ESE2001

• There are two types of energy: stored and working.
• Potential energy is stored energy and the energy of position, represented by the equation 𝑚𝑚𝑚𝑚𝑚 = 𝑚𝑚𝑚𝑚𝑚, where m (kg) is the mass, h (m) is the height and g = 9.81 m/s^2 is the acceleration due to gravity.
• Potential energy is energy waiting to be converted into motion or kinetic energy, represented by the equation 𝐸𝐸 𝑘𝑘𝑘𝑘𝑘 = 1 2 𝑚𝑚 𝑣𝑣 2, where m (kg) is the mass and v is the velocity (m/s).
• Heat and work are the only types of kinetic energy from a thermodynamic point of view.
• Energy is the capacity for doing work.
• An energy-efficient system will do a lot of work but an inefficient system will lose a lot of energy as waste heat.
• The laws of thermodynamics allow us to write energy balance reactions and to determine the efficiency of energy systems.
• Heat is the expression of the amount of kinetic energy that the atoms have, representing the energy of motion of atoms.
• A reaction is endothermic or exothermic does not define whether a reaction is spontaneous or not.
• The Second Law of Thermodynamics, stated by Rudolph Clausius in 1854, describes the direction in which all processes spontaneously occur, such as a hot object losing heat to its surroundings.
• The Second Law of Thermodynamics lead to the definition of a new state function called entropy, S, which fundamentally measures disorder.
• The equation for entropy is:
• ΔS = -1 + 2 J/K = +1 J/K, indicating that entropy has increased.
• In fact, the entropy of an isolated system always increases.
• Entropy intuition is a concept explained in the Wonders of the Universe - BBC Two, where Professor Brian Cox builds sandcastles in the Namib Desert to explain why time travels in one direction.
• Entropy is a law of physics that tells us any system tends towards disorder.
• Each mode of motion carries, on average, E = ½kT, where E is energy (J), k is the Boltzman constant (1.38 × 10^-23 m^2 kg s^-2 K^-1), and T is the temperature in Kelvin (K).
• A complex molecule carries more energy than a simple molecule at the same temperature.
• The second law of thermodynamics implies that there will always be some waste heat.
• The most efficient heat engine is called the Carnot engine, which efficiency is determined by the absolute temperature of the surroundings.
• The theoretical heat engine operates between two heat reservoirs, one at temperature TH and the other at temperature Tc.
• An amount of heat energy qh is transferred from the hot reservoir to the heat engine.
• The engine does work w on and rejects an amount of waste heat qc to the cold reservoir.
• The efficiency of this engine is the ratio of work delivered by the engine to the amount of heat energy taken from the hot reservoir.
• The most efficient heat engine that could possibly operate between the two heat reservoirs is the Carnot engine.
• Modern boilers can run at temperatures as high as 600 ° C.
• Environmental restrictions limit condenser water temperature to about 20 ° C.
• The best expected efficiency is 66 %.
• A real power plant has losses in energy due to hot stack gases, evaporation, friction losses, etc.
• The best plants so far have been hovering around 40 % efficiency.
• Nuclear plants have material constraints that force them to operate at somewhat lower temperatures than fossil plants and have efficiencies around 33 %.
• For every 3 units of energy entering the average thermal power plant, approximately 1 unit is converted to electricity and 2 units are rejected to the environment as waste heat, divided between stack gases (≈10%) and cooling water (≈57%).
• Most states restrict thermal discharge so that the rise above ambient stream temperature levels will be equal to less than 1 ° C.
• The first law of thermodynamics, developed around 1850 by Rudolf Clausius, concerns energy changes and leads to the definition of a new state function called enthalpy.
• The second law of thermodynamics, described in 1854 by Clausius, describes the direction in which all processes spontaneously occur, such as a hot object losing heat to its surroundings.
• The second law of thermodynamics leads to the definition of entropy, which fundamentally measures disorder.
• The first law of thermodynamics, also known as the law of conservation of energy, states that energy can neither be created nor destroyed, merely changed from one form into another.
• The first law of thermodynamics defines thermodynamic energy or internal energy for a thermodynamic system.
• 1 cal → 1 g H 2 O × 1 ° C = quantity of energy, 1 cal = 4.18 Joules, “Dietary” cal = 1 kcal = 1000 cal, Watt = rate of energy flow or energy per unit time (Joules/second), 1 KWh = 1KW × 1h = 1000 J/s × 3600 s = 3.6 × 10^6 J or 3.6 MJ.
• Every system possesses an internal energy, U.