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31 January 2023, 2:31 AM

At the beginning of the semester, we were divided into groups and assigned to sit together in our respective groups for every class. We help each other during the problems solving session in class. Based on my understanding, chapter 7 is about a process that mainly solves energy balances with respect to changes in temperature, pressure, and phase for non-reactive processes. This topic was quite simple for me because I learned about this topic during my last semester in thermodynamics subject. The first step in solving the problem is to analyze the system. There are two types of systems which are closed and open systems. Then identify the two forms of energy transfer between a system and its surroundings. Must write the energy balance equation and state the conditions under which each of the five terms can be neglected. I also learned how to read the steam tables.  Based on the problem, a statement must identify the objective of the problem. 

Analyzing the standard heat of reactions using Hess’ Law, the heat of formation, and the heat of combustions and then solving energy problems for reactive processes. It was the toughest part for me to solve. Because I am able to understand the flow of the topic but when it comes to problem-solving, I will get confused. Sometimes I got cried because of stress but I keep trying to do as many problems as possible which included drawing the hypothetical path, identifying the dry-bulb temperature, wet-bulb temperature, and humid volume of humid air using the Psychrometric chart to carry out material and energy balance calculations on a heating, cooling, humidification, or dehumidification process involving water. 

As the first step, we must understand the objective of the problem statement. Must perform all required material balance calculations by doing the degree of freedom. We need to apply all the bits of knowledge we learned from the mass balance subject. Then, need to form the energy balance equation whether it open or closed system. For an open system, the equation must include changes in enthalpy and for a closed system must include changes in internal energy. Need to state the assumptions before proceeding to the next step which helps to delete any of the terms that are either zero or negligible for the given process system. We can neglect the potential energy if there is no appreciable vertical separation between the inlet and outlet port, work can be neglected if there are no moving parts and kinetic energy is usually negligible if temperature changes of more than a few degrees, phase changes, or chemical reactions occur in the process.

After that, we need to choose a reference state for each species involved in the process to make the calculation of enthalpy easier. We need to construct an inlet and outlet enthalpy table with columns for initial and final amounts of each species and specific internal energies relative to the chosen reference states for a closed system while for the open system, we need to construct a table with columns for inlet and outlet stream components flow rates and specific enthalpies relative to the chosen reference states. To complete the table need to calculate the required values of internal energy or specific enthalpy. We need to construct a hypothetical path for each element to identify the specific enthalpy. There are a few ways to identify the specific enthalpy. One of the ways is to identify it from the table, sometimes we need to do interpolation to identify it. In some cases, we couldn’t get the specific enthalpy from the table so we need to do a hypothetical path. In the calculation of temperature changes, we need a trapezoidal rule using heat capacity. The polynomial expressions for Cp in table B.2 provide a basis for reasonably accurate estimations of enthalpy changes. Several rougher approximate methods follow for estimating the heat capacities in the absence of tabulated formulas. Kopp’s rule is a simple empirical method for estimating the heat capacity of a molecular compound using the sum of contributions (given in Table B.10) for each element in the compound. Lastly, we can solve the energy balance for whichever variable is unknown. 

Quizzes in between the learning process helped me a lot to understand the concept of each topic and also got to know my level of understanding of the topics. The discussions after having the quizzes also gave me a lot of benefits for me which can learn from my mistakes. Individual Assignments and group assignments help me to interact with my classmates to discuss the questions given and understand the objective of the question. We also got to share each other’s way of solving the problem and compare it. Test 1 was quite simple for me to do because of the knowledge from the previous subject and doing the past year's questions. Test 2 was a bit tough for me because of a lack of exercise. During that period our schedule was packed with a lot of assignments and projects so I didn’t get to manage the time. So, I got low marks on test 2. Then I put a lot of effort to do the exercises and past year’s questions to improve in test 3. But I Couldn’t get to do all the questions due to lack of time. Then I realized the exercises that I did were not enough and needed to do more exercises. Then, we had peer discussion sessions in which each group had to solve a question given by my lecturer and teach it to other teams. The session was helpful for us because we got to learn different questions with various methods of solving them. We also had an inter-group discussion to solve the question given. Before test 2 and test 3, we had a revision session in which we discussed and do preparation for the tests. Our lecturer provided us with a Jamboard link for us to ask doubts regarding the test. The mini-project had a big impact on my understanding of mass and energy balance. I learned how and where to use the techniques and formulas to solve problems. Lastly, I would like to thank Dr. Azizul. Because of his guidance, I was able to improve myself.