Work-heat conversion factor

If none of this work was wasted, we could use it to lift a 1000-lb rock up to the top of Mount Everest (which is about 26,000 ft high). But in the 1840s, Robert Mayer did not know the conversion factor of heat equivalent to work of 740 ft-lb per Btu. It had not been determined yet, because Dr. Mayer was the one who first discovered it. So Dr. Mayer had to use the following method. 

Normally, heat, work, and kinetic and potential energy terms are determined in different units. To evaluate AH, we will convert each term to kW (kJ/s) using conversion factors given on the inside front cover, first noting that m = (500 kg/h/3600 s/h) = 0.139 kg/s. 

An engineer who is working on the heat transfer analysis of a house in English units needs Ihe convection heat transfer coefficient on the outer surface of the house. But the only value he can find from his handbooks is 14 W/m - °C, which is in SI units. The engineer does not have a direct conversion factor between the two unit systems for the convection heat transfer coefficient. Using the conversion factors between W and Btu/h, m and ft, and C and "F, express the given convection heat transfer coefficient in Btu/h - °F. 

The specific heat is given in calmol K , so the right-hand side of Eq. (5.1) is in the units of cal. The mechanical work on the left-hand side of Eq. (5.1) is given in J. The conversion factor / has then the physical dimension calJ . Note that formally the conversion factor must be chosen (or inserted) in Eq. (5.1) to validate the equal sign. 

Experiments analogous to those just described were first performed by Joule in the 1840s [5]. Those experiments accomplished several things they fully discredited the old caloric theory of heat (a theory that considered heat to be transported by movement of a substance called caloric), they demonstrated that a temperature change can occur without heat transfer, and they provided a numerical conversion factor between equivalent amounts of heat and work. However for us. Joule s most important result leads to (2.1.27). 

James P. Joule, 1818-1889, English physicist. He found that the energy of an electric current can produce either heat or mechanical work, each with a constant conversion factor. 

Mechanical equivalent of heat n. A conversion factor that transforms work or kinetic energy into heat. Probably the best known one is 788ft-lb per British thermal unit others are 2545 Btu per horsepower-hour, 4.186 X lO ergs/cal, and3413Btu/kWh. In SI there is no need for such factors because work, heat, and electrical energy are all measured in joules (IJ = ImN = IWs). 

Sources of heat, such as are obtained by the burning of fuel, are transitory in charcK ter, and the only heat reservoir (or sink) which is per-mcmently available for man s use is the surface of the earth and the atmosphere. This permanent reservoir will be called the medium and its temperature (c. 290 K) has a decisive influence on the amount of work which may be obtained from any process. (If it were actually as low as 0 K it would be possible to operate heat engines at conversion factors close to unity, as may be seen from equation (1 126).)... 

For certain types of recM tion it is possible to obtain a direct conversion of chemical energy into electricity and thereby into mechanical work. Processes of heat transfer are thereby avoided and the conversion factor, I be heat engine does not come into the picture. This can be achieved whenever the reaction has an ionic mechanism and can be set up as a galvanic cell. The electrodes act in much the same manner as the semi-permeable membranes of the equilibrium box. That is to say, the reagents can be added to the system, and the recK tion products withdrawn, under reversible conditions. The two great prcu tical advantages of this method of operation are as follows ... 

Though Sadi Carnot used the caloric theory of heat to reach his conclusions, his later scientific notes reveal his realization that the caloric theory was not supported by experiments. In fact, Camot understood the mechanical equivalence of heat and even estimated the conversion factor to be approximately 3.7 joules per calorie (the more accurate value being 4.18 J/cal) [1-3]. Unfortunately, Sadi Carnot s brother, Hippolyte Camot, who was in possession of Sadi s scientific notes from the time of his death in 1832, did not make them known to the scientific community until 1878 [3]. That was the year in which Joule published his last paper. By then the equivalence between heat and work and the law of conservation of energy were well known through the work of Joule, Helmholtz, Mayer and others. (It was also in 1878 that Gibbs published his famous work On the Equilibrium of Heterogeneous Substances). 

In appearance, thermodynamics seems to be nothing more or less than a nice collection of abstract mathematical relations between the properties of matter valid for the various states in which this matter may prevail. It becomes more substantial when thermodynamics is applied, as in process technology. The extent to which one form of energy (e.g., heat) can be converted into another (e.g., work) or to which one form of matter (e.g., methane) can be converted into another form of matter (e.g., methanol or hydrogen) is traditionally governed by thermodynamics. But even if such conversions appear to be "technologically" feasible, their practical realization may still depend on the economic viability. Monetary units such as the dollar and concepts such as the cost of production factors (e.g., labor and capital) enter the analysis and often dominate the outcome. Interestingly... 

The fossil load factor is an important issue and its origin so evident and often unavoidable that we asked ourselves the question what the consequences are when this factor is reduced to zero. Whenever, in a biomass conversion process, a fossil fuel contribution was spotted, we replaced this contribution by one from biomass origin. For example, the process may require electricity, which is supplied by a nearby coal-fed power station. Then this amount of electricity was thought to be generated by a power station fed by biomass. Or the process may require heat or chemicals and again biomass is the raw material from which these requirements were met. Dr. Feng Wei made such an analysis for a process where a diesel-type product was obtained from wood chips as a feedstock. His work has been discussed as an example at the end of Chapter 13. 

Whenever the kinetics of a chemical transformation can be represented by a single reaction, it is sufficient to consider the conversion of just a single reactant. The concentration change of the remaining reactants and products is then related to the conversion of the selected key species by stoichiometry, and the rates of production or consumption of the various species differ only by their stoichiometric coefficients. In this special case, the combined influence of heat and mass transfer on the effective reaction rate can be reduced to a single number, termed the catalyst efficiency or effectiveness factor rj. From the pioneering work of Thiele [98] on this subject, the expressions pore-efficiency concept and Thiele concept have been coined. 

The discovery that exposure to exogenous chemicals could lead to cancer in humans was first made in the late 18th century, when Percival Pott demonstrated the relationship between cancer of the scrotum and the occupation of chimney sweepers exposed to coal tar/soot. Other examples noted later were scrotal cancers in cotton spinners exposed to unrefined mineral oils, and cancers of the urinary bladder in men who worked in textile dye and rubber industries due to their exposure to certain aromatic amines used as antioxidants. Experimental induction of cancer by chemicals was first reported in detail by Yamagiwa and Ichikawa in 1918, when repeated application of coal tar to the ear of rabbits resulted in skin carcinomas. Over the next few years, Kennaway and Leitch confirmed this finding and demonstrated similar effects in mice and rabbits from the application of soot extracts, other types of tar (e.g., acetylene or isoprene), and some heated mineral oils. These researchers also observed skin irritation sometimes accompanied by ulcers at the site of application of the test material. Irritation was thought to be an important factor in skin tumor development. However, not all irritants (e.g., acridine) induced skin cancer in mice and conversely, some purified chemicals isolated from these crude materials... 

The catalytic work on the zeolites has been carried out using the pulse microreactor technique (4) on the following reactions cracking of cumene, isomerization of 1-butene to 2-butene, polymerization of ethylene, equilibration of hydrogen-deuterium gas, and the ortho-para hydrogen conversion. These reactions were studied as a function of replacement of sodium by ammonium ion and subsequent heat treatment of the material (3). Furthermore, in some cases a surface titration of the catalytic sites was used to determine not only the number of sites but also the activity per site. Measurements at different temperatures permitted the determination of the absolute rate at each temperature with subsequent calculation of the activation energy and the entropy factor. For cumene cracking, the number of active sites was found to be equal to the number of sodium ions replaced in the catalyst synthesis by ammonium ions up to about 50% replacement. This proved that the active sites were either Bronsted or Lewis acid sites or both. Physical defects such as strains in the crystals were thus eliminated and the... 

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