NUCE 402 Chapter 3.2: Heat Removal in Reactors

Newton's law of cooling describes the rate of heat transfer as proportional to the temperature difference between the cooling medium and the surface.

Total thermal resistance is significant because it characterizes the overall resistance to heat transfer, impacting the efficiency of heat removal in nuclear systems.

The heat transfer coefficient changes with the flow regime; higher Reynolds numbers indicate turbulent flow, which requires different calculations for the coefficient.

<p>Dimensionless numbers help characterize flow and thermal properties, allowing for the prediction of heat transfer behaviors under varying conditions.</p> Signup and view all the answers

<p>The Dittus-Boelter equation provides an empirical relationship to estimate the heat transfer coefficient based on Reynolds and Prandtl numbers in turbulent flow conditions.</p> Signup and view all the answers

<p>Boiling allows lower coolant pressure and enhances heat transfer, leading to a lower cladding temperature.</p> Signup and view all the answers

<p>A BWR allows extensive boiling with a direct steam cycle, while a PWR permits limited boiling for enhanced heat transfer with an indirect steam cycle.</p> Signup and view all the answers

<p>DNB signifies a transition from effective nucleate boiling to film boiling, which decreases heat transfer and can lead to increased fuel temperatures.</p> Signup and view all the answers

<p>Higher flow velocity promotes the convection heat transfer mechanism and supports the persistence of bubbles, enhancing heat transfer efficiency.</p> Signup and view all the answers

<p>The design philosophy prioritizes the integrity of cladding to ensure that fission products remain within the fuel and prevent fuel melting.</p> Signup and view all the answers

<p>The expression for total thermal resistance is given by $R = \frac{1}{2k_f A} + \frac{1}{k_c A} + \frac{1}{hA}$. Each term represents conduction through the fuel, conduction through the coolant, and convection to the surrounding medium respectively.</p> Signup and view all the answers

<p>A high Reynolds number indicates turbulent flow, which enhances heat transfer effectiveness due to increased mixing and reduced thermal resistance.</p> Signup and view all the answers

<p>The Dittus-Boelter equation establishes that $h = 0.023 \times \left(\frac{k}{D} \right) Re^{0.8} Pr^{0.4}$, linking heat transfer coefficient to Reynolds and Prandtl numbers, which characterize fluid flow and thermal properties.</p> Signup and view all the answers

<p>Increased flow velocity enhances heat transfer leading to higher $q_{max}$, which in turn influences the temperature profiles $Tb$ and $Tm$ within the reactor.</p> Signup and view all the answers

<p>Dimensionless numbers like Reynolds and Prandtl numbers are critical for predicting flow regimes, transitions between laminar and turbulent flow, and overall heat transfer performance.</p> Signup and view all the answers

<p>1.9</p> Signup and view all the answers

<p>~750oF</p> Signup and view all the answers

<p>By increasing critical heat flux and decreasing hot channel factor.</p> Signup and view all the answers

<p>HCF is used to assess the maximum heat flux in relation to the average heat flux.</p> Signup and view all the answers

<p>It influences fuel loading patterns and reactor criticality.</p> Signup and view all the answers

<p>During DNB, nucleate boiling transitions to film boiling, causing a rapid increase in fuel temperature due to exposure to steam vapor.</p> Signup and view all the answers

<p>A BWR allows extensive boiling with a direct steam cycle, while a PWR limits boiling to enhance heat transfer with an indirect steam cycle.</p> Signup and view all the answers

<p>Lower coolant pressure during boiling facilitates more effective heat transfer to the coolant, leading to a lower cladding temperature.</p> Signup and view all the answers

<p>Critical Heat Flux (CHF) marks the point at which heat transfer efficiency drastically decreases, signifying the onset of DNB.</p> Signup and view all the answers

<p>Boiling patterns are measured by changing the surface temperature of heated pipes and observing flow pattern changes, which indicate heat transfer effectiveness.</p> Signup and view all the answers