Reducing pollutants (which may result from fluid evaporation) and/or fluid loss generally are major concerns for both industry and the public. These concerns are often of particular concern in the chemical and petroleum industries where substantial sums of money are lost yearly due to the evaporation of volatile substances. Moreover, environmental concerns require stringent regulation of fluid pollutants and toxins contained in standing fluids; thus, evaporation of volatile substances pose both an environmental and a financial burden.
Moreover, these concerns are not limited to bodies of toxic fluids. For example, the evaporation of non-toxic materials is also problematic in regions permanently subjected to arid weather or areas temporarily experiencing unusual drought conditions. The reduction of evaporation or the control of energy transfer may be critical to the viability of industry in those geographical regions.
The phase change process that occurs during evaporation of a fluid may be influenced by a variety of factors. Factors that drive the evaporation rate, typically expressed in pounds of product per minute, include wind speed, the molecular weight of the fluid constituents, the exposed surface area of the fluid, vapor pressure of the fluid, and temperature. Even a small evaporation rate extended over a relatively long period of time can result in a very large loss of product.
One method of controlling evaporation is to reduce the surface area of the fluid exposed to the environment. In prior art systems, hollow plastic spherical balls have been used to cover the fluids surfaces and reduce evaporation. When deposited on a body of fluid, balls of similar size arrange themselves into a close-packed cover, often referred to as a ball blanket or floating blanket. Plastics frequently selected to make the prior art balls include high-density polyethylene, polypropylene, and polyvinylidene fluoride, depending on the temperature, sunlight exposure, and properties of the fluid and environment where the balls will be used.
Such floatable balls can cover only approximately 91% of the surface of the fluid because their spherical configuration only allows them to engage in point-to-point contact. Hence, prior art balls provide a floating ball blanket that has a plurality of gaps. These gaps leave open space for fluid loss by evaporation, heat loss by such evaporation, and heat transfer by convection from the surface of the fluid. It has also been found in actual practice that because such spherical floatable balls float high in the fluid, much less than 91% of the fluid surface is in contact with the ball. Thus, surface evaporation and heat transfer by convection are not sufficiently reduced as may be desired.
Furthermore, the spherical shape of the floatable ball allows each ball to roll freely as the fluid is agitated or exposed to wind. This rolling action may produce further loss of fluid as the fluid that wets the bottom of the ball surface readily evaporates when it is rolled upwardly and is exposed to the atmosphere.
Consequently, systems have been developed that more completely cover the fluid surface and/or prevent rolling of the floating balls. Typical of such an approach is the device set forth in U.S. Pat. No. 3,998,204. The '204 patent describes a floatable ball having contoured flat surfaces surrounding its equatorial plane. The ball is rigid and contains ballast in its bottom portion so that its flat surfaces are vertically oriented and juxtaposed to each other. When the fluid surface is uniform or non-oscillatory, the collective surface-to-surface contacts between the equatorial planes of these balls provide a substantially gapless or uninterrupted floating ball blanket. Similarly, U.S. Pat. No. 5,188,550 discloses a plurality of buoyant devices having more substantial flat vertical surfaces for greater coverage in undulating surface conditions. As is known to those skilled in the art, these approaches allow a floating device to float upright when the center of gravity of the device is sufficiently below the center of buoyancy of the fluid. Because the center of buoyancy is partly determined by the center of gravity of the fluid, such approaches are limited in application to fluids having specific gravities, i.e. densities, that are within a relatively limited range.
Other prior art evaporation and energy reduction techniques and systems which cumulatively form a barrier are disclosed in U.S. Pat. Nos. 4,749,606; 4,582,048; 4,467,786; 4,458,688 and 4,270,232. As is known to those skilled in the art, these devices and techniques suffer barrier breach when confronted with undulatory surface conditions.
Thus, there still exists a need for a better approach to provide a barrier that can function effectively on a variety of fluids and under a variety of environmental conditions including undulating fluid surfaces, but which is also easy to deploy and economical to manufacture and maintain.