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# Tutor profile: Trevor C.

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Trevor C.
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## Questions

### Subject:Physics (Heat Transfer)

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Question:

How should a problem involving steady state heat transfer and temperatures across a composite material be approached?

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Trevor C.

In a steady-state situation, the heat transfer will be limited to the thermal resistance of each material region that the heat is being transferred across. The applicable thermal resistances for each material, calculated from the respective thermal conductivity and thickness of each component material, can be summed together in a single equation to calculate the heat transfer rates and effective temperatures at any given location within the material. Contact resistances and convective heat transfer resistances must also be taken into account for solid-solid boundaries and solid-fluid boundaries, respectively.

### Subject:Nuclear Engineering

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Question:

Describe the six factor formula for reactor criticality, and each of its components.

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Trevor C.

The six factor formula is used to calculate the effective criticality of the reactor, or its ability to sustain a nuclear reaction. A $$k$$ value of 1 means that the reactor is critical and self-sustaining, while a value of $$k>1$$ or $$k<1$$ means that the reactor is super-critical or sub-critical, respectively. The six factor formula consists of: 1. $$\eta$$, representing the number of neutrons produced per neutron absorption 2. $$f$$, representing the probability that a neutron will be absorbed in the fuel as opposed to another particle in the reactor 3. $$p$$, representing the fraction of neutrons that slow down from fast energies to thermal energies without being absorbed 4. $$\epsilon$$, representing the ratio of total fissions to the number of fissions resulting from thermal absorptions 5. $$P_{FNL}$$, representing the probability that a fast-spectrum neutron won't leave the reactor volume (leakage) 6. $$P_{TNL}$$ probability that a thermal neutron won't leave the reactor volume (leakage) The effective criticality $$k$$ is the product of these six factors.

### Subject:Chemical Engineering

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Question:

In what cases would a PFR be used instead of CSTR in a chemical reaction process?

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Trevor C.

A PFR is able to achieve a faster reaction rate due to higher concentrations of reactants, as opposed to a CSTR where the reactants are diluted instantly into a homogeneous mixture. This gives PFR's a high volumetric conversion efficiency. They also don't require as much additional mechanical mixing as would need to take place in a CSTR to assure homogeneity. Finally, a PFR works exceptionally well in continuous operations. This makes PFRs most useful for large-scale processes where high conversion and minimal equipment cost are priorities. However, a PFR may not be the best choice when reversible or secondary reactions are kinetically favored, as the high concentrations may lead to decreased yield of the desired product. In these cases, a CSTR may be more efficient.

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