Liquefying temperature

Fig. 2.28. Cooling efficiency figure of a screw and a piston compressor operating with R404A at a liquefying temperature of 30 °C.

Liquefier temperature The temperature attained in the molten polymer at the time of extrusion. It is controlled operated by the band heater that can be increased or decreased as per necessity. 

Theoretically, the extruded filament diameter should accord with the diameter of the extruding nozzle orifice. However, practically not only the nozzle orifice determines the filament diameter but also the process parameters like liquefier temperature, extrusion pressure and deposition speed control the filament diameter. That means the accuracy of the filament diameter depended on the appropriate setting of these parameters. This study focused on the fabrication of scaffolds with the filaments that should be of the same dimension as the extruding nozzle orifice. 

Fig. 6 Surface morphology of the extruded filament at different extrusion pressure of (a) 4 bar, (b) 5 bar and (c) 6 bar while the liquefier temperature and dispensing speed were remained constant as 160°C and 4 mm/sec, respectively...

Fig. 7 Surface condition of filament deposition parts which were deposited by deposition speed of (a) 3 mm/sec, (b) 4mm/sec and (c) 5 mm/sec, under liquefier temperature 165°C and extrusion pressure 4 bar...

Fig. 8 The effect of process parameters on scaffolds pore size (a) liquefier temperature, (b) extrusion pressure and (c) deposition speed...

Fig. 5 Surface morphology of extruded filament at the liquefier temperatures of (a) 150°C, (b) 160°C and (c)165°C under extrusion pressure of 4 bar and deposition speed of 5 mm/sec...

The extrusion pressure and the dispensing speed were also varied while maintaining the optimal liquefier temperature constant. Both the extrusion pressure and the dispensing speed also influenced the filament diameter. Fig. 6... 

The influences of the most important process parameters namely, liquefier temperature, extrusion pressure and deposition speed that control the extrusion process of the polymer into 3D scaffold were successfully investigated in this preliminary study. The analysis results show that these parameters had direct influences on the extruded filament diameter that ultimately affected the scaffold quality. The optimal values of the process parameters were found to be as liquefier temperature of 165T, extrusion pressure of 4 bar and dispensing speed of 4mm/sec. Through optimization of the process parameter the scaffolds with required characteristics could be produced. This study provides a useful and effective guideline for extrusion based TE scaffold fabrication. 

Carbon dioxide (COj) will solidify at the temperatures required to liquefy natural gas, and high quantities can make the gas unsuitable tor distribution. Removal is usually achieved in contacting towers. 

Ammonia is a colourless gas at room temperature and atmospheric pressure with a characteristic pungent smell. It is easily liquefied either by cooling (b.p. 240 K) or under a pressure of 8-9 atmospheres at ordinary temperature. Some of its physical and many of its chemical properties are best understood in terms of its structure. Like the other group head elements, nitrogen has no d orbitals available for bond formation and it is limited to a maximum of four single bonds. Ammonia has a basic tetrahedral arrangement with a lone pair occupying one position ... 

Chlorine has a boiling point of 238 K and is a greenish-yellow diatomic gas at room temperature. It can be liquefied by cooling or by a pressure of a few atmospheres at room temperature. 

Deliquescence and efflorescence. A substance is said to deliquesce (Latin to become liquid) when it forms a solution or liquid phase upon standing in the air. The essential condition is that the vapour pressure of the saturated solution of the highest hydrate at the ordinary temperature should be less than the partial pressure of the aqueous vapour in the atmosphere. Water will be absorbed by the substance, which gradually liquefies to a saturated solution water vapour will continue to be absorbed by the latter until an unsaturated solution, having the same vapour pressure as the partial pressure of water vapour in the air, is formed. In order that the vapour pressure of the saturated solution may be sufficiently low, the substance must be extremely soluble in water, and it is only such substances (e.g., calcium chloride, zinc chloride and potassium hydroxide) that deliquesce. 

Mix 100 g. of ammonium chloride and 266 g. of paraformaldehyde in a 1-litre rovmd-bottomed flask fitted with a long reflux condenser containing a wide inner tube (ca. 2 cm. diameter) the last-named is to avoid clogging the condenser by paraformaldehyde which may sublime. Immerse the flask in an oil bath and gradually raise the temperature. The mixture at the bottom of the flask liquefies between 85° and 105° and a vigorous evolution of carbon dioxide commences at once remove the burner beneath the oil bath and if the reaction becomes too violent remove... 

In a 500 ml. bolt-head flask provided with a thermometer (reaching almost to the bottom) and a calcium chloride (or cotton wool) guard tube, place 100 g. of a-bromo-wo-valerj l bromide and 50 g. of dry, finely-divided urea. Start the reaction by warming the flask on a water bath the temperature soon rises to about 80°. Maintain this temperature for about 3 horns the mass will liquefy and then resolidify. Transfer the sticky reaction product to a large beaker containing saturated sodium bicarbonate solution, stir mechanically and add more saturated sodium bicarbonate solution in small quantities until effervescence ceases. Filter at the pump, suck as dry as possible and dry the crude bromural upon filter paper in the air. RecrystaUise the dry product from toluene. Alternatively, recrystaUise the moist product from hot water (ca. 700 ml.). The yield of pure brommal, m.p. 154-155°, is 28 g. 

The critical temperature, of a gas is the temperature above which the gas cannot be liquefied no matter how high the pressure. 

The critical pressure, P, is the lowest pressure which will liquefy the gas at its critical temperature. 

Liquefied natural gas (LNG) natural gas that has been Hquefied by reducing its temperature to 111 K at atmospheric pressure. It remains a Hquid at 191 K and 4.64 MPa (673 psig). 

Liquefied natural gas (LNG) also plays a large role in both the transportation and storage of natural gas. At a pressure of 101.3 kPa (1 atm), methane can be Hquefted by reducing the temperature to about — 161°C. When in the Hquid form, methane occupies approximately 1/600 of the space occupied by gaseous methane at normal temperature and pressure. In spite of the very low temperature of the Hquid, LNG offers advantages for both shipping and storing natural gas. 

Liquefied Petroleum Gas (LPG). Certain specific hydrocarbons, such as propane, butane, pentane, and their mixtures, exist in the gaseous state under atmospheric ambient conditions but can be converted to the Hquid state under conditions of moderate pressure at ambient temperature. This is termed Hquefied petroleum gas (LPG). Liquefied petroleum gas (qv) is a refinery product and the individual constituents, or light ends (Table 4), are produced during a variety of refining operations. 

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