Water cycle vapor

One form of solar heat does offer interesting possibilities and is refeiTcd to as OTEC (Ocean-Thermal Energy Conversion). The OTEC power plant principle uses the solar heat of ocean surface water to vaporize ammonia as a working fluid in a Rankine cycle. After the fluid is expanded in the turbine, it is condensed by the 22°C colder... 

The Water Cycle. The evaporation of water from land and water surfaces, the transpiration from plants, and the condensation and subsequent precipitation of rain cause a cycle of transportation and redistribution of water, a continuous circulation process known as the hydrologic cycle or water cycle (see Fig. 86). The sun evaporates fresh water from the seas and oceans, leaving impurities and dissolved solids behind when the water vapor cools down, it condenses to form clouds of small droplets that are carried across the surface of the earth as the clouds are moved inland by the wind and are further cooled, larger droplets are formed, and eventually the droplets fall as rain or snow. Some of the rainwater runs into natural underground water reservoirs, but most flows, in streams and rivers, back to the seas and oceans, evaporating as it travels. 

The saturation vapor pressures of HDO and H2 0 are lower than those of H2 0, both over liquid and solid phases. These differences play an important role in the course of the atmospheric water cycle as they cause fractionation effects at vapor/liquid and vapor/solid phase changes, with the condensed phase in equilibrium with vapor being enriched in heavy isotopes. The fractionation coefficient a is defined as the ratio of D/H or in the condensed phase to the value of... 

The condensation of water vapor and its precipitation from the atmosphere in the form of rain, snow, sleet, or hail are important not only for the water cycle, but also because they bring to the earth surface other atmospheric constituents, primarily those substances that have a pronounced affinity toward water in the condensed state. Cloud and precipitation elements may incorporate both aerosol particles and gases. The uptake mechanisms are discussed in this chapter, together with the inorganic composition of cloud and rain water that they determine. These processes are, in principle, well understood. Another subject requiring discussion is the occurrence of chemical reactions in the liquid phase of clouds. The oxidation of S02 dissolved in cloud water is considered especially important. As a result of laboratory studies, the conversion of S02 to sulfate is now known to proceed by several reaction pathways in aqueous solution. 

Others expect water vapor emissions in a hydrogen energy economy (assumption is that half of the present energy supply is covered by hydrogen) to be reducible down to the respective level presently given by the fossil and nuclear economy which is a 0.005 % share of the total atmospheric water cycle. In order to reach the above reduction factor, hydrogen losses need to be decreased from currently estimated 10 % over the whole chain to 2 - 3 %. Today s world energy economy emits around 20 10 kg of water per year [134]. 

The water cycle is driven by processes that force the movement of water from one reservoir to another. Evaporation from the oceans and land is the primary source of atmospheric water vapor (Fig. 2.36). Water vapor is transported, often over long distances (which characterize the type of air masses), and eventually condenses into cloud droplets, which in turn develop into precipitation. Globally, there is as much water precipitated as is evaporated, but over land precipitation exceeds evaporation and over oceans evaporation exceeds precipitation (Fig. 2.35). The excess precipitation over land equals the flow of surface and groundwater from continents to the oceans. Flowing water also erodes, transports and deposits sediments in rivers, lakes and oceans, affecting the quality of water. 

All the water on Earth is connected in a global water cycle ( Figure 18.15). Most of the processes depicted here rely on the phase changes of water. For instance, warmed by the Sun, liquid water in the oceans evaporates into the atmosphere as water vapor and condenses into liquid water droplets that we see as clouds. Water droplets in the clouds can crystallize to ice, which can precipitate as hail or snow. Once on the ground, the hail or snow melts to liquid water, which soaks into the ground. If conditions are right, it is also possible for ice on the ground to sublime to water vapor in the atmosphere. 

Figure 11.3 is a schematic of a steam power plant and Fig. 11.4 is the P-Fq diagram for the widely used Rankin engine cycle. The pump takes water exiting the condenser at temperature (Zj) and pressure (Pj) and raises the pressure to P at, essentially, a constant temperature [from point (1) to point (2) in Fig. 11.4]. The water is vaporized and, possibly, superheated to temperature (Z2) at, essentially, a constant pressure (P2) [from point (2) to point (3) in Fig. 11.4] in the boiler and superheater...

The water cycle is a process in which water continuously moves through the environment by the processes of evaporation, condensation, and precipitation. Liquid water on Earth evaporates. In the air, water vapor condenses on dust particles, forming clouds. Liquid water returns to Earth in the form of precipitation. Precipitation soaks into the ground and flows into bodies of water. 

Many measurements were made to determine the content of water vapor in the atmosphere of Mars. Some examples are the MAWD (Mars Atmospheric Water Detector) on board of Viking 1 and Viking 2 orbiters or measurements made with Mars Global Surveyor Mission and Mars Express. Very often the IR band about 1.38 pm was used. Such measurements are important input factors for understanding the annual water cycle on Mars. For example Fedorova et al., 2010 [128] report on Viking observation of water vapor on Mars explaining some discrepancies of the results obtained by different instruments. 

Wordsworth et al 2010 [367] made a three dimensional global circulation model (GCM) of the early martian climate. In their model CO2 condensation, cloud formation and a water cycle was included. Local water vapor feedbacks compensate reduced CO2 warming effects. In general CO2 clouds lead to a substantial warming. 

A close examination of the amounts of heats involved in these steps, 629, 1752 and 536 (all in kJ/kg) respectively for the power plant cycle of Example 3.12, suggests that the most important one, with respect to efficiency, is the temperature at which water is vaporized which, in turn, is determined by the boiler pressure. 

Stea.ming Retjuirements. The steaming of fixed beds of activated carbon is a combination of thermal swing and displacement purge swing. The exothermic heat released when the water adsorbs from the vapor phase is much higher than is possible with heated gas purging. This cycle has been successhiUy modeled by equiUbrium theory (128). 

Fig. 6. In a binary electricity generation plant, the hydrothermal water from the weU, A, is passed through a heat exchanger, B, where its thermal energy is transferred to a second, more volatile working fluid. The second fluid is vaporized and deflvered to a turbine, D. After exiting the turbine the spent working fluid is cooled and recondensed in another heat exchanger, E, using water or air as the coolant, F. It is then fed back to the primary heat exchanger to repeat the cycle. Waste hydrothermal fluid, C, can be reinjected into the producing field.

Absorption Systems. Absorption refrigeration cycles employ a secondary fluid, the absorbent, to absorb the primary fluid, refrigerant vapor, which has been vaporized in the evaporator. The two materials that serve as the refrigerant—absorbent pair must meet a number of requirements however, only two have found extensive commercial use ammonia—water and water—Hthium bromide. 

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