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Authors analyze the structure of jet impingement systems used for computer cooling. We propose the algorithm for optimal synthesis of such systems. The total heat transfer coefficient is being minimized in this process. It corresponds to the minimization of the heat transfer surface when the heat flux is given. Authors show that the optimal sequenc...
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Compressor cooling is a promising method for increasing the efficiency of aero engines. This paper shows that the application of this method is not limited to the thermodynamic effect of extracting the net heat flow, but also extends to the heat-flux distribution provided by the cooling. To demonstrate this, we conducted an extensive numerical stud...
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Searching optimal piston motion path (OPMP) by using optimal control theory for various thermal cycles is an important task in finite time thermodynamics. Some optimization objectives have been used in this type of researches, including maximum work output (MWO) and minimum entropy generation (MEG). This paper introduces maximum ecological function (MEF) into OPMP problem for light-driven engine (LDE) with generalized radiative heat transfer law (HTL) [q∝Δ(Tn)]. The LDE is with working fluid of reacting system [A]⇌[B] and irreversibilities of piston friction and heat conduction. Numerical examples of OPMPs at MEF with Newtonian (n=1), linear phenomenological (n=−1) and radiative (n=4) HTLs are provided. The results are compared with those obtained by MWO and MEG objectives as well as different HTLs. Utilizing MEF as objective can effectively accomplish entropy generation reduction with a little decrease in work output. Time-parametrized piston velocity, working fluid temperature and piston position for MEF are situated between those for MEG and MWO. Moreover, OPMPs for MEF with different HTLs are also quite different. Although all of the values of ecological function are negative for three special HTLs, work output and ecological function decrease with the increase in n, and entropy generation increases when n increases.
Applying optimal control theory and finite time thermodynamics, a practical Otto cycle heat engine with friction, pressure drop and heat transfer losses is studied. The maximum ecological function is taken as optimization objective, and the optimal piston motion configuration of the Otto cycle is obtained with the Newton’s heat transfer law between the working fluid and the environment. The fuel consumption and the total cycle time are fixed in the optimization. The optimal piston motion laws corresponding to the maximum ecological function configuration when the piston motion accelerations are unconstrained and constrained are obtained, respectively. By numerical examples, the piston motion optimal configurations under different optimization objectives and heat transfer laws are compared.
A new engine patent was awarded to Meletis and Georgiou in 1998. The engine is with vane rotor and the rotor is fully balanced and symmetric. It also has an exhaust gas recirculation (EGR) process. Symmetric rotor mechanism leads much smother running, and EGR process makes working fluid (WF) preheated before entering to compression stage which provides very high temperature after compression so that the compression ignition can be implemented. An irreversible (practical) Meletis–Georgiou heat engine cycle (IMGC) model with irreversible heat transfer loss (IHTL) as well as internal irreversibility loss (IIL) is built by applying finite-time thermodynamic theory. A non-linear relation between specific heat (NLRSH) of WF and WF’s temperature is considered. Analytical expressions of output work and thermal efficiency versus compression ratio (CPR) of the IMGC are derived. Performance analyses and optimizations of the IMGC are done using numerical calculations. Both of output work and thermal efficiency of the IMGC with NLRSH of WF and its temperature are larger than those with constant specific heat of WF at the same CPR. There are an optimal CPR make output work approaches maximum and another optimal CPR make thermal efficiency approaches maximum. The range of maximum output and maximum thermal efficiency gives the design optimization criterion for the IMGC, which means the thermodynamic trade-off optimization with the two performance indicators for the IMGC. Effect features of IHTL, IIL, NLRSH and other parameters on the optimal performances and optimization criterion are analyzed.
