s variations of the refrigeration cycle in accordance with the apparatus in Figure 5 and with the dashed line the T-s variations of the refrigeration cycle in accordance with the heat pump in Figure 1 at the same temperature in the evaporation unit;

Figure 8: Schematic block representation of a system according to an embodiment of the present invention;

Figure 9: Graphical representation of Duhring's rule for an NaOH/water solution taken from McCabe et al., 2005.

Figure 10: Graphical representation of Duhring's rule for a water/NaCl solution taken from Elsayed, Wu, Chow Desalination Volume 504, 15 May 2021, 114955 High salinity seawater boiling point elevation: Experimental verification

DETAILED DESCRIPTION

For the purposes of the present invention, the definition “comprising” does not exclude the presence of further components/stages not expressly mentioned after this definition.

On the other hand, the definition consisting of or consisting in excludes those types of components/stages not expressly mentioned in this definition.

A weak acid is defined as an acid with a pKa comprised between 4 and 6, preferably 5, preferably acetic acid or formic acid.

A weak base is defined as a base with pKa comprised between 8 and 10, preferably 9.

The process according to the present invention makes it possible to obtain already overheated vapour in a heat pump and/or refrigeration cycle machine. Specifically, the process of the present invention makes it possible to remove critical units present in the prior art and to avoid additional steps for overheating the saturated vapour.

It should be noted that the process of the present invention makes it possible to define a new thermodynamic cycle of the refrigeration type for use in heat pumps and refrigeration machines.

The process according to the present invention can be implemented in a system collectively designated with 100 to operate a thermodynamic cycle of the refrigeration type, described below.

Specifically, the process of the present invention involves operating on the working fluid in a cyclic manner in a series of phase transitions of the same working fluid by exchanging heat with a cold environment and a hot environment. It should be noted that for the purposes of the present invention, the working fluid is the solvent of a solution.

The working fluid may be aqueous, organic. In particular, the working fluid may be an aqueous mixture (e.g. water/methanol, water/ammonia, water/acetic acid) or pure water.

According to a preferred embodiment, the working fluid is water in the liquid and vapour state.

The process of the present invention comprises a step a) of evaporating the working fluid by generating a vapour flow. Preferably, the working fluid in step a) is initially in the liquid state until it evaporates to the gaseous state. More preferably, the vapour flow generated is in a saturated vapour condition.

Specifically, during step a) the working fluid heats up by receiving heat from the cold environment until it evaporates.

It should be noted that the working fluid in the liquid state has initial temperature and pressure conditions.

Preferably, the working fluid in its liquid state has initial pressure and temperature conditions where the pressure is in the range of 10 kPa to 200 kPa and the temperature in the range of -30 °C to 120 °C.

For particular working fluids such as hydrogen, nitrogen or noble/inert gases or their mixtures, the temperature in the liquid state is cryogenic (-253 °C to -190 °C).

Step a) is carried out in an evaporation unit 10 of the system 100.

In accordance with the process of the present invention, step a) provides for overheating the vapour flow by at least partial, preferably total, dissolution of at least one non-volatile solute in the working fluid and heating the resulting solution until the boiling temperature of the solution is reached, resulting in the production of overheated vapour consisting essentially of the working fluid. Specifically, the solution obtained by combining the working fluid and the non-volatile solute has a boiling temperature higher than the boiling temperature of the working fluid.

Preferably, step a) involves adding at least one non-volatile solute to the working fluid in the liquid state to form a solution with a boiling temperature higher than the boiling temperature of the working fluid alone in the liquid state. It should be noted that this addition of solute can be accomplished in a start-up cycle, with possible additions in subsequent cycles, since due to its chemical and physical properties the solute is non- volatile and is therefore kept confined for the most part, preferably all of it in both dissolved and non-dissolved form, within the evaporation unit 10 and/or circulated in units in which the working fluid is at least partly in the liquid state.

Thus, the boiling of the solution and subsequent evaporation of the working fluid results in the generation of an overheated working fluid vapour.

It is noted that the enthalpy gap to go from the boiling temperature of the working fluid to the boiling temperature of the solution is bridged by the evaporation unit 10. In this way, the outgoing vapour is in an overheated condition ready for the subsequent steps.

As illustrated in Figure 6, the solid line on the T-s diagram shows a higher temperature in the a-b section than the temperature in the same a-b section for the state-of- the-art T-s diagram. Moreover, as is well known, exceeding the bell curve results in overheated vapour entering the area.

Due to the solution of working fluid and at least one non-volatile solute, the average boiling temperature of the solution increases and thus when the solution reaches boiling point, the vapour produced, consisting essentially of working fluid in a gaseous state since by definition the solute is non-volatile, has a higher temperature than it would have without the solute.

It should be noted that the non-volatile solute is of the solid type and can be added to step a) in the liquid state by pre-heating depending on the type of solute and/or in the solid state configured to dissolve at least partially, preferably totally, during the heating that takes place in step a).

In Figure 7, an alternative process mode to the previous one in Figure 6 is illustrated, in which the process operates at the same temperature as the prior art in Figure 1 and features vapour overheating. Advantageously, operating in this way is useful when the temperature difference between the heat pump and the cold utility is too small. It should be noted that at least one non-volatile solute has a boiling temperature above the boiling temperature of the working fluid, thus increasing the boiling temperature of the solution.

Preferably, the vapour flow generated in step a) has pressure and temperature conditions where the pressure is in the range of 10 kPa and 200 kPa and the temperature is substantially within the range between the value corresponding to the saturation temperature of the pure solvent and the same temperature plus the boiling point elevation of the solution depending on the type of solvent, type of solute and solute concentration. For example, with water as a solvent, the temperature would preferably be comprised between -30°C and 120°C.

In accordance with a preferred embodiment, step a) involves increasing the boiling temperature of the solution by increasing the concentration of the non-volatile solute in the solution in accordance with Duhring's rule. Specifically, vapour overheating is a function of the non-volatile solute, single or multiple, and its concentration in the solution. It is noted that for the same non-volatile solute, the vapour is more overheated the more the solution is concentrated in the solute up to the solubility limit.

In accordance with a preferred embodiment, the non-volatile solute is NaOH. The boiling point of the solution comprising water and NaOH varies depending on the concentration of the solute as can be derived from the diagram in Figure 9.

Preferably, the overheated vapour flow generated in step a) has pressure and temperature conditions in equilibrium with the solution that generated it, and therefore where the pressure is in the range of 10 kPa and 200 kPa and the temperature is substantially within the range between the value corresponding to the saturation temperature of the pure solvent and the same temperature plus the boiling point elevation of the solution depending on the type of solvent, type of solute and solute concentration. For example, with water as a solvent, the temperature would preferably be comprised between -30°C and 120°C.

It should be noted that the use of the non-volatile solute avoids the temperature increase and the overheating step in the b-b’ section of Figure 4 by means of the state-of- the-art exchanger 5 and the subsequent cooling section d-d’.

In accordance with an alternative embodiment, the non-volatile solute can for example be selected from CaCh, NaCl, KC1, KCIO3, nitrites, nitrates, phosphites, sulphites or sulphates when the working fluid is water. By way of example, the boiling temperature of water as a function of NaCl concentration is shown in Figure 10.

It should be noted that the working fluid can be different from water; as stated above, it can be selected from at least one water-soluble polar organic solvent or mixtures thereof preferably at least one water-soluble C1-C4 alcohol or mixtures thereof preferably at least one apolar solvent, preferably at least one linear or branched C4-C8 hydrocarbon or at least one silicone oil.

Preferably the at least one C1-C4 alcohol is methanol, more preferably in a mixture with water. When said working fluid is a C4-C8 hydrocarbon it is preferably selected from butane, pentane, hexane in their branched or cyclic linear forms.

When the polar solvent is a C1-C4 alcohol and especially when it is mixed with water, or it is an aqueous mixture of a weak acid, preferably acetic acid or formic acid, or an aqueous mixture of a weak base, preferably ammonia, the solutes are the same as those used when the only working fluid is water alone, so it is selected from NaOH, CaCh, NaCl, KC1, KCIO3, nitrites, nitrates, phosphites, sulphites or sulphates.

When the fluid is a hydrocarbon, the solute is selected from a variety of waxes or lipophilic compounds.

Finally, when the working fluid consists of a silicone oil, this is preferably selected from: a silicone polymer soluble in said silicone oil. The process of the present invention comprises the step b) of compressing the vapour flow from step a) by increasing the temperature and pressure of the vapour flow. It should be noted that step b) is carried out in a compression unit 20 of the system 100.

Preferably, the compressed vapour flow generated in step b) has pressure and temperature conditions where the pressure is in the range of 200 kPa and 15000 kPa.

It should be noted that in the T-s diagram, step b) includes the b-c section where an increase in temperature and pressure can be seen in the overheated vapour field in Figures 6, 7

The process of the present invention comprises the step c) of condensing by yielding heat to an external environment of at least a portion of the compressed vapour fluid, preferably all of it, from step b) by generating a condensate flow. It should be noted that step c) is carried out in a condensation unit 30 of the apparatus 100.

During step c), the working fluid in the gaseous state releases sensible and latent heat until it condenses. It is noted that the condensing unit 30 exchanges heat with a hot environment.

Preferably, the condensate flow generated in step c) has pressure and temperature conditions where the pressure is in the range of 200 kPa to 15000 kPa and the temperature in the range of 40 °C to 340 °C.

It should be noted that in the T-s diagram in Figures 6 and 7, step c) in section c-d, there is a temperature drop until the bell-shaped curve of the change of state is reached and the working fluid subsequently changes state from vapour to liquid.

The process of the present invention comprises step d) of laminating at least a portion of the condensate flow, preferably all of it, from step c) by lowering the temperature and pressure of the condensate flow to obtain the working fluid substantially at the initial temperature and pressure conditions. It can be seen that in the T-s diagram in Figures 6 and 7, step c) includes the d-c section where there is a drop in temperature and pressure until the working fluid basically returns to its initial conditions and is then sent to step a) then to the evaporation unit 10 for the next cycle.

It should be noted that step d) is carried out in a lamination unit 40 of the apparatus 100.

The process of the present invention comprises the step e) of sending the working fluid from step d) to step a).

In this way, the process is repeated cyclically, allowing the exchange of heat with the hot and cold environment that define the utilities of interest for a heat pump or refrigeration machine.

It should be noted that the refrigeration-type thermodynamic cycle defined by the process of the present invention thus makes it possible to exploit the boiling temperature variation of a solution with one or more non-volatile solutes to produce a overheated vapour of the working fluid without introducing critical heat exchange units.

In accordance with a preferred embodiment, step a) comprises the sub-step al .1) of mixing in the evaporation unit 10 the working fluid in its liquid state with at least one nonvolatile solute until the relevant solution is obtained, preferably by partial or total dissolution of the solute. Subsequently, step a) comprises a sub-step al.2) of heating the solution obtained in step al.l) until the boiling temperature of this solution is reached. In the case of solute added in the solid state, sub-step al.2) involves at least partially, preferably totally, dissolving the relevant non-volatile solute and then reaching the boiling temperature of the solution. Once the boiling temperature is reached, step a) comprises the sub-step al.3) of generating overheated vapour essentially consisting of the working fluid in thermal equilibrium with the boiling solution to be sent to step b). Specifically, overheated vapour is generated as the boiling of the solution occurs at a higher temperature than the boiling temperature of the working fluid, so that in the liquid-gas state transition, vapour is produced from the already overheated working fluid, as can be seen from the straight line a-b state transition, e.g. in Figures 6, 7. Finally, step a) comprises the sub-step al.5) of separating by evaporation the non-volatile solute remaining in solution in a solute flow from the overheated vapour flow before sending the overheated vapour to step b). Preferably, the solute flow is kept within the evaporation unit so that it cyclically mixes with the working fluid from step d) of the subsequent cycle.

In accordance with an alternative embodiment to the above, step a) comprises the sub-step of a2.1) heating the solution of working fluid and non-volatile solute preferably in the evaporation unit 10. It is noted that the non-volatile solute can be added in liquid form from a recycle as outlined below and/or added in a solid state in the initial start-up step and/or in the control step during subsequent cycles. If solute is added in the solid state, it is provided that step a2.1) has enough solvent and is at a suitable temperature to dissolve the solute and obtain the solution. The single or multiple solute may also not dissolve completely. In a preferred mode, the quantity of solute is such that it can dissolve completely and, under the operating conditions of the invention, i.e. in a dissolved liquid phase or in a single liquid phase, does not crystallise in a way that could lead to fouling. In other words, it is preferable for the solute fraction to remain within the region of solubility or undersaturation and more preferably below the Maier-Ostwald-Bereich crystallisation curve (Di Pretoro, Manenti, Crystallisation, 2020, Springer), typically recognisable from phase diagrams known to a person skilled in the art once the solvent, solute and operating conditions are known.

Step a) includes the sub-step a2.2) of reaching the boiling temperature of the solution. Once the boiling temperature of the solution has been reached, step a) includes the sub-step a2.3) of generating the overheated vapour flow essentially consisting of the working fluid in thermal equilibrium with the generating solution to be sent to step b). As with the previous embodiment, overheated vapour is generated by increasing the boiling temperature of the solution. Subsequently, step a) comprises the sub-step a2.4) of separating by evaporation the non-volatile solute flow from the overheated vapour flow before sending the overheated vapour to step b). Finally, step a) comprises the sub-step a2.5) of mixing the solute flow with the condensate flow from step c) to sub-cool the condensate flow before entering step d). In fact, the solute flow has a lower temperature than the condensate flow.

Further subject matter of the present invention is to provide a system 100 for operating a refrigeration cycle of the type described above. Specifically, the process according to the present invention is preferably conducted in the system 100 which can be attributed to a heat pump or a refrigeration cycle machine depending on which environment (hot or cold) is of interest; if it is the cold utility i.e. the cold environment, then it is understood to be refrigerators or refrigeration cycles, whereas if it is the hot utility, i.e. the hot environment, then it is understood to be a heat pump.

For the purposes of the present invention, a system is defined as an assembly of one or more operating units associated with each other and configured to perform one or more steps of a process. It should be noted that the operating units can be in fluid communication so that the outflows are the inflows of one or more subsequent operating units.

As will be clear from the description, each operating unit carries out one or more steps of the process according to the invention.

The system comprises operating units connected in series to define a cycle.

Specifically, the system 100 comprises an evaporation unit 10 configured to evaporate the working fluid and generate a overheated vapour flow. Preferably, the evaporation unit 10 comprises at least one evaporator. The system 100 comprises a compression unit 20 configured to compress the vapour flow generated by the evaporation unit 10 and generate a compressed, and thus higher temperature, vapour flow. Preferably, the compression unit 20 comprises at least one compressor. The system 100 comprises a condensation unit 30 configured to condense the compressed vapour flow generated by the compression unit 20 and generate a condensate flow. Preferably, it comprises at least one condenser, e.g. in the form of a heat exchanger. The system 100 comprises a lamination unit 40 configured to laminate the condensate flow generated by the condensation unit 30 and obtain the working flow to be sent to the evaporation unit 10. Preferably, the lamination unit 40 comprises at least one lamination valve.

It should be noted that the evaporation unit 10 is in fluid communication downstream with the compression unit 20 and upstream with the lamination unit 40, and that the condensation unit 30 is in fluid communication downstream with the lamination unit 40 and upstream with the compression unit 20, thus defining a cycle. Preferably, it is noted that the connections between the units are hydraulic.

In accordance with the preferred embodiment, the evaporation unit 10 is configured to generate an overheated vapour stream by heating a solution of the working fluid with at least one non-volatile solute to boiling point. Such a solution is preferably obtained by at least partial dissolution of a non-volatile solute in the working fluid, as described above, and has a higher boiling temperature than the temperature of the working fluid thus permitting the production of overheated vapour.

In accordance with a preferred embodiment, the system also comprises a separation unit configured to separate the overheated vapour flow and the solute flow so that any residual solute is not sent to the compression 20 and condensation 30 unit.

In accordance with a preferred embodiment that can be combined with the previous one, the system 100 comprises a mixing unit configured to mix the solute flow with the condensate flow to sub-cool the condensate flow. Specifically, the mixing unit provides for sending the solute flow separated in the evaporation unit 10 upstream of the condensation unit 30 in order to mix it with the condensate from the condensation unit 30. Preferably, the mixing unit provides to send the solute flow downstream of the condensation unit 30 and upstream of the lamination unit 40. This allows steps a2.1-a2.5 to be carried out for sub-cooling the working fluid.

Claims

1. A process for operating on a working fluid according to a thermodynamic refrigeration cycle comprising the cyclic steps of: a) evaporating a working fluid in the liquid state in an evaporation unit (10) by generating a vapour stream; the working fluid having initial temperature and pressure conditions; b) compressing at least a portion of the vapour flow from step a) into a compression unit (20) by increasing temperature and pressure of the vapour flow; c) condensing, by giving off heat to an external environment, at least a portion of the compressed vapour fluid from step b) by means of a condensation unit (30) generating a condensate flow; d) laminating at least a portion of the condensate flow from step c) by means of a lamination unit (40) by lowering the temperature and pressure of the condensate flow to obtain the working fluid substantially at the initial temperature and pressure conditions; e) sending the working fluid from step d) to step a); characterised in that step a) involves overheating the vapour flow by at least partial dissolution of at least one non-volatile solute in the working fluid and by heating the resulting solution until the boiling temperature of the solution is reached and consequently producing overheated vapour consisting essentially of the working fluid, said solution having a boiling temperature higher than the boiling temperature of the working fluid.

2. The process according to claim 1, wherein step a) involves increasing the boiling temperature of the solution by increasing the concentration of the non-volatile solute in said solution in accordance with Duhring's rule. 3. The process according to claim 1 or 2 wherein step a) comprises the sub-steps of: al.l) mixing the working fluid in the liquid state with a non-volatile solute in the evaporation unit (10) until the corresponding solution is obtained; al.2) heating the solution obtained in step a.1.1) until the boiling temperature of said solution is reached; al.

3) generating overheated vapour essentially consisting of the working fluid in a thermal equilibrium with the boiling solution to be sent to step b); al.4) separating, by evaporation, the non-volatile solute in a solute flow from the overheated vapour flow before sending the overheated vapour to step b).

4. The process according to claim 1 or 2, wherein step a) comprises the sub-steps of: a2.1) heating the solution of working fluid and non-volatile solute; a2.2) reaching the boiling temperature of the solution; a2.3) generating the overheated vapour flow essentially consisting of the working fluid in a thermal equilibrium with the solution that generated it to be sent to step b); a2.4) separating the non-volatile solute in a solute flow from the overheated vapour flow by evaporation before sending the overheated vapour to step b). a2.5) mixing the solute flow with the condensate flow from step c) to sub-cool the condensate flow before entering step d), the solute flow having a lower temperature than the temperature of the condensate flow.

5. The process according to any one of claims 1 to 4, wherein

- the working fluid has initial pressure and temperature conditions where the pressure is in a range of 10 kPa and 200 kPa and the temperature is in a range of -30 °C and 120 °C

- the vapour flow generated in step a) has pressure and temperature conditions where the pressure is in a range of 10 kPa and 200 kPa and the temperature in a range of - 30 °C and 120 °C;

- the compressed vapour flow generated in step b) has pressure and temperature conditions where the pressure is in a range of 200 kPa and 15000 kPa and the temperature is in a range of 40 °C and 400 °C;

- the condensate flow generated in step c) has pressure and temperature conditions where the pressure is in a range of 200 kPa and 15000 kPa and the temperature is in a range of 5 °C and 350 °C.

6. The process according to any one of claims 1 to 5, wherein the working fluid is selected from: water, an aqueous solution of a weak base preferably ammonia or a weak acid preferably acetic acid or formic acid, at least one water-soluble polar organic solvent and associated aqueous mixtures; at least one apolar solvent or silicone oil.

7. The process according to claim 6, wherein the water-soluble organic polar solvent is selected from at least one C1-C4 alcohol or an aqueous mixture of said at least one alcohol.

8. The process according to claim 6 wherein the apolar solvent is at least a linear, branched or cyclic C4-C8 hydrocarbon.

9. The process according to claim 7, wherein said C1-C4 alcohol is methanol, preferably in a mixture with water.

10. The process according to claim 8, wherein the C4-C8 hydrocarbon is preferably selected from butane, pentane, hexane.

11. The process according to any one of claims 6, 7, 9, wherein, when the working fluid is water, an aqueous mixture of acetic acid or ammonia, a water-soluble polar solvent preferably in a mixture with water, the non-volatile solute is selected from NaOH, CaCh, NaCl, KC1, KCIO3, nitrites, nitrates, phosphites, phosphates, sulfites and/or sulfates.

12. The process according to any one of claims 6, 8, 10 wherein, when the apolar solvent is a C4-C8 hydrocarbon, the solute is selected from waxes or lipophilic compounds.

13. The process according to claim 6, wherein, when the solvent is a silicone oil, the solute is a silicone compound, also polymeric, or a silicate.

14. A system for operating a refrigeration cycle comprising operating units connected in series in a cycle:

- an evaporation unit (10) configured to evaporate a working fluid and generate a vapour flow;

- a compression unit (20) configured to compress the vapour flow generated by the evaporation unit (10) and generate a condensed vapour flow;

- a condensation unit (30) configured to condense the condensed vapour flow generated by the compression unit (20) and generate a condensate flow;

- a lamination unit (40) configured to laminate the condensate flow generated by the condensation unit (30) and obtain the working fluid to be sent to the evaporation unit; characterised in that the evaporation unit (10) is configured to generate an overheated vapour flow by heating a solution of the working fluid with at least one nonvolatile solute to the boiling point, the solution having a higher boiling temperature than the temperature of the working fluid

15. The system according to claim 14, wherein:

- the evaporation unit (10) comprises at least one evaporator;

-the compressor unit (20) comprises at least one compressor;

-the condensation unit (30) comprises at least one condenser;

- the lamination unit (40) comprises at least one lamination valve.

16. The system according to claim 14 or 15, further comprising

- a separation unit configured to separate the overheated vapour flow and the solute flow

- a mixing unit configured to mix the solute flow with the condensate flow to sub- cool the condensate flow.