Conservation of Energy First Law of Thermodynamics ENGR302I

True or False? Energy is conserved, only if no friction is present. Energy can be converted from one form to another. Work can be entirely converted to heat and vice versa. An ideal heat engine that works with no friction is 100% efficient. Construction of a time machine, although possible, must wait a very long time. ENGR302I

Thermal Energy What is heat? Energy Conversion Efficiency Applications Heat and Temperature Energy Conversion Conservation of Energy (1st Law) Availability of Energy (2nd Law) Efficiency Applications ENGR302I

Nature of Heat Historical Perspective Heat and Temperature Aristotle (Phlogiston) Lavoisier (caloric) William Thompson (motion) Heat and Temperature ENGR302I

Temperature Conversion Temperature Conversion Formula Following are the temperature conversion equations for converting degrees centigrade (C), fahrenheit (F), and kelvin (K). F = 1.8 C + 32 (1) C = (F – 32) / 1.8 (2) K = C + 273 (3) ENGR302I

Modes of Heat Transfer Conduction Convection Radiation Transfer of heat from molecule to molecule Convection Transfer of heat by bulk motion Natural vs. Forced Convection Radiation Transfer of heat by electromagnetic waves. Unlike conduction and convection, radiative heat transfer requires no medium. ENGR302I

Electromagnetic Spectrum ENGR302I

First Law of Thermodynamics Historical Perspective Richard Meyer Kelvin Joule Energy Conversion First law efficiency ENGR302I

Energy Conversion Devices EXAMPLES OF DIFFERENT KINDS OF ENERGY CONVERSIONS FROM/TO MECHANICAL THERMAL CHEMICAL ELECTRICAL LIGHT Bicycle Friction Bomb Wind generator Sparks Heat Engines Heat exchanger Pyrolysis Thermo-couple Luminescence   Rockets Food Metabolism Fuel cell/ Battery Candle Electric Motor Resistor Electrolysis Transformer Light bulb Galvanometer Solar collector Photosynthesis Solar cell Fluorescence ENGR302I

Availability of energy Second Law of Thermodynamics ENGR302I

Second Law of Thermodynamics Natural Direction and Arrow of Time Entropy Consequence of the Second law Heat cannot, by itself flow from a low to a high temperature Work can be completely converted to heat. But heat cannot be completely converted to work. ENGR302I

Why work is more valuable than heat? True or false: Which one is better? An electric heater or a gas heater? True or false: Which one is better? A gas hot water heater or a solar water heater? ENGR302I

A very simple heat engine A very simple heat engine. The air in (B) has been heated, increasing the molecular motion and thus the pressure. Some of the heat is transferred to the increased gravitational potential energy of the weight as it is converted to mechanical energy.

Heat Engines A heat engine is any device that uses heat to perform work. No real engine can have an efficiency greater than that of a Carnot engine when both engines work between the same two temperatures. ENGR302I

Claims, Lies and bigger lies An engine manufacturer makes the following claims: The heat input of the engine is 9 kW at 375 K. The heat output is 4 kW at 225 K. Do you believe these claims? hactual = 1 - Qc/Qh = 1- 4/9 = 0.56 Hideal = 1 - Tc/Th = 1 - 225/375 = 0.4 ENGR302I

Living Organisms A living organism is an example of a heat engine which transforms light energy into chemical energy ENGR302I

Hurricane A hurricane is an elegant example of a natural Carnot heat engine. It draws heat from the ocean, releases some of it to the atmosphere via radiative cooling, and does work during this process. ENGR302I

True or false: Heat can never flow from a cold reservoir to a hot one. ENGR302I

True or false: A perfect engine produces no thermal pollution. ENGR302I

Basic Elements of a Heat Engine ENGR302I

Thermal Devices Internal Combustion Engines Gasoline, diesel, and gas turbine Refrigerator, Air Conditioners, and Heat Pumps Thermal Powerplants ENGR302I

Thermal Power Plants ENGR302I 1-2 Steam Turbine: High temperature, high pressure steam is expanded in a turbine. Work is produced in form of the shaft work. Turbine usually runs a generator to produce electricity, 2-3 Condenser: The output of the turbine is low temperature steam capable of doing little work. Steam is cooled in a condenser to liquid water, ready to be recycled to start another loop. 3-4 Feed Water Pump: Work is needed to pressurize water to the boiler pressure. 4-1 Boiler: Water is boiled and eventually heated to superheated steam. Fossil fuel, nuclear or other types of fuel can be used as a source of heating. ENGR302I

Power Plant Operation (II) According to the second law of thermodynamics, the higher the boiler pressure (temperature), and the lower the condenser temperature, the higher is the efficiency of the power plant. ENGR302I

Power Plants Gasoline Engines Diesels Jet Engines How does it work? Power Plants Gasoline Engines Diesels Jet Engines Refrigerators and A/C Heat Pumps ENGR302I

How does a refrigerator work? ENGR302I

If you leave your refrigerator door open, the temperature in the room will be... Higher Lower The same ENGR302I

How does a heat pump work? ENGR302I

True or False? Energy is conserved, only if no friction is present. Energy can be converted from one form to another. Work can be entirely converted to work and vice versa. An ideal heat engine that works with no friction is 100% efficient. Construction of a time machine, although possible, must wait a very long time. ENGR302I