Investigations for effect of Al2O3–H2O nanofluid flow rate on the efficiency of direct absorption solar collector

The efficiency of conventional tube‐ in plate type solar collectors is limited due to higher heat losses for surface based solar energy absorption and indirect transfer of heat from hot absorber surface to working fluid having poor heat transfer properties flowing through tubes. In this paper, a prototype direct absorption solar collector having gross area 1.4 m2 working on volumetric absorption principle is developed to investigate the effect of using Al2O3–H2O nanofluid as heat transfer fluid at different flow rates. Experimentation was carried using distilled water and 0.005% volume fractions of 20 nm size Al2O3 nanoparticles at three flow rates of 1.5, 2 and 2.5 lpm. ASHRAE standard 93-86 was followed for calculation of instantaneous efficiency of solar collector. Use of nanofluid improves the optical and thermo physical properties that result into an increase in the efficiency of the collector in all cases of using nanofluids in place of water. Collector efficiency enhancement of 8.1% and 4.2% has been observed for 1.5 and 2 lpm flow rate of nanofluid respectively. Optimum flow rate of 2.5 and 2 lpm towards maximum collector efficiency have also been observed for water and nanofluid respectively

Optimization of operating parameters of earth air tunnel heat exchanger for space cooling: Taguchi method approach

Abstract In the present study, CFD-based parametric analysis is carried out to optimise the parameters affecting the temperature drop and heat transfer rate achieved from earth air tunnel heat exchanger (EATHE) system. ANSYS FLUENT 15.0 is used for CFD analysis, and k-ε model and energy equation were considered to define the turbulence and heat transfer phenomena. For a straight EATHE system configuration, four design and operating parameters, i.e., diameter of the pipe (A), length of pipe (B), inlet air velocity (C), and inlet air temperature (D), are considered at four different levels in Taguchi method. The Taguchi method is used to obtain maximum air temperature drop and heat transfer rate. The best combination of parameters for achieving a maximum drop in air temperature is A1B4C1D4 and that for obtaining maximum total heat transfer rate is A4B4C4D4. Statistical analysis reveals the percentage contribution of different factors for air temperature drop in the following order: inlet air temperature (57.80%), diameter of pipe (20.66%), length of pipe (12.03%), and air velocity (9.51%), while, for heat transfer rate, pipe diameter (53.28%), inlet air temperature (30.87%), air velocity (9.40%), and length of pipe (6.45%)

Clinicopathological study of cerebellar astrocytoma in children

Introduction: The first successful treatment of a pediatric brain tumor was in 1879 when Sir William Macewen successfully removed a meningioma from a 14-year-old girl. Brain tumors are the most common form of solid tumors and the leading cause of death from solid tumors in children (SEER program 1975–1999). Materials and Methods: Study area: This study was conducted at Bangur Institute of Neuroscience (BIN) and S.S.K.M Hospital. Study Population: Patients attending BIN OPD and admitting in BIN and S.S.K.M Hospital wards were selected. Inclusion Criteria: The following criteria were included in the study: (a) Patients with the diagnosis of cerebellar astrocytomas after magnetic resonance imaging investigation, (b) patients giving consent to be included in the study, and (c) patient willing to come for follow up. Study Period: The study period was 2 years (from September 1, 2010, to December 31, 2012). Sample Size: All diagnosed cases of cerebellar astrocytoma during the stated period. Exclusion Criteria: Patients not willing for the study were excluded from the study. Study Design: This was a non-randomized prospective clinical study. Pilocytic astrocytomas are the most common pediatric brain tumors in our population and are most commonly located in the cerebellum. Results: Most of the patients, 20 (90.9%), had neurological improvement on discharge. 1 patient (4.5%) died during the hospital course. The follow-up time period ranged from 3 months to 2 years, with a mean follow-up period of 1.5 years. Recurrence was observed in 5 patients (22.72%), but reoperation was done in 3 patients (13.63%). Of them, 1 patient (4.5%) received radiotherapy in spite of that recurrence was developed in 1.5 years. 2 patients (9.09%) have been kept under observation because these are asymptomatic. The solid consistency of tumors led to a poor prognosis, as it was associated with a greater number of ICU admissions, recurrence of tumors, and repeat surgeries (13.63%). The follow-up time period ranged from 3 months to 2 years, with a mean follow-up period of 1.5 years. Conclusion: A “wait and see” strategy is justified in patients with non-progressive recurrent or residual cerebellar LGG after primary tumor resection (23.30) radiotherapy can be considered

Comparison of CPAP preoxygenation versus conventional preoxygenation on duration of safe apnoea time in patients undergoing elective surgery under general anaesthesia

Anesthesia induction usually leads to apnoea, during apnoea, oxygenation depends on the oxygen reserves stored within the body .While breathing room air these stores are quantitatively low. As we cannot perfectly predict the difficulty in airway management, desirability of maximal preoxygenation is theoretically present for all patients. Induction of general anaesthesia per se as also the use of 100% oxygen during preoxygenation results in the development of atelectasis in dependent lung regions within minutes of anaesthetic induction. Therefore this randomized, controlled study was undertaken to compare the effect of CPAP (continuous positive airway pressure) preoxygenationvs conventional preoxygenation on duration of safe apnoea time in patients posted for elective surgery under general anaesthesia. After obtaining approval from the institutional review board and institutional ethics committee and prior consent from participants, 60 adult patients scheduled for elective surgery under general anaesthesia were randomized into two groups- PEEP group and ZEEP group. Patients in PEEP group were preoxygenated with CPAP of 5 cm of H2O with 100% oxygen for five minutes and in ZEEP group no CPAP was used. Duration of safe apnoea time (taken as till Spo2 reached 94%) and ABG analysis at various time intervals was done for each group.The comparison of normally distributed continuous variables between the groups was performed using Student’s t test. Nominal categorical data between the groups were compared using Chi-squared test or Fisher’s exact test as appropriate. P value less than 0.05 was considered statistically significant. We found out that the duration of safe apnoea time was significantly longer in PEEP group (408.90 ± 32.73) as compared to ZEEP group (257.70 ± 12.79 s) ( P value less than 0.001).PaO2 after preoxygenation was also significantly higher in PEEP group (416.62 ± 28.72 mmHg) as compared to ZEEP group (367.02 ± 14.29 mmHg) ( P value less than 0.001).We concluded that the application of continuous positive airway pressure during preoxygenation is a simple, well tolerated technique that may have advantages especially in those patients in whom difficulty in airway management is anticipated, those who are at increased risk of desaturation such as morbidly obese patients and when assisted ventilation is not applied such as during rapid sequence induction