Evaporation, sloped

A cocurrent evaporator train with its controls is illustrated in Fig. 8-54. The control system applies equally well to countercurrent or mixed-feed evaporators, the princip difference being the tuning of the dynamic compensator/(t), which must be done in the field to minimize the short-term effects of changes in feed flow on product quality. Solid concentration in the product is usually measured as density feedback trim is applied by the AC adjusting slope m of the density function, which is the only term related to x. This recahbrates the system whenever x must move to a new set point. 

Single-Effect Evaporators The heat requirements of a singleeffect continuous evaporator can be calculated by the usual methods of stoichiometry. If enthalpy data or specific heat and heat-of-solution data are not available, the heat requirement can be estimated as the sum of the heat needed to raise the feed from feed to product temperature and the heat required to evaporate the water. The latent heat of water is taken at the vapor-head pressure instead of at the product temperature in order to compensate partiaUv for any heat of solution. If sufficient vapor-pressure data are available for the solution, methods are available to calculate the true latent heat from the slope of the Diihriugliue [Othmer, Ind. Eng. Chem., 32, 841 (1940)]. 

It can be seen from Figure 13.5 that for the air-water system a straight line, of slope equal to the enthalpy of dry saturated steam (2675 kJ/kg), is almost parallel to the isothermals. so that the addition of live steam has only a small effect on the temperature of the gas. The addition of water spray, even if the water is considerably above the temperature of the gas, results in a lowering of the temperature after the water has evaporated. This arises because the. latent heat of vaporisation of the liquid constitutes the major part of the enthalpy of the vapour. Thus, when steam is added, it gives up a small amount of sensible heat to the gas, whereas when hot liquid is added a small amount of sensible heat is given up and a very much larger amount of latent heat is absorbed from the gas. 

Because of the irregular rainfall distribution, mean precipitation values have little meaning in the (semi)-arid zone, if not also the range of variation is indicated. This variability refers to both temporal and spatial variability. Temporal variability affects not only the onset and duration of the rains in the year, but plays also a role in year-by-year differences. The variability is highest in the hyper-arid zone, where the mean precipitation value is composed of a few intensive rainstorms. When these fall on a heated barren surface - as is often the case in the arid zone - a part of it is immediately evaporated and lost for soil processes. High rainfall intensity results on the other hand in a rapid saturation of the surface layers and creates lateral runoff and erosion, in particular on sloping land. Many arid and semi-arid soils show therefore features of gully and sheet erosion. 

The gradual frequency increase from points B to C is explained by the mass decrease due to the evaporation of water deposited between layers from the subphase. The amount of incorporated water (W2 / ng) and its evaporation speed (v / ng min- ) were calculated from the frequency change and the initial slope of the time course between points B and C, respectively. The cadmium octadecanoate LB films were observed to incorporate W2 = 209 5 ng of water with 4 layers of LB films (W, = 232 3 ng) at the first dipping cycle cadmium octadecanoate were transferred on a substrate with the water of almost the same mass of LB films. 

To enable a practical building scrubber design, bunds will be insulated to minimise the rate of evaporation from a major liquid chlorine release (i.e. at least to a rate that can be treated by the scrubber). The bunds will slope to a sump to collect small liquid spills, minimising the surface area of the spill and hence minimising the chlorine evaporation rate. 

The banks around evaporation ponds can be built from the existing soil and excavated earth. It is suggested that a layer the topsoil be removed from the pond area, and the subsoil underneath be used to form the inside of the bank. The outer slope of the bank can be covered in the removed topsoil, as this promotes the regrowth of vegetation (Singh and Christen 2000). An example of this is shown in Fig. 7.4. 

Suggested dimensions for evaporation ponds are given by Singh and Christen (2000), and these can be seen in Fig. 7.5. The banks surrounding the pond should be a minimum of 1 m high and 2.4 m wide to allow for vehicular access. To reduce erosion, it is recommended that the slope of the inner bank should be 1 5 and the outside bank a slope of 1 2. 

The vegetation zones along the slope and at the crest are subjected to oxidant exposure differently. Even though the lower chaparral receives longer exposure, the peak concentrations coincide more closely with the maximal evaporative stress for the day. There is some support for the hypothesis that stomates would be closed during this period and that pollutant uptake would be lower. There is in fact very little visible injury to the species in this zone. In contrast, the daily oxidant peak occurs well after the temperature and vapor-pressure gradient maximums in... 

For evaporation-condensation dynamics, there is a simple way to convert the equation of motion (16) for a single step to the equation of motion for a vicinal surface at a slope 5 1, assuming steps have a contact repulsion. The idea is that, if we scale... 

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