Fume Hood Wall and Bottom Jets to Prevent Flow Separation
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Solution Overview
Problem
Conventional laboratory fume hoods equipped with support jet technology still experience flow separation and backflow issues, which compromise escape safety and energy efficiency, despite previous improvements in air curtain and baffle designs.
Innovation Solution
The design incorporates elongate passages for compressed air jets along side walls and base plates, with specific nozzle geometries and pressure control systems to prevent flow separation, ensuring that compressed air jets maintain direction and reduce turbulence across at least 75% of the workspace depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional support jet technology is used with short passages, then the device complexity is reduced, but flow separation occurs and escape safety deteriorates
Solution Approach 1:
The patent changes the geometric parameters of the air outlet nozzles, specifically increasing the passage length to at least 3 times the hydraulic diameter of the outlet opening. This parameter change transforms the flow characteristics from separated to attached flow, preventing backflow and improving escape safety without requiring complex additional components
2Reliability
If compressed air jets are provided along side walls and worktop, then turbulence is reduced and retention capacity is improved, but energy consumption increases
Solution Approach 1:
The patent applies compressed air jets locally at critical areas where backflow and turbulence occur, specifically along the side walls and worktop front edge. By targeting only these specific locations rather than providing uniform air distribution throughout the workspace, the system improves retention capacity while minimizing overall energy consumption
3Reliability
If elongate passages with length L ≥ 3 times hydraulic diameter are used, then flow separation is prevented and escape safety is improved, but the nozzle geometry complexity increases
Solution Approach 1:
The patent establishes a specific quantitative parameter relationship where the passage length L must be at least 3 times the hydraulic diameter of the outlet opening. This clear parameter specification provides manufacturing guidance while achieving the flow attachment effect, balancing manufacturing precision requirements with escape safety improvements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly reduces energy consumption by minimizing the required exhaust air volume while maintaining or improving escape safety, as demonstrated by PIV measurements showing reduced turbulence and enhanced air flow directionality.
Implementation Method 1
a flow separation already occurs a relatively short distance behind the level of the sash and consequently dangerous backflow areas can develop on the side walls
Implementation Method 2
the inflowing room air can detach itself at the downstream end of the baffles. This effect is amplified when room air enters the fume cupboard at an angle to the side walls
Implementation Method 3
They not only prevent flow separation of the incoming room air at the downstream end of the hollow profiles, but also reduce any wall friction effects, so that there can be significantly less turbulence and thus backflow areas in these areas. The room air entering the work space glides, so to speak, on a dynamic, rearward-moving air cushion along the walls and the worktop into the rear area of the work space
Data Source
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AI summary
The invention relates to a fume hood (1) for a laboratory space, comprising a first hollow profiled element (10, 10'), which is arranged on a front-side end face of each side wall (36) and which has a first pressure chamber (10b, 10b') having a plurality of first openings (10d, 10d'), from which air jets in the form of wall jets (100) consisting of compressed air can be output along the associated side wall (36) into the working space. At least one of the first openings (10d, 10d') is connected to the first pressure chamber (10b, 10b') by means of an elongate channel (10c, 10c'), wherein the channel has a length that is at least 3 times the hydraulic diameter of the first opening in order to avoid flow separation of the wall jet (100) from the side wall (36) in a region from the front side of the working space to at least 25% of the depth of the working space. The invention further relates to a fume hood, wherein such a hollow profiled element (20, 20') is arranged on a front-side end face of the bottom plate (34).