Introduction to Thermodynamics

Introduction to Thermodynamics
Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Introduction to Thermodynamics Project Lead The Way, Inc. Copyright 2010

Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms The study of the effects of work, heat flow, and energy on a system Movement of thermal energy Engineers use thermodynamics in systems ranging from nuclear power plants to electrical components. Thermodynamics is the study of the effects of work, heat, and energy on a system. Put another way: nothing happens without heat flow. Thermodynamics is the study of heat flow (thermo – heat dynamics – movement) Physicists talk of heat flowing like a fluid. What is a thermodynamic system? A thermodynamic system is a part of the physical world as described by its thermodynamic properties such as temperature, volume, pressure, concentration, surface tension, and viscosity. All of these things combine to tell us about the thermodynamic state of a system. The system is the object of interest. The surroundings are everything else. For example, in a car, the system could be the engine burning gasoline. The surroundings would be the pistons, radiator, exhaust system, etc. SYSTEM SURROUNDINGS BOUNDARY Project Lead The Way, Inc. Copyright 2008

Thermal Energy versus Temperature
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Thermal Energy is kinetic energy in transit from one object to another due to temperature difference. (Joules) Temperature is the average kinetic energy of particles in an object – not the total amount of kinetic energy particles. (Degrees) If a 100 gram mass is at the same temperature as a 200 gram mass, the average kinetic energy of the particles in both masses is the same. However, the total amount of kinetic energy in the 200 gram mass is twice the amount in the 100 gram mass. Heat is the energy transferred from one object to another due to temperature differences. Heat does NOT like differences. It tries to even out any differences. We can only talk about heat in terms of a change in energy. Heat/energy flows from hot to cold. Temperature is a measure of how fast molecules are vibrating. Temperature #1 Temperature #2 Heat Project Lead The Way, Inc. Copyright 2008

Temperature Scales Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Scale Freezing point of water Boiling point of water Celsius 0°C 100°C Fahrenheit 32°F 212°F Kelvin 273K 373K Matter is made up of molecules in motion (kinetic energy) An increase in temperature increases motion A decrease in temperature decreases motion Absolute Zero occurs when all kinetic energy is removed from a object 0 K = -273° C Project Lead The Way, Inc. Copyright 2008

Thermodynamic Equilibrium
Introduction to Thermodynamics Principles Of Engineering Unit 1 – Lesson 1.3 Energy Applications Thermal equilibrium is obtained when touching objects within a system reach the same temperature. When thermal equilibrium is reached, the system loses its ability to do work. (Touching objects) Zeroth Law of Thermodynamics: If two systems are separately found to be in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other. (Not touching objects) There are four laws of thermodynamics. Zeroth Law (Thermodynamic Equilibrium): The law states that if two systems are separately found to be in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other; that is, all three systems are at the same temperature. Put another way: There is not heat flow between objects if those objects have the same temperature. This seems obvious but it’s purpose is to verify that temperature is a valid indicator for thermal equilibrium for systems not in contact with each other. Object #2 Object #3 Object #1 (Thermometer) Object #1 Object #2 Project Lead The Way, Inc. Copyright 2008

Thermal Energy (heat) Transfer
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms The transfer or movement of thermal energy Four types of transfer Evaporation Convection Conduction Radiation 100% efficiency is unattainable ALL processes are irreversible Evaporation: Students dip fingers into rubbing alcohol and shake them. Evaporation is a cooling process. Molecules of a liquid are in motion over a statistical velocity range. Some go fast enough to leave the liquid and if they are going fast enough, they stay gone from the liquid and the molecule is added to the air around the liquid. These escaping molecules take their energy with them – thus a cooling process. Radiation: The process by which energy is transmitted through a medium, including empty space, as electromagnetic waves. This energy travels at the speed of light. This is also referred to as electromagnetic radiation (EM radiation). One of the most common examples of this is the heat transferred from the Sun to the Earth. Radiation from the sun means we can live. Other examples are microwave ovens, campfires. All bodies radiate energy. However, the net exchange is from hot objects to cold objects. Even a cold object is radiating. How much it is radiating depends on its temperature. An object has to be over 1000Kelvins to radiate in the visible range of the electromagnetic spectrum and you get a red glow. Over 1700Kelvins and you get a white glow from the object. When an object maintains the same temperature it means it is absorbing and emitting the same amount of radiation. Convection: Heat transfer via bulk movement of a fluid or gas. Process by which the warmer part of the mass will rise (less dense) and the cooler portion will sink (more dense). If the heat source is stationary, convection cells may develop as the rising warm fluid cools and sinks in regions on either side of the axis of rising. Put another way: Convection is the transfer of heat energy occurring by a movement of currents; this typically occurs in a gas or liquid state. Fluid: magma in side the earth Plasma: convection zone of the sun gas: ocean breezes because the earth cools and heats more quickly than the water. Conduction: Heat transfer via contact between two different masses. If one of the two masses is hotter, it’s molecules are vibrating fasters, they collide with slower moving molecules of the lower temperature mass and transfer some of their energy to them. Once again, heat is flowing from a high temperature to a low temperature. This transfer of heat works better in solids than liquids. Put another way: Conduction is the transfer of heat by the movement of warm matter. For example, a metal spoon placed in a hot cup of soup will feel warm to your hand because the heat from the soup is conducted through the spoon. Examples of good thermal conductors: metals (more free electrons to move around more easily and collide and conduct heat more easily. Examples of good thermal insulators: wood, cloth (less free electrons to move around and collide. Gasses are good thermal insulators because their molecules are farther apart so less collisions so less heat transfer. Project Lead The Way, Inc. Copyright 2010

Convection Occurring in the Sun

Thermal Energy Transfer
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Convection The transfer of thermal energy by movement of fluid (liquid or gas) When fluid is heated, it expands, becomes less dense, and rises. Boiler heating systems circulate heat throughout a home without pumps through the use of convection. Convection: Process by which, in a fluid being heated, the warmer part of the mass will rise and the cooler portion will sink. If the heat source is stationary, convection cells may develop as the rising warm fluid cools and sinks in regions on either side of the axis of rising. Put another way: Convection is the transfer of heat energy occurring by a movement of currents; this typically occurs in a gas or liquid state. Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Conduction The transfer of thermal energy within an object or between objects from molecule to molecule A metal spoon placed in a hot cup of soup will feel warm to your hand. The heat from the soup is conducted through the spoon. Conduction: The transfer of heat within an object or between objects by molecular activity, without any net external motion. This transfer of heat works better in solids than liquids. Put another way: Conduction is the transfer of heat by the movement of warm matter. For example, a metal spoon placed in a hot cup of soup will feel warm to your hand because the heat from the soup is conducted through the spoon. ©iStockphoto.com Project Lead The Way, Inc. Copyright 2008

1st Law of Thermodynamics
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Law of energy conservation applied to a thermal system Thermal energy can change form and location, but it cannot be created or destroyed. Thermal energy can be increased within a system by adding thermal energy (heat) or by performing work in a system. First Law of Thermodynamics (Conservation of Energy): The law that heat is a form of energy, and the total amount of energy of all kinds in an isolated system is constant. It is an application of the principle of conservation of energy. The internal energy of a system changes from an initial value to a final value due to heat and work. When work and heat are involved in a process, the internal energy of the substance can change. The internal energy depends only on the state of a system, not on the method by which the system arrives at the given state. The energy entering a system must equal the energy leaving the system. Project Lead The Way, Inc. Copyright 2008

1st Law of Thermodynamics
Introduction to Thermodynamics 1st Law of Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Example: Using a bicycle pump Pumping the handle results in what? Applying mechanical energy into the system Mechanical energy is converted into thermal energy through friction (the pump becomes hot) The total increase in internal energy of the system is equal to what? The applied mechanical energy ©iStockphoto.com Project Lead The Way, Inc. Copyright 2008

2nd Law of Thermodynamics
Introduction to Thermodynamics 2nd Law of Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Thermal energy flows from hot to cold When you touch a frozen pizza with your hand, thermal energy flows in what direction? Hand → Pizza ©iStockphoto.com 2nd Law: Heat flows spontaneously from a substance at a higher temperature to a substance at a lower temperature and does not flow spontaneously in the reverse direction. Connected Physics Video on heat engine here. A heat engine is any device that uses heat to perform work. It must have three features to be a heat engine. Heat is supplied to the engine at a relatively high input temperature from a place called the hot reservoir. Part of the input heat is used to perform work by the working substance of the engine, which is the material within the engine that actually does the work. The remainder of the input heat is rejected to a place called the cold reservoir, which has a temperature lower than the input temperature. For a heat engine, you want to maximize efficiency by producing a large amount of work for as little input heat as possible: When you touch a cooked pizza with your hand, thermal energy flows in what direction? Pizza → Hand ©iStockphoto.com Project Lead The Way, Inc. Copyright 2008

2nd Law of Thermodynamics
Introduction to Thermodynamics 2nd Law of Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Entropy is the measure of how evenly distributed heat is within a system. - A system tends to go from order to disorder Order Disorder A general statement of the idea that there is a preferred direction for any process. This law deals with the variable called entropy: the function of the state of a thermodynamic system whose change in any differential reversible process is equal to the heat absorbed by the system from its surroundings divided by the absolute temperature of the system. Put another way: Entropy is a measure of how evenly distributed heat is within a system. As energy changes forms it’s usefulness decreases. The best way to think about entropy is to say it is a measure of disorder, or the amount of unusable energy in a system. You can’t put an egg back together once you cracked it open. If you beat the egg, you can’t unbeat it. You can’t reverse the direction of stirring and have it go back to how it was. Or, if you gather all the smoke, ash, wood, etc from a fire, you can’t put it back together. Hard to put back together = high entropy. So disorder is increasing in the world so less available/usable energy. Firewood has low entropy (molecules in order) when stacked and high entropy when burning (molecules in disorder). The total amount of energy in the world does not change, but the availability of that energy constantly decreases. Project Lead The Way, Inc. Copyright 2008

Thermal Energy Transfer Equations
Introduction to Thermodynamics Thermal Energy Transfer Equations Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms The SI unit of heat is the Joule. However, lots of times, heat is presented as calories/kilocalories. Especially since these have actual definitions in the physical world: 1Kilocalorie = 1C = the amount of heat needed to raise the temperature of 1 kg of water by 1° C – specifically from 14.5 to 15. 5°C. (pressure of 1atm). 1 calorie = 1c = the amount of heat needed to raise the temperature of 1 g of water by 1°C specifically from 14.5 to 15.5°C. For completeness (and with a big sigh) BTU (British Thermal Unit): The amount of heat needed to raise the temperature of 1 lb of water by 1°F specifically from 63 to 64°F. Conversion Factors: 1BTU = 252c=.252C 1C = 4186J = 4.19 KJ 1c = 4.186J How much the temperature of something changes as heat is added depends on the properties of that material. Given the same mass and the same about of energy added, the material will react very differently in terms of temperature change. This is one of the tiles from the space shuttle. It is built to withstand 2300°F. This equation tells us the amount of heat required to change the temperature of a substance: NOTE that this is for a liquid or a solid. We aren’t going into gas laws but this equation doesn’t work for gasses. Q = mC∆T heat is mcat Q – heat required M – mass C – specific heat constant for a given material T – temperature Implications: Greater C means more energy to change its temperature. +Q energy has been added to the system and you have a temperature increase. -Q energy has been taken from the system and you have a temperature decrease Calorimeter: measures the Q Show connect ed physics video on colorimeter. We could do this with all our food if we really wanted to know how many Calories we ate – but then we couldn’t eat the food. Project Lead The Way, Inc. Copyright 2008

Thermal Energy Transfer Equations
Introduction to Thermodynamics Thermal Energy Transfer Equations Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms P = delta Q/delta t Draw arrow from first formula to second k constant for the material – big k is easily transfer energy so good conductor This is for conduction, steady state heat transfer. Use this for heat transfer through a wall if the wall is uniform. Project Lead The Way, Inc. Copyright 2008

Calculating Energy Transfer
Introduction to Thermodynamics Calculating Energy Transfer Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Calculate the energy transferred when a block of aluminum at 80.0°C is placed in 1.00 liter (1kg) of water at 25.0°C if the final temperature becomes 30.0°C. Q Step 1. List all known values Mass of water = mwater = 1 kg 4184 Specific heat capacity of water = cw= change in temperature = ΔTwater = 30.0°C – 25.0°C = 5.0°C 900. cAl = change in temperature = ΔTAl = 80.0°C – 30.0°C = 50.0°C Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Step 2. List all unknown values Q = energy transferred mAl = mass of the Al block Step 3. Select equations to solve unknown values Step 4. Solve for Qwater Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Calculating Energy Transfer Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Calculate the energy transfer in a wall section measuring 2m by 1m by 0.04m thick with a thermal conductivity of Opposing sides of the wall section have a temperature of 10°C and 5°C after one hour. Q Step 1. List all known values Area of thermal conductivity = A = 2m * 1m = 2m2 k =0.10 Thermal conductivity = Thickness of material = L = 0.04m Difference in temperature = ΔT = 10°C - 5°C = 5°C Change in time = Δt = 1 hour = 3600s Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Step 2. List all unknown values P = Rate of energy transfer Q = Energy transfer Step 3. Select equations to solve unknown values Step 4. Solve in terms of Q Step 5. Combine equations Project Lead The Way, Inc. Copyright 2008

U-Value Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Coefficient of Heat Conductivity The measure of a material’s ability to conduct heat Draw lines from metric to equivalent customary: P – power = energy/time in watts (W) or BTU/hr A – area involved = meter squared or feet squared T – Change in temperature = Celcius for metric/Farenheit for customary. To convert: Tc = (5/9)*(Tf-32); Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit Tf = (9/5)*Tc+32; Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit Metric system U.S. customary system Project Lead The Way, Inc. Copyright 2008

R-Value Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Thermal Resistance of a Material The measure of a material’s ability to resist heat The higher the R-value, the higher the resistance The R-value is equal to the reciprocal of a material’s U-value. Bulk R-value = R-value Object 1 + R-value Object 2 + … = Total R-Value Project Lead The Way, Inc. Copyright 2008

Calculating R-Value Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Determine the R-value of the wall cavity below 1 in. foil-faced polyisocyanurate (R=7.20) Fiberglass batt (R=19) 1 in. air space (R=0.17) 5/8 in. drywall (R=0.56) Brick 2 ¼ x 3 ½ x 8 (R=0.8) What is the R-value at a stud location? Wall cavity R-value 0.56 +19.00 + 0.8 0.56 + 0.8 = 27.7 =15.6 2x6 construction (2x6 R=6.88) Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Thermal Energy Transfer Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Radiation The process by which energy is transmitted through a medium, including empty space, as electromagnetic waves Stefan’s Law All objects lose and gain thermal energy by electromagnetic radiation. ©iStockphoto.com Electromagnetic waves transfer to food and other matter Radiation: The process by which energy is transmitted through a medium, including empty space, as electromagnetic waves. This energy travels at the speed of light. This is also referred to as electromagnetic radiation (EM radiation). One of the most common examples of this is the heat transferred from the Sun to the Earth. Stephan’s Law tells the rate at which an object radiates energy: P = σAe(Ts4 – T4) Units of watts, J/s σ – Stephan boltzman constant: x 10-8 A – surface area of the object e – emissivity based on material Dark material are close to 1 and shiny material are close to 0. Ts – temperature of surroundings T – temperature of object Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Thermal Energy Transfer Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Prior to dressing for school, a student watches the morning weather to decide what clothes to wear. The bedroom is 65ºF and the student’s skin is 91.4ºF. Determine the net energy transfer from the student’s body due to radiation transfer during the 15.0 minutes spent watching the morning weather. Note: Skin emissivity is 0.90, and the surface area of the student is 1.30m2. Step 1. List all known values Area Emissivity constant Stefan’s constant Bedroom temperature Skin temperature Change in time ©iStockphoto.com Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Thermal Energy Transfer Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Step 2. List all unknown values P = Rate of energy transfer Q = Energy transfer ©iStockphoto.com Step 3. Select equations to solve unknown values Step 4. Apply known values to The equal sign with the dot over it indicates rounding. Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Step 4 (continued). Apply known values to Step 5. Combine equations and solve ©iStockphoto.com 93,500J of energy are transferred from the student’s body during the 15 minutes spent watching the morning weather. Project Lead The Way, Inc. Copyright 2008

Third Law of Thermodynamics
Absolute zero/heat flow. It is impossible to reach a temperature of absolute zero.

Applications of Thermal Energy
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Solar thermal energy and geothermal energy are just a few applications of thermal energy in general. Solar thermal energy is used to heat water in homes or buildings, swimming pools, and space heating for buildings. Passive thermal energy means that no mechanical equipment is required, much like the interior of a car heating up in the summer. Active thermal energy requires a mechanical device called a heat collector to absorb the heat for circulation purposes. Some basic types of concentrating heat collectors are: Parabolic trough: These troughs consist of a heat transfer fluid that circulates throughout the absorber tubes shown above. These tubes then pass the heated fluid to a central location where it is used to generate steam. The steam is transferred to a turbine or generator which uses the steam to produce power or electricity. Parabolic dish: This dish contains an engine system that converts the collected heat into mechanical power. There is a heat transfer fluid that is a part of the engine system. This fluid is compressed when cold, heated after being compressed, and then processed through a piston which produces a desired work. Power tower: The mirrors surrounding the tower rotate to continuously focus the sunlight onto a receiving panel at the top of the tower. The receiver panel (appears as a bright light in the image above) contains a fluid inside of it that is used to collect heat from the sunlight. Photovoltaic (PV) cells: These heat collectors convert sunlight into electricity to run small equipment by creating a direct current (DC). PV cells generate electricity for businesses with an additional step. The grids that collect the DC current from the PV cells must then send the power to inverters to convert the direct current (DC) into an alternating current (AC). Project Lead The Way, Inc. Copyright 2008

Examples of Solar Energy
Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Image #1: This is an example of how a pool is heated in Oregon using solar heat collectors. Image #2: This is an example of how solar energy can be used to maintain a consistent level of illumination within a room. Lens collectors and reflective light piping is used to control the lighting within a large research facility. Image #3: This is an example of a school that is using evacuated tubes as a solar water heating collector. Image #4: This is an example of both active and passive heat collection used in Arizona. This house has large windows facing the south and has a greenhouse, both of which allow for a passive means of warming rooms of the house. This house consists of a rooftop solar water heater and reflective windows that serve as an active means of warming or cooling the house. All images were obtained from the following URL: Project Lead The Way, Inc. Copyright 2008

Geothermal Energy Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Energy generated from the thermal energy stored beneath the Earth’s surface Also refers to the heat that is collected from the atmosphere; for instance, near the oceans Geothermal energy refers to the energy generated from the heat that is stored beneath the Earth’s surface. It also refers to the heat that is collected from the atmosphere; for instance, near the oceans. The United States maintains the largest geyser geothermal plants in the world. The first image is of an ordinary geyser and the second image is of the West Ford Flat Geothermal Cooling Tower. This tower is part of The Geysers, which is the largest geothermal power plant in the world. Project Lead The Way, Inc. Copyright 2008

Resources Introduction to Thermodynamics Principles Of EngineeringTM Unit 1 – Lesson 1.2 Energy Forms Energy Information Association. (n.d.). Energy kid’s page. Retrieved March 23, 2008, from McGraw-Hill dictionary of engineering. (2nd ed.). New York, NY: McGraw-Hill. NASA. (2008). Glenn research center. Retrieved March 23, 2008 from National Renewable Energy Laboratory. (2007). TroughNet. Retrieved March 23, 2008, from U.S. Department of Energy. (2008). Solar energy technologies program. Retrieved March 23, 2008, from Project Lead The Way, Inc. Copyright 2008

Introduction to Thermodynamics

Similar presentations

Presentation on theme: "Introduction to Thermodynamics"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Introduction to Thermodynamics

Similar presentations

Presentation on theme: "Introduction to Thermodynamics"— Presentation transcript:

Similar presentations

About project

Feedback