Final answer:
A compressor is the device used to increase the pressure and density of a gas, according to NFPA 853. It is distinct from entrainment devices, and is crucial in applications where high-pressure gas is needed.
Step-by-step explanation:
A device used for increasing the pressure and density of a gas according to NFPA 853 is known as a compressor. Compressors are instrumental in various applications, from natural gas processing to refrigeration. In the context provided by the figures, while entrainment devices like Bunsen burners, atomizers, aspirators, and chimneys utilize the principle of creating low pressures to move or mix fluids, it is the compressor that is specifically designed to increase the pressure and subsequently the density of a gas. As seen in figure 14.11(a), gauges are necessary to monitor such pressure changes in gas cylinders, which are often subjected to compression.
Moreover, it is important to note that when energy is added to a gas system, as mentioned in point 71, the work done by the gas can increase due to an increase in the gas's volume, its pressure, or both. Compressors play a crucial role in this by adding energy to the system, enabling the compression of the gas which increases its pressure. Factors such as gas compressibility and intermolecular attractions also affect the behavior of real gases under differing conditions, as detailed in point 105.