Chapter-V
THEORITICAL ANALYSIS
The performance of the PEM fuel cell is evaluated by a thermodynamic analysis, which is of two types, viz., energy analysis and exergy analysis. The energy analysis is made by applying the first law of thermodynamics to the fuel cell. The efficiency is defined by considering the heat input to the fuel cell and the work output from the fuel cell. In the exergy analysis the fuel cell and the surrounding environment are considered together. The efficiency is defined based on the maximum or available energy which is calculated by considering the entropy lost to the environment. Thus the exergy analysis takes into account the second law of thermodynamics in addition to the first law. In this chapter a theoretical analysis
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Total exergy transfers by heat, work and mass from the PEM fuel cell are, respectively, defined as:
Σ(Ex) ̇_heat=(1-T_o/T_FC )×r_HL×Q ̇_FC (28)
Σ(Ex) ̇_work=W ̇_FC (29)
Σ(Ex) ̇_(mass,in)=(Ex) ̇_(H_(2,in) )+(Ex) ̇_(O_(2,in) )=(n ̇×ex)_(H_(2,in) )+(n ̇×ex)_(O_(2,in) ) (30)
It is noted that the inlet oxygen and hydrogen gases are normally humidified before entering the cell. However, the mass flow rate of the water used to humidify the oxygen and hydrogen streams is negligible. This simplification will have only negligible effects on the exergy analysis results presented subsequently because the flow rate of humidification water is small and it is at near-environmental conditions (implying its specific exergy is small) [21].
Σ(Ex) ̇_(mass,out) =( Ex) ̇_(H_(2,out) )+(Ex) ̇_(O_(2,out) )+(Ex) ̇_(H_2 O,pro)=〖 (n ̇×ex)〗_(H_(2,out) )+(n ̇×ex)_(O_(2,out) )+(n ̇×ex)_(H_2 O,pro) (31)
The general thermodynamic irreversibility equation for a PEM fuel cell can be also written as:
Or as a general algebraic
* Note the mass down in the table at the end of the first page.
The experiment is aimed at giving a better understanding of the osmosis process and the different conditions in which osmosis occurs. INTRODUCTION When a cell membrane is said to be selectively permeable, it means that the cell membrane controls what substances pass in and out through the membrane. This characteristic of cell membranes plays a great role in passive transport. Passive transport is the movement of substances across the cell membrane without any input of energy by the cell.
type of energy is lost or gained, and whether or not a factor that is
= 3 ´ E(C-H) + 1 ´ E(C-O) + 1 ´ E(O-H) + 1.5 ´ E(O=O)
Variance (2) Standard Deviation () Reaction 1 7.6 x 10-4. 2.76 x 10-2.
Mass of O = Mass of crucible, cover, KClO3 and MnO2 after heating (Step # 11) - Mass of crucible, cover, KClO3 and MnO2 before heating (Step # 5)
Full combustion should generate two products only: carbon dioxide and water vapour. Hypothesis Within a molecule there are bond energies that hold the atoms together. When the fuel combusts, a chemical reaction takes place, this breaks the bonds, this requires energy, and makes new bonds, this gives out energy. The energy differences between the two tell us how much energy was given out or taken in. We can show this in a graph.
be yes as I will then be able to use enthalpy change of reaction to
The report is written to explain DSC, the thermal analysis technique. In this technique the differential analysis on the base of reference material is done at different temperature. A very close and similar technique is DTA (Differential Thermal Analysis) . In these technique the material is heated at different temperature although sometimes isothermal analysis also done for specific applications. The temperature is recorded for any heat release or absorption. So the heat capacity is measured at those temperatures. Two possible modes for DSC are power compensation mode and heat flux mode DSC. So, DSC is a technique which measure the heat capacity at various temperature of material and reference.
The purpose of the experiment is to identify and understand reactions under kinetic and thermodynamic control. A reaction under kinetic and thermodynamic control can form two different types of products. A reaction under kinetic control is known to be irreversible and the product is formed quickly. A reaction under thermodynamic control is known to require rigorous conditions. It is also reversible. The final product is more stable than the product made by kinetic control. The chart below shows the two types of reaction coordinates:
Thermodynamics is the branch of science concerned with the nature of heat and its conversion to any form of energy. In thermodynamics, both the thermodynamic system and its environment are considered. A thermodynamic system, in general, is defined by its volume, pressure, temperature, and chemical make-up. In general, the environment will contain heat sources with unlimited heat capacity allowing it to give and receive heat without changing its temperature. Whenever the conditions change, the thermodynamic system will respond by changing its state; the temperature, volume, pressure, or chemical make-up will adjust accordingly in order to reach its original state of equilibrium. There are three laws of thermodynamics in which the changing system can follow in order to return to equilibrium.
dwell on the factors that preclude the attainment of ideal-performance of the system. Analysis based on the combined first and second law of thermodynamics commonly known as availability analysis or exergy analysis is particularly suited for achieving more efficient resource use since it enables the locations, types and true magnitudes of waste and loss to be determined. This information is quite helpful for the design of thermal systems, for directing the efforts to reduce the sources of inefficiency in the existing systems and evaluate system economics. [1, 2 & 3].
A heat engine is a method that executes the transformation of thermal energy or the heat to mechanical energy. That mechanical energy can be used as a mechanical work. This work can be manifest by bringing a working material from a high heat condition to a lower heat condition, by that the heat engine will produce calorific power that creates higher temperature conditions of the working substance. After generating a higher temperature state to the working substance a work will be p...
At the cathode the hydrogen ions gain an electron. They are discharged and are converted into hydrogen gas: 2H (+) + 2e (-) → H2 At the anode, the hydroxide, not the sulphate ions are discharged. Water and oxygen gas are formed: 4OH (-) → 2 H2O + O2 + 4e (-) The hydrogen gas can be collected and measured. The greater the volume of hydrogen gas formed over a set period of time, the faster electrolysis is occurring.
Bushby, Lisa. "Hydrogen Fuel Cells." : Energy of the Future (EnvironmentalChemistry.com). N.p., 22 Aug. 2006. Web. 04 Sept. 2013.