Thermal Mechanical Valves

Thermal mechanical valves Thermally actuated mechanical valves Thermally driven mechanical valves... 

Fig. 11. The mechanical valves can be replaced by thermal or chemical modulating devices. In principle, this modification circumvents the need of reliable mechanical valves and offers a more flexible system s . An example is the thermal oxidative modulation of methane in air. Figure 12 shows a concentration profile during 8 days, determined with an experimental modulation CC set up...

The total flow rate is controlled by a commercial mass flow controller (MFC), which contains an internal servo mechanism that links a mechanical valve to a resistance thermal device (RTD). The RTD measures mass flow (rather than gas velocity) by the change of electrical resistance in a sensing wire heated by an adjacent hot wire. Because this measurement is affected by the specific heat of the gas, the MFC must be calibrated for each individual gas. The desired MFC flow is set by applying a voltage to the MFC that corresponds to the voltage generated by the RTD at that flow. A comparator in the MFC opens or closes the internal valve to balance the RTD and the applied voltage. 

Mechanical equipment that performs an action to relieve pressure when the normal operating range of temperature or pressure has been exceeded. Physical relief devices include pressure relief valves, thermal relief valves, rupture disks, rupture pins, and high temperature fusible plugs. 

The gate is the termination of a flow channel, and is a critical functional zone in an HR system. It governs the functioning of the nozzle, regardless of whether it is located in the nozzle or inside the actual mould cavity. The gate plays the part of a thermal or mechanical valve. Gate control concerns both melt flow control and gate closure (open time). 

Since mechanical valves provide a physical barrier to the backflow of combustion products through the combustor inlet during the positive-pressure phase of the pulse combustion cycle, the unidirectional flow is the fundamental feature of valved pulse combustors. There are, however, certain problems associated with the design of mechanical valves, such as minimizing valve inertia, protection from corrosion, and resistance to material fatigue due to thermal stress. These specific problems are of major importance in heavy-duty pulse combustors operated at large pressure amplitudes (Kentfield, 1993). 

The thermal valve concept can be illustrated in a very simple way (Fig. V-10). It consists of a bell-shaped compartment submerged in the pool surrounding the in-pool heat exchanger and is provided with one or more mechanical valves (depending on the need for the flow area) on the upper part of the bell (called the pilot valve). The compartment is open in its lower part. 

Fuel cell systems are heterogeneous systems consisting of various chemical, thermal, mechanical, and electrical systems. The fuel cell system involves a large number of these components besides the cell itself depending on its application. Some of the major components that are typical in a fuel cell power system are the fuel cell stack, fuel processing module, power conditioning unit, and of course many auxiliary components such as pumps, pipes, filters, valves, and sensors. 

Other PUS components, such as nozzles, plenums, piping, pumps, heat exchangers, valves, expansion joints, etc., have design characteristics that affect their susceptibility to in-service degradation. Their susceptibility is also affected by the chemical composition and thermal-mechanical history of the steel and the stresses (both applied and residual) acting on the steel. 

Fluid-filled bulbs dehver enough power to drive controller mechanisms and even directly actuate control valves. These devices are characterized by large thermal capacity, which sometimes leads to slow response, particularly when they are enclosed in a thermal well for process measurements. Filled-system thermometers are used extensively in industrial processes for a number of reasons. The simplicity... 

Chlorimet 2 has 63 percent Ni and 32 percent Mo and is somewhat similar to Hastelloy B-2. It is available only in cast form, mainly as valves and pumps. This is a tough alloy, very resistant to mechanical and thermal snock. It can be machined with carbide-tipped tools and welded with metal-arc techniques. 

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.

Piping joints shall be selected to suit the piping material, with consideration of joint tightness and mechanical strength under expected service and test conditions of pressure, temperature, and external loading. Layout of piping should, insofar as possible, minimize stress on joints, giving special consideration to stresses due to thermal expansion and operation of valves (particularly a valve at a free end). 

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