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7/27/2019 Units Operations: Processing and Handling
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P.E. Review Session
III-A. Unit Operations
by
Mark Casada, Ph.D., P.E. (Mech. Engr.)
Lead Scientist and Agricultural EngineerUSDA-ARS
Grain Marketing and Production Research Center
Manhattan, Kansas
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NCEES Topics
Unit Operations 8%
Characterization of Biological Products 4%
Processing & Handling
Mass transfer between phases Principles of unit operations Standards, codes, and regulations Principles of postharvest storage
(Covered previously)
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Unit Operations
What are Unit Operations?
Common operations that constitute a process, e.g.:
pumping, cooling, dehydration (drying), distillation,
evaporation, extraction, filtration, heating, size reduction,and separation.
How do you decide what unit operations apply to
a particular problem? Experience is required (practice).
Carefully read (and reread) the problem statement.
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Principles of Unit Operations
Mass BalanceInflow = outflow + accumulation
Energy BalanceEnergy in = energy out + accumulation
Specific equationsFluid mechanics, pumping, fans, heat transfer,
drying, separation, etc.
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IllustrationJam Production
Jam is being manufactured from crushed fruit with14% soluble solids.
Sugar is added at a ratio of 55:45
Pectin is added at the rate of 4 oz/100 lb sugar
The mixture is evaporated to 67% soluble solids
What is the yield (lbjam/lbfruit) of jam?
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IllustrationJam Production
mJ = ? (67% solids)
mf= 1 lbfruit (14% solids)
ms =1.22 lbsugar
mp =0.0025 lbpectin
mv = ?
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IllustrationJam Production
mJ = ? (67% solids)
mf= 1 lbfruit (14% solids)
ms =1.22 lbsugar
mp =0.0025 lbpectin
mv = ?
Total Mass Balance:
Inflow = Outflow + Accumulation
mf+ ms = mv + mJ + 0.0
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IllustrationJam Production
mJ = ? (67% solids)
mf= 1 lbfruit (14% solids)
ms =1.22 lbsugar
mp =0.0025 lbpectin
mv = ?
Total Mass Balance:
Inflow = Outflow + Accumulationmf+ ms = mv + mJ + 0.0
Solids Balance:
Inflow = Outflow + Accumulation
mfCsf + msCss = mJCsJ + 0.0
(1 lb)(0.14lb/lb) + (1.22 lb)(1.0lb/lb) = mJ(0.67
lb/lb)
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IllustrationJam Production
mJ = ? (67% solids)
mf= 1 lbfruit (14% solids)
ms =1.22 lbsugar
mp =0.0025 lbpectin
mv = ?
Total Mass Balance:
Inflow = Outflow + Accumulationmf+ ms = mv + mJ + 0.0
Solids Balance:
Inflow = Outflow + Accumulation
mfCsf + msCss = mJCsJ + 0.0
(1 lb)(0.14lb/lb) + (1.22 lb)(1.0lb/lb) = mJ(0.67
lb/lb)
mJ = 2.03 lbJam/lbfruit
mw = 0.19 lbwater/lbfruit
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IllustrationJam Production
mJ = ? (67% solids)
mf= 1 lbfruit (14% solids)
ms =1.22 lbsugar
mp =0.0025 lbpectin
mv = ?
What if this was a continuous flow concentrator
with a flow rate of 10,000 lbfruit/h?
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Principles of Unit Operations
Mass Balance:Inflow = outflow + accumulation
Chemical
concentrations:
Energy Balance:
Energy in = energy out + accumulation
t
Ci
1m
1,iC2,iC2m
t
T
1m
1T
2T2mK
KT
m
J/kgcapacity,heatspecificc
e,temperatur
kg/srate,flowmass
p
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Principles of Unit Operations
Mass Balance:Inflow = outflow + accumulation
Chemical
concentrations:
Energy Balance:
Energy in = energy out + accumulation
t
C
VmCmCi
ii
22,11,
t
TVcTcmTcm ppp
2211
(sensible energy)
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Principles of Unit Operations
Mass Balance:Inflow = outflow + accumulation
Chemical
concentrations:
Energy Balance:
Energy in = energy out + accumulation
t
C
VmCmCi
ii
22,11,
t
TVcTcmTcm ppp
2211
(sensible energy) total energy = mh
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Illustration Apple Cooling
An apple orchard produces 30,000 bu of apples a year, andwill store of the crop in refrigerated storage at 31F.Cool to 34F in 5 d; 31F by 10 d.
Loading rate: 2000 bu/day
Ambient design temp: 75F (loading) decline to 65F in20 d
Estimate the refrigeration requirements for the 1st 30 days.
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Apple Cooling
qfrig
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Principles of Unit Operations
Mass BalanceInflow = outflow + accumulation
Energy BalanceEnergy in = energy out + accumulation
Specific equationsFluid mechanics, pumping, fans, heat transfer,
drying, separation, etc.
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Illustration Apple Cooling
qfrig
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Illustration Apple Cooling
qfrigenergy in = energy out + accumulation
qin,1+ ... = qout,1+ ... + qa
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Illustration Apple Cooling
qfrigenergy in = energy out + accumulation
qin,1+ ... = qout,1+ ... + qa
Try it -
identify: qin,1 , qin,2 , ...
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Illustration Apple Cooling
Try it...
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Apple Cooling
qr
qm
qm
qb
qsqe
qso
qfrig
qin
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Apple Cooling
Sensible heat terms
qs = sensible heat gain from apples, W
qm = heat from lights, motors, people, etc., Wqso = solar heat gain through windows, W
qb = building heat gain through walls, etc., W
qin = net heat gain from infiltration, W
qe = sensible heat used to evaporate water, W
1 W = 3.413 Btu/h, 1 kW = 3413. Btu/h
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Apple Cooling
Sensible heat equations
qs = mload cpA T
qr = mtot Hresp
qm = qm1 + qm2 + . . .
qb = (A/RT) (TiTo)
qin = (Qacpa/vsp) (TiTo)
qso = ...
0
0
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Apple Cooling
definitions
mload = apple loading rate, kg/s (lb/h)
Hresp = sp. rate of heat of respiration, J/kgs (Btu/lbh)mtot = total mass of apples, kg (lb)
cpA = sp. heat capacity of apples, J/kgC (Btu/lbF)cpa = specific heat capacity of air, J/kgC (Btu/lbF)
Qa = volume flow rate of infiltration air, m3/s (cfm)
vsp= specific volume of air, m3/kgDA (ft
3/lbDA)
A = surface area of walls, etc., m2 (ft2)RT = total R-value of walls, etc., m
2C/W (hft2F/Btu)
Ti = air temperature inside,C (F)
To = ambient air temperature,C (F)
qm1
, qm2
= individual mechanical heat loads, W (Btu/h)
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Example 1
An apple orchard produces 30,000 bu of apples a year, and willstore of the crop in refrigerated storage at 31F. Cool to34F in 5 day; 31F by 10 day.
Loading rate: 2000 bu/day
Ambient design temp: 75F (at loading)declines to 65F in 20 day
A = 46 lb/bu; cpA = 0.9 Btu/lb
F
What is the sensible heat load from the apples on day 3?
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Example 1
qr
qm
qm
qb
qsqe
qso
qfrig
qin
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Example 1
qs = mloadcpAT
mload = (2000 bu/day 3 day)(46 lb/bu)
mload = 276,000 lb (on day 3)
T = (75F 34F)/5 = 8.2F/day
qs = (276,000 lb/day)(0.9 Btu/lbF)(8.2F/day)
qs = 2,036,880 Btu/day = 7.1 ton
(12,000 Btu/h = 1 ton refrig.)
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Example 2
Given the apple storage data of example 1,
= 46 lb/bu; cpA = 0.9 Btu/lbF;
What is the respiration heat load (sensible) from the apples onday 1?
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Example 2
qr = mtot Hresp
mtot = (2000 bu/day 1 day)(46 lb/bu)
mtot = 92,000 lb
qr= (92,000 lb)(3.4 Btu/lbday)
qr= 312,800 Btu/day = 1.1 ton
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Unit Operations Examples
Sterilization (food engineering)
Heat exchangers
Evaporation (food engineering) Drying
Postharvest cooling
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First order thermal death rate (kinetics) ofmicrobes assumed (exponential decay)
D = decimal reduction time = time, at a giventemperature, in which the number of microbes is
reduced 90% (1 log cycle)
tko
DeNN
D
ttk
N
ND
o
ln
Sterilization
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Sterilization
The z value is the temperature increase that will result in atenfold increase in death rate The typical z value is 10C (18F) (C. botulinum)
Fo = time in minutes at 250F that will produce the same
degree of sterilization as the given process at temperature T Standard process temp = 250F (121.1C)
Thermal death time: given as a multiple of D Pasteurization: 46D
Milk: 30 min at 62.8C (holder method; old batch method)15 sec at 71.7C (HTST high temp./short time)
Sterilization: 12D
Overkill: 18D (baby food)
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Sterilization
Thermal Death Time Curve(C. botulinum)(Esty & Meyer, 1922)
t= thermal death time, min
z T
oFt)F250(
10
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Sterilization
Thermal Death Time Curve(C. botulinum)(Esty & Meyer, 1922)
t= thermal death time, min
z = DTfor 10x change in t,
FFo = t@ 250F (std. temp.)
z
z
T
oFt)F250(
10
2.7
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Sterilization
Thermal Death Rate Plot
(Stumbo, 1949, 1953; ...)
D = decimal reduction time
tk
o
D
eNN
D
t
N
N
o
ln
0.01
0.1
1
10
100 110 120 130
Temperature, C
DecimalReductionTime
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Sterilization
Thermal Death Rate Plot
(Stumbo, 1949, 1953; ...)
D = decimal reduction time
tk
o
D
eNN
D
t
N
N
o
ln
0.01
0.1
1
10
100 110 120 130
Temperature, C
DecimalReductionTime
121.1
0.2
z
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Sterilization equations
z
T
T DD)250(
250 10
N
NDF oo log250
z
FT
o tF)250(
10
zCT
o tF)1.121(
10
z
TT
D
D o
o
log
T
T
o
oo
D
F
D
F
N
N
log
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Sterilization
Popular problems would be:
Find a new D given change in temperature
Given one time-temperature sterilization process,find the new time given another temperature, orthe new temperature given another time
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Example 3
If D = 0.25 min at 121C, find D at 140C.z = 10C.
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Example 3
equation D121 = 0.25 min
z= 10C
substitute
solve ...
answer:
z
TT
D
D o
o
log
C
CCD
10
1401.121
min25.0log 140
min003.0140 D
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Example 4
The Fo for a process is 2.7 minutes. Whatwould be the processing time if the processing
temperature was changed to 100C?
NOTE: when only Fo is given, assume standard
processing conditions:
T = 250F (121.1C); z = 18F (10C)
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Example 4
Thermal Death Time Curve(C. botulinum)(Esty & Meyer, 1922)
t= thermal death time, min
z =D
Tfor 10x change in t,
CFo = t@ 121.1C (std. temp.)
zT
oFt)C1.121(
10
2.7
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Example 4
z
T
oFt)C1.121(
10
C10
)C100C1.121(
10min)7.2(
t
min348t
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Heat Exchangers
me TAUq D
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Heat Exchangers
me TAUq D lmTAU D
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Heat Exchangers
lmme TAUTAUq DD
D
D DD
D
TT T
ln
T T T T
ln
T T T T
lnlm T
T
Hi Co Ho Ci
T T
T T
Hi Ci Ho Co
T T
T THi Co
Ho Ci
Hi Ci
Ho Co
max min
max
min
( ) ( ) ( ) ( )
counter parallel
qTcmTcm CCCHHH DD
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Heat Exchangers
subscripts: H hot fluid i side where the fluid enters
C cold fluid o side where the fluid exits
variables: m = mass flow rate of fluid, kg/s
c = cp = heat capacity of fluid, J/kg-K
C= mc, J/s-K
U= overall heat transfer coefficient, W/m2-K
A = effective surface area, m2
DTm = proper mean temperature difference, K orC
q = heat transfer rate, W
F(Y,Z) = correction factor, dimensionless
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Example 5
A liquid food (cp = 4 kJ/kgC) flows in the inner pipeof a double-pipe heat exchanger. The food enters theheat exchanger at 20C and exits at 60C. The
flow rate of the liquid food is 0.5 kg/s. In the annualsection, hot water at 90C enters the heatexchanger in counter-flow at a flow rate of 1 kg/s.
Assuming steady-state conditions, calculate the exittemperature of the water. The average cp of water is
4.2 kJ/kg
C.
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Example 5
Solution
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Time Out
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Reference Ideas
Full handbook The one you use regularly
ASHRAE Fundamentals.
Processing text
Henderson, Perry, & Young (1997),Principles of Processing Engineering
Geankoplis (1993), Transport Processes
& Unit Operations.
Need Marks Suggestion
Standards
ASABE Standards, recent ed. Other text Albright (1991),Environment...
Lower et al. (1994), On-Farm Drying and...
MWPS-29 (1999),Dry Grain Aeration
Systems Design Handbook. Ames, IA: MWPS.
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Studying for & taking the exam
Practice the kind of problems you plan towork
Know where to find the data See presentation III-B
(Characterization of Biological Products )
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Example 5
Solution90C
60C
?
20C
wwwfff TcmTcm DD
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Example 6
Find the heat exchanger area needed fromexample 5 if the overall heat transfer coefficient
is 2000 W/m2C.
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Example 6
Find the heat exchanger area needed fromexample 5 if the overall heat transfer coefficient
is 2000 W/m2C.
Data:
liquid food, cp = 4 kJ/kgC
water, cp = 4.18 kJ/kgC
Tfood,inlet = 20
C, Tfood,exit = 60
CTwater,inlet = 90C
mfood = 0.5 kg/s
mwater= 1 kg/s
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Example 6
Solution
lme TAUq D
CCC Tcmq D
90C
60C
71C
20C
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More about Heat Exchangers
Effectiveness ratio (H, P, & Young, pp. 204-212)
One fluid at constant T: R
D
Tlmcorrection factors
a
b
inba
aacooling
C
CR
C
AUNTU
TT
TTE
,,
)(
)(
min,1
21
),( YZFTAUq lm D
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Evaporator (Concentrator)
mS
mFmP
mV
Juice
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Evaporator
Solids mass balance:
Total mass balance:
Total energy balance:
PPFF XmXm
PVF mmm
PpPPgvVSfgSFpFF TcmhmhmTcm )(
lblbion,ConcentratX
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Example 7
Fruit juice concentrator, operating @ T =120F
Feed: TF = 80F, XF = 10%
Steam: 1000 lb/h, 25 psia
Product: XP = 40%
Assume: zero boiling point rise
cp,solids = 0.35 Btu/lbF, cp,w= 1 Btu/lbF
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Example 7
mS
mFmP= ?
mV
Juice(120F)
TF= 80F
XF= 0.1 lb/lbTP= 120F
XP= 0.4 lb/lb
TV= 120F
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Example 7
Steam tables:
(hfg)S= 952.16 Btu/lb, at 25 psia (TS= 240F)
(hg)V= 1113.7 Btu/lb, at 120F (PV= 1.69 psia)
Calculate: cp,mix= 0.35 X + 1.0 (1X)
Btu/lbF
cpF= 0.935 Btu/lbF
cpP= 0.74 Btu/lbF
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Example 7
mS
mFmP= ?
mV
Juice(120F)
TF= 80F
XF= 0.1 lb/lbTP= 120F
XP= 0.4 lb/lb
TV= 120F
hg= 1113.7 Btu/lb
hfg= 952.16 Btu/lb
cpF= 0.935
Btu/lbF cpF= 0.74 Btu/lbF
hlbskgPPFFSSXmXm ,
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Example 7
Solids mass balance:
Total mass balance:
Total energy balance:
PpPPVgVSfgSFpFF TcmhmhmTcm )()(
PPFF XmXm
PVF mmm
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Example 7
Solve formP:
mP
= 295 lb/h
VgXFpFXPpP
SfgSPhRTcRTc
hmm
)()1(
)(
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Mass Transfer Between Phases
Psychrometrics
A few equations
Psychrometric charts(SI and English units, high, low and normal temperatures; chartsinASAE Standards)
Psychrometric ProcessesBasic Components:
Sensible heating and cooling
Humidify or de-humidify
Drying/evaporative cooling
M T f B Ph
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Mass Transfer Between Phasescont.
Grain and food drying
Sensible heat
Latent heat of vaporization
Twb
Psychrometrics
Moisture content: wet and dry basis, and equilibrium
moisture content (ASAE Standard D245.6)Airflow resistance (ASAE Standard D272.3)
M T f B Ph
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Mass Transfer Between Phasescont.
0
5
10
15
20
25
0 20 40 60 80 100
Relative Humidity, %
Equilib
riumMoistureContent,%
0C
20C
40C
ASAE Standard D245.6 .Use previous revision (D245.4) for constants
or
use psychrometric charts in Loewer, et al., 1994
M T f B t Ph
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Mass Transfer Between Phasescont.
Loewer, et al. (1994)
M T f B t Ph
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Mass Transfer Between Phasescont.
Effect of temperature on
moisture isotherms (corn data)
0
5
10
15
20
25
0 20 40 60 80 100
Relative Humidity, %
EquilibriumMo
isture
Content,%
0C
20C
40C
D i P
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Drying Processcont.
rhe
Twb
TG To
rho
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Use of Moisture Isotherms
Relative Humidity, %
EquilibriumMoistureContent,%
Air Temp.
Grain Temp.
Me
rho
To
rhe
Mo
TG
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Drying (Deep Bed)
Drying grain (e.g., shelled corn) with the drying airflowing through more than two to three layers ofkernels.
Dehydration of solid food materials multiple layers drying & interacting
(single, thin-layer solution is a single equation)
wb
db
db
wbM
MM
M
1
11
1
)1()1( 2,21,1 wbwb MWMW
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Grain Bulk Density
kg/m3 lb/bu[1]
Corn, shelled 721 56
Milo (sorghum) 721 56
Rice, rough 579 45
Soybean 772 60
Wheat 772 60
1Standard bushel. Source: ASAE D241.4
Basic Drying Process
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Basic Drying ProcessMass Conservation
Compare: moisture added to air
to
moisture removed from product
Basic Drying Process
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Basic Drying ProcessMass Conservation
inaoutaa ,, D
Fan
grainofmasstotalgm
ina,:ratiohumidity
MCgraininchangeD gW
outa,:ratiohumidity
am
Basic Drying Process
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Basic Drying ProcessMass Conservation
Try it:
Total moisture conservation equation:
Basic Drying Process
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Basic Drying ProcessMass Conservation
ggaa Wmtm DD
Compare: moisture added to air
to
moisture removed from product
Total moisture conservation:
Basic Drying Process
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Basic Drying ProcessMass Conservation
ggaa Wmtm DD
Compare: moisture added to air
to
moisture removed from product
Total moisture conservation:kgas
skgwkga
kgwkgg
kgg
Basic Drying Process
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Basic Drying ProcessMass Conservationcontd
aa
gg
m
Wmt
D
D
Calculate time:
Assumes constant outlet conditions
but outlet conditions often change as product dries
use deep-bed drying analysis for non-constant outletconditions(Henderson, Perry, & Young sec. 10.6 for complete analysis)
D i P
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Drying Process
Assume falling rate period, unless
Falling rate requires erh or exit air data
Drying
Rate
Time
Constant
Rate Falling
Rate
erh = 100%aw = 1.0
erh < 100%aw < 1.0
EvaporativeCooling
(Thin-layer)
Drying Process
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Drying Processcont.
Twb
Drying Process
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Drying Processcont.
Twb
erh
ASAE D245.6
E l 8
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Example 8
Hard wheat at 75F is being dried from 18% to12% w.b. in a batch grain drier. Drying will bestopped when the top layer reaches 13%. Ambient
conditions: Tdb = 70F, rh = 20%
Determine the exit air temperature early in thedrying period.
Determine the exit air RH and temperature at theend of the drying period?
E l 8
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Example 8
Part II
Use Loewer, et al. (1994 ) (or ASAE D245.6)
RHexit = 55%
Texit = 58FTwb
emc=13%rhexit
Texit
E l 8
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Example 8
Loewer, et al. (1994)
13%
E l 8
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Example 8
Part I
Use Loewer, et al. (1994 ) (or ASAE D245.6)
Texit = Tdb,e = TG = 53.5F
Twb
emc=18%
Tdb,e
Cooling Process
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Cooling ProcessEnergy Conservation
Compare: heat added to air
to
heat removed from product
Sensible energy conservation:
gggaaa TcmTctm DD
IIinitialg TTT D
Cooling Process
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Cooling ProcessEnergy Conservation
Compare: heat added to air
to
heat removed from product
Sensible energy conservation:
gggaaa TcmTctm DD
Total energy conservation:
gggaa Tcmhtm DD
IIinitialg TTT D
Cooling Process
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Cooling Process(and Drying)
Cooling Process
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Cooling Process(and Drying)
Twb
erh
Airflow in Packed Beds
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Airflow in Packed BedsDrying, Cooling, etc.
Source: ASABE D272.3, MWPS-29
Design Values for Airflow Resistance in Grain
0.1
1
10
100
0.001 0.01 0.1 1 10
Pressure Drop per Foot, inH2O/ft
Airflow,cfm/ft
2Corn (PF=1.5)
Sunflower (PF=1.5)
Soybeans (PF=1.3)
Barle PF=1.5
Wheat (PF=1.3)
Milo (PF=1.3)
Standards Codes & Regulations
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Standards, Codes, & Regulations
Standards
ASABE
Already mentioned ASAE D245.6 and D272.3
ASAE D243.3 Thermal properties of grain and
ASAE S448 Thin-layer drying of grains and crops
Several others
Others not likely for unit operations
Fin l Th ht
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Final Thoughts
Study enough to be confident in your strengths
Get plenty of rest beforehand
Calmly attack and solve enough problems to passemphasize your strengths
Plan to figure out some iffy problems AFTER
doing the ones you already know
Aeration Fan Selection
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Aeration Fan Selection
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LF x MS x (depth) + 0.5DP = (inH2O/ft)design x (depth) + 0.5
4. Total airflow: cfm = (cfm/bu) x (total bushels)
or: cfm = (cfm/ ft2) x (floor area)
5. Select fan to deliver flow & pressure (fan data)
Aeration Fan Selection
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Aeration Fan Selection
00.2
0.4
0.6
0.8
1
1.2
1.4
0 500 1000 1500 2000 2500 3000
Airflow, cfm
StaticPressure,inH
2O
System
Fan
Aeration Fan Selection
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Aeration Fan Selection
Example
Wheat, Oklahoma, fall aeration
10,000 bu bin 16 ft eave height
pressure aeration system
Aeration Fan Selection
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Aeration Fan Selection
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LF x MS x (depth) + 0.5
4. Total airflow: cfm = (cfm/bu) x (total bushels)or: cfm = (cfm/ ft2) x (floor area)
5. Select fan to deliver flow & pressure (fan data)
Aeration Fan Selection
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Aeration Fan Selection
Recommended Air f low Rates for Dry Grain
(Foster & Tuite, 1982):
Recommended rate*, cfm/bu
Storage
TypeTemperate
Climate
Subtropic
Climate
Horizontal 0.05 0.10 0.10 0.20
Vertical 0.03 0.05 0.05 0.10
*Higher rates increase control, flexibility, and cost.
Select lowest airflow (cfm/bu) for cooling rate
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Select lowest airflow (cfm/bu) for cooling rate
Approximate Cooling Cycle Fan Time:
Airflow rate (cfm/bu)
Season 0.05 0.10 0.25Summer 180 hr 90 hr 36 hr
Fall 240 hr 120 hr 48 hr
Winter 300 hr 150 hr 60 hr
Spring 270 hr 135 hr 54 hr
Aeration Fan Selection
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Aeration Fan Selection
cfm/ft2 = (0.8) x (16 ft) x (0.1 cfm/bu)
cfm/ft2 = 1.3 cfm/ft2
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
Aeration Fan Selection
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Aeration Fan Selection
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LFx MS x (depth) + 0.5
4. Total airflow: cfm = (cfm/bu) x (total bushels)or: cfm = (cfm/ ft2) x (floor area)
5. Select fan to deliver flow & pressure (fan data)
Pressure drop: DP = (inH2O/ft) x MS x (depth) + 0.5(note: M = 1 3 for wheat)
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(note: Ms = 1.3 for wheat)
Airflow Resistance in Grain (Loose-Fill)
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10
Pressure Drop per Foot, inH2O/ft
Airflow,cfm/ft2 Corn
Barley Milo
Soybeans
Wheat
0.028
1.3
Pressure drop: DP = (inH2O/ft)design x (depth) + 0.5
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g
Design Values for Airflow Resistance in Grain(w/o duct losses)
0.1
1
10
100
0.001 0.01 0.1 1 10
Pressure Drop per Foot, inH2O/ft
Airflow,cfm/ft2 Corn
Barley Milo
Soybeans
Wheat
0.037
1.3
Aeration Fan Selection
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Aeration Fan Selection
DP = (0.028 inH2O/ft) x 1.3 x (16 ft) + 0.5 inH2O
DP = 1.08 inH2O
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LFx MS x (depth) + 0.5
Aeration Fan Selection
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Aeration Fan Selection
DP = (0.037 inH2O/ft) x (16 ft) + 0.5 inH2O
DP = 1.09 inH2O
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)design x (depth) + 0.5
Aeration Fan Selection
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Aeration Fan Selection
cfm = (0.1 cfm/bu) x (10,000 bu)
cfm = 1000 cfm
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LF x MS x (depth) + 0.5
4. Total airflow: cfm = (cfm/bu) x (total bushels)
Aeration Fan Selection
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Aeration Fan Selection
1. Select lowest airflow (cfm/bu) for cooling rate
2. Airflow: cfm/ft2 = (0.8) x (depth) x (cfm/bu)
3. Pressure drop: DP = (inH2O/ft)LF x MS x (depth) + 0.5
4. Total airflow: cfm = (cfm/bu) x (total bushels)or: cfm = (cfm/ ft2) x (floor area)
5. Select fan to deliver flow & pressure (fan data)
Aeration Fan Selection
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Aeration Fan Selection
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Axial Flow Fan Data (cfm):
Aeration Fan Selection
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Aeration Fan Selection
Selected Fan:
12" diameter, hp, axial flow
Supplies: 1100 cfm @ 1.2 inH2O
(a little extra 0.11 cfm/bu)
Be sure of recommended operating range.
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