Direct heat exchange

For direct heat exchange in an L/L dispersion, Calderbank and Moo-Young [67] determined the following process relationships see also Section 6.6 and Fig. 

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Unhke other refrigeration systems, the chiUed-water flow rate is of no particular importance in steam-jet system design, because there is, due to direct heat exchange, no influence of evaporator tube velocities and related temperature differences on heat-transfer rates. Widely varying return chiUed-water temperatures have Uttle effect on steam-jet equipment. 

There are two types of snow cooling system. One is direct heat exchanging system and the other is indirect heat exchanging system. Direct heat exchanging system is the same as the forced convection type. Room air is circulated between a room and a stored snow room by fans and cooled directly. The advantages of this system are... 

From these reasons, almost large snow cooling systems adopted indirect heat exchanging system. In indirect system, a water-water-type heat exchanger is used between primary and secondary system. Figure 186 shows an application of direct heat exchange system. 

Nagano, K., S. Takeda, T. Mochida, and K. Shimakura, 2004. Thermal characteristics of a direct heat exchange system between granules with phase change material and air, Appl. Thermal Eng., 24 (14-15), 2131-2144. 

Fig. 10.3 Direct heat exchange network for example process...

The temperature of the reaction mass can be decreased through direct heat exchange by the addition of a relatively cold liquid. The overall decrease in temperature leads to a lower reaction rate, and the active quantity of the reaction mass is decreased, which reduces the energy production per unit mass. This implies that some kind of mixing is available. Of less importance is the solubility between the cold liquid and the reaction mass. Thus, if water is added to an organic solvent which has a specific gravity less than 1, and the water does not dissolve in the reaction mass, the ultimate effect may be less than desired if mixing is not adequate. 

The use of rotary desiccant wheels for dehydration has been practiced for several decades. Carl Munters [13] created the first rotary adsorbers by impregnating corrugated paper with LiCl and then ran the rotor using direct heat exchange to regenerate the sorbent. More recently Munters, NTI and others have developed improved adsorbents for rotary dehydrators. 

There are three basic types of chemical reactors developed for the MTG process l) adiabatic fixed-bed, 2) fluidized-bed, and 3) direct heat exchange. The first two were developed by Mobil and the last by Lurgi. 

Cooling. The gaseous effluent is cooled to between 40 and 45°C by indirect and direct heat exchange, and the residual gases are scrubbed, purged, and fecompressed and... 

Synthesis with oil recycle in the presence of iron catalysts of the synthetic ammonia type. Storch and his co-workers (U.S. Bureau of Mines, Bruceton, Pennsylvania) have carried out exhaustive research and development work on hydrocarbon synthesis since the end of World War II. Two variations of the process were particularly investigated, both using oil for direct heat exchange (71). One method employs the... 

Early in 1950 we had developed a catalytic composition and structure which is now known as the Oxycat. The porcelain structure was conceived to minimize pressure drop and direct heat exchange between reactants and the catalysts and at the same time bear temperatures as high as 2000° F. On such a structure a catalytic film of 0.002-in. thickness was found to be adequate for maximum activity and useful life. 

Direct heat exchange by mixing the two streams that are exchanging heat. 

Unless exotic materials are used, heat exchangers should not be used for cooling and/or condensing process streams with temperatures above 1,150 F. Instead, use the following heuristic for direct heat exchange. 

Streams of solid particles are commonly heated or cooled directly or indirectly. Heat transfer is much more rapid and controllable when using direct heat exchange. 

Figure 5.5 illustrates the single-shell continuous/ semi-continuous concept. The oil is pumped continuously via a vacuum deaerator and direct heat exchanger to the top section of the deodorizer,... 

Note that direct heat exchange between the top and bottom streams is more thermodynamically efficient than via a separate heat pump fluid. Table 2 shows stream temperatures and pressure for the case when the top column pressure is 21.6 bar. 

RVACS - Reactor vessel auxiliary cooling system DHX - Direct heat exchanger PRACS - Primary reactor auxiliary cooling system RV -Reactor vessel... 

The engineering contractor who designed the slurry pumparound rate for 700,000 Ib/hr vapor flow was mistaken. He forgot that the superheated reaction vapors were cooled primarily by evaporating cycle oil and not through direct heat exchange with the relatively cool slurry oil pumparound. 

Three types of air preheaters are typically used direct heat exchange, heat exchange via an intermediate circulating oil, and heat exchange by a massive heat-transfer wheel with metal baskets (Lungstrom type). 

A circulating fluidized bed ean also be constructed in a concentric configuration as an internally circulating fluidized bed. The riser is usually located in the interior with the downcomer as an outer armulus (e.g., Fusey el al., 1986). Such geometries simplify construction, facilitate direct heat exchange between the riser and the downcomer, and simplify the design of high-pressure systems. 

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