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81.
声制冷机是一种新型制冷机,具有无机械运动部件,可靠性高寿命长,采用惰性气体为工质无污染等优点.驻波型热声制冷机的声功泵热效应是不可逆过程,内部不可逆损失导致热声制冷机效率偏低,制约了热声制冷机的发展和应用.本文研究了线性范围内驻波型制冷机换热器和回热器内的可压缩振荡流动与传热过程的熵产,分析了板间距,振荡频率和温度梯度对熵产的影响。 相似文献
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利用数值模拟的方法,通过改变冲击雷诺数Rej(20000-35000)、旋转数Ro(0-0.0117)等参数,分析旋转条件下半受限单孔冲击射流的流动和换热特性,讨论了旋转对冲击射流的流场结构和换热特性的影响.研究结果表明:冲击射流在离心力和哥氏力的共同作用下发生弯曲,造成冲击靶面上的冲击斑随着旋转数Ro的增加而不断偏移,显著影响了冲击的冷却效果.冲击靶面的平均Nu数随着冲击雷诺数Rej的增加而增加;当旋转数Ro增加时,冲击靶面的平均Nu数先增加,后减小,然后再增加.计算结果和试验结论基本一致. 相似文献
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C. Monthus T. Garel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):39-45
The directed polymer in a 1+3 dimensional
random medium is known to present a disorder-induced phase
transition. For a polymer of length L, the high temperature
phase is characterized by a diffusive behavior for the end-point
displacement R2 ∼L and by free-energy fluctuations of order
ΔF(L) ∼O(1). The low-temperature phase is characterized by
an anomalous wandering exponent R2/L ∼Lω and
by free-energy fluctuations of order ΔF(L) ∼Lω
where ω∼0.18. In this paper, we first study the scaling
behavior of various properties to localize the critical temperature
Tc. Our results concerning R2/L and ΔF(L) point towards
0.76 < Tc ≤T2=0.79, so our conclusion is that Tc is equal
or very close to the upper bound T2 derived by Derrida and
coworkers (T2 corresponds to the temperature above which the ratio
remains finite as L ↦
∞). We then present histograms for the free-energy, energy and
entropy over disorder samples. For T ≫Tc, the free-energy
distribution is found to be Gaussian. For T ≪Tc, the free-energy
distribution coincides with the ground state energy distribution, in
agreement with the zero-temperature fixed point picture. Moreover the
entropy fluctuations are of order ΔS ∼L1/2 and follow a
Gaussian distribution, in agreement with the droplet predictions,
where the free-energy term ΔF ∼Lω is a near
cancellation of energy and entropy contributions of order L1/2. 相似文献
89.
X. Zhang G. Hu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):389-393
In this work, we introduce a spatiotemporal modulation for
excitability into an excitable medium, the Barkley model. The
modulation can make the spiral wave tip meandering. Various types of
periodic spiral and quasiperiodic meandering spiral motions can be
observed numerically by varying the modulation. And the theoretical
analysis for the conditions of Hopf bifurcation, based on an
ordinary-differential-equation (ODE) model, is applied to well
explain the rich behaviors of numerical simulations. 相似文献
90.
P. Ravi 《Molecular physics》2017,115(14):1657-1666
Methyl-, nitro- and N→oxide substituted triazolones are of interest in the contest of high-energy density compounds and have been found to have true local energy minima at the B3LYP/aug-cc-pVDZ level. The optimised structures, harmonic frequencies and thermodynamic values for all the model molecules have been obtained in their ground state. The velocity of detonation (D) and detonation pressure (P) have been evaluated by the Kamlet–Jacob equations using the crystal density and the heat of explosion. The estimated performance properties are higher (D = 9.92–10.27 km/s, P = 48.10–52.52 GPa) compared with 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s, P = 42.0 Gpa). The higher densities are possibly due to the intramolecular hydrogen bonds and the layered structures in the crystal lattice. We speculate that the calculated heat of explosion and the density are for the gas phase compounds and in the reality they should be for the solid phase which would diminish the magnitude of the calculated values. The –N→O and –NO2 group leads to the desirable consequences of higher heat of explosion and diminished sensitivities. The substituting of N–H hydrogen atom(s) of triazolones for a –CH3 group decreases melting point, heat of formation and density; however, the methyl group increases the thermal stability. 相似文献