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  • Users: BretCahill
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  1. BretCahill

    Two Stage Recuperator Effectiveness

    So the overall effectiveness of regenerators in series can be determined by adding the HTUs, for example, a regenerator with ? = 50% in series with a regenerator of ? = 75% has an overall ? of 80%. Or overall ? = (?/(1-?) + ?/(1-?). . .) / (?/(1-?) + ?/(1-?). . . + 1) (Subscripts omitted)...
  2. BretCahill

    Two Stage Recuperator Effectiveness

    If the mass flow rates / heat capacities are the same on both sides, what would be the overall effectiveness of two regenerators in series with different effectivenesses? Bret Cahill
  3. BretCahill

    heat transfer coefficient - backwards

    Conductivity, viscosity and density of air change pretty much with temperature. Maybe you could get ball park figures using cold to hot data for hot to cold over 50 degrees but anything much greater than that might give wildly different results. Bret Cahill
  4. BretCahill

    Ni-Cr Now Cheaper Than Steel On Unit Power Basis

    Maybe Ni-Cr alloy hasn't had any big price fluctuations lately. In any event, steel is used for more than engines. Signs have been popping up "will remove your junker for free." It will be interesting to see if they clean out those cars that ran off the road/cliff and into the canyon. Bret...
  5. BretCahill

    Air Tank Boosting for Dire Traffic Situations

    United States Patent 4,162,281 Ingraham July 24, 1979 -------------------------------------------------------------------------------- Carburetor fuel atomization apparatus Abstract Apparatus for feeding compressed air to an automobile carburetor including a compressor, a compressed...
  6. BretCahill

    Air Tank Boosting for Dire Traffic Situations

    Fluid mechanics calculators are fun to play around with to get some numbers. Google "Reynolds Numbers" for something like: http://www.efunda.com/formulae/smc_fluids/calc_pipe_friction.cfm#calc and check my numbers: 0.018 cP viscosity for air @ 70 degrees F 114.7 psi abs pressure at tank...
  7. BretCahill

    Air Tank Boosting for Dire Traffic Situations

    These ballpark calculations are for a 2 l engine. This will work for larger engines but the air pressure or the tank size and tubing size will need to be increased accordingly. The 1/2" tubing would run from the 8 gallon 100 psi tank -- 8 cu ft of air at STP -- to the regulator under the hood...
  8. BretCahill

    Ni-Cr Now Cheaper Than Steel On Unit Power Basis

    Someone recently complained about the high cost of the materials used in gas turbines. Until recently this was true on both a unit power basis as well as a unit weight basis. Now with steel trading at $400/ton and comparing the cost of Ni-Cr alloy in a large turbofan to the steel in a vehicle...
  9. BretCahill

    Air Tank Boosting for Dire Traffic Situations

    A turbo charger manfacturer said air tank boosting would be the same as nitrous -- the original idea was to be used along with turbochargers to eliminate turbo lag. Then I considered that the only time I really need to move fast is scooting across a busy intersection which takes two - 5...
  10. BretCahill

    Cost/Benefit of Multi Engine Vehicles

    GE has a 100 + ton industrial gas turbine that gets 60% efficiency -- the highest for any engine or power plant -- but that really hasn't been the case for smaller GT engines where diesel has been better. The Abrams tank has been criticized because its 1500 kW gas turbine is so inefficient it...
  11. BretCahill

    Work Required for Heat Transfer Enhancement

    For awhile I was afraid I was going to get a dimensionless number named after me! I can rest easy now. Bret
  12. BretCahill

    Cost/Benefit of Multi Engine Vehicles

    If we had cheap efficient small gas turbines it would be nice to use a small (10- 15kW) GT engine in a series hybrid to get 60 - 80 mpg _most of the time_. A larger (150 kW) GT engine would also fit under the hood for direct parallel power -- they want $5,000 for a hybrid generator -- when it...
  13. BretCahill

    Cost/Benefit of Multi Engine Vehicles

    Reciprocating engines for motor vehicles still cost > $10/kW so it will be awhile before fuel costs make multi-engine vehicles economical, assuming it will ever happen. DOE or DOT has some regulations ready to go to require semi rigs to have APUs (aux. power units) because tractors waste...
  14. BretCahill

    Work Required for Heat Transfer Enhancement

    It's not all that big a deal to assume a flow rate and get some Nusselt number(s), boundary layer thicknesses, temperature differences, conductivities, surface areas etc. to determine a Q for ONE situation -- especially if you don't need two or 3 decimal place accuracy. But to save everyone...
  15. BretCahill

    Work Required for Heat Transfer Enhancement

    I may have fortuitously stumbled across a situation that might be replicated in other heat exchangers to enhance transfer. It now seems so obvious it's hard to believe I can't find anything similar in the literature. In fact, it's hard to believe it took _me_ 5 years to see it even though it...
  16. BretCahill

    Work Required for Heat Transfer Enhancement

    This concerns the mechanical energy required to get a certain heat duty and/or effectiveness while factors such as heat exchanger volume are set. One strategy might be to use long thin tubes and have a lot of surface area and the only work required will be moving the fluids through the tubes...
  17. BretCahill

    Air Tank Boosting for Dire Traffic Situations

    I can usually find my "new" ideas in minutes and they are often decades old. This might be an exception: Eliminate turbo lag and shaft driven superchargers with something much more useful to most commuters: a two to 5 second burst of air from a pressure vessel that would help scoot any under...

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