Units Flashcards
nutritionist’s calories
Cal or kcal = 1000 cal
1 cal = ? J
4.18 J
The mass balance states
input = output
X + Y = 100
Standardization
the process where the fat content of milk products is adjusted by the addition of cream or skim-milk.
input-output = accumulation
steady state is achieved when
there is no accumulation of material, i.e. input = output
batch operations, normally runs on
runs on a time basis (hourly)
100 = m+C
[m = mass of water removed; C = mass of concentrate produced]
If 100 kg h-‘ of liquid containing 12% total solids is to be concentrated to produce a liquid containing 32% total solids, how much water is removed each hour?
100 = m+C
100 x 0.12= C x 0.32
It is assumed that the water leaving the evaporator contains no solid. Thus, C = 37.5kg , m = 62.5kg
Water needs to be removed at the rate of 62.5 kg h^-1
accumulation
input +production-output = accumulation
kgm^-3 is equivalent to
g l ^-1
In a spontaneous change, heat (energy) is always transferred from _______ to ___________, until ___________ is achieved
from an object at a high temperature to one at a lower temperature
until thermal equilibrium is achieved
- C = ? *F
* F = ? *C
- C = (*F- 32) x (5/9)
* F= (9/5) x *C +32
absolute zero = 0 K
all molecular motion stops and the kinetic energy of the molecule becomes zero.
K = ? *C
- 15 + *C
Carnot efficiency (CE)
a measure of the conversion of heat to work
CE = [(Heat 1 - Heat 2) / Heat 1] x 100
Electric current (A)
a measure of the flow of electrons
unit = ampere (A)
One ampere (1 A) is
flow of electrons which, when flowing down two long parallel conductors, of negligible cross-sectional area, placed 1 metre apart in a vacuum produces between the two wires a force of 2x 10^-7 N per metre of the length
Luminous intensity unit
candela (cd)
units of velocity
m s^-1
surface area of a circle
r x r x pi
surface area of a sphere
4 x pi x r x r = pi x Dx D
1 m^2 = ? cm^2 = ? ft ^2
10^4 cm^2 = 10.76 ft ^2
volumetric flow rate (Q)
units
Volume of fluid that passes through a given volume of space per unit of time
m^3 s^-1
volume of a sphere
(4/3) x pi x r^3
surface-area-to-volume ratio
[2 (r + h) ] / rh
When heating an object, maximize the surface-area-to-volume ratio will
maximize the heat transfer rate and reduce the time required
volume unit
m^3
Density
mass/ volume kg m^-3
Specific gravity
the mass of a substance divided by the mass of an
equal volume of water
has no units
velocity
as distance covered divided by time taken to cover that distance.
m s^-1
average velocity (v)
volumetric flow rate Q (m^3 s^-1) / cross-sectional area A (m^2)
m s^-1
average velocity for a pipe or tube with diameter D
v = Q / pi x r^2
Momentum units
kg m s^-1
angular velocity
the velocity of an object moves in a circle of radius r
angle subtended per unit time : (w) or (N)
(w) rad s^-1 (N) rev s^-1
(w) = 2 pi N
1 rad = ? *
1 rev = ? rad
2 pi rad = 1 rev = 360*
1 rad = 57.3*
acceleration
the rate of change in velocity
m s^-2
terminal velocity
An object moving with a constant velocity has no acceleration
gravity
9.81 m s^-2.
Force
units
masses, electric charges, magnetic poles, nuclear particles
kg m s^-2 or N
rheology
study of the deformation of objects under the influence of applied forces
Newton’s second law of motion
when an object changes momentum, it is subjected to a force Fand that the magnitude of the force is proportional to the rate of change in momentum.
force = rate of change in momentum
centrifugal force
an outward force acting on the object, to balance the centripetal force and keep the object in the same relative position when moving round a circle a constant tip speed
m r w^2 = [m v^2] / r
centripetal force
an inward force apply to an object when it is moving round a circle at a constant tip speed.
It is constantly changing its velocity because of its change in direction.
centripetal force (N) = mass (kg) x centripetal acceleration (m s^-2) = m v^2 / r
centripetal acceleration
centripetal acceleration (m s^-2) = v^2 / r or r w^2
v = velocity (m/s) r = circular radius (m)
Newton’s third law
for every acting force there is an equal and opposite reaction force
pressure
force / applied surface area
kg m^-1 s^-2 or N m^-2 or Pa
units of fluid density
kg m^-3
absolute pressure
p = p g h
p = fluid density (kg m^-3) g = gravity (m s^-2) h = height of fluid head (m)
absolute pressure = gauges pressures + atmospheric pressure
Positive pressure
gauges pressures > atmospheric pressure
Vacuum pressure
gauges pressures < atmospheric pressure
Shear stress.
The effect of a force acting parallel to a given area.
Frequency:
v = n/t = s^-1 or Hz
Period
T = t/n = 1 / v = 2pi/ w (s)
Different velocity
- Force acts same line velocity
- Force acts perpendicular to velocity
- Force acts towards “o” and perpendicular to velocity
- Forces is variable proportional to its distance to “o”
Surface area of a cylinder
pi D L + 2 x pi r^2
Work
a moving force through distance. It’s energy
kg m^-2 s or J
Power
the rate of doing work.
= work done/ time
Watt = joule / second [ W or J s^-1]
thermal conductivity
J s ^-1 m^-1 K^-1 or W m^-1 K^-1
electricity bills unit
k W h
pumping power
(pi - po) /pg
pi = inlet pressure po = outlet pressure p = fluid density (kg m^-3) g = gravity (m s^-2)
theoretical power Po (W) delivered to the fluid
Po (W) = mass flow rate (kg s^-1) X head developed (m) x
acceleration due to gravity (m s^-2)
molarity of solution
concentration / molecular weight
concentration
mass of solid / total volume
or weight/ weight
no of moles
mass / molecular weight
