APPLICATION OF THERMODYNAMICS

1. Thermodynamics Cycle2. Carnot Cycle3. Otto Cycle4. Diesel Cycle5. Rankine Cycle

Thermodynamics Cycle

The process which runs from the initial state and returns again to that initial state after the gas does work is called cycle.

In the process a - b, the gas expands in adiabatic process and the work done by the gas is the area of plane abV2Vp its value is negative.

In process b - c the compressed gas in isothermal process is the area of plane bcV1V2, its value is positive.

In process c - a . The gas does not do any work because its volume is constant.

The process c – a is an isochoric process which is done to make the gas return to its initial state.

The total external work done by the gas in one cycle a – b – c – a is the area of plane abca.

A thermodynamics cycle can occurs in a heat engine, such as otto engine, diesel engine, and steam engine. In an Otto engine, the cycle occuring is called Otto cycle. In a diesel engine, the cycle occurring is called diesel cycle. While in a steam engine, the cycle occuring is called Rankine cycle.

Carnot CycleThis Carnot engine is assumed as an ideal heat engine which works cyclically and is reversible between two temperatures without any loss of energy. This imaginary Carnot engine consist of a cylinder containing ideal gas and covered with a piston that can move alternatingly in the cylinder.

Figure 8.16 shows the work process of Carnot engine to produce Carnot cycle. Entire of process in the Carnot cycle can be represented in pressure (P) against volume (V) graph as follows.

Based on the graph above, then the carnot cycle consist of the following steps.

Step 1 The engine absorbs heat from the heat source or high temperature reservoir T1 so that the ideaL gas in the engine experiences isothermal expansion (temperature of system is equal to temperature of reservoir). The expanded gas applies a work on the piston, so that the gas volume are changes from v1 to v2. This expansion is shown in Figure 8.16, with changes from state a to b along an isothermal graph. During this isothermal gas expansion, the gas receives heat equal to Q1.

Step 2 The heat source is removed so that there is no heat input to the system. The gas still expands adiabatically and applies works to change gas volume from V2 to V3 In this process the gas temperature decreases to T2. This process is shown in Figure 8.16 with change of state from b to c along an adiabatic graph.

Step 3. The gas experiences isothermal compression by giving away an amount of Q2 heat the low temperature reservoir T2, In this process, the gas volume decreases from v3 to v4. This compression is shown in Figure 8.16, with change of state from c to d along an isothermal graph.

Step 4. The gas experiences adiabatic. compression and returns to its initial state. In this process, a work is applied on the gas so that the gas volume decreases from V4 to V1. This compression is shown in Figure 8.l6, with change of state from d to a along an adiabatic graph.

Total work which done by gas in one cycle is equal to wide of area in cycle.Because during process of Carnot cycle the gas accept kalor Q1 from high temperature reservoir and free a heat Q2 to low temperature reservoir. Hence the work is done by gas according to first law of Thermodynamic is

Q = U + W atau Q1 - Q2 = 0 + W

W = Q1 − Q2

Otto CycleThe Otto engine was made by Nikolaus August Otto (1832-1891),a technician born in Holzhausen, Germany. This Otto engine is usu-ally used in automobiles and airplanes.

An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical spark ignition reciprocating piston engine.

The Otto cycle is constructed out of: TOP and BOTTOM of the loop: a pair of parallel adiabatic processes. LEFT and RIGHT sides of the loop: a pair of parallel isochoric processes.

Otto cyclea – b and c - d process : adiabatic processb – c and d - a process : isochoric process

Diesel CycleThe Diesel engine was made by the German engineer Rudolf Chris-tian Karl Diesel (1858-1913). The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine.The Diesel engine is usually used in electric generators, trucks, buses, and several types of cars.

Diesel cyclea - b process : isobaric processb - c and d - a process : adiabatic processc - d process : isochoric process

Rankine CycleThe Rankine engine was made by William John Macquorn Rankine, a Scottish polymath and Glasgow University professor.

The Rankine cycle is a cycle that converts heat into work. The Rankine cycle is the fundamental thermodynamic underpinning of the steam engine.The Rankine cycle is sometimes referred to as a practical Carnot cycle because, when an efficient turbine is used, the TS diagram begins to resemble the Carnot cycle. The main difference is that heat addition (in the boiler) and rejection (in the condenser) are isobaric in the Rankine cycle and isothermal in the theoretical Carnot cycle.

a - b and c - d process : isobaric processb – c and d - a process : adiabatic process

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