Science Reviewer First Law of Thermodynamics (ΔU = Q – W) Heat Pump (Refrigeration System)
-is a device that reverses the direction of the heat
Energy When heat is added to the system, some of it flow
-the ability to do work remains in the system increasing its energy while -ex: refrigerators and air conditioners
the rest leaves the system as the system does
Law of Conservation of Energy work. Spontaneous Process
Energy cannot be destroyed nor created; it can ΔU (change in internal energy) -higher to lower temperature
only be transformed. Q (heat) -does not require any external energy
W (work) -Second Law of Thermodynamics is applied
Forms of Energy Non-Spontaneous Process
Second Law of Thermodynamics -lower to higher temperature
Potential Energy -needs mechanical energy to occur
-stored by an object as a result of its position Heat flows naturally from hot to cold systems.
Kinetic Energy Heat will never bi itself, flow from a cold Refrigeration
-possessed by bodies in motion temperature to a hot temperature with no input of -refers to transfer of heat from cold to warm
Chemical Energy work.
Principles of Mechanical Refrigeration
-stored in the chemical bonds of molecules Sign Conventions
Electrical Energy
-energy of moving electrons Heat is positive when it enters the system;
Thermal Energy negative when it leaves the system.
-produced through the vibration and motion of Work is positive when it is done by the system;
molecules negative when it is done on the system.
Sound Energy
-audible energy released through vibration of Heat
-is a waste energy
molecules
-energy in transit that cannot be stored
Radiant Energy
-is used in cooking, drying, running a machine, etc.
-aka light energy; can take form of visible light
and invisible waves Effects of Heat
Nuclear Energy
-stored in the nucleus of an atom ΔT (change in temperature)
-fusion (combine) and fission (apart) Phase Change (gain or loss of heat)
Formula: Internal Energy
-energy within a substance How:
Mechanical Energy -it is the grand total of all energies inside a substance
-Em = Peg + KE = constant -is affected by heat Receiver – R-12 (refrigerant) in liquid form;
Gravitational Potential Energy high pressure
-Peg = mgh Heat will stop from flowing only if two objects Expansion Valve – liquid to gas; decrease in
Kinetic Energy are said to be thermal equilibrium. pressure and temperature
-KE = 1/2 mv² Ex: fever thermometer Evaporator – liquid to gas; low pressure and
Heat is an energy. Energy is the capacity to do temperature
Joules work. Therefore, heat has the capacity to do Compressor – gas; increase in pressure and
-unit of energy work. temperature
-J = N x M It is not correct to say that a substance contains
heat. The substance has internal energy, not heat.
By: Dustin C. Francisco (9-Savanna) 1
Condenser – gas to liquid; goes back to receiver
Volume is inversely proportional with pressure
and temperature during compression.
Heat Engine
-is a device that changes thermal energy into
mechanical work
-2-stroke or 4-stroke
Four Cycle Strokes in a Gasoline Engine
Intake
-mixture of gases fill up the combustion
chambers
-piston moves down
Compression
-mixture of gases is compressed Thermal Efficiency
-piston moves up -performance measure of an engine
Combustion/Power -there is no 100% efficient engine
-mixture of gases ignited by spark plug -Qc (energy removed by heat/energy in cold
-piston moves down reservoir)
Exhaust -Qh (energy added by heat/energy in hot reservoir)
-exhaust gases expel through exhaust valve -Tc (absolute temperature in cold reservoir)
-piston moves up -Th (absolute temperature in hot reservoir)
Parts of Four-Stroke Engine Equations:
Work
-W = Qh – Qc
Efficiency
-E = W (or Qh – Qc) / Qh x 100%
Qh
-Qh = W + Qc
Qc
-Qc = W - Qh
By: Dustin C. Francisco (9-Savanna) 2
Carnot Engine Efficiency Formula
-by Sadi Carnot
-maximum efficiency of an engine
-never 100% though
-equation: Ecarnot = 1 – Tc / Th x 100%
The temperatures should be on the Kelvin scale.
273.15 + the temperature in Celsius = Kelvin
Internal Combustion Engines
-combustion takes place inside the combustion
chamber
ex: gasoline, diesel engine, human body
External Combustion Engines
-combustion takes place outside the engine
-ex: steam, piston engine, atmosphere
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By: Dustin C. Francisco (9-Savanna) 3
