Calculate the irreversibility for the process described in Problem 4.210 E, assuming that the he

Calculate the irreversibility for the process described in...

Key Concepts

Irreversibility

Irreversibility is a measure of the inherent loss or degradation of energy quality during a thermodynamic process. It quantifies the difference between the actual work output of a process and the maximum possible work output that would be achieved under ideal, reversible conditions. This concept is critical in understanding why real processes never reach 100% efficiency and how energy disperses irrecoverably.

Entropy Generation

Entropy generation refers to the increase in entropy within a system due to irreversible processes such as friction, mixing, or heat transfer across finite temperature differences. As entropy is a measure of disorder or energy dispersal, its production indicates the degree of irreversibility in a process, and it directly relates to the loss of available energy.

Second Law of Thermodynamics

The Second Law of Thermodynamics underpins the concept of irreversibility by stating that the total entropy of an isolated system cannot decrease over time; it either increases or remains constant. This law implies that real processes are inherently irreversible, as they generate additional entropy, thereby limiting the conversion of absorbed heat into useful work.

Heat Transfer Processes

Heat transfer processes involve the exchange of heat between a system and its surroundings, often with a specified thermal reservoir at a constant temperature. When such processes occur with a finite temperature difference between the system and its environment, they introduce irreversibilities that contribute to entropy generation, ultimately impacting the efficiency and work potential of the system.

Exergy Destruction

Exergy destruction, also known as lost work potential, is a concept that quantifies the amount of useful energy that is rendered unavailable due to the irreversibilities in a process. By relating the exergy loss directly to the entropy generation (often using the ambient temperature as a reference), this concept provides insight into the degree of inefficiency and the thermodynamic cost of irreversibility in real systems.

Transcript

00:01 In this question we have a piston cylinder arrangement as shown in the figure.

00:04 It contains air initially at a pressure of 45 lbf per inch square.

00:13 The initial temperature is 60 for a height and when the piston is at the lower position as shown in the figure, the initial volume is 9 feet cube.

00:27 The volume of the whole cylinder up to the stop is 36 feet cube and now an airline is connected to this piston cylinder arrangement.

00:43 The pressure inside the air line is 75 lbf per inch square and the temperature is 1 ,100 ranking.

00:56 And now when the valve is opened, air enters into this piston cylinder arrangement and the final pressure inside the cylinder becomes 60 lbf per inch square and final temperature becomes 630 rancine.

01:17 If the inlet mass is 7 .152 lbm and the surrounding temperature is 61 for height then we are required to calculate the irreversibility for this process.

01:34 So let's see how to solve this question.

01:37 So first of all let's apply the formula to calculate initial mass of the air so we can write m1 is equal to p1 initial volume v1 multiplied by r into initial temperature t 1.

01:50 Now let's substitute all the values so we will have m1 is equal to 45 into 9 into 12 square divided by 53 .34 into 519.

02:07 So this will be equals to 2 .104 lbm and now refer table f .5.

02:21 So from there properties corresponding to state 2, that means when the pressure is 60 lbf per inch square and the temperature is 630 then kind, the properties can be written as hi is equals to 266.

02:39 13 btu per lbm u1 is equal to 88 .68 btu per lbm and u2 is equal to 107 .62 btu per albm.

03:05 Now let's apply the formula to calculate work done so we can write work done during process 1 to 2 and this will be equals to p1 into final volume let's say this is v2 minus initial volume v1 now let's substitute all the values so we can write work done during process 1 to 2 2 and this will be equals to 45 into 36 minus 9 multiplied by 12 square upon 778 so this will be equals to 224 .9 british thermal units and now let's apply the formula to calculate mass inside the cylinder that is the final mass...

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