Lecture 2

Noor Shazliana Aizee Bt Abidin

FORMS OF ENERGYTHERMAL ENERGY – HEATCHEMICAL ENERGY – IN FUELS OR

BATTERIESKINETIC ENERGY – IN MOVING

SUBSTANCESELECTICAL ENERGYGRAVITATIONAL ENERGY – POTENTIAL

ENERGYOTHERS

EQUATIONS, UNITSFORCE (N) = MASS (kg) X ACCERATION (m

s-2)

ENERGY(J) = FORCE (N) X DISTANCE (m)

POWER (W) = RATE AT WHICH ENERGY IS CONVERTED FROM ONE FORM TO ANOTHER OR TRANSFERRED FROM ONE PLACE TO ANOTHER.

MORE DEFINITIONSONE WATT (power) = ONE JOULE PER

SECOND1kWh (energy) = 1000 w X 3600 s/h =

3.6x106 JENERGY IS OFTEN MEASURED IN

QUANTITIES OF FUEL SUCH AS tonnes OIL OR COAL (1 tonne = 2,205 pounds)

NATIONAL ENERGY STATISTICS OFTEN USE THE UNIT OF “million tonnes of oil equivalent” 1Mtoe = 41.9PJ = 41.9x1015J

FORMS OF ENERGYFUNDAMENTALLY 4 TYPESkinetic, gravitational, electrical, nuclear

KINETIC ENERGY = ½ X mass X speed2

THERMAL ENERGY IS FORM OF KINETIC ENERGY – i.e. movement of molecules

0 degrees Kelvin corresponds to zero molecular motion

REMEMBER: temp(K) = temp(oC) + 273

GRAVITATIONAL ENERGYPOTENTIAL ENERGY PE = FORCE X DISTANCE = WEIGHT X

HEIGHT = m x g x hIMPORTANT FOR SOME ENERGY STORAGE

TECHNOLOGIESHYDROPOWER – PUMPED STORAGE

ELECTRICAL ENERGYCHEMICAL ENERGY (BATTERY) IS

ELECTRICAL ENERGYCHEMICAL ENERGY FROM BURNING A

FUEL IS CONVERTED TO THERMAL (kinetic energy)

Power (watts) = voltage (volts) x current (amps)

ELECTROMAGNETIC ENERGY – RADIATION (X-RAYS, UV, IR, VISIBLE, MICROWAVES, RADIO WAVES) frequency x wavelength = velocity of light f x = c

THERMODYNAMICSCONSERVATION OF ENERGY = FIRST LAW

OF THERMODYNAMICSSECOND LAW OF THERMODYNAMICS =

THERE IS A LIMIT TO THE EFFICIENCY OF ANY HEAT ENGINE (SOME OF THE ENERGY MUST BE REJECTED AS LOWER TEMPERATURE HEAT)

WORLD CONSUMPTION OF ENERGYIN 2002 451 EJ (exajoules) = 451 x 1018 J =

10,800MtoeWORLD POPULATION = 6.2 billion peopleAVERAGE ANNUAL CONSUMPTION per

PERSON = 350 GJ per year

Fluid dynamicsFluid dynamics has a wide range of

applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and reportedly modeling fission weapon detonation.

The solution to a fluid dynamics problem typically involves calculating various properties of the fluid, such as velocity, pressure, density, and temperature, as functions of space and time.

Equations of fluid dynamicsThe foundational axioms of fluid dynamics

are the conservation laws, specifically, conservation of mass, conservation of linear momentum (also known as Newton's Second Law of Motion), and conservation of energy (also known as First Law of Thermodynamics). These are based on classical mechanics and are modified in quantum mechanics and general relativity. They are expressed using the Reynolds Transport Theorem.

Conservation of MomentumIn the absence of an external force, the

momentum of a system remains unchanged.

total momentum before = total momentum after

(m1v1 + m2v2)before = (m1v1 + m2v2)after

As an example lets look at the cannon below. Let's assume that the cannon has a mass of 500 kg (mc) and the cannonball has a mass of 10 kg (mb). If the cannon launches the cannonball at a velocity of 200 m/s, what is the velocity of the cannon?

We can attack this problem using the conservation of momentum formula in equation above. Before the cannon is fired we know that its velocity, vc, is zero and the velocity of the cannonball, vb, is zero.

(mcvc + mbvb) = (500 kg x 0 m/s + 10 kg x 0 m/s) = 0

Now if the total momentum is zero before the cannon firing, the conservation of momentum tells us that it must be zero after the cannon fires.

(500 kg x vc + 10 kg x 200 m/s) = 0(500 kg x vc + 2000 kg.m/s) = 0

500 kg vc = -2000 kg.m/s

vc = -4 m/s

We have used the conservation of momentum to calculate that the cannon recoils with an initial velocity of -4 m/s, that is, 4 m/s in the opposite direction of the cannonball.

kg500s/m.kg200

vc

ViscosityViscous problems are those in which fluid friction has

significant effects on the fluid motion.Viscosity is a measure of the resistance of a fluid which is

being deformed by either shear stress or extensional stress. In everyday terms (and for fluids only), viscosity is "thickness." Thus, water is "thin," having a lower viscosity, while honey is "thick," having a higher viscosity.

Dynamic viscosity is measured with various types of rheometer. Close temperature control of the fluid is essential to accurate measurements, particularly in materials like lubricants, whose viscosity can double with a change of only 5 °C. For some fluids, it is a constant over a wide range of shear rates. These are Newtonian fluids.

The fluids without a constant viscosity are called non-Newtonian fluids. Their viscosity cannot be described by a single number. Non-Newtonian fluids exhibit a variety of different correlations between shear stress and shear rate.

TurbulenceIn fluid dynamics, turbulence or turbulent

flow is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.

Flow that is not turbulent is called laminar flow. While there is no theorem relating Reynolds number to turbulence, flows with high Reynolds numbers usually become turbulent, while those with low Reynolds numbers usually remain laminar.

Heat transferConduction

Convection

Radiative heat transferThe term radiation covers a vast array of

phenomena that involve energy transport in the form of waves.

In this section, we deal only with a particular kind of radiation, called thermal radiation .

Thermal radiation refers to electromagnetic radiation in the wavelength range of 10 7 to 10 4 m and encompasses mainly the range of infrared radiation.

It is so called because its practically sole effect is thermal, i.e. cooling of the emitting body and heating of the receiving body.

Above the absolute temperature of zero °K, all substances emit electromagnetic radiation.

The intensity and the ‘ color ’ (wavelength distribution) of the radiation strongly depend on the temperature of the source.

In contrast with conduction and convection, heat transfer by radiation does not require the presence of a material medium.

Thank you.