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WO1999048992A1 - Circuit de refrigeration a boucle secondaire - Google Patents

Circuit de refrigeration a boucle secondaire Download PDF

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Publication number
WO1999048992A1
WO1999048992A1 PCT/US1999/003661 US9903661W WO9948992A1 WO 1999048992 A1 WO1999048992 A1 WO 1999048992A1 US 9903661 W US9903661 W US 9903661W WO 9948992 A1 WO9948992 A1 WO 9948992A1
Authority
WO
WIPO (PCT)
Prior art keywords
refrigerant
refrigeration system
refrigeration
heat transfer
temperature
Prior art date
Application number
PCT/US1999/003661
Other languages
English (en)
Inventor
Gregory J. Sherwood
Original Assignee
Minnesota Mining And Manufacturing Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Minnesota Mining And Manufacturing Company filed Critical Minnesota Mining And Manufacturing Company
Publication of WO1999048992A1 publication Critical patent/WO1999048992A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D17/00—Arrangements for circulating cooling fluids; Arrangements for circulating gas, e.g. air, within refrigerated spaces
    • F25D17/02—Arrangements for circulating cooling fluids; Arrangements for circulating gas, e.g. air, within refrigerated spaces for circulating liquids, e.g. brine
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/10—Liquid materials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2205/00—Aspects relating to compounds used in compression type refrigeration systems
    • C09K2205/10—Components
    • C09K2205/11—Ethers
    • C09K2205/112—Halogenated ethers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/22—Refrigeration systems for supermarkets

Definitions

  • the present invention relates to heat transfer media, and in particular to the use of hydrofluoroethers (HFEs) as low temperature heat transfer media.
  • HFEs hydrofluoroethers
  • Another factor that removes many heat transfer agents from consideration is their toxicity. This is the case, for example, with ammonia and with many of the ethyl ene glycols. The toxicity of these materials, by ingestion, inhalation, or transdermal absorption, makes them dangerous to handle and unsuitable for commercial food handling environments. Still other heat transfer agents are disfavored because of their flammability. This is the case, for example, with most ethers and hydrocarbons. The risk of flammability is particularly great where the heat transfer agent is subject to large positive pressures within the refrigeration cycle. Other heat transfer agents are disfavored because they are gases at normal operating temperatures. An example of this type of refrigerant is ammonia.
  • secondary loop systems are also more compact in design, can be factory built, and are capable of operating with an extremely small charge of refrigerant. Furthermore, in secondary loop systems, the vapor compression process of the refrigeration cycle is centralized, and can be operated from a
  • the HFEs of the present invention are nonflammable, nontoxic, environmentally benign, and have a high heat transfer capacity and low viscosity over the required operating temperatures. Furthermore, since these materials have high boiling points and low freezing points, they are not prone to phase changes over the required operating temperatures, and do not require pressurized systems.
  • FIG. 1 is a schematic drawing of a secondary loop refrigeration system suitable for installation in a supermarket;
  • FIGS. 2 and 2a are graphs depicting the pressure drop factor as a function of temperature for some embodiments of the present invention as well as several prior art heat transfer fluids
  • FIGS. 3 and 3a are graphs depicting the heat transfer factor as a function of temperature for some embodiments of the present invention as well as several prior art heat transfer fluids
  • FIGS. 4 and 4a are graphs depicting the temperature difference factor as a function of temperature for some embodiments of the present invention as well as several prior art heat transfer fluids; and FIGS. 5-7 are graphs depicting the theoretical specific pump power requirements of several conventional secondary cooling fluids compared with C 4 F 9 OCH 3 , C F OCH 3 and C F 9 OC H 5 respectively.
  • secondary loop refrigeration system refers to a system in which a heat transfer medium is used to transport energy from a heat source to a primary refrigeration system.
  • secondary loop refers to the path over which the heat transfer medium travels while it is being cycled between the heat source and the primary refrigeration system.
  • second refrigerant refers to the heat transfer medium in the secondary loop.
  • FIG. 1 illustrates the configuration of a typical secondary loop refrigeration system 10 suitable for installation in a grocery store.
  • the goods to be refrigerated are arranged in a series of display cases 12 located throughout the store.
  • Each display case is fitted with one or more refrigeration coils that are in open communication with a network of liquid feedlines 14 which convey the secondary refrigerant from the primary refrigeration system 16 to the display cases.
  • energy enters the display cases in the form of ambient heat, and is transferred to the secondary refrigerant by way of the refrigeration coils.
  • the transfer of heat to the secondary refrigerant is typically facilitated by the use of fans, which circulate air around the goods in the display case and over the surfaces of the refrigeration coils.
  • the warmed primary refrigerant is circulated through a rooftop compressor 24.
  • heat is extracted from the primary refrigerant and expelled to the environment.
  • the primary refrigerant is liquefied and cooled.
  • the primary refrigerant is then expanded and returned to the primary-to-secondary heat exchanger.
  • Equation 1 may be simplified to
  • F ⁇ (F p 2/7 )/F ⁇ (Equation 3)
  • F p the Pressure Drop Factor
  • F ⁇ the Heat Transfer Factor.
  • the Pressure Drop Factor is an estimate of the pressure drop, or loss due to friction, as a fluid flows through a tube. As such, it is a function of both fluid properties and system properties.
  • Ri and R 2 are the same or different and are selected from the group consisting of substituted and nonsubstituted alkyl, aryl, and alkylaryl groups and their derivatives. At least one of Ri and R contains at least one fluorine atom, and at least one of Ri and R contains at least one hydrogen atom. Optionally, one or both of Ri and R may contain one or more caternary or noncaternary heteroatoms, such as nitrogen, oxygen, or sulfur, and/or one or more halogen atoms, including chlorine, bromine, or iodine.
  • caternary or noncaternary heteroatoms such as nitrogen, oxygen, or sulfur
  • halogen atoms including chlorine, bromine, or iodine.
  • R f and R are defined as above for Ri and R 2 , except that R f contains at least one fluorine atom, and R contains no fluorine atoms. More preferably, R is a noncyclic branched or straight chain alkyl group, such as methyl, ethyl, n-propyl, wo-propyl, «-butyl, zso-butyl, or t-butyl, and R f is a fluorinated derivative of such a group.
  • R] and R 2 or R f and R are chosen so that the compound has at least three carbon atoms, and the total number of hydrogen atoms in the compound is at most equal to the number of fluorine atoms.
  • Compounds of this type tend to be nonflammable.
  • Specific examples of preferred heat transfer media for use in the present invention include C 3 F 7 OCH 3 , C 3 F 7 OC 2 H 5 , C 4 F 9 OCH 3 , and C 4 F 9 OC 2 H 5 .
  • the heat transfer media of the present invention may be used alone or in conjunction with one or more other heat transfer media of the invention or with one or more other heat transfer media as are known to the art.
  • the heat transfer media of the present invention may be used as a pure compound, or as a blend, solution, or mixture (azeotropic or otherwise) with one or more other materials.
  • Such other materials may include other heat transfer media, either of the present invention or as are known to the art, or one or more substances used to induce a freezing point depression or boiling point elevation.
  • an energy efficient secondary loop refrigeration system such as can be used in refrigerated supermarket display cases, may be constructed utilizing a hydrofluoroether, such as those depicted above by Formula II, as a secondary refrigerant where the hydrofluoroether communicates with the air to be refrigerated via a countercurrent heat exchanger.
  • the hydrofluoroether may be used at even moderate temperatures, for example, at 0°C or higher, in a manner that both minimizes the size and the energy requirements of the refrigeration system.
  • the most useful countercurrent heat exchangers will be those of a tube- fin design.
  • Direct expansion refrigeration systems are widely used to remove heat from air using this type of heat exchanger.
  • the refrigerant expanding in the tubes of the coil maintains the temperature of the inside of the tubes at a near constant level, and air passes over the coil and transfers heat to the relatively cooler surfaces of the fins and tubes.
  • the required operating temperature of the coil is determined by the conditions of the air entering and leaving the coil.
  • the thermal load removed from the refrigerated air by the secondary refrigerant is two fold: (1) the sensible heat measured by the drop in temperature of the air; and (2) the latent heat of fusion of water as the moisture in the air condenses on the cooler surfaces of the coil.
  • the latent load is not measurable by temperature change in the air but rather is a function of the dew point of the air. If the temperature of the cooler surfaces of the coil is below the dew point of the air and below the freezing point of water, the moisture will condense and freeze on the surface in the form of ice or frost.
  • the latent load can be quite substantial, varying from 30 to 50% of the total thermal load for medium temperature operation (typically "medium temperature” are dairy or meat display cases with air entering the coil between about 4°C and 7°C and leaving the coil between about -7°C and -3°C).
  • medium temperature dairy or meat display cases with air entering the coil between about 4°C and 7°C and leaving the coil between about -7°C and -3°C.
  • a typical coil would need to operate at a temperature
  • the temperature of the coil in currently employed commercial systems usually is below the dew point of the entering air, causing condensation at the leading edge of the coil fins and freezes. Frost also occurs along the fin until the dew point of the air contacting the coil fins is equal to the temperature of the surface, and although the air still has a capacity to carry water vapor, its efficiency is limited by the temperature of the coil.
  • frost will continue to build on the fins until the flow of air is reduced.
  • a defrost cycle is started that warms the coil above the freezing temperature of water and the frost is melted and drained away.
  • These cycles can be as frequent as four times a day and can take as long as an hour to complete. Product temperatures may rise above unacceptable levels during these cycles.
  • a secondary refrigerant comprising a hydrofluoroether allows for the design of a refrigeration coil where sensible heat can be transferred from the air while maintaining the heat transfer surface (fin and tube ) above the dew point of the air.
  • the latent load (frost formation) can be substantially reduced or even possibly eliminated.
  • Examples Examples 1-4 illustrate the improved performance characteristics of the heat transfer media of the present invention, compared to prior art heat transfer media.
  • the thermal conductivities of C 4 F 9 OC H 5 , C 4 F OCH 3 , C 3 F 7 OCH 3 , and C 6 F ] were determined using a transient, hot-wire thermal conductivity cell over the temperature range of -50°C to +50°C, according to ASTM D 2717-86. A platinum wire was used in the measurements. The wire was 20 cm in length, 0.17 mm in diameter, and had a resistance of 120 ⁇ at 20 °C. The thermal conductivities are set forth in Tables 1-4.
  • the densities of the fluids of Example 1 were determined from 0°C to +50°C using a using a Mettler-Parr Model DMA45 densitometer. For temperatures below 0°C, densities were determined by extrapolation of the measured densities with a linear curve fit. The densities are set forth in Tables 1-4.
  • the kinematic viscosity of the fluids of Example 1 were measured according to ASTM D 4486-85 over the temperature range of -60°C to 25°C. The results were curve fit to five data points. The resulting kinematic viscosities are set forth in Tables 1-4.
  • the specific heats of the fluids of Example 1 were measured by differential scanning calorimetry according to ASTM E 1269-90 over a temperature range of -30°C to 58°C . For temperatures below -30°C, specific heats were determined by extrapolation of the measured specific heats with a linear curve fit. The specific heats are shown in Tables 1-4.
  • FIGS. 2 and 2a depict the Pressure Drop Factor as a function of temperature for several heat transfer media.
  • the viscosity of a fluid has the greatest influence on the Pressure Drop Factor.
  • a low viscosity indicates that the fluid enters turbulent flow sooner given the same fluid velocity.
  • the frictional forces from the tube walls are translated into the fluid, forcing it to churn and mix.
  • the frictional forces also increase, as does the Pressure Drop Factor.
  • the Heat Transfer Factor curves are essentially linear for all of the fluids of interest, although the slopes of these curves vary significantly.
  • the aqueous solutions generally follow the same slope, but are shifted along the ordinate by the different freezing point depressants added to the water. Relative to the non-aqueous fluids, the slopes of the curves for the aqueous solutions are quite steep, and indicates that their ability to transfer heat drops off rapidly as the operating temperatures of secondary systems is approached. Below -20°C, C F 9 OCH 3 holds the highest value of the Heat Transfer Factor.
  • Examples 6-8 To illustrate the magnitude of the shift in power requirements brought about by small differences in the Temperature Difference Factor, the Pump Power Ratio (E p ⁇ /E p2 ) was determined as a function of temperature in accordance with Equation 2 for Tyfoxit ® 1.15, Tyfoxit ® 1.21 (inhibited alkali emanate solutions commercially available from Tyforop Chemie GmbH, Hamburg, Germany), an aqueous solution of 25% by weight ethyl alcohol, and an aqueous solution of 33% by weight of propylene glycol.
  • the reference medium used was C 4 F 9 OCH as shown in FIG. 5, C 3 F OCH 3 as shown in FIG. 6, and C 4 F 9 OC 2 H 5 as shown in FIG. 7.
  • the compound C F OCH 3 is especially effective as a secondary heat transfer medium.
  • the fluorinated ethers C 4 F 9 OCH 3 , C F 9 OC 2 H 5 , and c-C 6 F ⁇ OCH were tested for flash point by the standard method defined by ASTM D3278-89. Each compound was determined to have no flash point.
  • GWP Global warming potential
  • GWP is the integrated potential warming due to the release of 1 kilogram of sample compound relative to the warming due to 1 kilogram of CO 2 over a specified integration time horizon (ITH) using the following equation:
  • each of the fluorinated ethers of the present invention has an unexpectedly lower atmospheric lifetime than the corresponding hydrofluorocarbon, that is, the hydrofluorocarbon having the same carbon number.
  • the fluorinated ethers of the present invention are thus more environmentally acceptable than the hydrofluorocarbons (which have previously been proposed as chloro fluorocarbon replacements).
  • ODP Ozone Depletion Potential
  • a secondary refrigeration system was needed for large events at stadiums and arenas. In order to meet customer demands, the system had to be capable of chilling several cases of plastic bottles of soda from room temperature (30°C) to serving
  • a traditional refrigeration system was used to cool a large reservoir of liquid.
  • the chilled liquid was then pumped from the reservoir to a coil in a blast cooler. Air in the cooler was then circulated at high velocity to remove thermal energy from the bottles and transfer it to the cooled coil.
  • the large reservoir of liquid served as a "thermal flywheel" capable of absorbing a large amount of energy.
  • the thermal energy is removed from the reservoir at a lower rate with the refrigeration system to prepare for another cycle.
  • the following examples illustrates the relative performance and energy requirements of for a supermarket display case designed with countercurrent heat exchanger to transfer heat from the secondary refrigerant to the chilled air.
  • One such case was designed using HFE-7100TM as a secondary refrigerant, and another using a 33% propylene glycol/water secondary refrigerant.
  • HFE-7100TM as a secondary refrigerant
  • propylene glycol/water secondary refrigerant for purposes of a side-by-side comparison of these two designs, the following load requirements were specified.
  • a computer model was used to predict the performance of an air cooling heat exchanger.
  • Ubiquitous in display cases is the tube-fin heat exchanger, built using a bank of tubes and fins mounted perpendicular to the axis of the tube.
  • the heat transfer calculations used in the model are explained in the text Introduction to Heat Transfer by Frank P. Incropera and David P. Dewitt, 1990 by John Wiley & Sons.
  • Heat transfer from the air to the heat exchanger can be calculated using the configuration of the tube bank and the size, spacing, and material type of the fin.
  • the heat transfer from the tube bank to the secondary fluid can be calculated knowing the thermal transport properties of the fluid and the tube inside diameter and arrangement of the flow path of the fluid.
  • the computer model considers all the input conditions of the air, secondary refrigerant, and heat exchanger configuration and calculates the amount of energy that can be transferred from the air to the secondary refrigerant. In addition, a prediction can be made regarding the exiting temperature and humidity of the air and the required flow rate of the liquid.
  • the model was employed to predict the design parameters of the two cases using the following physical properties of the two refrigerants:
  • Air Velocity (meters per minute) 67.6 34.4
  • hydrofluoroether heat exchangers require much less material to manufacture and hence reduce cost involved in their manufacture.
  • the reduced mass of metal makes the exchanger much more dynamic from a thermal sense, so defrost can occur more quickly with less energy.
  • the fluid volume of the hydrofluoroether exchanger also in nearly an order of magnitude lower than that for the propylene glycol exchanger.
  • secondary refrigeration coils designed for a hydrofluoroether also exhibit significant defrosting advantages.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Combustion & Propulsion (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
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Abstract

La présente invention concerne une technique et un procédé qui font intervenir certains hydrofluoroéthers (HFE) comme agent de transfert thermique dans des circuit de réfrigération à boucle secondaire. Ces hydrofluoroéthers sont ininflammables, non toxiques, sans danger pour l'environnement et possèdent un pouvoir de transfert thermique élevé ainsi qu'une faible viscosité dans la plage de températures requise. Comme ils possèdent par ailleurs des points d'ébullition élevés et des points de congélation bas, ces produits ne sont pas exposés à des changements de phase dans leurs plages respectives de fonctionnement et ne nécessitent pas de pressurisation du circuit.
PCT/US1999/003661 1998-03-25 1999-02-19 Circuit de refrigeration a boucle secondaire WO1999048992A1 (fr)

Applications Claiming Priority (2)

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US4760798A 1998-03-25 1998-03-25
US09/047,607 1998-03-25

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WO1999048992A1 true WO1999048992A1 (fr) 1999-09-30

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001027216A1 (fr) * 1999-10-08 2001-04-19 3M Innovative Properties Company Hydrofluoroethers utilises comme fluides de transfert de chaleur dans des traitements a basse temperature necessitant une sterilisation
JP2002020737A (ja) * 2000-07-12 2002-01-23 Asahi Glass Co Ltd 冷却用媒体および冷却方法
EP1306769A3 (fr) * 2001-08-31 2003-05-21 Horiba, Ltd. Système de détermination d'un indice d'émission de gaz par effet de serre
WO2008120250A1 (fr) * 2007-03-30 2008-10-09 Tekno-Ice S.R.L. Installation pour la fabrication de crème glacée

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5042262A (en) * 1990-05-08 1991-08-27 Liquid Carbonic Corporation Food freezer
WO1997014762A1 (fr) * 1995-10-20 1997-04-24 Minnesota Mining And Manufacturing Company Hydrofluoroethers utilises comme frigorigenes basse temperature
US5819549A (en) * 1996-10-16 1998-10-13 Minnesota Mining And Manufacturing Company Secondary loop refrigeration system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5042262A (en) * 1990-05-08 1991-08-27 Liquid Carbonic Corporation Food freezer
WO1997014762A1 (fr) * 1995-10-20 1997-04-24 Minnesota Mining And Manufacturing Company Hydrofluoroethers utilises comme frigorigenes basse temperature
US5713211A (en) * 1995-10-20 1998-02-03 Minnesota Mining And Manufacturing Company Hydrofluoroethers as low temperature refrigerants
US5819549A (en) * 1996-10-16 1998-10-13 Minnesota Mining And Manufacturing Company Secondary loop refrigeration system

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001027216A1 (fr) * 1999-10-08 2001-04-19 3M Innovative Properties Company Hydrofluoroethers utilises comme fluides de transfert de chaleur dans des traitements a basse temperature necessitant une sterilisation
US6303080B1 (en) 1999-10-08 2001-10-16 3M Innovative Properties Company Hydrofluoroethers as heat-transfer fluids in low temperature processes requiring sterilization
JP2002020737A (ja) * 2000-07-12 2002-01-23 Asahi Glass Co Ltd 冷却用媒体および冷却方法
EP1306769A3 (fr) * 2001-08-31 2003-05-21 Horiba, Ltd. Système de détermination d'un indice d'émission de gaz par effet de serre
WO2008120250A1 (fr) * 2007-03-30 2008-10-09 Tekno-Ice S.R.L. Installation pour la fabrication de crème glacée

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