67 research outputs found
Heterogeneous nanofluids: natural convection heat transfer enhancement
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case
Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment
The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment
Epidemiology and genetics of hypertrophic cardiomyopathy
Background: Hypertrophic cardiomyopathy (HCM) is a heart muscle
disorder and is known to be inherited as an autosomal dominant trait.
Mutations in several sarcomeric, cytoskeletal and mitochondrial genes
have been reported in HCM. Though many cases of HCM are being
identified, there is limited data regarding the epidemiology and
genetics of HCM in India. Aim: Therefore the present study is
envisaged at identifying the epidemiological variables in HCM and
fitting a probability model assuming dominant mode of inheritance in
HCM, which may in turn shed light on the heterogeneity of this complex
disorder. Materials AND Methods: The 127 HCM cases were divided into
subtypes based on pattern of hypertrophy. Chi square analysis, odds
ratio, probability, relative frequency, penetrance and heritability
estimates were calculated apart from epidemiological variables.
Results: The HCM subtypes revealed the heterogeneous nature of the
condition suggesting that the genes/mutations involved in their
pathogenesis are different and this is supported by distinctive
differences observed in their probability, heritability and penetrance
estimates apart from epidemiological variables. An increased male
preponderance was observed with the sex ratio being 3.7:1. The age at
onset was found to be more than a decade early in familial cases (30
± 10 yrs) compared to non familial cases (44 ± 14 yrs). Chi
square analysis revealed obstructive HCM to be following autosomal
dominant mode of inheritance where as non-obstructive HCM was
significantly deviating. The level of deviation was significantly high
for the middle onset group compared to early and late onset groups,
therefore this group may be considered as an admixture wherein
genes/gene modifiers and environmental variables may be contributing to
the heterogeneity and this is further supported by odds ratio.
Conclusions: The study thus brings out the complexity of HCM and
suggests that modes of inheritance other than autosomal dominant may be
encountered in a subset of HCM especially in asymmetric septal
hypertrophy, apical, concentric and mid cavity obstruction subsets and
hence a mixed model of inheritance is the best fit for such complex
disorders
Measurement of the Thermal Conductivity of Silicon Dioxide Nanofluid and Development of Correlations
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