1.

Ideal Vapour-Compression Refrigeration Cycle and its assumptions: (i) Constant pressure (P) in condenser and evaporator.(ii) Isentropic (S) process in Compressor.(iii) State 1 is saturated vapour, state 3 is saturated liquid.

2.

Actual Vapour-Compression Refrigeration Cycle(i) Compression in compressor is not isentropic, irreversibility due to heat losses, pressure losses and temperature difference. [Isentropic compressor efficiency](ii) Pressure drop when refrigerant flows through the condenser, evaporator and piping network.(iii) Difficult to control state 4 and state 8 to be saturated liquid and saturated vapour respectively.3. Unit mass consideration

Cascade Vapour-Refrigeration Cycle(i) Enable the use of different refrigerants to suit the different operating conditions of individual cycles, especially for low temperature applications.(ii) Performance of vapour compression cycle can be improved.

4.

Gas Refrigeration SystemsReverse of Brayton Gas Turbine Power Cycle.Throttling fails to reduce temperature of gas, use turbine instead.Ideal Vapour Compression Heat Pump Cycle5.

6.

7.

8.

9.

Closed System

Otto Cycle: Ideal cycle for Spark-Ignition Engines(i) 2 isentropic processes, 2 constant volume heat transfer processes.(ii) In analysis of cold air standard Otto Cycle, specific heats of working are treated as constant.

10.

Closed System

Diesel Cycle: Ideal cycle for Compression-Ignition Engines(i) Only air is compressed during compression stroke, avoids auto ignition, and thus operates at much higher compression ratios.(ii) 2 isentropic processes, 1 constant pressure heat addition process and 1 constant volume heat rejection process.

11. Pressure ratio

12.

Actual Gas-Turbine Cycles, deviation from idealized Brayton Cycle.13.

Brayton Cycle with Regeneration:(i) Highest possible temperature that state 5 can reach is the temperature of state 4.(ii) Regenerator effectiveness is introduced:

14.

Reheat

Intercooling15.

Ideal Jet-Propulsion Cycle:(i) Aircraft is assumed stationary; hence air enters diffuser at a certain speed and will leave diffuser at zero speed.(ii) Air leaves turbine at zero speed in ideal case.(iii) Idea of relative velocity

16.

Vapour Power Cycle: Ideal Rankine Cycle(i) 2 isentropic processes and 2 constant pressure heat transfer processes.(ii) State 1 is at saturated liquid phase, while state 2 is in compressed liquid region.

17.

Actual Vapour Power Cycle18.

19.

Ideal Reheat Ranking Cycle:(i) Superheating of steam is constrained by maximum temperature due to metallurgical limit. (ii) Reheat + superheating achieve higher thermal efficiency without increasing the wetness of fluid at turbine exit.(iii) Reheating requires usage of more than one turbine stage [High Pressure, Intermediate Pressure and Low Pressure turbines].(iv) Cycle comprises of 3 isentropic processes (2 expansions and 1 compression), 2 constant pressure heating (superheat + reheat) processes and 1 constant pressure heat rejection (condensation) process.

20.

One of the main causes of lower efficiency of Rankine cycle compared to Carnot cycle is that heat addition takes place over a range of (low) temperatures. Utilize regeneration to heat feedwater (liquid leaving pump) by extracting steam from turbine.21.

y

1 - y

Ideal Regenerative Rankine Cycle-1: Ideal open feedwater heater(i) Open feedwater heater: Steam extracted from turbine is mixed with feedwater exiting pump one. Both state 1 and state 3 will be saturated liquid for ideal cycle. (ii) Steam extraction at intermediate pressure and use of an additional feed water pump is required.(iii) Isentropic processes and constant pressure heat transfer processes.

22.

Ideal Regenerative Rankine Cycle-2: Ideal closed feedwater heaters(i) Steam extracted from turbine does not mix with feedwater exiting pump one.(ii) In ideal feedwater heater, feedwater is heated to the exit temperature of extracted steam (which leaves heater as saturated liquid).

23.

24.

Combined Gas-Vapour Power Cycles:(i) Combined Gas turbine-Steam turbine power plant.(ii) Make use of desirable characteristics of gas turbine cycle at high temperature; heat energy rejected from exhaust gases is recovered by transferring it to the steam in a heat exchanger (boiler for steam cycle).(iii) Energy balance at heat exchanger enables the relative mass flow rate of gas and steam to be determined.

25.

No process heat is supplied if all fluid flows through this path.Maximum rate of process heat produced if all fluid flows through this path.An example of Ideal Cogeneration Plant:(i) Cogeneration produces more than one useful form of energy, such as process heat, cooling and electric power. (ii) State 4 and state 5 have same pressure. State 9 and 10 also have same pressure. State 7 and state 8 are saturated liquid.(iii) Processes involved in this example are isentropic processes, constant pressure heat transfer/mixing processes and throttling process.(iv) Utilization factor is used as a measure for cogeneration:26. Ideal Gas Mixtures: Systems involving two or more gaseous components such as combustion products, air water vapour mixtures. Molar analysis [number of moles of each component] or gravimetric analysis [mass of each component].

27.

28. Average molar mass of a mixture:

Average gas constant of mixture:

29. Daltons Law: Each gas component fills the entire volume. Pressure of gas mixture is the sum of pressures each gas would exert if it existed alone at the mixture temperature and volume.

Amagats Law: Each gas component exerts same pressure. Volume of gas mixture is the sum of volumes each gas would occupy if it existed alone at the mixture temperature and pressure.

30.

31. Air Water vapour mixture [moist air] in psychrometrics:

Air

Water vapour

Constant pressure 1 to 2: Dew point temperature at point 2.Constant volume 1 to 3: lower temperature than dew point.Constant temperature 1 to 4: Water added to mixture until saturation occurs. [Same T, same Pg]

Vapour pressure

32.

33. Wet bulb temperature is used to approximate the adiabatic saturation temperature. [Sling psychrometer]

Dry bulb temperature: Ordinary air temperature measured with thermometer.

Same vapour pressure for same specific humidityPsychrometric chart [total air-water vapour pressure is 1 atm (101 kPa)]

34. Air conditioning applications: (i) Cooling, Dehumification and Reheating

(ii) Adiabatic Mixing

35. Closed system

Control Volume

36. Standard compositions for dry air: 21% Oxygen and 79% Nitrogen.

(i) Nitrogen is assumed to be inert, does not take part in chemical reaction.(ii) If moisture is present, it has to be considered separately in the reaction. Moisture does not react with anything, simply shows up as additional H2O in the product.

37.

38.

Conservation of mass + complete combustion Deduce minimum / theoretical / stoichiometric amount of air required for process. [Balanced chemical equation]

39. For actual (non-stoichiometric) combustion:Amount of air is either greater than or less than the theoretical amount. [% of theoretical air]Excess air results in free oxygen, whereas rich mixture/deficient air results in incomplete combustion, with hydrogen taking first priority to combine with (limited) oxygen [CO, C].

Water vapour is often present in products of combustion. Its dew point temperature needs to be determined [using partial pressure and mole fraction analysis (Daltons Law)].

If , we then have . This allows us to determine the amount of water vapour remains uncondensed in the product mixture.40. Conservation of Energy for Reacting Systems:(i) Standard reference state:; energies become.(ii) At reference state, stable elements/compounds such as oxygen, nitrogen, hydrogen and carbon are assigned a value of zero enthalpy.(iii) : Enthalpy of formation at reference state, energy absorbed or released when compound is formed from its elements at reference state.

Exothermic, negative valueEndothermic, positive value

41. Specific enthalpy of a compound [molar] at a state other than the reference state:

42. Energy Equation for Reacting Systems

Control Volume

: Molar flow rate of reactant : Molar flow rate of product

Closed System

*Ideal gas

43. Introducing enthalpy of combustion:

44. Any H2O formed as vapour in product.Water component in liquid form (product).

45. Adiabatic flame temperature: Energy residing in combustion products is maximum for adiabatic combustion process.(i) Maximum final product temperature.(ii) Complete combustion + Stoichiometric conditions.(iii) Evaluated iteratively.

Adiabatic flame temperature can never be achieved due to:Heat losses, extra air dilute products, incomplete combustion, and dissociation.Actual combustion processAdiabatic flame temperature