Showing papers by "S.V. Prabhu published in 2013"
TL;DR: The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal and the temperature dependent emissivity is found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism.
Abstract: Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%–40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.
110 citations
TL;DR: In this paper, the authors measured the heat transfer coefficient and pressure drop in a horizontal tube under low pressure and low flow (LPLF) conditions of subcooled boiling, and derived the correlation for single phase diabatic pressure drop ratio (diabatic to adiabatic) as a function of viscosity ratio (wall temperature to fluid temperature).
44 citations
TL;DR: An experimental investigation is performed to substantiate the capability of a charge coupled device camera to measure local temperature and emissivity of different materials heated to temperatures above 500 °C by two-colour pyrometric technique using colorimetric method.
Abstract: An experimental investigation is performed to substantiate the capability of a charge coupled device camera to measure local temperature and emissivity of different materials heated to temperatures above 500 °C by two-colour pyrometric technique using colorimetric method. Materials investigated are Inconel 718 with pyromark (high temperature paint), Inconel 718, stainless steel SS 304 and SS 316. Centerline temperature and emissivity distribution is obtained for target plates maintained at constant temperature by AC heating while complete temperature and emissivity distribution is provided for plates heated by flame impingement. The obtained results are compared with a calibrated infrared camera and thermocouples and the temperature distribution is found to be in close agreement. These results pertain to partially oxidized metal alloys covered in this study. Deviation in the measurement of emissivity can be attributed to its dependence on wavelength range, oxidation, and sensitivity of the image detector.
40 citations
TL;DR: In this article, the safety distances from different fires with different fuels are computed for different open pool fires for circular pool diameters of 0.5m, 0.7m and 1.0m.
18 citations
TL;DR: In this article, the impingement cooling of turbine blade leading edge is modeled by considering impingements of a row of jets on a semi-circular concave surface, where wall static pressure measurements are made along the spanwise line through the stagnation and two other circumferential locations.
16 citations
TL;DR: In this paper, the influence of shape and diameter on the radiative properties of open pool fires was investigated, and both circular and square shapes of equivalent surface area were considered. But the results were limited.
Abstract: This study is an experimental investigation of the influence of shape and diameter on the radiative properties of open pool fires. Circular and square shapes of equivalent surface area are consider...
15 citations
TL;DR: In this paper, the authors characterize the temperature and emissive power distributions for a fire safety measurement with respect to a girder, and characterize these distributions for the same girders.
Abstract: Radiative properties such as temperature and emissive power distributions are very essential for fire safety measurements. The objective of this study is to characterize these distributions for a g...
14 citations
TL;DR: In this article, two identical cone shapes are machined with their base circle surfaces joined together with a small step in between them and differential pressure measurement is done across the apex of the cones.
12 citations
TL;DR: In this article, the authors explored novel pressure averaging technique for wafer cone flowmeter design and its robustness in the presence of double 90° bend (out-of-plane) and gate valve as a source of upstream flow disturbance.
10 citations
TL;DR: In this paper, the heat transfer to a cask engulfed in a diesel pool fire was investigated and the results showed that the heat transferred to the cask was not significantly worse than that of a conventional pool fire.
Abstract: Characterization of the heat transfer to a cask engulfed in pool fire is extremely important. Experiments are carried out on diesel pool fires of diameters 0.5, 0.7, and 1.0 m with stainless steel ...
9 citations
TL;DR: In this paper, experiments were carried out for a circular orifice and a nozzle for the same contraction ratio to explore the heat transfer characteristics, and it was found that higher Nusselt number for the orifice than the nozzle are due to different shock structures and shear layer dynamics.
Abstract: Experiments are carried out for a circular orifice and a nozzle for the same contraction ratio to explore the heat transfer characteristics. The pressure ratios covered in this study are 2.36, 3.04, 3.72, 4.4 and 5.08 for jet to plate distances (z/d) of 2, 4, 6 and 8. The presence of vena contracta and absence of the stagnation bubble in the orifice flow are confirmed from the surface pressure distributions. It is found that higher Nusselt number for the orifice than the nozzle are due to different shock structures and shear layer dynamics. Peak Nusselt number is found as high as 84 % than that for the nozzle. In the wall jet region, the heat transfer rates for the orifice and nozzle are almost of the same order, thus producing steeper temperature gradients under similar operating conditions. The average heat transfer rates are almost 25 % higher for the orifice than that of the nozzle. The recovery factors are in general higher in case of orifice than the nozzle. However, this has not resulted in decreasing the heat transfer rates due to shear layer dynamics.
TL;DR: In this paper, the effect of the profile of a convergent nozzle on the local heat transfer distribution of a smooth flat surface impinged normally by an underexpanded air jet was investigated.
Journal Article•
01 Sep 2013-World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering
TL;DR: In this article, the authors explored flow visualization experiments with various blunt shaped bluff bodies placed inside a circular pipe, which mainly comprise of modifications of trapezoidal cylinder, most widely used in practical applications, such as vortex flowmeters.
Abstract: The present study explores flow visualization experiments with various blunt shaped bluff bodies placed inside a circular pipe. The bodies mainly comprise of modifications of trapezoidal cylinder, most widely used in practical applications, such as vortex flowmeters. The present configuration possesses the feature of both internal and external flows with low aspect ratio. The vortex dynamics of bluff bodies in such configuration is seldom reported in the literature. Dye injection technique is employed to visualize the complex vortex formation mechanism behind the bluff bodies. The influence of orientation, slit and after body shape is studied in an attempt to obtain better understanding of the vortex formation mechanism. Various wake parameters like Strouhal number, vortex formation length and wake width are documented for these shapes. Vortex formation both with and without shear layer interaction is observed for most of the shapes. Keywords—Flow visualization, Reynolds number, Strouhal number, vortex, vortex formation length, wake width.
TL;DR: In this article, a pure radiative heat-flux measuring gauge (RHFG) is developed for measuring the contribution of radiation heatflux component while operating in high temperature conditions without the need of cooling water supply.
Abstract: It is important to develop an inexpensive and robust gauge for measuring the contribution of radiation heat-flux component while operating in high temperature conditions without the need of cooling water supply. This work presents a new compact radiative heat-flux gauge (RHFG) for measuring the radiative heat-flux from combustion systems operating at high operating temperatures (∼1200 K). Various types of total heat-flux meters (convective and radiative) are available for measuring heat-flux. In this study, pure radiative heat-flux measuring gauge (RHFG) is developed. Quartz plate is used as a window of RHFG acting as media to transfer pure radiative heat from the heat source. Copper plate is used as the heat sensing element. A thermocouple is brazed to the copper plate to measure the rate of heat transfer to the sensing element. The mathematical modeling, numerical analysis and construction methodology of RHFG is discussed. Initially, a large sized gauge (G1) is fabricated and calibrated with cone calorimeter. The measured response time of 670 s is observed for G1. Numerical analysis is carried out to optimize the size of RHFG and reduce the response time. Four different gauges with various dimensions (G2, G3, G4 and G5) are analyzed numerically and a response time of 208, 17, 14 and 12 s respectively is observed. The gauge, G5 is manufactured and calibrated with cone calorimeter with known radiative heat-flux and the experimental response time of 13 s is observed. This RHFG is of low cost, simple to manufacture, rugged and requires no water cooling even for high temperature combustion applications.