物理代写|热力学代写thermodynamics代考|Balancing the Availability of a System

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物理代写|热力学代写thermodynamics代考|Balancing the Availability of a System

Energy can move into or out of a system through a work input or output, heat transfer, or mass transfer. If a fluid mass can flow through a system, such as a heat exchanger, a turbine, or a pump, the system is defined as an open system. If mass can’t flow through a system, as in a piston/cylinder arrangement, the system is defined as a closed system. Thus work and heat transfer processes are the only means by which energy can be transferred in a closed system.
You can use the first law of thermodynamics to write an energy balance on a system. Because availability is a thermodynamic property related to energy, a balance equation for availability can also be written for a system. The availability balance on a system has the following four components:
$\sim \boldsymbol{A}{\mathrm{ta}}$ : Energy availability can be transferred into the system by heat transfer, work, or mass flow. $\sim A{\text {out }}$ : Availability can be transferred from the system by heat transfer, work, or mass flow.

$\sim A_{\text {deatroyed }}:$ Availability can be destroyed within a system by irreversibilities such as friction, heat transfer through a finite temperature difference, mixing, chemical reactions, and unrestrained expansion, among other ways.
$\Delta A_{\text {system: }}$ : Availability can be stored or released within a system, causing a change in availability of the system.
You write the availability balance of a system using the preceding components of availability with the following equation:
$$A_{\mathrm{n}}-A_{\text {out }}-A_{\text {destroyed }}=\Delta A_{\text {system }}$$
The units for availability are the same as for energy: kilojoules in the SI system and British thermal units in the English system. The uppercase variable $A$ indicates that the property includes mass (extensive form). You use the lowercase form of the variable $a$ for the intensive form (on a per-unit-mass basis). The availability balance equation can be written on a rate basis using a dot above the variable $(\dot{A})$ as usual with other rate equations, as shown here:
$$\dot{A}{\text {in }}-\dot{A}{\text {out }}-\dot{A}{\text {destroged }}=\frac{d A{\text {system }}}{d t}$$
The following sections describe each of the components of availability in detail.

物理代写|热力学代写thermodynamics代考|Transferring availability using work processes

Availability can be transferred into $\left(A_{\text {in }}\right)$ or out of $\left(A_{\text {out }}\right)$ a system using work. Typically, this transfer is accomplished by shaft or boundary work, but other forms of work exist (see Chapter 4). In a reversible work process, the availability transferred using work $\left(A_{\text {work }}\right)$ equals the useful work $\left(W_{\text {useful }}\right)$. If the process involves boundary work, the work on the surroundings ( $W_{\text {surr }}$ ) must be subtracted from the actual work $\left(W_{\text {act }}\right)$ to determine the useful work, because some of the work is used to push the atmosphere out of the way. The availability transferred to a system by boundary work is found using this equation:
$$A_{\text {work }}=W_{\text {usetul }}=W_{\text {act }}-W_{\text {surr }}$$
In a process that begins at State 1 and ends at State 2, the surroundings work $\left(W_{\text {surr }}\right)$ equals the atmospheric pressure $\left(P_0\right)$ times the change in volume of the system $\left(V_2-V_1\right)$, as shown in this equation:
$$W_{\text {surr }}=P_0\left(V_2-V_1\right)$$
For an open system, a reversible work process doesn’t have to work against the surroundings; however, flow work is accounted for by enthalpy, so the useful work ( $\left.W_{\text {usctul }}\right)$ equals the actual work $\left(W_{\text {act }}\right)$. In this case, the availability transfer by work $\left(A_{\text {work }}\right)$ is found by this equation:
$$A_{\text {work }}=W_{\text {usedul }}=W_{\text {act }}$$
The availability of the fluid increases when work is input to a system, as in a pump or a compressor, and the availability of a fluid decreases when work is done by the system, as in a turbine or an expansion stroke of a piston.

热力学代写

物理代写|热力学代写thermodynamics代考|Balancing the Availability of a System

$\sim \boldsymbol{A}{\mathrm{ta}}$:可用能量可以通过传热、做功或质量流传递到系统中。$\sim A{\text {out }}$:可用性可以通过传热，功或质量流从系统传递。

$\sim A_{\text {deatroyed }}:$ 在一个系统中，可用性可以被不可逆性破坏，比如摩擦、有限温差的热传递、混合、化学反应和无约束的膨胀等等。
$\Delta A_{\text {system: }}$:可用性可以在系统内存储或释放，从而导致系统可用性的变化。

$$A_{\mathrm{n}}-A_{\text {out }}-A_{\text {destroyed }}=\Delta A_{\text {system }}$$

$$\dot{A}{\text {in }}-\dot{A}{\text {out }}-\dot{A}{\text {destroged }}=\frac{d A{\text {system }}}{d t}$$

物理代写|热力学代写thermodynamics代考|Transferring availability using work processes

$$A_{\text {work }}=W_{\text {usetul }}=W_{\text {act }}-W_{\text {surr }}$$

$$W_{\text {surr }}=P_0\left(V_2-V_1\right)$$

$$A_{\text {work }}=W_{\text {usedul }}=W_{\text {act }}$$

有限元方法代写

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MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

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