EAS446lec2 - EAS44600 Groundwater Hydrology Lecture 2: The...

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EAS44600 Groundwater Hydrology Lecture 2: The Hydrologic Cycle Dr. Pengfei Zhang Water Water exists in three phases: liquid, solid, and vapor. On the phase diagram (Figure 2-1), the point at which vapor, solid, and liquid all exist in equilibrium is called the triple point of water (T = 273.16 °K or 0.01 °C and P = 611.21 Pa or 4.58 torr). The maximum density of liquid water is near 4 °C, not the freezing point. Therefore, water expands upon freezing, and ice floats on water. Figure 2-1. Phase diagram of water. As water changes its physical phase (e.g., from liquid to vapor or from liquid to solid), heat is either absorbed or released. The heat associated with a phase change of a substance is called the latent heat . The latent heat values of water during phase changes are tabulated in Table 2-1. Table 2-1. Latent heat values of water. T Vaporization/Condensation Freezing/Melting Sublimation/Deposition 0 °C 2.50×10 6 Jkg -1 3.34×10 5 Jkg -1 2.83×10 6 Jkg -1 100 °C 2.25×10 6 Jkg -1 Water vapor may serve as a vehicle for transferring heat from the point of evaporation to the point of condensation. For example, water in the tropics may be evaporated by intense solar radiation (a process uses about 2.4×10 6 J for each kilogram of water evaporated). The water vapor may then move toward the mid-latitudes and be re-condensed to liquid in a cloud. The condensation process releases 2.4×10 6 J sensible heat per kilogram of water condensed. The latent heat of vaporization/condensation carried by one kilogram of water (2.4×10 6 J) is 2-1
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equivalent to the kinetic energy of a 2,200 lb automobile moving at 156 mph, or the potential energy of raising this automobile from the ground to the top of an 80-story building! The Hydrologic Cycle The endless movement of water between the Earth’s biosphere, atmosphere, lithosphere, and hydrosphere is called the hydrologic cycle. Water on the Earth may be temporarily stored in various reservoirs including atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater. Water continuously moves from one reservoir to another by way of evaporation, transpiration, condensation, precipitation, runoff, infiltration, groundwater flow, sublimation, and melting (Figure 2-2).
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This note was uploaded on 12/29/2010 for the course EAS 44600 taught by Professor Pengfeizhang during the Spring '10 term at CUNY City.

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EAS446lec2 - EAS44600 Groundwater Hydrology Lecture 2: The...

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