A 12-ft^3 rigid tank contains refrigerant-134a at 30 psia...

A $12-\mathrm{ft}^{3}$ rigid tank contains refrigerant-134a at 30 psia and 55 percent quality. Heat is transferred now to the refrigerant from a source at $120^{\circ} \mathrm{F}$ until the pressure rises to 50 psia. Assuming the surroundings to be at $75^{\circ} \mathrm{F}$, determine $(a)$ the amount of heat transfer between the source and the refrigerant and $(b)$ the exergy destroyed during this process. Answers: (a) 447 Btu, (b) 77.8.

Key Concepts

Exergy Destruction and Second Law Analysis

Exergy destruction quantifies the irreversibility in a thermodynamic process, representing the loss of potential work due to entropy generation. It is determined by comparing the actual heat transfer with the maximum possible work that could be obtained if the process were completely reversible under a given environment temperature. This concept is central to understanding and quantifying process inefficiencies and the degradation of energy quality in thermodynamic systems.

Heat Transfer in Closed Systems

In a closed system, especially one undergoing a constant volume process, heat transfer is the primary means of energy change since work interactions are absent. The analysis involves applying the first law of thermodynamics to determine how the internal energy of the system changes as heat is added or removed. This concept is essential for quantifying the amount of energy transferred during processes such as heating a refrigerant in a rigid tank.

Saturated Mixture Quality

Quality in a saturated mixture refers to the mass fraction of the vapor phase in a liquid-vapor mix. It is used to characterize the state of a substance when it exists partially as a liquid and partially as a vapor. This concept is vital in thermodynamic calculations as it helps determine properties such as internal energy or enthalpy by knowing the contributions from both the liquid and the vapor phases.

Rigid Tank Process

A rigid tank process is one that occurs in a closed system with a constant volume. In such processes, there is no work done by volume expansion or compression, so any heat added or removed directly changes the internal energy of the system. Understanding a rigid tank process is crucial when dealing with phase-change problems because the fixed volume constraint affects how pressure, temperature, and quality evolve during heating or cooling.

Transcript

Please give Ace some feedback