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This publication will discuss water carryover from the environmental control system with respect to causes and indicated corrective or preventative action. In addition, condensation on structure will be reviewed with possible preventative action described.

This report covers the design parameters for various methods of humidification applicable to aircraft, the physiological aspects of low humidities, the possible benefits of controlling cabin humidity, the penalties associated with humidification, and the problems which must be solved for practical aircraft humidification systems. The design information is applicable to commercial and military aircraft. The physiological aspects cover all aircraft environmental control applications.

This SAE Aerospace Information Report (AIR) covers the design parameters for various methods of humidification applicable to aircraft, the physiological aspects of low humidities, the possible benefits of controlling cabin humidity, the penalties associated with humidification, and the problems which must be solved for practical aircraft humidification systems. The design information is applicable to commercial and military aircraft. The physiological aspects cover all aircraft environmental control applications.

This document supplements and in some cases supersedes the recommendations presented in ARP 85D, which refers to subsonic civil transports.

Like the technologies to which it contributes, the science of instrumentation seems to be expanding to unlimited proportions. In considering instrumentation techniques, primary emphasis was given in this section to the fundamentals of pressure, temperature, and flow measurement. Accent was placed on common measurement methods, such as manometers, thermocouples, and head meters, rather than on difficult and specialized techniques. Icing, humidity, velocity, and other special measurements were touched on briefly. Many of the references cited were survey articles or texts containing excellent bibliographies to assist a more detailed study where required.

Like the technologies to which it contributes, the science of instrumentation seems to be expanding to unlimited proportions. In considering instrumentation techniques, primary emphasis was given in this section to the fundamentals of pressure, temperature, and flow measurement. Accent was placed on common measurement methods, such as manometers, thermocouples, and head meters, rather than on difficult and specialized techniques. Icing, humidity, velocity, and other special measurements were touched on briefly. Many of the references cited were survey articles or texts containing excellent bibliographies to assist a more detailed study where required.

The fluid flow treated in this section is isothermal, subsonic, and incompressible. The effects of heat addition, work on the fluid, variation in sonic velocity, and changes in elevation are neglected. An incompressible fluid is one in which a change in pressure causes no resulting change in fluid density. The assumption that liquids are incompressible introduces no appreciable error in calculations, but the assumption that a gas is incompressible introduces an error of a magnitude that is dependent on the fluid velocity and on the loss coefficient of the particular duct section or piece of equipment. Fig. 1A-1 shows the error in pressure drop resulting from assuming that air is incompressible. With reasonably small loss coefficients and the accuracy that is usually required in most calculations, compressible fluids may be treated as incompressible for velocities less than Mach 0.2.

The fluid flow treated in this section is isothermal, subsonic, and incompressible. The effects of heat addition, work on the fluid, variation in sonic velocity, and changes in elevation are neglected. An incompressible fluid is one in which a change in pressure causes no resulting change in fluid density. The assumption that liquids are incompressible introduces no appreciable error in calculations, but the assumption that a gas is incompressible introduces an error of a magnitude that is dependent on the fluid velocity and on the loss coefficient of the particular duct section or piece of equipment. Fig. 1A-1 shows the error in pressure drop resulting from assuming that air is incompressible. With reasonably small loss coefficients and the accuracy that is usually required in most calculations, compressible fluids may be treated as incompressible for velocities less than Mach 0.2.