Thermodynamics: Systems and Control Volumes

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Questions and Answers

What defines the specific volume of a substance?

The volume per unit mass (correct)

The total mass of the substance

The mass per unit volume

The density of the substance

Which of the following units is used for density in the SI system?

cm3/g

kg/m3 (correct)

lb/ft3

g/cm3

How is mass associated with a particular volume V determined?

By integrating density over the volume (correct)

By subtracting the density from the volume

By multiplying density with volume

By taking the density as a constant value

Why is the volume V9 considered the smallest volume for which matter can be a continuum?

It has a large number of particles Signup and view all the answers

Which property varies from point to point within a system and is classified as intensive?

Specific volume Signup and view all the answers

What is the SI unit for specific volume?

m3/kg Signup and view all the answers

In certain applications, how might properties like specific volume be expressed?

On a molar basis Signup and view all the answers

What is the significance of the mole in the context of specific volume?

It equals the molecular weight of a substance Signup and view all the answers

What happens to the composition of the system during combustion?

It becomes products of combustion. Signup and view all the answers

What is the area called where mass flows across a boundary?

Control volume Signup and view all the answers

In thermodynamic analyses, why is it simpler to use a control volume instead of a closed system?

Mass flows are easier to visualize within a region of space. Signup and view all the answers

Which components typically cross the boundary of a control volume in an automobile engine?

Air, fuel, and exhaust gases Signup and view all the answers

What is often depicted in a schematic for engineering analysis of a control volume?

The boundary surrounding the volume and mass flows Signup and view all the answers

What type of system is defined by a fixed quantity of matter passing through a device?

Closed system Signup and view all the answers

How do engineers often analyze devices like turbines and pumps?

Through studying mass flow across control volumes Signup and view all the answers

What is the primary reason for using control volumes in thermodynamics?

To facilitate the study of mass flow and energy transfer Signup and view all the answers

What is the name of the stress component that is normal to the area in a fluid?

Normal stress Signup and view all the answers

How is the pressure typically defined when referring to a fluid in motion?

Absolute pressure Signup and view all the answers

In fluid mechanics, what varies with the orientation of the area?

Shear stresses Signup and view all the answers

What does a manometer measure?

Pressure Signup and view all the answers

What happens to normal stress when a fluid is in motion compared to when it is at rest?

It remains the same. Signup and view all the answers

When measuring pressure in a fluid, what does the term 'equal elevations in a continuous mass' imply?

The pressures are equal. Signup and view all the answers

What is the lowest possible value of absolute pressure?

0 kPa Signup and view all the answers

Which statement best describes the relationship between pressure and depth in fluids?

Pressure increases with depth. Signup and view all the answers

What is the primary function of a diaphragm in a pressure sensor?

To alter an inductance when force is applied. Signup and view all the answers

According to Archimedes' principle, what does the buoyant force acting on a submerged body equal?

The weight of the displaced liquid. Signup and view all the answers

What does the equation for buoyant force involve in terms of fluid properties?

The density of the fluid and the volume of the object. Signup and view all the answers

What is the relationship between Celsius and Kelvin temperatures?

T1⬚C = T1K - 273.15 Signup and view all the answers

How does pressure change with depth in a liquid according to the content?

Pressure increases as depth increases. Signup and view all the answers

What temperature corresponds to the triple point of water on the Celsius scale?

0.018°C Signup and view all the answers

In the context of a rectangular block submerged in a liquid, which variable represents the volume of the block?

V Signup and view all the answers

What is the line that connects Kelvin and Celsius with respect to the ice point?

273.15 K to 0°C Signup and view all the answers

What effect does an increase in liquid density have on the buoyant force acting on a submerged object?

It increases the buoyant force. Signup and view all the answers

How much does a temperature increase of 100 K correspond to in Fahrenheit degrees?

180°F Signup and view all the answers

What happens to the buoyant force if the volume of the displaced liquid increases?

It increases proportionally. Signup and view all the answers

What direction does the buoyant force act on a submerged body?

Vertically upward. Signup and view all the answers

What is the formula to convert degrees Celsius to degrees Fahrenheit?

T1⬚F = 1.8T1⬚C + 32 Signup and view all the answers

What is the Celsius temperature at absolute zero?

-273.15°C Signup and view all the answers

What is the relationship between the degrees Fahrenheit and Rankine?

T1⬚F = T1⬚R - 459.67 Signup and view all the answers

How many Celsius degrees correspond to the temperature interval between the ice point and steam point?

100 degrees Signup and view all the answers

How is the number of kilomoles of a substance calculated?

By dividing the mass in kilograms by the molecular weight Signup and view all the answers

What signifies that a property is on a molar basis?

A bar positioned over the symbol Signup and view all the answers

What is the value of Avogadro's number?

6.022 × 10^23 Signup and view all the answers

What units are typically used for the variable y on a molar basis?

m3/kmol and ft3/lbmol Signup and view all the answers

In the context of pressure, what happens at a small area A in a fluid at rest?

A compressive force is exerted on area A Signup and view all the answers

Which of the following principles helps to understand the behavior of fluids at rest?

The continuum viewpoint of pressure Signup and view all the answers

What is the formula for the relationship between y and its molar counterpart?

y = My Signup and view all the answers

What is the molecular weight in the equation used to find kilomoles when represented in kg/kmol?

Weight in kg per kmol Signup and view all the answers

Study Notes

Combustion and System Composition

Combustion alters the composition of a system, transforming the initial combustible mixture into products of combustion.

Control Volumes

Thermodynamic analyses of devices with mass flow (e.g., turbines, pumps) can be performed using control volumes.
Control volumes are defined regions in space, through which mass flows.
Mass crosses the boundary of a control volume.
A control volume can be used to model an engine, where air, fuel, and exhaust gases cross the boundary.

Systems and Control Volumes

Systems are a specific quantity of matter.
Control volumes are a region of space.

Density and Specific Volume

Density is the mass per unit volume, an intensive property that can vary within a system.
Mass of a volume is determined by integration of density over the volume.
Specific volume is the volume per unit mass (reciprocal of density).
Specific volume, like density, is an intensive property.
Units for density are kg/m³ (or g/cm³)
Units for specific volume are m³/kg (or cm³/g)

Molar Basis

Properties can be expressed on a molar basis, using kilomoles (kmol) or pound moles (lbmol).
Number of kilomoles (n) = mass (m) / molecular weight (M). A similar equation exists for lbmol.
Molar specific volume (y) is volume per kmol or lbmol.
Relationship between molar and mass-based specific volume: y = My

Pressure

Pressure is normal force per unit area exerted by a fluid.
Pressure is a point property, and can vary locally within a fluid at rest. Examples: Atmospheric pressure variation with elevation. Pressure variation with depth in water.
In a moving fluid, forces on an area passing through a point can be resolved into normal and shear stresses.
Normal stress at a point in a fluid is assumed to be equal to pressure, except when otherwise stated.
Unless explicitly stated otherwise, pressure refers to absolute pressure (pressure relative to a vacuum).

Pressure Measurement

Manometers and barometers measure pressure using liquid columns (mercury, water, oil).
Equal elevations in a continuous mass of liquid or gas at rest have equal pressures.
Pressure sensors (e.g., piezoelectric sensors) use a diaphragm and a change in inductance, resistance, or capacitance to measure pressure.

Buoyancy

Buoyant force is the resultant pressure force on a body submerged in a liquid.
Buoyant force acts vertically upward.
Buoyant force equals the weight of the displaced liquid, by Archimedes’ principle.

Temperature Scales

Temperature scales like Celsius and Fahrenheit are related to the Kelvin scale.
Celsius temperature = Kelvin temperature - 273.15
Fahrenheit temperature = 1.8 * Celsius temperature + 32

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Description

Explore the principles of combustion and how it affects the composition of a system. This quiz delves into the concept of control volumes in thermodynamics, focusing on their application to devices like turbines and pumps. Test your understanding of density and specific volume within various systems.