Thermodynamics
"Future ME! Thermodynamics - ang pag-aaral ng energy at heat. Paano ito nagta-transfer, nagiging work, at nag-drive ng power systems!"
1. Thermodynamic Laws š
Thermodynamics ay nag-study kung paano energy (especially heat) ay nag-transform at nag-transfer.
| Law | Statement | Example |
|---|---|---|
| Zeroth Law | Thermal equilibrium: heat flows from hot to cold until same temp | Hot water in cup cools down to room temp |
| First Law | Energy conservation: ĪU = Q - W (Heat in = Energy change + Work out) | Engine absorbs heat, some becomes work (motion), rest is internal energy |
| Second Law | Entropy always increases: efficiency always <100%, heat flows hotācold | No perfect engine; some heat always lost to environment |
| Third Law | Absolute zero (-273Ā°C) cannot be reached; entropy approaches zero | Cooling always requires energy; can't reach absolute zero |
2. Heat Transfer Modes š„
Heat moves in 3 main ways - alam mo lahat para sa power systems!
Conduction
Heat flow through material (direct contact). Example: Metal spoon in hot water - handle gets hot.
Formula: Q = kĆAĆ(Tā-Tā)/d
Convection
Heat flow via fluid movement (air/water). Example: Hot air rises, cold sinks - boiling water circulation.
Natural (gravity) vs Forced (fan/pump)
Radiation
Heat transfer via electromagnetic waves (no contact needed). Example: Sunlight, infrared heaters.
Stefan-Boltzmann Law: Q ā Tā“
3. Thermodynamic Cycles ā»ļø
Cycles na nag-convert heat into mechanical work - foundation ng lahat ng engines!
| Cycle | Application | Process | Efficiency |
|---|---|---|---|
| Otto Cycle | Gasoline engines (cars) | IntakeāCompressāIgniteāExhaust (4 strokes) | ~30-40% |
| Diesel Cycle | Diesel engines (trucks, generators) | Higher compression ratio, self-ignition | ~40-50% (more efficient!) |
| Rankine Cycle | Steam power plants | Boil waterāExpand steamāCondenseāPump | ~35-45% |
| Brayton Cycle | Gas turbines (jet engines, power plants) | Compress airāIgniteāExpandāExhaust | ~30-40% |
4. Temperature & Heat Relationships š”ļø
Key Concepts
5. Thermodynamic Processes š
| Process | Constant | Example |
|---|---|---|
| Isobaric | Pressure (P) constant, V & T change | Boiling water at atmospheric pressure |
| Isochoric | Volume (V) constant, P & T change | Heating gas in closed rigid container |
| Isothermal | Temperature (T) constant, P & V change | Piston moving slowly in water bath |
| Adiabatic | No heat transfer (Q=0), P, V, T all change | Rapid gas compression (PV^Ī³ = constant) |
6. Applications in Power Systems ā”
š Internal Combustion Engines: Otto/Diesel cycles convert fuel chemical energy ā mechanical work
ā” Power Plants: Rankine cycle converts heat (coal/nuclear) ā steam ā electricity
āļø Gas Turbines: Brayton cycle used in jet engines and power generation
āļø Refrigeration: Reverse Rankine cycle removes heat from cold space (air conditioning)
š Combined Cycles: Multiple cycles together (gas turbine + steam turbine) for better efficiency
7. Practice Questions š
Common Board Exam Questions
Q1: State the First Law of Thermodynamics and explain ĪU = Q - W.
A: Energy conservation. ĪU = change in internal energy, Q = heat absorbed, W = work done by system. Heat in = internal energy change + work out
Q2: Why is Diesel cycle more efficient than Otto cycle?
A: Diesel has higher compression ratio (15-20 vs 8-12), reaching higher temperatures. More heat converted to work before expansion ends.
Q3: Explain the Second Law of Thermodynamics and entropy.
A: Entropy (disorder) always increases. No engine is 100% efficient; heat always flows from hot to cold. Some energy always lost as waste heat.
Q4: Differentiate conduction, convection, and radiation.
A: Conduction = direct contact, Convection = fluid movement, Radiation = electromagnetic waves (no medium needed). All three transfer heat from hot to cold.
Q5: What is thermal efficiency and why can't it reach 100%?
A: Ī· = Useful work / Heat input. Cannot reach 100% due to 2nd Law - some heat must be rejected to environment. Max = Carnot efficiency = 1 - (T_cold/T_hot)
Q6: In Rankine cycle, what are the four main processes?
A: 1) Pump (liquid pressurized), 2) Boiler (heat added, waterāsteam), 3) Turbine (steam expands, does work), 4) Condenser (steamāliquid, heat rejected)
š„ ME Challenge š„
Master thermodynamics! Understand the 4 laws, heat transfer modes, engine cycles, and efficiency. Heat = Work!
Energy always wins - apply the laws everywhere in mechanical engineering!
Test Your Knowledge! š§
Ready ka na ba? Take the practice quiz for Thermodynamics to reinforce what you just learned.
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