1. EVAPORATION
HEAT TRANSFER
COEFFICIENTS AND
SINGLE EFFECT
EVAPORATORS
By
T.Shivakumar
B.Pharmacy
Shiva.pharmacist@gmail.com
2. PROCESS DESCRIPTION
• OBJECTIVES
– CONCENTRATE SOLUTE
– RECOVER SOLVENT
– FORM CRYSTALS
• MECHANISM
– HEAT EXCHANGE WITH
PHASE CHANGE
– BATCH OR CONTINUOUS
http://www.niroinc.com/html/evaporator/rising_film_evaporators.html
3. DESIGN FACTORS
• SOLUTION FLUID VISCOSITY
– HEAT TRANSFER COEFFICIENTS
– PRESSURE DROPS
• SOLUTE SOLUBILITY
– SUPERSATURATED CONDITION
• MATERIALS (BIO-MATERIALS)
http://www.aai-
MAY BE HEAT SENSITIVE csi.com/images/evaporator.
jpg
– DEGRADATION TEMPERATURE
• ELEVATED PRESSURE
• BOILING POINT ELEVATION
4. EVAPORATION DESIGN
FACTORS
• HIGH TEMPERATURE
REACTIONS
• FOAMING
• SCALING AND
CORROSION
http://www.aquasant-
mt.com/Foam.159.0.html?&L=1
http://www.champ-
tech.com/images/products/p
ipe.jpg
5. OTHER DESIGN FACTORS
• SPECIFIC HEAT
• HEAT OF CONCENTRATION
• FREEZING POINT VS. CONCENTRATION
• GAS LIBERATION
• TOXICITY
• EXPLOSION HAZARDS
• NEED FOR STERILITY
6. EVAPORATION COMPARED
WITH DISTILLATION
• SOLUTE IN EVAPORATION IS
GENERALLY NON-VOLATILE, RELATIVE
TO SOLVENT
http://www.novasep.com/technologies/i http://www.schoolscience.co.uk/conten
mg/evaporation-graph2.gif t/4/chemistry/petroleum/knowl/images/
still.jpg
14. EVAPORATOR
CONFIGURATION
• SINGLE STAGE EVAPORATORS
• HEAT TRANSFER q = UA(T s−T1 ) (8.2 − 1)
15. MULTI-EFFECT EVAPORATORS
• STEAM FROM ONE EFFECT IS THE HEAT SOURCE
FOR THE SECOND EFFECT
http://www.nukem.de/global/downloads/englisch/Evaporation.pdf
16. MULTI-EFFECT COUNTERFLOW
CONFIGURATION
• FIGURE 8.2-3 FEED-FOREWARD
– PRESSURE IS REDUCED IN EACH STAGE
– FEED & STEAM ENTER THE SAME STAGE
IN THE TRAIN
• FIGURE 8.2-4 – FEED-BACKWARD
– PRESSURE IS INCREASED IN EACH STAGE
– FEED & STEAM ENTER FROM OPPOSITE
ENDS OF THE TRAIN
17. PARALLEL FEED
• SOLAR EVAPORATION SYSTEM
http://www.rio5.com/proceedings/Solar/da_Silva_et_al_201-206.pdf
18. EVAPORATOR HEAT
TRANSFER
• OVERALL HEAT TRANSFER
COEFFICIENTS – SEE TABLE 8.3-1
• NEED TO KNOW RANGE TO REVIEW
QUOTED DESIGNS
• NOTE THAT PLATE & FRAME CAN HAVE
HIGHER COEFFICIENTS THAN SHELL &
TUBE.
19. CHANGE OF PHASE HEAT
TRANSFER
• SECTION 4.8 FOR
SUMMARY OF
MECHANISMS
• FIGURE 4.8-1
– CONVECTION
– NUCLEATE
– TRANSITION
– FILM http://www.scielo.br/img/revistas/jbsmse/v
27n1/25372f10.gif
20. HEAT TRANSFER
COEFFICIENTS
• BASED ON ΔT
NUCLEATE BOILING
CONFIGURATION EQUATION RANGE REFERENCE
HORIZONTAL q/A, kW/m2 < 16 (4.8-1)
HORIZONTAL 16 < q/A, kW/m2 (4.8-2)
< 240
VERTICAL q/A, kW/m2 < 3 (4.8-3)
VERTICAL 3 < q/A, kW/m2 < (4.8-4)
63
FORCED Psys = kPa (4.8-5)
CONVECTION IN
TUBES
FILM BOILING
HORIZONTAL (4.8-6)
TUBE
21. OTHER CORRELATIONS
• FOR EACH
CONFIGURATION
• PERRY’S PAGE 5-22
• HANDBOOK
– http://www.wlv.com/product
s/databook/ch5_3.pdf
• CONVECTIVE BOILING
IN COILED TUBES
– http://www.graham-
mfg.com/downloads/12.pdf
• BASED ON SURFACE
– http://www.energy.kth.se/in
dex.asp?
pnr=10&ID=125&lang=0
22. SINGLE STAGE MODELS
• MASS AND ENERGY BALANCES
PRODUCT VAPOR
FEED SOLUTION
F, TF,xF,hF V,TBP,yV,HV
L, TBP,xL,hL
CONDENSATE
STEAM
C,TC,hC PRODUCT LIQUID
S,TS,HS
F = L +V S = C
23. MASS & ENERGY BALANCES
• COMPONENT MASS BALANCE
xF F = xL L NO SOLUTE IN VAPOR
• SYSTEM HEAT BALANCE
Fh F +SH S = LhL +VH V + Sh S (8.4 − 6)
Fh F +Sλ = LhL +VH V λ = ∆H vap (8.4 − 7)
q = Sλ (8.4 − 8)
24. OTHER DESIGN FACTORS
• LOWER EVAPORATION PRESSURE
– WILL INCREASE EFFECTIVE ΔT
– LOWER EVAPORATOR AREA
– INCREASED SOLVENT CONDENSER AREA
– HIGHER VELOCITIES MIST ELIMINATION
• BOILING POINT ELEVATION
– REDUCES EFFECTIVE ΔT WITH
INCREASING CONCENTRATION
25. BOILING POINT ELEVATION
• DÜRING’S RULE –
SOLUTION BOILING
POINT IS LINEARLY
RELATED TO PURE
WATER NBPt AT PSYS
• FIGURE 8.4-2
http://www.nzifst.org.nz/unito
perations/unopsassets/fig8-
3.gif
26. ENTHALPY-
CONCENTRATION
• HEAT OF
MIXING
EFFECTS
• NON-IDEAL
Dharmendira Kumar, M.; Ashok Kumar, P.; Rajendran, M., Salt Effect
on the Enthalpy of Mixing of 1,4-Dioxane + Acetic Acid at 303.15 K , J.
Chem. Eng. Data; (Article); 2003; 48(6); 1422-1424.
