Indian Journal of Chemical TechnologyVol. 4, September 1997, pp. 2U-216

Thermal and physical properties of some organic liquids: Theircondensation patterns on teflon coated mild steel substrates

R Chandrasekharan& T Venkatram

Departmentof Chemical Engineering,Indian Instituteof Technology, Madras 600 036, India

Received24 September 1996;accepted20 December 1996

An analysis of the thermal and physical properties of organic vapours and steam condensing on teftoncoated mild steel (m.s.) substrate in different patterns has been carried out. Photographs of the pattern ofvapours (other than filmwise) have been presented. The properties of thirty three vapours experimented fortheir pattern of condensation are tabulated. Eventhough for steam, the coefficients are higher than for

I

organic vapours, for both filmwise and dropwise condensation (d.c.), due to its advantageous physicalproperties and the extent of augmentation in d.c. is also higher, it was observed from the experiments that

there is advantageous enhancement for organic vapours also inspite of their physical properties being atdisadvantageous levels and their characteristic changes with other parameters like temperature. Thesecharacteristics wherever possible are discussed.

It is well known that d.c patterns once induced andstably maintained enhance the capacity of thecondenser; also the high vapour side coefficientsobtained result in augmentation of overallcoefficients which inturn reduce the size of thecondenser for a given heat duty. In the chemicalindustries, amongst the heat exchangers employed,about sixty percent consist of vapour on one sideeither as heating medium or used for condensingand recovery of valuable vapours in the form ofcondensate. Even a little progress achieved in thestable maintenance of d.c. results in substantialeconomy in the capital cost of condensers.

After decades of continuous investigations somesuccess has been met with, in the maintenanae ofstable dropwise condensation (d.c.) pattern of steamunder some limited and controlled conditions. The

- 1

surfaces developed were teflon coated ,2 d3chromplated and unpromote to quote some. In

the beginning promoters like waxes and fats weretried and were found to be short living. With suchpromoters, if organic vapours are condensed theywill simply be washed off with the dissolving actionof these vapours especially at their saturation

. 4temperatures. Topper and ~aer have conductedqualitative experiments with a few organic vapourson teflon coated brass tubes and reported that some

of them were condensing in d.c. pattern, while someshowed filmwise condensation. It was found4 thatsurface tension of the organic liquids has a bearingon the pattern of condensation. In this caseadvantage was taken of the temperature resistanceupto -250°C and chemical inertness of the tefloncoating. From the earlier investigations, it wasidentified that steel and aluminium were not givingd.c. of steam when coated Withpromoters, unlike onother metals. This was identified to be due to the

oxidising tendency of these metals.In the present study, an attempt has been made to

investigate into the condensing pattern of organicvapours on teflon coated mild steel (m.s.) plates.This system was chosen as m.s. is an economicalmaterial of construction and when teflon was

registered on it, besides preventing oxidation of thesurface it may condense organic vapours in d.c.patterns resulting in the development of highperformance surfaces Withthese systems. A total of33 vapours were tested qualitatively for the patternsand out of them 13 vapours have shown somepositive behaviour.

Experimental ProcedureThe experimental facility employed for

identifying the condensation patterns of each of the

212 INDIAN J. CHEM. TECHNOL., SEPTEMBER 1QQ7

Buty I Acrtatr

WQtrr

Nitro Brnzrnr

Carbon -Disulphidr

Anlllnr

Gly c rrinr - Welt.,

Fig.l-Qualitative study - (pattern of condensatio~ :-+' dropwise)

33 vapours is a teflon coated, air cooled m.s. platehaving the dimensions of 100 mm height x 100 mmbreadthx10 rom thickness. The teflon coatingthickness is 22.5 microns. Other details of this testfacility and its operation are described elsewhere5.Analar reagents of organic liquids and distilledwater were used for generating vapours and steam,respectively, for condensation. The photographs ofthe patterns of condensation showing dropwisepattern are shown in Figs 1 and 2; and non filmwiseand mixed pattern are shown in Fig.3, respectively.The vapours showing d.c. pattern are tested further

. 6for endurance and data acquired for thermalcoefficients and enhancement in their performanceover f.c.

Results and Discussion

The pattern of condensation of each vapour, itsthermal and physical properties are detailed in Table

1. It can be inferred that steam has advantageouslyhigh latent heat, specific heat and thermalconductivity over organic vapours leading to a moreelevated position when d.c. is induced. According toTopper and Baer4, with their limited experiments ona few vapours, liquids with more than 18 dyne/cmonly can condense in d.c. pattern. In the presentexperiments some anomalous behaviour was noticedwith some vapours like cyclohexanol showing f.c.pattern. Besides, if the system is subjected topressure resulting in elevation of boiling point, thelatent heat, surface tension and viscosity can beexpected to change. Properties like surface tension,specific heat, viscosity and thermal conductivity ofany fluid change with temperature. For water theyseem to change advantageously, whereas for organicliquids it is otherwise from the heat transfer point ofview. In spite of these types of disadvantages andthe high thermal resistance offered by the tefloncoating, inducing d.c. was reported6 to have a

CHANDRASEKHARAN & VENKA TRAM: PROPERTIES OF ORGANIC LIQUIDS 213

WQt~r CQrbon-Disulphld~TS=100'51 T5 z 45,34 .

",.thy' Alcohol Glyc.rln.-Wal.rT5-62·75 . T5=102'5

Fig.2--Pattem of condensation of vapour chosen forquantitativestudy

positive effect in augmenting the overall coefficientby 13-44%over f.c.

Conclusions

1 Eventhough teflon coating was found to inducd.c. with some organic vapours, it is noautomatic for all vapours.

2 The variation of thermal and physical propertiewith pressure and temperature has to be know

for a better understanding of the enhancement ithermal performance with different vapoursAlso, their level of augmentation besidedepending on their thermo physical properties iprobably a function of other properties likpolarity of the molecules.

3 Surface tension criteria of inducing d.c. pattern 0any vapour is to be confirmed only wit

N-~Table I-Condensation patterns and physical properties of different organic vapours

S.No. Source of vapour

Pattern ofMolecularBoilingLatent AT 293K (20°e)condensation

wt., Mpoint,heat,SpecificSurfaceSpecificViscositY-1lThermalPrandtl

=

(760 mmAfgkJ/ggravity,tension,heat,centi-poise conductivity no.Npr

Hg), TB,K(293/crx 103,Cp k,W/rn-k

277)K

N/mkJ/Kg-KI

Aniline [C6HsNH2]· Dropwise93.13457.40476.901.02242.902.174.4290.17754.14732

Benzaldehyde [C6Hs,CHO] Dropwise106.13452.00362.181.04640.041.791.393

Butylaetate Dropwise116.16398.00309.000.88223.302.220.7320.137

[CH3COO(CH2)3CH3] Z4 Carbondisulphide [CS2] Dropwise76."139319.25352.131.22533.070.990.3630.144-0- (298)*(285)*~

-5Decahyd~onaphthalene [CIOH1S]Dropwise138.25458.30-0.872-1.65---

6 Ethylene glycol Dropwise62.07470.00800.14U1547.702.3919.900.261182.21~

(")[HO.CH2·CH2·OH]::I:

7Glycerene Dropwise92.09563.00198.841.26063.402.35149.000.29411869.13

tr:l

....•.[CHpH.CHOH.CH2OH] (323/277)·

?:

~8Glycerene-water [33.6%-66.4%] Dropwise-375.501567.911.0820270.84**4.10500.664**57.50**35.72tr:l

(")9Nitrobenzene [C6Hs.N02] Dropwise123.11483.90331.111.20543.901.422.030.16417.66::I:

Z(291/277)·0

10Water [H2O] Dropwise18.016373.002259.101.00072.444.221.0020.6786.225J''''

(277/277)*

entr:l11

Methyl alcohol [CH3OH] Mixed32.043337.701100.340.792422.612.580.5970.2027.5093"'l:l-l:::;: 12n-Propanol [CH3CH2.CH2.OH] Mixed60.09370.80688.300.80423.782.452.2560.156(285)* 40.2188tr:l-13Toluene [C6Hs.CH3] Non-filmwise92.13383.80363.430.86627.551.800.590.1357.8673?:

tl:l-

tr:l~ 14Acetone [CH3CO.CH3] Filmwise58.08329.50521.280.79221.162.170.33110.1903.771:;tl15

iso-Amylacetate Filmwise130.18415.00130.550.87624.701921.3750.148-\0~(288/277)·

\0oil

[CH 3COO. CH2·CH2.CH( CH 3)2] (303)*-...j

16iso-Amyl alcohol Filmwise88.15405.00441.310.81323.802.874.0040.14280.9771

[(CH3h/CH.CH2·CH2·OH](288/277)·

17n-Amyl alcohol Filmwise88.15410.90504.950.8170-2.983.310.16260.8343

[CH3(CH2h·CH2·0H] 18Benzene [C6H6] Filmwise78.11353.10433.360.8728.891.700.64680.1586.9471

19iso-butanol Filmwise74.12381.10578.850.80522.802.395.5820.142 (285)

[(CH3h·CH.CH2·0H]

(291/277)*20

Sec. Butyl alcohol Filmwise74.12372.5561.640.80823.52.364.210.15364.7073

[CH3·CH2·CH(OH).CH3]

(283)·

"'

~t

II ..•".

Table l-Condensation patterns and'physical properties ofdifIerent organic vapours-Contd.

S.No.

Source of vapour Pattern ofMolecular. BoilingLatent AT 293K (20DC)condensation

wt.,Mpoint,heat,SpecificSurfaceSpecificViscosity-)!Thcm1a1Prandtl

(760 mm

AfgkJ/ggravity,tension,heat,centi-poise concbEtivity no.N ••.gHg), TB,K

(2931ax103,Cp k,Wfm-k>277)K

N/m~JIK.&~!C ~21

Catbontetrachloride [CCI4] Filmwise153.84349.80194.911.59526.950.84(323)*0.9690.103-~22

Chloroform [CHCL3] Filmwise119.33334.20247.031.48927.140.980.580.1035.520en

23Cyclohexane Filmwise84.16353.70357.700.77925.501.840.66--

~

[CH2 «CH2· CH2)2>CH2] ~24

Cyclohexanol Filmwise100.16434.10453.030.962134.23±0.31.756.80--[CH2«CH2·CH2h>CHOH] 25

n-Decoic Acid Filmwise172.27--0.890-----SIP

<[CH3·(CH2)g·COOH]~26

Ethyl Acetate Filmwise88.10350.1427.490.90123.901.960.4500.1525.7857

[CH3·COO.C2Hs]~

27Ethylether [(C2Hs)20] Filmwise74.12307.40351.290.70817.302.290.23320.132-

(303)*28Ii-Heptane [C7HI6] Filmwise100.20371.40320.310.684-1.530.4090.141-"'1:1

(273)·~

29

Methyl-isobutyl ketone Filmwise100.16389.30795.950.8004-2.080:60--trl[CH3·CO.CH2·CH(CH3)2]

d30

Paraldehyde [C6HI203] Filmwise132.162397.00104.760.9943-1.830.25570.1712.7265trlen31

n-pentane Filmwise72.15309.30357.570.6315.482.140.2400.125-~[CH3·CH2·CH2·CH2·CH3]

(291/277)·(278)·(272)

~32

iso-propyl alcohol [(CH3h.CHOH] Filmwise 60.09355.50667.410.78921.702.682.307020.14143.98

33p-xylene [C6HiCH3)2] Filmwise106.16411.15339.980.8628.371.660.6480.143-~

(303)·(5·Temperature given in paranthesis for physical properties not available at 293 K (20°)

t"'"··Values computed by addition Source ~i-International critical tables, McGraw-Hili Book Co., (1930)

-ii-Perry H and Chilton H., Chemical Engineers Hand Book', McGraw Hill Book Co., N.Y., (1975)

0en

iii-Lange N A, 'Hand Book of Chemistry', Tenth Edition, McGraw Hill Book Co., N.Y. (1967) iv-Hand Book of Chemistry and Physics, (1960-61)v-McAdams W H, 'Heat Transmission', McGraw-Hili Book Co, (1954)vi-Fraas A P and Ozisik M N, 'Heat Exchanger Design', John Wiley and Sons, Inc., (1964)

N

-V\

216 INDIAN 1. CHEM. TECHNOL., SEPTEMBER 1997

M~thylalcohol

Empty frame

n- Propanol

Tolue ne

Fig.3---Qualitative study - (pattern of condensation (.142> non­filmwise and mixed)"

experimentation.

4 Inspite of possessing thermally disadvantageou

properties for organic vapours, inducing of d.cseems to be advantageous in their performance.

AcknowledgementThe authors wish to thank Council of Scientific

and Industrial Research, New Delhi for financialassistance during the tenure of this work.

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(1972) 205.3 Venkatram T & Kuloor N R, Indian J Technol, 2(3) (1964)

73.

4 Topper L & Baer E, J Coll Sci, 10 (1955) 225.5 Chandrasekharan R & Venkatram T, Proc Eighth Natl Heat

Mass Transfer ConfWaltair, HMT-E21-85 (1985) 473.6 Chandrasekharan R & Venkatram T, Indian J Technol,

26(1)(1988)41.