1. A CENTURY OF TRANSPORT A Personal Tour by Stuart W. Churchill
DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING
THE UNIVERSITY OF PENNSYLVANIA

2. OBJECTIVES
TO REVIEW EVOLUTION OF THE SKILLS AND RESOURCES OF CHEMICAL ENGINEERS IN DEALING WITH TRANSPORT
TO DESCRIBE NOT ONLY THE “STATE OF THE ART”, BUT ALSO TO TELL THE STORY OF HOW WE GOT THERE
PREFERENCE IS BEING GIVEN TO THOSE PARTICULAR ASPECTS OF TRANSPORT IN WHICH I HAVE BEEN INVOLVED

3. WHAT IS TRANSPORT?
THE COMBINED TREATMENT OF FLUID MECHANICS, HEAT TRANSFER, AND MASS TRANSFER AS TRANSPORT RATHER THAN AS SEPARATE TOPICS BECAME NOT ONLY FASHIONABLE BUT ALSO THE GENERAL PRACTICE IN EDUCATION WITH THE PUBLICATION IN 1960 OF THE MOST INFLUENTIAL BOOK IN THE HISTORY OF CHEMICAL ENGINEERING, NAMELY TRANSPORT PHENOMENA BY BOB BIRD, WARREN STEWART, AND ED LIGHTFOOT.
ALTHOUGH OUR UNDERSTANDING OF TRANSPORT HAS EVOLVED OVER THE CENTURY AND THE APPLICATIONS HAVE EXPANDED, THIS SUBJECT NOW HAS A DECREASED ROLE IN EDUCATION AND PRACTICE BECAUSE OF COMPETITION FROM NEW TOPICS SUCH AS BIOTECHNOLOGY AND NANOTECHNOLOGY. THESE LATTER TOPICS INVOLVE TRANSPORT BUT MOSTLY AT SUCH A SMALLER SCALE THAT WHAT I WILL BE DESCRIBING IS APPLICABLE, IF AT ALL, ONLY IN A QUALITATIVE SENSE OR AS A GUIDE TO THE DEVELOPMENT OF EQUIVALENT RELATIONSHIPS.

4. CONTINUITY AND CONSERVATION
THE EQUATIONS OF CONSERVATION - THE NAVIER STOKES EQUATIONS AND THEIR COUNTERPARTS FOR ENERGY AND SPECIES - ARE THE STARTING POINT OF MOST THEORETICAL WORK ON TRANSPORT. I WILL NOT TRACE THE DEVELOPMENT OF THESE EQUATIONS NOR EXAMINE THEIR VALIDITY EXCEPT TO CITE ONE CONTRARY OPINION FROM A RENOWNED PHYSICIST.
GEORGE E. UHLENBECK, ONE OF MY TEACHERS AND MENTORS, FRUSTRATED BY HIS FAILURE TO CONFIRM OR DISPROVE THE NAVIER-STOKES EQUATIONS BY REFERENCE TO STATISTICAL MECHANICS, WHICH HE CONSIDERED TO BE A BETTER STARTING POINT, ONCE WROTE THE FOLLOWING:

5. “QUANTITATIVELY, SOME OF THE PREDICTIONS FROM
THESE EQUATIONS SURELY DEVIATE FROM EXPERIMENT,
BUT THE VERY REMARKABLE FACT REMAINS THAT
QUALITATIVELY THE NAVIER-STOKES EQUATIONS ALWAYS
DESCRIBE PHYSICAL PHENOMENA SENSIBLY.
THE MATHEMATICAL REASON FOR THIS VIRTUE OF THE
NAVIER-STOKES EQUATIONS IS COMPLETELY MYSTERIOUS
TO ME.”

6. CONCEPTUAL AND COMPOUND VARIABLES
SOME OF UNIQUE CONCEPTS AND COMPOUND VARIABLES OF TRANSPORT HAVE BECOME SO COMMONPLACE THAT WE MAY NO LONGER APPRECIATE HOW INVALUABLE THEY ARE, OR REMEMBER WHERE THEY CAME FROM AND THEIR LIMITS OF VALIDITY.
I WILL CALL TO YOUR ATTENTION A FEW OF THEM :

7. 1) THE HEAT TRANSFER COEFFICIENT AND ITS ANALOGUES 2) THE EQUIVALENT THICKNESS FOR PURE CONDUCTION 5) MIXED-MEANS IN GENERAL 6) FULLY DEVELOPED FLOW 7) THE FRICTION FACTOR FOR ARTIFICIALLY ROUGHENED TUBES 8) THE FRICTION FACTOR FOR COMMERCIAL (NATURAL) ROUGHNESS 9) THE EQUIVALENT LENGTH 10) “PLUG FLOW” 11) INTEGRAL BOUNDARY-LAYER THEORY

8. 12) POTENTIAL FLOW AND THE THIN-BOUNDARY-LAYER CONCEPT 13) FREE STREAMLINES PREDICT = FOR ORIFICE. THE COEFFICIENTREAL VALUE IS ) CRITERIA FOR TURBULENT FLOW IN PIPES: OSBORNE REYNOLDS IN 1883 REYNOLDS: Re = 2100 OR a+ = a(τw ρ)½ /μ = Re(f/8)½ 56 MODERN: LAMINAR: a+ ≤ 45 [Re ≤ 1600]; TURBULENT: a+ ≥ 150 [Re ≥ 4020]

9. 15) FULLY-DEVELOPED CONVECTION UNIFORM HEATING THE NEAR-ATTAINMENT OF ASYMPTOTIC VALUES OF (T−T0)/(Tm−T0) AS A FUNCTION OF r/a AND OF THE LOCAL HEAT TRANSFER COEFFICIENT UNIFORM WALL-TEMPERATURE THE NEAR-ATTAINMENT OF ASYMPTOTIC VALUES OF (Tw−T)/(Tw−Tm) AS A FUNCTION OF r/a AND OF THE LOCAL HEAT TRANSFER COEFFICIENT 16) THE BOUSSINESQ TRANSFORMATION MOST NOTABLY THE REPLACEMENT OF –g – (∂p/∂x)/ρ BY gβ(T – T∞) 17) THE RADIATIVE HEAT TRANSFER COEFFICIENT LINEARIZATION ALLOWS USE WITH OHM’S LAWS 18) BLACK-BODY AND GRAY-BODY RADIATION

10. 19) ASYMPTOTIC SOLUTIONS FOR TURBULENT FREE CONVECTION NUSSELT IN 1915: h APPROACHES INDEPENDENT FROM x AS x → ∞ REQUIRES Nux Grx1/3 FRANK-KAMENETSKII IN 1937: h INDEPENDENT OF k AND μ REQUIRES Nux Grx1/2 Pr ECKERT AND JACKSON IN 1951: INTEGRAL BOUNDARY LAYER THEORY Nux Grx0.4 CHURCHILL IN 1970: Nux → A Rax1/3 AS Pr → ∞ AND x → ∞ Nux → B (RaxPr)1/3 AS Pr → 0 AND x → ∞ SEEMINGLY VALIDATED BY LIMITED EXPERIMENTAL DATA 20) OHM’S DERIVED IN 1827 EXPRESSIONS FOR STEADY-STATE ELECTRICAL CONDUCTION REGULARLY APPLIED IN CHEMICAL ENGINEERING FOR OTHER LINEAR BEHAVIOR

11. SPECIAL FORMS OF TRANSPORT
1) FLUIDIZED BEDS: THE ALMOST EXCLUSIVE DOMAIN OF CHEMICAL ENGINEERS DICK WILHELM AND MOOSUN KWAUK IN ) INCIPIENT FLUIDIZATION: −∆P = L(1− ε)g(ρs− ρ) 2) HEIGHT OF EXPANDED BED: L(1− ε) = L (1− ε) 3) MEAN INTERSTITIAL VELOCITY: um0 = uT εn AFTER MORE THAN 60 YEARS, FLUIDIZATION IS STILL A LIVELY SUBJECT OF RESEARCH 2) PACKED BEDS MAJORITY OF CONTRIBUTIONS HAVE BEEN BY CHEMICAL ENGINEERS, AGAIN BECAUSE OF THE APPLICABILITY TO CATALYSIS EARLY EXAMPLE – SABRI ERGUN IN 1952:

12. SEVERAL YOU MAY NOT KNOW ABOUT
3) LAMINAR CONDENSATION
NUSSELT IN 1916 FOR A FILM FALLING DOWN A VERTICAL PLATE:
HERE, Г IS THE MASS RATE OF CONDENSATION PER UNIT BREADTH
SEVERAL YOU MAY NOT KNOW ABOUT
4) MIGRATION OF WATER IN POROUS MEDIA
MEASUREMENTS BY JAI P. GUPTA OF THE WATER CONCENTRATION IN SAND DURING
FREEZING AT A SUBCOOLED SURFACE REVEALED THAT WATER MIGRATES TO THE
FREEZING FRONT FASTER THAN CAN BE EXPLAINED BY DIFFUSION. THE VARIATION
OF SURFACE TENSION WITH TEMPERATURE WAS FOUND TO BE THE CAUSE.
5) CONVECTION DRIVEN BY A MAGNETIC FIELD
STUDIED IN DEPTH AND ALMOST EXCLUSIVELY BY HIROYUKI OZOE. APPLICATIONS:
ZOCHRALSKI CRYSTALIZATION AND SEPARATION OF GASES IN SPACE VEHICLES
AND STATIONS.

13. 6) THERMOACOUSTIC CONVECTION INCORPORATION OF FOURIER’S EQUATION IN THE UNSTEADY-STATE, ONE-DIMENSIONAL DIFFERENTIAL ENERGY BALANCE RESULTS IN: MATHEMATICIANS HAVE LONG RECOGNIZED THAT THIS MODEL PREDICTS AN INFINITE RATE OF PROPAGATION OF ENERGY. CATTANEO IN 1948, MORSE AND FESHBACH IN 1953, AND VERNOTTE IN 1958 INDEPENDENTLY PROPOSED THE SO-CALLED HYPERBOLIC EQUATION OF CONDUCTION TO AVOID THAT DEFECT: HERE, uT IS THE VELOCITY OF A THERMAL WAVE. THIS CONCEPT IS PURE RUBBISH! NUMERICAL SOLUTIONS OF THE EQUATIONS OF CONSERVATION AND EXPERIMENTAL MEASUREMENTS BY MATTHEW BROWN CONFIRMED OUR CONJECTURE THAT THE WAVE IS GENERATED BY COMPRESSIBILITY WITHOUT THE NEED FOR ANY SUCH A HEURISTIC.

14. 7) THERMAL CONDUCTION THROUGH DISPERSIONS
MAXWELL IN 1873, USING THE PRINCIPLE OF INVARIANT IMBEDDING, DERIVED AN APPROXIMATE SOLUTION FOR THE ELECTRICAL CONDUCTIVITY OF DISPERSIONS OF SPHERES.
IN 1986 I FOUND THAT, WHEN RE-EXPRESSED IN THERMAL TERMS AND RE-ARRANGED IN TERMS OF ONE DEPENDENT AND ONE AND INDEPENDENT VARIABLE, THIS SOLUTION PROVIDED A LOWER BOUND AND A FAIR REPRESENTATION EVEN FOR THE EXTREME OF A PACKED BED AND EVEN FOR GRANULAR MATERIALS.

16. SIMILARITY TRANSFORMATIONS
A FEW FAMILIAR EXAMPLES 1) TRANSIENT THERMAL CONDUCTION 2) THE THIN BOUNDARY-LAYER TRANSFORMATION OF PRANDTL IN ) THE POHLHAUSEN TRANSFORMATION OF 1921 FOR FREE CONVECTION 4) THE LÉVÊQUE TRANSFORMATION OF ) THE INTEGRAL TRANSFORMATION OF DUDLEY A. SAVILLE IN 1967 FOR FREE CONVECTION THE HELLUMS-CHURCHILL METHODOLOGY OF 1964 COMPUTERIZED IN 1981 BY CHARLES W. WHITE, III

17. CONVENTIONAL CORRELATING EQUATIONS
POWER-LAW RELATIONSHIPS BASED ON LOGARITHMIC PLOTS OF DIMENSIONLESS GROUPS
SCATTER IS USUALLY DUE TO:
1) UNRECOGNIZED PARAMETERS
2) WRONG CHOICE OF DIMENSIONLESS GROUPINGS
3) NON-LOGARITHMIC DEPENDENCE
A CLASSICAL EXAMPLE FOLLOWS:

19. DIMENSIONAL ANALYSIS OF A LIST OF VARIABLES
RAYLEIGH HAD “THE LAST WORD” WHEN IN 1915 HE DERIVED
Nu = A Ren Prm + B Re2n Pr2m + Re3n Pr4m
HE EMPHASIZED THAT THIS ONLY MEANT THAT
Nu = Φ{Re, Pr}
SUBSEQUENT “CONTRIBUTIONS TO DIMENSIONAL ANALYSIS” ARE BEST IGNORED
INFERENCES
POWER-DEPENDENCES OCCUR ONLY FOR ASYMPTOTIC BEHAVIOR
WE SHOULD STOP DRAWING LINES THROUGH SCATTERED DATA ON LOG-
LOG PLOTS

20. A CORRELATING EQUATION FOR ALMOST EVERYTHING
IN 1972 WE BEGAN TESTING AS A GENERAL EXPRESSION FOR CORRELATION:
WE CALLED THIS THE CHURCHILL–USAGI EQUATION OR CUE.
THE INCORPORATION OF ASYMPTOTES IMPROVED ACCURACY BOTH NUMERICALLY AND FUNCTIONALLY BEYOND ALL EXPECTATIONS .
WE WERE NOT THE FIRST TO UTILIZE THIS EXPRESSION: EARLIER USERS INCLUDE ANDY ACRIVOS AND TOM HANRATTY.
OUR CONTRIBUTIONS WERE:
1) TO RECOGNIZE ITS FULL POTENTIAL
2) TO DEVISE AN OPTIMAL PROCEDURE FOR DETERMINATION OF THE ARBITRARY EXPONENT n BASED ON THE ALTERNATIVE FORMS:

21. AND
OUR FIRST APPLICATION - LAMINAR FREE CONVECTION FROM AN ISOTHERMAL VERTICAL PLATE IN THE THIN LAMINAR BOUNDARY LAYER REGIME - RESULTED IN:
GRAPHICAL EVALUATION OF n :

22. FOR n = 9/4, PER THE GRAPH:

23. A SUBSEQUENT EARLY APPLICATION
THE VELOCITY DISTRIBUTION IN TURBULENT FLOW IN A ROUND TUBE ASYMPTOTES COMBINATION

24. THE CANONICAL PLOT

25. THE CONVENTIONAL PLOT OF THE SAME VARIABLES

26. RESTRICTIONS ON THE CUE
ASYMPTOTES MUST BE KNOWN, DERIVED, OR FORMULATED
ASYMPTOTES MUST INTERSECT ONCE AND ONLY ONCE
ASYMPTOTES MUST BOTH BE UPPER BOUNDS OR LOWER BOUNDS
ASYMPTOTES MUST BOTH BE FREE OF SINGULARITIES
BEHAVIOR MUST BE REASONABLY SYMMETRICAL WITH RESPECT TO THE ASYMPTOTES (CANNOT EXPECT TO BE FULFILLED EXACTLY)

27. GUIDELINES
DIFFERENTIATION AND INTEGRATION LEAD TO AWKWARD EXPRESSIONS.
DIFFERENTIATE OR INTEGRATE ASYMPTOTES AND DEVISE A SEPARATE
CORRELATING EQUATION WITH A DIFFERENT COMBINING EXPONENT.
STATISTICAL ANALYSIS IS UNNECESSARY:
THE EXPRESSION IS SO INSENSITIVE TO THE VALUE OF n THAT A RATIO
OF INTEGERS MAY BE CHOSEN.
ELI RUCKENSTEIN DERIVED A THEORETICAL VALUE OF 3 FOR n FOR FREE AND
FORCED CONVECTION. THIS VALUE HOLDS FOR MOST OTHER
COMBINATIONS OF ASSISTING OR OPPOSING MECHANISMS.
IN SOME INSTANCES, A THEORETICAL RATIONLIZATION EXISTS FOR n = 1 OR n = –1.

28. MULTIPLE VARIABLES
MAY BE INCORPORATED IN ASYMPTOTES AS IS GrX IN THE PRIOR EXAMPLE, NAMELY:
MAY BE INTRODUCED SERIALLY, AS IN:

29. TRANSITIONAL BEHAVIOR
REQUIRES SPECIAL MEASURES
THE INTERMEDIATE (TRANSITIONAL) ASYMPTOTE IS SELDOM KNOWN BUT CAN ALMOST ALWAYS BE REPRESENTED BY AN ARBITRARY POWER LAW.
DIRECT SERIAL APPLICATION FAILS IF y0 IS A LOWER AND y∞ AN UPPER BOUND, AND VICE VERSA.

30. THIS ANOMALY CAN BE AVOIDED BY USING “STAGGERED” VARIABLES SUCH AS:
WHICH FOLLOWS FROM APPLICATION OF THE CUE TO y0 AND y1 , NAMELY:
AND THEN IN TURN TO y∞, NAMELY:

31. A SPECIFIC APPLICATION OF “STAGGERING” IS PROVIDED BY THE INDICATED EXPRESSION FOR THE EFFECTIVE VISCOSITY OF A PSEUDOPLASTIC
THIS PROCESS AND RESULT SUGGESTS THE POWER-LAW MAY BE A MATHEMATICAL ARTIFACT

32. A GENERALIZED REPRESENTATION FOR TRANSITION
HICKMAN IN 1974 CARRIED OUT NUMERICAL CALCULATIONS FOR A SERIES OF BIOT NUMBERS.
HIS RESULTS AND CORRELATION CAN BE RE-EXPRESSED IN TERMS OF THE CUE AS:
HERE, THE SUBSCRIPTS J AND T DESIGNATE UNIFORM AND ISOTHERMAL HEATING OR COOLING, BUT THIS EXPRESSION CAN BE ADAPTED AS A GENERALIZED ONE FOR ALL TRANSITIONAL PROCESSES.
A GENERALIZED REPRESENTATION FOR TRANSITION

33. THE STATUS AND FUTURE OF THE CUE

34. ANALOGIES HAVE A PERVASIVE ROLE IN CHEMICAL ENGINEERING EXAMPLES:
THE EQUIVALENT DIAMETER (THE CHOICE IS NOT UNIQUE)
THE ANALOGY OF MACLEOD
THE ANALOGY BETWEEN HEAT AND MASS TRANSFER (TO BE EXAMINED IN DETAIL SUBSEQUENTLY)
THE ANALOGY BETWEEN ELECTRICAL AND THERMAL CONDUCTION
THE ANALOGY OF EMMONS FOR ALL BUOYANT PROCESSES (FREE CONVECTION, FILM CONDENSATION, FILM BOILING, AND FILM MELTING)

35. A NEW ANALOGY BETWEEN CHEMICAL REACTION AND CONVECTION
THE RADICAL ENHANCEMENT AND ATTENUATION OF CONVECTION BY ENERGETIC CHEMICAL REACTIONS HAVE BEEN KNOWN FOR OVER 40 YEARS BUT IS NOT EVEN MENTIONED IN TEXTBOOKS.
EARLIEST INVESTIGATORS INCLUDE THIBAULT BRIAN, BOB REID, AND SAMUEL BODMAN IN THE PERIOD , JOE SMITH IN 1966, AND LOUIS EDWARDS AND ROBERT FURGASON IN 1968.
WHILE MODELING COMBUSTION IN 1972 I BECAME AWARE OF THIS EFFECT, AND MANY YEARS LATER DERIVED THE FOLLOWING:
THIS EQUATION MAY BE INTERPRETED AS AN ANALOGY RELATING
THE LOCAL RATE OF HEAT TRANSFER, AS REPRESENTED BY Nux ,
TO THE LOCAL MIXED-MEAN RATE OF REACTION AS REPRESENTED BY

36. ILLUSTRATIVE REPRESENTATIONS
LAMINAR FLOW
HERE K0x = k0x/um IS THE DIMENSIONLESS DISTANCE THROUGH THE REACTOR

37. TURBULENT FLOW

38. TURBULENT FLOW
FOR OVER HALF OF OUR CENTURY, PRANDTL AND HIS STUDENTS, COLLEAGUES, AND CONTEMPORARIES UTILIZED DIMENSIONAL AND SPECULATIVE ANALYSIS TO DEVISE AN INGENIOUS STRUCTURE FOR THE THEN-INTRACTABLE PROCESS OF TURBULENT FLOW.
ONE OF THEIR IMPRESSIVE CHARACTERISTICS WAS RESILIANCE; IF ONE APPROACH WAS FOUND TO BE FLAWED, THEY TRIED ANOTHER AND ANOTHER.
TIME-AVERAGING OF THE EQUATIONS OF CONSERVATION
OSBORNE REYNOLDS IN 1895 SPACE-AVERAGED THESE EQUATIONS FOR A ROUND TUBE
THIS WAS THE GREATEST SINGLE ADVANCE OF ALL TIME IN TURBULENT FLOW.
THE EDDY DIFFUSIVITY CONCEIVED OF BY BOUSSINESQ IN 1877
THE POWER LAW FOR THE FRICTION FACTOR
BLASIUS IN 1913 INFERRED FROM EXPERIMENTAL DATA THAT f WAS INVERSELY PROPORTIONAL TO Re1/4.
UNFORTUNATELY, THIS IS A CRUDE APPROXIMATION THAT DOES NOT APPLY TO ANY FINITE RANGE OF Re.

39. THE POWER LAW FOR THE VELOCITY DISTRIBUTION
PRANDTL IN 1921 RECOGNIZED THAT THE POWER-LAW OF BLASIUS FOR THE FRICTION FACTOR REQUIRED:
HE ALSO RECOGNIZED ITS FAILURE IN BOTH LIMITS FOR ANY EXPONENT.
WALL-BASED VARIABLES
PRANDTL IN 1926 USED DIMENSIONAL ANALYSIS TO DERIVE:
THESE DIMENSIONLESS VARIABLES AND SYMBOLS HAVE REMAINED IN ACTIVE AND PRODUCTIVE USE FOR OVER 80 YEARS.
THE UNIVERSAL LAW OF THE WALL
PRANDTL NEXT CONJECTURED THAT NEAR THE WALL THE DEPENDENCE ON a+ SHOULD PHASE OUT LEADING TO:

40. THE UNIVERSAL LAW OF THE CENTER
PRANDTL SIMILARLY CONJECTURED THAT THE VELOCITY FIELD NEAR THE CENTERLINE MIGHT BE INDEPENDENT OF THE VISCOSITY LEADING TO:
THE MIXING LENGTH CONCEIVED BY PRANDTL IN 1925
THE SEMI-LOGARITHMIC VELOCITY DISTRIBUTION
THE CONJECTURE OF PRANDTL THAT NEAR THE WALL THE MIXING LENGTH WOULD DEPEND LINEARLY ON THE DISTANCE FROM THE WALL (NAMELY THAT l = ky) LEAD HIM TO:
THE 3/2-POWER EXPRESSION FOR THE VELOCITY DEFECT
PRANDTL IN 1925 FURTHER CONJECTURED THAT THE MIXING LENGTH MIGHT APPROACH A CONSTANT VALUE AT THE CENTERLINE LEADING TO THE FOLLOWING ERRONEOUS EXPRESSION:

41. AN OVERALL EXPRESSION FOR THE MIXING-LENGTH
IN 1930, IN ORDER TO ENCOMPASS A WIDER RANGE OF BEHAVIOR, VON KÁRMÁN PROPOSED:
A SEMI-LOGARITHMIC EXPRESSION FOR THE MIXED-MEAN VELOCITY AND THE FRICTION FACTOR
VON KÁRMÁN AND PRANDTL INDEPENDENTLY CONJECTURED THAT, IN SPITE OF ITS FAILURES NEAR THE WALL AND NEAR THE CENTERLINE, THE INTEGRATION OF THE SEMI-LOGARITHMIC EXPRESSION FOR THE VELOCITY OVER THE CROSS-SECTION MIGHT YIELD A GOOD APPROXIMATION FOR THE MIXED-MEAN VELOCITY AND THEREBY THE FRICTION FACTOR, NAMELY :

42. AN IMPROVED DERIVATION OF THE SEMI-LOGARITHMIC VELOCITY DISTRIBUTION
MILLIKAN IN 1938 RECOGNIZED THAT THE ONLY EXPRESSION CONFORMING TO BOTH “THE LAW OF THE WALL” AND “THE LAW OF THE CENTER” WAS:
THIS ALTERNATIVE DERIVATION OF “THE LAW OF THE TURBULENT CORE NEAR THE WALL,” WHICH IS FREE OF ANY HEURISTICS, REVEALS THAT TWO ERRONEOUS CONCEPTS (THE MIXING LENGTH AND ITS LINEAR VARIATION NEAR THE WALL) FORTUITOUSLY LED TO A VALID RESULT.
THE LINEAR VELOCITY DISTRIBUTION VERY NEAR THE WALL
PRANDTL POSTULATED THAT VERY, VERY NEAR THE WALL THE SHEAR STRESS DUE TO THE TURBULENT FLUCTUATIONS AND THE EFFECT OF CURVATURE WOULD BE EXPECTED TO BE NEGLIGIBLE, LEADING TO:
THIS EXPRESSION CAN BE NOTED TO CONFORM TO “THE LAW OF THE WALL.”

43. THE TURBULENT SHEAR STRESS VERY NEAR THE WALL
IN 1932, EGER MURPHREE, A CHEMIST, AND SOMEWHAT LATER, CHARLIE WILKIE, A CHEMICAL ENGINEER, AND HIS ASSOCIATES PROPOSED THAT:
THE EXISTENCE OR NON-EXISTENCE OF THE TERM IN (y+)3 WAS DISPUTED FOR OVER 50 YEARS.
THIS ISSUE WAS FINALLY SETTLED DEFINITIVELY BY THE RESULTS OF DNS, INCLUDING THOSE OF RUTLEDGE AND SLEICHER, AND OF LYONS, HANRATTY, AND MCLAUGHLIN, WHICH ALSO DETERMINED α ≈

44. POST-PRANDTL MODELING
THE k-ε MODEL
FOLLOWS FROM THE CONJECTURES OF KOLMOGOROV, PRANDTL, AND BATCHELOR
EMPIRICAL EQUATIONS FOR k AND ε WERE DEVISED BY LAUNDER AND SPALDING IN 1972.
THE PREDICTIONS OF FLOW NEAR THE WALL REMAIN POOR.
IT IS NEVERTHELESS OUR BEST RESOURCE FOR MODELING DEVELOPING FLOW.
DIRECT NUMERICAL SIMULATION (DNS)
CHARLES SLEICHER AND TOM HANRATTY AND THEIR DOCTORAL STUDENTS FOLLOWED THE LEAD OF KIM, MOIN AND MOSER IN 1987 AND USED DNS TO PREDICT TURBULENT FLOW IN PARALLEL-PLATE CHANNELS.
NUMERICAL SOLUTIONS ARE STILL LIMITED TO RATES OF FLOW JUST ABOVE THE MINIMUM FOR FULLY DEVELOPED TURBULENCE, NAMELY, Re = 4000.
DNS REQUIRES EXCESSIVE COMPUTATION FOR ROUND TUBES OR ANNULI.

45. LARGE-EDDY SIMULATION (LES)
THIS MODEL, AS DEVISED BY SCHUMANN IN 1975, RELAXES THE RESTRICTION ON THE RATE OF FLOW BY UTILIZING DNS ONLY FOR THE FULLY TURBULENT CORE, BUT IS INACCURATE NEAR THE WALL BECAUSE OF THE USE OF THE k-ε MODEL WITH ARBITRARY WALL-FUNCTIONS.
THE FUTURE OF NUMERICAL SIMULATION
WE SORELY NEED A NEW ALGORITHM OR CONCEPT THAT WILL EXTEND THE PREDICTIONS OF TURBULENT FLOW TO ROUND TUBES AND LARGE REYNOLDS NUMBERS, AS PROMISED BUT NOT DELIVERED BY DNS AND LES.

46. THE LOCAL FRACTION OF THE SHEAR STRESS DUE TO TURBULENCE
IN 1995, CHRISTINA CHAN AND I PROPOSED THE DIRECT CORRELATION OF EXPERIMENTAL AND COMPUTED VALUES FOR THE TURBULENT SHEAR STRESS, THEREBY AVOIDING THE HEURISTICS SUCH AS THE EDDY VISCOSITY AND THE MIXING LENGTH.
OUR FIRST CHOICE OF A DIMENSIONLESS VARIABLE WAS:
WE SUBSEQUENTLY PROPOSED THE FOLLOWING IMPROVED ONE, WHICH IS FINITE AT THE CENTERLINE:
IS SEEN TO BE THE LOCAL FRACTION OF THE SHEAR STRESS DUE TO THE TURBULENT FLUCTUATIONS.
IT IS WELL-BEHAVED FOR ALL CONDITIONS AND, IN CONTRAST TO , IS FINITE AT THE CENTERLINE.

47. IT IS EASY TO SHOW THAT:
THIS RESULT CONFIRMS THAT, DESPITE ITS HEURISTIC ORIGIN AND THE CONTEMPT OF MANY “PURISTS,” THE EDDY VISCOSITY REALLY HAS SOME PHYSICAL SIGNIFICANCE.
AT THE SAME TIME, THE EDDY VISCOSITY IS INFERIOR TO IN TERMS OF SIMPLICITY AND SINGULARITIES, AND IS THEREFORE NOW OF HISTORICAL INTEREST ONLY.
THE EXPRESSION FOR THE MIXING LENGTH REVEALS THAT IT IS INDEPENDENT OF ITS MECHANISTIC AND HEURISTIC ORIGIN. HOWEVER, IT IS ALSO REVEALED TO BE UNBOUNDED AT THE CENTERLINE OR THE CENTRAL PLANE OF A PARALLEL PLATE CHANNEL.
HOW DID SUCH AN ANOMALY ESCAPE ATTENTION FOR MORE THAN 70 YEARS? ONE EXPLANATION IS THE UNCRITICAL ACCEPTANCE BY PRANDTL OF THE PLOT OF VALUES OF THE MIXING LENGTH OBTAINED FROM THE “ADJUSTED” EXPERIMENTAL VALUES OF NIKURADSE, FOLLOWED BY THE UNCRITICAL EXTENSION OF RESPECT FOR PRANDTL AND VON KÁRMÁN TO ALL OF THEIR DERIVATIONS.

48. AN ALGEBRAIC CORRELATING EQUATION FOR THE TURBULENT SHEAR STRESS
IN 2000 WE DEVISED, USING THE CUE, THE FOLLOWING THEORETICALLY-BASED EXPRESSION FOR THE LOCAL FRACTION OF THE TOTAL SHEAR STRESS DUE TO TURBULENCE:
THIS EXPRESSION COMBINES ASYMPTOTES FOR THREE REGIONS AND THE LATEST EXPERIMENTAL DATA FOR u+ AS WELL AS FOR
ACCORDING TO THE ANALOGY OF MCLEOD, THIS EXPRESSION IS APPLICABLE FOR PARALLEL–PLATE CHANNELS IF b+ IS SUBSTITUTED FOR a+. WE HAVE ALSO ADAPTED IT FOR CIRCULAR CONCENTRIC ANNULI.
THE ULTIMATE PREDICTIVE EQUATION FOR THE FRICTION FACTOR IN A ROUND TUBE IS:
AN ITERATIVE SOLUTION IS REQUIRED TO DETERMINE THE FRICTION FACTOR FOR A SPECIFIED VALUES OF Re = 2a+um+ AND e/a, BUT CONVERGENCE IS VERY RAPID.

49. THE CORRESPONDING EXPRESSION FOR THE FRICTION FACTOR OF ALL REGIMES OF FLOW (LAMINAR, TRANSITIONAL, AND TURBULENT) AND ALL EFFECTIVE ROUGHNESS RATIOS IS:
HERE, fl = 16/Re (POISEUILLE’S LAW), ft = (Re/37530)2, AND fT IS THE ABOVE EXPRESSION FOR FULLY TURBULENT FLOW. THIS EXPRESSION IS A COMPLETE REPLACEMENT FOR AND IMPROVEMENT ON ALL EXPRESSIONS AND PLOTS FOR THE FRICTION FACTOR.
ALTHOUGH IT OBVIATES THE NEED FOR ONE, IT IS CAN READILY BE PROGRAMMED TO PRODUCE SUCH A PLOT IN EVERY DETA.
EXPERIMENTAL DATA FOR TURBULENT FLOW OF GREATEST HISTORICAL SIGNIFICANCE
BLASIUS IN 1913
NIKURADSE IN 1930, 1932, and 1933
COLEBROOK IN
ZAGAROLA IN 1996

50. TURBULENT CONVECTION
UNFOLDS PRIMARILY THROUGH ANALOGIES BETWEEN MOMENTUM AND ENERGY TRANSFER.
THE SOLUTION OF SLEICHER IN 1956, USING AN ANALOG COMPUTER, IS A PARTIAL EXCEPTION; IT WAS UPGRADED IN 1969 BY NOTTER AND SLEICHER USING A DIGITAL COMPUTER.
A GENERALIZED CORRELATING EQUATION FOR FORCED CONVECTION
IN 1977, I DEVISED, USING THE CUE WITH 5 ASYMPTOTES AND FOUR COMBINING EXPONENTS, A CORRELATING EQUATION FOR Nu FOR ALL Pr AND ALL Re (INCLUDING THE LAMINAR, TRANSITIONAL, AND TURBULENT REGIMES). THE SAME STRUCTURE BUT DIFFERENT ASYMPTOTES WERE PROPOSED FOR UNIFORM HEATING AND UNIFORM WALL TEMPERATURE. THESE EXPRESSIONS ARE HERE COMPARED GRAPHICALLY WITH EXPERIMENTAL DATA AND A FEW NUMERICALLY COMPUTED VALUES.

51. BECAUSE IT WAS NOT REPRODUCED IN MOST OF THE POPULAR TEXTBOOKS.
THE ALGEBRAIC CORRELATING EQUATION SHOWN IN THE PLOT SHOULD HAVE REPLACED ALL POWER-LAW EXPRESSIONS, BUT IT DID NOT…
WHY?
BECAUSE IT WAS NOT REPRODUCED IN MOST OF THE POPULAR TEXTBOOKS.

52. THE FRACTION OF THE LOCAL HEAT FLUX DENSITY DUE TO THE TURBULENT EDDIES
IN 2000, THE MODEL OF CHAN AND CHURCHILL FOR FLOW WAS EXTENDED TO CONVECTION USING:
IT PROVES CONVENIENT TO REPLACE IN THE DIFFERENTIAL ENERGY BALANCE BY A MORE CONSTRAINED VARIABLE, NAMELY THE TURBULENT PRANDTL NUMBER RATIO:
PETER ABBRECHT IN 1956 DETERMINED THE EDDY CONDUCTIVITY EXPERIMENTALLY IN A DEVELOPING TEMPERATURE FIELD AND CONFIRMED HIS CONJECTURE THAT THIS RATIO IS INDEPENDENT OF THE TEMPERATURE FIELD AND THEREBY OF THE THERMAL BOUNDARY CONDITION. IT FOLLOWS THAT , AND Prt /Pr ARE, AS WELL.
FROM THE ANALOGY OF MACLEOD IT FOLLOWS THAT kt/k, , AND Prt/Pr, ARE IDENTICAL FOR A ROUND TUBE AND A PARALLEL-PLATE CHANNEL IN TERMS OF a+ AND b+, RESPECTIVELY.

53. ALGEBRAIC ANALOGIES BETWEEN MOMENTUM AND HEAT TRANSFER
THE REYNOLDS ANALOGY
OSBORNE REYNOLDS IN 1874 POSTULATED THAT MOMENTUM AND ENERGY WERE TRANSPORTED AT EQUAL MASS RATES FROM THE BULK OF THE FLUID TO THE WALL BY THE OSCILLATORY RADIAL MOTION OF TURBULENT EDDIES AND THEREBY OBTAINED A RESULT THAT CAN BE EXPRESSED IN MODERN TERMS FOR A ROUND TUBE AS:
Nu =Pr Re (f/2)
THE PRANDTL-TAYLOR ANALOGY
PRANDTL G.I. TAYLOR INDEPENDENTLY IN 1910 AND 1916 DEVISED AN IMPROVEMENT, NAMELY:
THE REICHARDT ANALOGY
THE ANALOGY DEVELOPED BY REICHARDT IN 1951 IS FAR MORE ACCURATE FUNCTIONALLY AND NUMERICALLY THAN THAT OF PRANDTL AND TAYLOR, BUT IS ALSO FAR MORE COMPLICATED
ITS BASIC STRUCTURE HAS BEEN UTILIZED IN MOST SUBSEQUENT ANALOGIES, INCLUDING THOSE OF FRIEND & METZNER IN 1958, PETUKHOV IN 1970, GNIELINSKI IN 1976, AND MY OWN IN 1997

54. A REINTERPRETATION AND IMPROVEMENT OF THE REICHARDT ANALOGY
CHURCHILL, SHINODA, AND ARAI IN 2000 NOTED THAT THE REICHARDT ANALOGY COULD BE INTERPRETED AS AN INTERPOLATING EQUATION IN THE FORM OF THE CUE.
CHURCHILL AND ZAJIC IN 2001 TOOK ADVANTAGE OF THIS REINTERPRETATION TO DEVISE GREATLY IMPROVED ANALOGIES FOR ALL VALUES OF Pr AND Re. AS AN EXAMPLE, THEIR EXPRESSION FOR Pr ≥ Prt IS: .

55. THE COLBURN ANALOGY
ALIAN COLBURN IN 1933 COMBINED THE FOLLOWING EMPIRICAL CORRELATING EQUATIONS OF E.C. KOO, A DOCTORAL STUDENT AT MIT, FOR THE FRICTION FACTOR, AND OF DITTUS AND BOELTER FOR THE NUSSELT NUMBER:
f = 0.046/Re AND Nu = ARe.0.8Prn.
HE TOOK THE RATIO OF THESE TWO EXPRESSIONS, CHOSE AN ARBITRARY VALUE OF A = 0.023, AND A ROUNDED-OFF VALUE FOR n TO OBTAIN:
f/2 = Nu/RePr1/3 .
HE NAMED THE GROUPING ON THE RIGHT-HAND SIDE THE j – FACTOR.
THIS EXPRESSION TOGETHER WITH AN EMPIRICAL CORRELATING EQUATION FOR THE FRICTION FACTOR, REMAINS IN USE TO THIS DAY, ALTHOUGH, AS I WILL SHOW YOU, IT IS SERIOUSLY WRONG FUNCTIONALLY IN EVERY RESPECT AND NUMERICALLY AS WELL.

56. A GRAPHICAL COMPARISON OF THE ACCURACY OF THE PREDICTIONS OF SEVERAL ANALOGIES
OUR NEW ANALOGY SHOULD REPLACE ALL PRIOR ANALOGIES AND CORRELATING EQUATIONS BECAUSE IT IS BOTH SIMPLER AND MORE ACCURATE.

57. DEVISING ALGORITHMS FOR THE NUMERICAL SOLUTION OF THE EQUATIONS OF CONSERVATION
THE APPLICATION OF ELECTRONIC COMPUTERS TO TRANSPORT, BEGINNING AROUND 1950, ORIGINALLY REQUIRED THE DEVELOPMENT OF SPECIAL-CASE ALGORITHMS. THIS WAS AN IMPORTANT ELEMENT IN THE WORK OF MY DOCTORAL STUDENTS, AS OUTLINED HERE.
NATURAL CONVECTION IN ENCLOSURES
THE FIRST NUMERICAL SOLUTION OF THE PARTIAL DIFFERENTIAL EQUATIONS OF CONSERVATION BY WILLIAM R. MARTINI IN HIS SOLUTION WAS INCOMPLETE BUT DEMONSTRATED PROMISE.
THE FIRST COMPLETE TWO-DIMENSIONAL NUMERICAL SOLUTION OF THE PARTIAL DIFFERENTIAL EQUATIONS OF CONSERVATION BY J. DAVID HELLUMS IN 1960.
THE USE OF A STREAM-FUNCTION AND VORTICITY FORMULATION FOR NUMERICAL SOLUTIONS BY JAMES O. WILKES IN 1963
THE CONCEPT OF A FALSE TRANSIENT FOR THE STREAM-FUNCTION FOR NUMERICAL SOLUTIONS BY M. R. SAMUELS IN 1967
THE CONCEPT OF THE VECTOR POTENTIAL AND THE FIRST THREE-DIMENSIONAL NUMERICAL SOLUTIONS BY KHALID AZIZ, GEORGE HIRASAKI, AND DAVID HELLUMS AT RICE UNIVERSITY IN 1967
A NON-CONSERVATIVE FORMULATION TO IMPROVE CONVERGENCE BY HUMBERT H.-S. CHU IN 1976

58. THE DYNAMIC DISPLAY OF COMPUTED STREAKLINES BY PAUL P.-K. CHAO IN 1982
THE DISCOVERY THAT OSCILLATIONS IN RAYLEIGH-BÉNARD-TYPE CONVECTION ARE BETWEEN PLANFORMS BY HIROYUKI OZOE AND COWORKERS AT KYUSHU UNIVERSITY
THE USE OF PHOTOGRAPHED PARTICLE STREAKLINES AND COMPUTED ONES TO DISPLAY THREE-DIMENSIONAL MOTION BY HIROYUKI OZOE AND CO-WORKERS AT OKAYAMA UNIVERSITY IN 1983

59. OTHER RELATED APPLICATIONS INVOLVING THE DESIGN OF NUMERICAL ALGORITHMS
A TRANSIENT SOLUTION FOR STEADY STATE CONCENTRIC FLOW BY WARREN SEIDER IN 1971
THE USE OF THE MARKER-AND-CELL METHOD TO LOCATE THE MOVING BOUNDARY IN THREE-DIMENSIONAL EXTRUSION BY EDDY A. HAZBUN IN 1973
THE DISCOVERY OF OSCILLATIONS IN CZOCHRALSKI CRYSTALLIZATION BY VICKI BOOKER AND COWORKERS AT TSUKUBA UNIVERSITY IN 1995
DEFINITIVE STUDIES OF COMBINED MAGNETIC AND GRAVITATIONAL CONVECTION BY HIROYUKI OZOE AND COWORKERS AT KYUSHU UNIVERSITY AND AGH UNIVERSITY, KRAKOW
HANRATTY AND CO-WORKERS DEVISED, BEGINNING IN 1995, LAGRANGIAN ALGORITHMS FOR DNS CALCULATIONS, AND THEREBY CONFIRMED THEORETICALLY THEIR 1977 OBSERVATION, BASED ON ELECTROCHEMICAL MEASUREMENTS, THAT THE DEPENDENCE OF MASS TRANSFER ON Sc DIFFERS FROM THAT OF HEAT TRANSFER ON Pr.
THE LESSON FROM THESE EXAMPLES IS THAT THE PREDICTION OR SIMULATION OF TRANSPORT OFTEN DEPENDS ON CONCEPTUAL INNOVATION, EITHER MATHEMATICALLY OR PHYSICALLY

60. SIMULATION
SIMULATION IN THE CURRENT SENSE ALLOWS US TO USE CORRELATIONS FOR TRANSPORT TO PREDICT COMPLEX BEHAVIOR FOR THE PURPOSES OF DESIGN AND ANALYSIS.
THE ADVANCEMENT AND CURRENT STATE OF SIMULATION ARE BEYOND THE SCOPE OF MY PRESENTATION. HOWEVER, IT IS APPROPRIATE HERE TO NOTE THAT THIS PROCESS INVOKES A HIDDEN RISK, NAMELY THE POSSIBLE ERROR DUE TO OUT-OF-DATE AND ERRONEOUS CORRELATING EQUATIONS IMBEDDED IN COMPUTER PACKAGES.
SIMULATION HAS ANOTHER ROLE THAT HAS BEEN IMPLICIT IN THIS PRESENTATION, NAMELY THE PREDICTION OF DETAILED BEHAVIOR FROM “FIRST PRINCIPLES” IN ORDER TO PRODUCE “COMPUTED VALUES” AS A SUPPLEMENT TO EXPERIMENTAL DATA IN THE CONSTRUCTION OF CORRELATING EQUATIONS.

61. SUMMARY
I HAVE PRESENTED A FEW ILLUSTRATIONS OF OUR PROGRESS OVER THE PAST CENTURY IN PREDICTING TRANSPORT. THEY ARE JUST THAT – ILLUSTRATIONS; I HAVE BEEN HIGHLY ARBITRARY IN MY CHOICES.
SOME OF THE PROGRESS CONSISTS OF THE ABANDONMENT OF FAMILIAR CONCEPTS – A PAINFUL PROCESS AND ONE THAT RISKS THE APPEARANCE OF CRITICISM OF IDOLS OF MINE AS WELL AS YOURS. I TRUST THAT IF THEY WERE HERE THEY WOULD APPROVE. IN THAT REGARD, I RECALL W.K. LEWIS, IN AN ANECDOTAL LECTURE AT AN AIChE MEETING, MENTIONING THAT THE LEWIS NUMBER COMMEMORATED HIS WORST CONCEPTUAL ERROR.
MOST OF THE ADVANCES THAT I HAVE DESCRIBED TODAY ORIGINATED IN ACADEMIC RESEARCH. I WAS ABLE TO IDENTIFY ADVANCES STEMMING FROM INDUSTRIAL RESEARCH ONLY IN THE RARE INSTANCES WHEN THEY HAVE BEEN RELEASED FROM SECRECY AND APPEARED IN THE LITERATURE.
THE ULTIMATE CERTIFICATION OF ADVANCES IN TRANSPORT IS THEIR ADOPTION FOR DESIGN, OPERATION, AND ANALYSIS, BUT THAT IS DIFFICULT TO QUANTIFY, EXCEPT PERHAPS BY THEIR “APPEARANCE” IN COMPUTATIONAL PACKAGES. A FEW ADVANCES WERE MENTIONED THAT HAVE A MORE LIMITED BUT NEVERTHELESS IMPORTANT ROLE, NAMELY IMPROVEMENT IN UNDERSTANDING.

62. CONCLUSIONS
SOME OF YOU WHO WORK IN PROCESS DESIGN OR OPERATION MAY DISMISS WHAT I HAVE SAID AS MATHEMATICALLY-ORIENTED AND ONCE-REMOVED FROM PRACTICALITY. THAT IS A DANGEROUS INFERENCE.
IN THE EARLY DAYS OF THE AIChE, CORRELATING EQUATIONS WERE DEVISED BY DRAWING A STRAIGHT LINE THROUGH A LOG-LOG PLOT OF EXPERIMENTAL DATA. OVER THE CENTURY WE HAVE COME TO REALIZE THAT EXPRESSIONS SO-DERIVED ARE ALMOST CERTAINLY IN ERROR FUNCTIONALLY, AND THEREBY MAY BE IN SERIOUS ERROR NUMERICALLY AS WELL, OUTSIDE OF A NARROW RANGE. IF YOU ARE CLINGING TO ANY SUCH EXPRESSIONS INVOLVING PRODUCTS OF ARBITRARY POWER-FUNCTIONS, FOR EXAMPLE THE COLBURN ANALOGY, YOU ARE DANGEROUSLY OUT OF DATE.
OVER THE CENTURY, THE MOST OBVIOUS CHANGE IN PREDICTING TRANSPORT IS THE DEVELOPMENT OF POWERFUL COMPUTER HARDWARE AND USER-FRIENDLY SOFTWARE. HOWEVER, THE ACCURACY OF NUMERICAL SOLUTIONS DEPENDS CRITICALLY UPON THE VALIDITY OF THE MODEL, ON CONVERGENCE, AND ON STABILITY.

63. TRUSTING MODELS AND/OR THEIR SOLUTIONS, WHOSE LIMITS OF ACCURACY AND VALIDITY HAVE NOT BEEN TESTED WITH EXPERIMENTAL DATA, IS EQUIVALENT TO BELIEVING IN THE EASTER BUNNY.
THE MOST RELIABLE EXPRESSIONS FOR THE PREDICTION OF TRANSPORT ARE THOSE THAT HAVE A THEORETICAL STRUCTURE AND HAVE BEEN CONFIRMED BY BOTH EXPERIMENTAL DATA AND NUMERICAL SIMULATIONS. THE PRINCIPAL IMPROVEMENT NEEDED WITH RESPECT TO THE PREDICTION OF TRANSPORT IS FOR A METHODOLOGY FOR THE ACCURATE PREDICTION OF DEVELOPING TURBULENT FLOW AND OF CONVECTION IN THAT REGIME. THE k-ε MODEL PURPORTS TO FULFILL THIS NEED, BUT IT IS HIGHLY INACCURATE NEAR THE WALL, WHICH IS THE MOST CRITICAL REGION.
THE CURRENT LACK OF INTEREST IN AND SUPPORT FOR RESEARCH IN TRANSPORT IS PRIMARILY A CONSEQUENCE OF THE SHIFT OF SUPPORT AND INTEREST FROM CHEMICAL TO BIOLOGICAL PROCESSING, AND OF A RELATED SHIFT OF INTEREST FROM PROCESS TO PRODUCT DESIGN. I FORESEE A PARTIAL REVERSAL AS ENERGY CONVERSION BECOMES A NATIONAL FOCUS.

64. SOONER OR LATER IT WILL BE REALIZED THAT A FUNDAMENTAL AND BROAD UNDERSTANDING OF TRANSPORT IS ESSENTIAL FOR IMPROVED PROCESSING; WHETHER THERMAL, CHEMICAL, OR BIOLOGICAL, WHETHER BATCH OR CONTINUOUS, AND WHETHER ON A NANO-SCALE OR A MACRO-SCALE. ITS STUDY AND ADVANCEMENT REMAIN ESSENTIAL TO CHEMICAL ENGINEERING.