Update Content - 2025-01-16

content/zettels/heat_transfer.md

@@ -0,0 +1,131 @@
++++
+title = "Heat Transfer"
+author = ["Dehaeze Thomas"]
+draft = false
++++
+
+Tags
+:
+
+
+## Conduction (diffusion) {#conduction--diffusion}
+
+The _conduction_ corresponds to the heat transfer \\(P\\) (in watt) through molecular agitation within a material and is specified with:
+\\[ P = \frac{\lambda \cdot A \cdot \Delta T}{L} \quad [W] \\]
+with:
+
+-   \\(\lambda\\) the thermal conductivity in \\([W/m \cdot K]\\)
+-   \\(A\\) the surface area in \\([m^2]\\)
+-   \\(\Delta T\\) the temperature difference in \\([K]\\)
+-   \\(L\\) the length of the barrier in \\([m]\\)
+
+
+## Convection {#convection}
+
+The convection corresponds to the heat transfer through flow of a fluid.
+It can be either _natural_ or _forced_.
+
+The _forced convection_ \\(P\\) (in watt) can be described with:
+\\[ P = h A (T\_0 - T\_f) \quad [W] \\]
+with:
+
+-   \\(h\\) the convection heat transfer coefficient in \\([W/m^2 \cdot K]\\).
+    \\(h \approx 10.5 - v + 10\sqrt{v}\\) with \\(v\\) the velocity of the object through the fluid in \\([m/s]\\)
+-   \\(A\\) the surface area in \\([m^2]\\)
+-   \\(T\_0\\) the temperature of the object in \\([K]\\)
+-   \\(T\_f\\) the temperature of the convecting fluid in \\([K]\\)
+
+Note that clean-room air flow should be considered as forced convection.
+
+
+## Radiation {#radiation}
+
+_Radiation_ corresponds to the heat transfer \\(P\\) (in watt) through the emission of electromagnetic waves from the emitter to its surroundings is:
+\\[ P = \epsilon \cdot \sigma \cdot A \cdot (T\_r^4 - T\_s^4) \\]
+with:
+
+-   \\(\epsilon\\) the emissivity which corresponds to the ability of a surface to emit energy through radiation relative to a black body surface at equal temperature.
+    It is between 0 (no emissivity) and 1 (maximum emissivity)
+-   \\(\sigma\\) the Stefan-Boltzmann constant: \\(\sigma = 5.67 \cdot 10^{-8} \\, \frac{W}{m^2 K^4}\\)
+-   \\(A\\) the surface in \\([m^2]\\)
+-   \\(T\_r\\) the temperature of the emitter in \\([K]\\)
+-   \\(T\_s\\) the temperature of the surrounding in \\([K]\\)
+
+The emissivity of materials highly depend on the surface finish (the more polished, the lower the emissivity).
+Some examples are given in <tab:emissivity_examples>.
+
+<a id="table--tab:emissivity-examples"></a>
+<div class="table-caption">
+  <span class="table-number"><a href="#table--tab:emissivity-examples">Table 1</a>:</span>
+  Some examples of emissivity (specified at 25 degrees)
+</div>
+
+| Substance                  | Emissivity |
+|----------------------------|------------|
+| Silver (polished)          | 0.005      |
+| Silver (oxidized)          | 0.04       |
+| Stainless Steel (polished) | 0.02       |
+| Aluminium (polished)       | 0.02       |
+| Aluminium (oxidized)       | 0.2        |
+| Aluminium (anodized)       | 0.9        |
+| Copper (polished)          | 0.03       |
+| Copper (oxidized)          | 0.87       |
+
+<div class="exampl">
+
+Let's take a polished aluminum plate (20 by 20 cm) at 125K (temperature of zero thermal expansion coefficient of silicon) surrounded by elements are 25 degrees (300 K):
+\\[ P = \epsilon \cdot \sigma \cdot A \cdot (T\_r^4 - T\_s^4) = 0.36\\, J \\]
+
+</div>
+
+
+## Heat {#heat}
+
+The _heat_ \\(Q\\) (in Joules) corresponds to the energy necessary to change the temperature of the mass with a certain material specific heat capacity:
+\\[ Q = m \cdot c \cdot \Delta T \\]
+with:
+
+-   \\(m\\) the mass in \\([kg]\\)
+-   \\(c\\) the specific heat capacity in \\([J/kg \cdot K]\\)
+-   \\(\Delta T\\) the temperature different \\([K]\\)
+
+<div class="exampl">
+
+Let's compute the heat (i.e. energy) necessary to increase a 1kg granite by 1 degree.
+The specific heat capacity of granite is \\(c = 790\\,[J/kg\cdot K]\\).
+The required heat is then:
+\\[ Q = m\cdot c \cdot \Delta T = 790 \\,J \\]
+
+</div>
+
+<a id="table--tab:specific-heat-capacity"></a>
+<div class="table-caption">
+  <span class="table-number"><a href="#table--tab:specific-heat-capacity">Table 2</a>:</span>
+  Some examples of specific heat capacity
+</div>
+
+| Substance           | Specific heat capacity [J/kg.K] |
+|---------------------|---------------------------------|
+| Air                 | 1012                            |
+| Aluminium           | 897                             |
+| Copper              | 385                             |
+| Granite             | 790                             |
+| Steel               | 466                             |
+| Water at 25 degrees | 4182                            |
+
+
+## Heat flow {#heat-flow}
+
+The heat flow \\(P\\) (in watt) is the derivative of the heat:
+\\[ P = \cdot{Q} = \frac{dQ}{dt} = \frac{dT}{R\_T} = C\_T \cdot dT \\]
+with:
+
+-   \\(Q\\) the heat in [W]
+-   \\(R\_T\\) the thermal resistance in \\([K/W]\\)
+-   \\(C\_T\\) the thermal conductance in \\([W/K]\\)
+
+
+## Bibliography {#bibliography}
+
+<style>.csl-entry{text-indent: -1.5em; margin-left: 1.5em;}</style><div class="csl-bib-body">
+</div>