MHI Energy 101:  

Please feel free to use the Power and Energy calculator below 

JOULE (J) is the unit of energy in SI units 
WATT (J/s) is a unit for Power 

Entropy has the units of Joules/Kelvin (J/K).

Part 1(a):  Introduction to Energy, Power and Thermodynamics

Power multiplied by the time of use of that power, gives you energy.  The SI unit for energy is Joules (J) and the SI unit for power is Watts (W).  Since a Joule is a very small quantity we use kJ and kW instead.   kJ is the symbol for a Kilo Joule=1000 Joules.  BTU is an alternate unit for energy- the letters stand for British Thermal Units. For quick conversion purposes it is useful to remember that that 1 kJ is approximately equal to a BTU (more accurately 1BTU=1.054 kJ). The amount of useful (or usable) energy of an energy source is measured relative to a base state.   A base state could be room temperature and one atmospheric pressure, but you can choose your own base state because the energy change does not depend on any particular base state. 

If we were looking to convert between units of power then the conversion is 1kW= 0.2931 BTU/hr.  When you pay your electric bill you pay for “units” (an electric company nomenclature) which stands for 1kW.hr (a measure of energy) = 3.6 Million Joules.  In the US we approximately pay 8-12 cents (US) per unit.  The calculator(s) below will help you to convert energy from one type of unit to another and if you know the time over which the energy is delivered, it will allow you to calculate the power (i.e. the (energy-used)/time).  Note that the word unit is now used in a more scientific sense.  You can do more with the calculator.  If you wanted to get a feel for the amount of energy used in terms of equivalent amount of gasoline burnt, or in terms of how much ice the same energy could melt, you can do that too; so have fun while familiarizing yourself with the calculator!

Often, a common mistake is to confuse BTU (energy) and BTU/hr (power) by people especially in the gas-heating field.  So be careful. When you pay for a device that converts one form of energy into another form, the device cost is most often related to the power rating (e.g. kW or BTU/hr).  A new high-power car will cost you more than a new low-power car!  Capital cost (the cost of equipment) is linked to its power rating and the running cost is linked to amount of energy used.  For various historical reasons we use many different symbols for power and energy.   

Recap:  We often encounter power and energy in our daily lives.  Power is oomph!  Power is the amount of energy that is converted in a unit of time.  Generally speaking, power is the rate at which you can do something, e.g. higher power can make an automobile accelerate faster, make a reaction go faster, produce more, and so on.    When we use energy in one form and convert it to another form, most often we also pay for the device which converts the energy depending on our objective.  Cars, refrigerators, heaters, and motors are often priced by their horsepower (power); light bulbs are often priced by their output watts (power).  We also pay for the energy input whether it is a material or just electrons.  Natural gas is priced by its combustible energy content namely therms (energy) and of course the supply-demand situation of the gas; electricity by kilowatt-hours (energy).  Temperature conversion devices are also priced by their power (examples are Airtorches); Furnaces are priced by KiloWatts (power) and their temperature capability in Kelvin (K); and air conditioners by tons or BTU's per hour (again power).  Expect to pay a little more when you are looking for a higher power equipment!  Or expect to earn more when delivering products or service with a high-power high-productivity device.   When you purchase an energy conversion device, let’s say one that converts electrical energy to thermal energy (e.g. a GlowPanel or Thermoplate), the device will often be rated by its "power".  This number enables you to calculate how much energy you will use by simply multiplying the rated power by the hours (or fraction of hours) used.  When using electric power the commonly used units of energy are kilowatt-hours. Each electric unit that you pay for is normally one kilowatt-hour (also called one unit).  When you pay for units, your US electric utility bill shows the price for the kWh (units), which you have used during normal usage and the price for units used in a "demand penalty" condition (peak hour use).  You should always carefully watch this penalty number and contact your electric utility provider to find ways for reducing the "penalty" charge.   This is why energy efficiency is important to you.   Devices like Airtorches or MHI steam devices are highly power-transfer efficient. 

Thermodynamics:  Thermodynamics is an evolving science that deals with energy, power, shapes, reactions, and phases.  It may be the most important subject that you should learn about, one that is used across multiple disciplines from propulsion, information exchange, materials science to climatology.  The science of thermodynamics is concerned with issues like energy and other variables that define the direction of any spontaneous process.  Thermodynamics also enables you to understand whether equilibrium conditions exist both in your system and when the system interacts with the surroundings.   Equilibrium simply means that there are no net mechanical or chemical forces on your system (or on an atom in your system should you want to break substances down to the level of atoms).  The internal equilibrium of a system implies that the intensive variables such as pressure and temperature are the same at every point in the system.   Of course, in classical thermodynamics we assume the continuum of the substance (i.e. the density) is unchanged regardless of how finely we divide the system. 

There are many variables that one learns about in thermodynamics.  Each variable is important as provides important information on how energy may be used in the best manner for an objective.   A thermodynamic variable is one that is always fixed if at least two other thermodynamic variables are fixed for a pure material.    Alternately if we execute a cycle and arrive back at the same pressure and temperature then we arrive back to the same value of all other thermodynamic variable (we are still talking about a pure element or ideal gas as our system).  In thermodynamics we first learn about intensive and extensive variables.  Intensive variables are those that do not change with mass, e.g., Temperature, Density and Pressure.  In contrast Energy, Volume and Entropy are some thermodynamic variables called extensive variables.   By dividing by the mass we change these extensive variables into their corresponding intensive quantities. For a pure material, fixing any two intensive variables fixes the other variables, like energy density or entropy density when at equilibrium.  Intensive variables are those that are measured with devices like thermocouples, pressure gauges and so on.  

When a system is at equilibrium it is deemed to be at a fixed and well defined state (i.e. a state at which all thermodynamic variables are unchanging with time).  In classical thermodynamics a process is one that happens between different states of a system.   A process path is defined as the path taken between two equilibrium conditions.  A change (i.e. a process) happens because the system is pushed out of its complacent equilibrium state by a change in the surroundings. For example, the external temperature could be changed which pushes the system to respond to the change and establish a new equilibrium state.   In thermodynamics, we  are often concerned with the changes in the equilibrium values of the variables between states (i.e. after a process has taken place).   Classical thermodynamics does not deal with an on-going process except to establish that the change in state could have been brought about by the measurable (quantifiable) exchange of heat or work or mass or combinations during the process.  One could have the same change in the state of a system however enabled by different combinations of exchange of heat, mass or work. This is to say that the particular path taken between two known states does not influence the starting or ending equilibrium state. This analogous to saying if we went from Cincinnati to New York, it does not matter which path we took if our objective was solely to go between these towns and we had no other constraints of time, money, route etc.  Like GPS coordinates fix a position, thermodynamic variables fix a particular state.  However as we read on we we be able to develop ideas about efficiency of a process based on the thermodynamic variables and we will learn that some pathways are impossible.

Energy is always conserved and such a conservation law is known as the first law of thermodynamics.  Energy cannot be created or destroyed but it can have different forms such as thermal energy mechanical energy, nuclear energy or chemical energy.  Chemical energy can be exchanged between atoms and elements primarily by electrons i.e. not involving the nucleus of an atom.  Chemical energy is stored in the bonds between atoms.   When there is an exchange of chemical energy between atoms and molecules we call it a chemical reaction.  If the temperatures of the reaction involve very high-energy density interactions, the nucleus gets involved in the exchange and it then becomes a nuclear reaction, which has so much more high-energy density exchange possibilities that it dwarfs any chemical reaction energy.    Above 2,000K-10,000K we begin to encounter nuclear reactions.  A small teaspoonful of nuclear energy can power your car for 100 years when comparing this to the amount of chemical energy (gasoline) we need today!

When you convert energy from one form to another, you create something called entropy.    If you generate new entropy during any process, the process is called irreversible because when you generate entropy you automatically degrade the quality of energy for its useful work potential; therefore, entropy becomes a measure for energy degradation.   Entropy can only be created, never destroyed.   On the other hand, energy can neither be created nor destroyed. Sometimes the entropy production is so small that you could approximate it as reversible (theoretically you can convert mechanical energy to mechanical energy without penalty).  Some electrochemical and photosynthesis processes at short wave lengths are processes where energy is converted to other forms of energy without any significant generation of new entropy.  Thus, these processes are approximated as being close to reversible processes.  This is why Fuel-Cells are important.  Almost no process is really reversible because in real processes you encounter a conjugate flux-force relationship which equals the entropy generation rate density multiplied by the temperature (units of energy rate density).  For example, in the diffusion of atoms, a force called a chemical potential gradient acts on atoms and causes a flux.  All flux-force combinations produce new entropy.   In thermodynamic terms, any gradient in potential (i.e. the difference of a thermodynamic property with distance), including gradients in temperature, composition, height or charge can cause energy or mass to flow spontaneously with a corresponding generation of entropy.   Whenever entropy is generated, the process is called irreversible.  Note that the word irreversible also has the connotations to the directionality of time and heat flow and that neither reversible nor irreversible is inherently good or bad - remember it depends on your objective.  Both time and energy flow "spontaneously", only in a certain direction.  Irreversibility or the production of entropy on the other hand can determine shapes - but we are getting ahead of ourselves (we will encounter this in the MHI 102 Energy Module currently under construction).  Entropy is not conserved; it cannot be destroyed but it can be generated.  Sometimes entropy is also associated with order and work potential (when measured at the same temperature).  You should be aware that entropy can be thermal or configurational, so at the same temperature an object could have different entropies depending on how atoms and molecules are configured although the energy content is the same. When you increase the temperature of an object its thermal disorder increases with temperature as does its energy.  What this really means is that the atoms have more energy because of atomic scale kinetic energy in a gas, or more vibrational energy in a solid.   (Note: Atoms vibrate in a solid approximately 10^13 per second always but the amplitude of vibrations increases with temperature).  In other words, more order is equal to less entropy; more disorder equals higher entropy regardless of the energy content.  When we make such comparisons it is a good idea to compare the values by normalizing the amounts, e.g. energy per unit mass, or per unit mole or per unit volume.  

Almost always any thermodynamic efficiency of interest is always tied to your objective for your process.   If your sole objective is heat transfer then 100% efficiencies are possible.   When you possess energy with the lowest entropy, you possess the most useful form of energy for conversion to work; should work be your objective.  However, the inherent value of the energy (quality) to you depends on what you need it for.  For example, if you are cold and you need heat, your objective is not for an ordered form of energy but more for an increase in body temperature, which is best gained by heat transfer to you from a hotter reservoir.  Similarly many chemical processes require heat for faster process kinetics.   On the other hand, with an automobile, it seems important that you be able to order the energy of the automobile motion in order to stay within a lane!   Of course you could end up creating more disorder in the universe because of a law by Claussius which states that you have to dump some of the heat at a lower temperature in order to obtain work from heat.  The transfer of heat across a temperature gradient is a way to generate new entropy. 

Q: What is Green? 

Answer: By now you can guess that best overall efficiency has something to do with Green.

Using the best energy efficient device is important because you degrade (or waste) the least amount of energy for your objective. Words like Sustainability, Recycling and Green all imply preservation and lowering the wastage of materials and energy.  As energy can neither be created nor destroyed, wasting energy really means degrading it the least, when you use energy.

Q:  What do sustainable innovations mean?

Answer:  The answer will be in MHI module 103 which is currently under construction but for now you could look up recent articles on the web with key words.  For example type-in “US. Energy Activity and Innovation” in your search bar and see what comes up.