1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2009 SAE International All rights reserved. No part of this publication m
3、ay be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR1204A AEROSPACE INFORMATION REPORT AIR1204A Issued 1979-05 Reaffirmed 2007-12 Revised 2009-06
5、 Superseding AIR1204 (R) Control of Water Carryover from the Environmental Control System and Condensation on the Structure RATIONALE This document is intended to address the issue of excess moisture on aircraft. AIR1204 was originally released in 1979. This Rev A version brings the document up to d
6、ate with regard to Environmental Control System design and design best practices that have evolved since this documents original release. TABLE OF CONTENTS 1. SCOPE 3 1.1 Purpose . 3 1.2 Field of Application 3 2. REFERENCES 3 2.1 Applicable Documents 3 2.1.1 SAE Publications . 3 3. BACKGROUND 4 4. C
7、AUSES OF WATER CONDENSATE . 4 4.1 Environmental Control System . 4 4.1.1 Entrained Moisture from the ECS Refrigeration Unit 4 4.1.2 Moist Air Bypassing Water Removal Devices . 4 4.1.3 Low-pressure Water Separation Anomalies . 5 4.1.4 Liquid Water Accumulation . 5 4.2 Condensation on Cold Surfaces .
8、5 4.2.1 Structural Condensation . 5 4.3 Humidifiers 5 4.4 Occupants . 6 5. EFFECTS OF WATER CONDENSATE . 6 5.1 Environmental Control System . 6 5.1.1 Rain-in-the-plane 6 5.1.2 Damage to ECS Equipment 6 5.1.3 Collateral Damage to Equipment 6 5.2 Window Visibility . 6 5.3 Structural Condensation . 6 5
9、.3.1 Wet Insulation Blankets 6 5.3.2 Water/Ice Accumulation in Bilge . 6 5.3.3 Overboard Icing . 7 5.3.4 Rain-in-the-plane 7 Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1204A Page 2 of 15
10、6. CONTROL OF EXCESS MOISTURE . 7 6.1 Environmental Control System Water Carryover 7 6.1.1 General ECS Suggestions 7 6.1.2 Air Cycle Systems . 7 6.1.3 Vapor Cycle Systems 12 6.2 Humidifiers 13 6.3 Structural Condensation . 13 6.3.1 Condensation Reduction Strategies . 13 6.3.2 Strategies for Manageme
11、nt of Condensed Water 14 7. NOTES 15 7.1 Revision Indicator 15 Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1204A Page 3 of 15 1. SCOPE This Aerospace Information Report (AIR) outlines the
12、design considerations and criteria for the control of water carryover from the environmental control system (ECS) with respect to causes and indicated corrective or preventative action. In addition, condensation on structure will be reviewed with possible preventative action described. 1.1 Purpose T
13、his publication will discuss water carryover from the environmental control system and condensation on structures, with the following purpose: a. To define sources of water that may cause condensation in the aircraft. b. To outline means for minimizing or controlling the condensate. 1.2 Field of App
14、lication The material presented herein is primarily applicable to multi-engine transport airplanes, but in some cases may apply to other types of aircraft, military or civil. 2. REFERENCES All pertinent and/or reference documents are listed herein. 2.1 Applicable Documents The following publications
15、 form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of purchase order. In the event of conflict between the text of this document and references cited herei
16、n, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale PA 15096-001, Tel: 877-606-7323 (ins
17、ide USA and Canada) or 724-776-4970 (outside USA), www.sae.org. AIR1609 Aircraft Humidification ARP147 Environmental Control Systems Terminology ARP987 The Control of Excess Humidity in Avionics Cooling Proceeds of Moisture Ingress in Aircraft Insulation Symposium, Abbotsford BC Canada, August 5 199
18、3, sponsored by SAE Aerospace Continuing Professional Development Group Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1204A Page 4 of 15 3. BACKGROUND Uncontrolled moisture inside the fusela
19、ge of aircraft is a potential source of increased maintenance and expense to operators and can lead to complaints and ill will from passengers. Uncontrolled moisture can manifest itself in the following ways: a. Condensation dripping on passengers. b. Moist air condensing on exposed structure and on
20、 mechanical or electrical equipment. It can also become trapped and be subjected to freezing due to subsequent temperature reduction. c. Structural corrosion, electrical shorts, insulating material weight increase and loss of insulating properties result from this water accumulation. 4. CAUSES OF WA
21、TER CONDENSATE The sources of excess moisture within an aircraft can include the Environmental Control System (ECS), condensation on cold surfaces, occupants and humidification systems. 4.1 Environmental Control System The ECS can cause uncontrolled water condensation in the following ways: 4.1.1 En
22、trained Moisture from the ECS Refrigeration Unit Inefficient water separation in the ECS results in carryover of water condensate and humid air into the cabin. This problem is commonly associated with air cycle refrigeration systems. Low design efficiency, inadequate drainage systems or failure mode
23、s of water collectors or separators will produce an unnecessarily large carryover of entrained water in the form of fog or water droplets and occasionally ice particles. Some of this water settles out in low points throughout the ducting system, including overhead areas. From there, it may accumulat
24、e until its volume, airplane attitude, etc. may cause sudden spilling of large amounts of water into the cabin, or it may subsequently re-evaporate when the supply air is less than saturated. Visible fog streamers can occur at cold air outlets during high humidity conditions. Formation of these stre
25、amers which is usually a result of entrained moisture in the conditioned cabin supply air in conjunction with supply air temperature is cooler than the dew point at the surrounding cabin pressure. 4.1.2 Moist Air Bypassing Water Removal Devices The air entering the cabin is not dehumidified unless i
26、t passes through the refrigeration unit and the water separator or collector. For temperature control, some refrigeration cycles bypass a portion of the hot supply air around the refrigeration unit and mix it with the refrigerated air downstream. This bypassed air, therefore, adds to the moisture le
27、ft in refrigerated air that is due to the normal water separator design inefficiencies. It should be pointed out that the proportion of bypassed air to the total air is small, particularly on hot humid days at low altitudes, where maximum refrigeration is required. However, on a humid day with coole
28、r or moderate temperature, the moisture from the bypass air will cause higher compartment humidity. As the altitude is increased and the supply air becomes colder, more air bypasses the refrigeration package. Note that the supply air becomes dryer as altitude increases. Refrigeration cycles that byp
29、ass air around the water removal devices include the conventional chilled-recirculation systems used on A320 and 767-200/300. Refrigeration cycles that do not bypass the water removal devices include the simple/bootstrap system on 747-400 and the condensing cycle system used on 777 and 767-400. Copy
30、right SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1204A Page 5 of 15 4.1.3 Low-pressure Water Separation Anomalies Water separator anti-icing systems may malfunction or be set to maintain temperatur
31、es too close to the freezing point. In the latter case, normal control tolerances can cause continuous or intermittent freezing. Freezing of the water separator forces the moisture laden supply air through the relief valve bypass system introducing moisture in the form of water droplets and/or fog i
32、nto the cabin and into direct air cooled electronic equipment. Undersized water drains plugged with lint, dirt, etc. can severely degrade low pressure water separator effectiveness. 4.1.4 Liquid Water Accumulation Liquid water can accumulate in low points of air conditioning distribution ducting sys
33、tems, pack discharge or other ducts that encounter free moisture - especially after system shutdown on the ground. To preclude this accumulation, drains should be placed at low points of ducting systems in which entrained moisture is present. Drains should be oversized to avoid blockage. Drain hole
34、sizes of about 3.1 mm (0.125 in.) diameter have been found to be acceptable for large commercial installations, but drain sizes should be established and verified for each application without the requirement for periodic servicing of the drain. Drains should carry water to a location where the water
35、 can go overboard. Drained water should be prevented from coming into contact with equipment that can be harmed by water. 4.2 Condensation on Cold Surfaces Condensation forms on parts of the cold air outlets where cabin air comes in contact with cold, high conductivity (usually metal) parts. Condens
36、ation forms when relatively warm, moist ambient air comes in contact with chilled cold air ducts which are not insulated or insufficiently insulated. 4.2.1 Structural Condensation Most condensation on the airplane structure occurs during flight when the temperature of both the outside air and the st
37、ructure are very cold. Structure temperatures are usually below the dew point of the cabin air, causing condensation to form during most flights. In addition, because structure temperatures are normally below the freezing point of water, most condensation forms as frost. Condensation results when mo
38、ist air moves to the cold structure. The cabin air passes through small gaps in the insulation coverage and cools rapidly. Buoyancy forces induce a continuous flow of air and continuous movement of moisture to the cold structure. The rate of condensation depends on the rate of buoyancy-driven air mo
39、vement to the structure as well as the cabin humidity level. In-flight cabin humidity levels are low from a standpoint of human comfort (approximately 10 to 20 percent relative humidity, depending on flight conditions and occupant loading). However, the dew point of cabin air is much higher than air
40、craft skin temperature and most of the moisture it contains will condense as air moves over the cold structure. Structure directly connected to the (cold) outer skin is the prime area of condensation. Leaking cold air ducting joints can also reduce the temperature of adjacent surfaces and result in
41、condensation. Structural or insulation blanket condensation occurs where virtually trapped volumes obtain moisture at sea level and are subject to subsequent cold soaking at altitude. 4.3 Humidifiers Humidifiers can be a source of condensate, particularly if they are improperly operated. Operation o
42、f humidifiers at high altitude can result in frost build-up on cold structure. As the airplane descends increased temperatures and aircraft attitude changes can result in water dripping in occupied compartments. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo repro
43、duction or networking permitted without license from IHS-,-,-SAE AIR1204A Page 6 of 15 4.4 Occupants Human occupant metabolic activity is a source of moisture in aircraft cabins. Certain cargo such as agricultural products or animals can also contribute to moisture problems. 5. EFFECTS OF WATER COND
44、ENSATE Water condensation within the aircraft affects many areas such as ECS, window fogging, structure, along with other items described in following paragraphs. 5.1 Environmental Control System The effects of excess water from the ECS are summarized in this sub-section: 5.1.1 Rain-in-the-plane Wat
45、er droplets discharged into the cabin from the ECS can spatter passengers and interior trim, which may stain clothing and cabin finish. Re-evaporation of this water into the cabin air adds to the humidity of the cabin. Condensate forming on parts of the cold air outlets or structure may also drip on
46、 passengers and interior trim with the same effects. This dripping in the cabin is often referred to as “rain-in-the-plane”. 5.1.2 Damage to ECS Equipment Besides general corrosion concerns, slugs of liquid water ingested by rotating equipment, such as ACM turbines, can cause component failure. In s
47、ome cases, air bearings within the ECS pack may be affected by condensate, resulting in excessively high starting torque, which may prevent the air cycle machine from functioning. ECS components should be designed to be robust and tolerant of liquid water ingestion, while at the same time the system
48、 should be designed to safely manage and control any liquid water generated within the system. 5.1.3 Collateral Damage to Equipment Free moisture in the electrical equipment cooling air supplied by the ECS can cause electrical shorts and equipment failures. 5.2 Window Visibility Condensation may result in fogging of windows that may impair visibility. 5.3 Structural Condensation The effects of moisture caused by structural condensation are as follows: 5.3.1 Wet Insulation Blankets Condensation on structural members runs down onto the insulation blankets and soaks into the insulation at improp
