torr (torr) to bar (bar) conversion

What is torr?

Torr is a unit of pressure measurement commonly used in vacuum applications. Let's delve into its definition, origin, and relevance.

Definition of Torr

The torr is a unit of pressure defined as 1/760 of standard atmospheric pressure. In other words, 760 torr is approximately equal to one atmosphere (atm).

$$1 \text{ torr} \approx \frac{1}{760} \text{ atm}$$

It is also nearly equal to one millimeter of mercury (mmHg). More precisely:

$$1 \text{ torr} \approx 1 \text{ mmHg}$$

Origin and History

The torr is named after Italian physicist and mathematician Evangelista Torricelli (1608–1647), who invented the barometer in 1643. Torricelli's experiment demonstrated that air pressure could support a column of mercury, paving the way for pressure measurement.

Relation to Pascal (Pa)

The pascal (Pa) is the SI unit of pressure. The relationship between torr and pascal is as follows:

$$1 \text{ torr} \approx 133.322 \text{ Pa}$$

Therefore, to convert from torr to pascals, you can use the formula:

$$\text{Pressure in Pa} = \text{Pressure in torr} \times 133.322$$

Real-World Examples and Applications

Torr is commonly used in fields that involve vacuum systems, such as:

• Vacuum pumps: Vacuum pump performance is often rated in torr or millitorr (mTorr). For example, a roughing pump might achieve a vacuum of 10$^{-3}$ torr.
• Scientific instruments: Mass spectrometers, electron microscopes, and other analytical instruments require high vacuum conditions, often specified in torr or microtorr (µTorr).
• Semiconductor manufacturing: Vacuum processes, such as chemical vapor deposition (CVD) and sputtering, use vacuum levels measured in torr to control deposition rates and film quality.
• Space research: Simulating space environments requires extremely low pressures, which are measured in torr or even smaller units like picotorr (pTorr).
• Vacuum Furnaces: Sintering, brazing, and heat treating of materials at reduced pressures, which improves the properties of the final product.

Interesting Facts

• While torr and mmHg are often used interchangeably, they are technically slightly different due to variations in the definition of standard gravity.
• The unit "micron" (µ) is sometimes used as a unit of pressure, where 1 micron = 1 mTorr.
• The lowest pressure ever achieved in a laboratory setting is on the order of $10^{-17}$ torr.

What is bar?

The bar is a metric unit of pressure, widely used in science, engineering, and industry. It's a convenient unit because it is close to standard atmospheric pressure on Earth. Below is detailed information about bar, it's origin, and some real-world examples.

Definition of Bar

The bar is defined as exactly $100,000$ Pascals ($10^5 Pa$). The Pascal (Pa) is the SI unit of pressure, defined as one Newton per square meter ($N/m^2$). Therefore:

$1 \, bar = 100,000 \, Pa = 10^5 \, N/m^2$

Origin and History

The bar was introduced by British physicist Sir Napier Shaw in 1909. The goal was to have a unit of pressure that was close to atmospheric pressure but based on the metric system. The term "bar" comes from the Greek word "βάρος" (baros) meaning "weight."

Relation to Atmospheric Pressure

Standard atmospheric pressure at sea level is approximately $1.01325$ bar. Because of this proximity, the bar and millibar (1 mbar = 0.001 bar) are frequently used in meteorology to measure atmospheric pressure. Historically, meteorologists used millibars, but now the SI unit, the hectopascal (hPa), is also widely used (1 hPa = 1 mbar).

Real-World Examples and Applications

• Tire Pressure: Car and bicycle tire pressures are often measured in bar or PSI (pounds per square inch). For example, a car tire might be inflated to 2.5 bar.
• Weather Reports: Atmospheric pressure in weather reports can be given in millibars or hectopascals, where 1013.25 mbar is standard atmospheric pressure.
• Scuba Diving: Divers often use bar to measure the pressure of compressed air in their tanks. A typical scuba tank might be filled to 200 bar.
• Industrial Processes: Many industrial processes, such as hydraulic systems and pressure testing, use bar as a convenient unit of measurement.
• Geology: Pressures deep within the Earth are often measured in kilobars (kbar), where 1 kbar = 1000 bar.
• Vacuum: While bar is not commonly used for measuring high vacuum, it's relevant when discussing rough or backing vacuum levels. For high vacuum, units like Torr or Pascal are more typical.

Interesting Facts

• The bar is a metric unit but not an SI unit. The SI unit for pressure is the Pascal (Pa).
• The millibar (mbar) is commonly used in meteorology.
• 1 bar is approximately equal to 0.987 atmospheres (atm).