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Friday, 9 December 2016
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Thursday, 8 December 2016
Types of Mechanical Forces
A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force in SI system is the newton (N) and CGS system is dyne. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are negligible. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for civil engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties of materials. There are three main types of mechanical forces that can act on a body. They are:
1. Tensile force 2. Compressive force and 3. Shear force
Types of Mechanical Forces
A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force in SI system is the newton (N) and CGS system is dyne. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are negligible. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for civil engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties of materials. There are three main types of mechanical forces that can act on a body. They are:
1. Tensile force 2. Compressive force and 3. Shear force
Difference between the petrol engine and diesel engine
The temperature at the end of the compression
is less for the petrol engine.
Thus a spark plug is needed for the compression. In case of the diesel engine the temperature at the end of the compression is above the self-ignition temperature of the fuel.
Hence the fuel ignited is allowed to enter the
cylinder due to the high temperature.
No spark plug is required for the diesel
engine.
For the separate entry of the fuel after the compression stroke, a nozzle is provided for the diesel engines.
In case of the petrol engine they do not have
the nozzle.
In petrol engine the air and the fuel, are mix inside a carburetor before entering the engine cylinder. In diesel engine there is no mixing of air and fuel before suction stroke. Hence diesel engine does not have a carburetor.
Heat addition must take place at the constant volume for petrol engine. It takes place at the constant pressure for diesel engine
For the same compression ratio, the efficiency of a petrol engine is higher than that of the diesel engine. This is theoretical.
In an actual practice the compression ratio of a diesel engine is 1.5 times to 2 times more than that of a petrol engine.
Hence the diesel engine efficiency is much
higher.
Under some conditions the air fuel ratio for the petrol engine must be 16 and for the diesel engine case the ratio of the air fuel mixture must be 25 to 35.
Difference between 2 stroke and 4 stroke Engine
In the 2 stroke engine it consists of one cycle
with one rotation
In the 4 stroke engine it consists of one cycle
with two rotations.
The inlet and the exhaust valves of the 4 stroke engine are replaced by 3 ports in a 2 stroke engine.
In 2 stroke engine the lubrication oil must be
mixed with the petrol
In case of 4 stroke engine the lubrication and the fueling must take place separately
In the 2 stroke engine due to the presence of the lubrication oil, some of the lubrication oil must be combusted during the time of heat addition. Hence there is more friction and loss of work in 2 Engine
The power available in the 2 stroke engine is
only 70% of the calculated power
In 4 stroke engine the power available is 90%
of the calculated power
In 2 stroke engine the transfer port and the exhaust port are opened at the same time. Hence some fresh air fuel mixture will be escaped out of the engine cylinder, due to which there is loss of fuel.
For single cylinder engine the size of the flywheel is bigger than the 4 stroke engine.
Due to the above reason the 2 stroke engine on the roads are replaced by the 4 stroke engine
The overall efficiency of a 4 stroke engine is much higher than that of a 2 stroke engine.
What skills do mechanical engineers need?
The essence of engineering is problem solving. With this at its core, mechanical engineering also requires applied creativity — a hands on understanding of the work involved — along with strong interpersonal skills like networking, leadership, and conflict management. Creating a product is only part of the equation; knowing how to work with people, ideas, data, and economics fully makes a mechanical engineer.
What tasks do mechanical engineers do?
Careers in mechanical engineering call for a variety of tasks.
· Conceptual design · Analysis · Presentations and report writing · Multidisciplinary teamwork · Concurrent engineering
· Benchmarking the competition
· Measurements · Data Interpretation · Developmental design
· Research · Analysis (FEA and CFD)
· Working with suppliers
· Project management · Sales · Prototyping · Consulting · Testing · Customer service
Read tips for healthy life
1. Avoid fried eggplant
It soaks up oil quickly, like a sponge—more than
any other vegetable, even more than French fries.
Try grilling, broiling, baking, steaming, or braising
it instead of frying.
2. Follow these guidelines for cooking eggs
You need not cook eggs to the hard and rubbery
stage. Boiling an egg in its shell at 140° for 3H
minutes should kill virtually all bacteria.
Scrambled eggs and omelets are fine if cooked
just past the runny, moist stage (they should be
set, but don’t have to be rock hard). If you’re
frying eggs, “over easy” is best: fry them for
about 3 minutes on one side, then about 1 minute
on the other.
3. Eat sweet potatoes
Despite their sweet taste, they have about the
same number of calories per ounce as white
potatoes.
A 3 ounce baked sweet potato contains three
times the recommended daily amount of beta
carotene, half theRDA for vitamin C, and just 100
calories.
Avoid the typical package of ground poultry,
which usually contains skin and too much fat.
Look for ground turkey breast; it should be
labeled 96 to 98% fatfree (by weight).
4. Try veggie burgers
They’re served in many restaurants, and you’ll
find them in frozen, refrigerated, or mix form in
the grocery store. Veggie burgers may be
primarily soy and/or may contain any
combination of mushrooms, onions, peppers, rice,
oats, barley, bulgur (cracked wheat), rye, gluten
(wheat protein), beans, spices, and egg whites.
In a restaurant, ask the waiter what’s in the
veggie burger and how it’s cooked. Some veggie
burgers are almost fatfree, but some are high in
fat, especially if nuts or cheese are major
ingredients.
5. Eat beans and other legumes
Beans, lentils, and dried peas are all good
sources of soluble fiber, which, if consumed
regularly, may help lower blood cholesterol levels.
6. Cook with fresh herbs
They contain powerful antioxidant compounds,
according to a USDA analysis. Herbs that scored
highest by far were oregano and marjoram—just a
tablespoon or two of the chopped herbs would
supply significant amounts of antioxidants.
Fresh herbs are more potent (in flavor and
antioxidant power) than their dried counterparts,
and culinary herbs in general have more
antioxidant potential than medicinal ones, such
as ginkgo.
7. To boost your calcium, eat sardines
When eaten with their small edible bones, three
small fish (one ounce each) supply 370
milligrams of calcium, more than a cup of milk.
Canned salmon, also eaten with its bones,
supplies nearly as much calcium.
8. Drink tea
It contains enough fluoride to help prevent tooth
decay, and is also rich in substances called
polyphenols, which act as antioxidants and thus
may help protect against cancer.
Tea drinking may also help strengthen bones.
Besides the fluoride, flavonoids and other
compounds in tea may be good for bones. Some
people still worry that tea could weaken bones
because of its caffeine, but several studies have
now shown this is not the case.