THERMAL MANAGEMENT SYSTEM

Abstract

The present invention provides a thermal management system comprising a housing having an interior space; a heat-generating component disposed within the interior space; a heat exchanger; and a working fluid liquid disposed within the interior space wherein the heat-generating component is in contact with the working fluid. The working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant and anti-static additives. The system is constructed wherein a constant cyclical flow of working fluid is maintained across the heat-generating components, on to the heat exchanger and then back to the heat-generating component.

The present invention provides a method of thermal management of a heat-generating component comprising partially immersing a heat-generating component in a working fluid and transferring the heat from the heat-generating component using the working fluid in a constant cyclical flow of working fluid across the heat-generating components, on to a heat exchanger and then back to the heat-generating component.

Claims

1. A thermal management system comprising: a housing having an interior space; a heat-generating component disposed within the interior space; a heat exchanger; and a working fluid liquid disposed within the interior space such that the heat-generating component is in contact with the working fluid; wherein the working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant additive and an anti-static additive, wherein the thermal management system is constructed such that a constant cyclical flow of working fluid is maintained across the one or more heat-generating components, on to the heat exchanger and then back to the heat-generating component.

2. The thermal management system of claim 1, wherein the antioxidant additive comprises a hindered phenol.

3. The thermal management system of claim 2, wherein the antioxidant additive is selected from the group consisting of 2,6-di-tert-butylphenol, di tert-butylated hydroxytoluene, methylene-4,4′ bis-(2.6-tert-butylphenol), 2,2′-methylene bis-(4,6 di-tert-butylphenol), 1,6-hexamethylene-bis-(3,5 di tert-butyl-hydroxyhydrocinnamate), ((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)thio) acetic acid, C10-C14isoalkyl esters, 3,5 di tert-butyl-4-hydroxyhydrocinnamic acid, C7-C9alkyl esters, tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane, thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate, octadecyl 3,5 di-tert-butyl-4-hydroxyhydrocinnamate, 2,5-di-tert-butylhydroquinone and mixtures thereof.

4. The thermal management system of claim 1, wherein the antistatic additive is selected from the group consisting of di C8-C10, branched, C9 rich, alkylnaphthalene sulphonic acid, alkylated benzotriazoles and benzotriazole.

5. The thermal management system of claim 1, wherein the thermal management system further comprises a pump, wherein the pump is configured to move the working fluid to and from the heat exchanger.

6. The thermal management system of claim 1, wherein the heat-generating component comprises a server.

7. The thermal management system of claim 1, wherein the heat-generating component is a battery.

8. The thermal management system of claim 1, wherein the heat-generating component is one or more of a battery, an e-motor and an inverter within an electric vehicle.

9. A method of thermal management of a heat-generating component comprising the steps of at least partially immersing a heat-generating component in a working fluid; and transferring the heat from the heat-generating component using the working fluid in a constant cyclical flow of working fluid across the one or more heat-generating components, on to a heat exchanger and then back to the heat-generating component, wherein the working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant additive; and an antistatic additive.

10. The method of claim 9, wherein said method comprises the steps of pumping the working fluid to a heat exchanger; transferring heat from the working fluid; and returning said working fluid to the heat-generating component.

11. The method of claim 9, wherein the antioxidant additive is a hindered phenol.

12. The method of claim 13, wherein the antioxidant additive is 2,6-di-tert-butyl-4-methylphenol.

13. The method of claim 9 wherein the antistatic additive is selected from the group consisting of di C8-C10, branched, C9 rich, alkylnaphthalene sulphonic acid, alkylated benzotriazoles, benzotriazole and mixtures thereof.

14. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates a simplified circuit for a thermal management system of the present invention.

[0016] FIG. 2 is an illustration of a battery comprising a number of cells within a thermal management system according to the invention.

SUMMARY OF THE INVENTION

[0017] The present invention provides a thermal management system comprising: [0018] a housing having an interior space; [0019] a heat-generating component disposed within the interior space; [0020] a heat exchanger; and [0021] a working fluid liquid disposed within the interior space such that the heat-generating component is in contact with the working fluid;
wherein the working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant additive and an anti-static additive, wherein the thermal management system is constructed such that a constant cyclical flow of working fluid is maintained across the one or more heat-generating components, on to the heat exchanger and then back to the heat-generating component.

[0022] The present invention also provides a method of thermal management of a heat-generating component comprising the steps of at least partially immersing a heat-generating component in a working fluid; and transferring the heat from the heat-generating component using the working fluid in a constant cyclical flow of working fluid across the one or more heat-generating components, on to a heat exchanger and then back to the heat-generating component, wherein the working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant additive; and an antistatic additive.

[0023] The present invention also provides for the use of a Fischer-Tropsch derived base fluid in a working fluid in contact with a heat-generating component in a thermal management system to improve anti-aging properties of the working fluid, wherein the working fluid also comprises an antioxidant additive and an anti-static additive.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present inventors have surprisingly found that a highly efficient system and method for immersion thermal management of a heat-generating component may be provided wherein a heat-generating component is in direct contact with a working fluid and wherein said working fluid comprises a Fischer-Tropsch derived base fluid; an antioxidant additive; and an antistatic additive.

[0025] The heat-generating component is preferably an electrical element. Typical electrical elements that may benefit from the system and method described herein include computer servers, batteries, inverters, electric motors and fuel cells, or any combination of these.

[0026] One or more heat-generating components may be cooled within the thermal management system of the invention.

[0027] The thermal management system of the invention comprises a housing having an interior space; a heat-generating component disposed within the interior space; and a working fluid liquid disposed within the interior space such that the heat-generating component is in direct contact with the working fluid. The heat-generating component may be partially immersed, and up to fully immersed, in the working fluid.

[0028] The thermal management system is constructed such that a constant cyclical flow of working fluid is maintained across the one or more heat-generating components, on to a heat exchanger and then back to the heat-generating component.

[0029] The heat exchanger may be disposed within or external to the housing.

[0030] The thermal management system may comprise a liquid circuit with a pump and a heat exchanger. In this embodiment, the pump operates to move the working fluid from the heat-generating component to and from the heat exchanger.

[0031] Heat is transferred from the heat-generating component to the working fluid. The working fluid may then be pumped away from the heat-generating component to a heat exchanger. Heat may then be transferred from the working component via the heat exchanger. The working fluid may then be returned to the heat-generating component.

[0032] As well as functioning to remove heat from the heat-generating component disposed therein, the thermal management system may also be suitable to provide heat to the heat-generating component at certain times during the functioning of said component, e.g. at start-up or during running in cold environments. In this embodiment of the invention a source of heating will be included in the thermal management system. Such a source of heat may comprise an internal heat source or an external heat source. A control mechanism will also be included in the thermal management system to allow switching between cooling and heating embodiments of the system.

[0033] A suitable internal heat source may involve a battery with a load to form a heat-generating circuit. Suitable external heat sources include heat pumps, phase change materials capable of releasing heat upon the phase change, electric heaters and heaters burning ethanol, bioethanol or other fuels.

[0034] The working fluid comprises a Fischer-Tropsch derived base fluid and an antioxidant additive. Preferably, the working fluid also comprises an antistatic additive.

[0035] Fischer-Tropsch derived base fluids are known in the art. By the term “Fischer-Tropsch derived” is meant that a base fluid is, or is derived from, a synthesis product of a Fischer-Tropsch process.

[0036] Fischer-Tropsch derived base fluids are often classified by the starting material in the Fischer-Tropsch process, i.e. ‘X-to-liquids’ or ‘XTL’, with X standing for said starting material. Biomass-to-liquid (BTL), coal to liquids (CTL), gas-to-liquid (GTL) and power-to-liquid (PTL) processes are some examples of Fischer-Tropsch processes producing base fluids. Preferably, the Fischer-Tropsch derived base fluid is a GTL (Gas-To-Liquids) base fluid.

[0037] Suitable Fischer-Tropsch derived base fluids including oils that may be conveniently used in the Fischer-Tropsch derived working fluid are those as for example disclosed in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO 0157166.

[0038] The Fischer-Tropsch derived base fluids for use in the invention preferably have kinematic viscosities at 100° C. of at most 4 mm.sup.2/s.

[0039] A particularly preferred Fischer-Tropsch derived base fluid for use in the working fluid herein is a Fischer-Tropsch derived base oil with a kinematic viscosity at 100° C. in the range of from 2 to 4 mm.sup.2/s, for example GTL 3 (having a kinematic viscosity at 100° C. of approximately 3 mm.sup.2/s).

[0040] Another particularly preferred Fischer-Tropsch derived base fluid for use in the working fluid herein is a Fischer-Tropsch derived base fluid produced from a gas oil stream, preferably a dewaxed gas oil stream, from a GTL process, wherein said fluid has a kinematic viscosity at 40° C. in the range of from 2.0 to 11 mm.sup.2/second. Preferably said Fischer-Tropsch derived base fluid produced from a gas oil stream has a kinematic viscosity at 40° C. of at least 2.1 mm.sup.2/second, more preferably at least 2.2 mm.sup.2/second. Also preferably, said fluid has a kinematic viscosity at 40° C. of at most 10.0 mm.sup.2/second, more preferably at most 7.0 mm.sup.2/second, most preferably at most 6.0 mm.sup.2/second.

[0041] In one embodiment of the invention the working fluid comprises a mixture of more than one Fischer-Tropsch derived base fluid. For example, the working fluid may comprise both a Fischer-Tropsch derived base oil with a kinematic viscosity at 100° C. in the range of from 2 to 4 mm.sup.2/s and a Fischer-Tropsch derived base fluid produced from a gas oil stream.

[0042] The total amount of Fischer-Tropsch derived base fluids incorporated in the working fluid is preferably in the range of from 60.0 to 99.9 wt. %.

[0043] Other components within the working fluid may include one or more additional base oils including mineral oils and synthetic oils. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing. Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), alkyl benzenes, alkyl naphthalenes and dewaxed waxy isomerates.

[0044] In one preferred embodiment, the working fluid comprises one or more additional base oils selected from alkyl benzenes, alkyl naphthalenes and mixtures thereof. If present, the one or more additional base oils selected from alkyl benzenes, alkyl naphthalenes and mixtures thereof are present in no more than 35 wt % with respect to the total weight of the working fluid. Preferably the one or more additional base oils selected from alkyl benzenes, alkyl naphthalenes and mixtures thereof are present in an amount in the range of from 1 to 30 wt % with respect to the total weight of the working fluid.

[0045] The working fluid preferably has a pour point of less than or equal to −40° C., more preferably less than or equal to −50° C., measured according to ISO 3016.

[0046] The working fluid also preferably has a flash point of at least 100° C., more preferably at least 110° C., most preferably at least 120° C., and preferably at most 240° C., according to ASTM D93.

[0047] The working fluid preferably has a kinematic viscosity at 40° C. of at least 2.0 mm.sup.2/s, more preferably at least 2.1 mm.sup.2/s, most preferably at least 2.2 mm.sup.2/s, measured according to ISO 3104. The working fluid preferably has a kinematic viscosity at 40° C. of at most 22.0 mm.sup.2/s, more preferably at most 11.0 mm.sup.2/s, most preferably at most 10.0 mm.sup.2/s.

[0048] The thermal conductivity of the working fluid at 20° C. is preferably at least 0.135 w/mK, measured according to ASTM D7896.

[0049] The specific heat capacity of the working fluid at 20° C., according to ASTM D 1269, is preferably at least 1.9 kJ/kg*K, more preferably at least 2.0 kJ/kg*K.

[0050] The antioxidant additive is suitably a hindered phenolic antioxidant additive, sterically hindered monohydric, dihydric and trihydric phenols, sterically hindered dinuclear, trinuclear and polynuclear phenols.

[0051] Sterically hindered phenolic antioxidants of particular interest may be selected from the group consisting of 2,6-di-tert-butylphenol (available under the trade designation “IRGANOX™ L 140” from BASF), di tert-butylated hydroxytoluene (“BHT”), methylene-4,4′-bis-(2.6-tert-butylphenol), 2,2′-methylene bis-(4,6-di-tert-butylphenol), 1,6-hexamethylene-bis-(3,5-di-tert-butyl-hydroxyhydrocinnamate) (available under the trade designation “IRGANOX™ L109” from BASF), ((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)thio) acetic acid, C.sub.10-C.sub.14isoalkyl esters (available under the trade designation “IRGANOX™ L118” from BASF), 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C.sub.7-C.sub.9alkyl esters (available under the trade designation “IRGANOX™ L135” from BASF,) tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane (available under the trade designation “IRGANOX™ 1010” from BASF), thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate (available under the trade designation “IRGANOX™ 1035” from BASF), octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (available under the trade designation “IRGANOX™ 1076” from BASF), 2,5-di-tert-butylhydroquinone and mixtures thereof.

[0052] Particularly preferred antioxidants for use herein are di-tert-butylated hydroxytoluene (“BHT”) and C.sub.7 to C.sub.9 alkyl esters of 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, (available under the trade designation “IRGANOX™ L135” from BASF).

[0053] In one embodiment of the invention, more than one antioxidant additive may be present in the working fluid.

[0054] Optionally, an additional amine antioxidant, for example an alkylated or styrenated diphenylamine, may be added to the working fluid.

[0055] Examples of amine antioxidants are aromatic amine anti-oxidants for example N,N′-Di-isopropyl-p-phenylenediamine, N,N′-di-sec-butyl-p-phenylenediamine, N,N′-bis(1,4-dimethyl-pentyl)-p-phenylenediamine, N,N′-bis(1-ethyl-3-methyl-pentyl)-p-phenylene-diamine, N,N′-bis(1-methyl-heptyl)-p-phenylenediamine, N,N′-dicyclohexyl-p-phenylene-diamine, N,N′-diphenyl-p-phenylenediamine, N,N′-di(naphthyl-2-)-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine, N′-cyclohexyl-N′-phenyl-p-phenylenediamine, 4-(p-toluene-sulfoamido)diphenylamine, N,N′-dimethyl-N,N′-di-sec-butyl-p-phenylenediamine, diphenylamine, N-allyldiphenylamine, 4-isopropoxydiphenylamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine, e.g. p,p′-di-tert-octyldiphenylamine, 4-n-butylaminophenol, 4-butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol, 4-octadecanoylaminophenol, di(4-methoxyphenyl)amine, 2,6-di-tert-butyl-4-dimethylamino-methylphenol, 2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, N,N,N′,N′-tetramethyl-4,4′-diaminodiphenylmethane, 1,2-di(phenylamino)ethane, 1,2-di[(2-methylphenyl)amino]ethane, 1,3-di(phenylamino)-propane, (o-tolyl)biguanide, di[4-(1′,3′-dimethyl-butyl)phenyl]amine, alkylated phenyl alpha naphthylamines, e.g. tert-octylated N-phenyl-1-naphthylamine, mixture of mono- and dialkylated tert-butyl-/tert-octyldiphenylamines, 2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine, phenothiazine, N-allylphenothiazine, tert-octylated phenothiazine, 3,7-di-tert-octylphenothiazine, Also possible amine antioxidants are those according to formula VIII and IX of EP1054052, which compounds are also described in U.S. Pat. No. 4,824,601.

[0056] The total amount of the one or more antioxidant additives present in the working fluid is preferably at least 0.1 wt %, more preferably at least 0.15 wt % and preferably at most 3.0 wt %, more preferably at most 2.0 wt % with respect to the total weight of the working fluid.

[0057] The antistatic additive for use herein is preferably selected from those containing alkyl substituted naphthalene sulfonic acids, benzotriazole and substituted benzotriazoles.

[0058] Substituted benzotriazole compounds for use herein may be represented by the formula (I).

##STR00001##

wherein R.sup.4 may be hydrogen or a group represented by the formula (II)

##STR00002##

or by the formula (III)

##STR00003##

wherein:
c is 0, 1, 2 or 3;

[0059] R.sup.1 and R.sup.2 are hydrogen or the same or different straight or branched alkyl groups of 1-18 carbon atoms, preferably a branched alkyl group of 1-12 carbon atoms; R.sup.3 is a straight or branched C.sub.1-4 alkyl group, preferably R.sup.3 is methyl or ethyl and C is 1 or 2; R.sup.5 is a methylene or ethylene group; R.sup.6 and R.sup.7 are the same or different alkyl groups of 3-15 carbon atoms, preferably of 4-9 carbon atoms.

[0060] Preferred compounds are 1-[bis(2-ethylhexyl)-aminomethyl]benzotriazole, methylbenzotriazole, dimethylbenzotriazole, ethylbenzotriazole, ethylmethylbenzotriazole, diethylbenzotriazole and mixtures thereof. Other preferred compounds include (N-Bis(2-ethylhexyl)-aminomethyl-tolutriazole, non-substituted benzotriazole, and 5-methyl-1H-benzotriazole.

[0061] Preferred alkyl substituted naphthalene sulfonic acids include di C8-C10, branched, C9 rich, alkylnaphthalene sulphonic acid, such as those commercially available as “Stadis 450” from Innospec.

[0062] The content of the above antistatic additive in the working fluid herein is preferably above 0.5 mg/kg and more preferably above 1 mg/kg with respect to the total weight of the working fluid. A practical upper limit may vary depending on the specific application of the lubricating composition. This concentration may be up to 3 wt. %, preferably however in the range of from 1 mg/kg to 1 wt. % with respect to the total weight of the working fluid. However, such compounds may be advantageously used at concentrations below 1000 mg/kg and more preferably below 300 mg/kg with respect to the total weight of the working fluid.

[0063] It has also been surprisingly found that the use of a Fischer-Tropsch derived base fluid in a working fluid also comprising such antioxidant and antistatic additives in contact with a heat-generating component in a thermal management system provides said working fluid with improved anti-aging properties. By ‘anti-aging properties’ herein, is meant at least one property selected from electrical conductivity at 24 and/or 90° C. (measured according to IEC 60247), appearance and sludge formation (measured according to visual rating), relative permittivity (measured according to IEC 60247) and discoloration (measured according to ISO 2049) is maintained at a suitable level over time. Preferably, the use of a Fischer-Tropsch derived base fluid in a working fluid also comprising antioxidant and antistatic additives in contact with a heat-generating component in a thermal management system provides said working fluid with improved conductivity levels over time.

DETAILED DESCRIPTION OF THE DRAWINGS

[0064] FIG. 1 shows a suitable liquid circuit for the thermal management system of the present invention. In FIG. 1, a heat-generating component (1) is disposed within a housing (2). Working fluid flows (3) through the interior space of the housing (1) and then through connecting pipework (4) to one or more heat exchanger (5). In this embodiment, said flow is maintained by a pump (6).

[0065] FIG. 2 is an illustration of a battery comprising a number of cells within a thermal management system according to the invention. In this embodiment, a number of pouch cells (7) are disposed within a housing (not shown). The flow of the working fluid across and between the pouch cells (7) is indicated by the arrows (8).

[0066] The present invention will now further be illustrated by the following, non-limiting, examples.

Examples

[0067] Six blends of working fluid formulations were produced according to the components listed in Table 2. The base oils used were an API Group I base oil commercially available as HVI60 from Shell and a Fischer-Tropsch derived base oil commercially available as GTL 3 from Shell. The base oil characteristics are indicated in Table 1.

TABLE-US-00001 TABLE 1 Test API Group I GTL3 Base method Base oil oil Colour ISO 2049 0.4 <0.2 Kinematic Viscosity ISO 3104 4.5 2.7 @ 100° C. Kinematic Viscosity ISO 3104 23.4 9.8 @ 40° C. Pour point ISO 3016 −15 −42 Flash point ISO 2592 216 200

[0068] The antioxidant additive used in the Examples was di-tert-butylated hydroxytoluene (BHT) and the anti-static additive was Stadis 450, ex. Innospec. Stadis 450 is indicated to contain 10-25% di C8-C10, branched, C9 rich, alkylnaphthalene sulphonic acid.

[0069] The working fluids (900 mL per fluid) were each placed in 1000 mL beakers. A copper and steel coil was also placed in each beaker. Such coils were of the type used in the ASTM D493 test method for oxidation stability, but of half the usual size.

[0070] To prepare the copper and steel wire coils, 112 mm of low metalloid steel wire with a diameter of 1.59 mm and an electrolytic copper wire, length also 112 mm but with a diameter of 1.63 mm were placed beside each other. The wires were then twisted to a coil which was then used for the test.

[0071] The beakers containing the oil samples and coils were then kept in an oven (with air ventilation) at 120° C. The beakers were uncovered.

[0072] At each of the times indicated in Table 2 below, an oil sample of 125 mL was taken and tested. Electrical conductivity was tested according to IEC 60247. The appearance was tested by a visual assessment. The colour of the sample was tested according to ISO 2049

[0073] These Examples, representative of using the working fluids in a thermal management system, clearly demonstrate that working fluids comprising a Fischer-Tropsch derived base fluid (blends 1 to 3) have and maintain over time better conductivity and appearance characteristics, when compared with working fluids comprising an API Group I base oil (blends 4 to 6). These characteristics are further improved by the addition of an antioxidant additive (blend 2). Blend 2 demonstrates maintenance of electrical conductivity at low levels as well as maintenance of good appearance and colour characteristics. The further addition of an anti-static additive to a working fluid comprising a Fischer-Tropsch derived base fluid and an antioxidant additive maintains the electrical conductivity of said fluid over time at an excellent level that prevents static build up and short circuits. These improvements are not seen for the equivalent blends in working fluids comprising an API Group I base oil (blends 4 and 5).

TABLE-US-00002 TABLE 2 Blend 1 Blend 2 Blend 3 Blend 4 Blend 5 Blend 6 Gp 1 Base oil — — — 99.7999 99.8 100 GTL3 Base oil 99.7999 99.8 100 — — — Antioxidant 0.2 0.2 — 0.2 0.2 — Antistatic 0.00045 — — 0.00045 — — Electrical Conductivity (pS/m) @ 90° C. fresh oil 35 0.04 0.04 140 14.4 8.7 after 1 week 0.7 0.8 0.9 1358 425 826 after 2 weeks 0.2 0.7 2.5 1358 1190 1752 after 3 weeks 33 0.4 0.5 3738 3502 3734 after 4 weeks 63 0.8 151 5345 4967 5531 Appearance fresh oil clear, free of clear, free of clear, free of clear, free of clear, free of clear, free of deposit deposit deposit deposit deposit deposit after 1 week clear, free of clear, free of clear, free of clear, free of clear, free of clear, free of deposit deposit deposit deposit deposit deposit after 2 weeks clear, free of clear, free of clear, free of dark, deposit dark, free of dark, free of deposit deposit deposit deposit deposit after 3 weeks clear, slight deposit clear, slight deposit clear, slight deposit dark, deposit dark, deposit dark, deposit after 4 weeks hazy, some deposit hazy, some deposit hazy, some deposit hazy, sludge hazy, sludge hazy, sludge Colour fresh oil <0.2 <0.2 <0.2 0.4 0.4 0.4 after 1 week <0.2 <0.2 <0.2 6.7 6.2 5.8 after 2 weeks <0.2 <0.2 <0.2 >8 >8 8 after 3 weeks 0.2 0.4 0.6 >8 >8 >8 after 4 weeks 1.2 1.3 1.8 >8 >8 >8