What is a key limitation to traveling outside our Solar System in search for life?
a. We have the wrong type of fuel source to power a spacecraft
b. We lack spacecraft that can escape Earth's gravity.
c. We lack a decent place to send spacecraft outside of our Solar System.
d. We have no way to communicate with an alien civilization.
e. We have not yet been able to develop the technology to travel far distances.
e
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The following steady-state stage II creep rates were recorded for a nickelbase superalloy at a constant tensile stress of 200 MPa.
It is known that the exponent of the stress in the creep-rate equation is n = 5.
(a) What would be the total stage II creep strain for this alloy at 913 K and a tensile stress of 200 MPa. in 1 year of service?
(b) Predict the stage II creep rate of this alloy at 891 K and a tensile stress of 300 MPa.
(c) Determine the enthalpy of activation for creep in eV/atom for this alloy.
A steam-heated single-pass tubular preheater is designed to raise 5.6 kg/s of air from 200C to 75°C, using saturated steam at 2.6 MPa(abs). It is proposed to double the flow rate of air and, in order to be able to use the same heat exchanger and achieve the desired temperature rise, it is proposed to increase the steam pressure. Calculate the steam pressure necessary for the new conditions and comment on the design characteristics of the new arrangement.
GIVEN
• Steam-heated single-pass tubular preheated heating air
• Air flow rate ( m a)= 5.6 kg/s
• Air temperature
? Ta,in = 20°C
? Ta,out = 75°C
• Saturated steam pressure (ps) = 2.6 MPa = 2.6 × 106 N/m2
FIND
• The steam pressure necessary for a double m a with the same temperature rise
SKETCH
PROPERTIES AND CONSTANTS
the saturation temperature (Ts) of steam at 2.6 × 106 N/m2 = 225°C
Which of the following sources of energy presents the fewest pollution problems under normal operating conditions?
a. Coal b. Natural gas c. Nuclear fission d. Hydroelectric power
Industry has been faster to adopt conservation measures than private homeowners
What will be an ideal response?