Surface condensers drive

There are three potential types of OTEC power plants opcii-cyclc, closed-cycle, and hybrid systems. Open-cycle OTEC systems exploit the fact that water boils at temperatures below its normal boiling point when it is under lower than normal pressures. Open-cycle systems convert warm surface water into steam in a partial vacuum, and then use this steam to drive a large turbine connected to an electrical generator. Cold water piped up from deep below the oceans surface condenses the steam. Unlike the initial ocean water, the condensed steam is desalinated (free of salt) and may be collected and used for drinking or irrigation. 

A surface condenser condensing the steam from a process turbine drive operates at 1.0 in. Hg abs. The condensing load is 85,000 Ibs/hr steam. WTat is the capacity of the ejector ... 

A design of turbine whereby the driving force is provided by exhaust steam condensing in a surface condenser. 

Steam used to drive a turbine can be extracted at an intermediate pressure, for further use of the low-pressure steam. Rarely is the steam vented to the atmosphere, as this wastes steam, and the condensate is also lost. Many turbines exhaust steam, under vacuum, to a surface condenser. The lower the pressure in the surface condenser, the greater the amount of work that can be extracted from each pound of steam (see Chap. 17). 

As discussed above, a thermodynamically unstable surface will reduce its total surface energy by forming facets. From the point of view of kinetics, gradients in the chemical potential on a nonequilibrium surface will drive the movement of surface materials toward equilibrium. The transport mechanisms are the same as those that can operate during sintering (47) (a) surface diffusion, (b) bulk diffusion, (c) evaporation-condensation, and (d) plastic or viscous flow. 

The low surface tension accounts for the tendency of PDMS-containing materials to accumulate at air-substrate surfaces. At condensed interfaces, such as that between organic oils and water, the same surface tension driving force does not exist for PDMS to accumulate at the interface. PDMS has a... 

In one case, a spare duty of more than 6.0 million Btu/h (1.5 million kcal/h) was found to exist in a condenser. This duty could be utilized to condense over 2.5 tons/h of nearby waste low-pressure steam to a useful condensate. As a safe margin, we decided to condense only 1.5 tons/h. No additional driving force was necessary, since the steam pressure was always higher than that of the surface condenser. The con-... 

Untreated water from the Columbia River was supplied as coolant to the dump condensers, as well as to the reactor coolant pump drive turbine surface condensers and the local turbine generator condenser. This condenser cooling water was then returned to the river. Untreated water was also supplied to the water treatment facility for the filtered water, sanitary water, and demineralized water systems (see Figure 3-16). The entire untreated water system was supplied by four pumps each with a capacity of 400,000 L/mln (105,000 gal/min). Water was supplied from the 181-N river pumphouse to points of process use through two separate headers (WHC 1989a). 

Surface condensers are used in conjunction with condensing steam turbines that drive large centrifugal compressors. As depicted in Exhibit 4-25 the exhaust steam enters the top of the condenser and passes through the shell, which is filled with tubes. Cold water is pumped through the tubes while hot exhaust steam passes around the outside. Hot water, called condensate, results and collects in the hot well at the bottom of die condenser. 

Because this type of operation essentially involves the Nusselt theory with enhanced liquid flow, a heat transfer coefficient approach is used for calculative purposes, rather than transfer units. Temperature differences are calculated as if a surface condenser were being used. If a single-component vapor is condensing at a constant pressure, the temperature difference at the liquid coolant inlet is T — q. Similarly, the temperature difference at the liquid coolant outlet is Ti — to- This is true because the vapor temperature remains constant from the first drop of condensate to the last drop. Thus, the logarithmic mean temperature driving force is ... 

In molecular distillation, the permanent gas pressure is so low (less than 0 001 mm. of mercury) that it has very little influence upon the speed of the distillation. The distillation velocity at such low pressures is determined by the speed at which the vapour from the liquid being distilled can flow through the enclosed space connecting the still and condenser under the driving force of its own saturation pressure. If the distance from the surface of the evaporating liquid to the condenser is less than (or of the order of) the mean free path of a molecule of distillate vapour in the residual gas at the same density and pressure, most of the molecules which leave the surface will not return. The mean free path of air at various pressures is as follows —... 

Boiling is to be inside Tin. 12 BWG steel tubes, 8 ft long. Condensing steam at 50 psig is available for heating. An overall coefficient U = 300 Btu/(hr) (fP)(°F) is expected. For the given duty and a total driving force of 45°F, the inside surface required is 157 fP. This is equivalent to 96 tubes. 

A, free diameter of the connection to the chamber B, cylindrical opening by the movement of D C, opening between condenser wall and valve plate D, valve plate, hydraulic valve drive E, condensation surface of the refrigerated coils F, in- and outlet of the refrigerant G, tube connection to the vacuum pump H, water drain during defrosting of the condenser pch and pm pressure in the chamber and in the condenser, respectively. 

Simple sublimation is a batch-wise process in which the solid material is vaporised and then diffuses towards a condenser under the action of a driving force attributable to difference in partial pressures at the vaporising and condensing surfaces. The vapour path between the vaporiser and the condenser should be as short as possible in order to reduce mass-transfer resistance. Simple sublimation has been used for centuries, often in very crude equipment, for the commercial production of ammonium chloride, iodine, and flowers of sulphur. 

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