Search

Thermal management is becoming ever more important in passenger vehicles in the trend of vehicle electrification. Even though most of the passenger vehicles still have relatively conventional thermal management systems, advanced technologies have been increasingly developed. The internal combustion engine have had the central role in thermal management but due to the powertrain hybridization and electrification, the engines are nowadays more efficient, smaller in size, and running less frequently. Especially for plug-in hybrid and electric vehicles, engines are not always used or not even available, and, thus, there is no excess heat readily available. This paper reviews the present technology for the thermal management of electrified powertrains in passenger vehicles. In this context, thermal management takes into account the cooling and heating systems for the powertrain components, and different methods to develop and improve thermal systems efficiency. This paper investigates the recent technology advances for improving energy efficiency of thermal systems. The research focus is on the hybrid and electric vehicles and especially on the challenges of improving thermal energy efficiency and performance.

[EN]A relationship between stability and self-optimization is found for weakly dissipative heat devices. The effect of limited control on operation variables around an steady state is such that, after instabilities, the paths toward relaxation are given by trajectories stemming from restitution forces which improve the system thermodynamic performance (power output, efficiency, and entropy generation). Statistics over random trajectories for many cycles shows this behavior as well. Two types of dynamics are analyzed, one where an stability basin appears and another one where the system is globally stable. Under both dynamics there is an induced trend in the control variables space due to stability. In the energetic space this behavior translates into a preference for better thermodynamic states, and thus stability could favor self-optimization under limited control. This is analyzed from the multiobjective optimization perspective. As a result, the statistical behavior of the system is strongly influenced by the Pareto front (the set of points with the best compromise between several objective functions) and the stability basin. Additionally, endoreversible and irreversible behaviors appear as very relevant limits: The first one is an upper bound in energetic performance, connected with the Pareto front, and the second one represents an attractor for the stochastic trajectories, Junta de Castilla y León, SA017P17 ; Universidad de Salamanca, 2017/X005/1 ; National Natural Science Foundation of China, 11405032

Classical and quantum electronic circuits provide ideal platforms to investigate stochastic thermodynamics and they have served as a stepping stone to realize Maxwell's demons with highly controllable protocols. In this article we first review the central thermal phenomena in quantum nanostructures. Thermometry and basic refrigeration methods will be described as enabling tools for thermodynamics experiments. Next we discuss the role of information in thermodynamics which leads to the concept of Maxwell's demon. Various Maxwell's demons realized in single-electron circuits over the past couple of years will be described. Currently true quantum thermodynamics in superconducting circuits is in focus of attention, and we end the review by discussing the ideas and first experiments in this exciting area of research., 21 pages, 6 figures + 5 pages, 2 figures

[EN]The connection between Carnot-like and low-dissipation refrigerators is proposed by means of their entropy generation and the optimization of two uni ed, compromise-based gures of merit. Their optimization shows that only a limited set of heat transfer laws in the Carnot-like model are compatible with the results stemming from the low-dissipation approximation, even though there is an agreement of the related physical spaces of variables. A comparison between two operation regimes and relations among entropy generation, e ciency, cooling-power and power-input are ob- tained, with emphasis on the role of dissipation symmetries. The results extend previous ndings for heat engines at maximum power conditions., CONACYT-M EXICO; Junta de Castilla y Leon under project SA017P17.

The trade-off between large power output, high efficiency and small fluctuations in the operation of heat engines has recently received interest in the context of thermodynamic uncertainty relations (TURs). Here we provide a concrete illustration of this trade-off by theoretically investigating the operation of a quantum point contact (QPC) with an energy-dependent transmission function as a steady-state thermoelectric heat engine. As a starting point, we review and extend previous analysis of the power production and efficiency. Thereafter the power fluctuations and the bound jointly imposed on the power, efficiency and fluctuations by the TURs are analyzed as additional performance quantifiers. We allow for arbitrary smoothness of the transmission probability of the QPC, which exhibits a close to step-like dependence in energy, and consider both the linear and the non-linear regime of operation. It is found that for a broad range of parameters, the power production reaches nearly its theoretical maximum value, with efficiencies more than half of the Carnot efficiency and at the same time with rather small fluctuations. Moreover, we show that by demanding a non-zero power production, in the linear regime a stronger TUR can be formulated in terms of the thermoelectric figure of merit. Interestingly, this bound holds also in a wide parameter regime beyond linear response for our QPC device., Comment: To be submitted to Entropy, Special Issue "Quantum Transport in Mesoscopic Systems", comments are welcome

Quantum thermodynamics addresses the emergence of thermodynamic laws from quantum mechanics. The viewpoint advocated is based on the intimate connection of quantum thermodynamics with the theory of open quantum systems. Quantum mechanics inserts dynamics into thermodynamics, giving a sound foundation to finite-time-thermodynamics. The emergence of the 0-law, I-law, II-law and III-law of thermodynamics from quantum considerations is presented. The emphasis is on consistency between the two theories, which address the same subject from different foundations. We claim that inconsistency is the result of faulty analysis, pointing to flaws in approximations.

Combustion simulation in two-stroke engines becomes necessary not only for engine performance prediction but also for scavenge evaluation, since in-cylinder pressure and temperature are highly influenced by combustion process evolution. Combustion simulation by using a Wiebe function is appropriate to be included in a 1D engine code for providing design criteria with fast and accurate calculations; the main drawback is the determination of the four Wiebe parameters needed to build up the in-cylinder heat release. This paper deals with a detailed methodology for heat release determination in two-stroke engines under a wide range of running conditions; obtained empirical data will serve for building ad-hoc Wiebe functions, whose four parameters will be finally correlated with engine related parameters derived from 1D simulations. Two different engines, with three exhaust systems each, varying engine speed and spark-ignition timing were used to obtain correlations far from particular situations. A multiple regression analysis stated that charge density, residual gas fraction, spark timing and mean piston speed were the significant engine parameters that influence on Wiebe parameters. Finally, two scenarios were considered regarding Wiebe parameters: (a) specific correlations different for each engine gave coefficient of multiple determination values higher than 98% when predicting indicated mean effective pressure, (b) a global correlation used for both engines provided R2 values of 93% in the 50 cc and 91% in the 125 cc engine. © 2010 Elsevier Ltd. All rights reserved.

The fuel used in combustion applications has significant influence on irreversibility generation and hence the exergetic efficiency of the system. This work discusses a method of estimating the availability destructions and exergetic efficiencies of combustion for different classes of fuels viz. hydrogen, hydrocarbons, alcohols and biodiesel surrogates. A ranking of these fuels is presented based on their exergetic efficiencies during isobaric and isochoric combustion. It is observed that availability destruction is greater for heavier hydrocarbon fuels and oxygenated fuels with higher oxygen fraction. Though unsaturated hydrocarbon fuels are associated with lower availability destruction, they result in poor exergetic efficiency as a significant fraction of the fuel availability is lost in the products. Hydrogen and acetylene are identified as the fuels with maximum and minimum exergetic efficiencies respectively. Optimum exergetic efficiency is obtained for reactant mixtures on the leaner side of fuel-air stoichiometry. Availability destruction increases with exhaust gas recirculation (EGR) and decreases with oxygen enrichment of the supplied air. However, oxygen enrichment entails significant chemical availability losses and lowers exergetic efficiency. Preheating the reactants is found to be effective in mitigating availability destruction. � 2010 Elsevier Ltd. All rights reserved.

[EN] The present study tries to be a contribution for the development of more precise theoretical models for predicting the dissipation of heat through the combustion chamber walls of reciprocating (internal combustion) IC engines. A fast response thermocouple was embedded in the combustion chamber of a single cylinder engine to measure instantaneous wall temperatures. The heat flux was obtained by solving the one-dimensional transient energy equation with transient boundary conditions using the Fast Fourier Transform. The engine was tested under different operating conditions to evaluate the sensitivity of the measurement procedure to variations of three relevant combustion parameters: injection pressure, air temperature and oxygen concentration at the intake. The local heat flux obtained was compared with other relevant parameters that characterize the thermal behaviour of engines, showing, in most of the cases, correlation among them. The results showed that the instantaneous heat flux through the walls and hence the local wall temperatures are strongly affected by the ignition delay and the start of combustion. © 2010 Elsevier Ltd.

The goal of this comment note is to express my concerns about the recent paper by Tian Zhao et al. (Entropy 2018, 20, 542). It is foreseen that this comment will stimulate a fruitful discussion of the issues involved. The principle of the least thermodynamic action is applicable for the analysis of the Carnot cycle using the entropy (not heat) generation extrema theorem. The transversality conditions of the variational problem provide the rectangular shape of the ST diagram for the Carnot cycle.

In this work, biogas was used in a compression ignition (CI) engine in the homogeneous charge compression ignition (HCCI) mode as well as in the dual-fuel mode together with diesel. In the HCCI mode, the charge temperature and amount of diesel injected into the intake manifold were used to control combustion. The presence of carbon dioxide in biogas suppresses the high heat release rates normally encountered in neat-diesel-fuelled HCCI engines. Efficiencies close to diesel operation together with extremely low levels of nitric oxide (NO) and smoke were attained in a brake mean effective pressure (BMEP) range from 2.5 bar to 4 bar in the biogas-diesel homogeneous charge compression ignition (BDHCCI) mode. Proper control over the charge temperature was essential. Thermal efficiency was higher and NO, hydrocarbon, carbon monoxide, and smoke levels were lower than in the biogas-diesel dual-fuel mode. Thus, the BDHCCI mode is a viable option for using biogas in CI engines in the medium-load ranges. Operation of the engine in the CI mode with diesel below a BMEP of 2.5 bar, then in the HCCI mode up to a BMEP of 4 bar, and in the dual-fuel mode at higher BMEPs could lead to good overall performance and low emissions. � IMechE 2009.

Ingeniería industrial

Even if not so ancient, the history of the heat engine efficiency at maximum power expression have been yet turbulent. More than a decade after the publication of the seminal article by Curzon and Ahlborn in 1975, one's rediscovered two older works by Chambadal and Novikov, both dating from 1957. Then, some years ago, the name of Yvon arose from a textual reference to this famous relation in a conference article published in 1955. Thanks to an historical study of French written books not anymore published for a long time, and since never translated in other languages, we bring to light in this paper that this relation was actually firstly proposed by Henri B. Reitlinger in 1929., Comment: 6 pages, 3 figures

Experimental results are presented that describe the effects of embedded, longitudinal vortices on heat transfer and film injectant downstream of two staggered rows of film cooling holes with compound angle orientations. Holes are oriented so that their angles with respect to the test surface are 30 deg in a spanwise/normal plane projection, and 35 deg in a streamwise/normal plane projection. A blowing ratio of 0.5, nondimensional injection temperature parameter θ of about 1.5, and free-stream velocity of 10 m/s are employed. Injection hole diameter is 0.945 cm to give a ratio of vortex core diameter to hole diameter of 1.6–1.67 just downstream of the injection holes (x/d = 10.2). At the same location, vortex circulation magnitudes range from 0.15 m2/s to 0.18 m2/s. By changing the sign of the angle of attack of the half-delta wings used to generate the vortices, vortices are produced that rotate either clockwise or counterclockwise when viewed looking downstream in spanwise/normal planes. The most important conclusion is that local heat transfer and injectant distributions are strongly affected by the longitudinal embedded vortices, including their directions of rotation and their spanwise positions with respect to film injection holes. Differences resulting from vortex rotation are due to secondary flow vectors, especially beneath vortex cores, which are in different directions with respect to the spanwise velocity components of injectant after it exits the holes. When secondary flow vectors near the wall are in the same direction as the spanwise components of the injectant velocity (clockwise rotating vortices R0–R4), the film injectant is more readily swept beneath vortex cores and into vortex upwash regions than for the opposite situation in which near-wall secondary flow vectors are opposite to the spanwise components of the injectant velocity (counter-clockwise rotating vortices L0–L4). Consequently, higher St/St0 are present over larger portions of the test surface with vortices R0–R4 than with vortices L0–L4. These disruptions to the injectant and heat transfer from the vortices are different from the disruptions that result when similar vortices interact with injectant from holes with simple angle orientations. Surveys of streamwise mean velocity, secondary flow vectors, total pressure, and streamwise mean vorticity are also presented that further substantiate these findings.

While cooling of the microchip continues to receive significant interest in most electronic devices, portable platforms such as notebooks, multi-use cellular phones, and ultra-mobile personal computers (PCs) present unique thermal management challenges as well. Cooling non-processor components such as wireless devices and the skin of the device are becoming the important thermal management drivers, and volume and power constraints are limiting the practicality of including larger or additional conventional fans. Ionic wind engines are devices which generate air flow with no moving parts, and feature low power consumption and a small volumetric footprint. An ionic wind is produced when positive air ions are accelerated in a particular direction by an electric field, and exchange momentum with neutral air molecules, thus generating a body force on the air. In the presence of an existing bulk flow, an ionic wind distorts the boundary layer and increases the local cooling effect at a heated wall. A free-standing ionic wind engine with an electrode gap of approximately 1 mm has been constructed. Experiments show that the ionic wind engine can enhance the local heat transfer coefficient of a low-speed flow by as much as 50%. The impact of the ionic wind is shown to increase with current and decrease as the bulk flow increases.

In this paper we analyze in depth the lost work in an irreversible process (i.e. W-Lost = W-Rev - W-Irrev). This quantity is also called 'degraded energy' or 'energy unavailable to do work'. Usually in textbooks one can find the relation W-Lost T Delta S-U, which, for many processes, is not suitable for evaluation of the lost work. Here we find for W-Lost a more general relation in terms of internal and external entropy production, pi(int) and pi(ext), quantities which also enable the Clausius inequality to be written in a simple form. Examples are given for elementary processes.

The paper presents an integrated methodology for both the design optimization and the performance evaluation of free-piston Stirling engines (FPSE) suitable for space applications. In particular, the prediction of the dynamic behaviour is the problem here considered in more detail. To this aim, a stability criterion is established, based on the assumption of a thermodynamic reference model, able to take Into account the main energy losses. In this way, it is possible to define useful "design rules" that must be observed In order to guarantee a correct behaviour of the engine. In the reported design example, such behaviour is verified by means of a previously developed code which performs a dynamic and thermo-dynamic simulation.

The theoretical investigation includes the design of a simulation program in EES, Matlab or similar of the Stirling engine. Initially an isothermal model is made(constant temperatures in cylinder volumes. hot and cold heat exchanger and regenerator). After that a new model is made, which differs from the former by having adiabatic cylinder volumes. When the basic model is working properly, heat transfer and flow losses in the heat exchangers are included.For the experimental investigation, an existing 9 kW Stirling engine in the laboratory is used. Data acquisition and measuring equipment on the engine is part of the project. Experiments are made using different workin gases in the engine (Helium, Nitrogen, Hydrogen, Carbon Dioxide, ...) Part of the project is intallation of suitable data acquisition and making the engine control system work properly. Finally results from calculations are compared with results from measurements in the laboratory. Outgoing

To simplify analysis of an internal combustion engine, air-standard cycles are conceived. Air is assumed to behave like an ideal gas. In practice, air-standard analysis provides useful indication of the trends that the engine is likely to follow. Air-standard Otto and Joule-Brayton cycles are bona fide assumption and cannot represent the complex combustion process occurring in the internal combustion engines. In this paper, the complex combustion process is represented by a parameter called fuel-flame temperature. The effect of combustion on the thermoeconomic performances of Otto and Joule-Brayton engines are studied. It is observed that the efficiency at maximum power is less than the Curzon-Ahlbom efficiency. The economic performance of the engine deteriorates due to combustion. The efficiency of the engine corresponds to maximum specific-power output, depends not only on the fuel-flame temperature, but also on the specific heats of the air and fuel. Ideal gas assumption of the working fluid is relaxed in this paper. Although somewhat idealized, the effect of combustion on the performance and economics of the internal combustion engines gives a reasonable design goal and better understanding of the real-heat engine. (C) 1998 , Ltd.

Analysis of ideal internally reversible regenerative heat engines is presented in this paper, from finite resources point of view. Thermo-economic performances of a regenerative heat engine depend on the nature of polytropic processes and oil the efficiency of regeneration. The study of the effects of regeneration efficiency, on the resource allocation for optimal performance of generalized regenerative engine, is also presented in this paper. Thermo-economic performances of an internally reversible regenerative heat engine, with perfect regeneration, are equivalent to those of internally reversible Carnot, Otto and Joule-Brayton engines. Concurrent employment of the first and the second laws ensure the optimal allocation of finite resources simultaneously with minimization of entropy generation. The operating regions both for operation and design of such regenerative engines are identified from the power-efficiency characteristic. The results are derived without assuming any particular equation of state associated with the working fluid.

International audience