First, there are certain sign conventions. It could be defined in a different way, but things are traditionally done in a certain way. Second, if work going out of the system is defined as positive, then it is quite logical that work going into a system should have the opposite sign.
In this case, V would be negative, and work w would be positive.
when work is positive and when playing is negative
Yes Work can be positive or Negative.
what is positive and negative
The positive crankcase ventilation or PCV system uses engine vacuum to draw crankcase vapors into the intake where they are directed into the combustion chamber and burned. This keeps pressure from developing in the crankcase which could otherwise cause gaskets and seals to leak. It also reduces sludge build up by drawing out water vapor. Once the engine reaches 212 degrees Fahrenheit (100 degrees Celsius) water in the oil turns to steam and is extracted with the other engine vapors.
The question should really be "How does positive crankcase ventilation work?" You can't ventilate a crank, it's either solid (roller bearing crank) or the only spaces are oilways. Positive crankcase ventilation, PCV, is used to prevent a build-up of combustion gases in the crankcase. The piston rings prevent most combustion gases getting down the sides of the pistons and into the crankcase but a little does sneak past. This is called 'blow by' and increases as the engine wears. If there was no ventilation, pressure would build in the crankcase and cause oil leaks and other trouble. In early engines the crankcase was just vented to atmoshere via an oil trap so combustion gas fumes and some oil vapour escaped into the air. Later, to prevent this, the crankcase was vented instead to a low pressure part of the inlet system. The engine then consumes its own fumes. Originally this was just a flow restricting hole to the inle manifold but complication has crept in over the years. We have seen one-way valves, 'gulp valves' and similar all intended to hold the crankcase pressure just below atmospheric and get the engine to consume it own fumes without upsetting fuelling accuracy. On diesel engines and supercharged engines a pressure lower than atmospheric can be created by putting a venturi in the the inlet. On a conventional gasoline engine the inlet is always below atmospheric pressure. Mark www.top-biker.com
Its called Positive Cranck Shaft Ventilation PCV Valve. a one-way valve on a motor-vehicle engine for regulating a pollution control system that draws crankcase fumes into the cylinders for burning. Besides totally eliminating crankcase emissions as a source of air pollution, the constant recirculation of air through the crankcase helps remove moisture which otherwise would cause sludge to form. Thus the PCV valve extends the life of the oil and engine.
In thermodynamics, work done by the system is considered positive. Work done on the system is considered negative.
A thermodynamic work is said to be positive when the system does work on the surroundings. This occurs when energy is transferred from the system to the surroundings, resulting in a decrease in the internal energy of the system.
If work is done on the system then it has a negative sign. If work is done by the system then it has a positive sign.
All four-stroke engines have crankcase back pressure because gases blow by the piston rings. They used to just drill a hole in the crankcase to let it out; when the government figured out this was a major source of pollution, they required the gases be captured and burned. To make this work, the hole is fitted with a one-way check valve and a hose. The hose is routed to the air intake on the carb or fuel injection. This is called "positive crankcase ventilation" (or "PCV") because the intake system's vacuum sucks the gases out of the crankcase. The valve is there for safety reasons: if the engine backfires through the carb, the PCV valve keeps your engine from exploding - which happened before the PCV system was invented. If you're getting back pressure, this system isn't working. And the problem's usually that the PCV valve is clogged or stuck shut. They should be replaced every year at the start of boating season, but since yours is clogged replace it now. If you pay $10 for one you went to a really expensive store.
work done on the system: when a surrounding does work on the system the total energy increases so work done is positive..........
Solar ventilation, as it concerns residential homes, is a system that helps remove hot air from the attic and other areas of the house by using the sun's power. The system is comprised of a solar panel, a fan, and a duct that helps to circulate the air.
The kind of ventilation systems that Panasonic fans work with is HVAC. HVAC is heating, ventilation, and air conditioning; it is the technology of comfort.
If there will be employees who work within the building for extended periods of time I would suggest installing some form of ventilation system. Many storage facilities decide whether to use ventilation system or not based on what the building will be used to store inside.
First, there are certain sign conventions. It could be defined in a different way, but things are traditionally done in a certain way. Second, if work going out of the system is defined as positive, then it is quite logical that work going into a system should have the opposite sign.