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The prediction of the maximum operating temperature in electric machines is very important to ensure that the machine can produce the required power safely. Accurate thermal modeling is required to predict the heat transfer coefficient (HTC) of walls between coolant and heat sources and estimate the temperature in the machine. Analytical calculation of HTC is difficult for sophisticated geometric bodies since the dimensionless correlations are only available for simple geometries. To reduce the effort required to develop a thermal model of the cooling system of an electric machine, a two-way hybrid multiphysics approach using finite-element analysis (FEA) and computational fluid dynamics (CFD) to determine the HTC and evaluate the thermal performance of a liquid-cooled electric machine is presented in this article. In this study, a 60-kW switched reluctance machine (SRM) is used as an example model to evaluate its thermal performance. In the hybrid multiphysics approach, using the HTC estimated by CFD and heat generation in the machine as the inputs, the FEA is used to determine the maximum steady-state temperature in the machine. An analytical approach is also implemented to determine the HTC of the example SRM to correlate with the HTC obtained using a hybrid approach. The analytical HTC is used in FEA to obtain the temperature distribution in the machine. The temperature obtained from hybrid and analytical approaches is compared. The SRM considered in this study is built and tested for different operating points. The machine is tested for a long time to record the steady-state temperature at different operating points. Results obtained from the hybrid approach are validated with the experimental temperature data. [ABSTRACT FROM AUTHOR]

Catalysis of hydrolysis of the P-O(super 5') bond in RNA by ribonucleases results in the deposition of the 2',3'-cyclic phosphodiester intermediate. Catalysis by imidazole buffer or hydroxide ion does not involve an accumulation of the intermediate. 31P NMR spectroscopy reveals that the intermediate is deposited during catalysis by bovine seminal ribonuclease, monomeric bovine pancreatic ribonuclease A, RNase T(sub1) and barnase.

Bovine pancreatic ribonuclease A (RNase A) catalyzes the cleavage of the P-O(5') bond in RNA. Although this enzyme has been the object of much landmark work in bioorganic chemistry, the nature of its rate-limiting transition state and its catalytic rate enhancement had been unknown. Here, the value of k(cat)/K(m) for the cleavage of UpA by wild-type RNase A was found to be inversely related to the concentration of added glycerol. In contrast, the values of k(cat)/K(m) for the cleavage of UpA by a sluggish mutant of RNase A and the cleavage of the poor substrate UpOC(6)H(4)-p-NO(2) by wild-type RNase A were found to be independent of glycerol concentration. Yet, UpA cleavage by the wild-type and mutant enzymes was found to have the same dependence on sucrose concentration, indicating that catalysis of UpA cleavage by RNase A is limited by desolvation. The rate of UpA cleavage by RNase A is maximal at pH 6.0, where k(cat) = 1.4 × 10(3) s(-1) and k(cat)/K(m) = 2.3 × 10(6) M(-1)s(-1) at 25°C. At pH 6.0 and 25°C, the uncatalyzed rate of [5,6-(3)H]Up[3,5,8-(3)H]A cleavage was found to be k(uncat) = 5 × 10(-9) s(-1) (t(1/2) = 4 years). Thus, RNase A enhances the rate of UpA cleavage by 3 × 10(11)-fold by binding to the transition state for P-O(5') bond cleavage with a dissociation constant of <2 × 10(-15) M.