Thermal compression

Thermal Compression—Ot the two vapor-compression methods, thermal compression requires less capital but yields lower heat recovery than does mechanical compression. A steam-jet booster is used to compress a fraction of the vapor leaving the evaporetor so that the pressure and temperature are raised. Thermal compression is normally applied to the first effect on existing evaporators or where the conditions are right for the application in single-effect units. 

The thermal energy savings depend on the available motive-steam pressure end the compression ratio. From steam-jet performance curves, the ratio of suction vapor to motive steam flow rates is obtained and matched with the total steam requirements for the evaporator. The difference in the low rates between the existing evaporator steam without thermal compression and motive steam is the steam savings. The motive steam rate is the new steam consumption. The 

A steam-jet thermocompressor is employed when low-pressure steam is used for the evaporation and the available steam pressure is high. The Jet compressor essentially replaces the existing pressure regulator or reducing valve that controls the steam pressure (and temperature) for evaporation and can be applied easily to single-effect and multi-effect units under the right conditions. 

The variability in energy savings and capital costs still depends on the existing evaporator conditions. For existing multi-effect units in which the total amount of first-effect vapor is now used in the second effect, the choice and location of the steam-jet thermocompressor are more complicated because the heat balances and heat-transfer rates are affected for each evaporator reaction. The economics may still be favorable to justify the technical evaluation and modification. Since the limitations of steam-jet thermocompressors are a compression ratio below 1.8 and new heat-transfer rates, the first effect normally becomes the best location. 

If high-pressure steam Is available and a demand exists for low-pressure exhaust steam, as is the normal case for multi-effect units, a steam-turbine-driven compressor drastically reduces the operating costs of the compressor as compared to those for electrically driven units. In this case, the turbine exhaust can be passed on to the next effect of an existing multi-effect unit. If electrical costs are low, the choice based on operating costs would be an electrically driven compressor. The total energy consumption is nearly identical with either drive. 

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There are two common refrigeration systems, mechanical and thermal compression. In the mechanical system work is done in compressing a gas, the refrigerant. The energy thus added plus the amount of refrigeration required must be removed in a condenser, usually by cooling water. The calculations necessary and some typical values are given in references 20 and 21. 

The thermal compression or absorption refrigeration systems are less common. They do not require a compressor. Their energy source is steam, natural gas, or waste heat. This system requires much more cooling water than the previous one, but may be economical if a large amount of waste heat is available.21 See references 20 and 21 to determine heat and cooling water requirements. 

The first physical change to consider with UHPLC is the compression of the eluent in the piston chamber that produces thermal heating. The change in temperature related to a change in pressure (dT/dP) can be estimated per Equation 13.2 in which Cp represents eluent heat capacity, a is the thermal compression/expansion coefficient, T is the temperature in K, and V is molar volume. 

At present metal hydrides, owing to their unique properties, find applications (Figure 2) in many fields of science and technology, associated with hydrogen storage, thermal compression, separation, electrochemistry, switchable mirror, etc. 

Figure 14. Thermal compression of hydrogen using hydrides...

FIGURE 7.1 Comparison of the Sogami prediction for the thermal compression of colloidal crystals with that of Rundquist et al. [32] (DLVO prediction). 

Thin gold or aluminum wire, with a diameter of 0.025-0.075 mm, is used to make a connection between the bonding pad and the sensor. This wire bonding is performed using standard microelectronic techniques such as thermal compression or ultrasound bonding. The external lead wire is then bonded onto the bonding pad. Because of the thinness of the metallic film of the pad, the external lead wire connection is usually made by thermal compression. Similar to the connection of the thick-film sensor, the conductive epoxy is first applied to the connecting joint and then covered with insulation epoxy or silicone. 

Validate the entire thermal compression process in a pilot scale system that includes purification provisions and boosts hydrogen pressure to over 5,000 psig. The flow rate capability of the pilot-scale system will be similar to that required for overnight refueling of a hydrogen fuel cell automobile. 

Another useful thermal characterization technique is thermal compression in which a polymer fabric or biotextile is subjected to different loads at different temperatures. The thickness, pore size, and distribution can be monitored at each condition to prepare ideal scaffolds for tissue engineering. PolyCethylene terephthalate) (PET) nonwoven fiber scaffolds have been prepared for tissue engineering by thermal compression and simultaneous characterization. Applying pressure near the T of the polymer ( 70°C) yielded better control of the pore size distribution and smaller pore sizes, which led to faster and wider proliferation of Irophoblast andNIH 3T3 cells on the scaffold [9]. 

During machining, the material subsurface is heated temporarily to high temperatures. By this the surface-near layers expand as a result of thermal compressive stress. The surface-near layers deform plastically in a state of reduced yield strength. After cooling down to room temperature, tensile residual stresses result. As in machining both mechanical and thermal influences act concurrently, they interfere with each other strongly nonlinear. A simple superposition is not... 

Specific steam consumption with thermal compression (t/t, related to steam and solution vapor) 0.5 0.33 0.17 0.12... 

Compression evaporation could be defined as an evaporation process in which part, or all, of the evaporated vapor is compressed by means of a suitable compressor to a higher pressure level and then condensed the compressed vapor provides part of all of the heat required for evaporation. Compression evaporation is frequently called recompression evaporation. All compression methods use the vapors from the evaporator and recycle them to the heating side of the evaporator. Compression can be achieved with mechanical compressors or with thermal compressors. Thermal compression uses a steam jet to compress a fraction of the overhead vapors with high pressure steam. Mechanical compression uses a compressor driven by a mechanical drive (electric motor or steam turbine) to compress all the overhead vapors. 

Thermal compression is the term used to describe the application of a steam jet ejector or thermocompressor to an evaporator in order to increase the steam economy. A typical system is illustrated in Figure 18-1. Steam jet thermocompressors can be used with either single or multiple-effect evaporators. As a rule-of-thumb, the addition of a thermocompressor will provide an improved... 

The thermocompressor design is very similar to that of steam jet ejectors used for producing vacuum. The standard types of ejectors used for thermal compression are shown in Figure 18-2. Each ejector consists of three basic... 

Figure 18-2 Ejectors used for thermal compression, (a) Single nozzle type, (b) Spindle operated type, (c) Multiple nozzle type.

Perhaps the highest thermal vapor compression technology in any field can be found in the water desalination industry. Technology in that industry has advanced to designs with more than eight successive effects with steam economies over 12. Thermal compression evaporators beyond seven effects In process industries does not appear to be economical because mechanical vapor compression systems offer a better alternative. 

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