Wish my professor explained as you do, bravo! He basically has us teaching ourselves and creates his own problems on quizzes and tests that don’t resemble the textbooks. I do feel ready for anything now though
Great video! You definitely gave me a deep understanding for the Otto-cycle, and how to solve problems with heat input, net work, efficiency and so forth. I just have a small question: To find the work and heat using the first equation of thermodynamics, why did you not find the u-values for air at different temperatures in the air-table, and then take the difference in those values to calculate the input or output of heat or work? For example: u3-u2=q2-3 => q2-3=value for u at 1100K- value for u at 738K. I heard there was something about "cold" air, but I really couldn't understand why you had to use q/w=+-Cv*Delta(T).
2 years too late, but in “cold” calculations you don’t use the tables to find the properties. If you re-arrange the first and second entropy equations, you get that u2-u1 = Cv(T2-T1) and h2-h1 = Cp(T2-T1)
1. An air-standard Diesel cycle has a compression ratio of 16 and a cutoff ratio of 2. At the beginning of the compression process, air is at 95 kPa and 27°C. Accounting for the variation of specific heats with temperature, determine (a) the temperature after the heat-addition process, (b) the thermal efficiency, and (c) the mean effective pressure. Answers: (a) 1724.8 K, (b) 56.3 percent, (c) 675.9 kPa Please help
cv = 0.718 kJ/kg*K. It is given in the last sentence of problem statement. Original value taken from Table A-20 of the textbook we use, by Moran et.al.
Wish my professor explained as you do, bravo! He basically has us teaching ourselves and creates his own problems on quizzes and tests that don’t resemble the textbooks. I do feel ready for anything now though
6 Years later this dude just saves my ass for the Report I have to do on Otto engines.
Obrigado professor. Aula muito boa! Deus te abençoe sempre!
How did you get p4?!
Great video! You definitely gave me a deep understanding for the Otto-cycle, and how to solve problems with heat input, net work, efficiency and so forth. I just have a small question: To find the work and heat using the first equation of thermodynamics, why did you not find the u-values for air at different temperatures in the air-table, and then take the difference in those values to calculate the input or output of heat or work? For example: u3-u2=q2-3 => q2-3=value for u at 1100K- value for u at 738K. I heard there was something about "cold" air, but I really couldn't understand why you had to use q/w=+-Cv*Delta(T).
2 years too late, but in “cold” calculations you don’t use the tables to find the properties. If you re-arrange the first and second entropy equations, you get that u2-u1 = Cv(T2-T1) and h2-h1 = Cp(T2-T1)
nice job done by you guys
Exceptional job sir
1. An air-standard Diesel cycle has a compression ratio of 16 and a cutoff ratio of
2. At the beginning of the compression process, air is at 95 kPa and 27°C.
Accounting for the variation of specific heats with temperature, determine (a)
the temperature after the heat-addition process, (b) the thermal efficiency, and
(c) the mean effective pressure. Answers: (a) 1724.8 K, (b) 56.3 percent, (c)
675.9 kPa
Please help
What value did you use for c_v at 11:15? How did you get it?
cv = 0.718 kJ/kg*K. It is given in the last sentence of problem statement. Original value taken from Table A-20 of the textbook we use, by Moran et.al.
8:24 what was that? haha
I think it was his dog
u wrote wrong formula for w12, it should be cp (T2 - T1). (not cv)
For whatever reason I believe that cv(T2-T1) is the right formula even though the process 1 to 2 has a change of volume.