SIXTY MINUTES: Bloom Box, Projected As Cost Effective Fuel Cell
in [Basics]
|
Prev: Be ready to be killed, or take action to stop the global suicide. Scandal at CERN.
Next: OPERATIONS AND SUPPLY MANAGEMENT 12-E JACOBS Test Bank and solution manual
From: Bret Cahill on 25 Feb 2010 22:57 > http://en.wikipedia.org/wiki/Fuel_cell#Efficiency The high theoretical or real efficiencies of fuel cells are analogous to the high theoretical or real efficiencies of low pressure ratio highly recuperated gas turbine engines, over 80% below a 2:1 pressure ratio. Regenerate / recuperate enough and the thermo cycle approaches isothermal addition and rejection of heat -- Carnot efficient. You just need to spend a whole lot of money on a really big heat exchanger. Alternatively you can use ceramic turbine blading in an external rotor gas turbine to increase inlet temperatures but ceramics degrade just like fuel cell materials degrade. Sooner or later you start thinking, if it is high maintenance like a duck, if it has the same high cost as a duck, if it has all the same sorry limitations as a duck . . . The distinction between heat vs charge / electric power starts to seem rather superficial from a results oriented POV. Bret Cahill
From: pamela on 28 Feb 2010 21:50
Bret Cahill wrote: >>>>> There is no fundamental difference between fuel cells and heat >>>>> engines. > Fuel cells explicitly involve chemistry and chemical reactions. Heat engines explicitly involve temperature differences, which do not necessarily involve chemical reactions .... nuclear will do quite readily. From :Entropy Analysis: an introduction to chemical thermodynamics" by Normal C Craig ISBN 1-56081-593-6 Page 3, Near the bottom "When thermal energy is involved, however, we find a one-wayness in energy conversions. Electrical and mechanical energies can be transformed completely into thermal energy, but the inverse transformations are not possible from thermal energy at any given temperature. The limitations of the conversion of thermal energy into other forms of energy are central to the second law of thermodynamics." This specialness of thermal energy conversin is the reason for the specific focus upon the Carnot cycle for thermal energy as it defines specifically the theoretical limits of such conversions. There is no such major issue with the conversion of other forms of energy into thermal energy -- that can be essentially a perfect conversion. The issues of the different behaviors of other forms of energy have been taken care of in thermodynamics for probably a century. Beginning Chapter 4 "Entropy Principle : The Second Law" "The first law of thermodynamics places no limits on energy exchanges provided energy is conserved. Experience teaches us that the weight-lifted energy of a raised book can be completely converted into thermal energy of a table top and the book when the book land on the table.The reverse process in which energy is conserved [the thermal energy flowing cohesively back to the point of book impact and then impulsively throwing the book back into the air]is, however, impossible. Similarly, there are limitations on the transfer of thermal energy from a cold body to a hot body. A chemical reaction has a favored direction even though energy is conserved in both directs. Thus, where thermal energy is involved, we find a one-wayness in first law possible energy transactions." "This chapter introduces the second law of thermodynmics and the entropy function that is the heart of this law. The entropy function is the index of change for all processes. It confirms the one-wayness of dropped books interacting with tble tops. The entropy function tells whether a chemical reaction can occur as written and when a reaction hs reached equilibrium......" What can you quote on this subject from your Thermodynamics books that you have read and understood? You sound ignorant of the modern approach to Thermodynamics. The modern stuff is much better than the way it was taught long ago when I was an undergraduate. I am glad for certain internet sites which are devoted to spreading the gospel of the modern approach, and to libraries for the modern Thermodynamics books borrowed and subsequently bought. I feel confident that you will run off spouting mostly buzz words and speculations and possibly strange hypotheses that have already been covered one way or another by those skilled in the field. |