This invention relates to chemical concentration control and, more particularly, to an arrangement for controlling the chemical concentration of a biocide in a coolant circulating in a cooling system.
Conventional cooling systems, such as that used in a space station, contain an aqueous-based coolant to cool the space station operating systems. Conventionally, the cooling systems include a biocide to reduce or prevent growth of microorganisms. Particular biocides, such as silver-salt, undesirably precipitate out of the coolant and become ineffective as a biocide. Furthermore, silver precipitation may lead to galvanic corrosion with metals and coatings of parts within the system. Alternative biocides may be less likely to precipitate out, but several key challenges remain before implementation.
One challenge is introducing the biocide into the cooling system under microgravity conditions without allowing the biocide to escape into the surrounding cabin. Another challenge includes designing a handling system that is capable of controlling the biocide concentration in the coolant by selectively removing or delivering biocide. Finally, the handling system should be relatively simple and inexpensive.
Accordingly, there is a need for a simple arrangement to introduce and remove biocide from a coolant system with minimal risk of cabin exposure.
The control arrangement according to the present invention includes two sorbent beds that cooperate to control a chemical concentration in a fluid. One of the sorbent beds selectively removes the chemical if the concentration is too high and the other sorbent bed selectively releases the chemical if the concentration is too low.
In one example, the sorbent beds are connected in a cooling system to control a biocide concentration in coolant circulating through the cooling system. A controller selectively opens and closes valves to control coolant flow through the sorbent beds. The controller changes the biocide concentration by a predetermined amount by controlling the fluid flow rate and flow time through the sorbent beds.
Accordingly, the control arrangement according to the present invention provides a simple arrangement for automatically introducing or removing biocide in a cooling system and reduces the need to manually handle the biocide.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
A control assembly 18 connected to the conduit 14 maintains a desirable biocide concentration in the circulating coolant. The control assembly 18 removes biocide if the concentration becomes higher than desired and introduces biocide if the concentration becomes lower than desired. The control assembly 18 provides the benefit of maintaining the biocide concentration within a desired range without having to manually introduce or remove the biocide using external connections or complex pumps.
If the biocide concentration is too high or too low, the controller 30 opens the valve 28a to divert coolant flow into the control assembly 18. Sorbent beds 32 and 34 adjust the biocide concentration. If the concentration is lower than desired, the sorbent bed 32 introduces biocide into the coolant to increase the concentration. If the concentration is greater than desired, the sorbent bed 34 removes biocide to lower the concentration.
The controller 30 controls metering valves 36a and 36b to selectively divert coolant flow into either of the sorbent beds 32 or 34. The controller 30 utilizes the metering valves 36a and 36b to control the coolant volume flowing into either sorbent bed 32 or 34. This allows control of the biocide concentration by varying the fluid flow rate and flow time through either of the sorbent beds 32 or 34. The rate at which the sorbent beds 32 and 34 respectively introduce and remove biocide can be determined empirically such that the controller 30 changes the biocide concentration a predetermined amount by controlling the fluid flow rate and flow time through either of the sorbent beds 32 or 34. The resulting adjusted concentration of the coolant can be determined manually or automatically using known methods.
Check valves 38a and 38b near the outlets of the sorbent beds 32 and 34 prevent backflow of coolant. When coolant flows through one of the sorbent beds 32 or 34, the controller 30 opens the corresponding check valve 38a or 38b to allow the coolant to flow back into the conduit 14 through the valve 28b. The controller closes the other check valve 38a or 38b to prevent backflow into the inactive sorbent bed 32 or 34.
In the illustrated example, the sorbent bed 32 includes a porous material 40, such as a carbon material, alumina, acrylic ester, or polymethylmethacrylate. Optionally, the porous material 40 may be granulized in a known manner to form granules 42. The porous material 40 is structurally robust to withstand coolant flow without cracking. Biocide is impregnated into pores of the porous material 40 by soaking the porous material 40 in a solution of solvent and biocide and subsequently evaporating out the solvent to leave the biocide immobilized within the porous material 40. The biocide diffuses from the pores of the porous material 40 into coolant passing between the granules 42 to increase the biocide concentration in the coolant. In one example, a biocide concentration gradient between the pores of the porous material 40 and the coolant provides a driving force for diffusion of the biocide into the coolant.
In the illustrated example, the sorbent bed 34 includes an adsorbent material 46, such as activated carbon. The activated carbon material is granulized in a known manner and held in a support 47 such as a canister or netting. In other examples, a zeolite, clay, activated alumina, silica or combination thereof is used. Other known adsorbents may also be used. The adsorbent material 46 removes biocide from the passing coolant to reduce the biocide concentration. As is known, adsorbent materials include surfaces that bind other substances. The carbon of the adsorbent material 46 binds biocide to remove it from the coolant. Given this description, those of ordinary skill in the art will recognize that other types of sorbent beds 32 and 34 may be used in other fluid systems, such as but not limited to controlling concentrations of other types of chemicals or biocides in aqueous or non-aqueous fluids.
Each of the sorbent beds 32 and 34 includes spring members 48. The spring members 48 compress and compact the sorbent beds 32 and 34. During operation of the control assembly 18, for example, sorbent bed 32 shrinks as it is depleted of biocide. If the sorbent bed 32 is not compacted, there is risk of excess space within the sorbent bed 32 that may allow the coolant to bypass the sorbent bed 32 without delivery of biocide. Thus, the spring members 48 compact the porous material 40 to minimize the excess space produced by shrinkage.
Under microgravity conditions and the pressure of the flowing coolant, the granules of sorbent bed 34 may move. The spring member 48 prevents significant movement of the granules and maintains a relatively tight packing of granules.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.