Tag: Mechanical Engineering

Disaggregated Measurement

Disaggregated Measurement

Disaggregated Measurement

12/11/17

“How does California specify how all building loads must be measured?”

 

Most areas of the developed world have stringent building energy standards that include analysis for measurement. And as such, California is no exception. But it does so in a very special way. California title 24 (the building energy codec) stipulates that all new buildings must sort their energy loads (HVAC, lighting, etc.) into discrete piles in a method known as Disaggregated Measurement. This way, each subset can be monitored for its energy consumption.

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ASHRAE Standard 90.1

ASHRAE Standard 90.1

ASHRAE Standard 90.1

12/10/17

“What is the basis for building energy efficiency in the U.S and much of the world?”

 

With the onset of global warming, energy efficiency has become a great necessity. As such, buildings in the U.S must now follow a certain standard so that after construction they will meet the sustainability requirements dictated by ASHRAE Standard 90.1. ASHRAE Standard 90.1 is a compilation of all of the codes for building energy efficiency (with the exception of low rise residential units) and is updated every three years to ensure that the next set of codes will be 15 percent more efficient than the previous.

Stirling Cycle

Stirling Cycle

Stirling Cycle

12/09/17

“How can we describe the operation of a Stirling Engine?”

 

Stirling Engines are very interesting machines. However, how exactly can we describe how they operate? Well, let’s use our engineering mindset to find out. First, let’s start with an isothermal expansion in which the working fluid is heated by an external source in Phase 1. Then, let’s go through a constant volume heat removal by passing the working fluid through a regenerator in Phase 2. Afterwards, the system should undergo an isothermal compression in Phase 3. This will lead up to Phase 4, a constant volume heat addition bringing the working fluid back to the beginning of the Stirling Cycle. Stirling cycles operate much like Carnot cycles except that their heat addition/removal process is constant volume.

The Brayton Cycle

The Brayton Cycle

The Brayton Cycle

12/08/17

“What is the fundamental process for jet engines?”

 

Jet engines are some of the most advanced pieces of technology in the world. However, how exactly do they work? Well, let’s use our engineering mindset to find out. First, let’s start with a working fluid, and compress it in an adiabatic manner for Part 1. Afterwards, let’s inject some fuel to induce a constant pressure explosion in Part 2. This should cause an adiabatic expansion for Part 3. To finish everything off, let’s go through with a constant pressure heat rejection in Part 4. This cycle is known as The Brayton Cycle and the efficiency can be given by the equation Nu = 1 – t1/t2 = 1 – (p1/p2)^((k-1)/k).

The Rankine Cycle

The Rankine Cycle

The Rankine Cycle

12/07/17

“How can we predict the performance of steam turbines?”

 

Steam turbines are some of the most used energy systems in the world. As such, it would be very practical to analyze how they consume energy. However, because of intricacies in internal operations, the Carnot Cycle will not work. So how can we use our engineering mindset to model steam turbines? Well, let’s use our engineering mindset to find out. To begin, let’s pump our working fluid from a lower pressure to a higher one in Process 1-2. Then, this high-pressure liquid will enter a boiler to be heated by an external source at a constant pressure until it becomes a dry, saturated vapour in Process 2-3. Afterwards, let’s put this through a turbine, generating power. This Process 3-4 will decreases the temperature and pressure of the vapour, and some condensation may occur. Finally, let’s end this by putting the water through a condenser and condensing it to a liquid at constant pressure until it becomes a saturated liquid in Process 4-1. This cycle is known as a Rankine Cycle and has become the foundation for all steam turbine energy systems.

Air Standard Assumptions

Air Standard Assumptions

Air Standard Assumptions

12/06/17

“What are the common assumptions for analyzing Power engines?”

 

Power engines are very complex machines. As such, we will have to simplify them a bit when performing analysis. So how can we use our engineering mindset to solve this problem? Well, let’s make some assumptions. First Since these systems are fluid based, and the air is the simplest fluid to analyze, let’s say that air is the primary working fluid. Second, let’s say that all processes are ideal and reversible. Third, have combustion is modelled by a heat addition process. Fourth finally, let the exhaust process is a heat rejection process. These are known as the Air Standard Assumptions and are some of the most fundamental aspects of thermodynamics

Entropy Changes of an Ideal Gas

Entropy Changes of an Ideal Gas

Entropy Changes of an Ideal Gas

12/05/17

“How does the entropy of an ideal gas change with time?”

 

When an ideal gas undergoes a nonadiabatic process, it’s entropy is bound to change. However, how can we quantify such a change? Well, let’s use our engineering mindset to figure this out. One way would be to look at a thermodynamic property table, find the specific enthalpies for different temperatures, and then take the difference in values. Another way would be to plug in the equation delta s = C_v*ln(t2/t1) + R*ln(v2/v1) or delta s = C_p*ln(t2/t1) – R*ln(p2/p1).