FR2726281A1 - Heat-exchange liq. for cold storage of foodstuffs - Google Patents

Abstract

A heat-exchange liq. (I), for use in cooling plants and/or preservation of foodstuffs, consists of an aq. soln. of ethylene glycol (EG) or propylene glycol (PG), contg. methanol at 3-10 wt. % of (I). Also claimed are a compsn. (II) for preparing (I) by mixing with water, contg. 10-30 wt. % MeOH and the remainder EG or PG; and the use of MeOH as additive to a heat-exchange liq. as above, for improving the heat-exchange properties, esp. by reducing the kinematic viscosity of the mixt. Pref. (I) contains 10-40 wt. % EG or PG. Esp. (I) comprises 60-80 wt. % water, 3-5 wt. % MeOH and the remainder of EG or PG. (I) opt. further contains a corrosion inhibitor (e.g. Na borate or meta-silicate) and/or an agent to discourage ingestion of a foodstuff which has contacted (I) (pref. less than 1 wt. % of an emetic or repellent).

Description

COLD-CARRYING LIQUID AND COMPOSITION FOR THE PREPARATION OF SUCH A
LIQUID
The present invention relates to a coolant liquid, that is to say thermal transfer, intended for use in cooling installations and / or preserving food products more particularly; the present invention also relates to a composition for the preparation of such a coolant and to the use of an additive to a coolant.

 The technical field of the invention is that of manufacturing cooling and food storage facilities.

 The present invention relates more particularly to cold distribution installations, that is to say cooling and / or preservation of food products either temporarily stored in cold rooms, or arranged in display cabinets or refrigerated display cabinets. food products at points of sale such as supermarkets in particular.

 In such installations, it is usual to provide a hydraulic circuit in which circulates (propelled by a pump in particular) a heat transfer liquid, making it possible to transfer thermal energy from the place of use, that is to say from the cold room or the refrigerated display case, to a refrigeration unit which constitutes a heat sink, for example a cooling installation comprising a compression, absorption or adsorption refrigeration unit.

 It is known to use in such installations different heat transfer fluids which are generally in the liquid phase at normal atmospheric conditions of pressure and temperature, and sometimes called coolants.

 The document "Refrigerants and their fields of application", Verney and Malek, Revue générale du froid, May 1991, pages 21 to 25, describes and compares the performance of different refrigerants belonging mainly to two groups, namely aqueous solutions of inorganic salt on the one hand, and aqueous solutions of ethyl and propyl glycol on the other hand.

 It is known to use aqueous ethylene glycol solutions as a heat transfer fluid or liquid in cooling and / or food storage facilities, although precautions must be taken due to the toxicity of this type of product. liquid.

 However, as mentioned in the document referenced above, page 25 in particular, these aqueous solutions have the major drawback of having a relatively high kinematic viscosity at temperatures of the order of -10 C, in particular between -5 C and -10 C, which results in that the heat exchanges with such a fluid in this temperature range are relatively bad; indeed, the viscosity of an aqueous solution comprising in percentage by volume of the order of 40% of ethylene glycol, is of the order of 11 centistocks at -10 ° C., or of the order of (11 × 10 -6) m2 per second.

 An objective of the present invention is to provide a coolant liquid whose kinematic viscosity around -10 C is reduced, in order to improve the heat exchange characteristics of such a coolant liquid.

 It is of course conceivable, to decrease the kinematic viscosity of such a coolant based on an aqueous solution of ethylene glycol to decrease the percentage by volume or by mass of ethylene glycol in the aqueous solution, this which has the disadvantage of raising the freezing point of the coolant, the freezing point for example of an aqueous solution of ethylene glycol comprising about 20% by volume of ethylene glycol being close to -9 C; a freezing point of this order of magnitude is generally not acceptable for the use of the coolant as a heat transfer liquid for a cooling or food storage system, taking into account the temperatures which must be kept in the cooling or storage chambers of these food products.

 It is also known from the document cited to use methanol (which is very flammable) as a coolant for special applications.

 The object of the present invention is more particularly to provide a coolant having a low kinematic viscosity while having a freezing point less than -10 C, for example close to -20 C.

 The solution to the problem posed consists in providing a coolant (or heat carrier or heat-transfer liquid, that is to say thermal transfer) for cooling and / or preservation of food products which essentially consists of an aqueous solution of ethylene glycol (or propylene glycol) and with methanol whose proportion by mass in the liquid is between 3% and 10%.

According to preferred embodiments of the invention
- said cooling liquid comprises, in proportion by mass, between 10% and 40% of ethylene glycol or of propylene glycol
- Said coolant comprises, in proportion by mass, about 60% to 80% of water, about 3% to 5% of methanol and the complement of ethylene glycol or propylene glycol, or about 15% to 37%
- Said coolant liquid further comprises a corrosion inhibitor, such as for example sodium borate or sodium methasilicate
- said coolant liquid further comprises a deterrent to ingesting a food product placed in contact with said liquid
- Said coolant preferably contains, in proportion by mass, less than 1% of a bitter product, which bitter product is preferably chosen from emetic products or repellents;
- said bitter product contains denatonium benzoate (C28 H34 N2 03) for example described in US Patent 3,080,327 (JESSIE EVELYN
HAY);
the proportion by mass of the denatonium benzoate in the coolant liquid is between 0.0001% and 0.1% and preferably close to 0.01% to 0.001%.

 The solution to the problem posed also consists in providing a composition for the preparation, by mixing with water (for example distilled) essentially, of a carrier liquid for cooling installation and / or preservation of food products; the composition for the preparation of the coolant is essentially constituted by 10% to 30% in proportion by mass of methanol, and the balance to 100%, that is to say 70% to 90% being essentially constituted by ethylene glycol or propylene glycol .

According to preferential modes:
- Said composition also comprises a corrosion inhibitor
- Said composition also comprises a bitter product such as an emetic or a repellent
In other words, the invention consists in using methanol as an additive to a carrier liquid for cooling and / or preserving installations for food products, which carrier liquid consists essentially of an aqueous solution of ethylene glycol. or propylene glycol, to improve the heat transfer performance of said liquid, in particular by reducing the kinematic viscosity of the mixture obtained, that is to say allowing a mixture to be obtained whose kinematic viscosity is lower than the kinematic viscosity of the refrigerated liquid carrier without said additive.

 Indeed, it has been surprisingly found that, in accordance with the invention, the addition in the proportions in accordance with the invention of methanol in an aqueous solution of ethylene glycol, makes it possible to obtain a kinematic viscosity reduced compared to the kinematic viscosity of the same coolant without methanol as an additive, and also allows to obtain a freezing point below -10 C and therefore compatible with the use of the coolant for applications or installations cooling and / or preservation of food products.

 According to the need, in order to partially remedy at least the slightly toxic nature of the ethylene glycol contained in the aqueous solution, it is advantageous in accordance with one of the aspects of the invention to use an additional additive playing a deterrent role and preventing the ingestion of a food product which would have been soiled due to accidental contact with the coolant which is conveyed in a heat exchanger located either in a cold room or in a display case to the sale of food products.

 The invention also provides coolants and compositions allowing their preparation at a very reduced cost.

 The numerous advantages provided by the invention will be better understood through the following description which illustrates without any limiting character, particular embodiments of the invention.

Example # 1
32% of ethylene glycol, 3.8% of methanol and 64.2% of water are mixed under normal pressure conditions and at a temperature of 20 ° C., in proportion by mass, to obtain a coolant in accordance with the invention.

These percentage by mass of the various main constituents of the coolant liquid correspond to percentages by volume at 20 ° C.
- 30% ethylene glycol, 5% methanol and approximately 65% water.

 One observes for such a coolant liquid an appearance of the first crystals at a temperature of about -20 C, during a freezing test of the coolant liquid.

 We can measure a kinematic viscosity of the coolant liquid thus obtained whose value is lower by 2 x 10-6 to 3 x 10-6 m2 per second than the value of the viscosity of a coolant liquid with the same percentage by volume of ethylene glycol and devoid of methanol, namely comprising 30% by volume of ethylene glycol and approximately 70% of water.

The following characteristics are also obtained for a coolant liquid according to the above composition example.
- flash point: around 65 ",
- kinematic viscosity: approximately 3 x 10-6 m2 per second,
- specific heat: 3.7 kilojoule / (kilo degrees centigrade),
- thermal conductivity: 0.47 watt / (meter degree centigrade),
- specific mass: 1060 kilos per m3,
The last four characteristics above are measured at a temperature close to minus 7.5 C.

 We thus obtain in accordance with this first embodiment of a coolant liquid according to the invention, a coolant liquid whose freezing point is sufficiently low to allow to maintain at temperatures close to -5 C to -10 C enclosures containing food products and whose kinematic viscosity is low enough to allow improved heat exchange thanks in particular to a higher Reynolds number.

Example # 2
A liquid carrier liquid is prepared as in Example No. 1, to which 0.1 gram of denatonium benzoate is added per liter of liquid carrier liquid.

 The physical characteristics above are measured for the liquid obtained, and values identical to those obtained in Example 1 are obtained.

Example # 3
A mixture similar to that of Example 1 is produced by replacing the ethylene glycol with propylene glycol and a substantial reduction in the viscosity of the mixture obtained is obtained (by comparison with the viscosity of the same mixture devoid of methanol ).

Claims (9)

 1. Refrigerant carrier liquid for cooling and / or preservation of food products characterized in that it is essentially constituted by an aqueous solution of ethylene glycol (or propylene glycol) and by methanol whose proportion by mass in the liquid is between 3% and 10%.  2. Liquid according to claim 1 characterized in that it comprises, in proportion by mass, between 10% and 40% of ethylene glycol or propylene glycol.  3. Liquid according to any one of claims 1 to 2 characterized in that it comprises, in proportion by mass, about 60% to 80% of water, about 3% to 5% of methanol and the complement of ethylene glycol or propylene glycol, about 15% to 37%.  4. Liquid according to any one of claims 1 to 3 characterized in that it further comprises a corrosion inhibitor, such as for example sodium borate or sodium methasilicate.  5. Liquid according to any one of claims 1 to 4 characterized in that it further comprises a product dissuading from ingesting a food product placed in contact with said liquid, which liquid preferably contains, in proportion by mass, less than 1% of a bitter product, which bitter product is preferably chosen from emetic products or repellent products.  6. Composition for the preparation, by mixing with water essentially, of a carrier liquid for cooling installation and / or preservation of food products, characterized in that it is essentially constituted by 10% to 30 in proportion by mass of methanol, the balance to 100%, ie 60% to 90% being essentially constituted by ethylene glycol or propylene glycol.  7. Composition according to claim 6 characterized in that it further comprises a corrosion inhibitor.  8. Composition according to any one of claims 6 to 7 characterized in that it also a bitter product such as an emetic or a repellent.  9. Use of methanol as an additive to a carrier liquid for cooling and / or preservation of food products, which carrier liquid consists essentially of an aqueous solution of ethylene glycol or propylene glycol, to improve performance for thermal transfer of said liquid, in particular by reducing the kinematic viscosity of the mixture obtained.