mechanical engineering

More Than You Ever Wanted to Know About Mechanical Engineering: Thermodynamic Efficiency

We’re starting to take a look at some of the basic tools for analysis of heat, energy, and thermodynamic systems. One concept that will come up over and over for us is efficiency.

It’s a pretty familiar concept. Efficiency is how much you get out for what you put in. Or, more formally, the ratio of your desired output to your required input. In equations, we’ll write it as η.

Say, for example, you have a motor drawing 60W from an electric outlet and doing 52W of shaft work. In this case, the motor is about 86% efficient.

Suppose, instead of drawing electrical power from the mains, your motor is supplied by a generator. The generator will have an efficiency of its own, which is the electrical power it outputs over the mechanical work that goes into it. Say it takes 100W to spin the generator and it can produce 80W of electricity from that shaft work for an efficiency of 80%.

If we want to know the overall efficiency of the system that comprises both the motor and the generator, we just multiply their individual efficiencies together.

Note that the overall efficiency of a system will always be lower than the individual efficiencies of its components.

Major types of Engines

Straight In-line

This is the type of engine that you find in your quotidian car. Nothing fancy, just all pistons arranged parallel along the vertical direction.


V in-line

Now, this is the sort of the engine that you find on sports cars like the Ferrari. When you hear sports enthusiasts go ‘ Whoa, that’s a V-12! ‘ - it just means that the engine has a V-type arrangement with 12 cylinders.


V +  Inline = V-inline

Commonly referred to as the VR engine.

The name VR6 comes from a combination of V engine (German: V-Motor), and the German word “Reihenmotor” (meaning “inline engine” or “straight engine”)

Volkswagen’s VR6 engines, and the later VR5 variants, are a family of internal combustion engines, characterized by a narrow-angle (10.5° or 15°) V engine configuration.


                    a: straight engine, b: V engine, c: VR engine


W engine

A W engine is a type of reciprocating engine ( again created by Volkswagen) arranged with its cylinders in a configuration in which the cylinder banks resemble the letter W, in the same way those of a V engine resemble the letter V.


Bugatti Veyron’s W16 engine

A W16 engine is used on the Bugatti Veyron. That’s 16 cylinders!



Flat Engine

Flat engines offer several advantages for motorcycles, namely: a low centre of gravity, smoothness, suitability for shaft drive, and (if air-cooled) excellent cooling of the cylinders. You can find them on aircrafts as well


Radial Engine (aka the dancing starfish)

They were used mostly in small aircraft for the propeller

The big advantage of radials was their large frontal area, which meant they could be air cooled, meaning less maintenance, failures, and of course a lower cost of initial purchase and maintenance.


Wankel Engine

This engine has only 3 moving parts and can make a lot of power.However, they are pretty inefficient, the last car to use this was a Mazda RX-8.


Axial Engine

The axial engine is a very interesting design. But they are not widely used because they are just hard to make and running these things at high RPM’s  is a challenge.

Duke engines are equipped with this type.


Jet engine

Commonly jet engines refer to the engines that are found on, well Jets!

Suck,squeeze,bang and blow

Air is sucked in through the front and  squeezed. A controlled explosion follows and the exhaust is blown out through the back

But, Jet engines also include the engines that are found on rockets, hybrids and water-jets. And their mode of operation is different than the one mentioned above.

Pretty cool eh?

Have a great day!



PC: Howstuffworks, Duke, MichaelFrey, Azure.km

** There is also the Stirling Engine. It’s amazing and a topic for an another post. But if you are interested do check out more about it here.


EDIT :  Had forgotten about the VR and the W-engines. My bad! Thanks for pointing it out.:D.

EDIT2: The suck squeeze bang and blow illustration was incorrect. Ergo, changed that.

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The Strandbeest: Art and Engineering.

Created by Dutch artist Theo Jansen, the Strandbeest is created by rudimentary objects such as PVC piping, wood and sails and contains no electrical or motorised parts; it is instead powered by the wind. 

The Strandbeest has steadily evolved into more complex working structures. Some even having the ability to store wind power in the absence of a breeze, being able to nail pins into the sand when wind power becomes too great, and even sensing when they have entered the water or encountered an object so they can then avoid the obstruction. 

Theo Jansen is ever improving and changing these creatures, and does have a final plan for them saying: “over time, these skeletons have become increasingly better at surviving the elements such as storms and water, and eventually I want to put these animals out in herds on the beaches, so they will live their own lives”.

(Youtube)

Help an Immigrant Trans Woman Afford Grad School

The short and sweet version is this: I’m a Queer Trans Woman trying to pay for Graduate School. I’ve been Admitted to NYU to study Mechanical Engineering. If I can’t afford it, not only am I not able to attend school, I would have to leave the country as well, since my F-1 visa is only valid whilst in school. Supporting me is supporting Queer and Trans people in STEM and also helping a Trans Woman stay in the only place she’s ever been able to call home.

The long version goes like this:

 I’ve been living in the US for five years, I did my Undergrad here. I realized I was trans here. I made the best friends I’ve ever had here. After college I moved to NYC to start my transition. I’ve now been on HRT 3 months and am presenting as my gender full time.

When I moved I thought I’d be able to go on Optional Practical Training (a Work permit for International Students) and get a job to finance my transition. When I was denied OPT, I had to adjust my goals until reaching the point where I’m willing to do anything just to stay. I was planning on taking a couple years before attending Grad School, but I pushed that forward in order to stay in the country.

I applied to the NYU Polytechnic School of Engineering for the Mechanical Engineering program. I applied under my name and gender, despite not having yet changed them legally, and I got accepted! However, now I may have to be forced not to attend due to lack of funding.

  As an International student, any form of Federal aid is barred from me, including Fafsa and Federal Student Loans. A large number of non-federal forms of aid are also barred or available at increased difficulty, for instance, I’m trying to obtain a private student loan, which is often easy for Grad Students, but I’m required to have mine cosigned by an U.S. Citizen of which I know none with good credit.

 All the money donated will be used to pay for tuition. The current goal will only cover one semester. If the campaign is successful, I may raise the goal to cover other semesters. It is a 2 year (4 semester) program.

Please, consider donating anything you can or at the very least signal Boosting. I would like to reiterate that, for me, going to school means more than continuing my education and adding to the lacking Queer presence in STEM. It also means survival, since New York, for all its issues, is the only place I’ve ever felt safe and welcomed. It’s a feeling no one should ever have to give away.

https://www.youcaring.com/TransToNYU

Constant-velocity joints (aka homokinetic or CV joints) allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive vehicles, and many modern rear wheel drive cars with independent rear suspension typically use CV joints at the ends of the rear axle halfshafts and increasingly use them on the propshafts (drive shafts).

[Source: https://www.behance.net/ ]

External image

A surviving geared fragment of the Antikythera mechanism. The device was discovered in 1900 as part of a shipwreck off the Greek island of Antikythera, and is thought to have been constructed around 100 BC. It is believed to have been used for calculating various astronomical measurements and is considered by some to be the first known analog computer.

More Than You Ever Wanted to Know About Mechanical Engineering: The First Law of Thermodynamics

If we’re going to talk about heat transfer, we’ve got to talk a little bit about thermodynamics. We’ll take it one law at a time.

The first law of thermodynamics just boils down to conservation of energy.

In a closed system, the total energy present remains constant. The only way the amount of energy present can change is if energy is put into the system or taken out. There are two ways to make energy cross system boundaries like this: either by heat transfer or by work done. So for a closed system, the total change in energy of the system is the net amount of heat put in minus the net amount of work out.

In addition to a closed system, this principle can also be applied to a control volume - that is, a defined region of space that mass can enter and leave. Mass entering will carry energy in with it, and mass leaving will carry energy out with it.

In the situation in which you are considering a control volume in the midst of a constant flow of incompressible fluid, you can consider the heat transfer occurring to be a function of the temperature difference between the fluid entering and the fluid exiting, the mass flow rate of the fluid (mass transferred per unit time), and the specific heat of the fluid, c, which is a physical property of the fluid - basically, how much energy you have to put into it to raise its temperature.

This is a simplified equation, and many situations involving fluid flow require consideration of additional factors, but for now it’ll work for us. We’ll get into the more complicated stuff later.