Mechanical heat switch

Argon Gap -Heat Transfer -Thermal Switch Mechanism... 

The AHTR uses a guard vessel for two functions. The first function is part of a thermal switch mechanism that ensures low losses of heat during normal operations but efficient removal of decay heat during shutdown or off normal conditions. The second function of the guard vessel is to provide a backup in the event of vessel failure and catch the core and the liquid salt within the core. 

Figure 4.1 Schematic diagram of a coupled column system. The first column (ID) is connected to the second column (2D) tlirough the interface or valve system. The interface can be a diiect coupling, a live T-union, a complex multiport valve, or a thermal or cryogenic modulation system. The stimulus can be the switching of the valve, abalancing pressure to divert flow towards 2D, an added flow that is used in pressure tuning, or the drive mechanism for the modulator. The line to detector 1 will normally be a non-retaining section of column. In a two-oven system, ID and 2D will be in different ovens the dotted line indicates separately heated zones.

Electromechanical Controls. Electro-mechanical control devices are typically used for load control (lighting, ventilation, and heating) in buildings with no feedback signal. The most common device is the electromechanical timer, in which a small motor coupled to a gearbox is able to switch electrical contacts according to a predefined time schedule. They are still in use today, applied to loads with simple scheduling requirements. 

In the case of LNT, different proposals have been advanced to explain the mechanisms governing the NO, release. Recent papers suggested that the NO release is provoked by the heat generated upon the reducing switch (thermal release) [40], by the decrease of the gas-phase oxygen concentration that destabilizes the stored nitrates [41], by spillover and reduction of N02 onto reduced Pt sites or by the establishment of a net reducing environment, which decreases the equilibrium stability of nitrates [12,42,43],... 

Other types of thermal switches have been built, e.g. mechanical switches which can be turned on and off easily, but which produce heat in the switching and are therefore used at T > IK. Thermal contact is made by pressing together metallic surfaces. Conductance of a few mW/K can be obtained in the on state [14,30,41-45]. Another disadvantage of these switches are the large forces (typically 10 kg) needed to produce a good contact. Nowadays, the use of these switches is not common. 

As demonstrated above, the heat current from D to S can be switched between different values. However, in many cases, like in an analog circuit, we need to continuously adjust the current Js and/or Jo in a wide range by adjusting the control temperature Tg. In Fig.11 we demonstrate this modulator/amplifier function of our transistor. The basic mechanism of such modulator/amplifier is the same as that of the switch but we consider here different parameter values. It is seen that in the temperature interval Tq (0.05,0.135), the heat current through the segment G remains very small ((—10-5 10-5), within the shadow strip in Fig. 10, while the heat currents Js and Jg continuously increase from 5 x 10-5 to 2 x 10-4. 

Several mechanisms have been previously proposed for oscillations. Due to the fact that oscillations exist for Lewis numbers both less and greater than 1, it seems that the thermodiffusive mechanism alone cannot explain these oscillations. To study the role of the heat of reaction, a numerical experiment is performed by switching off the heat of the gas-phase reactions (squares in Fig. 26.2). HBs are found between 75% and 85% H2 in air, but the HBs lie within the multiplicity regime IiEi in Fig. 26.2 and oscillations are not stable. 

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