E 
energy
J; [F] [L]
E_{c} mechanical pump energy, E_{f}
friction energy, E_{h} heat energy, E_{i}
Bond's work index in grinding (energy to reduce unit mass from infinitely
large particle size to 100mm),
E_{k} kinetic energy, E_{p} potential
energy, E_{r} pressure energy 
f 
friction
factor; dimensionless
ratio of actual drying rate to maximum drying rate, dimensionless 
fc 
crushing
strength of material kg m^{1} s^{2}; [M] [L]^{1}
[t]^{2} 
F 
force N, kg
m s^{2}; [F], [M] [L] [t]^{2}
F_{c} centrifugal force, F_{d} drag
force, F_{e} external force, F_{f}
friction force, F_{}_{g} gravitational force;
F_{s} accelerating force in sedimentation,
F_{l}
mass ratio of liquid to solid in thickener feed; dimensionless
time to sterilize at 121°C min; [t]

(Fo) 
Fourier
number (kt/crL^{2});
dimensionless 
(Fr) 
Froude
number (DN^{2}/g); dimensionless 
F(D) 
Cumulative
particle size distribution, F'(D) particle size distribution;
dimensionless 
g 
acceleration
due to gravity m s^{2}; [L] [t]^{2} 
G 
mass
rate of flow kg m^{2}s^{1} ; [M] [L]^{2 }[t]^{1} 
(Gr) 
Grashof
number (D^{3}r^{2}bgDt/m^{2});
dimensionless 
h 
heat
transfer coefficient J m^{2} s^{1}°C^{1};
[F] [L]^{1} [t]^{1}[T]^{1
}h_{c }convection, h_{h} condensing
vapours on horizontal surfaces, h_{r} radiation, h_{s}
surface, h_{v} condensing vapours on vertical surface^{
} 
H 
enthalpy,
kJ kg^{1}; [F] [L] [M]^{1}, H_{s},
enthalpy saturated vapour, Ha, Hb, Hc,enthalpy in refrigeration
system 

Henry's
Law constant, atm mole fraction^{1,} kPa mole fraction^{1};
[F] [L]^{2} 
k 
constant 

constant of proportionality 

friction loss factor; dimensionless 

thermal conductivity J m^{1} s^{1 }°C^{1}
; [F] [L]^{1} [t]^{1} [T]^{1} 
k'_{g} 
masstransfer
coefficient
k_{g} gas masstransfer coefficient, k_{'g}
masstransfer coefficient based on humidity difference, k_{l}
liquid mass transfer coefficient (units and dimensions from context) 
K 
constant, K^{'}, K^{''}, etc. 
K' 
masstransfer coefficient through membrane, kg m^{2} h^{1};
[M] [L]^{2} [t]^{1}; for ultrafiltration m s^{1},
for reverse osmosis kg m2 h1 kPa^{1} 
K_{K}

Kick's constant m^{3} kg^{1} ; [L]^{3} [M]^{1} 
K_{R} 
Rittinger's constant m^{4} kg^{1}; [L]^{4}
[M]^{1} 
K_{s} 
rate constant for crystal surface reactions m s^{1}; [L]
[t]^{1} 
K_{d}

mass transfer coefficient to the interface, m s^{1}; [L]
[t]^{1} 
K_{g} 
overall
gas mass transfer coefficient 
K_{l} 
overall
liquid mass transfer coefficient 
L 
flow rate of heavy phase kg h^{1} ; [M] [t]^{1} 

half thickness
of slab for Fourier and Biot numbers m; [L]


length m; [L] 

ratio of liquid to solid in thickener underflow; 
L_{c} 
thickness of filter cake, equivalent thickness of filter cloth and
precoat m; [L] 
(Le) 
Lewis
number (h_{c}/k'_{g}c_{p})
or (h_{c}/k_{g}c_{s})
dimensionless

m 
mass
kg; [M] 

number,
general 
(M) 
mixing
index, dimensionless 
M 
molecular
weight; dimensionless 

molal
concentration (kg) moles m^{3} ; [M] [L]^{3} 
n 
number,
general 
N 
number of particles in sample; 

rotational
frequency, revolutions/minute or
s ; [t]^{1} 
(Nu) 
Nusselt number (h_{c}D/k); dimensionless 
p 
partial pressure Pa; [F] [L]^{2} 

p_{a} partial pressure of vapour in air, p_{s}
saturation partial pressure 

factor in mixing and in grinding, dimensionless; factor in particle
geometry in grinding, fractional content in mixing; dimensionless 
P 
constant in
freezing formula; dimensionless;
power
N m s^{l, J s1}; [F] [L] [t]^{1}


pressure Pa; [F] [L]^{2} 
P_{s} 
pressure on surface Pa; [F] [L]^{2} 
(Po) 
Power number (P/D^{5}N^{3}r);
dimensionless 
(Pr) 
Prandtl number (c_{p}m/k);
dimensionless 
q 
heat flow rate J s^{1}; [F] [L] [t]^{1} 

fluid flow rate m^{3} s^{1}; [L]^{3} [t]^{1} 

reduction
ratio factor in particle geometry in grinding and mixing; dimensionless 
Q 
quantity
of heat J; [F] [L] 
r 
radius
m; [L] 

r_{n} neutral radius in centrifuge 

specific resistance of filter cake kg m^{1}; r' specific
resistance of filter cake under 1 atm pressure [M] [L]^{1} 
R 
constant in
freezing formulae; dimensionless
resistance to
flow through filter; dimensionless

R 
Universal
gas constant 8.314 kJ mole^{1 }K^{1}; m^{3}kPa
mole^{1}K^{1} , [L]^{2 }[t]^{2
}[T]^{1} ; 0.08206 m^{3} atm mole^{1}
K^{1}

(Re)
RH

Reynolds number
(Dvr/m)
and (D^{2}Nr/m);
dimensionless
relative humidity
p/p_{ , }% ; dimensionless

s

compressibility of filter cake; dimensionless 

distance m ; [L] 

standard deviation of sample compositions from the mean in mixing;
dimensionless 
s_{o}
, s_{r} 
initial and random values of standard deviation in mixing; dimensionless 
(Sc) 
Schmidt number (m/rD);
dimensionless 
(Sh) 
Sherwood number (K'd/D); dimensionless 
SG 
specific gravity; dimensionless 
t 
time s, h, min (from context) ; [t] 

t_{f}
, freezing time h 
T 
temperature °C or T K; [T] 

T_{av} mean temperature, T_{a} air,
T_{s} surface, T_{c} centre 

T_{m} mean temperature in radiation 
U 
overall heattransfer coefficient J m^{2} s^{1 }°C^{1}
; [F] [L]^{1} [t]^{1} [T]^{1} 
v 
velocity m s^{1} ; [L] [t]^{1} 
V 
flow rate of light phase kg h^{1}; [M] [t]^{1} 

volume
m^{3}; [L]^{3} 

volumetric flow rate m^{3} s^{1}; [L]^{3}
[t]^{1} 
w 
solid content per unit volume kg m^{3}; [M] [L]^{3}


mass
of dry material kg [M] 

weight
kg; [F] 
W 
work N m ; [F] [L] 

mass
of material dried kg; [M] 
x 
concentration in heavy phase kg m^{3}; [M] [L]^{3}


distance, thickness m; [L] 

fraction,
mole or weight, dimensionless 

mean 
X 
moisture content on dry basis ; dimensionless 

X_{c} critical moisture content, X_{f} final
moisture content, X_{o} initial moisture content; 

thickness of slab m ; [L] 
y 
concentration in light phase kg m^{3}; [M] [L]^{3} 

fraction, mole or weight, dimensionless 
Y
Y_{s}, Y_{a} 
humidity, absolute kg kg^{1}; humidity difference; dimensionless
humidity of saturated air, humidity of air 
z 
height m; [L] 

temperature difference for 10fold change in thermal death time °C,
[T] 
Z 
depth, height of fluid m; [L] 


a 
absorbtivity; dimensionless 
b 
coefficient of thermal expansion m m^{1} °C^{1};
[T]^{1} 

b_{1},
b_{2}
length ratios in freezing formula; dimensionless 
d 
thickness of layer for diffusion m; [L] 
D 
difference 

Dt_{m}
logarithmic mean temperature difference °C; [T] 
e 
emissivity; dimensionless 

roughness factor; dimensionless 
h 
efficiency of coupling of freezing medium to frozen foodstuff 

airdrying
efficiency, % , dimensionless 
l 
latent
heat kJ kg^{1}; [F] [L] [M]^{1} 

shape
factor for particles, dimensionless 
m 
viscosity kg s^{1} m^{1}; Pa s, N s m^{2};
[M] [t]^{1} [L]^{1} ; [F] [t] [L]^{2} 
p 
ratio of circumference to diameter of circle , 3.1416 
P 
total pressure Pa; [M] [L]^{1}[t]^{2}
, [F] [L]^{2} 

osmotic pressure kPa; [F] [L]^{2} 
r 
density kg m^{3}; [M] [L]^{3} 
s 
StefanBoltzman constant, 5,73 x10^{8} kg m^{2}
s^{3} °C^{4 , J m2 s1 K4} ; [M] [t]^{3}
[T]^{4} or [F] [L]^{1} [t]^{1}
[T]^{4} 
t 
shear
stress in a fluid Pa; [F] [L]^{2} 
f 
fin efficiency; dimensionless 
w 
angular velocity radians s ^{1}, [t]^{1}
