Heat plate-type

Thermoduric, Thermophilic, andPsychrophihc Bacteria. Thermoduric bacteria survive but do not grow at pasteurization temperatures. They are largely non spore-forming, heat-resistant types that develop on surfaces of unclean equipment. These bacteria are determined by subjecting a sample to laboratory pasteurization and examining it by the agar plate method. 

Standard glass coils with 0.18 to 11.1 m (2 to 120 fF) of heat-transfer surface are available. Also available are plate-type units made of impervious graphite. 

When the solute has a large heat of solution or when the feed gas contains high percentages of the solute, one should consider the use of internal coohng coils or intermediate external heat exchangers in a plate-type tower to remove the heat of absorption. In a packed tower, one could consider the use of multiple packed sections with intermediate hquid-withdrawal points so that me hquid coiild be cooled by external heat exchange. 

The Fischer-Tropsch reaction is highly exothermic. Therefore, adequate heat removal is critical. High temperatures residt in high yields of methane, as well as coking and sintering of the catalyst. Three types of reac tors (tubular fixed bed, fluidized bed, and slurry) provide good temperature control, and all three types are being used for synthesis gas conversion. The first plants used tubular or plate-type fixed-bed reactors. Later, SASOL, in South Africa, used fluidized-bed reactors, and most recently, slurry reactors have come into use. 

Plate-type design (space heaters) Type of heat exchanger characterized by a substantial proportion of its heat output being by way of radiant energy. 

Example 10-26. Determine Contact Stages Actually Required for Direct Contact Heat Transfer in Plate-Type Columns... 

Plates are available with effective heat transfer area from 0.03 to 3.5 m and up to 700 can be contained within the frame of the largest plate-type heat exchanger, providing over 2400 m of surface area. Flow ports and associated pipework are sized in proportion to the plate area and control the maximum liquid throughput. 

Bypassing in a plate-type exchanger is less of a problem and more use is made of the flow separation which occurs over the plate troughs since the reattachment point on the plate gives rise to an area of very high heat transfer. 

It generally is considered that resistance due to fouling is lower with plate heat exchangers than with tubular units. This is the result of four advantages of plate-type exchangers ... 

A small-scale PROX system was manufactured in a type of heat exchanger using non-pellet catalyst. Pt-Ru catalyst screened was impregnated on the support sheet. The support sheet was made by coating y-AlaOs on porous SUS-mesh plate (thickness 1.0 mm). The surface area of the catalyst sheet was 96 mVg. The catalyst sheet was applied to a heat exchanger type reactor of PROX as shown in Fig. 2. The PROX reactor was manufactured as a unit module and tested. Fig. 3 is the test-set of the PROX. Air was applied as the coolant. 

Different from sole combinations of micro devices, this refers to a total system with many functional elements and flow-distribution and, recollecting zones, typically composed of 2-D plate-type architecture. Each of these plates usually has a separate fimction, comprising imit operations and reaction. Frequently, micro mixing and micro heat exchange fimctions and corresponding elements are employed. Often, the system can be composed of different elements resulting in different process flow combinations. Such an approach may be termed a construction kit. 

For certain applications multi-pass arrangements are used. When a plate heat exchanger is used instead of the tubular unit, boiling on the heating surfaces is avoided by increasing the static head using a line restriction between the plate pack and the separator. Compared with tubular units, lower circulation rates and reduced liquid retention times are important advantages. Plate-type units are discussed further in Section 14.7.7. 

Figure 5.1 Few common types of heat exchangers, (a) Double-tube type (b) shell-and-tube type (c) coil-type and (d) plate-type.

Conduction of heat through the plates ol plate-type heat exchangers and regenerators. 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

Kolb et al. [52] applied small externally heated sandwich-type reactors for catalyst screening for propane steam reforming. Two plates of 2 mm thickness were attached to each other and bonded by laser welding. The reactors where 41 mm long and 10 mm wide carrying 14 channels each, which were 25 mm long, 500 pm wide and 250 pm deep on each plate, thus resulting in a total channel cross-section of 500 pm x 500 pm when mounted. 

Thermal conductivity of plate-type reactors and reactors with corrugated insert are evaluated with use of structural two-dimensional model depending on directions of heat flow by formulas [3] ... 

Hot plates are also used to heat one type of material so that a second may be heated. These secondary heaters may include water baths, oil baths, sand traps, or aluminum plates. Water and oil baths are typically used to heat a drying flask on vacuum evaporators. Oil baths are more messy and require special clean up, but the oil (typically a silicone oil) will not evaporate during drying processes that can take up to several hours. Stronski came up with a very simple and easy solution to limit water evaporation. Stronski8 recommended that the user float Styrofoam popcorn or chips up to three inches deep on water. This suggestion not only limited evaporation, but extended the maximum controlled temperature range. 

From the usual plate-type distillation and absorption columns, it was but natural to attempt to devise stagewise equipment for G/S processing, for better heat economy and better utilization of the contacting media. But instability of the downcomer for solids transfer between stages remained for many years an unsolved hydrodynamic problem, and even to this data, the stable operation of many solids downcomers still depends on mechanical devices. 

Figure 1.2 shows a steam>cracked hydrogen cecovery and purification flow sheet by Joule Thomson expansion and heat transfer by means of plate-type heat exchangers. The hydrogen recovery rate, at a purity of 98 per cent volume, is thus more than 98J per cent, from an effluent whose inidffl content is 70 per cent I olume ... 

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