# How Do You Calculate Work, Internal Energy, and Heat in Compressed Air?

• febbie22
In summary, In this conversation, the question is asked about determining the work done, change in internal energy, and heat received or rejected by a gas that is compressed from 1 kg of air at 100 kPa and 0.025 m3 to 150 kPa, using the law pv1.3 = constant. The specific heats are given as Cv = 0.718 kJ/kg K and Cp = 1.005 kJ/kg K. The attempt at a solution involves using equations to calculate the work done and change in internal energy, but the specific equation for internal energy is missing. The expert suggests using the equation U2-U1= Q + W to solve for the internal energy.
febbie22

## Homework Statement

1 kg of air at a pressure of 100 kPa occupying a volume of 0.025 m3 is
compressed to a pressure of 150 kPa according to the law
pv1.3 = constant.

Determine:
(i) Work done on or by the gas; (6)
(ii) Change in internal energy of the gas; (6)
(iii) Heat received or rejected by the gas; (4)

Take Cv = 0.718 kJ/kg K, Cp = 1.005 kJ/kg K

## Homework Equations

In attachment the password is exam

## The Attempt at a Solution

I think i can do the first part fine:

W= ((100*10^3) * 0.025 - (150*10^3) * 0.0183) / -0.3
= 816.67

Its the second part that i don't get as it asks for the change in internal energy before the heat received

is there a equation to calculate the internal energy as there is one here:

U2-U1= Q + W

but i would need to work out Q before U2-U1

any help would be much appreciated

#### Attachments

• EN2702 THERMOFLUIDS Jan 10.pdf
303.6 KB · Views: 585
The internal energy of an ideal gas is CvnT=CvPV/R.

## 1. What is the Non Flow Energy Equation?

The Non Flow Energy Equation is a mathematical equation used to calculate the amount of energy present in a system at a specific point in time. It takes into account all forms of energy, including potential, kinetic, and internal energy, and can be used to analyze various physical systems, such as thermodynamic systems.

## 2. How is the Non Flow Energy Equation different from the Flow Energy Equation?

The Non Flow Energy Equation differs from the Flow Energy Equation in that it accounts for all forms of energy present in a system, while the Flow Energy Equation only considers the energy associated with a flowing fluid. The Non Flow Energy Equation is also applicable to a wider range of systems, including non-flowing and non-fluid systems.

## 3. What are the assumptions made when using the Non Flow Energy Equation?

When using the Non Flow Energy Equation, it is assumed that the system being analyzed is closed, meaning that no mass or energy is entering or leaving the system. It is also assumed that there is no change in the internal energy of the system, and that any changes in potential and kinetic energy can be accounted for.

## 4. How is the Non Flow Energy Equation used in thermodynamics?

The Non Flow Energy Equation is a fundamental equation in thermodynamics and is used to analyze and understand the energy changes that occur in various physical systems. It is often used in conjunction with other thermodynamic equations, such as the First Law of Thermodynamics, to solve for unknown variables or to predict the behavior of a system.

## 5. What are the applications of the Non Flow Energy Equation?

The Non Flow Energy Equation has many applications in various fields, including thermodynamics, fluid mechanics, and heat transfer. It is used to analyze and design various systems, such as power plants, refrigeration systems, and engines. It is also used in research and development to understand the energy changes that occur in different processes and to optimize energy efficiency.

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