![]() ![]() Clean benches can be used for certain clean activities, such as the dust-free assembly of sterile equipment or electronic devices, and they should never be used when handling cell culture materials or drug formulations, or when manipulating potentially infectious materials. These devices only provide product protection. Horizontal laminar flow or vertical laminar flow “clean benches” are not biosafety cabinets these pieces of equipment discharge HEPA-filtered air from the back of the cabinet across the work surface toward the user, and they may expose the user to potentially hazardous materials. Vertical flow hoods, on the other hand, provide significant protection to the user and the cell culture. The flow can be horizontal, blowing parallel to the work surface, or it can be vertical, blowing from the top of the cabinet onto the work surface.ĭepending on its design, a horizontal flow hood provides protection to the culture (if the air flowing towards the user) or to the user (if the air is drawn in through the front of the cabinet by negative air pressure inside). (round) pipe flow is ~2300 (but you have rectangular channels, could maybe pick the hydraulic diameter), and for a free jet I found a number of 1300, but take that with a grain of salt.Īll in all, you're back to gut feelings.Laminar flow hoods protect the working environment from dust and other airborn contaminants by maintaining a constant, unidirectional flow of HEPA-filtered air over the work area. The problem is to find the critical Reynolds number that applies to your situation, which is not exactly standard.Ĭritical Re for e.g. The width of the fume hood? (But this is only ~one width long, so hardly counts as a "channel".) Do you pick the width at the end of the small channels in your filter? (but they are triangular/have a non-constant diameter, and flow through the walls to boot). The choice of length scale is important here. With this you get the flow velocity, and you can build a Reynolds number, and if this is higher than a critical number, you'll get turbulent flow. ![]() exhaust filter size, and building conditioned air losses. cfm) achieved is the same.Įverything hinges on the pressure loss across the filter (i guess pretty high) and the resulting volume flux of the whole system (depending on the characteristic/power of your fan). The horizontal laminar airflow cabinet is best suited for maximal product protection. My guess/gut feeling is that (due to high pressure loss and flow through a porous medium) the air leaves the filter in a laminar fashion (even if it was turbulent before), so what kind of fan you use shouldn't matter if e.g. I think that such a deep filter will eliminate the need for a screen. Would this be totally wrong? If so, is there a way to build the DIY flow hood to achieve a laminar flow using one of these inline centrifugal fans? It seems to me that so long as the plenum is air tight besides the entry point(fan location) and exit point(HEPA filter), the plenum will achieve a static pressure (based upon the cfm of air driven by the fan and the resistance of the HEPA filter) and flow smoothly out of the HEPA. The argument is that the air pushed by these fans is turbulent and so will exit the HEPA filter in a turbulent fashion. The main question is whether these inline fans will produce laminar flow. The build for a laminar flow hood using these inline fans look, generally, like the two samples at the bottom of this link ( ). ![]() Many people are interested in using inline centrifugal fans because they are cheaper than squirrel blowers, more quiet, more energy efficient, and potentially more compact. It is generally accepted that a squirrel blower is effective at creating this laminar flow using the set up in the image posted above. Air potentially contaminated with infectious agents may be blown towards the worker. ![]() They are designed to provide a sterile environment to protect the product. These devices do not provide any protection to the worker. So for years on the mycology, plant tissue culture, and DIY laboratory websites there has been this ongoing debate on how to achieve laminar flow in a home built laminar flow hood. Laminar Flow Hoods (Clean Benches) A Laminar Flow Hood (LFH), is not a biological safety cabinet. ![]()
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