Mr Abd Hamid

Week 11 to Week 13 (Second law of thermodynamics and entropy change)

Not all processes that obey the first law may occur spontaneously because the first law of thermodynamics only takes into consideration the conservation of the quantity of energy in the universe. However, in reality, the actual process only occurs in the direction of degradation of the quality of energy. Energy of higher quality is associated to higher temperature and lower entropy. Hence, at the end of the process, the quality of energy decreases, and the entropy of the universe increases.

Besides, the calculations of the thermal efficiency of heat engine and coefficient of performance (COP) of refrigeration cycle are also introduced. These are followed by the Carnot heat engine thermal efficiency and Carnot COP; these ideal devices are not existent but could be models for engineers to design the instruments with better performances. Moreover, with this in mind, maximum value of thermal efficiency or COP is no longer 100% but that of Carnot thermal efficiency or COP.

For any actual process, the entropy generation is always greater than zero; only for reversible processes, it is zero. If it is found to be less than zero, then the process is impossible.

Week 8 to Week 10 (balance on reactive process)

Before going deeply in this chapter, I must recall the thing in chapter 9 such as extent of reaction, atomic or molecular species, excess air =excess oxygen, limiting reactant and fractional conversion. In this chapter, heat of reaction can be calculate:

a)             Hess’ Law (Series of reactions and calculate the main or target heat of reaction)

                i) Reference state: 25 c and 1 atm

b)            Heat of formation method (* reference state of substance in table B10) and Tableb1

c)             Heat of combustion method ( Refer table B1)

Week 1  to Week 4(Non-reactive process)

In this chapter (nonreactive chemical process), I learnt about enthalpy change and also internal energy in the chemical process. The value for enthalpy n internal energy we can find them in the steam table. Pressure and temperature are affecting the value of steam table. Before we solved the chemical process problem, we have to determine its reference state which can find it in table B2 and B8. Then, we have find its energy change in the process which there are two ways to determine its energy change by heat capacities estimation (integration) and enthalpy table (B8) which can find the answer straight away. Last but not least, I learnt about hypothetical path which it like two ways to find the targets substance. Estimation of Latent Heat Delta Hv can be determined by using Trouton's Rule. While, estimation of heat capacity of liquid and solid by using Kopp's Rule. The heat capacity of atomic is available in Table B10.

 There are several procedures need to follow in energy balance calculation:

a)             Basis (mass or mole as a basis)

b)            Mass/Mole Balance (* remember mass balance info)

c)             Reference State: Substance (phase,temperature,pressure) (* use at inlet or outlet as ref state)(*based on tables   B8 n B3)

d)            Preparation of Inlet-Outlet Enthalpy Table

e)            Determination of Enthalpy,  from Table B5,B6,B7,B8 or using Heat capacity equation given in Table B2.

f)             Calculation of Enthalpy: Hypothetical Process Path must be sketched for phase changes or multiphase except for water or steam.

g)             Calculation Heat, Q = nH (out) - nH(in), unit kJ/s (kW)-Inlet-Outlet Enthalpy Table must be referred for convenience.

h)            Sometime, from Q (given in question or adiabatic condition), the unknown mass or mole flow rate can also be calculated.

i)              Box for final Numerical Answer

Week 5 to Week 7 (nonreactive chemical process)

Within these two weeks, I learnt about pshychometric chart. There are several characteristics of this chart:

a)             Dry bulb temperature ( x-axis)

b)            Absolute humidity (y-axis, moisture content, ha  kg H2O (v)/kg Dry air

c)             Relative humidity (hr) and saturation curve (hr=100%)

d)            Dew point (using constant pressure line-horizontal and saturation curve)

e)            Wet bulb temperature (twb)

f)             Humid volume (kg HA/kg DA)

g)             Enthalpy (using adiabatic line  or wet temperature line)

f)             Enthalpy deviation

Alhamdulilah, now I become a 2nd year students. For this semester, I’m taking Energy Balance or this semester. 1^st day of class, I have been introduce to syllabus of study such as Balances on Non-reactive Processes, Energy Balance For Reactive Processes, the 2^nd Law of Thermodynamics and Power and Refrigeration System.

Besides, I learned what state properties are and how I want to use hypothetical process path in solving problems. A very important thing in state properties is reference state. (Temperature, Pressure, Phase) must be written in the answer sheet. The hypothetical process paths just can be use if occur PHASE CHANGE ONLY and have many ways to achieve a target by change it PHASE and TEMPERATUREonly. If there are no large diffrerences in pressure(<20 atm), assume the substance as an ideal gas.

I learnt about multi-phase system which includes single-component phase equilibrium, the Gibbs phase rule, one condensable component and multi component gas-liquid system. In this chapter, we need to apply Raoult’s  Law for single condensable species, explain the meaning of ideal solution and the applicability of Henry's law and Roult's law and lastly know how to use T-xy and P-xy diagram to determine the bubble compositions and relative amounts of each phase in a two phase mixture and the effects of varying temperature and pressure on bubble point, dew point, and phase amounts and compositions. As for me, this chapter is quite hard for because we really the understand the concept of single-phase and multi-phase. The consequences we did not understand the concept maybe we can't solve the questions and need a lot of time to solve