Conversion of thermal energy


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Conversion of thermal energy : 

Conversion of thermal energy CHEMICAL ENERGY SOURCES


INTRODUCTION The development of particular type of fuel cells and batteries holds promise for. Running small and light commercial vehicles in the beginning followed by for heavy vehicles. Rural electrification of remote small villages having a population of 100—500 through rechargeable power batteries. the Government to provide electricity for lighting rural areas where laying of transmission faces hazards.

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The Department of Non-conventional Energy Sources (DNES), India, has been .promoting R&D efforts relating to chemical and electrochemical sources of energy keeping in view their potential role in the long term. The Department extended support for studies relating to Beta, Alumina for Sodium Sulphur batteries, Lithiumion conductors for solid state batteries, fuel cell materials and development of high energy density storage batteries suitable for photo voltaic and other applica­tions.

Types of Fuel Cells : 

Types of Fuel Cells Following fuels are mostly used in fuel cells : 1) Hydrogen, (2) Fossil fuel, (3) Hydrocarbon fuel, (4) Alcohol fuel, 5) Hydrazine fuel. There are discussed in the following sections. Hydrogen, oxygen (H2, O2) cell of primary systems is already described using 40% KOH solution as electrolyte Ion Exchange Membrane cell. The basic design of the cell, which consists of a solid electrolyte Ion-exchange membrane, electrocatalysts and gas feed tubes

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The desired properties of an ideal ion-exchange membrane electrolyte are : (i) High ionic conductivity. (ii) Zero electronic conductivity. (Hi) Low permeability of fuel and oxidant. (iv) Low degree of electro-osmosis. (v) High resistance to dehydration. (vi) High resistance to its oxidation or hydrolysis and, (vii) Mechanical stability.

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this method should be valuable, provided that there are suitable substances which can undergo photo chemical dissociation. The sequence of reactions which are taking place in this fuel cell can be represented as follows : Electrochemical : A + B * AB + electricity Photochemical : AB + light A + B Overall : Light + electricity The nitric oxide—chlorine fuel cell, in which the overall reaction is, 2 NO +C12 2NOCl the product nitrosyl chloride is decomposed Photochemically to chlorine and nitrous oxide.

Advantages and Disadvantages of Fuel Cell : 

Advantages and Disadvantages of Fuel Cell It has very high conversion efficiencies as high as 70 per cent have been observed, since it is a direct conversion process and does not involve a thermal process. In the conventional thermal process for generating electricity, heat energy produced by combustion of the fuel is converted partially into mechanical energy in a steam turbine and then into electricity by means of a generator. The efficiency of a heat engine is limited by the operating temperatures, and in the large modern steam-electric plants above 40 per cent of the heat energy of the fuel is converted into electrical energy. Fuel cells, on the other hand, are not heat engines and are not subjected to their temperature limitations.

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Fuel cells can be installed near the use point, thus reducing electrical transmission requirements and accompanying losses. Conse­quently considerably higher efficiencies are possible. They have few mechanical components; hence, they operate fairly quietly and require little attention and less maintenance. Atmospheric pollution is small if the primary energy source is hydrogen, the only waste product is water ; if the source is a hydrocarbon, carbon dioxide is also produced, Nitrogen oxides, such as accompany combustion of fossil fuels in the air, are not formed in the fuel cell. Some heat is generated by a fuel cell, but it can be dissipated to the atmosphere or possible used locally.

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There is no requirement for large volumes of cooling water such as are necessary to condense exhaust system from a turbine in conventional power plant. As fuel cells do not make noise, they can be readily accepted in residential areas. The fuel cell takes little time to go into operation The space requirement for fuel cell power plant is consider­ably less as compared to conventional power plants

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Disadvantages The main disadvantages of fuel cells are their high initial costs and low service life.

Fuel cells and their applications : 

Fuel cells and their applications

problem : 

problem A hydrogen-oxygen fuel cell operates at 25°C. Calculate the voltage output of the cell, the efficiency, and the electric work output per mole of H2 consumed and per mole of H2O produced. Also compute the heat transferred to the surroundings. Given : ΔH°298° k = -285838 kJ/kg mole ΔG°W8°k = -237191 kJ/kg mole. Sol. According to equation H2 + 20H- 2 H2O + 2e-, there are two electrons transferred per molecule of H2, so that r\e = 2. The cell voltage is given as:

Batteries : 

Batteries A battery is defined as a combination of individual cells, A cell is the elemental combination of materials and electrolyte constituting the basic electro-chemical energy storer. There are two principal divisions of a battery : Primary Batteries non-chargable, e.g. "drycell" flash light batteries. In primary batteries the chemical reactions are non­reversible. Secondary Batteries rechargeable, e.g. a. lead acid battery. There are many types of secondary batteries. The chemical reactions are reversible in secondary batteries. Secondary batteries are of chief interest for solar electrics (Solar and wind energy, electrical storage), and we therefore discuss here about secondary batteries or storage batteries.

Definitions of Fundamental Quantities : 

Definitions of Fundamental Quantities Open circuit voltage (OCV). The battery or cell terminal voltage with R load = ∞, i.e. no load. Energy capacity of a battery is of 3 types : (a) Energy stored (watt-hours or kilowatt-hours) (6) Energy stored weight (watt-hours/kg) (c) Energy stored/volume (watt-hours/ma). Power capacity is the rate at which stored energy can safely be taken out of a battery and restored. Specific power is the maximum rated power output per kg, the battery can supply. Rating various batteries by specific power permits rapid performance comparisons of different kinds of batteries. Energy Efficiency of a battery is, defined as : useful energy out (watt-hrs) Energy Efficiency = re-charge-energy (watt-hrs)

Types of battery arrangement : 

Types of battery arrangement

Basic heat theory : 

Basic heat theory The famous statement by Kelvin Plank of second law of thermodynamics is : "It is impossible for an heat engine to produce work in a complete a cycle if it exchanges heat with a single reservoir." Clausius statement convey the same principle in different words "It is impossible to construct a device which operate in a closed cycle and produces no effect other than transfer of heat from a cooler body to a hotter body."

Thank you : 

Thank you

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