Although I’m an Principle of Work. We’ll work with his today, and we’ll introduce a unit of measurement used to quantify formula known as the work .Newton , that is, the amount of dynamic energy available to influence the movement of an object, and is calculated by the formula,work
where .Newton In the image below, was obtained by way of direct personal experience working in my own garden. I’ve found that it takes approximately 40 pounds of force to push a wheelbarrow loaded with dirt across level ground. Because one pound of force is equal to 4.45 NewtonsNewtons the amount of force I exerted is expressed as,,[40
If 178 performed is expressed as,work
Next time we’ll explore the special relationship between .workCopyright 2015 – Philip J. O’Keefe, PE Engineering Expert Witness Blog ____________________________________ |

## Posts Tagged ‘energy’

### de Coriolis’ Formula to Compute Work and the Newton

Sunday, November 29th, 2015### How Condensers Increase Efficiency Inside Power Plants

Wednesday, December 4th, 2013
Last time we ran our basic power plant steam turbine without a condenser. In that configuration the steam from the turbine exhaust was simply discharged to the surrounding atmosphere. Today we’ll connect it to a condenser to see how it improves the turbine’s efficiency. As discussed in a previous blog, enthalpy his,_{1 }
If the condenser vacuum exists at a pressure of 0.6 PSI, a realistic value for a power plant condenser, then referring to the steam tables in the Van Wylen and Sonntag thermodynamics book, we find that the enthalpy
and the amount of useful work that the turbine can perform with the condenser in place would therefore be,
h1474 BTU/lb – 847 BTU/lb = 627 BTU/lb_{2} = So essentially with the condenser present, the work of the turbine is increased by 168 BTU/lb (627 BTU/lb – 459 BTU/lb). To put this increase into terms we can relate to, consider this. Suppose there’s one million pounds of steam flowing through the turbine each hour. Knowing this, the turbine power increase,
Now according to
A typical automobile has a 120 HP engine, so this equation tells us that the turbine horsepower output was increased a great deal simply by adding a condenser to the turbine exhaust. In fact, it was increased to the tune of the power behind approximately 550 cars! What all this means is that the stronger the vacuum within the condenser, the greater the difference between h will be. This results in increased turbine efficiency and work output, as evidenced by the greater numeric value for _{2}W. Put another way, the turbine’s increased efficiency is a direct result of the condenser’s vacuum forming action and its recapturing of the steam that would otherwise escape from the turbine’s exhaust into the atmosphere.This wraps up our series on the power plant water-to-steam cycle. Next time we’ll use the power of 3D animation to turn a static 2D image of a centrifugal clutch into a moving portrayal to see how it works. ________________________________________ |

### Enthalpy and the Potential for More Work

Monday, November 18th, 2013
Last time we learned how enthalpy is used to measure heat energy contained in the steam inside a power plant. The higher the steam pressure, the higher the enthalpy, and vice versa, and we touched upon the concept of Let’s revisit the equation introduced last time, which allows us to determine the amount of useful work output:
h_{2} Applied to a power plant’s water-to-steam cycle, enthalpy As for enthalpy Next week we’ll see how the condenser, and more specifically the vacuum inside of it, sets the platform for increased energy production, a/k/a
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### Vacuum in a Power Plant Condenser

Tuesday, November 5th, 2013
Last time we discussed the key functions of the make-up valve in the power plant water-to-steam cycle. Today we’re going to talk about a As discussed previously, the condenser is a piece of equipment that turns turbine exhaust steam back into water. The water that’s formed during this process is known as condensate, and its density is higher than that of the steam it shares space with inside the condenser. That difference in density is what creates the vacuum inside the condenser vessel. Put another way, the increase in density along with the condenser’s airtight design prevent air from rushing in from outside to occupy any of the space inside the condenser, a desirable condition from an efficiency standpoint. But to understand how all this works we’ll first have to gain an understanding of what is meant by The huge difference in their volumes is due to the fact that steam contains more than five times the heat energy that unheated water does. That energy makes the molecules in a cloud of steam more active, causing them to collide against each other with great force, spread apart, and occupy a larger space. If you’re wondering what change in density has to do with vacuum in the condenser, allow me to offer an analogy. Ever canned any produce, like tomatoes, in glass jars to over-winter? Not likely, as this once common survival tactic has nearly become a lost art. But the vacuum created inside the condenser is much like the vacuum created within a mason jar during canning. Inside the glass mason jar, a small space is intentionally left between the tomatoes and lid. During the process of boiling, or heat sterilization, this space fills with steam. Then during cooling the trapped steam condenses into water. This condensation creates the vacuum that sucks down on the jar’s lid, giving it an airtight seal, a condition which won’t allow bacteria to grow on our canned foods. You see, like us bacteria need oxygen to live, but thanks to the vacuum inside our cooked mason jar no air containing oxygen will remain inside to harbor it. Next time we’ll continue our discussion on vacuum to see how it’s used to increase a steam turbine’s efficiency.
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### Wire Size and Electric Current – Joule Heating

Sunday, March 20th, 2011 Ever take a peek inside the toaster while you’re waiting for the toast to pop up? If so, you would have noticed a bright orange glow. That glow is produced when the toasting wires heat up, which in turn creates a nice crusty surface on your bread or waffle. It’s the same phenomenon as when the filament inside an incandescent bulb glows. The light and heat produced in both these cases are the result of the Joule, pronounced “jewel,” effect at work.
To understand Joule heating, let’s first refresh our memories as to electrical current resistance. We learned previously that wire is not a perfect conductor, and as such resistance to flow is encountered. This resistance causes power to be lost along the length of wire, in accordance with this equation: Power Loss = I Where Anyway, to see how the equation works, let’s look at an example. Suppose we have 12 feet of 12 AWG copper wire. We are using it to feed power to an appliance that draws 10 amperes of electric current. Going to our handy engineering reference book, we find that the 12 AWG wire has an electrical resistance of 0.001588 ohms per foot, “ohm” being a unit of electrical resistance. Plugging in the numbers, our equation for total electrical resistance becomes: R = (0.001588 ohms per foot) × 12 feet = 0.01905 ohms And we can now calculate power loss as follows: Power = I Instead of using a 12 AWG wire, let’s use a smaller diameter wire, say, 26 AWG. Our engineering reference book says that 26 AWG wire has an electrical resistance of 0.0418 ohms per foot. So let’s see how this changes the power loss: R = (0.0418 ohms per foot) × 12 feet = 0.5016 ohms Power = I This explains why appliances like space heaters and window unit air conditioners have short, thick power cords. They draw a lot of current when they operate, and a short power cord, precisely because it is short, poses less electrical resistance than a long cord. A thicker cord also helps reduce resistance to power flow. The result is a large amount of current flowing through a superhighway of wire, the wide berth reducing both the amount of power loss and the probability of dangerous Joule heating effect from taking place. Our example shows that the electric current flowing through the 12 AWG wire loses 1.905 watts of power due to the inconsistencies within the wire, and this in turn causes the wire to heat up. This is Joule heating at work. Joule heating of 50.16 watts in the thinner 26 AWG wire can lead to serious trouble. When using a power cord, heat moves from the copper wire within it, whose job it is to conduct electricity, and beyond, on to the electrical insulation that surrounds it. There the heat is not trapped, but escapes into the environment surrounding the cord. If the wire has low internal resistance and the amount of current flowing through it is within limits which are deemed to be acceptable, then Joule heating can be safely dissipated and the wire remains cool. But if the current goes beyond the safe limit, as specified in the American Wire Gauge (AWG) table for that type of wire, then overheating can be the result. The electrical insulation may start to melt and burn, and the local fire department may then become involved. That’s it for wire sizing and electric current. Next time we’ll slip back into the mechanical world and explore a new topic: the principles of ventilation. _____________________________________________ |