ASHRAE FUNDAMENTALS SI CH 31-2017 Physical Properties of Secondary Coolants (Brines).pdf

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1、31.1CHAPTER 31PHYSICAL PROPERTIES OF SECONDARY COOLANTS (BRINES)Salt-Based Brines 31.1Inhibited Glycols . 31.4Halocarbons 31.12Nonhalocarbon, Nonaqueous Fluids 31.12N many refrigeration applications, heat is transferred to a second-Iary coolant, which can be any liquid cooled by the refrigerant andu

2、sed to transfer heat without changing state. These liquids are alsoknown as heat transfer fluids, brines, or secondary refrigerants.Other ASHRAE Handbook volumes describe various applica-tions for secondary coolants. In the 2014 ASHRAE HandbookRefrigeration, refrigeration systems are discussed in Ch

3、apter 13,their uses in food processing in Chapters 23 and 28 to 42, and icerinks in Chapter 44. In the 2015 ASHRAE HandbookHVAC Appli-cations, solar energy use is discussed in Chapter 35, and snow melt-ing and freeze protection in Chapter 51. Thermal storage is coveredin Chapter 51 of the 2016 ASHRA

4、E HandbookHVAC Systems andEquipment.This chapter describes physical properties of the more commonsecondary coolants based on ethylene glycol, propylene glycol,sodium chloride, or calcium chloride and provides information ontheir use. Less widely used secondary coolants such as ethyl alcoholor potass

5、ium formate are not included in this chapter, but theirphysical properties are summarized in Melinder (2007). Physicalproperty data for nitrate and nitrite salt solutions used for stratifiedthermal energy storage are presented by Andrepont (2012). Thechapter also includes information on corrosion pr

6、otection. Supple-mental information on corrosion inhibition can be found in Chapter49 of the 2015 ASHRAE HandbookHVAC Applications and Chap-ter 13 of the 2014 ASHRAE HandbookRefrigeration. 1. SALT-BASED BRINESPhysical PropertiesWater solutions of calcium chloride and sodium chloride havehistorically

7、 been the most common refrigeration brines. Tables 1 and2 list the properties of pure calcium chloride brine and sodium chlo-ride brine. For commercial grades, use the formulas in the footnotesto these tables. For calcium chloride brines, Figure 1 shows specificheat, Figure 2 shows the ratio of mass

8、 of solution to that of water,Figure 3 shows viscosity, and Figure 4 shows thermal conductivity.Figures 5 to 8 show the same properties for sodium chloride brines.Table 1 Properties of Pure Calcium Chloride* BrinesPure CaCl2, % by MassSpecific Heat at 15C, J/(kgK)Crystallization Starts, CDensity at

9、16C, kg/m3Density at Various Temperatures, kg/m3CaCl2Brine 20C 10C 0C 10C0 4184 0.0 0.0 9995 3866 2.4 52.2 1044 1042 10416 3824 2.9 63.0 1049 1051 10507 3757 3.4 74.2 1059 1060 10598 3699 4.1 85.5 1068 1070 10689 3636 4.7 96.9 1078 1079 107710 3577 5.4 108.6 1087 1088 108611 3523 6.2 120.5 1095 1097

10、 109512 3464 7.1 132.5 1104 1107 110413 3414 8.0 144.8 1113 1116 111414 3364 9.2 157.1 1123 1126 112315 3318 10.3 169.8 1132 1140 1136 113316 3259 11.6 182.6 1141 1150 1145 114217 3209 13.0 195.7 1152 1160 1155 115218 3163 14.5 209.0 1161 1170 1165 116219 3121 16.2 222.7 1171 1179 1175 117220 3084 1

11、8.0 236.0 1180 1189 1185 118221 3050 19.9 249.6 118922 2996 22.1 264.3 1201 1214 1210 1206 120223 2958 24.4 278.7 121124 2916 26.8 293.5 1223 1235 1231 1227 122325 2882 29.4 308.2 123226 2853 32.1 323.1 124227 2816 35.1 338.5 125328 2782 38.8 354.0 126429 2753 45.2 369.9 127529.87 2741 55.0 378.8 12

12、8930 2732 46.0 358.4 129432 2678 28.6 418.1 131634 2636 15.4 452.0 1339Source: CCI (1953)*Mass of Type 1 (77% min.) CaCl2= (mass of pure CaCl2)/(0.77). Mass of Type 2 (94% min.) CaCl2= (mass of pure CaCl2)/(0.94)._The preparation of this chapter is assigned to TC 3.1, Refrigerants and Secondary Cool

13、ants.31.2 2017 ASHRAE HandbookFundamentals (SI)Fig. 1 Specific Heat of Calcium Chloride Brines(CCI 1953)Fig. 2 Density of Calcium Chloride Brines(CCI 1953)Fig. 3 Viscosity of Calcium Chloride Brines(CCI 1953)Fig. 4 Thermal Conductivity of Calcium Chloride Brines(CCI 1953)Physical Properties of Secon

14、dary Coolants (Brines) 31.3Table 2 Properties of Pure Sodium ChlorideaBrinesPure NaCl,% by MassSpecific Heat at 15C, J/(kgK)CrystallizationStarts, CDensity at 16C, kg/m3Density at Various Temperatures, kg/m3NaCl Brine 10C 0C10C20C0 4184 0.0 0.0 10005 3925 2.9 51.7 1035 1038.1 1036.5 1034.06 3879 3.6

15、 62.5 1043 1045.8 1043.9 1041.27 3836 4.3 73.4 1049 1053.7 1051.4 1048.58 3795 5.0 84.6 1057 1061.2 1058.9 1055.89 3753 5.8 95.9 1065 1069.0 1066.4 1063.210 3715 6.6 107.2 1072 1076.8 1074.0 1070.611 3678 7.3 118.8 1080 1084.8 1081.6 1078.112 3640 8.2 130.3 1086 1092.4 1089.6 1085.613 3607 9.1 142.2

16、 1094 1100.3 1097.0 1093.214 3573 10.1 154.3 1102 1108.2 1104.7 1100.815 3544 10.9 166.5 1110 1119.4 1116.2 1112.5 1108.516 3515 11.9 178.9 1118 1127.6 1124.2 1120.4 1116.217 3485 13.0 191.4 1126 1135.8 1132.2 1128.3 1124.018 3456 14.1 204.1 1134 1144.1 1140.3 1136.2 1131.819 3427 15.3 217.0 1142 11

17、53.4 1148.5 1144.3 1139.720 3402 16.5 230.0 1150 1160.7 1156.7 1154.1 1147.721 3376 17.8 243.2 1158 1169.1 1165.0 1160.5 1155.822 3356 19.1 256.6 1166 1177.6 1173.3 1168.7 1163.923 3330 20.6 270.0 1174 1186.1 1181.7 1177.0 1172.024 3310 15.7 283.7 1182 1194.7 1190.1 1185.3 1180.325 3289 8.8 297.5 11

18、9025.2 0.0aMass of commercial NaC1 required = (mass of pure NaCl required)/(% purity).Fig. 5 Specific Heat of Sodium Chloride Brines(adapted from Carrier 1959)Fig. 6 Density of Sodium Chloride Brines(adapted from Carrier 1959)31.4 2017 ASHRAE HandbookFundamentals (SI)Brine applications in refrigerat

19、ion are mainly in industrialmachinery and in skating rinks. Corrosion is the principal problemfor calcium chloride brines, especially in ice-making tanks wheregalvanized iron cans are immersed.Ordinary salt (sodium chloride) is used where contact with cal-cium chloride is intolerable (e.g., the brin

20、e fog method of freezing fishand other foods). It is used as a spray to air-cool unit coolers to preventfrost formation on coils. In most refrigerating work, the lower freez-ing point of calcium chloride solution makes it more convenient to use.Commercial calcium chloride, available as Type 1 (77% m

21、ini-mum) and Type 2 (94% minimum), is marketed in flake, solid, andsolution forms; flake form is used most extensively. Commercialsodium chloride is available both in crude (rock salt) and refinedgrades. Because magnesium salts tend to form sludge, their pres-ence in sodium or calcium chloride is un

22、desirable.Corrosion InhibitionAll brine systems must be treated to control corrosion and depos-its. Historically, chloride-based brines were maintained at neutralpH and treated with sodium chromate. However, using chromate asa corrosion inhibitor is no longer deemed acceptable because of itsdetrimen

23、tal environmental effects. Chromate has been placed onhazardous substance lists by several regulatory agencies. For exam-ple, the U.S. Agency for Toxic Substances and Disease Registrys(ATSDR 2016) Priority List of Hazardous Substances ranks hexa-valent chromium 17th out of 275 chemicals of concern (

24、based onfrequency, toxicity, and potential for human exposure at NationalPriorities List facilities). Consequently, hexavalent chrome and sev-eral chromates are also listed on several state right-to-know hazard-ous substance lists, including New Jersey, California, Minnesota,Pennsylvania and others.

25、Instead of chromate, most brines use a sodium-nitrite-based in-hibitor ranging from approximately 3000 mg/kg in calcium brines to4000 mg/kg in sodium brines. Other, proprietary organic inhibitorsare also available to mitigate the inherent corrosiveness of brines.Before using any inhibitor package, r

26、eview federal, state, andlocal regulations concerning the use and disposal of the spent fluids.If the regulations prove too restrictive, an alternative inhibition sys-tem should be considered.2. INHIBITED GLYCOLSEthylene glycol and propylene glycol, when properly inhibitedfor corrosion control, are

27、used as aqueous-freezing-point depres-sants (antifreeze) and heat transfer media. Their chief attributes aretheir ability to efficiently lower the freezing point of water, their lowvolatility, and their relatively low corrosivity when properly inhib-ited. Inhibited ethylene glycol solutions have bet

28、ter thermophysicalproperties than propylene glycol solutions, especially at lower tem-peratures. However, the less toxic propylene glycol is preferred forapplications involving possible human contact or where mandatedby regulations. If a heat transfer fluid may have incidental food con-tact, then it

29、 should be made from propylene glycol that meets U.S.Pharmacopeia (USP 2016) Food Chemical Codex (FCC) specifica-tions. Avoid other, less pure grades of propylene glycol: they cancontain toxic or unwanted impurities that also adversely affect per-formance characteristics (e.g., foaming propensity, c

30、orrosion).Physical PropertiesEthylene glycol and propylene glycol are colorless, practicallyodorless liquids that are miscible with water and many organic com-pounds. Table 3 shows properties of the pure materials.The freezing and boiling points of aqueous solutions of ethyleneglycol and propylene g

31、lycol are given in Tables 4 and 5. Note thatincreasing the concentration of ethylene glycol above 60% by masscauses the freezing point of the solution to increase. Propyleneglycol solutions above 60% by mass do not have freezing points.Instead of freezing, propylene glycol solutions supercool andbec

32、ome a glass (a liquid with extremely high viscosity and theappearance and properties of a noncrystalline amorphous solid). Onthe dilute side of the eutectic (the mixture at which freezing pro-duces a solid phase of the same composition), ice forms on freezing;on the concentrated side, solid glycol s

33、eparates from solution onfreezing. The freezing rate of such solutions is often quite slow, but,in time, they set to a hard, solid mass.Physical properties (i.e., density, specific heat, thermal con-ductivity, and viscosity) for aqueous solutions of ethylene glycolcan be found in Tables 6 to 9 and F

34、igures 9 to 12; similar data foraqueous solutions of propylene glycol are in Tables 10 to 13 andFigures 13 to 16. Densities are for aqueous solutions of industriallyinhibited glycols, and are somewhat higher than those for pureglycol and water alone. Typical corrosion inhibitor packages do notsignif

35、icantly affect other physical properties. Physical properties forthe two fluids are similar, except for viscosity. At the same concen-tration, aqueous solutions of propylene glycol are more viscous thansolutions of ethylene glycol. This higher viscosity accounts for themajority of the performance di

36、fference between the two fluids.Fig. 7 Viscosity of Sodium Chloride Brines(adapted from Carrier 1959)Fig. 8 Thermal Conductivity of Sodium Chloride Brines(adapted from Carrier 1959)Physical Properties of Secondary Coolants (Brines) 31.5The choice of glycol concentration depends on the type of pro-te

37、ction required by the application. If the fluid is being used to pre-vent equipment damage during idle periods in cold weather, such aswinterizing coils in an HVAC system, 30% by volume ethylene gly-col or 35% by volume propylene glycol is sufficient. These concen-trations allow the fluid to freeze.

38、 As the fluid freezes, it forms aslush that expands and flows into any available space. Therefore,expansion volume must be included with this type of protection. Ifthe application requires that the fluid remain entirely liquid, use aconcentration with a freezing point 3 K below the lowest expectedte

39、mperature. Avoid excessive glycol concentration because itincreases initial cost and adversely affects the fluids physical prop-erties.Additional physical property data are available from suppliers ofindustrially inhibited ethylene and propylene glycol.Corrosion InhibitionInterestingly, ethylene gly

40、col and propylene glycol, when notdiluted with water, are actually less corrosive than water is withcommon construction metals. However, once diluted with water (asis typical), all aqueous glycol solutions are more corrosive than thewater from which they are prepared: when uninhibited glycols ther-m

41、ally degrade and oxidize with use, they form acidic degradationproducts, which create an increasingly more corrosive environmentif corrosion inhibitors and pH buffering compounds are not present.The amount of oxidation is influenced by temperature, degree ofaeration, and type of metal components to

42、which the glycol solutionis exposed. In general, hydronic heating systems cause more degra-dation of glycol-based heat transfer fluids than do chilled-water sys-tems. It is therefore necessary for glycol-based heat transfer fluidsnot only to use corrosion inhibitors that are effective at protectingc

43、ommon metals from corrosion, but also to contain additional addi-tives to buffer or neutralize the acidic glycol degradation productsthat form during use. Corrosion inhibitors form a surface barrier thatprotects metal from attack, but their effectiveness is highly depen-dent on solution pH. Failure

44、to compensate for glycol degradationTable 3 Physical Properties of Ethylene Glycol and Propylene GlycolPropertyEthylene GlycolPropylene GlycolRelative molecular mass 62.07 76.10Density at 20C, kg/m31113 1036Boiling point, Cat 101.3 kPa 198 187at 6.67 kPa 123 116at 1.33 kPa 89 85Vapor pressure at 20C

45、, Pa 6.7 9.3Freezing point, C 12.7 Sets to glass below 51CViscosity, mPasat 0C 57.4 243at 20C 20.9 60.5at 40C 9.5 18.0Refractive index nDat 20C 1.4319 1.4329Specific heat at 20C, kJ/(kgK) 2.347 2.481Heat of fusion at 12.7C, kJ/kg 187 Heat of vaporization at 101.3 kPa, kJ/kg 846 688Heat of combustion

46、 at 20C, MJ/kg 19.246 23.969Sources: Dow Chemical (2001a, 2001b)Fig. 9 Density of Aqueous Solutions of Industrially Inhibited Ethylene Glycol (vol. %)(Dow Chemical 2001b)Fig. 10 Specific Heat of Aqueous Solutions of Industrially Inhibited Ethylene Glycol (vol. %)(Dow Chemical 2001b)Fig. 11 Thermal C

47、onductivity of Aqueous Solutions of Industrially Inhibited Ethylene Glycol (vol. %)(Dow Chemical 2001b)31.6 2017 ASHRAE HandbookFundamentals (SI)Table 4 Freezing and Boiling Points of Aqueous Solutions of Ethylene GlycolPercent Ethylene GlycolFreezing Point, CBoiling Point, C at 100.7 kPaBy Mass By

48、Volume0.0 0.0 0.0 100.05.0 4.4 1.4 100.610.0 8.9 3.2 101.115.0 13.6 5.4 101.720.0 18.1 7.8 102.221.0 19.2 8.4 102.222.0 20.1 8.9 102.223.0 21.0 9.5 102.824.0 22.0 10.2 102.825.0 22.9 10.7 103.326.0 23.9 11.4 103.327.0 24.8 12.0 103.328.0 25.8 12.7 103.929.0 26.7 13.3 103.930.0 27.7 14.1 104.431.0 28

49、.7 14.8 104.432.0 29.6 15.4 104.433.0 30.6 16.2 104.434.0 31.6 17.0 104.435.0 32.6 17.9 105.036.0 33.5 18.6 105.037.0 34.5 19.4 105.038.0 35.5 20.3 105.039.0 36.5 21.3 105.040.0 37.5 22.3 105.641.0 38.5 23.2 105.642.0 39.5 24.3 105.643.0 40.5 25.3 106.144.0 41.5 26.4 106.145.0 42.5 27.5 106.746.0 43.5 28.8 106.747.0 44.5 29.8 106.748.0 45.5 31.1 106.749.0 46.6 32.6 106.750.0 47.6 33.8 107.251.0 48.6 35.1 107.252.0 49.6 36.4 107.253.0 50.6 37.9 107.85