Intensification of heat exchanger performance utilizing nanofluids

Heat exchangers are widely utilized in different thermal systems for diverse industrial aspects. The selection of HEx depends on the thermal efficiency, operating load, size, flexibility in operation, compatibility with working fluids, better temperature and flow controls, and comparatively low capital and maintenance costs. Heat transfer intensification of heat exchangers can be fulfilled using passive, active, or combined approaches. Utilizing nanofluids as working fluids for heat exchangers have evolved recently. The performance of heat exchangers employed different nanofluids depends mainly on the characteristics and improvement of thermophysical properties. Regarding the unique behavior of different nanofluids, researchers have attended noteworthy progress. The current study reviews and summarizes the recent implementations carried out on utilizing nanofluids in different types of heat exchangers, including plate heat exchangers, double-pipe heat exchangers, shell and tube heat exchangers, and cross-flow heat exchangers. The results showed that nanofluids with enhanced thermal conductivity, although accompanied by a considerable decrease in the heat capacity and raising viscosity, has resulted in performance enhancement of different heat exchangers types. So, the performance evaluation criterion that combines the thermal enhancement and increases the pumping power for any type of heat exchangers is requisite to evaluate the overall performance properly. The challenges and opportunities for future work of heat transfer and fluid flow for different types of heat exchangers utilizing nanofluids are discussed and presented

Evaluation of Van A-B genes frequency in Vancomycin Resistant Enterococci spp., isolated from clinical samples of Imam Hossein Teaching Hospital in Tehran.: A molecular study of vancomycin-resistant-enterococci.

Abstract Background: Antibiotic resistance is an important cause of treatment failure and re-infection in enterococci. In this study, the frequency of phenotype and genotype of Van A-B genes in Vancomycin resistant enterococcus isolated from a clinical sample of Imam Hossein Hospitals in Tehran was determined. Materials and Methods: In this descriptive cross-sectional study in 2018, a total of 76 vancomycin-resistant enterococci in Imam Hossein Hospitals in Tehran were evaluated, including those from blood, urine, sputum, and wound. The frequency of phenotype and genotype of Van A-B genes in them was determined by MIC Epsilometer test and Multiplex Real-time PCR. Results: The 160 isolates of enterococci collected from different hospital wards revealed that 76 (47%) enterococci were resistant by applying MIC E-test; interestingly, all VRE isolated showed high-level vancomycin resistance. The Real-time-PCR assay demonstrated vanA gene in 76 (100%) VRE isolates. Considering to controls no van B gene was detected in this assay. Based on bacterial phenotype tests, the results showed that 82% and 18% of the isolates were E. faecium and E. faecalis, respectively. Conclusion: Totally, it may be concluded that Van A gene is more accompanied by high-level Vancomycin Teicoplanin resistance in common enterococci species. The frequency of Vancomycin resistance entrocooci is increasing especially among ICU admitted patients. For effective treatment MIC test and Van A-B genotyping seem to be essential