The Otto Cycle
“How can we describe the operation of a spark ignition engine?”
Spark ignition engines (also known as Internal Combustion Engines) were the backbone of 20th-century vehicles. And since us engineers love to describe things, how can we do so in a systematic manner? Well, to start, let’s analyze how several key variables change over time. To start, let’s draw in some air into the piston/cylinder under a constant pressure. Also, let’s label this process 0-1. Then, let’s move the piston such that an adiabatic compression takes place from the bottom dead centre (maximum height) to top dead centre (minimum height) in process 1-2. Afterwards, let’s represent the ignition as a constant volume heat transfer in process 2-3. This should soon cause an adiabatic expansion back to bottom dead center in process 3-4. Then, let’s complete the cycle with a constant pressure heat rejection in process 4-1. Afterwards, let’s reject the air at a constant pressure in the final process 1-0. This is known as the Otto cycle and is one of the most powerful tools for a Mechanical Engineer.
“How can we measure the velocity of a fluid without using any moving parts?”
Measuring the velocity of a fluid is one of the most useful things we can do. With this, we can find out how much mass is flowing within a system, and adjust all calculations accordingly. But since fluids lack any form of defined shaped, measuring their average velocity can be very difficult. So how can we use our engineering mindset to solve this problem? Well, to begin, let’s look at how pressure moves within a system. A fluid’s total pressure is made of up both static pressure (the default, inert pressure) and velocity pressure (the pressure associated with the momentum of the fluid).
Since it is rather simple to obtain the total and static pressures and use their values to find the final velocity, let’s build a machine to do exactly that. Since fluids move steadily through a pipe, let’s start with that. And since we want to find the total velocity of a fluid, let’s also put the fluid through the hole. Then let’s also have holes perpendicular to the main tube to measure the static pressure. Then let’s subtract the difference to get the velocity pressure, and divide by the fluid’s density to obtain the fluid velocity. This machine is known as a pilot tube and is used widely in airplanes to measure the airspeed and HVAC systems to find the refrigerant flow rate.
“How can we remove without using a gas?”
When most people think of a heat removal device, they probably visualize a fan based systems which released cooled air. However, using a gas can be hard to control, and may also require a lot of room. So how can we use our engineering mindset to solve this problem? Well, what if we were to replace the primary medium with a liquid, such as water? This would allow us to take advantage of water’s higher specific heat capacity, density, and thermal conductivity to optimize efficiency while ensuring that operations are non-toxic and inexpensive. This increased capacity made water cooling very popular in computer and automotive hardware enthusiasts since this process takes less space and can deliver more cooling. On the downside, using water might accelerate corrosion in metallic substances.
Vapor Compression Cycle
“How do most AC systems work?”
While absorption refrigeration systems are great for many applications, sometimes we just want a more traditional technology for our cooling needs. So how exactly do most AC systems actually work? Well, let’s use our engineering mindset to find out.
Let’s start with the basics. Our goal is to take heat from one space and transport it to another. One very common way to do this is to use a heat exchanger. But to ensure continuous cooling, we must ensure that we have a constant supply of fluid at a temperature we desire. To build this system, let’s start with four components: a compressor, a condenser, an expansion valve, and an evaporator. Then, let’s have a refrigerant enter the compressor at a low temperature in a gaseous state, and do work on it to increase its temperature and pressure. Then, let’s have it enter the condenser, where heat is transferred into a nearby medium. Afterwards, let’s run it through an expansion valve to cool it and release pressure while turning some of the gas into a liquid. Finally, let’s pull it through an evaporator, which is basically a heat exchanger that allows the cold fluid to absorb heat from the surrounding medium (and therefore cool it) and gasify it. Once the fluid leaves the evaporator, it enters the compressor and the process (known as the vapor compression cycle) will start again.
Nonintrusive Load Monitoring
“How can we determine the appliances in a building just from its energy consumption?”
As Engineers, it would be very useful to analyze the types of appliances within a building. However, doing so requires a heavy upfront investment in a large multitude of sensors.
Or does it?
After many years of research, Engineers and Scientists have developed a method known as Nonintrusive Load Monitoring, which takes in data from a building’s energy uses, parses out all of the patterns, and recognizes which appliances are in the unit. Although novel and affordable, one serious drawback with this technology is privacy concerns, since large organizations will be able to snoop in on the appliances that an individual possesses.
Fault Detection and Diagnosis
“How can we monitor a facility for component breakdowns?”
When running industrial facilities, components are very prone to failure, which can cause large amounts of money and energy to be wasted. So how can we make sure that these facilities are protected from such failures? Well, what if we were to implement a network of sensors that would collect data from a facility, which would then be parsed through algorithms. If any of this data finds any strange patterns, it can sort out the underlying cause and solve any issues. This technology is known as Fault Detection and Diagnosis and is one of the most fascinating facets of industrial operations management.
“How do can we apply the laws of physics and chemistry to make a refrigerator?”
Refrigerators allow us to survive in the modern world, whether it be in keeping our buildings cool or our food fresh. However, how exactly do these systems work? Well, let’s look at one such approach.
First, let’s start with a solution of hydrogen and ammonia in a boiler. Then, let’s apply heat to separate out these two substances, leading the ammonia gas to a higher pipe and the hydrogen to a lower pipe to be mixed later. Once this is complete, let’s send the ammonia gas through a heat exchanger to condense it into a liquid. Afterwards, let’s shove this new liquid with the hydrogen gas in a freezer (evaporator). The highly reactive chemical reaction will absorb a large amount of heat from the surroundings. The ammonia gas will then be evaporated with a second heat exchanger and sent back to the original boiler, starting the process all over again!
Absorption Refrigeration is commonly implemented in food storage in commercial vehicles and in buildings for waste heat recovery.