Designing and Simulating a Control System - Report Example

NAME: xxxxxxxxxx TUTOR: xxxxxxxxx DATE: xxxxxxxxxx TITLE: Designing and Simulating a Control Sytem. ©2016 ABSTRACT The design and simulation of a vapor compression refrigeration control system will be discussed in the paper. The control system under consideration is based on industrial, large-scale use and is specialized in cooling of electronic equipment. The approach used in design and simulation of the refrigeration control system is based on energy conservation concept. The primary objective here is to demonstrate in detail the design and simulation of a vapor compression refrigeration cycle at a micro-scale level. The component's functions and properties of the refrigerator i.e. condenser, evaporator, compressor as well as the expander and capillary tube are given in detail herein. The simulation will get based on the assumption that the refrigeration cycle for this case will be completed nearly at the same point where it was begun. The parameters such as the cold space temperatures, ambient air temperatures as well as condensation and evaporation temperatures, evaporator heat loads are all given as predetermined parameters. The refrigerant chosen for the refrigeration under consideration is R-134A, and a simulation program code is developed to interpolate its thermos-physical properties. The theory behind the modeling used is also addressed in detail. The plant details such as performance, stability, observability, controllability and time response are also dealt with in detail by this report. Detailed and step by step description of the design of various system components such as controllers and observers are also given in the report. The importance of simulation experiments as used for most industrial purposes is also addressed in this report. Keywords: Refrigeration, evaporator, condenser, vapor compression refrigeration cycle (VCRC). CHAPTER ONE INTRODUCTION The demand for increased energy efficiency standards for performance of all electronic equipment necessitates for advanced research, design and development of more efficient systems. Most control systems have attracted the attention of most researchers and inventors with the aim of discovering more advanced and efficient control system. Most energy-related agencies both at the national and international level continuously impose more stringent standards for energy efficiency for any systems within the society. Moreover, consumers have a higher tendency of selecting and utilizing systems that have the most effective and efficient energy utilization. Thus, leaving the designers with fewer options but to develop more efficient systems. The research for exceptional efficiency has, therefore, never stopped. Refrigeration is one control system that has been in the spotlight due to its vast use both at domestic as well as at the industrial levels. In the year 1834, the first Vapor compression cycle refrigeration system was developed by Jacob Perkin`s, and it was named “Ice Machine”. This type of a system has been in use for decades and centuries and has been the basis from which more advanced and efficient systems got developed. For decades, efforts have been made to miniaturize this technology to meet the trends and other uses within the society. Therefore, several efforts have been made to miniaturize refrigeration. The most common areas of application of micro refrigeration systems include; Aviation and space exploration industries. Military use. Automotive. Medical fields. Micro refrigeration systems have had advantages such as compactness as well as increased coefficient of performance and low mass flow rates.   Operation of a Vapor Compression Refrigeration Cycle The most common vapor compression refrigeration cycle is composed of four main parts. These includes the condenser, expansion valve, evaporator, and the compressor. However, with advancement in its technologies, several other elements have been incorporated into the system to ensure increased efficiency and better control of the whole refrigeration process. The purpose of a refrigeration system is to create a cold environment by rejecting heat from an object and delivering it to the environment. Work has to be done by the refrigerator in rejecting heat from the object to the environment based on the second law of thermodynamics. Figure 1: Refrigeration Process The main components of a typical vapor compression refrigeration cycle (VCRC) are as shown in the diagram below. Figure 2: The Basic Components of a Vapor Compression Refrigeration Cycle From the diagram above, refrigeration process is a procedural process that takes the parts numbered in figure 2 above. 1-2 Vapor Compression stage In this step, the low pressure and temperature vapor refrigerant from the evaporator is drawn into the compressor through the inlet of the suction valve within the compressor. The refrigerant gets compressed to very high pressure and temperature and discharged into the condenser through another outlet valve. 2-3 Condenser The condenser consists of coils of pipes from which the high pressure and temperature refrigerant from the compressor are condensed. The latent heat of the refrigerant is given up to the condenser to the surrounding condensing unit. Note: This is the main reason the condensers of many refrigeration systems commonly at the back of the refrigerators are hot or have a higher temperature than the environment. 3-4 Expansion Valve The expansion valve is there to allow controlled passage of the high pressure and temperature refrigerant from the condenser. The refrigerant after passing this valve experiences a significant drop in temperature. 4-1 Evaporator The evaporator consists of several coils through which the liquid-vapor refrigerator which low temperature passes. The refrigerant, therefore, absorbs latent heat of vaporization from the media within the cooling space thus resulting in reduced temperature. Thus, resulting in cooling of the media within the refrigerator`s cooling space. Temperature entropy diagram The refrigeration process describe above can be described ideally by the temperature entropy diagram below. Figure 3: Temperature - Entropy diagram of an ideal VCRC Pressure- enthalpy diagram For a typical VCRC, the system follows a pressure-enthalpy path as shown by the diagram below. Figure 4: Pressure - Enthalpy diagram for a VCRC Thus from the two diagrams, during compression, the low-pressure vapor (saturated) is compressed to high pressure to super-heated steam at a constant entropy. The super-heated vapor from the compressor is saturated into liquid under constant pressure. The high-pressure liquid and temperature from the condenser are expanded to low temperatures and pressure at a constant enthalpy. The low-pressure liquid-vapor mixture boils to saturated vapor in the evaporator at a constant pressure. An ideal vapor compression refrigeration cycle can never be achieved in practice. This phenomenon is more significant especially in micro refrigeration channels where space is minimized. This is attributed to the small dimensions of the system under consideration. Micro-scale vapor compression cycles “Micro” is a named derived from the units of the hydraulic diameters of the condenser and evaporator channels in a vapor compression refrigeration cycle. The table below gives the various dimensions of the hydraulic channel diameters. Channel Class Channel Hydraulic Diameter Conventional channel >3mm Mini-channel 200µm to 3mm Micro-channel 10µm to 200µm Transitional micro-channel 1µm to 10µm Transitional Nano-channel 0.1µm to 1µm Nano-channel 0 m=M2 when e Read More