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Mechanical Engineering


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Everything posted by dudleybenton

  1. Recent power outages in California before the current fires reveal the weakness of "green" power solutions. While these sound good, in practice they are not resilient and have little reserve, thus falter when stretched. This trend will only worsen. Managing diverse power resources is a rapidly growing field creating jobs. You might want to explore this topic.
  2. Please repost with description. The pdf says "unavailable".
  3. I have seen this same thing many times. The overall surfaces are experiencing typical corrosion, which can be surprisingly difficult to prevent. The more extreme spots (especially the ones circled) were initiated by handling (bumped, scraped, dinged). The less extreme spots arise from debris that is no longer present, but facilitated and concentrated the chemical attach at those locations. These surfaces are not in the least unusual. Preventing this from happening requires considerable diligence and at least one of several available coatings. Note that if you coat a surface and it has any flaw
  4. If you're going to eventually make a living, ditch the Mac and get a Windows laptop. I am no fan of Bill Gates or Windows, but I accept the facts of life as they are. Unless you're going to work for the government or stay in academia, LINUX is also out. The vast majority of engineering software runs on Windows and most businesses circulate documents and spreadsheets created with MSO. There is no need to buy a new machine. Good reconditioned laptops are readily available on the Web for $200. After decades of industrial use, I can also say that Dell laptops significantly outlast all others. [No,
  5. There are many creative designs for cooling chips, especially graphics processors, created by users with available parts. I am surprised that you have not found images of these with a Google search. Try different search patterns and don't give up.
  6. If there is any way you could co-op (work for a company who builds agricultural mechanization devices for several months each year) that would be most enlightening. I know a recent graduate of the university here who has already participated in exciting implementations and has several job offers to choose from. This is a wonderfully productive and growing profession.
  7. I recently spoke to a friend who is hiring young engineers to work at several large power plants needing modernization. He said that the new hires know how to operate battling robots using their iPhone and 3D print useless plastic objects but don't understand thermodynamics or heat transfer. Please prove him wrong by mastering the foundations of industry! This website can help make that possible.
  8. We need more details to address this question. Do you mean an air powered siphon? Do you mean air bubbles rising in a vertical pipe producing an upward movement of the surrounding water? A picture of the device would help.
  9. Two months before my third birthday I changed all the light bulbs on the Christmas tree to be red yellow green red yellow green... I dismantled the radio at age seven and the television at eight. These were the old kind with vacuum tubes and did not survive the process. I rebuilt my first engine at eleven and was working as a professional mechanic by fourteen—before I could drive a car. I have a grandson who is three and destined for the same path. My father didn't know which end of a screwdriver to hold. The engineer gene came from my maternal grandfather.
  10. Fluids above the critical temperature are called "super critical." We sometimes call a liquid above the critical pressure "super critical." For example, in most large coal-fired steam power plants, the feedwater entering the boiler is about 4400 psia (30 MPa). The critical point is where the saturated liquid and vapor are indistinguishable; that is, a distinction is physically meaningless. There are no bubbles formed when boiling a liquid above the critical pressure. This is why you must have special equipment to clean (i.e., "polish") the feedwater in a supercritical coal-fired plant, as the
  11. The seawater probably flowed on the inside of the 90/10 Cu-Ni tubes at about 7 ft/sec (2 m/s), so multiply nD²π/4 to get volumetric flow then by density to get mass flow. You get surface area the same way. The overall heat transfer coefficient, U, is probably about 5 BTU/hr/ft²/ºF (25 W/m²/ºC). The delta-T is probably about 15ºF to 25ºF (8ºC to 14ºC). The specific heat of natural gas is about 0.5 BTU/lbm/ºF (2 kJ/kg/ºC). From that you can calculate the flow rate of natural gas and estimate the heat transfer capacity.
  12. There are several excellent texts on this subject. I always recommend Lindon Thomas' Heat Transfer because he's been a friend for many years. This is a large topic. To get a meaningful answer, you must further qualify your question. What type of heat exchanger? What do you expect it to do? What fluids? What temperatures? What flow rates? Heat exchangers are used for everything from natural gas to peanut butter.
  13. You will find many projects on ResearchGate where graduate students are investigating heat transfer within enclosures with a variety of conditions and fluids. You should be able to find something informative to your particular problem there. The complexity of the solutions varies considerably, so look for something on the level you're interested in pursuing.
  14. While pressure is clearly absolute (i.e., zero has a clear definition), temperature is most often with respect to some state (e.g., minimal crystalline structure). We can readily measure conditions and calibrate pressure instruments on an absolute basis. We don't have the same flexibility with temperature and so we recognize this in our measurements, calculations, and formulations. Also, heat is defined as that form of transient energy that crosses a system boundary by virtue of a temperature *difference*, not an *absolute* temperature.
  15. We know theoretically how pressure and density must interact at the critical point. Specifically, the first two partials (dP/drho and d²P/drho²) must be zero at the critical point for it to exist. This is mathematically equivalent to having three roots at the critical point. Simple equations of state (e.g., van der Waals) can reproduce this behavior, but may not fit data well anywhere else. In fact, the critical compressibility for a van der Waals fluid is Zc=3/8, which is larger than any known substance. The liquid densities are also off by a factor of 1/3 to 1/2 for the van der Waals EoS, as
  16. I cover this at some length in my book, "Thermodynamic and Transport Properties of Fluids." The Ebook is free on these days: 4/16,4/24,5/2 at this link https://www.amazon.com/dp/B07Q5L1CHT The software is always free at this link http://dudleybenton.altervista.org/software/index.html and one of the Excel AddIns (also free) may be helpful.
  17. You misunderstand the principle. Whether some working fluid is hot or cold compared to what humans consider normal atmospheric conditions isn't what determines whether or not a device is efficient. When I taught thermodynamics at university, I would always give a test question regarding a cup of coffee cooling to room temperature or a can of beer warming to room temperature. Both generate entropy (dS>0). I work out this example in my book, Thermodynamics. There are several reasons we build power plants using steam instead of air as the working fluid. The latent heat is a very important part
  18. Some of these items are more important than others. The basic design of heat exchangers is driven by the application. Consider a fuel gas heater and an oil cooler on a typical stationary gas turbine, such as you might find at a combined cycle power plant. You will not likely ever need to clean the fuel gas heater. The operating pressure will exceed 40 atm. You wouldn't use a plate design. The oil cooler might need to be cleaned several times per year. A plate design held together with threaded rods is often used. It's easy to dismantle and clean. The working pressure isn't too high, it doesn't
  19. I have always stressed both theory and practice. It has served me well throughout my long career. I've literally crawled in and out of power plants, paper mills, and various industrial facilities all over the world. I can solve a differential equation while replacing a CV joint. For inspiration and real-life examples, please read my book entitled, "Living Math," available on Amazon http://www.amazon.com/dp/B01LXZYLVX The eBook will be free on March 17 and 25, then April 4, 10, and 18.
  20. The answers you get to this question may not be what you're looking for. "Extraction" has a definite meaning in the context of steam turbines. In a Rankine cycle with regenerative heating, steam is bled off the turbine at various stages and directed to feedwater heaters, which raise the temperature of the compressed liquid upward toward the inlet of the boiler, as with an economizer. This actually decreases the power output of the steam turbine, but it increases the efficiency of the overall process. This is often illustrated in textbooks, showing that the regenerative Rankine cycle is more re
  21. You are quite right. The true uncertainty of the process you're describing is much more complicated than it may seem from reading the literature. I have a particular interest in this subject, work for a company that is intimately concerned with such things, and am currently collaborating with a group retired professors to adequately address this gap in the literature. Not only does the sensor itself present multiple uncertainties, at the very least both random and systematic, but the sampling process also contains uncertainty. So does the analog-to-digital conversion. Thermocouples have greate
  22. The attached data set is derived from actual performance of an engine that is very well maintained, as is the instrumentation. Sadly, this is not often the case in the power industry, making this an extraordinary data set. In the spreadsheet you will find the ambient conditions, operational controls, fuel data, reported performance, and regressions. These regressions (for generator output and heat input) are curve fits you can use for various analyses and can be scaled to match your specific engine. EOH is equivalent operating hours, which is the literal running time plus adjustments for start
  23. This would be a good project for a team of seniors or a graduate student. Consider prevailing wind as it varies over the face of the Earth and where to best deploy turbines. You can get daily data from about 15,000 stations from the NCDC server, which is operated by NOAA. It's in files called GSOD (Global Surface Summary of the Day). Information on the data sets and coverage are available on their web site. The animation below shows typical values over decades just for illustration. The other figure shows station locations. Most of the stations are in heavily populated areas.
  24. I have already suggested the cube covered with a folded graph under the topic of natural draft cooling tower curves. You might also use spheres of different color and size, as illustrated in the two attached animations created with Tecplot. Similar animations can be created with TP2, a free tool available on the web.
  25. From aerodynamics to hydrodynamics, the MacCormack method of alternating differences has proven to be a powerful way of modeling fluid flow. There are many articles on the web, for instance, Wikipedia has a page on this topic. This technique was brought from aerospace to hydroelectric reservoirs by my mentor, Dr. William R. Waldrop. Several techniques are discussed in the attached paper. Calculated flows from a typical reservoir are shown in these two figures. The source code (C or FORTRAN) is available for free. TVA3-519.pdf
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