Dynamic Pool Boiling Heat Transfer Due to Exponentially Increasing Heat Input-A Review

AbstractThe boiling heat transfer, specifically transient or unsteady heat transfer has found much practical importance in the engineering applications. Since, explosive boiling occurs during enormous power excursion in the liquid cooled reactor, the safety evaluation of a nuclear reactor is of vital importance. This paper reviews the transient boiling heat transfer which is the study of transition mechanism from natural convection or nucleate boiling to film boiling and critical point of heat flux using the various wetting fluid as working medium (Distilled water, ethanol, fluorinert liquid, etc.) caused by exponentially increasing heat input at various periods. The survey is also extended to study the heating element (wire, rod, film) usually made of aluminum or platinum under a subcooled or saturated condition of working fluid at atmospheric or higher system pressure. During the quasi-steady or rapid transient, an aspect of dynamic boiling like the onset of boiling, delay period, temperature overshoot, homogenous nucleation, heterogeneous nucleation, transient CHF, bubble growth, vapor coalescence and vapor collapse has been analyzed. Moreover, a visualization study of differently oriented test piece at a different heating rate and different phase of boiling has been qualitatively discussed

Comparative Study on the Effect of Leading Edge Protuberance of Different Shapes on the Aerodynamic Performance of Two Distinct Airfoils

This study investigated the effect of leading-edge protuberances on the aerodynamic performance of two distinct airfoils with low Reynold’s number (Re): E216 and SG6043. Three protuberance shapes, namely sinusoidal, slot, and triangular, were considered. The amplitudes (A) of protuberances considered were 0.03c, 0.06c, and 0.11c, and the wavelengths (W) were 0.11c, 0.21c, and 0.43c, where c is the chord of the airfoil. The numerical and experimental analyses were performed in the angle of attack (AoA) range of 0° to +20° at and Re of 105. The numerical investigation was performed using the commercial computational fluid dynamics package ANSYS FLUENT. The SST k-ɷ model was used to simulate turbulent flow. The experimental force measurements were conducted using a highly sensitive three-component force balance in a subsonic wind tunnel facility. The flow physics was analyzed using vorticity contours in streamwise and spanwise slices and static pressure distribution contours. The smoke flow visualization technique was used to observe flow streamlines, boundary layer separation, and reattachment over the airfoil surface. The result indicated that the triangular and slot protuberances were the most beneficial for improving poststall lift and reducing skin friction drag. The operating mechanism involved a shift in pressure distribution due to leading-edge alterations and flow energization by secondary flow emanating from the protuberances

A Robust Technique for Detection, Diagnosis, and Localization of Switching Faults in Electric Drives Using Discrete Wavelet Transform

Detection, diagnosis, and localization of switching faults in electric drives are extremely important for operating a large number of induction motors in parallel. This study aims to present the design and development of switching fault detection, diagnosis, and localization strategy for the induction motor drive system (IMDS) by using a novel diagnostic variable that is derived from discrete wavelet transform (DWT) coefficients. The distinctiveness of the proposed algorithm is that it can identify single/multiple switch open and short faults and locate the defective switches using a single mathematical computation. The proposed algorithm is tested by simulation in MATLAB/Simulink and experimentally validated using the LabVIEW hardware-in-the-loop platform. The results demonstrate the robustness and effectiveness of the proposed technique in identifying and locating faults

Saluvankuppam coastal temple excavation and application of soil micromorphology

The 26 December 2004 tsunami exposed an inscription of the 10th century engraved on a rock boulder at Saluvankuppam, 6 km north of Mamallapuram. The inscription indicates the existence of a Subramanya temple. The temple and the mound around the granite inselberg were excavated by the Archaeological Survey of India, Chennai Circle. The excavation exposed the entire Subramanya temple complex constructed over a period of time (4th/5th CE to 12th/13th CE). The temple complex and the litho sections reveal phases of temple building activity. The cement and lime used for the temple complex contain fragments of shells. Soil micromorphology technique was applied to understand the type of textures and fabric in soil sediments, bricks, potsherds, well rims, bone fragments, etc., using a polarized microscope. Thin sections of the laterite bricks which formed the foundation indicate high content of hematite, magnetite, kaolinite patches and the porosity of the laterite brick varies from 5% to 10% only, whereas thin sections of potsherds indicate that the firing temperature was fairly low and that the pots were well fired. Geoarcheology study of this temple complex indicates that a number of naturally occurring raw materials have been used for constructing this temple that were locally available

Heat flux correlation models for spray evaporative cooling of vibrating surfaces in the nucleate boiling region

New empirical correlation models are constructed to characterise heat transfer associated with spray evaporative cooling of vibrating surfaces - a process involving complex two-phase physics well beyond current numerical simulation capabilities. The proposed correlation models, which account for dynamic, rather than just static surface conditions as in existing models, are constructed using dimensional analysis involving the Generalized Buckingham Π-Theorem. Experimentally-measured spray evaporative cooling data is used to fit the model using the Vibrational Reynolds number and a dimensionless acceleration number which better correlate the influence of surface frequency and amplitude in the nucleate boiling regime. Different coolant flow-rates through a full-cone spray nozzle are used to cool a flat circular test-piece acting as a horizontal surface. The test-piece surface is excited by a shaker through a range of low and high vibration frequencies and amplitudes. The results show that surface dynamic effects certainly influence nucleate boiling, but they also show that surface vibration does not have the same effect for all excess temperatures - dynamic effects can either increase or decrease heat transfer depending on the heat transfer mechanism. These new models are important for thermal management in several areas, particularly involving batteries, power electronics, and electrical machines in automotive and aerospace applications

General anaesthetic and airway management practice for obstetric surgery in England: a prospective, multi-centre observational study

There are no current descriptions of general anaesthesia characteristics for obstetric surgery, despite recent changes to patient baseline characteristics and airway management guidelines. This analysis of data from the direct reporting of awareness in maternity patients' (DREAMY) study of accidental awareness during obstetric anaesthesia aimed to describe practice for obstetric general anaesthesia in England and compare with earlier surveys and best-practice recommendations. Consenting patients who received general anaesthesia for obstetric surgery in 72 hospitals from May 2017 to August 2018 were included. Baseline characteristics, airway management, anaesthetic techniques and major complications were collected. Descriptive analysis, binary logistic regression modelling and comparisons with earlier data were conducted. Data were collected from 3117 procedures, including 2554 (81.9%) caesarean deliveries. Thiopental was the induction drug in 1649 (52.9%) patients, compared with propofol in 1419 (45.5%). Suxamethonium was the neuromuscular blocking drug for tracheal intubation in 2631 (86.1%), compared with rocuronium in 367 (11.8%). Difficult tracheal intubation was reported in 1 in 19 (95%CI 1 in 16-22) and failed intubation in 1 in 312 (95%CI 1 in 169-667). Obese patients were over-represented compared with national baselines and associated with difficult, but not failed intubation. There was more evidence of change in practice for induction drugs (increased use of propofol) than neuromuscular blocking drugs (suxamethonium remains the most popular). There was evidence of improvement in practice, with increased monitoring and reversal of neuromuscular blockade (although this remains suboptimal). Despite a high risk of difficult intubation in this population, videolaryngoscopy was rarely used (1.9%)

Gothic spaces and the tropical city: reading the crocodile fury, haunting the tiger, life's mysteries

Beth Yahp's The Crocodile Fury (1992), K.S. Maniam's Haunting the Tiger (1996), and Shirley Lim's Life's Mysteries (1995) articulate the ambivalence of interpreting the cultural beliefs of the Malays, Chinese, and Indians of the former Malaya with the evolving spiritual beliefs of Christianity and Catholicism influenced by British colonisation. In Beth Yahp's The Crocodile Fury the ghosts of the colonial past vie for power with the demons of Chinese cultural beliefs in a convent situated in the liminal space between the jungle and the urban environment. The convent is a "civilised space" with the jungle as an encroaching wilderness haunted by Chinese gods and the female vampire ghost Pontianak of the Malay cultural tradition. Similarly, Maniam's short stories in Haunting the Tiger situate the supernatural and the abject in the liminal spaces between the city and the jungle to express the metaphorical exile experienced by the Indian and Chinese diaspora in Malaysia. The trope of liminality is most evident in Shirley Lim's short stories in Life's Mysteries where the domestic and urban space of culture are viewed through prisms of imprisonment and disempowerment. The authors uncover the psychological and social exile experienced by colonised subjects through the gothic themes of shadows, darkness and the underworld

Numerical study on effect of boundary layer trips on aerodynamic performance of E216 airfoil

Simulation is carried out to find the performance of airfoil E216 using Transition γ-Reθ model at Reynolds number of 100,000. Flow behaviour and effect of angle of attack (AOA) on laminar separation bubble (LSB) formation are examined. The results are validated with wind tunnel experimental results. LSB formation is clearly spotted in the velocity vector plot and coefficient of pressure distribution over airfoil. LSB moved upstream towards the leading edge with increase in AOA. Effect of boundary layer trip on LSB formation over the airfoil and performance of airfoil are studied. Two different trip locations, 17% of chord and 10% of chord from leading edge, and different trip heights (0.3 mm, 0.5 mm, 0.7 mm, 1 mm) are investigated in this study. Results showed that boundary layer trip could eliminate LSB partially or completely and improve aerodynamic performance of the airfoil. Maximum improvement in drag by 15.48% and lift to drag ratio by 21.62% are obtained at angle of attack of 60. In all the cases, improvement in performance is observed only up to trip height of 0.5 mm