READING COMPREHENSION: METRIC EXPANSION OF SPACE

Metric expansion of space

The metric expansion of space is the increase of distance between distant objects in the universe with time.

It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space. In other words, the universe is not expanding "into" anything outside of itself.

Metric expansion is a key feature of Big Bang cosmology and is modeled mathematically with the FLRW metric. This model is valid in the present era only at relatively large scales (roughly the scale of galactic superclusters and above). At smaller scales matter has clumped together under the influence of gravitational attraction and these clumps do not individually expand, though they continue to recede from one another. The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past) and partly to the repulsive force of dark energy, which is of a hypothetical nature, but it may be the cosmological constant. Inertia dominated the expansion in the early universe, and according to the Lambda-CDM model (ΛCDM model) the cosmological constant will dominate in the future. In the present era they contribute in roughly equal proportions.

It is also possible for a distance to exceed the speed of light times the age of the universe, which means that light from one part of space generated near the beginning of the Universe might still be arriving at distant locations (hence the cosmic microwave background radiation). These details are a frequent source of confusion among amateurs and even professional physicists.

What space is the universe expanding into?

A graphical representation of the expansion of the universe with the inflationary epoch represented as the dramatic expansion of the metric seen below.

Over time, the space that makes up the universe is expanding. The words 'space' and 'universe', sometimes used interchangeably, have distinct meanings in this context. Here 'space' is a mathematical concept and 'universe' refers to all the matter and energy that exist. The expansion of space is in reference to internal dimensions only; that is, the description involves no structures such as extra dimensions or an exterior universe.

Finite space theory does not suppose space has an edge, but rather that space wraps around on itself. If it were possible to travel the entire length of space without going faster than light, one would simply end up back in the same place, like going all the way around the surface of a balloon (or a planet like the Earth).

The notion of more space is local, not global; we do not know how much space there is in total. The embedding diagram has been arbitrarily cut off a few billion years past the Earth and the quasar, but it could be extended indefinitely, even infinitely, provided we imagine it as curling into a spiral of constant radius rather than a circle. Even if the overall spatial extent is infinite we still say that space is expanding because, locally, the characteristic distance between objects is increasing.

A graphical representation of the expansion of the universe with the

inflationary epoch represented as the dramatic expansion of the metric seen on the left.

Hubble's law

Technically, the metric expansion of space is a feature of many solutions to the Einstein field equations of general relativity, and distance is measured using the Lorentz interval. This theoretical explanation provides a possible explanation of the observed Hubble's law which might indicate that galaxies that are more distant from us appear to be receding faster than galaxies that are closer to us.

In spaces that expand, the metric changes with time in a way that causes distances to appear larger at later times, so if our universe is a Big Bang universe, we would observe phenomena associated with metric expansion of space. If we lived in a space that contracted (a Big Crunch universe) we would observe phenomena associated with a metric contraction of space instead.

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READING COMPREHENSION: CENTRIFUGAL PUMP

Centrifugal pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping. Centrifugal pumps are used for large discharge through smaller heads.

How it works

Like most pumps, a centrifugal pump converts mechanical energy from a motor to energy of a moving fluid; some of the energy goes into kinetic energy of fluid motion, and some into potential energy, represented by a fluid pressure or by lifting the fluid against gravity to a higher level.

The transfer of energy from the mechanical rotation of the impeller to the motion and pressure of the fluid is usually described in terms of centrifugal force, especially in older sources written before the modern concept of centrifugal force as a fictitious force in a rotating reference frame was well articulated. The concept of centrifugal force is not actually required to describe the action of the centrifugal pump.

In the modern centrifugal pump, most of the energy conversion is due to the outward force that curved impeller blades impart on the fluid. Invariably, some of the energy also pushes the fluid into a circular motion, and this circular motion can also convey some energy and increase the pressure at the outlet

Vertical centrifugal pumps

Vertical centrifugal pumps are also referred to as cantilever pumps. They utilize a unique shaft and bearing support configuration that allows the volute to hang in the sump while the bearings are outside of the sump. This style of pump uses no stuffing box to seal the shaft but instead utilizes a "throttle Bushing". A common application for this style of pump is in a parts washer.

Multistage centrifugal pumps

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts.

If we need higher pressure at the outlet we can connect impellers in series.

If we need a higher flow output we can connect impellers in parallel.

All energy added to the fluid comes from the power of the electric or other motor force driving the impeller.

Problems of centrifugal pumps

·         Cavitation—the NPSH of the system is too low for the selected pump

·         Wear of the Impeller—can be worsened by suspended solids

·         Corrosion inside the pump caused by the fluid properties

·         Overheating due to low flow

·         Leakage along rotating shaft

·         Lack of prime—centrifugal pumps must be filled (with the fluid to be pumped) in order to operate

·         Surge

READING COMPREHENSION: HYBRID VEHICLES

Hybrid vehicle

A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors.

Power

Power sources for hybrid vehicles include:

·    On-board or out-board rechargeable energy storage system (RESS)                                                                                                                                                                                                              

·         Compressed air

·         Coal, wood or other solid combustibles

·         Electricity

·         Electromagnetic fields, Radio waves                                                         

·         Compressed or liquefied natural gas

·         Human powered e.g. pedaling or rowing

·         Hydrogen

·         Liquid nitrogen

·         Petrol or Diesel fuel

·         Solar

·         Wind

·         Waste heat from internal combustion engine.

Engine type

When the term hybrid vehicle is used, it most often refers to a Hybrid electric vehicle. These encompass such vehicles as the AHS2 (Chevrolet Tahoe, GMC Yukon, Chevrolet Silverado, Cadillac Escalade, and the Saturn Vue), Toyota Prius, Toyota Camry Hybrid, Ford Escape Hybrid, Toyota Highlander Hybrid, Honda Insight, Honda Civic Hybrid Lexus RX 400h and 450h and others. A petroleum-electric hybrid most commonly uses internal combustion engines (generally gasoline or Diesel engines, powered by a variety of fuels) and electric batteries to power the vehicle. There are many types of petroleum-electric hybrid drivetrains, from Full hybrid to Mild hybrid, which offer varying advantages and disadvantages.

Continuously outboard recharged electric vehicle (COREV)

Given suitable infrastructure, permissions and vehicles, BEVs can be recharged while the user drives. The BEV establishes contact with an electrified rail, plate or overhead wires on the highway via an attached conducting wheel or other similar mechanism. The BEV's batteries are recharged by this process—on the highway—and can then be used normally on other roads until the battery is discharged.

This provides the advantage, in principle, of virtually unrestricted highway range as long as you stay where you have BEV infrastructure access. Since many destinations are within 100 km of a major highway, this may reduce the need for expensive battery systems. Unfortunately private use of the existing electrical system is nearly universally prohibited

Hybrid fuel (dual mode)

In addition to vehicles that use two or more different devices for propulsion, some also consider vehicles that use distinct energy sources or input types ("fuels") using the same engine to be hybrids, although to avoid confusion with hybrids as described above and to use correctly the terms.

Fluid power hybrid

Hydraulic and pneumatic hybrid vehicles use an engine to charge a pressure accumulator to drive the wheels via hydraulic or pneumatic (i.e. compressed air) drive units. The energy recovery rate is higher and therefore the system is more efficient than battery charged hybrids, demonstrating a 60% to 70% increase in energy economy in EPA testing. Under tests done by the EPA, a hydraulic hybrid Ford Expedition returned 32 miles per US gallon (7.4 L/100 km; 38 mpg_-imp) City, and 22 miles per US gallon (11 L/100 km; 26 mpg_-imp) highway. UPS currently has two trucks in service with this technology.

While the system has faster and more efficient charge/discharge cycling and is cheaper than gas-electric hybrids, the accumulator size dictates total energy storage capacity and requires more space than a battery.

Environmental impact of hybrid car battery

Though hybrid cars consume less petroleum than conventional cars, there is still an issue regarding the environmental damage of the hybrid car battery. Today most hybrid car batteries are one of two types: (1) nickel metal hydride, or (2) lithium ion; both are regarded as more environmentally friendly than lead-based batteries which constitute the bulk of gasoline car starter batteries today. There are many types of batteries. Some are far more toxic than others. Lithium ion is the least toxic of the three mentioned above.

The toxicity levels and environmental impact of nickel metal hydride batteries—the type currently used in hybrids—are much lower than batteries like lead acid or nickel cadmium.

 However, nickel-based batteries are known carcinogens, and have been shown to cause a variety of teratogenic effects.

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