Heat-moisture exchangers

D. Ventilator Tubing Condensate and Heat-Moisture Exchangers... 

Figure 3 Mechanically ventilated patient in the upright position. The ventilator humidifies the air which is carried through the inspiratory tubing to the wye junction into the endotracheal tube and the patient s lower respiratory tract. The humidified air is expired out the expiratory phase tube to a trap. If a heat-moisture exchanger (HME) is inserted between the swivel adapter and wye junction, the humidifier can be turned off and there is no condensate in the circuit. (From Ref. 181, with permission.)...

Kirton OC, DeHaven B, Morgan J, Morejon O, Civetta J. A prospective, randomized comparison of an in-line heat moisture exchange filter and heated wire humidifiers Rates of ventilator associated early-onset (community-acquired) or late-onset (hospital-acquired) pneumonia and incidence of endotracheal tube occlusion. Chest. In Press. 

Use single patient heat-moisture exchanger, adequate disinfection of heated humidifier between patients... 

The main location of hygroscopic mediums is inside heat and moisture exchange (HME) filters. 

De Freitas, C.R. Littlejohn, R.N. (1987) Cave climate assessment of heat and moisture exchange. Journal of Climatology 7, 553-569. 

In the latter case, the hot-melt adhesives are applied in the form of films (also perforated for moisture exchange) as heat-sealing adhesives. The film is put between the two webs to be bonded and is then melted in heating presses or by means of an iron. The melt penetrates the tissue and, after cooling, forms a firm bond, thus stiffening the tissue. 

The closuring system is not fully effective (some moisture exchange is likely to occur with most closure systems, even heat seal systems involving foil laminates may allow low permeation via the edge seals). 

Theoretically, the amount of heat required for the evaporation of 1 kg of moisture under standard conditions is 2200-2700 kJ/kg. The upper limit of this value refers to the removal of bound moisture. The only drying regime in which such a result could be obtained is the adiabatic equilibrium in which there is no heating of a solid body and accompanying moisture that is, they enter at the evaporating temperature. Furthermore, no additional heat is exchanged to the evaporated vapor and gas carrier, and there is no heating of the dryer body and the ambient air. 

Hurni J, Feihl F, Lazor R, Leuenberger P, Perret C. Safety of combined heat and moisture exchanger filters in long-term mechanical ventilation. Chest 1997 111 686-691. 

Chalon J, Markham JP, Ali MM, Ramanathan S, Turndorf H. The Pall Ultipor breathing circuit filter—an efficient heat and moisture exchanger. Anesth Anal 1984 63 566-570. 

Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

Dryers. A drying operation (see Drying agents) needs to be viewed as both a separation and a heat-exchange step. When it is seen as a separation, the obvious perspective is to cut down the required work. This is accompHshed by mechanically squeezing out the water. The objective is to cut the moisture in the feed to the thermal operation to less than 10%. In terms of hardware, this requires centrifuges and filters, and may involve mechanical expression or a compressed air blow. In terms of process, it means big crystals. 

Natural gas from MESA s wells flows into a gathering system where pressure is increased to 7 bar (100 psig). Multiple booster stations raise it to 34 bar (500 psig) before gas enters the plant for separation. When gas enters the LNG recovery unit, its pressure must be raised again to 66 bar (950 psig). It is then subjected to a molecular sieve process for moisture removal. A series of heat exchangers lowers the temperature to -34°C (-30°E). 

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