Aerodynamic valves

The aerodynamic valves have a specially designed inlet (e.g., a profiled orifice in the inlet pipe, contoured diffuser, or a shrouding duct) in which the fluid flow characteristics act as a physical barrier (fluid diode) to the backflow of combustion products. Such pulse combustors are termed the valveless combustors. Example of valveless pulse combustor is shown in Figure 23.4 (Putnam et al., 1986). 

Based on the manner in which fuel and air charge the combustion chamber, pulse combustors are divided into two general categories those with mechanical valves and those with aerodynamic valves (also called valveless combustors). Mechanical valves can be further divided into three types flapper valves, reed valves, and rotary valves. 

Aerodynamic valves employ the fluid mechanical properties of specially designed inlets to act as a physical barrier to the backflow of combustion products out of the combustor through the inlet section. The main advantage of aerodynamic conflgurations is lack of valves and moving parts so the risk of mechanical breakdown or failure is eliminated. This is a key consideration for heavy-duty pulse combustion burners where the inlet section undergoes severe operating conditions. 

Ventilation for buildings - Air terminal devices - Aerodynamic testing of dampers and valves. Superseded BS 6821 1988... 

EN. 17.51, Ventilation for buildings—Air terminal devices—Aerodynamic testing of clampers and valves. 

Metered-Dose Inhalers and Nasal Aerosols Content uniformity, aerodynamic particle size distribution, microscopic evaluation, water content, leak rate, microbial bioburden, valve delivery, extractables, leachables from plastic and elastomeric components. 

In special cases such as multiple valve installation, the aerodynamic noise level may warrant more detailed determination. However, this is a decision of the system designer familiar with all the local conditions and regulations and, more importantly, implantation of the valves within the site. 

Section 3 Control valve aerodynamic noise prediction method... 

The noise sources in control valves include mechanical vibration (usually below 100 dBA) hydrodynamic noise caused by liquid turbulence, cavitation, or flashing (usually below 110 dBA) and aerodynamic noise (can reach 150 dBA). In control valve design, aerodynamic noise can be a major problem. Aerodynamic noise generation, in general, is a function of mass flow rate and the pressure ratio (p /pf) across the valve. The point at which sonic speed is reached in the valve vena contracta is a function of the valve design. 

Berry, J., Kline, L., Naini, V., Chaudhry, S., Hart, J., and Sequeira, J. (2004), Influence of the valve lubricant on the aerodynamic particle size of a metered dose inhaler, Drug. Dev. Ind. Pharm., 30, 267-275. 

The FisoNeb and Pulmosonic nebulizers both operate at a frequency of 1.3 MHz that generates a mass median aerodynamic diameter (MMDA) of 4-6 pm [9,10]. The Pulmosonic nebulizer has been reported not to deliver many particles smaller than 2 pm and, therefore, is unsuitable for pentamidine administration [10]. The Portosonic (DeVilbiss) device is a 2.3-MHz ultrasonic nebulizer and may offer the combination of less than 2-pm MMAD and a high output. In any study using ultrasonic nebulizers, the output and particle size of each device need to be periodically sampled, because the frequency of the piezoelectric crystal may alter with age [10]. Any MMADs between 0.5 and 2 pm are available. The Respirgard nebulizer II has one-way valves that control a drug reservoir, allow entrainment of room air in patients whose minute ventilation is... 

Metered-dose inhalations and nasal aerosols should be evaluated for appearance (including content, container, and the valve and its components), color, taste, assay, degradation products, assay for cosolvent (if applicable), dose content uniformity, labeled number of medication actuations per container meeting dose content uniformity, aerodynamic particle size distribution, microscopic evaluation, water content, leak rate, microbial limits, valve delivery (shot weight), and extractables and leachables from plastic and elastomeric components. Samples should be stored in upright and inverted/on-the-side orientations. 

For example, systems that must have close control of flow should use two proportioning valves that act in tandem to maintain a balanced hydraulic or aerodynamic system. The primary, or master, valve should control flow to the downstream process. The second valve, slaved to the master, should divert excess flow to a bypass loop. This master-slave approach ensures that the pumps and other upstream system components are permitted to operate well within their operating envelope. 

An alternative design of a pulse combustor is a so-called valveless combustor in which the mechanical valves are replaced with an aerodynamic diode in the form of a profiled orifice in the inlet pipe, contoured diffuser, or a shrouding duct [28] (Figure 20.15). Similarly to the combustor with mechanical valves, the high-temperature gases from a combustion chamber start to flow just after a... 

Fomataro-Clerici L, Zajac DJ. Aerodynamic characteristics of tracheostomy speaking valves. J Speech Hear Res 1993 36(3) 529-532. 

Zajac DJ, Eomataro-Clerici L, Roop TA. Aerodynamic characteristics of tracheostomy speaking valves an updated report. J Speech Lang Hear Res 1999 42(1) 92-100. 

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