• Title, Summary, Keyword: entropy generation

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A Study on the Entropy Generation of Single Fin-Tube Heat Exchanger (단일 핀-관 열교환기에서 엔트로피 생성에 관한 연구)

  • Pak, Hi-Yong;Lee, Kwan-Soo;Kim, Byoung-Kue
    • Solar Energy
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    • v.10 no.1
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    • pp.14-21
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    • 1990
  • The entropy generation rate in a fin-tube heat exchanger is investigated as a basis for thermodynamic optimization associated with single fin-tube heat exchanger. The entropy generation (irreversibility)analysis is used to find the optimum design factor and investigate total entropy generation, optimum dimensions of fin length, tube inner and outer diameters, and fin spacing on the variation of design factors. The results of this study are as follows: As the outer diameter increases, optimum !in spacing and fin length increase but the entropy generation and optimum inner diameter decrease; As fin thickness increases, the entropy generation of system and optimum fin spacing increase; As fin length increases, entropy generation and optimum outer diameter increase.

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Entropy Generation Minimization in MHD Boundary Layer Flow over a Slendering Stretching Sheet in the Presence of Frictional and Joule Heating

  • Afridi, Muhammad Idrees;Qasim, Muhammad;Khan, Ilyas
    • Journal of the Korean Physical Society
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    • v.73 no.9
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    • pp.1303-1309
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    • 2018
  • In the present paper, we study the entropy analysis of boundary layer flow over a slender stretching sheet under the action of a non uniform magnetic field that is acting perpendicular to the flow direction. The effects of viscous dissipation and Joule heating are included in the energy equation. Using similarity transformation technique the momentum and thermal boundary layer equations to a system of nonlinear differential equations. Numerical solutions are obtained using the shooting and fourth-order Runge-Kutta method. The expressions for the entropy generation number and Bejan number are also obtained using a suggested similarity transformation. The main objective of this article is to investigate the effects of different governing parameters such as the magnetic parameter ($M^2$), Prandtl number (Pr), Eckert number (Ec), velocity index parameter (m), wall thickness parameter (${\alpha}$), temperature difference parameter (${\Omega}$), entropy generation number (Ns) and Bejan number (Be). All these effects are portrayed graphically and discussed in detail. The analysis reveals that entropy generation reduces with decreasing wall thickness parameter and increasing temperature difference between the stretching sheet and the fluid outside the boundary layer. The viscous and magnetic irreversibilities are dominant in the vicinity of the stretching surface.

Entropy Generation Analysis for Various Cross-sectional Ducts in Fully Developed Laminar Convection with Constant Wall Heat Flux

  • Haghgooyan, M.S.;Aghanajafi, C.
    • Korean Chemical Engineering Research
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    • v.52 no.3
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    • pp.294-301
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    • 2014
  • This study focuses on analysis and comparison of entropy generation in various cross-sectional ducts along with fully developed laminar flow and constant uniform wall heat flux. The obtained results were compared in ducts with circular, semicircular, and rectangular with semicircular ends, equilateral triangular, and square and symmetrical hexagonal cross-sectional areas. These results were separately studied for aspect ratio of different rectangular shapes. Characteristics of fluid were considered at average temperature between outlet and inlet ducts. Results showed that factors such as Reynolds number, cross section, hydraulic diameter, heat flux and aspect ratio were effective on entropy generation, and these effects are more evident than heat flux and occur more in high heat fluxes. Considering the performed comparisons, it seems that semicircular and circular cross section generates less entropy than other cross sections.

Numerical Study of Entropy Generation with Nonlinear Thermal Radiation on Magnetohydrodynamics non-Newtonian Nanofluid Through a Porous Shrinking Sheet

  • Bhatti, M.M.;Abbas, T.;Rashidi, M.M.
    • Journal of Magnetics
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    • v.21 no.3
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    • pp.468-475
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    • 2016
  • In this article, entropy generation on MHD Williamson nanofluid over a porous shrinking sheet has been analyzed. Nonlinear thermal radiation and chemical reaction effects are also taken into account with the help of energy and concentration equation. The fluid is electrically conducting by an external applied magnetic field while the induced magnetic field is assumed to be negligible due to small magnetic Reynolds number. The governing equations are first converted into the dimensionless expression with the help of similarity transformation variables. The solution of the highly nonlinear coupled ordinary differential equation has been obtained with the combination of Successive linearization method (SLM) and Chebyshev spectral collocation method. Influence of all the emerging parameters on entropy profile, temperature profile and concentration profile are plotted and discussed. Nusselt number and Sherwood number are also computed and analyzed. It is observed that entropy profile increases for all the physical parameters. Moreover, it is found that when the fluid depicts non-Newtonian (Williamson fluid) behavior then it causes reduction in the velocity of fluid, however, non-Newtonian behavior enhances the temperature and nanoparticle concentration profile.

Entropy analysis in a cilia transport of nanofluid under the influence of magnetic field

  • Abrar, Muhammad N.;Haq, Rizwan Ul;Awais, Muhammad;Rashid, Irfan
    • Nuclear Engineering and Technology
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    • v.49 no.8
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    • pp.1680-1688
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    • 2017
  • In this study, analysis is performed on entropy generation during cilia transport of water based titanium dioxide nanoparticles in the presence of viscous dissipation. Moreover, thermal heat flux is considered at the surface of a channel with ciliated walls. Mathematical formulation is constructed in the form of nonlinear partial differential equations. Making use of suitable variables, the set of partial differential equations is reduced to coupled nonlinear ordinary differential equations. Closed form exact solutions are obtained for velocity, temperature, and pressure gradient. Graphical illustrations for emerging flow parameters, such as Hartmann number (Ha), Brinkmann number (Br), radiation parameter (Rn), and flow rate, have been prepared in order to capture the physical behavior of these parameters. The main goal (i.e., the minimizing of entropy generation) of the second law of thermodynamics can be achieved by decreasing the magnitude of Br, Ha and ${\Lambda}$ parameters.

ONLINE TEST BASED ON MUTUAL INFORMATION FOR TRUE RANDOM NUMBER GENERATORS

  • Kim, Young-Sik;Yeom, Yongjin;Choi, Hee Bong
    • Journal of the Korean Mathematical Society
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    • v.50 no.4
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    • pp.879-897
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    • 2013
  • Shannon entropy is one of the widely used randomness measures especially for cryptographic applications. However, the conventional entropy tests are less sensitive to the inter-bit dependency in random samples. In this paper, we propose new online randomness test schemes for true random number generators (TRNGs) based on the mutual information between consecutive ${\kappa}$-bit output blocks for testing of inter-bit dependency in random samples. By estimating the block entropies of distinct lengths at the same time, it is possible to measure the mutual information, which is closely related to the amount of the statistical dependency between two consecutive data blocks. In addition, we propose a new estimation method for entropies, which accumulates intermediate values of the number of frequencies. The proposed method can estimate entropy with less samples than Maurer-Coron type entropy test can. By numerical simulations, it is shown that the new proposed scheme can be used as a reliable online entropy estimator for TRNGs used by cryptographic modules.

Thermal Characteristics of Cross-flow Small Scale Heat Exchanger (소형 직교류 열교환기의 열적 특성에 관한 연구)

  • Kum, Sungmin;Yu, Byeonghun;Rhee, Kwan-Seok;Lee, Seungro
    • Journal of Energy Engineering
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    • v.22 no.1
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    • pp.44-50
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    • 2013
  • This study was experimentally investigated NOx and CO emissions characteristics with various equivalence ratios using premixed type of burner installed small heat exchanger. The effectiveness of heat exchanger and the entropy generation number were also calculated. As results, the heat transfer rate increases with increasing equivalence ratio due to increase the flame temperature. According to the emission characteristics and the effectiveness, the optimal operating equivalence ratio is 0.75 in the range of this experiment. Consequently, the area of the heat exchanger should be increased to reduce the entropy generation number and to increase the effectiveness.

Review of Entropy Wave in a Gas Turbine Combustor (가스터빈 연소기에서 엔트로피파에 대한 고찰)

  • Kim, Daesik;Yoon, Myunggon
    • Journal of the Korean Society of Combustion
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    • v.23 no.1
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    • pp.28-35
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    • 2018
  • Entropy waves(or hot spots) in a gas turbine combustor are generated by irregular heat release from flames, then can be coupled with acoustic waves when they are accelerated at the exit of the combustor. This coupling mechanism between the entropy and the acoustic waves is generally known to be one of the triggers for combustion instability, which is commonly called "indirect" combustion noise. This paper reviews the fundamental theories on generation, propagation, and coupling with acoustic field of entropy waves and recent research results on the indirect combustion noise for gas turbine combustors.

Chinese Prosody Generation Based on C-ToBI Representation for Text-to-Speech (음성합성을 위한 C-ToBI기반의 중국어 운율 경계와 F0 contour 생성)

  • Kim, Seung-Won;Zheng, Yu;Lee, Gary-Geunbae;Kim, Byeong-Chang
    • MALSORI
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    • no.53
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    • pp.75-92
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    • 2005
  • Prosody Generation Based on C-ToBI Representation for Text-to-SpeechSeungwon Kim, Yu Zheng, Gary Geunbae Lee, Byeongchang KimProsody modeling is critical in developing text-to-speech (TTS) systems where speech synthesis is used to automatically generate natural speech. In this paper, we present a prosody generation architecture based on Chinese Tone and Break Index (C-ToBI) representation. ToBI is a multi-tier representation system based on linguistic knowledge to transcribe events in an utterance. The TTS system which adopts ToBI as an intermediate representation is known to exhibit higher flexibility, modularity and domain/task portability compared with the direct prosody generation TTS systems. However, the cost of corpus preparation is very expensive for practical-level performance because the ToBI labeled corpus has been manually constructed by many prosody experts and normally requires a large amount of data for accurate statistical prosody modeling. This paper proposes a new method which transcribes the C-ToBI labels automatically in Chinese speech. We model Chinese prosody generation as a classification problem and apply conditional Maximum Entropy (ME) classification to this problem. We empirically verify the usefulness of various natural language and phonology features to make well-integrated features for ME framework.

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