Which particle plays the key role in sustaining a fission reaction?
A) quark
B) proton
C) gamma photon
D) electron
E) neutron
E
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Green coffee beans, after harvesting, are dried and roasted in a fluidized-bed roaster. This type of roaster has hot air typically at 2500C, and the air blows through a screen or perforated plate above which the beans float in an agitated suspension (fluidization) in the hot air as they get heated. As the beans heat up, they get dried and roasted to the required condition. They are typically flat ellipsoids that have an average volume of 44 mm3 and an average surface area of 66 mm2. For a flavorful and aromatic medium roast, the beans have to be heated to 2000C. If the beans are initially at 220C at the time they enter the roaster and the convective heat transfer coefficient of the heating air is 20 W/(m2 K), determine the required roasting time. Coffee bean thermophysical properties are
k=0.184 W/(m K), c=2.564 kJ/(kg K) and ?=552 kg/m3
GIVEN
• Green coffee beans with average volume V=44 mm3 and average surface area As=66 mm2
• Initial temperature of beans(To) = 22°C
• Roaster hot air temperature(T?) = 250°C
• Heat transfer coefficient ( ch ) = 20 W/(m2 K)
• Length of the oven(L)=3.5 m
FIND
• The heating time required for beans to reach to 200°C
ASSUMPTIONS
• Constant thermal conductivity
• End effects are negligible
SKETCH
PROPERTIES AND CONSTANTS
Given For beans Thermal conductivity (k) = 0.184 W/(m K)
Density (?) = 552 kg/m3 Specific heat (c) = 2.564 kJ/kg=2564 J/kg
What happens when a solar nebula contracts?
A) It flattens out. B) It spins faster. C) It heats up. D) All of the above E) None of the above
An infinite universe is one of the assumptions of the cosmological principle
Indicate whether the statement is true or false
The wearing away of soil and rock and the subsequent downslope movement of the fragments are called
a. erosion. b. weathering. c. cross-cutting. d. deposition.