The engine performance impact of soybean oil ethyl ester blending into diesel fuel was analyzed employing heat release analysis, in-cylinder exergy balances and dynamometric tests. Blends with ...concentrations of up to 30% of soybean oil ethyl ester in volume were used in steady-state experiments conducted in a high speed turbocharged direct injection engine. Modifications in fuel heat value, fuel–air equivalence ratio and combustion temperature were found to govern the impact resulting from the addition of biodiesel on engine performance. For the analyzed fuels, the 20% biodiesel blend presented the best results of brake thermal efficiency, while the 10% biodiesel blend presented the best results of brake power and
sfc (specific fuel consumption). In relation to mineral diesel and in full load conditions, an average increase of 4.16% was observed in brake thermal efficiency with B20 blend. In the same conditions, an average gain of 1.15% in brake power and a reduction of 1.73% in
sfc was observed with B10 blend.
Passive cooling of electronic components by natural convection heat transfer is the least expensive, quietest and most reliable method of heat rejection. However, some characteristics intrinsic to ...the phenomenon, such as a non-linear interaction between heat sources difficult its practical application. The objective of this work is to study the natural convection heat transfer optimization through genetic algorithms. Four cases were studied: one heat source, two heat sources with same dissipation rate, and two heat sources with different dissipation rates on a vertical wall. The results showed good agreement with literature and confirmed the methodology as computationally feasible for the optimal location of heat sources in a vertical wall.
Recently, a group of researchers proposed the concept of entransy by analogy with the electrical energy stored in a capacitor, the entransy being a measure of the ability of a body or a system to ...transfer heat. In comparative terms, the entransy dissipation rate is related with the loss of heat transfer ability just like the exergy destruction rate is proportional to the loss of work ability, being these losses caused by the irreversibilities related to the thermodynamic processes. Some authors have questioned the need for the concept of entransy, claiming that this concept is only an extension of a well established theory of heat transfer. The objective of this work is show the equivalence between the application of the concepts of entransy and entropy generation rate, which can be verified using various application examples. The application examples used here are the thermodynamic modeling of three physical models of solar energy collectors and a physical model of a sensible heat storage system. Analytical results are shown and compared. The results showed that the application of the concept of entransy provided identical expressions obtained by the concept of entropy generation, indicating a duplication of concepts.
This paper presents a new arrangement for the indicating measurement system utilized in the study of internal combustion engines. In this experimental configuration, the current polarized by a ...piezoelectric pressure transducer is converted into an analog signal proportional to the cylinder pressure variation rate, which constitutes the primary information for combustion heat release analysis. The proposed technique reduces the uncertainty in the pressure derivative data, providing more accurate heat release results than those obtained with the traditional transducer signal conditioning procedure, which requires the numerical derivation of in-cylinder pressure data supplied by a charge amplifier.
Laminar forced convection inside tubes of various cross-section shapes is of interest in the design of a low Reynolds number heat exchanger apparatus. Heat transfer to thermally developing, ...hydrodynamically developed forced convection inside tubes of simple geometries such as a circular tube, parallel plate, or annular duct has been well studied in the literature and documented in various books, but for elliptical duct there are not much work done. The main assumption used in this work is a laminar flow of a power flow inside elliptical tube, under a boundary condition of first kind with constant physical properties and negligible axial heat diffusion (high Peclet number). To solve the thermally developing problem, we use the generalized integral transform technique (GITT), also known as Sturm–Liouville transform. Actually, such an integral transform is a generalization of the finite Fourier transform where the sine and cosine functions are replaced by more general sets of orthogonal functions. The axes are algebraically transformed from the Cartesian coordinate system to the elliptical coordinate system in order to avoid the irregular shape of the elliptical duct wall. The GITT is then applied to transform and solve the problem and to obtain the once unknown temperature field. Afterward, it is possible to compute and present the quantities of practical interest, such as the bulk fluid temperature, the local Nusselt number and the average Nusselt number for various cross-section aspect ratios.
Professor Adrian Bejan on his 75th birthday Lage, José L.; Worek, William M.; Amon, Cristina H. ...
International communications in heat and mass transfer,
12/2023, Letnik:
149
Journal Article
A thermodynamic analysis (first and second laws) was performed for a coke dry quenching (CDQ) unit with all data obtained in the site and under the unit normal operating conditions. Expressions to ...evaluate the coke specific heat, enthalpy, entropy and physical and chemical exergies, as well as particulate material (dust) formation indices, and the loss of coke mass through chemical reactions, were developed and compared with the literature. The analysis was extended to a coke wet quenching (CWQ) unit, a process still largely used across the world. The procedure is fully described. The comparison between the performances of the CDQ and CWQ processes supports that such analysis can be a useful and accessible tool in the decision making process.
In this work, the flow over a discrete heat source flush mounted on a vertical adiabatic surface is studied. The two- and three-dimensional formulations were adopted in order to compare with the ...results presented in the literature. The flow was assumed incompressible and laminar with constant fluid properties under Boussinesq assumption. The finite volume control method was used for the discretization of the elliptic governing equations. The numerical results presented confirm in part the theoretical behavior and show the existence of a transition between the two- and three-dimensional plume. Additionally, similarity scales for the thermal boundary layer were proposed for the
xy and
zy planes. The presence of this region of transition emphasizes the complexity of this kind of flow, where two- or three-dimensional effects must not be studied separately, mainly on electronic packaging where heat sources are in that transition region.
