Mechanical Maintenance Tips

Heat engine efficiency

2010-12-30T17:10:00.001-08:00

1. Why it is not possible to have an engine with 100% efficiency?

The efficiency of a heat engine is given by:

Ƞ = 1 – T_sink/T_{source Where T is temperature (in K) of source and sink}

= (T_source– T_sink)/T_source

Thus, to attain 100% efficiency, T_sink MUST be equal to zero.

Let us assume that we make a heat engine with source at 300K and sink at 0K. As soon as the first cycle is complete, the engine will release some heat into sink, thus elevating its temp. Let us assume that this rise in temperature is as low as 1 K.

Then,

Ƞ= 1 – 1/300

= 300 – 1/300

= 299/300

= 99.6%; which is less than 100%!

Therefore, even if we make the sink temp 0K, it will remain so till 1^st cycle only. From the very next cycle, the efficiency of the engine will become less than 100%.

2. Effect of increasing T_source or decreasing T_sink on efficiency.

Let us assume that a heat engine operates between 400 K and 200 K.

The current efficiency is 50%

Let us assume that the source temp is increased by 100K (to 500K).

Then,

Efficiency = (500 – 200)/500

= 60%

Let us assume that the sink temp is decreased by 100K (to 100K).

Then,

Efficiency = (400 – 100)/400

= 75%

Thus, we see that decreasing the sink temperature has a greater effect on efficiency as compared to increasing the source temperature!

Fluid Power

2009-07-11T13:29:00.001-07:00

In the high school, we all came across the Pascal's Law. It says that when pressure is applied on an enclosed incompressible fluid, it gets transmitted equally in all directions.

Now, this leaves us with two very important points:

1. INCOMPRESSIBLE

2. FLUID

I'll take the 2nd one first. What is a fluid? To get the most simplistic answer I'd say, "Any thing that has the ability to flow is fluid". This most simple definition covers liquid as well as gases under the head "Fluid".

Now the first one. If an enclosed fluid is subjected to a force which tends to compress it, there are two possibilities. One is that the fluid's volume will decrease causing compression or if it does not compress under force, its pressure (force per unit area) will increase.

In modern industry, hydraulics play a key role. Enclosed systems using incompressible fluid are becoming more and more popular due to their versatility, reliability, compactness and accuracy. In older times, hydraulic systems used water as their prime fluid. A classic example of such system was the Tower Bridge of London which had steam engines to pump the river water into the lifting mechanisms of bascules. Modern hydraulic systems use hydraulic oils. In places where load is not an issue, pneumatic systems are used. These systems use compressed air for their operation.

I have seen systems using water, natural oil and now-a-days we normally use synthetic oil. Water was the most inexpensive fluid very easily available. The two most problamatic areas were:

1. It caused rusting of equipments

2. Getting contamination free water was tedious

Natural oil also had its own problems. Its quality rapidly deteriorated due to severe pressure and heat. This opened up the path for synthetic oils which are specifically designed for hydraulic systems.

TPM

2009-06-10T12:25:00.001-07:00

Now what is this? I know I am here after a long time, but I am not back with a puzzle. Rather, I am here with a concept that can solve most of your puzzles.

TPM or Total Productive Maintenance is a vast subject. Most of the time, we look upon the jobs of an operator and maintenance staff as being two distinct jobs. To some extent, it may be true. But the ultimate truth is: Both of them try to exploit the best out of the machine. Thus, the convergence focus is the concept of TPM.

The very base of TPM is 1s and 2s concepts. This has come from the Japanese concept of 5 – S. These 5 – S are:

Seiri
Seiton
Seiso
Seiketsu
Shitsuke

The first one i.e. "Seiri" refers to sorting of the workplace. In other words, it means removing unwanted / irrelevant material from the workplace. The second "Seiton" can be termed as: "A place for everything, Everything in its place".

So, what are you waiting for? Just go around and have a look. You'll definitely find some unused old inventory or used up spare waiting to be sold! Put the unwanted things OUT! Make a marked place for everything that is needed for day-to-day production. Keep everything in its place.

Now ask your workmen. They'll surely be happy now. After all, they need to spend less time searching for spares during breakdowns!

Which language do you speak?

2008-06-05T16:02:00.000-07:00

A bit confusing title? Huh....... who cares! NO ... YOU have to be careful. After all, it will reflect in the job you do.

It doesnt matter which language you speak till you can understand and speak the language of engineers। And what is the language of engineers?

Well, drawing is the language of engineers.

In day-to-day of professional life, we come across a lot of drawings. Normally, these are the orthographic projection of the equipment in 3 planes. The visible edges are represented by lines. The hidden edges and centre lines are represented by dotted lines. Important dimensions are given and some less important dimensions need to be derived. The important conventions are given in the bottom right corner.

Orthographic projections can be either in first angle or third angle projections. They are represented as follows:

Another system of drawing is the isometric projection. It is somewhat a 3D image of the equipment which shows only the visibe planes. It is made to visualize the actual object and is rarely used in day-to-day engineering.

The Maintenance attitude

2008-05-21T02:09:00.000-07:00

While working in the maintenance group of any industry, it is better to develop the maintenance attitude. This is the only way to be successful in managing the downtime and your customer! How to do it? Well, just keep your common sense working all the time.... that's all!

Know your process: In whatever industry you are working, your best tool will always be the complete knowledge of the process. If you are conversant with the ins and outs of your process, you can always maintain it well.

Know your equipment: The thorough know-how of the equipment and their specific maintenance requirements is also a must. If possible, keep a set of drawings, list of spares and list of suppliers along with lead time. All this comes handy during breakdowns.

Know your people: All the fingers are not the same. Same is applicable to people. Each one of us is specifically talented in different areas. Identify the strengths of your team and utilize them effectively.

Be ready for challenges and strive for the complete satisfaction of your customer (your operational people). Use all your five senses. The best part of being in the mechanical maintenance is that you can see almost everything. Equipments warn you before failing. The worst part is, we usually ignore the warnings and after the failure, the entire effort goes into putting the ball in others court!

Sharing is fun!

2008-05-20T03:25:00.001-07:00

In our day to day work life, we face many situations when small things we ignore come to our rescue. I'll share some basics of maintenance facts in my coming posts. It may be useful, it may not be! I don't care. For me, sharing is fun!