Evaporation from porous media is an important process in the field of science and engineering. Its context ranges from drying of wood, food products [Fernando et al., 2008], to water balance between soil and atmosphere [Shokri, 2013]. Constant research has been conducted to predict the phenomena of drying in porous media of which till today remains a challenge. It is understood that the drying behaviour can be affected by both the atmospheric demand (humidity, temperature and ambient air velocity) and by porous-medium pore space and its transport properties (thermal and hydraulic conductivities and vapour diffusion) [Lehmann et al., 2008]. Brakel [1980] and Prat [2002] had also discussed the strong interaction between the porous medium, transport properties and the atmospheric conditions that has led to a wide range of evaporative behavior. Figure 1 gives a general understanding of porous media from the field scale to the pore scale.
Figure 1: Observation scale in a porous medium (Szymkiewicz, 2013)
The evaporation process in the porous media is mainly characterised by stage-1, stage-2 and the transition from stage-1 to stage-2. Stage-1 is controlled by the atmospheric condition and is where the evaporation rate is rather high and constant whereas for stage-2, the evaporation rate is much lower and is dependent on the transport property of the porous media [Shokri & Or, 2011].The transition stage is where the recovery rate decreases instantly due to the mass transfer through the dry pore space through diffusion [Yiotis et al., 2005]. Experimental procedures and different modeling techniques (i.e., Acoustic measurement, neutron radiography, 3-D pore network model, X-ray synchrotron radiation and infrared thermography) were con...
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...he volumetric air content, ϕ is the porosity, D_atm is the vapour diffusion coefficient in free air, C_sat is the saturated vapour density at the secondary drying front, C_∞ is the water vapour density above the surface and ξ is the vapour diffusion length.
The primary objective of present work is to specifically describe: (a) evaluate the effects of temperature and relative humidity on evaporation in porous media; (b) to study the dynamics of transition from stage 1 to stage 2 evaporation as influenced by atmospheric conditions; and (c) to quantify the key controls for the transition from stage 1 to stage 2 in porous media with atmospheric conditions and particle sizes of sand samples. We seek to critically evaluate the evaporation rate at the onset of transition (end of stage 2) and compare with the predicted with using any vapour transport enhancement factors.
Pentane was observed to have the highest evaporation rate. Isopropanol had the lowest evaporation rate. Pentane is nonpolar and it’s strongest intermolecular force is London Dispersion Force. Because Isopropanol is polar and has strong hydrogen bonds, the bonds are harder to break and the evaporation rate was lower because it took more time to break this force. Pentane has a weaker molecular force than the hydrogen bonds so it evaporated faster than the Isopropanol.
Conductivity: Thermal conductivity of the growing media which is related to the wet or dry environment (W/(m-K).
This hypothesis was supported by the data found because 2 out of the 3 trials done, tap water evaporated the most over the 5 day period. For the first trial, saltwater lost 96 grams, stream water lost 98 grams, and tap water lost 100 grams. For the second trial, saltwater lost 67 grams, stream water lost 70 grams, and tap water lost 69 grams. For the third and final trial, saltwater lost 71 grams, stream water lost 72 grams, and tap water
The comparison between the vapour compression and vapour absorption systems are given in Table 1
There are numerous stages that take place simultaneously in the hydrologic cycle and this includes evaporation. This is when the water alters from a liquid state into a gas. The damp air from the water rises into the atmosphere and when it cools, the vapor condenses and shapes into clouds. But those billows are not the only form the vapors make; it can also materialize as dew, fog and mist, which blanket the Earth, characteristically on a rainy or humid day. Evaporation takes place when water changes from a liquid state into a gaseous state, and ascents out of the pores of the earth and into the atmosphere as a vapor (“How”). While evaporation is taking place, condensation is also occurring. When the temperature in the air plunges, the clouds become heavy and as a result they relieve themselves of the extra weight, which is called precipitation. This produces rain, hail, snow and sleet, conditioned upon the temperate. As the precipitation falls, it enters the surface of the ground and percolates into the soil, which is called infiltration. The more porous the land is, the more the infiltration can take place. However, the ground cannot hold all of that water and floods. The excess rainfall, which is also called runoff that has not been absorbed makes its way into bodies of water, such as small ponds, rivers, lakes and parts of the ocean (“Summary”).
History of drying and wetting: soil suction is less during wetting time than it is during drying time.
Temp: Mass of evap. dish: Mass of evap dish+contents: Mass of contents: Solubility g/100cm3 water
Trees kept the moisture in certain level in surrounding areas of trees by transpiration process. In the transpiration process trees inhales the water by their root and exhales water by their stomata.This process is called transpiration. By the transpiration process trees reduces the adjacent air temperature by some degrees. This reducation rate can vary from tree to tree and species to species. This level of changes makes huge impacts in arid and semi arid environment.
In a similar transpiration lab, performed by an AP student, the results showed that controlled was the fastest, wind the second, light and heat the third, and humidity the slowest. These results occurred because all four environments played a role in increasing evaporation which therefore increased the rate of evaporation. In the controlled environment, the room temperature helped increase the rate of evaporation (1.67mL/m²). In the wind environment, the blowing of air on the leaves increased the rate of evaporation (0.76 mL/m²). In the light and heat environment, the heat hitting the plant increased the rate of evaporation therefore increasing amount of water being transpired (0.93 mL/m²). In the humidity environment, the moist ...
Thermodynamics is the branch of science concerned with the nature of heat and its conversion to any form of energy. In thermodynamics, both the thermodynamic system and its environment are considered. A thermodynamic system, in general, is defined by its volume, pressure, temperature, and chemical make-up. In general, the environment will contain heat sources with unlimited heat capacity allowing it to give and receive heat without changing its temperature. Whenever the conditions change, the thermodynamic system will respond by changing its state; the temperature, volume, pressure, or chemical make-up will adjust accordingly in order to reach its original state of equilibrium. There are three laws of thermodynamics in which the changing system can follow in order to return to equilibrium.
The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration.
The rate of evaporation can increase if the gas pressure decreases around the liquid. Heat energy is used to break the bonds that hold water molecules together, that is why water easily evaporates at the boiling point but evaporates much slower at the freezing point. Net evaporation happens when the rate of evaporation surpasses the amount of condensation. Saturation occurs when these two process rates are equivalent when the humidity of the air is at one-hundred percent. On average, a fraction of the atoms in a glass of water has enough heat energy to escape from the liquid. Evaporation from the ocean is the primary device for supporting the surface-to-atmosphere part of the water cycle. Evaporation is the pathway where water moves from the liquid state back into the water cycle as atmospheric vapor. Studies have shown that the major bodies of water are nearly ninety percent of the moisture in the atmosphere from the evaporation of the water, the ten percent left is contributed from plant transpiration. Evaporation can only occur when water is available. It also requires the humidity of the surrounding atmosphere to be less than the evaporating surface. At one-hundred percent relative humidity, there is no more evaporation. The wind chill effect is one of the
Peoples are always trying different techniques to beat the scorching heat, specifically in summer season. Recently, there many methods that proved their quality in reducing the atmospheric temperature to the required rates. There are three main types of evaporative cooling systems which are sprinkler systems, pad systems and Fogger systems. This project interested in the last one. Fogger system is defined as a type of nozzles that sprays water with high-pressure (up to 200 psi) or low pressure (less than 50 psi) to the air as a fine fog or mist. These fine fog or mist evaporates into the outdoor air in order to cool this air which is located beside the fogger (Giacomelli, 2003).
Water Pollution is a current issue that has serious consequences; it progresses everyday in our lakes, oceans, rivers and other bodies of water.
A. When the water evaporates the mass of the water changes a lot but the density stays the same.