Browsing by Author "D.C. Agrawal"

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A finite speed Curzon-Ahlborn engine
(Institute of Physics Publishing, 2009) D.C. Agrawal
Curzon and Ahlborn achieved finite power output by introducing the concept of finite rate of heat transfer in a Carnot engine. The finite power can also be achieved through a finite speed of the piston on the four branches of the Carnot cycle. The present paper combines these two approaches to study the behaviour of output power in terms of isothermal expansion ratio V*2 and the temperature differences x and y present at the hot source and cold sink branches, respectively, for the benefit of undergraduate students. © 2009 IOP Publishing Ltd.
A Model for Mass Loss in Burned-out Filaments of Incandescent Lamps
(2005) V.J. Menon; D.C. Agrawal
We consider tungsten filaments burning in vacuum, having known properties as functions of temperature. The relevant heat and evaporation equations are solved analytically. For chemically pure tungsten this yields a new formula for the percentage mass loss at burn-out in agreement with the experimental value of about 32 percent. © 2005 Taylor & Francis Group, LLC. All rights reserved.
A model for mass loss in burned-out filaments of incandescent lamps
(2004) V.J. Menon; D.C. Agrawal
We consider tungsten filaments burning in vacuum, having known properties as functions of temperature. The relevant heat and evaporation equations are solved analytically. For chemically pure tungsten this yields a new formula for the percentage mass loss at burn-out in agreement with the experimental value of about 32 percent. © 2004 The Illuminating Engineering Society of North America.
A relation between mass loss and life of incandescent filament lamps
(SAGE Publications Ltd, 2010) D.C. Agrawal; V.J. Menon
The thermodynamics of a radiating and evaporating tungsten filament having a hot-spot defect are examined theoretically. Assuming quasi-steady-states for the main and the hot-spot segments, the time profiles of their temperatures and radii are derived in closed form. Explicit relations among the fractional mass loss, failure time and defect size ratio are obtained and compared against approximate expressions used by Gluck and King7 and by Elenbaas. 14 Numerical results computed for vacuum lamps support our theory. © 2010 The Chartered Institution of Building Services Engineers.
A simplified version of the Curzon-Ahlborn engine
(Institute of Physics Publishing, 2009) D.C. Agrawal
A simplified version of the Curzon-Ahlborn engine is proposed by assigning the same thermal resistance and same temperature difference at the upper and the lower isotherms of the Carnot cycle. The value of efficiency at the maximum power matches for all the three real heat engines reported by them but at the cost of marginally lower power output. The results are obtained in closed form and are easily reproducible by undergraduates using the componendo and dividendo rule and simple differentiation in contrast to considerable algebra and partial differentiation in the Curzon-Ahlborn derivation. © 2009 IOP Publishing Ltd.
A theory for the mortality curve of filament lamps
(2007) V.J. Menon; D.C. Agrawal
We demonstrate for the first time that the ejection of tungsten atoms from a hot filament can be modeled by a binomial distribution. The relevant ejection chance per atom may have an arbitrary temporal profile depending on the presence of uniform Richardson evaporation, hot spots and temperature variation along the wire. A normal approximation is made and the lamp is supposed to fail if the undecayed atomic fraction drops below a critical value. The resulting formula for the lamp's survival probability in terms of error function has one free parameter and is shown to be in excellent agreement with the experimental mortality curve. © ASM International.
A theory of filament lamp's failure statistics
(2006) V.J. Menon; D.C. Agrawal
We model the ejection of tungsten atoms from a hot filament by a binomial distribution. A normal approximation is made and the lamp is supposed to fail if the undecayed atomic fraction drops below a critical value. The resulting formula for the lamp survival probability has no free parameter and in shown to be in excellent agreement with the experimental mortality curve.
An experiment on surface tension using a double capillary method
(1984) D.C. Agrawal; V.J. Menon
[No abstract available]
Average annual rainfall over the globe
(American Institute of Physics Inc., 2013) D.C. Agrawal
The atmospheric recycling of water is a very important phenomenon on the globe because it not only refreshes the water but it also redistributes it over land and oceans/rivers/lakes throughout the globe. This is made possible by the solar energy intercepted by the Earth. The half of the globe facing the Sun, on the average, intercepts1 1.74×1017 J of solar radiation per second and it is divided over various channels as given in Table 1. It keeps our planet warm and maintains its average temperature2 of 288 K with the help of the atmosphere in such a way that life can survive. It also recycles the water in the oceans/rivers/ lakes by initial evaporation and subsequent precipitation; the average annual rainfall over the globe is around one meter. According to M. King Hubbert1 the amount of solar power going into the evaporation and precipitation channel is 4.0×1016 W. Students can verify the value of average annual rainfall over the globe by utilizing this part of solar energy. This activity is described in the next section. © 2013 American Association of Physics Teachers.
Boiling and the Leidenfrost effect in a gravity-free zone: A speculation
(1994) D.C. Agrawal; V.J. Menon
If gravity and hence bouyancy are absent, the heat transfer in the boiling of water is by conduction. This leads to the absence of the usual nucleate boiling and to the occurrence of film boiling and the Leidenfrost effect at a relatively early stage.
Calculation of the performance parameters of tungsten filament lamps using the exponent rules
(SAGE Publications Ltd, 2010) D.C. Agrawal
The experimentally known values of the 14 exponents associated with the exponent-rules for vacuum and gas-filled tungsten filament lamps are utilized to obtain the temperature dependence of performance parameters such as power demand, lumen output, life and efficacy. It is also shown that the data on emissivity of tungsten reported by Jones and Langmuir are consistent with theory in contrast to those obtained by Roser and Wensel. Further, the analysis predicts a higher power loss factor and a longer life for gas-filled tungsten filament lamps than for vacuum lamps. © The Chartered Institution of Building Services Engineers 2010.
Capillarity phenomenon in a gravity-free zone
(1995) D.C. Agrawal; V.J. Menon
The observations related to capillarity made during space flights are explained theoretically. This is achieved by using (i) Young's expression for the contact angle to predict the changing shape of the meniscus and (ii) the Poiseuille-Peiris-Tennakone formula to calculate the speed of the rising column.
Comment on 'the Stefan-Boltzmann constant in n-dimensional space'
(1998) V.J. Menon; D.C. Agrawal
The expression for the Stefan-Boltzmann constant in n-dimensions as obtained by Landsberg and De Vos is modified by the appropriate spin-degeneracy factor of the photon.
Comment on the concept of O+O internal conversion transition
(1985) V.J. Menon; D.C. Agrawal
[No abstract available]
Doppler effect in a stratified medium
(1984) V.J. Menon; D.C. Agrawal
A derivation of the Doppler effect in a stratified medium based upon the phase function and Galilean transformation is proposed. The results are applied to the case of sound moving in a gas under gravity with a velocity that obeys Rayleigh's formula. © 1984, American Association of Physics Teachers. All rights reserved.
Efficiency and efficacy of incandescent lamps
(American Association of Physics Teachers, 1996) D.C. Agrawal; Harvey S. Leff; V.J. Menon
Planck's radiation formula is used to estimate the dimensionless efficiency of incandescent lamps as a function of filament temperature, with typical values of 2%-13%. Similarly, using the known spectral luminous efficiency of the eye, the efficacy of incandescent light bulbs is estimated as a function of temperature, showing values of 8-24 L W-1 for bulbs of 10-1000 W. The efficiency and efficacy results compare favorably with published data and enable estimation of the filament temperature for any lamp of known efficacy. © 1996 American Association of Physics Teachers.
Engines and refrigerators with finite heat reservoirs
(1990) D.C. Agrawal; V.J. Menon
The authors investigate the effect of finiteness of the heat reservoirs on the thermal efficiency of engines and performance coefficient of refrigerators, employing a Carnot cycle. The efficiency and the performance are both lowered in comparison to the case of machines working between reservoirs at constant temperatures.
Finite-time Carnot refrigerators with wall gain and product loads
(1993) D.C. Agrawal; V.J. Menon
Finite-time thermodynamics is used to investigate theoretically the wall gain and product loads on a refrigerator based on an endoreversible Carnot cycle. Explicit formulas are obtained for the operating time, coefficient of performance, and the cooling rate and the procedure is illustrated numerically for typical refrigerators.
First law of thermodynamics from Hamiltonian viewpoint
(1995) V.J. Menon; D.C. Agrawal
For a closed universe containing several interacting composite bodies we interpret the first law of thermodynamics in terms of the differentials of Hamilton's canonical coordinates.
Growth responses of Vigna radiata seeds to laser irradiation in the UV‐A region
(1985) Sudha Rani Govil; D.C. Agrawal; K.P. Rai; S.N. Thakur
We have investigated the effect of pulsed nitrogen laser radiation (337.1 nm) on morphological characteristics and biochemical contents in seedlings from treated greengram (Vigna radiata L.) seeds, which were germinated and grown in Petri dishes for a week. The shoot and root lengths, and fresh and dry weights of the seedlings were maximum with the 30 min exposure, while protein was maximum with 20 min, RNA and DNA contents with 5 min exposure time. Chlorophyll content was not affected by the irradiation. Copyright © 1985, Wiley Blackwell. All rights reserved