BALANCE ON NON REACTIVE PROCESS
For the first part, I have been introduced to hypothetical process path which a procedure to calculate the actual ∆H followed by the process for a given series of steps. The same procedure can be used to calculate ∆U for any process.
Besides, I have been introduced about psychrometric chart or humidity chart. This chart mainly shows several properties of a gas-vapor mixture and is used extensively in the analysis of humidification, drying and air-conditioning processes. This chart is for air-water system at 1 atm circumstance. My lecturer, Dr Aznizam has explained how to use this chart.
- Dry-bulb temperature
- Absolute humidity
- Relative humidity
- Dew point
- Humid volume
- Wet-bulb temperature
- Specific enthalpy
- Enthalpy deviation
ENERGY BALANCE FOR REACTIVE PROCESS
From this chapter, I have learnt the concepts of heat of reaction or it can be called as enthalpy of reaction for a given process whether the process is exothermic(release heat) or endothermic(absorb heat). There are 3 ways to calculate the heat of reaction. Firstly, by using Hess's Law which is the easiest method among the three. This law is for calculating the desired heat of reaction for many series of undesired reaction. Somehow, I have learnt Hess's Law during my foundation which is only to calculate for 2 to 3 reaction. This time, I have to calculate the heat reaction for many series of reaction, 2nd method is using Heats of Formation and the third one is using Heat of Combustion method. All those three methods have objective of the same-calculate HEAT of REACTION.
As it names, for sure this chapter require me to do calculation for energy balance. In this chapter, there are two methods of determining the the value of Q which are Heat of Reaction Method and Heat of Formation Method. The most important thing to do energy balance is REFERENCE STATE, the reference state is( 25 degree and 1 atm). Also, for some process, I have to complete my mass balance before I can process with energy balance. So, below are the steps of performing energy balance:
1. Basis
2. Flow chart diagram
3. Mass balance
4. Reference state
5. Inlet-outlet enthalpy table-one of important element(fogotten to mention)
6. Energy balance..
SECOND LAW OF THERMODYNAMICS
For this chapter, the expectations to students are:
- able to define entropy and heat engine
- able to calculate the entropy changes of a given process
- able to develop isentropic, or adiabatic, efficiencies of various steady-flow engineering devices
n this chapter, for the first part, I have learnt about heat pump, heat engine and refrigerator. The most important thing is to know how to calcuate the efficiency for each device by knowing the desired output and required input.Also, I need to know to calculate the efficiency of carnot cycle(ideal) for each device.
Besides, I have learnt entropy, and there are a lot of cases which make my head keep spinning.. there are a lot of conditions and terms such entropy generation, changes in entropy, entropy transfer, entropy is the same and more. For example, there is a case where the device is at isentropic condition. So, the entropy at 1st point and 2nd point is the same. Method to calculate entropy change for liquid/solid and ideal gas is different.
POWER AND REFRIGERATION CYCLE
in this chapter I have been introduced about Rankine cycle which is the ideal cycle for vapor power cycles. The Rankine cycle does not involve any internal irreversibilities and consist of 4 processes:
- Isentropic compression in a pump
- Constant pressure heat addition in boiler
- Isentropic expansion in turbine
- Constant pressure in heat rejection in a condenser.
Then, I have to do energy analysis for each devices based on 1st Law of Thermo equation which is Q + W = ∆H.
Besides, I have learnt about ideal vapor-compression refrigeration which is a most widely uses cycle for refrigerators, air conditioners and heat pumps. This cycle consist of 4 processes:
- Isentropic compression in a compressor
- Constant-pressure heat rejection in a condenser
- Throttling in an expansion device
- Constant-pressure heat absorption in an evaporator