ES2554651B1 - THERMAL EXCHANGE NANOFLUID - Google Patents

Abstract

Thermal exchange nanofluid. # The present invention relates to a nanofluid comprising an organic synthetic oil that is a polyphenyl; nanoparticles comprising carbon; and at least one sulfone.

Description

DESCRIPTION

Thermal exchange nanofluid.

The present invention relates to a nanofluid comprising a thermal transfer fluid at high temperature and nanoparticles comprising carbon. Said nanofluid has improved thermal conductivity properties in an operating range of the initial fluid without compromising other relevant variables such as viscosity and stability. These features make it applicable to heat transmission systems. Therefore, the present invention could be framed in the field of thermal engineering. 10

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STATE OF THE TECHNIQUE

Heat exchange fluids are fluids used for heat transport in numerous industrial applications. These fluids are used to transport energy in the form of heat from the point of heat generation (burners, nuclear reactor cores, solar fields, etc.) to the system that will use it (thermal storage systems, steam generators, etc. .). The most commonly used thermal fluids are water, ethylene glycol, thermal oils and molten salts. A characteristic common to all of them is their low thermal conductivity, a fact that limits the efficiency of the heat exchange systems 20 that use them.

The idea of adding solid microparticles of high thermal conductivity to thermal fluids in order to increase the thermal conductivity of the mixture is old and the first models are from Maxwell in 1873. However, until a few decades ago this approach presented 25 practical problems for possible industrial application due to poor stability of the mixture and abrasion by the microparticles. In 1995 Choi proposed the use of nanoparticles to improve the thermal properties of thermal fluids and these fluids were called nanofluids.

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In most cases the nanoparticles inside the nanofluid form clusters. The size and shape of these clusters largely determine the thermal conductivity, viscosity and stability of the nanofluid. The stability of a nanofluid is defined as the lack of sedimentation of the nanoparticles or clusters of nanoparticles inside.

 35

It is essential for the proper functioning of a nanofluid to prevent nanoparticles or clusters of nanoparticles from sticking together when they collide because this would increase the size of the clusters and affect the stability of the clusters. Nanofluids can be stabilized by repulsion systems between nanoparticles. Stabilized correctly, they can be used in heat exchange systems designed initially for thermal fluids without particles, thus increasing their performance.

Nanofluids based on thermal oils can reach high working temperatures and therefore have greater industrial interest. Some of the current problems are the following:

 Four. Five

- Stability of the nanofluid based on organic compounds: it is necessary to use additives that superficially modify the nanoparticles and prevent their adhesion when they collide;

- stability of the nanofluid at high temperature: at a higher temperature, greater probability of shock of nanoparticles and therefore greater difficulty to stabilize, in addition, additives 50 used in organic nanofluids are usually valid for reduced temperature ranges;

- Availability of the nanoparticle material, should preferably be abundant, easy to obtain and low cost.

- Maximize thermal conductivity without increasing viscosity excessively.

 5

US6432320B1 describes chemically stabilized nanofluids, where the fluid is a heat transfer fluid selected from water, glycols, mineral and synthetic oils, organic and inorganic paraffins and eutectic, the nanoparticles are metallic or carbon. The additive used is an additive of the azole group most preferably used at 10% by weight. 10

International application WO2007103497 describes a nanofluid as a gear oil that exhibits viscosity and thermal conductivity higher than the base fluid. The nanoparticles used are graphite nanoparticles of non-spherical morphology and dispersants or alternatively non-ionic surfactants or a mixture of non-ionic and ionic are used. fifteen

There are several documents that cite the wide variety of components present in a nanofluid, that is, base fluid, nanoparticles and additives as surfactants. For example, patents US20090298725, WO2003004944A2 and US20070158609 describe nanofluids where the base fluid can be a synthetic organic oil and the nanoparticles can be carbon nanoparticles, and where additives are used as surfactants for stabilization. In the review by Ghadimi et al. (International Journal of Heat and Mass Transfer 54 (2011) 4051-4068) reviews different nanofluid preparation techniques and stabilization methods.

 25

However, there is still a great need to develop a thermal oil with which improved thermal conductivities are obtained along with an adequate viscosity and stability in a range of temperatures similar to those covered by the operating conditions provided for thermal oils.

 30

DESCRIPTION OF THE INVENTION

The present invention relates to a nanofluid comprising a high temperature thermal transfer fluid and nanoparticles comprising carbon. The nanofluid of the invention has the following advantages:

- The nanofluid of the invention can be used in a wide range of temperatures (from 15 ° C to 400 ° C);

- the nanofluid of the invention has a good stability over time in the operating temperature range 40;

- the viscosity of the nanofluid does not vary significantly compared to that of the base fluid;

- the nanofluid of the invention has improved thermal conductivity properties; Four. Five

- the use of the nanofluid of the invention not significant changes in the facilities where the base fluid is already used;

- The materials necessary for the preparation of the nanofluid are abundant and easily accessible.

In a first aspect, the present invention relates to a nanofluid comprising:

a) an organic synthetic oil that is a polyphenyl;

b) nanoparticles comprising carbon; Y

c) at least one sulfone. 5

By polyphenyl is meant a compound comprising 2 or more phenyls. The polyphenyl is selected from diphenyls, terphenyls, alkylated polyphenyls and their oxides.

A nanoparticle means a particle with a size below 500 nm. The 10 nanoparticles of the invention comprise carbon. Specifically, the nanoparticles of the invention are carbon nanoparticles or are carbon coated nanoparticles.

In the context of the invention, a sulfone is a compound of formula (I):

 fifteen

(I)

where R and R 'are independently C1-C10 alkyl, C3-C10 cycloalkyl, C5-C7 heteroaryl, phenyl, biphenyl, terphenyl, naphthyl, phenanthryl or anthracil, where R and R' can be independently substituted in any of their positions by 1 or more substituents selected from C1-C4 alkyl, -O-C1-C4 alkyl and -OH.

In an embodiment of the first aspect of the present invention the organic synthetic oil is selected from diphenyl, diphenyl oxide, o-terphenyl, m-terphenyl, p-terphenyl and any of its mixtures, preferably the organic synthetic oil is selected from diphenyl, diphenyl oxide 25 and any of its mixtures and even more preferably organic synthetic oil consists of 50% to 99% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of organic synthetic oil.

In a preferred embodiment of the first aspect of the present invention, the organic synthetic oil 30 consists of 73% to 73.5% by weight of diphenyl and diphenyl oxide to 100% by weight with respect to the total weight of the organic synthetic oil. That is, the organic synthetic oil is the eutectic mixture of diphenyl oxide and diphenyl. This synthetic oil has a wide range of operating temperatures (between 15ºC and 400ºC) and a low viscosity for the entire operating range of the fluid. 35

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 50% to 99% by weight of diphenyl and diphenyl oxide to complete 100% by weight with respect to the total weight of the organic synthetic oil; 40

b) nanoparticles comprising carbon; Y

c) at least one sulfone.

 Four. Five

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 73% to 73.5% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of the organic synthetic oil;

 fifty

b) nanoparticles comprising carbon; Y

c) at least one sulfone.

In one embodiment of the first aspect of the present invention, the nanoparticles are selected from carbon nanotubes, graphite nanoparticles, carbon nanofibers, amorphous carbon nanospheres, fulerenes, diamond nanoparticles, carbon coated nanoparticles and any of their mixtures.

In one embodiment of the first aspect of the present invention, the nanoparticles are 10 amorphous carbon nanospheres, preferably the nanoparticles are carbon black, carbon black is a material produced by the partial combustion of petroleum-derived organic products, and is formed by amorphous carbon nanospheres that can agglomerate forming clusters. The nanofluids of the invention comprising carbon black have provided excellent thermal conductivity and stability results. 15 They also have the advantage that carbon black is abundant and easily obtainable.

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 73% to 73.5% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of the organic synthetic oil; twenty

b) nanoparticles comprising carbon, where the nanoparticles are amorphous carbon nanospheres, preferably the nanoparticles are carbon black; Y

c) at least one sulfone.

In an embodiment of the first aspect of the present invention, the concentration of the 25 nanoparticles comprising carbon in the nanofluid is from 0.1% to 10% by volume with respect to the total volume of the nanofluid, preferably, the concentration of nanoparticles in the nanofluid. it is from 1% to 8% by volume with respect to the total volume of the nanofluid, more preferably the concentration of nanoparticles in the nanofluid is from 3% to 5% by volume with respect to the total volume of the nanofluid. 30

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 73% to 73.5% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of the organic synthetic oil;

b) nanoparticles comprising carbon, where the nanoparticles are amorphous carbon nanospheres, preferably the nanoparticles are carbon black; Y

c) at least one sulfone;

where the concentration of the nanoparticles is from 0.1% to 10% by volume with respect to the total volume of the nanofluid, preferably from 1% to 8% by volume, more than 3% to 5% by volume with respect to the total volume of the nanofluid

Preferably sulfone is a compound of formula (I) where R and R 'are independently C5-C7 heteroaryl, phenyl, biphenyl, terphenyl, naphthyl, phenanthryl or anthracil, where R and R' can be independently substituted in any of their positions. by 1 or more substituents selected from C1-C4 alkyl, -O-C1-C4 alkyl and -OH, more preferably R and R 'are independently phenyl, biphenyl, terphenyl, naphthyl, phenanthryl or anthracil, where R and R' may be independently substituted in any of their positions by 1 or more substituents selected from C1-C4 alkyl, -O-C1-C4 alkyl and -OH, and even more preferably R and R 'are phenyl, where R and R' can independently be substituted in any of its positions by 1 or more substituents selected from C1-C4 alkyl, -O-C1-C4 alkyl and -OH.

In one embodiment of the first aspect of the present invention, the sulfone is diphenyl sulfone.

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 73% to 73.5% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of the organic synthetic oil; 5

b) nanoparticles are amorphous carbon nanospheres, preferably the nanoparticles are carbon black; Y

c) diphenyl sulfone. 10

In an embodiment of the first aspect of the present invention, the nanofluid comprises:

a) an organic synthetic oil consisting of 73% to 73.5% by weight of diphenyl oxide; and diphenyl to complete 100% by weight with respect to the total weight of the organic synthetic oil; fifteen

b) nanoparticles are amorphous carbon nanospheres, preferably the nanoparticles are carbon black; Y

c) diphenyl sulfone; twenty

where the concentration of the nanoparticles is 0.1% to 10% by volume with respect to the total volume of the nanofluid, preferably, from 1% to 8% by volume, more than 3% to 5% by volume with respect to the total volume of the nanofluid .

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In an embodiment of the first aspect of the present invention, the nanoparticles: sulfone weight ratio is 2: 1 to 1: 2, preferably the nanoparticles: sulfone weight ratio is 1: 1.

A second aspect of the present invention relates to the use of nanofluid as described above as a heat exchange fluid.

A third aspect of the present invention relates to a process for obtaining the nanofluid as described above comprising the steps of:

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a) mix the organic synthetic oil and sulfone homogeneously with stirring; Y

b) dispersing the nanoparticles in the mixture obtained in step (a) with stirring. This stirring is carried out for a period between 30 min and 2 hours, preferably for 1 hour. 40

In an embodiment of the third aspect of the present invention, the stirring of step (b) is ultrasonic stirring. Ultrasound is a low destructive method for carbon nanoparticle structures and it is preferable that it be used for short and intermittent periods to avoid overheating in the suspension. Preferably the stirring with ultrasound is carried out for one minute.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Variation of thermal conductivity with temperature. kn / kbf: nanofluid conductivity ratio: base fluid conductivity. T: temperature in ° C; 3%, 5%: nanofluids of the invention, with nanoparticle concentrations of 3% and 5% by volume with respect to the total volume of the nanofluid, respectively.

FIG. 2. Variation of viscosity with temperature. μn / μbf: nanofluid viscosity ratio: base fluid viscosity; T: temperature in ° C; 3%, 5%: nanofluids of the invention, with nanoparticles concentrations of 3% and 5% by volume with respect to the total volume of the nanofluid, respectively.

FIG. 3. Variation of specific heat with temperature. Cpn / Cpbf: specific heat ratio of the nanofluid: specific heat of the base fluid; T: temperature in ° C; 3%, 5%: nanofluids of the invention, with nanoparticle concentrations of 3% and 5% by volume with respect to the total volume of the nanofluid, respectively.

FIG. 4. Comparison of the stability of the nanofluids of the invention. L: Transmitted light (%); D: days; 1: nanofluid of the invention; 2: nanofluid with nanoparticles and without sulfone or other additive; 3: nanofluid with nanoparticles and with SDS; 4: nanofluid with nanoparticles and with 20 SDBS.

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which demonstrates the effectiveness of the product of the invention.

Example 1. Procedure for obtaining a nanofluid of the invention

Nanofluids were prepared with a carbon black concentration of 5% and 3% in volume 30 with respect to the total nanofluid volume (density at 20 ° C = 1.8 g / ml). First, diphenyl sulfone was dissolved in Therminol VP1 or DowTherm A (eutectic mixture of diphenyl and phenyl oxide) by magnetic stirring for 1 hour. The carbon black was then added and dispersed by the application of ultrasound (Sonoplus HD2200 ultrasonic probe, Bandelin) for 1 minute. 35

 Volume concentration

 Eutectic mixture (ml) carbon black (g) mdiphenyl sulfone (g)

 3%

 100 5.57 5.57

 5%

 100 9.47 9.47

Table 1. Composition of two nanofluids of the invention.

Example 2. Thermal conductivity of the nanofluids of Example 1.

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The thermal conductivity was measured by transient hot wire, making use of a commercial device (KD2 Pro, Decagon Devices Inc.). Said device consists of a sensor / thermocouple that is introduced into the sample and generates a heat pulse while recording the evolution of the temperature of the sample over time. The following results were obtained: 45

 Temperature

 kn / kbf nanofluid 3% v / v kn / kbf nanofluid 5% v / v

 40 ° C

 - 1,159

 60ºC

 1,092 1,124

 80ºC

 1,089 1,166

 100ºC

 1,100 1,147

 140ºC

 1,071 1,179

Table 2. Thermal conductivity at different temperatures of the nanofluids of Example 1. kn / kbf: nanofluid conductivity ratio: base fluid conductivity.

It can be seen that the increase is constant with the temperature and that it depends on the amount of nanoparticles. These results are represented in figure 1.

Example 3. Viscosity of the nanofluids of Example 1.

 The viscosity of the samples is measured using a rheometer with a concentric 10 cylinder configuration. The complete rheogram was obtained by scanning speed gradients from 1 to 100s-1. The viscosity value taken as representative of the sample is that achieved at high shears and velocity gradients. The following results were obtained:

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 Temperature

 μn / μbf nanofluid 3% v / v μn / μbf nanofluid 5% v / v

 25ºC

 6,086 8,189

 40 ° C

 7,423 9,128

 60ºC

 9,120 10,358

 80ºC

 9,379 9,158

Table 3. Viscosity at different temperatures of the nanofluids of Example 1. μn / μbf: nanofluid viscosity ratio: base fluid viscosity.

These results are represented in Figure 2. It is observed that the viscosity increases and is proportional to the amount of nanoparticles up to 60 ° C. From this temperature the viscosity of the nanofluid does not depend on the amount of nanoparticles and decreases with temperature.

Example 4. Specific heat of the nanofluids of Example 1.

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Specific heat was measured by differential scanning calorimetry, following DIN51007. The samples are subjected to a temperature cycle consisting of an isothermal section for 5 minutes at 60 ° C, a heating ramp from 60 ° C to 150 ° C at 20 ° C / min, an isothermal section for 5 minutes at 150 ° C and a cooling ramp from 150 ° C to 60 ° C to 20 ° C / min. The following results were obtained: 30

 Temperature

 Cpn / Cpbf nanofluid 3% v / v Cpn / Cpbf nanofluid 5% v / v

 60ºC

 1,023 0.905

 75 ° C

 1,024 0.903

 90 ° C

 1,031 0.893

 105 ° C

 1,023 0.878

 120ºC

 1,016 0.865

 135 ° C

 1,015 0.857

 150ºC

 1,026 0.859

Table 4. Specific heat at different temperatures of the nanofluids of Example 1. Cpn / Cpbf: specific heat ratio of the nanofluid: specific heat of the base fluid.

These results are represented in Figure 3. A lower specific heat is observed in the nanofluid with 5% v / v carbon black than in 3% v / v.

Example 5. Stability of the 5% nanofluid of Example 1.

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The nanofluid was subjected to thermal cycles of 200 ° C-400 ° C. The thermal cycles were carried out in a system consisting of a hermetically sealed aluminum cuvette that is heated by a heating ring. Due to the low vapor pressure of some of the thermal oils used, it is necessary to pressurize the system to 15 bar to avoid boiling it. The system has a pressure transducer to regulate the pressurization pressure and two 10 K type thermocouples, one on the wall and one in the center of the cuvette to measure the fluid temperature. The entire system is regulated by a PID (Proportional Integrated Derivative) system to control the electrical power supplied to the heating ring from the measurement of the wall and fluid temperature.

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The nanofluids were subjected to ten thermal cycles between 200 ° C-400 ° C, with a heating ramp of 20 ° C / min and cooling ramp of 10 ° C / min. Subsequently, the stability over time was measured.

The stability of the nanofluid of the invention was compared with a volume concentration of 20 5% carbon black with other nanofluids using the same base fluid, the same concentration and the same type of nanoparticles, but a different additive.

The stability of the nanofluid is checked from the intensity of the laser radiation transmitted by the nanofluid in a glass cuvette with the nanofluid. The radiation comes from a laser diode that emits at 610 nm. The radiation has a 3 mm diameter beam shape. Laser radiation is measured by a photodiode with focusing lens and filter. The laser beam passes through the upper part of the nanofluid so that if the nanofluid is stable it must be constant over time. If the nanofluid is not stable, nanoparticle agglomeration and sedimentation occur. If there is sedimentation, the intensity transmitted in the upper part of the nanofluid increases with time since the clusters of nanoparticles formed settle and concentrate in the lower part of the cuvette.

The transmitted light of 4 fluids is represented in Figure 4, in all of them the base fluid is the eutectic mixture of diphenyl and phenyl oxide, and all of them contain 5% carbon black. 35

 Additive

 one

 diphenyl sulfone

 2

 SDBS - sodium dodecylbenzene sulfonate

 3

 SDS - Sodium Dodecyl Sulfate

 4

 without sulfone or other additive

Table 5. Nanofluids whose transmitted light is represented in Figure 4.

It can be seen that in the nanofluid of the invention there is no variation in the transmitted light for at least 5 days, and that it is therefore more stable than fluids 2 and 3 comprising sulphonate or sulfate instead of sulfone, and more than the nanofluid without additives.

Claims (16)

image 1 1.- Nanofluid comprising: a) an organic synthetic oil that is a polyphenyl; b) nanoparticles comprising carbon; and 5 c) at least one sulfone. 2. The nanofluid according to the preceding claim, wherein the organic synthetic oil is selected from diphenyl, diphenyl oxide, o-terphenyl, m-terphenyl, p-terphenyl and any of their mixtures. 10 3. The nanofluid according to any of the preceding claims, wherein the organic synthetic oil is selected from diphenyl, diphenyl oxide and any of its mixtures. 4. The nanofluid according to the preceding claim, wherein the organic synthetic oil consists of: - 50% to 99% by weight of diphenyl oxide; Y - diphenyl to 100% by weight with respect to the total weight of organic synthetic oil. 5. The nanofluid according to the preceding claim, wherein the organic synthetic oil consists of: - 73% to 73.5% by weight of diphenyl oxide; and 20 - diphenyl to 100% by weight with respect to the total weight of organic synthetic oil. 6. The nanofluid according to any of the preceding claims, wherein the nanoparticles are selected from carbon nanotubes, graphite nanoparticles, carbon nanofibers, amorphous carbon nanospheres, fulerenes, diamond nanoparticles, carbon coated nanoparticles and any of their mixtures 7. The nanofluid according to any of the preceding claims, wherein the nanoparticles are amorphous carbon nanospheres.  30 8. The nanofluid according to any of the preceding claims, wherein the concentration of the nanoparticles is from 0.1% to 10% by volume with respect to the total weight of the nanofluid. 9. The nanofluid according to any of the preceding claims, wherein the at least one sulfone is a compound of formula (I): (I) where R and R 'are independently C5-C7 heteroaryl, phenyl, biphenyl, terphenyl, naphthyl, phenanthryl or anthracil, where R and R' can be independently substituted in any of their positions by 1 or more substituents selected from C1-C4 alkyl, -O-C1-40 C4 alkyl and –OH, 10. The nanofluid according to the preceding claim, wherein the at least one sulfone is a compound of formula (I) wherein R and R 'are independently phenyl, biphenyl, terphenyl, naphthyl, phenanthryl or anthracil, where R and R' may be independently substituted in any of their positions by 1 or more substituents selected from C1-C4 alkyl, -O-C1-C4 alkyl and -OH. 11. The nanofluid according to any of the preceding claims, wherein the sulfone is diphenyl sulfone. fifty 12. The nanofluid according to any of the preceding claims, wherein the weight ratio nanoparticles: sulfone is from 2: 1 to 1: 2. 13. The nanofluid according to the preceding claim, wherein the weight ratio of 5 nanoparticles: sulfone is 1: 1. 14. Use of the nanofluid according to any of the preceding claims as a heat exchange fluid.  10 15. Procedure for obtaining the nanofluid according to claims 1 to 13, comprising the steps of: a) mix the organic synthetic oil and sulfone homogeneously with stirring; Y b) dispersing the nanoparticles in the mixture obtained in step (a) with stirring.  fifteen 16. The method according to the preceding claim, wherein the stirring of step (b) is ultrasonic stirring.