The performance of a double tube heat exchanger with V-cut twisted tape inserts (VCTT) and phase change material (PCM) dispersed nanofluid is investigated experimentally. The three water-based Al2O3, PCM, and Al2O3+PCM nanofluid with different concentrations (0.01-0.1% vol.) are used. The impacts of different geometric parameters, i.e., twist ratio (TR), depth ratio (DR) and width ratio (WR) of VCTT inserts on Nusselt number (Nu), friction factor (f) and entropy generation are examined. The outcomes expose that Nu and f increase as particle concentration increases and twisting ratio decreases. A higher Nu and f are generated by a higher DR or a lower WR. In all cases, the entropy generation of nanofluid is found to be lower than that of water. For all working fluids, a rise in TR, a fall in DR, and a rise in WR increases overall entropy generation.
In this paper, we improve earlier bounds on the extremal eigenvalues of positive definite matrices by introducing an increasing function and by considering a vector function of the eigenvalues. For various choices of the monotonic function we are able to obtain bounds for the extremal eigenvalues in terms of the traces of the matrix and its powers. Our bounds are a function of two parameters achieved by using Jensen's inequality. These bounds are relatively simple to compute.
Hot corrosion is a critical problem in a wide range of high-temperature applications. Ni–20Cr alloy is frequently used in such applications owing to its good hot-corrosion resistance. In the current work, thick Ni–20Cr plates in a thickness range of 6–10 mm were fabricated using cold spray-based additive manufacturing (CSAM). High-pressure cold spraying was used with nitrogen as the propellant gas. Pre- (substrate heating, SH) and post-heat treatments (hot isostatic pressing, HIP) were also performed to comprehend the changes in the deposit properties. The deposits were subjected to microstructural and mechanical characterization to explore the potential of cold spraying for CSAM of Ni–20Cr standalone products. The cold-sprayed plates were successfully developed without any oxide formation. HIP treatment was found to be useful to reduce porosity. The cold-sprayed substrate-heated Ni–20Cr deposits exhibited excellent oxidation resistance at a high temperature of 900 °C.
In this work, thick deposits of pure titanium (Ti), with a thickness of around 15 mm, were additively manufactured using high-pressure cold spraying. Nitrogen was employed as the process gas. Subsequently, the deposits were subjected to hot isostatic pressing (HIP). The HIP-treated Ti deposits were analyzed for their metallurgical and mechanical characteristics with the aim of exploring the viability of using cold spraying for the additive manufacturing of Ti components. Moreover, high-temperature cyclic oxidation testing was also performed on the HIP-treated Ti deposit to understand its stability at high temperatures. SEM/EDS showed a dense structure with marginal porosity for the HIP-treated Ti deposits, without any oxide formation, which was further confirmed via XRD analysis. An average microhardness of 214 HV was measured for the HIP-treated Ti deposits, which is close to that of the commercially available bulk titanium (202 HV). The high-temperature oxidation studies revealed that the cold-sprayed HIP-treated Ti has very good oxidation resistance, which could be attributed to the formation of protective titanium dioxide in its oxide scale.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.