Control-Volume Analysis of Mass

One of the most important topics of fluid mechanics is the control-volume analysis of mass. Apart from mass, energy and momentum are also considered integral parts of fluid mechanics. These topics generally deal with subjects like control volume; control mass, momentum equation, and continuity equation. Furthermore, the impact of jets on planes can also be analyzed by these topics. Control-volume is used to analyze the fluid dynamic system. This is generally considered as an imaginary surface that defines a volume of interest. However, the control volume can be of any nature, namely fixed or moving. It can also be rigid in the context of the study.   

System of control-volume analysis

The control-volume analysis of a system is nothing but a thermodynamic analysis. This can be classified into two main categories. The first type is known as control mass which denotes a fixed amount of matter. On the contrary, the type that generally deals over a region of space is known as control volume. This analysis has its impact on various fields, namely to solve the continuity equation or momentum equation. As per the theory of control mass, a fluid element is considered the main subject of analysis. In order to do that the amount of mass needs to be fixed. After that this mass is identified in the flow field and equations of properties are conserved with the help of the analysis. The property can be of many types like momentum, energy, or anything like that.

The mass that has been identified in the analysis keeps moving around the flow field. The properties related to the analysis correspond to the contents of the fluid element that were identified earlier. However, the result may vary from location to location. The other category of control-volume analysis is known as control volume. This is comparatively more useful in the field of analysis. A volume that is fixed arbitrarily at a certain place is identified in a flow field and the equations of conservation are written with the help of this. Properties involved in this equation can change over the period.

Objectives of control-volume analysis

Control-volume has a huge impact on its core subjects, namely mechanical engineering and so on. Therefore, it is needed to have certain aims and objectives of the analysis. Control-volume analysis has its major objectives that are directly related to the subject matter. The first and foremost objective of this analysis is to develop the conservation of mass principle. The conservation of mass principle helps to run the analysis more easily. However, developing conservation only will not work; it also needs to be applied properly so that it can provide better results. The proper application ensures a steady flow of the control volumes. This is another main objective of control-volume analysis. 

In this entire process, the application of certain laws becomes vital. Hence in this process, the first law of thermodynamics is applied to control volumes. Controlling the volumes is needed as it ensures the smoothness of the process. The next objective is to identify the energy that is carried by a fluid stream. This energy generally crosses a control boundary and is closely related to the properties used in the analysis. The energy that crosses a control boundary cannot be taken into consideration as it may affect the results of the analysis. Furthermore, correlating the properties with the analysis helps the process to be conducted in an efficient manner. Finally, the last and most important objective of the control-volume analysis is to solve the problems in energy balance that can interrupt the steady flow of devices used in the analysis. These devices can be of any type such as compressors, turbines, nozzles, heaters, and others.

Difference between system and control-volume

The term control-volume can be used for both open and closed systems. A fixed amount of mass can be chosen for closed systems, whereas it cannot be done for open systems to solve the equations. Therefore, a control-volume is chosen as the appropriate solution. Apart from this, there are some other major differences between these. A system is overall a general concept that is defined by a set of objectives involving some properties. These properties can share the same closed region of space; however, it is not compulsory.

A control-volume can also be a subset of the system or signals that are termed as inputs or outputs passing through the boundaries of the analysis. The control volume is considered a modeled part of the system. On the other hand, a system generally defines a system where a mass can enter and exit anytime. In case the flow rate of mass is constant in the system, the control-volume is also considered as constant.

Conclusion

The control-volume analysis of mass has significant effects on real life. The normal systematic approach has its disadvantages, and therefore, the control-volume is considered in the vast region of analysis. A control-volume is more focused on a specific concept that denotes a space inside some closed surface. It has its boundaries well-defined. These boundaries denote certain properties that ensure the smooth flowing of the system. Mechanical engineering is the most influenced area by control-volume.