Water accumulation

Some servo gauges also have the abiHty to measure interface. This can be very important when water accumulates in the bottom of the vessel over time (water bottoms). In this way, the user receives information on the accumulation of water (which will eventually need to be pumped out), and also gets a more accurate reading of the real level of the product being stored. 

Simplified Cycle. A simplified fossil steam cycle appears in Figure 19. The water accumulates in the bottom of the condenser, called the hotweU. It goes through a feed pump to pressurize it. The pressurized water passes through one or more feedwater heaters, which raise the temperature. The water then enters the boiler where heat from the fuel converts it to steam. The steam expands through the engine, usually a turbine, which extracts work. In the middle of the turbine some of the steam is extracted to supply heat to the feedwater heater. The remainder expands through the turbine and is condensed. The rejected heat is carried away by the condenser coolant, which is usually water, but sometimes air. The condensed steam then returns to the... 

Esters of medium volatility are capable of removing the water formed by distillation. Examples are propyl, butyl, and amyl formates, ethyl, propyl, butyl, and amyl acetates, and the methyl and ethyl esters of propionic, butyric, and valeric acids. In some cases, ternary azeotropic mixtures of alcohol, ester, and water are formed. This group is capable of further subdivision with ethyl acetate, all of the ester is removed as a vapor mixture with alcohol and part of the water, while the balance of the water accumulates in the system. With butyl acetate, on the other hand, all of the water formed is removed overhead with part of the ester and alcohol, and the balance of the ester accumulates as a high boiler in the system. 

Thermal contrac- Drumming at proper temperatures tion vacuum ere-. integrity walls ated which can suck air moisture prevent water accumulation on drum etc., into drum creating unwanted reaction or collapse of the drum. CCPS G-3 CCPS G-15 CCPS G-22 CCPS G-29... 

The piping around any facility, other than the straight pipe connecting the equipment, is made up primarily of a series of control stations. Flow from one vessel goes through a control station and into a piece of pipe that goe.s to another vessel. In addition to considering the use of block valves, check valves, etc., all control stations should be designed so that the control valve can be removed and any bypass valve is located above or on a level with the main control valve. If the bypass is below the con tiol valve, it provides a dead space for water accumulation and corrosion. 

Drains. Drains or drain seals must be provided in locations necessary to prevent water accumulation. 

A tank was installed in a concrete-lined pit. The pit was then filled with sand, and a layer of concrete 6 in. thick w as put over the top. Water accumulated in the pit, and the buoyancy of the tank was sufficient to break the holding-down bolts and push it through the concrete covering. 

As a part of any routine maintenance procedure, these discharge traps should periodically be manually bypassed to ensure that the trap is functioning, and no excessive water accumulation is evident. 

Emulsion breakers (dewatering agents) These functional materials are water-in-oil emulsion breakers that permit the separation of emulsified water. The water accumulates in the tank bottom and... 

This steam distillation removes ether, tetrahydrofuran, and other volatile neutral products. If too much water accumulates in the flask, it may be heated in an electric heating mantle after most of the ether has been removed. 

Bisphenol A Production of resins (polycarbonate and epoxy resins). Component in flame retardant production Antioxidant, preservative - River water mean values 0.016 pg L 1 (Europe) and 0.5 pg L"1 (US) [66]. -SW <0.001-1 pg U1 [9] - WW effluents mean values 1.5 pg L-1 [67] Not persistent in surface water. Rapidly biodegraded in aquatic environments [68] and removed in WWTP. Half-life 1-4 days [69] in water. Accumulated in anoxic sediments [9]... 

In reverse, the surfactant precipitates from solution as a hydrated crystal at temperatures below 7k, rather than forming micelles. For this reason, below about 20 °C, the micelles precipitate from solution and (being less dense than water) accumulate on the surface of the washing bowl. We say the water and micelle phases are immiscible. The oils re-enter solution when the water is re-heated above the Krafft point, causing the oily scum to peptize. The way the micelle s solubility depends on temperature is depicted in Figure 10.14, which shows a graph of [sodium decyl sulphate] in water (as y ) against temperature (as V). 

Rainbow trout exposed to naphthalene in surrounding water accumulate this hydrocarbon in eyes (14). The retention (including bioconversion products) may be related to observed morphological changes, such as cataract formation, which occurs in marine fish exposed to individual hydrocarbons ()8) and petroleum (19). Roubal et al. (20) have demonstrated that gills of salmonids are major sites forHischarging naphthalene, which implies that the more water-soluble hydrocarbons in general are cleared via this route. 

Similar observations were presented by Spernjak et al. [87], who also developed a transparent fuel cell to visualize the different behavior of treated and untreated DLs. This cell gave the indication that with treated DLs the water produced at the cathode side emerged as droplets on the surface of the material over the entire visible area. However, with the untreated DLs, water preferred to be in contact with the side walls of the channels with time, the water accumulated and formed films and slugs near the flow field walls. This behavior caused greater water management issues and lower gas transport toward the active catalyst areas. 

After testing a number of DLs with and without MPLs, Lin and Nguyen [108] postulated that the MPL seemed to push more liquid water back to the anode through the membrane. Basically, the small hydrophobic pores in the MPL result in low liquid water permeability and reduce the water transport from the CL toward the DL. Therefore, more liquid water accumulated in the CL is forced toward the anode (back diffusion). This reduces the amount of water removed through the cathode DL, decreases the number of blocked pores within the cathode diffusion layer, and improves the overall gas transport from the DL toward the active zones. 

One drawback of using the MPL is that the water saturation in the CL increases and causes more flooding [108]. Through neutron radiography imaging, Owejan et al. [147] were able to observe that MEAs that had cathode DLs with MPLs had better distribution of water over the active area at high current densities. DLs without MPLs tended to have more water accumulated in one location of the active area (closer to the outlet). One issue with this work was that the water accumulation observed was for the whole MEA and the water quantities were not separated between the anode and cathode sides. 

Schmitz et al. [184] tested various carbon fiber papers with different thicknesses as cathode DLs in PEM fuel cells. It was observed that the cell resistance dropped when the thickness of the DL increased thus, thicker materials are desired in order to improve the electrical conductivity. It was also mentioned that the optimal thickness for the DL is usually between the thinnest and the thickest materials because the two extremes give the lowest performance. In fact, in thin DLs, the water produced can fill pores within the material, resulting in flooding and the blockage of available flow paths for the oxygen. Similarly, Lin and Nguyen [108] concluded that thinner DLs (without MPLs) were more prone to liquid water accumulation than thicker ones. 

In recent years, the use of transparent fuel cells has increased substantially due to the need for a better understanding of liquid water accumulation on the surface of the DLs and flow through the FF channels. In most transparent cells, either the cathode or the anode (or both) has transparent polycarbonate end plates that act as windows and sit on top of the corresponding FF plates. These plates are normally thin and made out of metal, such as stainless steel or gold-plated brass, and their thickness is equal to the depth of the FF channels (i.e., the charmels are machined all the way through the plate). Thus, the transparent end plate also acts as part of the charmels. 

Ge and Wang [226] utilized a transparent fuel cell with two different FF designs—straight and serpentine—in order to study the water accumulation on the anode side of a fuel cell. No water accumulated on top of the DL surfaces in either FF design during all the tests. The literature contains many other examples of transparent cells used as tools to better understand the water transport mechanisms in fuel cells [111,227-232]. 

As briefly mentioned in Section 4.3.S.2, Atiyeh et al. [152] performed water balance measurements and calculations to determine the effect of using DLs with MPLs (on either or both cathode and anode sides). In their fuel cell test station, water collection systems were added in order to be able to collect and measure accurately the water leaving both anode and cathode sides of the fuel cell. Based on the operating conditions (e.g., pressures, temperatures, relative humidities, etc.) and the total amount of water accumulated at the outlets of the test station, water balance calculations were performed fo defermine the net water drag coefficient. Janssen and Overvelde [171] used this method to observe how different operating conditions and fuel cell maferials affected... 

In another study, Nakajima, Konomi, and Kitahara [144] studied the water accumulation in different components of the fuel cell at simulated start-up cycles. Each component was weighed before and after each test once a test was completed, water balance analysis was performed. Through this analysis, the effect of different diffusion layers was probed in detail, and it was concluded that the DLs with higher gas permeability were able to remove water more efficiently. It was also observed that the MPL was effective in improving start-up performance of the fuel cell by suppressing water accumulation at the CL and within the DL. 

Transparent fuel cells are also common tools used to visualize and observe the water accumulation inside FFs and on the surfaces of diffusion layers. Liu, Guo, and Ma [227] tested interdigitated and parallel flow fields wifh CFP DLs. It was observed that the former FF design enhanced the mass transfer when the gas flow was forced to pass through the DL. In fact, the water flooding areas in the interdigitated channels were substantially smaller than in the parallel channel. 

J. P. Owejan, T. A. Trabold, D. L. Jacobson, M. Arif, and S. G. Kandlikar. Effects of flow field and diffusion layer properties on water accumulation in a PEM fuel cell. International Journal of Hydrogen Energy 32 (2007) 4489-4502. 

Equations (6.59)-(6.61) represent a highly simplified scheme for evaluating various catalyst layer designs. Refinements of this crude framework for evaluating catalyst layer performance should address all transport limitations, account for water accumulation, and include two- and three-dimensional effects. 

The challenge for modeling the water balance in CCL is to link the composite, porous morphology properly with liquid water accumulation, transport phenomena, electrochemical kinetics, and performance. At the materials level, this task requires relations between composihon, porous structure, liquid water accumulation, and effective properhes. Relevant properties include proton conductivity, gas diffusivihes, liquid permeability, electrochemical source term, and vaporizahon source term. Discussions of functional relationships between effective properties and structure can be found in fhe liferafure. Because fhe liquid wafer saturation, 5,(2)/ is a spatially varying function at/o > 0, these effective properties also vary spatially in an operating cell, warranting a self-consistent solution for effective properties and performance. 

This is to assume that a dry membrane is hydrated by production water generated at the current density, I. For Nafion 112 and a reference current density of 1 A/cm, this is about 25 s Therefore, for low humidity cells where the membrane undergoes water content changes, the water accumulation term is essential for transient analyses. 

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