Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment

The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment

Experimental and numerical studies of choked flow through adiabatic and diabatic capillary tubes

Capillary tubes are extensively used in several cooling applications like refrigeration, electronic cooling etc. Local pressure variation in adiabatic straight capillary tube (mini channel) is studied experimentally and numerically with R134a as the working fluid. Experiments are performed on two straight capillary tubes. It is found that the diameter is the most sensitive design parameter of the capillary tube. Experiments are performed on five helically coiled capillary tubes to quantify the effect of pitch and curvature of helically coiled capillary tube on the pressure drop. Non dimensionalized factor to account coiling of capillary tube is derived to calculate mass flow rate in helically coiled capillary tubes. Flow visualization in adiabatic capillary tube confirms the bubbly nature of two phase flow. Numerical and experimental investigations in adiabatic capillary tube suggest that the use of positive displacement pump and choking at the exit of the channel ensures flow stability. (C) 2015 Elsevier Ltd. All rights reserved

EXPERIMENTAL INVESTIGATION OF THE 700 MWe CONTAINMENT SPRAY SYSTEM SPRAY NOZZLES/SYSTEM

The aim of the present work is to study a full cone pressure swirl nozzle (pressure swirl nozzles) and its configuration on a spray header for the 700MWe Indian Pressurized HeavyWater Reactor (IPHWR) Containment Spray System (CSS) (a FOAK system). The Reynolds number (Re) effect on coefficient of discharge (C-d), spray cone angle, SMD (D-32), droplet size distribution, and droplet velocity is investigated for full cone pressure swirl nozzles. Studies are performed to optimize the nozzle configuration on the spray header and the distribution of mass flux. The mass flux density studies are carried out in patternater facilities at IIT Bombay and the Kakrapar Atomic Power Project (KAPP). Water at room temperature is used for the spray in experimental investigation. The nozzle characterization experimental studies are carried out for Re ranging from 1.43 x 10(5) to 2.49 x 10(5). A particle droplet image analyzer (PDIA) is used for the measurement of droplet velocity, SMD (D-32), and drop size distributions. A simple CCD camera along with a diode laser and patternater software is used for the measurement of the spray cone angle. The catch and time technique is used to measure coefficient of discharge. The droplet flux distribution at different Z/D-o and R/D-o is also performed. Nukiyama-Tanasawa distribution and log-normal peak shifted distribution show a reasonably good confirmation with the present experimental studies

Experimental investigation of iodine removal and containment depressurization in containment spray system test facility of 700 MWe Indian pressurized heavy water reactors

As an additional safety measure in the new 700 MWe Indian pressurized heavy water reactors, the first of a kind system called containment Spray System is introduced. The system is designed to cater/mitigate the conditions after design basis accidents i.e., loss of coolant accident and main steam line break. As a contribution to the safety analysis of condition following loss-of-coolant accidents, experiments are carried out to establish the performance of the system. The loss of coolant is simulated by injecting saturated steam and iodine vapors into the containment vessel in which air is enclosed at atmospheric and room temperature, and then the steam-air mixture is cooled by sprays of water. The effect of water spray on the containment vessel pressure and the iodine scrubbing in a scaled down facility is investigated for the containment spray system of Indian pressurized heavy water reactors. The experiments are carried out in the scaled down vessel of the diameter of 2.0 m and height of 3.5 m respectively. Experiments are conducted with water at room temperature as the spray medium. Two different initial vessel pressure i.e. 0.7 bar and 1.0 bar are chosen for the studies as they are nearing the loss of coolant accident & main steam line break pressures in Indian pressurized heavy water reactors. These pressures are chosen based on the containment resultant pressures after a design basis accident. The transient temperature and pressure distribution of the steam in the vessel are measured during the depressurization. The pressure and temperature history of the system is measured using high temperature pressure transmitter and the K-type thermocouples. The iodine scrubbing is measured through periodic sampling from the vessel. The influence of the Sauter mean diameter (SMD) is studied on the depressurization rate of the vessel at different vessel pressures. Studies are performed to optimize the containment spray system configuration and to establish the phenomena with respect to Indian pressurized heavy water reactors. In all the experiments, the spray flow rate is kept constant, while the SMD is varied by using different spray nozzles. (C) 2017 Elsevier B.V. All rights reserved

An experimental study on the depressurization of the containment by water spray in a small scale facility

The containment of a nuclear reactor acts as the ultimate barrier for radionuclides to be leaked in the environment. Severe accidents in nuclear reactors may result in the pressurization of the containment and may provide different potential leak paths. So, to enhance the safety of new designs of Indian pressurized heavy water reactors, an additional safety measure called containment Spray System is introduced. The system is designed to cater/mitigate the conditions after design basis accidents. As a contribution to the safety analysis of condition post severe accident, experiments are carried out to investigate the system performance. The accidental conditions are simulated by injecting the saturated steam into the test vessel filled with air at atmospheric pressure and temperature. The effect of different spray parameters such as nozzle geometry, spray mass flow rate and Sauter mean diameter on vessel pressure and temperature is measured. Three initial vessel pressure 1.5 bar, 2.0 bar, 2.5 bar and five different nozzles with nozzle orifice diameter as 1.65 mm, 2.10 mm, 2.45 mm, 2.75 mm and 3.10 mm are chosen for the experimental investigation. The vessel pressures are chosen based on the post accidental conditions in Indian pressurized heavy water reactor. Experiments are conducted with water at room temperature as the spray medium. The experiments are carried out in a vessel of 500 mm diameter and 1200 mm height. These studies are carried out to optimize the containment spray system configuration for best effectiveness. It is seen that the Sauter mean diameter and nozzle geometry influences the depressurization rate of the vessel. The depressurization rate is inversely proportional to the Sauter mean diameter while it increases with the increase in the spray mass flow rate/Reynolds Number. (C) 2017 Elsevier Ltd. All rights reserved

Experimental investigations on melting of lead in a cuboid with constant heat flux boundary condition using thermal neutron radiography

Knowledge of the melting of lead (shielding material) in enclosures is of great importance in the design of transportation packages. An experimental investigation is carried out to study the melting of lead contained in a stainless steel cuboid. The size of the cuboid is 50 mm x 50 mm x 60 mm. Side vertical wall is maintained at a constant heat flux boundary condition. Visualisation of solid-liquid interface movement during melting of lead is carried out using neutron radiography at beamline E12 in CIRUS reactor in BARC. The beamline flux is 10(6) Neutrons/cm(2) s. Neutron radiography is a non-intrusive method for the characterization of melt front of melting of opaque materials. This method demonstrates dynamic capture of the progress of solid-liquid interface under the effects of natural convection in a non-intrusive manner. FLUENT is used as a numerical tool for the estimation of transient molten fraction and transient Nusselt number. Enthalpy-porosity method is employed for numerical investigation. Variation of molten fraction with time computed by numerical methodology compares reasonably well with those of experimental results. A correlation for average Nusselt number is suggested based on the numerical results and scale analysis. (c) 2012 Elsevier Masson SAS. All rights reserved