## Hlr

What is its reverse saturation current, I0 2. What is the load resistance that allows maximum power transfer 3. What is the efficiency of this cell with the load above 14.12 The power density of monochromatic laser light (586 nm) is to be monitored by a 1 x 1 mm silicon photodiode. The quantity observed is the short-circuit current generated by the silicon. Treat the diode as a perfect ideal device. 1. What current do you expect if the light level is 230 W m2 2. How does the temperature of the...

## References

Signaigo, Wheeler G. Lowell, and T. A. Boyd, Antiknock effect of tetraethyllead (Effectiveness of the tetraethyllead in increasing the critical compression ratio of individual hydrocarbons), Ind. Eng. Chem , 27 (5), 593-597, May 1935. Heywood, John B., Internal Combustion Engine Fundamentals, McGraw-Hill, 1988. Lane, Neill W. and William T. Beale, Free-piston Stirling design features, Eighth International Stirling Engine Conference, University of Ancona, Italy, May...

## Mhl

Where e0 is the permittivity of free space (8.9 x 1012 F m), d is the separation between the plates and k is the dielectric constant (k 1, because there is no dielectric, the capacitor being in vacuum). With an area of 1014 m2, C 8.9 x 1026 d farads. If the device can be built with a separation of 107 m between the plates, the capacitance will be about 1018 F. The lower cutoff frequency is Since for maximum power transfer, the load must match the generator, RL Rh. To have the lowest possible...

## Enthalpy Dependence on Temperature

Let AH be the enthalpy change owing to a chemical reaction. By definition, AH is equal to the sum of the enthalpies of the products of a reaction minus the sum of the enthalpies of all reactants. Thus, AH enthalpy of products enthalpy of reactants. When there is a single product, then the enthalpy change of the reaction can be expressed per kilomole of product by dividing AH by the number of kilomoles of product created. An equivalent definition holds for the free energies. In mathematical...

## P

Wnet W13 - Watm flRTi ln . (3.33) This means that the net work is exactly that owing to the isothermal expansion of the gas. Choose pi 1 MPa and assume that T1 Tatm 298 K and p3 Patm 0.1 MPa. The expansion ratio, r p1 p3, is 10 1. The net work per kilomole of fuel is 5.7MJ kmole of N2 or 204kJ kg of N2. It may be difficult to achieve isothermal expansion it would require an additional heat exchanger to warm up the nitrogen as it forces the piston down. However, something similar is required in...

## Hinged Contour Converters

Both the AquaBuOY and the Seadog mentioned are point absorbers because they interact with only a small ocean area. To generate large amounts of energy, a multitude of these devices must be deployed, each with its own piston and power takeoff equipment. The solution developed by Pel amis Wave Power, formerly (prior to 2007) known as Ocean Power Delivery, Ltd., although also using a system of buoys, is capable of interacting with a much larger ocean area. The 750-kW prototype called Pelamis (see...

## M

To set up the experiment, you would have to build the simple device illustrated in the figure. It consists of a wooden base large enough to support a standard piece of paper. A vertical piece of wood (back) is attached to the base, and mounted on it is a thin aluminum rectangle with a small hole in it. The aluminum must be thin enough (say, 1 mm or less) so that the sun can shine through the hole even when it is far from perpendicular to the plate. In the model we used, the hole was 129 mm...

## Info

Consider methanol, a fuel that has been proposed for both internal combustion (IC) engines and fuel cells. Methanol can be derived from fossil fuels and also from biomass. Being liquid at RTP conditions, it is a convenient fuel for automobiles. It has reasonable reactivity in fuel cells. In IC engines, methanol is first evaporated and then burned. The engine exhausts water vapor. In fuel cells, the methanol reacts in liquid form, but the product water is in vapor form. 1. What heat do you get...

## Relationship between Ecliptic and Equatorial Coordinates

Celestial longitude is measured along the ecliptic, while right ascension which is also a measure of longitude is measured along the equatorial plane. Clearly, a simple relationship must exist between these coordinates. Consider a right-handed orthogonal coordinate system with the center of Earth at the origin, in which the x-y plane coincides with the equatorial plane and the y-axis is aligned with the equinoctial line. The z-axis points north. Let s be a unit vector, starting from the origin...

## Find The Insolation On The Surface Facing True East

The inclination of the plane of the Martian equator referred to the plane of its orbit is 25.20 . The inclination of the plane of the Martian orbit referred to the ecliptic is 1.85 . The average daytime Martian temperature is 300 K (just a little higher than the average daytime Earth temperature of 295 K). The Martian night, however, is cold Average temperature is 170 K (versus 275 K, for Earth). The vernal equinox occurs on Mars day 213. Define a Martian hour, hm, as 1 24 of the annual average...

## Secondary Batteries Lead Acid

This extraordinary, first ever rechargeable battery, invented by the French physicist, Gaston Plante (1834-1889), has withstood the competition of numerous other batteries and is still in large-scale production after more than 150 years of use. Only the modern lithium ion cells seem to pose serious competition to Plante's invention. Lead-acid batteries have survived mainly because they are a low-cost, high power-to-mass device, capable of delivering large surge currents, albeit for a short time...

## Heat Removal from Fuel Cells

The operating temperature of a fuel cell depends on the type of cell. In any cell, if the temperature is to remain unchanged, an amount of heat power, Premov, equal to the generated heat power, Pheat must be removed from the device. This heat removal can be accomplished passively or by using special heat exchange schemes. Heat can, for example, be removed by using a rate of air flow in excess of that which is required to satisfy the oxygen demand of the cell. This same stream of air may also be...

## Gdb Of Reneawble

N PD 2 p*NA 7< D> -< D> S. (15.101) The efficiency formula derived above is correct only to first order. It ignores parasitic losses owing to friction and to the generation of vortices it disregards the reduction in wind velocity caused by the wind turbine itself it fails to take into account the interference of one wing blade on the next. In fact, Equation 15.101 predicts that with large enough solidities, the efficiency can exceed unity. We will discuss this question a little later....

## Energy Utilization

Most of the energy currently used in the world comes from nonrenew-able sources as shown in Figures 1.11 and 1.12, which display energy sources in 2001 for the whole world and for the United States, in 2008, respectively. The great similarity between these two charts should not come as a surprise in as much as the United States uses such a large fraction of the total world consumption. What may be unexpected is that most of the renewable resources (geothermal, biomass, solar, and wind) make...

## Caveat

In the following discussion, we will make a number of simplifications that introduce substantial errors in the results but still describe in general terms the way insolation varies throughout the year and during the day. Some of these errors can, as indicated further on, be easily corrected, and those that remain are of little consequence for the planners of solar energy collection systems. 1. We assume that the length of the period between successive sunrises is constant throughout the year....

## Free Energy

If the reaction under consideration occurs not in a calorimeter but in an ideal fuel cell, part (but not all) of the energy will be released in the form of electricity. It is important to investigate how much of the AH of the reaction will be converted into electric energy and to understand why some of the energy must take the form of heat even in the ideal case. Let Vrev be the voltage produced by the cell. Each kilomole of water (or of any other substance) contains N0 molecules, where N0...

## Nickel Iron

In the early competition between steam, internal combustion, and electric automobiles, the electric suffered (as do modern electric cars) from a limited range. These cars had a large fraction of their weight in lead-acid batteries. Thomas Edison, (1847-1931), using his usual empirical approach, tested many materials in search of elements for a battery that would outperform the ones currently being used. He finally settled on an iron-nickel oxide combination which had a moderate success, being...

## Heat of Combustion

(in Section 9.2) in which hydrogen and oxygen combine to form water. In rearranging four hydrogen atoms and two oxygen atoms to form two molecules of water, some energy is left over. Although the force that binds atoms into molecules is electric in nature, when H2 reacts directly with O2, only heat results because electrons and ions collide and their energy is randomized. Assume that a measured amount, p, of hydrogen is introduced into a constant-pressure calorimeter and is made to react with...

## Generalities

In mid-2008, if you looked up Hydrogen use in Google (English), you would find about 1,550,000 entries. Better than any other statistics, this attests to the enormous interest in this gas. Alone for the production of ammonia, there was a 46-fold increase in hydrogen utilization between 1946 and 2003, when over 19 million tons were produced. The impending massive introduction of fuel cells into the economy will cause the demand for hydrogen to rise much more rapidly in the near future....

## Introduction

Production of hydrogen by electrolysis is a relatively old art that has found industrial application in the food industry and in other activities that need only a moderate amount of the gas. Hydrogen produced by electrolysis has the advantage of being easily purified, whereas that produced from fossil fuels tends to contain several hard to remove contaminants. To a small extent, electrolytic hydrogen has been used for the synthesis of ammonia, but the low cost of oil prevalent up to 1972 and...

## The Ecology Question

We have shown that there is an almost unavoidable trend toward increasing energy utilization. We have also pointed out that at present the energy used is at least 85 of fossil origin. Finally, we have observed that the fossil fuel reserves seem ample to satisfy our needs for a good fraction of the next millennium. So, what is the problem Most of the easily accessible sources of oil and gas have already been tapped. What is left is getting progressively more expensive to extract. Thus, one part...

## AVR

Figure 3.15 One possible implementation of a Stirling engine. Real efficiency departs from from the theoretical because 1. The efficiency of mechanical heat engines increases with increasing compression ratio. The Stirling engine is no exception (see Problem 3.1). The internal volume of the heat exchangers and the regenerator causes the compression ratio to be smaller than if heat could be applied directly to Space 1. 2. The combustion gases leaving the input heat exchanger are still quite hot...

## Horizontal Axis Turbines propeller type

Blades of large horizontal axis wind turbines in the twenty-first century are much more slender than earlier ones that were more paddle-like. The shape depicted in Figure 15.20 is approximately the one used on the Vestas V90 3MW turbine. In the figure, the blade rotates clockwise with an angular velocity, w, so that the leading edge of the airfoil is exposed to an induced wind of magnitude u, which is a function of r, the distance from the axis of rotation. We are going to consider a small...

## Problems

4.1 An OTEC is to deliver 100 MW to the bus bar. Its warm water comes from a solar-heated pond that is kept at 33 C. The water exhausted from the heat exchanger is returned to this same pond at a temperature of 31 C. (There is a slight heat loss in the pipes.) To reestablish the operating temperature, the pond must absorb heat from the sun. Assume an average (day and night) insolation of 250 W m2 and an 80 absorption of solar energy by the water. Cold water is pumped from the nearby abyss at a...

## Anaerobic Digestion

Fermentation transforms a limited number of substances (sugars) into an ethanol water mixture from which the alcohol has to be recovered by means of an energy-intensive distillation. In contrast, anaerobic digestion, transforms many different vegetable and animal substances into methane, a gas that, being of rather low solubility in water, evolves naturally and can be collected with a minimal expenditure of energy. Fermentation is well understood, whereas digestion has been less studied...

## Mechanical Heat Engines

The driving agent of a heat engine is a temperature differential. A heat engine must have a source and a sink of heat. The heat source may be direct solar radiation, geothermal steam, geothermal water, ocean water heated by the sun, nuclear energy (fission, fusion, or radioactivity), or the combustion of a fuel. In developed countries, over 90 of the energy is derived from combustion of fuels, almost all of which are of fossil origin. When carbon burns completely in an oxygen atmosphere, the...

## Horizontal Forces

The power generated by a wind turbine is Pwind 27 2 Pair V3ir AwindVwind, (16.9) and that generated by a water turbine is Pwater 27 2pwatervwater AwaterVwater (16.10) Let us assume that both types of turbines have the same efficiency, 'q. If the two turbines generate the same amount of power, then pair vair Awind Pwater ater Awater (16.11) Awind _ pwater f vwater (16 12) The horizontal forces on the turbines are proportional to pv2A. Hence, Fwater Fair Pair vair Awind vwater If, for example,...

## The Freepiston Stirling Engine

As in the case of kinematic Stirling engines, there are numerous implementations of the free-piston version. Much of the development of this type of engine is owed to Sunpower Inc. of Athens, Ohio. Figure 3.16 shows a simple form of the engine dating from 1986. There is no rigid mechanical connection between piston and displacer. Both fit snugly in the cylinder with no intentional leakage. The motion of the displacer must lead that of the piston by more than 0 and less than 360 . The power...

## E e e e e

From now on, for clarity, we will omit most of the background of silicon atoms and covalent bonds from our drawings and show only the carriers and their corresponding donors or acceptors as in the figure in the preceding page. It must be emphasized that the donors and acceptors are not carriers because they cannot move. The left-hand drawing represents an n-material, and the right-hand one, a p-material. Both are electrically neutral, having an equal number of positive and negative charges. The...

## Rtp Free Energy

9.1 Every substance is endowed with a certain amount of energy and a certain amount of entropy. Although entropy is well defined, energy has no absolute value only changes in energy can be measured. For this reason (entirely by convention), the enthalpy of formation of elements in their natural state is taken as zero. Consider aluminum and oxygen. In their natural states, their standard enthalpy of formation (i.e., the energy of formation at RTP) is, as we said, zero. Every kilogram of aluminum...

## CD

Assuming no maintenance or operating cost, what is the cost of the generated kWh Use a utilization factor of 25 . 15.8 A sailboat has a drag, F, given by where F is in newtons, W is the velocity of the boat with respect to the water in m s , and a 80kg m. The sail of the boat has a 10 m2 area and a drag coefficient of 1.2 when sailing before the wind i.e., with a tailwind . When sailing before the wind, what is the velocity of the boat How much power does the...

## Free Energy System Using Photo Diode

14.1 What is the theoretical efficiency of cascaded photodiodes made of two semiconductors, one with a band-gap energy of 1 eV and the other with 2 eV when exposed to sunlight 14.2 As any science fiction reader knows, there are many parallel universes, each one with different physical laws. In the parallel universe we are discussing here, the black body radiation at a given temperature, T, follows a simple law P is the power density W m 2 and f is in Hz. f grows linearly with f to a value of 1...

## Building Is 300 M Tall And 50m Wide It Is Drag Coefficient Is

Where W is the velocity of the vehicle along the rail. Notice that the drag force above does not include any aerodynamic effect of the sail that propels the vehicle. Any drag on the sail has to be considered in addition to the vehicle drag. The wind that propels the vehicle is perpendicular to W and has a velocity, v 10 m s. It comes from the starboard side the right side of the vehicle . The sail is actually an airfoil with an area of 10.34 m2. It is mounted vertically that is, its chord is...

## Solid Polymer Electrolyte Fuel Cells

The solid-polymer electrolyte is conceptually the simplest type of fuel cell and, potentially, the easiest to manufacture. As the name suggests, the electrolyte is a solid membrane made of an ion-conducting polymer. The ion can be positive a cation , usually a proton, or negative an anion usually an OH. SPFCs are safer than liquid or molten electrolyte cells because they use noncorrosive and of course, nonspillable electrolytes. They can stand fairly large differential pressures between the...

## Fisher-pry Wind Power

2.2 a th tin ats 2 .'. a . 1.7 Thus, the market penetration formula can be written as '-f 2'2 T s 2 2T. lt 1J A remarkable and useful property of the market penetration function is its insensitivity to many factors that profoundly affect the overall market. Thus, although variations in political or geopolitical circumstances can substantially affect market volume, they frequently have a minimal effect on the fractional market share, probably because they influence simultaneously all competing...

## Thermoelectric Battery Consist Of 1000 Identical Thermocouples

5.1 The Russians are quite advanced in thermoelectrics and have recently developed a secret material for such use. Data are naturally, hard do obtain, but the CIA discovered that a thermoelectric cooler is being built capable of depressing the temperature by 100 K when the hot junction is at 300 K. What is the figure of merit of the thermocouple 5.2 The Seebeck coefficient of a junction is 1. At what temperature is the Peltier coefficient maximum 2. What is the coefficient at this temperature...

## Planetary Energy Balance

The relative stability of Earth's temperature suggests a near balance between planetary input and output of energy. The input is almost entirely solar radiation, which amounts to 173,000 TW 173,000 x 1012 W . Besides solar energy, there is a contribution from tides 3 TW and from heat sources inside the planet, mostly radioactivity 32 TW . Some 52,000 TW 30 of the incoming radiation is reflected back to the interplanetary space it is the albedo of Earth. All the remaining energy is degraded to...

## Heaving Buoy Converters

Although the particular arrangement for the conversion of wave energy into mechanical energy, and then, presumably into electricity depicted in Figure 16.2 does not appear to be practical, it serves to illustrate the manner in which more complicated devices of this class operate. It is a wave-operated pump consisting of a buoy attached to a long vertical pipe equipped with a check valve at the bottom. When a wave lifts the device, water in the pipe is accelerated upward because it cannot escape...

## Formic Acid

The fuel processors described in the previous subsubsection operate at relatively high temperatures gt 200 C . There are, however, clear advantages in working at room temperature. This has been done by Loges et al. 2008 using the catalytic decomposition of formic acid. Formic acid, HCOOH, is an inexpensive liquid of much lower toxicity than methanol, but able to carry, by weight, only about one third the hydrogen carried by the alcohol. Formally, it decomposes as Aqua regia royal water is a...

## Direct Formic Acid Fuel Cells DFAFCs

Fuel crossover has been a difficult problem for the DMFC designers. One obvious solution is to use a different fuel, such as formic acid. The tChu et al. 2000 at the U.S. Army Research Laboratory have developed an iron-cobalt tetraphenyl porphyrin catalyst that can promote the oxygen reduction to water Equation 9.30 but will not catalyze methanol oxidation Equation 9.29 . Consequently, it has possibilities as a cathode catalyst in DMFC.

## Activation Energy

Consider an inert container filled with a mixture of hydrogen and oxygen at 300 K and in the correct stoichiometric proportions to form water. One would expect that the two gases would promptly react forming water because of the large thermodynamic driving force the water vapor that would result from such a reaction has a free energy 228 MJ kmole lower than that of the gas mixture a system tends toward the configuration of the lowest possible free energy. It turns out, somewhat surprisingly,...

## Cellulose Hemicellulose Lignin

Figure 13.14 Flowchart of a typical Brazilian ethanol plant. Figure 13.14 Flowchart of a typical Brazilian ethanol plant. Each ton of cane yields 153 kg of sugars, mostly sucrose 2.54 GJ at 16.6 MJ kg , 276 kg of moist bagasse, or 138 kg of dry bagasse 2.5 GJ at 18.1 MJ hg , and 165 kg of moist straw or 140 kg of dry straw 2.14 GJ at 15.3 MJ kg . It can be seen that the sugars represent only roughly one-third of the available energy and that another third used to be lost by burning the straw in...

## Concentrators

Concentrators can be of the nonimaging or the focusing type. Either can be line concentrators 2-D or point concentrators 3-D . A solar collector consists of a concentrator and a receiver. The concentrator may be of the refracting lens or the reflecting mirror type. The receiver may be thermal or photovoltaic. Two important parameters describe the collector performance The concentration can be defined as either the ratio of the aperture area to the receiver area or as the ratio of the power...

## Tir

For each shape of the airfoil, pL and pD are determined experimentally in wind tunnels under specified conditions. The observed pressures are related to the dynamic pressure, 2pv2, by proportionality constants, CL and CD, called, respectively, the lift coefficient and the drag coefficient These coefficients are functions of the angle of attack and can be found in tabulations, many of which were prepared by National Advisory Committee for Aeronautics NACA the forerunner of NASA in the United...

## Osmosis

Salination engines are being seriously proposed as a possible energy converter, while the osmotic engine described in this section will probably never be more than an academic curiosity. Its study is nevertheless an interesting intellectual exercise. Osmosis is a quantitatively surprising phenomenon. If two solutions of different concentrations are separated by an osmotic membrane permeable to the solvent but not to the solute, then there is a net flow of the solvent from the more dilute to the...

## Specific Heat at Constant Volume

When, in a fixed amount of gas, the temperature is changed, the internal energy also changes. When the volume is kept constant as is the case of a mass of gas confined inside a rigid container , the rate of change of its tlf Avogadro's number is taken as the number of molecules per mole instead of kilomoles as one does when using the SI , then its value is 6.022 X 1023. internal energy with a change of temperature per kilomole of gas is called the specific heat at constant volume, cv Cv 1 VR J...

## Car Moves On A Flat Horizontal Road With A Steady Velocity Of 80 Km H. It Consumes Gasoline At A Rate Of 0.1 Liter Per

The objective of this exercise is to predict what impact the defunct federal coal liquefaction program would have had on the fuel utilization pattern. According to the first in, first out rule, the free variable, that is, the one that does not follow the market penetration rule, is the natural gas consumption fraction, fng. The questions are - What is the maximum value of fng Assume that fsyn the fraction of the market supplied by synthetic fuel is 0.01 in 1990 and 0.0625 in 2000. Please...

## JvK j

The value of j for air is 1.84 x 10 5 pascal second same as kg m_1 s-1 , and, contrary to one's gut feeling, is independent of pressure and density see the box at the end of this section . However, the ratio, j p, called the kinematic viscosity, increases when the pressure decreases. Fluids at low pressure exhibit great kinematic viscosity, and this explains why vacuum pumps need large-diameter pipes. For STP conditions, this ratio for air is 1 70,000 m2 s because p 1.29kgm 3. Since for any...

## T

Figure 15.5 From left to right a horizontal axis propeller type turbine, and two vertical axis machines a Gyromill and a Darrieus. Figure 15.5 From left to right a horizontal axis propeller type turbine, and two vertical axis machines a Gyromill and a Darrieus. Some wind turbines have the propeller upstream from the generator and some downstream. It has been found that the upstream placement reduces the noise produced by the machine. A propeller wind turbine that employs a ground-level...

## Radio Noise Generators

A subcommittee of the Committee on Government Operations of the House of Representatives of the Ninety-Fourth Congress of the United States heard, on June 11, 1976, testimony on Converting Solar Energy into Electricity A Major Breakthrough. Joseph C. Yater, the inventor, read a prepared statement. Although the implementation of the idea is improbable, we will discuss it here as an interesting intellectual exercise. The idea is fundamentally simple It is well known that a resistor generates...

## Gravimetric power density

Figure 9.38 A Ragone plot reveals at a glance the relative characteristics of different energy storage systems. Ideally, one should try for the northeast corner of the chart. To compare the performances of different energy storage system, let us plot their gravimetric energy density versus their gravimetric power density using logarithmic scales in what is called a Ragone plot, as we did in Figure 9.38. The ratio of the energy density Wh kg to the power density W kg is the number of hours the...

## The Market Penetration Function

The enormous body of literature accumulated throughout the centuries makes it impossible for even the most assiduous readers to have studied the writings of all scientists and philosophers of the past. Hence, modern writers have built up a large roster of often cited, rarely read authors whose ideas are frequently mentioned even when only nebulously understood. This is, for instance, the case of Thomas Robert Malthus. We all have an idea that he had something to say about population growth. In...

## Q Jl X X X

In the case of methane, all carbon valence electrons are engaged in identical a-bonds and, being directly between atoms, are well protected from external fields and, thus, firmly localized. 2. In double-bonded molecules ethene, C2H4, for example , the C C bond consists of one a- and one -bond. Each carbon has two hydrogens attached to it via a a-bond. Thus, each carbon forms three a-bonds and one -bond. The 3 a-bonds, which lye on a flat plane, are spaced 120...

## Foreword to the Second Edition

The public's widespread desire to become informed about energy has been, in part, satisfied by excellent media coverage and by a plethora of good books on the subject. Most of these books are, quite naturally, journalistically slanted and treat technology superficially. Granted that of the various components of the problem technology, economics, politics technology represents only a small fraction of the total, but it is the one fraction that must be tackled first. Those who need to understand...

## Overtopping Converters

Wave Dragon ApS originally a Danish company, which has now moved its center of operation to Wales is developing a fundamentally simple wave energy converter Figure 16.4 . It consists of a large floating basin or reservoir a few meters above sea level. Waves concentrated by a pair of reflector arms hit a ramp rising up and spilling into the reservoir. The water flows out back to the ocean driving a number of Kaplan turbines, thus, generating electricity. One advantage of this design is that the...

## Fuel Cells

It is said that the nineteenth was the century of mechanical engineering, the twentieth, that of electronics, and the twenty-first, that of biology. In fact, the twentieth century could just as well be known as the century of the mechanical heat engine. Counting cars, trucks, and buses, the United States alone, built, from 1900 to 1999, slightly more than 600 million vehicles. If one adds the rest of the world's automotive production and includes lawn mowers, motorcycles, motorboats, railroad...

## Tapered Channel System

An ingenious wave energy system was developed by a Norwegian company appropriately called Norwave. The system was demonstrated in a fjord at tThe British Isles consist essentially of two islands, the largest being, not surprisingly, Great Britain. On the southwest there is a peninsula known as Wales, the westernmost part of which is Pembrokeshire. tt In 1877, Giovanni Schiaparelli, using a favorable opposition of Mars, drew a detailed map of the planet and described what he perceived as canali....

## The Peltier Effect

Two different conductors, a and b, of identical cross section, A, are connected end-to-end as suggested in Figure 5.20. The surface, S, is the interface between them. Both conductors are at the same temperature, T, and a current, I, flows through them. Let the heat capacity of a typical conduction electron be ca in conductor a and cb in conductor b. The thermal energy associated with each typical electron is, respectively, caT and cbT. For instance, if the electron gas obeys the Maxwellian...

## Uih

Which arrangement leads to the best coefficient of performance 2. What is the Carnot efficiency of the system 3. Using a single thermocouple of the type described, what is the lowest temperature that can be achieved Heat is rejected at 300 K. 4. Under the conditions of Question 3, what is the necessary current 5. Using a single thermocouple of the type described, what is the best coefficient of performance when pumping heat from 270 K to 300 K 6. What is the current that yields the COP of...

## Characteristics of Fuel Cells

Reversible fuel cells will deliver to a load a voltage, VL Vrev, which is independent of the current generated. Their V-I characteristic is a horizontal line. Such ideal cells require reaction kinetics fast enough to supply electrons at the rate demanded by the current drawn. Clearly, reversible cells cannot be realized. In practical fuel cells, two major deviations from the ideal are observed 1. The open-circuit voltage, Voc, is smaller than Vrev. 2. The load voltage, VL, decreases as the load...

## Cr2o3 Convert To Ba2cro4

Cr2O3 s 4Ba OH 2 2Ba2CrO4 s 3H2O g H2 g 2BaCrO4 s Ba OH 2 Ba3 CrO4 2 s H2O g 2 g Notice that, since hydrogen evolves from Reaction 1 and oxygen from Reaction 2 which occur in different parts of the equipment, it is easy to separate these gases. Input reactants are Cr2O3 and BaCrO4. Products besides H2 and O2 are Ba2CrO4 and Ba3 CrO4 2. To recover the reactants, the last two chromates are made to react with water at low temperature 2Ba2CrO4 s Ba3 CrO4 2 5H2O Cr2O3 s 2BaCrO4 s Figure 10.12 Block...

## Oscillating Water Column OWCWavegen System

Another promising scheme for using ocean wave energy was constructed by the Scottish company WAVEGEN and was commissioned in November 2000. It bears the whimsical name LIMPET Land Installed Marine Powered Energy Transformer and is not a commercial unit, but rather, a further research and development unit. It is a scale-up of a 75-kW prototype that operated from 1991 to 1999. LIMPET is a 500-kW plant installed on the island of Islay. It is powered by the oscillating water column generated by...

## Voltas Cell

Volta's cell consisted of a zinc disk separated from a silver or copper disk by a sheet of paper soaked in salt. The voltage generated was quite low especially in view of the insensitive measuring instruments available at the time . This led to the stacking of many cells in series forming a pile or battery actually, the first bipolar configuration ever built. A Volta cell can be made by dipping a zinc and a copper electrode into a dilute say, 10 sulfuric acid solution. The zinc will oxidize...

## Electrolyzer Configurations Liquid Electrolyte Electrolyzers

Until relatively recently, almost all water electrolyzers used liquid electrolytes. Owing to its low conductivity, pure water cannot be used as an electrolyte it is necessary to add a substance that increases the conductivity. Although acids satisfy this requirement and are used in some electrolyzers , they are frequently avoided because of corrosion problems. Alkaline electrolytes are better they almost invariably use potassium hydroxide in concentrations of 25 to 30 about 6M . Potassium is...

## Methanation

The transformation of syngas into methane, part of the process of transforming any fossil fuel into the usually more valuable natural gas, is called methanation. Besides being of great industrial importance, metha-nation is of interest to us in this text because it provides a technique for eliminating most of the CO impurity from the stream of hydrogen produced from carbon-bearing fuels. The methanation reaction is This is the reverse of steam reforming of methane shown in Equation 10.8....

## The Energy Utilization Rate

The energy utilization rate throughout the ages can only be estimated in a rough manner. In early times, humans were totally nontechnological, not even using fire. They used energy only as food, probably at a rate somewhat below the modern average of 2000 kilocalories per day, equivalent to 100 W. Later, with the discovery of fire and an improved diet involving cooked foods, the energy utilization rate may have risen to some 300 W capita. t Fuels derived from recent biomass, such as ethanol...