The regenerative cooling technique with endothermic reactions is prospective for scramjet engines, in which the convective heat transfer characteristics are necessary for the thermal system design. In this work, the turbulent heat transfer characteristics of hydrocarbon fuels with endothermic chemical reactions were experimentally and numerically investigated. Three kinds of surrogates and two different pressures were employed to obtain various chemical endotherms, and the distributions of physical properties and dimensionless parameters were analyzed in the chemical region. Results showed that endothermic chemical reactions improved the convective heat transfer performance, even though the variations of fluid Reynolds number and Prandtl number brought by chemistry were small. Then, a dimensionless parameter was proposed to describe the proportion of chemical endotherm capacity. The numerical results revealed that the natural logarithm of Nusselt number enhancement changed linearly with the proposed dimensionless parameter, and the slopes were irrelevant to reactant types or chemical conditions. Last, by modifying the Dittus-Boelter correlation, a novel Nusselt number correlation was put forward for the endothermic reacting flow. Based on the analysis of the existing data and the formula form, continuously increasing the fuel chemical endotherm might bring a smaller benefit of Nusselt number augmentation.
To solve the heat management problem of supersonic aircraft, endothermic hydrocarbon fuels (EHFs) have been developed as both a coolant and a propellant. The pseudohomogeneous catalyst is an efficient way to improve the heat sink of EHFs. In this work, hydrocarbon soluble macrocyclic calixarene compound C-undecyl calix[4]2-(propylsulfanylmethyl)-resonrcinarene (C11–SC3) was synthesized and used as a stabilizer for hydrocarbon-dispersed Pt nanoparticles (Pt@C11–SC3). The morphological characterization results indicate that Pt nanoparticles are encapsulated by the calixarene, which helps the fabrication of ultrasmall Pt@C11–SC3. Ethylcyclohexane (ECH) was selected as a model substrate of EHFs to construct the Pt@C11–SC3/ECH nanofluid system for pseudohomogeneous catalytic cracking. The cracking test of the Pt@C11–SC3/ECH nanofluid was carried out in a batch reactor and a flow reactor under constant volume and pressure conditions. The distribution of cracking products displayed a significant improvement in terms of cracking conversion and a preferred heat absorbed reaction pathway, leading to a higher heat sink. There was a 16% maximum increase in heat sink in the constant pressure cracking tests with the addition of 0.01 wt % Pt@C11–SC3 at 700 °C. It provides a helpful method for heat sink enhancement of EHFs.
Yi Wu,Anqi He,Da Li,Limin Yang,Yizhuang Xu,Yukihiro Ozaki,Isao Noda
This study investigates single-crystal structures of Lu3+/erythritol and nine rare earth–glycerol complexes, revealing deprotonation of normally inert OH groups via μ2-bridging (so-called DIOμ2 phenomenon). The pH drops upon alditol addition correlate with the deprotonation extent, showing increased deprotonation with decreasing lanthanide ionic radius (lanthanide contraction) and exceptionally high deprotonation for Sc3+. In all the rare earth/alditol complexes with the DIOμ2 phenomenon, two μ2-bridges merge into an M2O2 cluster (M is a rare earth ion) that is not very stable due to the Coulombic repulsion between two M3+ and between two O–. To stabilize the M2O2 cluster, the formation of more auxiliary five- and six-membered chelating rings between rare earth ions and alditol ligands is needed. Increment of the number of auxiliary five- and six-membered chelating rings favors the DIOμ2 reaction. This is the reason why the DIOμ2 reaction shows a progressively enhanced tendency when the alditol ligands change from myo-inositol to glycerol to erythritol and galactitol. The reaction is endothermic, as an increased temperature enhances deprotonation. The above results may be useful in the rational design of catalysts that efficiently activate inert OH bonds and facilitate related chemical processes.
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