Aircraft Life Support Systems Part 2: Water and Waste System

INTRODUCTION

In the aircraft industry, several systems are designed to provide safety and comfort for the crew and passengers.

Regarding comfort, the water and waste system is designed to provide water for galleys and lavatories. Fresh water is stored and distributed while a different system deals with wastewater. That system includes a thoughtful engineering method to dispose of the different wastes that could occur during the flight.

OVERVIEW

Water must be supplied to different parts of the plane during flight. This water is kept in a tank in the compartment aft of the bulk cargo compartment. The whole system is made up of a passenger water system that stores, delivers, monitors and controls drinkable (potable) water for the galley units and lavatory sink basins.

In this blog, we are going to focus more specifically on the 737-classic model from Boeing.

Figure 1-Representation of different parts of the water and waste system
Figure 1-Representation of different parts of the water and waste system

The 3 main achievements of the water and waste system are the following:

  • Filling the water tank on land
  • Providing water during the flight
  • Storing toilet waste

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The water and waste system is made up of:

  • Potable water system aims to deliver fresh water to every needed part in the plane (including every component between the water tank and sinks)
  • Water tank pressurization system focuses on the pressurization of the water tank and air dealing with the tank (including air compressor, pressure regulator filter, pressure relief valve)
  • Wastewater system focuses on water related to lavatory and sinks / galleys wastewater (including drain masts)
  • Toilet system includes components related to flushing and toilet water (including waste tank)

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The water tank has a capacity of 34 gallons (about 0.15 m3). The water system in the plane needs to be pressurized for altitude just like the cabin, so it gets pressurized by an air inlet (linked to the pneumatic system). Therefore, the water quantity should not exceed 30 gallons (about 0.13 m3). Read More

Aircraft Life Support Systems Part 1: Oxygen System

INTRODUCTION

In the aircraft industry, several systems are designed to provide safety and comfort for crew and passengers while traveling. Oxygen gets rarified with altitude, so life support is a very important system

The cabin is pressurized in order to provide breathable air, but reaching a sea level pressure is not advisable since it would lead to a significant pressure differential between the aircraft exterior and the cabin interior. This difference could damage the aircraft structure.

Additionally, the cabin altitude is different from the flight altitude. In fact, the cabin altitude corresponds to the one reached according to the cabin pressure. Usually a commercial flight cruises at an altitude of 35,000 ft, but thanks to the pressurization system, the cabin altitude is around 6,000-8,000 ft.  Indeed, the oxygen system provides breathable oxygen to the crew and passengers if any problem were to occur during the flight.

AIRCRAFT EMERGENCY OXYGEN SYSTEM:

In a normal situation, a bleed air system is used to provide fresh air throughout the flight duration. The air is hot and must be cooled and pressurized to make it breathable.  In the event of an emergency, the plane is already equipped with oxygen systems which are linked to passengers and cabin crew through masks. In fact, there are two oxygen systems on board. One designed for the crew, and the second for the passengers.

If the cabin pressure drops making cabin altitude about 14,000 ft, the emergency system are be triggered. The emergency system provides oxygen to passengers for 15 to 20 minutes, and for the crew members for around 30 minutes. This is enough time for the aircraft to descend to a lower altitude and being the cabin altitude to a safe breathable level.

Here, the crew oxygen system schematic of the Boeing 737 class is shown in Figure 1.

Figure 1-Crew oxygen system
Figure 1-Crew oxygen system

The main challenges of oxygen equipment are:

  • Fitting the dimensions of the plane
  • Secure (no leakage for example)
  • Responsive (to cabin pressure and cabin altitude)
  • Easy for passengers to use the oxygen system through the deployed masks quickly, before the effects of altitude are felt:
  • At 25,000 ft: a person has 3 minutes of consciousness
  • At 41,000 ft: a person has 30 seconds of consciousness

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FLIGHT CREW OXYGEN

The flight crew oxygen should be designed and made with a lot of care, because if any trouble occurs during the flight, the crew must be able to handle the situation and take the airplane and its passengers down safely. Read More

The History of Turbochargers, Part 3

Hello! Welcome back to this third and final installment in our “History of the Turbocharger” Series. If you haven’t already, you can read the previous installments by clicking the links below:

Now, let’s see how the turbocharger went from an ace-in-the-hole for aircraft engines during World War II, to the go-to way to crank out horsepower in small engines.

Up until World War II, turbochargers were not a common sight in cars, and certainly not the most popular option for adding forced induction to an engine. Even following the war, some of the most notable post-war aircraft relied on piston engines as opposed to the modern turbojet engine, did not use turbochargers. Most R&D efforts for military aircraft propulsion was moving away from piston engines, and where piston engines were being used, they didn’t have turbos.

Take, for example, the Corvair B36. This behemoth of an airplane was adopted by the US Air Force for a short period of time after the war, but before the much more famous B52 Stratofortress was adopted. This gargantuan plane made use of a Pratt and Whitney radial engine similar to (although much larger than) the engines used in other US warplanes during World War II. Much like the other engines used by warplanes, these engines were typically not turbocharged, instead used geared superchargers to force more air into the 6(!) propeller engines.

B-36aarrivalcarswell1948
A Corvair B36 Peacemaker, which dwarfed the already big B29 Superfortress. By the time the Peacemaker Flew, piston engines were already being considered obsolete for most military and aviation applications.

From the get-go, this engine was quite dated, as the piston engines were maintenance heavy, and the unusual engine and propeller configuration gave the plane reliability issues. Additionally, the Peacemaker was retrofitted with 4 jet engines for use in takeoff as well as speed over a target to reduce the likelihood of being struck by enemy fire. It wasn’t long however, before the turbojet-powered B52 we all know and love was adopted. The B36 was more or less forgotten as a massive placeholder for the US Air Force for a short time following World War II. Read More

Performance Testing of Axial Compressors

Performance testing is a key part of the design and development process of advanced axial compressors.  These are widely used in the modern world and can be found in nearly every industry, and include the core compressor for aeropropulsion turbofan engines, as well as aeroderivative gas turbine engines for power generation.  An example of this are the turbine engines shown in Figure 1 and 2, which feature an industrial gas turbine and a high bypass ratio turbofan engine with a multistage high-pressure core compressor. The development time of these machines can involve numerous expensive design-build-test iterations before they can become an efficient and competitive product. This places a great importance on the accuracy of the data taken during the performance tests during the development of the compressor since the test data taken is often used to anchor the loss models within the design tools. Modern axial compressors typically have high aerodynamic loadings per stage for improved system efficiency and requires precise aerodynamic matching of the stages to achieve the required pressure ratio with high efficiency. Variable geometry inlet guide vanes and stators in the first few stages are typically required to provide acceptable operability while maintaining high efficiency and adequate stall margin.

Industrial gas turbine for power generation.
Figure 1. Industrial gas turbine for power generation. Source
Figure 2. Turbofan engine for aeropropulsion.
Figure 2. Turbofan engine for aeropropulsion. Source

Performance Testing of Axial Compressors

Axial compressors all undergo a thorough design and development phase in which performance testing is vital to their ultimate success as a product. Performance testing during the development phase of these high-power density machines can ensure that the design meets the specified requirements or can identify a component within the turbomachine which falls short of its expected performance, and may require further development, and possible redesign. Performance testing can also ensure that the unit can meet all the conditions specified and not merely the guaranteed condition. Aerodynamic performance testing multistage axial compressors during the early part of development is often done in phases. The development test program is planned and executed with a design of experiments approach and includes varying the air flow and shaft rotational speed as well as the variable geometry schedule in order to fully characterize the compressor. In the first phase, the front block of the compressor is built and tested at corrected (referenced) air flow rate, inlet pressure, temperature and shaft rotational speed. Instrumentation includes utilizing traditional rakes and surveys at the exit, to obtain spanwise distributions of pressure, temperature, and flow angles. Testing in phases is typically done for two reasons. Read More

Vertical Pumps: What Are They, Where Are They Used and How To Design Them?

Introduction

Vertical pump designs are similar to conventional pumps, with some unique differences in their applications.  Pumps use centrifugal force to convert mechanical energy into kinetic energy and increase the pressure of the liquid. Vertical pumps move liquids in the vertical direction upwards through a pipe. All pumps pressurize liquids, which are mostly incompressible. Unlike compressible gases, it is impossible to compress liquids, therefore the volumetric flow rate can not be reduced. Therefore liquids are transported by pumping and the inlet volume flow rate is equal to the exit volume flow rate.

Vertical centrifugal pumps are simply designed machines, and have similarities to their horizontal counterparts. A casing called a volute contains an impeller mounted perpendicularly on an upright (vertical) rotating shaft. The electric drive motor uses its mechanical energy to turn the pump impeller with blades, and imparts kinetic energy to the liquid as it begins to rotate. These pumps can be single stage or multistage with several in-line stages mounted in series.

The centrifugal force through the impeller rotor causes the liquid and any particulates within the liquid to move radially outward, away from the impeller center of rotation at high tangential velocity. The swirling flow at the exit of the impeller is then channeled into a diffusion system which can be a volute or collector, which diffuses the high velocity flow and converts the velocity into high pressure. In vertical pumps, the high exit pressure enables the liquid to be pumped to high vertical locations. Thus the pump exit pressure force is utilized to lift the liquid to high levels, and usually at high residual pressure even at the pipe discharge.

Applications of Vertical Pumps

An “in line” vertical pump is illustrated in Figure 1 (Reference 1), where the flow enters horizontally and exits horizontally and can be mounted such that the center line of the inlet and discharge pipes are in line with each other.  This is a centrifugal pump with a tangential scroll at the inlet that redirects the flow by 90 degrees and distributes it circumferentially and in the axial direction into the impeller eye. The discharge is a simple volute that collects the tangential flow from the impeller exit, and redirects it into the radial direction.

in line Pump - Figure 1
An “in line” Vertical Pump. Source

Figure 2 shows a vertical pump that has a vertical intake that directs the flow straight into the eye of the pump rotor. At the impeller exit, the tangential flow is collected by a volute and diffused in an exit cone. An elbow after the exit cone redirects the flow into the vertical direction to lift the liquid to the desired altitude. (Reference 2). Read More

Centrifugal Compressors for Fuel Cells

The development of fuel cell technologies and improvements in fuel cells power densities combine to make the use of fuel cells possible in different power sectors as primary or secondary power sources for commercial purpose, residential power requirements, and automobiles, etc. The fuel cell harnesses the chemical energy of a fuel along with an oxidizing agent by converting it into electrical energy through a pair of reactions. For example, in a hydrogen fuel cell, as shown in Figure 1, the hydrogen combines with oxygen from the air to produce electricity and releases water.

Fuel Cell System
Figure 1 Fuel Cell System [1]
The design of a fuel cell system is quite complex and depends on fuel cell types and their applications. With so many possible combinations of fuel cells, this article will not focus on different type of fuel cells, but on Air Management Systems which may significantly affect the overall performance of a fuel cell system.

Air Management Systems

Key sub-systems of any fuel cell system are the fuel processor, fuel cell stack, air management and power management systems. The air management system strongly affects the fuel cell stack efficiency and the power loss of the fuel cells. Therefore, it is necessary to develop a clean, reliable, cost-effective oil-free air system [2].

Major tasks in air management system are Air Supply, Air Cleaning, Pressurization and Humidification.
Read More

A Century of Chiller Technology

A convergence of technologies had to occur to make the modern, high-efficiency centrifugal chiller a reality. To appreciate the technology fully, we must go back in history and understand the origins of the air conditioning and refrigeration industry. Along the way, we will find an important diversion in aerospace and the critically important centrifugal compressor. Ultimately, we will find that the modern chiller is a testament to advanced technology that was developed in multiple fields.

Some of the first advances in and applications of modern industrial refrigeration were in the United States. In May 1922, Willis Carrier revealed the “Centrifugal Refrigeration Machine” – a very early incarnation of what we now call a chiller [1]. The first installation went to a Philadelphia candy manufacturer; it’s interesting to know that the birth of modern refrigeration and air conditioning started on a large scale. Back in those days, economy of scale enabled the technology to be developed. It was not until a decade later that the core technology began to be adopted into compact units that could be used in smaller businesses such as boutique shops. It took several more decades for smaller residential air conditioners to take off commercially.

Shown in the photograph below is Carrier’s first centrifugal chiller in his New Jersey factory [1].

First Centrifugal Chiller
Photo from [1]
The size of this machine is evident, as is the fact that its design, at the time, necessitated components be spread out in space for assembly and maintenance. By modern standards, the same footprint space could be used to accommodate a modern chiller with over 500 refrigeration tons in capacity. By comparison the original design has less than 100 refrigeration tons of capacity.

Read More

It’s Rocket Science – and it’s Dangerous!

Rockets have always fascinated us and to this day a rocket launch is still a global news event worth watching. The sheer noise, power and sight after you hear that “…3-2-1, Lift off!” leave us in awe. A masterpiece of engineering, the recent historic manned SpaceX Falcon 9 launch was no exception. Or was it?

The beginnings

From the outside, a rocket does not look especially advanced – a mere ‘stick’ with a big flame shooting out at one end. The principal concept is simple, too, but the inner workings of a modern liquid-fuel rocket are highly complex.

The first rockets are believed to have existed in China, around 1200. The invention of gunpowder was crucial to the development of these primitive rockets, which were fireworks initially and then weapons. Multistage so-called ‘fire arrows’ were documented during the early Ming Dynasty (Figure 1). The designs were based on bamboo sticks – still a little way off a Falcon 9.

Figure 1: The oldest known depiction of multistage rocket arrows, from 14th-century China. The top arrow reads ‘fire arrow’, the middle ‘dragon-shaped arrow frame’, and the bottom’complete fire arrow’. Source

With the rise of gunpowder, this crude rocket technology spread throughout the Middle East and Europe.

The next rocketry milestone came in the 1780s, when the Indian military developed Mysorean rockets with iron castings and successfully deployed them against the British East India Company. Read More

Modeling a Ground Source Heat Pump

Ground source heat pumps (GSHP) are one of the fastest growing applications of renewable energy in the world, with annual increase of 10% in about 30 countries over the past 15 years.  Its main advantage is that it uses normal ground or ground water temperatures to provide heating, cooling and domestic hot water for residential and commercial buildings. GSHP’s are proving to be one of the most reliable and cost-effective heating/cooling systems that are currently available on the market and have the potential of becoming the heating system of choice to many future consumers, because of its capacity for providing a variety of services such as heat generation, hot water, humidity control, and air cooling. Additionally,  they have the potential to reduce primary energy consumption, and subsequently provide lower carbon emissions, as well as operate more quietly and have a longer life span than traditional HVAC systems. The costs associated with GSHP systems are gradually decreasing every year due to successive technological improvements, which makes them more appealing to new consumers.

The basic purpose of a GSHP is to transfer heat from the ground (or a body of water) to the inside of a building. The heat pump’s process can be reversed, in which case it will extract heat from the building and release it into the ground. Thus, the ground is the main heat source and sink. During winter, the ground will provide the heat whereas in the summer it will absorb the heat.

A GSHP comes in two basic configurations: ground-coupled (closed-loop) and groundwater (open loop) systems, which are installed horizontally and vertically, or in wells and lakes. The type chosen depends upon various factors such as the soil and rock type at the installation, the heating and cooling load required, the land available as well as the availability of a water well, or the feasibility of creating one. Figure 1 shows the diagrams of these systems.

Two Basic Configurations
Figure 1. Two Basic Configurations of GSHP Systems. SOURCE: [1]
In the ground-coupled system (Figure 1a), a closed loop of pipe, placed either horizontally (1 to 2 m deep) or vertically (50 to 100 m deep), is placed in the ground and a water-antifreeze solution is circulated through the plastic pipes to either collect heat from the ground in the winter or reject heat to the ground in the summer. The open loop system (Figure 1b), runs groundwater or lake water directly in the heat exchanger and then discharges it into another well, stream, lake, or on the ground depending upon local laws. Between the two, ground-coupled (closed loop) GSHP’s are more popular because they are very adaptable.
Read More

Charles Parsons and His Contribution to Engineering

Welcome to this special edition of the SoftInWay blog! While we at SoftInWay are known for helpful articles about designing various machines, retrofitting, and rotordynamics, we believe it is also important to examine the lives of some of the men and women behind these great machines.

The compound steam turbine is one of the greatest inventions, not just in turbomachinery but around the world. Once it was introduced to the marine industry, the steam turbine exploded in popularity as a means of allowing ships to travel faster and farther than ever before. It would go on to become a critical part in the naval arms race that preceded the First World War. The steam turbine not only revolutionized marine and naval propulsion, it became one of the best ways to generate electricity. After its inception, the steam turbine became one of the best ways to reliably generate power on a large scale, and make electricity the regular utility that it is today. But who invented the modern steam turbine?

Sir Charles Parsons
Image courtesy of Wikimedia

Sir Charles Algernon Parsons, (1854 – 1931), is the inventor of the modern steam turbine. The work he undertook in his life had a massive impact on the world, continuing the legacy of James Watt by bringing steam technology into the modern era. Born on June 13th 1854 into an Anglo-Irish family, Sir Charles Parsons was born into a well-respected family with roots in County Offaly, Ireland. In fact the town now known as Birr was then known as Parsonstown, from the early 1600’s through to 1899. Parsons was the sixth son of the 3rd Earl of Rosse, and had a family lineage that had made great strides in the areas of military, political, and physical science. The family’s castle in Birr, which is still owned by the Parsons family and is the permanent residence of the 7th Earl of Rosse, was a rendezvous for men of science during the childhood of Sir Charles. Suffice it to say, there was no better place for a future-engineer to grow up. He alongside his brothers would receive private tutorship from Sir Robert Ball and Dr Johnstone Stoney, famous Irish astronomer and physicist, respectively. Read More