Heat transfer capacity, reduction

Design to allow for internal and external fouling resulting in reduction of heat transfer capacity... 

Continuous polymerization systems offer the possibiUty of several advantages including better heat transfer and cooling capacity, reduction in downtime, more uniform products, and less raw material handling (59,60). In some continuous emulsion homopolymerization processes, materials are added continuously to a first ketde and partially polymerized, then passed into a second reactor where, with additional initiator, the reaction is concluded. Continuous emulsion copolymerizations of vinyl acetate with ethylene have been described (61—64). Recirculating loop reactors which have high heat-transfer rates have found use for the manufacture of latexes for paint appHcations (59). 

Circffiation and heat transfer in this type of evaporator are strongly affected by the liquid level. Highest heat-transfer coefficients are achieved when the level, as indicated by an external gauge glass, is only about halfway up the tubes. Shght reductions in level below the optimum result in incomplete wetting of the tube walls with a consequent increased tendency to foul and a rapid reduction in capacity. When this type of evaporator is used with a liquid that can deposit salt or scale, it is customary to operate with the liquid level appreciably higher than the optimum and usually appreciably above the top tube sheet. 

After evacuation and at the start of heating, the trend of Tice approaches too close to the maximum tolerable Tice. A reduction in the operation control pressure (pc) will immediately stop this trend (Figure 2.88) (if the desired Tice is not reached p could be raised.) The slope of the function Tice =j[pt) can become unfavorably steep. In this case, the shelf temperature should also be lowered or raised, but the effect of this change will take time before an equilibrium state is reached again (e.g. 0.5-1 h) depending on the heat transfer conditions and the heat capacity of the shelves and the heat transfer medium. 

This project will identify the constraints that prevent existing fuel processors from reaching rated capacity in 30 seconds or less. A fundamental technical barrier is the thermal mass of the catalysts and stmctural materials. Reductions in thermal mass require improvements in catalyst materials and effective heat transfer. Other limiting factors are related to auxiliary equipment and process design, such as available gas blowers and burners, the fuel injection system, sensor response, and hot gas distribution within the processor. 

Second, solid layer formation by the product on the heat transfer surface requires either an increase in temperature driving force to maintain the same growth rate (therefore production rate) or leads to a reduction in capacity with increasing thickness. 

An eflicient compressor (oil-free type may be considered) for the refrigerant. Cooling tower of a little additional capacity shall be selected to take care of reduction in capacity in humid weather and fouling of condenser heat transfer surfaces. 

Reduction of the heat-transfer coefficient in an evaporator will lead directly to lost refrigeration capacity. A good indication of evaporator prob-... 

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