Fundamentals of Engineering Thermodynamics & Entropy | Mechanical Engineering Interview Questions

“Introduce yourself” – How does it feel when the interviewer throws the first ask? 

But wait… 

This isn't the real challenge. The real test begins when you're hit with mechanical engineering interview questions - questions that assess your core knowledge and understanding of key principles. 

The interviewer isn’t just testing your memorization, but your ability to apply these concepts practically. 

If you’re preparing for design engineer interview questions, then understanding fundamental concepts like engineering thermodynamics and applied thermodynamics is essential. A small mistake can lead to major system failures, which is why mastering them is crucial. 

At Skill-Lync, we’re dedicated to helping you master these core principles by breaking down interview questions related to mechanical engineering that are commonly asked by OEMs. Let’s dive into the questions in mechanical engineering interviews. 

1. What is thermodynamics and entropy? 

Now, let's take a real-world scenario to set the context: 

Imagine you’re analyzing a vehicle that’s consuming 15% more fuel than expected. The engine is running too hot, and there's a significant increase in energy waste. 

What could be the cause? Why is the engine losing so much energy? 

To understand this, we need to dive into thermodynamics and entropy. Let’s break them down. 

Understanding Thermodynamics & Entropy 

Let’s begin by understanding thermodynamics in simple terms. Thermodynamics is the study of heat, energy, and work. Here are a few core principles of thermodynamics: 

• Energy Transfer: Energy moves from one form to another, like electricity turning into heat in a toaster. 
• Work and Heat: Work is done when energy moves an object, while heat is the transfer of energy due to temperature differences. 
• System and Surroundings: A system is what we focus on (such as a car engine), while the surroundings are everything outside the system. 

Understanding these concepts is essential when answering design engineer interview questions, as they form the basis of how engineers approach system optimization. 

The First Law of Thermodynamics – Energy is Never Lost 

One of the most fundamental laws in thermodynamics is the Law of Conservation of Energy. It states that energy cannot be created or destroyed; it can only be transformed from one form to another. 

Here’s an example to make this clearer: Think about charging your phone. Electrical energy is converted into chemical energy, which is stored in the phone's battery. When you use the phone, that energy transforms again - into light, sound, and heat. The total energy stays the same, but it changes form. 

Entropy – The Measure of Disorder 

Next, let’s talk about entropy, which is important for understanding energy flow. 

Imagine your room: 

• When it’s neat and organized → low entropy 
• When it’s messy and chaotic → high entropy 

Entropy measures the amount of disorder or randomness in a system. In thermodynamics, nature always tends to move toward higher entropy, meaning things naturally become more disordered unless energy is applied to maintain order. 

The Second Law of Thermodynamics – Why Energy Gets Wasted 

Another key principle in thermodynamics is the Second Law, also known as the Law of Increased Entropy. This law states that in an isolated system, entropy always increases. 

To explain this with an example: A hot cup of coffee left on a table will eventually cool down. The heat from the coffee moves to the surrounding air, balancing the temperature. This is a natural movement toward disorder, or increased entropy. 

This law explains why machines are never 100% efficient - some energy always escapes as heat.  

Thermodynamics in Daily Life 

You might not realize it, but you see thermodynamics in action every day. For example, think about how a refrigerator works. It removes heat from the inside (cold area) and pushes it out, increasing the overall entropy in the environment. 

This principle shows why no engine can operate without energy loss - some of the energy always turns into heat.  

Conclusion 

As we wrap up, it’s clear that mastering thermodynamics and entropy is essential for understanding how mechanical systems work, diagnosing issues, and optimizing energy efficiency.  

This blog is part of our ongoing Mechanical Engineering Interview Questions.

Skill-Lync has released a FREE playlist covering Mechanical Engineering Interview Questions in detail! Check it out here.