ASHRAE FUNDAMENTALS IP 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 ChlorideaBrinesPure CaCl2,% by MassRatio of Mass to Water at 60FRelative Density, Degrees BaumcSpecific

9、 Heat at 60F,Btu/lbFCrystalli-zation Starts, FMass per Unit Volumebat 60F Ratio of Mass at Various Temperatures to Water at 60FCaCl2,lb/galBrine,lb/galCaCl2,lb/ft3Brine,lb/ft34F 14F 32F 50F0 1.000 0.0 1.000 32.0 0.000 8.34 0.00 62.405 1.044 6.1 0.924 27.7 0.436 8.717 3.26 65.15 1.043 1.0426 1.050 7.

10、0 0.914 26.8 0.526 8.760 3.93 65.52 1.052 1.0517 1.060 8.2 0.898 25.9 0.620 8.851 4.63 66.14 1.061 1.0608 1.069 9.3 0.884 24.6 0.714 8.926 5.34 66.70 1.071 1.0699 1.078 10.4 0.869 23.5 0.810 9.001 6.05 67.27 1.080 1.07810 1.087 11.6 0.855 22.3 0.908 9.076 6.78 67.83 1.089 1.08711 1.096 12.6 0.842 20

11、.8 1.006 9.143 7.52 68.33 1.098 1.09612 1.105 13.8 0.828 19.3 1.107 9.227 8.27 68.95 1.108 1.10513 1.114 14.8 0.816 17.6 1.209 9.302 9.04 69.51 1.117 1.11514 1.124 15.9 0.804 15.5 1.313 9.377 9.81 70.08 1.127 1.12415 1.133 16.9 0.793 13.5 1.418 9.452 10.60 70.64 1.139 1.137 1.13416 1.143 18.0 0.779

12、11.2 1.526 9.536 11.40 71.26 1.149 1.146 1.14317 1.152 19.1 0.767 8.6 1.635 9.619 12.22 71.89 1.159 1.156 1.15318 1.162 20.2 0.756 5.9 1.747 9.703 13.05 72.51 1.169 1.166 1.16319 1.172 21.3 0.746 2.8 1.859 9.786 13.90 73.13 1.180 1.176 1.17320 1.182 22.1 0.737 0.4 1.970 9.853 14.73 73.63 1.190 1.186

13、 1.18321 1.192 23.0 0.729 3.9 2.085 9.928 15.58 74.1922 1.202 24.4 0.716 7.8 2.208 10.037 16.50 75.00 1.215 1.211 1.207 1.20323 1.212 25.5 0.707 11.9 2.328 10.120 17.40 75.6324 1.223 26.4 0.697 16.2 2.451 10.212 18.32 76.32 1.236 1.232 1.228 1.22425 1.233 27.4 0.689 21.0 2.574 10.295 19.24 76.9426 1

14、.244 28.3 0.682 25.8 2.699 10.379 20.17 77.5627 1.254 29.3 0.673 31.2 2.827 10.471 21.13 78.2528 1.265 30.4 0.665 37.8 2.958 10.563 22.10 78.9429 1.276 31.4 0.658 49.4 3.090 10.655 23.09 79.6229.87 1.290 32.6 0.655 67.0 3.16 10.75 23.65 80.4530 1.295 33.0 0.653 50.8 3.22 10.80 24.06 80.7632 1.317 34

15、.9 0.640 19.5 3.49 10.98 26.10 82.1434 1.340 36.8 0.630 4.3 3.77 11.17 28.22 83.57Source: CCI (1953)aMass 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).bMass of water per unit volume = Brine mass minus CaCl2mass.cAt 60F._The prep

16、aration of this chapter is assigned to TC 3.1, Refrigerants and Secondary Coolants.31.2 2017 ASHRAE HandbookFundamentals Fig. 1 Specific Heat of Calcium Chloride Brines(CCI 1953)Fig. 2 Specific Gravity of Calcium Chloride Brines(CCI 1953)Fig. 3 Viscosity of Calcium Chloride Brines(CCI 1953)Fig. 4 Th

17、ermal Conductivity of Calcium Chloride Brines(CCI 1953)Physical Properties of Secondary Coolants (Brines) 31.3Table 2 Properties of Pure Sodium ChlorideaBrinesPure NaCl,% by MassRatio of Mass to Water at 59FRelative Density, Degrees BaumbSpecific Heat at 59F,Btu/lbFCrystalli-zation Starts, FMass per

18、 Unit Volume at 60F Ratio of Mass at Various Temperatures to Water at 60FNaCl,lb/galBrine,lb/galNaCl,lb/ft3Brine,lb/ft314F32F50F68F0 1.000 0.0 1.000 32.0 0.000 8.34 0.000 62.45 1.035 5.1 0.938 26.7 0.432 8.65 3.230 64.6 1.0382 1.0366 1.03416 1.043 6.1 0.927 25.5 0.523 8.71 3.906 65.1 1.0459 1.0440 1

19、.04137 1.050 7.0 0.917 24.3 0.613 8.76 4.585 65.5 1.0536 1.0515 1.04868 1.057 8.0 0.907 23.0 0.706 8.82 5.280 66.0 1.0613 1.0590 1.05599 1.065 9.0 0.897 21.6 0.800 8.89 5.985 66.5 1.0691 1.0665 1.063310 1.072 10.1 0.888 20.2 0.895 8.95 6.690 66.9 1.0769 1.0741 1.070711 1.080 10.8 0.879 18.8 0.992 9.

20、02 7.414 67.4 1.0849 1.0817 1.078212 1.087 11.8 0.870 17.3 1.090 9.08 8.136 67.8 1.0925 1.0897 1.085713 1.095 12.7 0.862 15.7 1.188 9.14 8.879 68.3 1.1004 1.0933 1.097114 1.103 13.6 0.854 14.0 1.291 9.22 9.632 68.8 1.1083 1.1048 1.100915 1.111 14.5 0.847 12.3 1.392 9.28 10.395 69.3 1.1195 1.1163 1.1

21、126 1.108616 1.118 15.4 0.840 10.5 1.493 9.33 11.168 69.8 1.1277 1.1243 1.1205 1.116317 1.126 16.3 0.833 8.6 1.598 9.40 11.951 70.3 1.1359 1.1323 1.1284 1.124118 1.134 17.2 0.826 6.6 1.705 9.47 12.744 70.8 1.1442 1.1404 1.1363 1.131919 1.142 18.1 0.819 4.5 1.813 9.54 13.547 71.3 1.1535 1.1486 1.1444

22、 1.139820 1.150 19.0 0.813 2.3 1.920 9.60 14.360 71.8 1.1608 1.1568 1.1542 1.147821 1.158 19.9 0.807 0.0 2.031 9.67 15.183 72.3 1.1692 1.1651 1.1606 1.155922 1.166 20.8 0.802 2.3 2.143 9.74 16.016 72.8 1.1777 1.1734 1.1688 1.164023 1.175 21.7 0.796 5.1 2.256 9.81 16.854 73.3 1.1862 1.1818 1.1771 1.1

23、72124 1.183 22.5 0.791 3.8 2.371 9.88 17.712 73.8 1.1948 1.1902 1.1854 1.180425 1.191 23.4 0.786 16.1 2.488 9.95 18.575 74.325.2 1.200 32.0aMass of commercial NaCl required = (mass of pure NaCl required)/(% purity).bAt 60F.Fig. 5 Specific Heat of Sodium Chloride Brines(adapted from Carrier 1959)Fig.

24、 6 Specific Gravity of Sodium Chloride Brines(adapted from Carrier 1959)31.4 2017 ASHRAE HandbookFundamentals Brine applications in refrigeration are mainly in industrial ma-chinery and in skating rinks. Corrosion is the principal problem forcalcium chloride brines, especially in ice-making tanks wh

25、ere galva-nized iron cans are immersed.Ordinary salt (sodium chloride) is used where contact with calci-um chloride is intolerable (e.g., the brine 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 wo

26、rk, the lower freez-ing point of calcium chloride solution makes it more convenient to use.Commercial calcium chloride, available as Type 1 (77% mini-mum) and Type 2 (94% minimum), is marketed in flake, solid, andsolution forms; flake form is used most extensively. Commercialsodium chloride is avail

27、able both in crude (rock salt) and refinedgrades. Because magnesium salts tend to form sludge, their pres-ence in sodium or calcium chloride is undesirable.Corrosion InhibitionAll brine systems must be treated to control corrosion and depos-its. Historically, chloride-based brines were maintained at

28、 neutralpH and treated with sodium chromate. However, using chromate asa corrosion inhibitor is no longer deemed acceptable because of itsdetrimental environmental effects. Chromate has been placed onhazardous substance lists by several regulatory agencies. For exam-ple, the U.S. Agency for Toxic Su

29、bstances and Disease Registrys(ATSDR 2016) Priority List of Hazardous Substances ranks hexa-valent chromium 17th out of 275 chemicals of concern (based onfrequency, toxicity, and potential for human exposure at NationalPriorities List facilities). Consequently, hexavalent chrome and sev-eral chromat

30、es are also listed on several state right-to-know hazard-ous substance lists, including New Jersey, California, Minnesota,Pennsylvania and others.Instead of chromate, most brines use a sodium-nitrite-basedinhibitor ranging from approximately 3000 ppm in calcium brinesto 4000 ppm in sodium brines. Ot

31、her, proprietary organic inhibitorsare also available to mitigate the inherent corrosiveness of brines.Before using any inhibitor package, review federal, state, andlocal regulations concerning the use and disposal of the spent fluids.If the regulations prove too restrictive, an alternative inhibiti

32、on sys-tem should be considered.2. INHIBITED GLYCOLSEthylene glycol and propylene glycol, when properly inhibitedfor corrosion control, are used as aqueous-freezing-point depres-sants (antifreeze) and heat transfer media. Their chief attributes aretheir ability to efficiently lower the freezing poin

33、t of water, their lowvolatility, and their relatively low corrosivity when properly inhib-ited. Inhibited ethylene glycol solutions have better thermophysicalproperties than propylene glycol solutions, especially at lower tem-peratures. However, the less toxic propylene glycol is preferred forapplic

34、ations involving possible human contact or where mandatedby regulations. If a heat transfer fluid may have incidental food con-tact, then it 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 propyle

35、ne glycol: they cancontain toxic or unwanted impurities that also adversely affect per-formance characteristics (e.g., foaming propensity, corrosion).Physical PropertiesEthylene glycol and propylene glycol are colorless, practicallyodorless liquids that are miscible with water and many organic com-p

36、ounds. Table 3 shows properties of the pure materials.The freezing and boiling points of aqueous solutions of ethyleneglycol and propylene glycol 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 increa

37、se. Propyleneglycol solutions above 60% by mass do not have freezing points.Instead of freezing, propylene glycol solutions supercool and be-come a glass (a liquid with extremely high viscosity and the appear-ance and properties of a noncrystalline amorphous solid). On thedilute side of the eutectic

38、 (the mixture at which freezing produces asolid phase of the same composition), ice forms on freezing; on theconcentrated side, solid glycol separates from solution on freezing.The freezing rate of such solutions is often quite slow, but, in time,they set to a hard, solid mass.Physical properties (i

39、.e., density, specific heat, thermal con-ductivity, and viscosity) for aqueous solutions of ethylene glycolcan be found in Tables 6 to 9 and Figures 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 indus

40、triallyinhibited glycols, and are somewhat higher than those for pureglycol and water alone. Typical corrosion inhibitor packages do notsignificantly affect other physical properties. Physical properties forthe two fluids are similar, except for viscosity. At the same concen-tration, aqueous solutio

41、ns of propylene glycol are more viscous thansolutions of ethylene glycol. This higher viscosity accounts for themajority of the performance difference between the two fluids.Fig. 7 Viscosity of Sodium Chloride Brines(adapted from Carrier 1959)Fig. 8 Thermal Conductivity of Sodium Chloride Brines(ada

42、pted from Carrier 1959)Physical Properties of Secondary Coolants (Brines) 31.5The choice of glycol concentration depends on the type of pro-tection 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

43、 HVAC system, 30% by volume ethylene gly-col or 35% by volume propylene glycol is sufficient. These concen-trations allow the fluid to freeze. As the fluid freezes, it forms aslush that expands and flows into any available space. Therefore, ex-pansion volume must be included with this type of protec

44、tion. If theapplication requires that the fluid remain entirely liquid, use a con-centration with a freezing point 5F below the lowest expected tem-perature. Avoid excessive glycol concentration because it increasesinitial cost and adversely affects the fluids physical properties.Additional physical

45、 property data are available from suppliers ofindustrially inhibited ethylene and propylene glycol.Corrosion InhibitionInterestingly, ethylene glycol and propylene glycol, when notdiluted with water, are actually less corrosive than water is withcommon construction metals. However, once diluted with

46、 water (asis typical), all aqueous glycol solutions are more corrosive than thewater from which they are prepared: when uninhibited glycols ther-mally degrade and oxidize with use, they form acidic degradationproducts, which create an increasingly more corrosive environmentif corrosion inhibitors an

47、d pH buffering compounds are not present.The amount of oxidation is influenced by temperature, degree ofaeration, and type of metal components to which the glycol solutionis exposed. In general, hydronic heating systems cause more degra-dation of glycol-based heat transfer fluids than do chilled-wat

48、er sys-tems. It is therefore necessary for glycol-based heat transfer fluidsnot only to use corrosion inhibitors that are effective at protectingcommon metals from corrosion, but also to contain additional addi-tives to buffer or neutralize the acidic glycol degradation productsthat form during use.

49、 Corrosion inhibitors form a surface barrier thatprotects metal from attack, but their effectiveness is highly depen-dent on solution pH. Failure to compensate for glycol degradationTable 3 Physical Properties of Ethylene Glycol and Propylene GlycolPropertyEthylene GlycolPropylene GlycolMolecular weight 62.07 76.10Ratio of mass to water at 68/68F 1.1155 1.0381Density at 68Flb/ft369.50 64.68lb/gal 9.29 8.65Boiling point, Fat 760 mm Hg 388 369at 50 mm Hg 253 241at 10 mm Hg 192 185Vapor pressure at 68F, mm Hg 0.05 0.07Freezing point