The phenomenon of ablation occurring in sacrificial concrete surrounding the nuclear reactor is studied by conducting experiments with oxyacetylene welding. The oxidizing flame produced from the oxyacetylene welding is a potential source of high heat flux and temperature exposed to the ferrosiliceous concrete (contains hematite aggregates) and ordinary concrete (without hematite aggregates). The ablation caused by the highintensity oxidizing flame is observed to be highly non-uniform. The maximum temperature rise, ablation depths and overall mass loss in ordinary concrete are observed to be higher compared to the ferrosiliceous concrete. The presence of hematite in ferrosiliceous concrete has reduced the heat diffusion, ablation depth and mass of ablated material inside the concrete and hence exhibited better ablation characteristics. A semi-infinite heat transfer model ignoring the effects of chemical reactions are formulated and estimated the approximate interfacial heat flux profiles develop at the interface between the flame and concrete. The outcomes of the study conclude that the ferrosiliceous concrete can withstand the high heat fluxes of the oxidizing flame, and hence, it will withstand the adverse scenario of the interaction of molten corium with concrete walls occurs during the failure of nuclear reactors.

The necessity of understanding the interaction of molten corium with the sacrificial concrete layer surrounding the nuclear reactors has been the motivation to perform MCCI experiments. Materials (zinc, aluminium and stainless steel) which have different melting temperatures and thermal properties are chosen and the experimental investigations are carried out by pouring molten metals in well-defined cavities of concrete test sections to study the ablation and thermal behaviour of the concrete. Coarse and fine aggregates of hematite are added to the cement to attain the required mechanical and thermal properties and provide better radiation shielding. The transient interaction of the molten metal with the concrete is measured using thermocouples. The measured subsurface temperatures are subsequently used to estimate the interfacial heat flux profiles by solving an inverse heat conduction problem using the sequential function specification method. The peak temperatures measured and peak heat flux values estimated in concrete samples interacted with zinc, aluminium and stainless steel are around 85 degrees C and 35 kW/m2, 105 degrees C and 58 kW/m2, and 468 degrees C and 65 kW/m2, respectively. There is no ablation during the interaction of zinc and aluminium with the concrete test sections. Though the melting temperature of stainless steel (1450 degrees C) is higher than the ablation temperature of the concrete (around 1200 degrees C), concrete did not undergo significant ablation due to the higher density and the strength offered by the addition of hematite aggregates. The results presented in the current study are accurate within the time period where the semi-infinite model is valid.

Subcooled flow boiling of water is widely observed in high heat flux and high mass flux (HHHM) cooling applications such as heat exchangers, refrigeration equipment, boiler tubes and nuclear reactor core fuel channels in pressurized heavy water reactors (PHWR). In this study, the focus is on investigating the local heat transfer coefficient (HTC) and pressure drop in a horizontal tube experiencing subcooled boiling of water under low pressure and HHHM conditions. The study encompasses different geometrical parameters such as tube diameter (5.5 mm , 7.5 mm , 9.5 mm and 12 mm ) and length (550 mm for each of the tubes). The operating parameters that are varied include mass flux (248-2000 kg/m2.s) and heat flux (0-1837 kW/m2). Infrared thermography is used to measure the local wall temperature. A non-dimensional correlation for the diabatic pressure drop ratio (ratio of diabatic pressure drop to adiabatic pressure drop) as a function of Jakob number (Ja), Boiling number (Bo) and diameter ratio is developed. Subcooled boiling pressure drop ratio for 5.5 mm , 7.5 mm and 9.4 mm diameter tubes is 2.23 which is independent of diameter. A correlation for the two phase local HTC during subcooled flow boiling conditions as a function of Ja , Bo and Prandtl number (Pr) is also developed.

Vortex generator can be used to enhance heat transfer as it is capable of providing better mixing. Vortex generator is easy to manufacture and install in heat transfer units without much additional cost. Present work is planned to investigate the effect of vortex generators on local heat transfer coefficient, critical heat flux (CHF) and pressure drop to ensure design and safety of heat transfer units with vortex generators. Experiments are carried out for three values of pitch 22, 32 and 41 mm and an angle of attack of 45 degrees of vortex generators with horizontal configuration in a smooth tube of diameter 11.9 mm, length 1,000 mm and 0.4 mm wall thickness with R-123 as the working fluid. The effect of mass flux (175-681 kg/m2s) and heat flux (7.9 - 221.7 kW/m2) are studied. Both horizontal and vertical-oriented configurations of the vortex generator are tested. Local wall temperature measurement is carried out with Infrared thermography. Comparing results with plain tube shows the heat transfer coefficient and CHF enhancement. Horizontal orientation (HO) of the vortex generator gives better results than the vertical orientation (VO). Heat transfer coefficient, CHF and pressure drop penalty increase with a decrease in the pitch of the vortex generator.

Catastrophic fire incidents in nuclear reactors can cause rapid ablation of the concrete during molten corium concrete interactions (MCCI). In this work, experimental and numerical analysis are carried out to evaluate the interfacial heat flux profiles between the concrete and molten metal. The granite based concrete which contained Ordinary Portland Cement (OPC) is used and it's interaction with the molten mixture of MnO and TiO2 are studied. The transient temperature distribution inside the concrete and ablation depths are measured after pouring the molten metal into the concrete cavity. It is observed that the maximum ablation occurred at the bottom of the cavity due to initial severe interaction of molten metal with the concrete. The ablation depths at the base and the side walls are 28 mm and 15 mm, respectively. Comparison with 1D heat transfer and semiinfinite model confirmed that heat transfer in concrete can be analysed using semi-infinite medium approach up to Fourier number of 0.45. An inverse heat transfer problem is solved using sequential function specification method and estimated the interfacial heat flux profiles from measured transient subsurface temperature distribution. Subsurface temperatures are measured using sheathed K-type thermocouples. Consistent with the experimental observations, higher heat fluxes are observed for thermocouples located at the bottom and lower heat flux are observed for thermocouples placed at the side walls and corners. The heat flux profiles rise from the beginning, reach to a peak value and then, gradually decreased with time. Heat flux values are observed to be in the range of 1-19 kW/m2. The experimental observations of this study are compared with the literature and the possible values of ablation depths for the case of the actual nuclear reactor are estimated.

Heavy density concrete made of hematite-based aggregates commonly known as ferro-siliceous sacrificial concrete (FSSC) can be used effectively against radiation shielding in case of nuclear melt down. However, performance assessment of such concretes on exposure to elevated temperatures are not available widely. In the present study, thermo-mechanical and thermophysical properties of hematite-based FSSC concrete are evaluated on exposure to elevated temperatures. The porosity and water absorption capacity of FSSC are investigated on its exposure to higher temperatures ranging from 30 °C to 1000 °C. Similarly, various thermo-mechanical [compression, split tension, modulus of elasticity (MOE)] and thermophysical (specific heat, thermal conductivity, thermal diffusivity, and thermal effusivity) properties are evaluated on exposure to elevated temperatures. The mechanical properties of the concrete such as compression, split tension, MOE decrease monotonically with increase in the exposed temperature. Porosity and water absorption of the concrete increases with the increase in temperature. Relationship between damage and the exposed temperature can be described by Weibull model. Thermophysical property such as specific heat of the concrete increases, while thermal conductivity, thermal diffusivity and effusivity decrease with the increase in temperature. Correlations for the variation in thermal conductivity, specific heat and thermal diffusivity are proposed. The variations in the mechanical and thermophysical properties are explained through the porosity variations and correlation coefficient between porosity and various mechanical and thermophysical properties.

An experimental investigation was conducted to examine critical heat flux (CHF), boiling pressure drop, and local heat transfer coefficient in a horizontal channel with transverse grooves for flow boiling with R-123. Measurement of the wall temperature of the channel was done using a thermal camera. Five test sections were used for the study. A combination of groove pitch (p) of 18.6 and 11 mm and groove height (e) of 1 mm and 0.55 mm were used for the study. The groove pitch-to-height (p/e) ratios used were 11, 20, 18.6, and 33.8. Experiments were carried out for different heat fluxes in the range from 180 to 1259 kW/m2, six different mass fluxes from 180 to 1259 kg/m2s, and Reynolds numbers from 5834 to 51770. In the grooved channel compared with the smooth tube, an improvement in heat transfer and CHF with the higher pressure drop was found. The boiling heat transfer coefficient increases with a decrease in (p/e) ratio. The enhancement of heat transfer coefficient and CHF improves with a decrease in (p/e) ratio. The maximum enhancement of CHF for (p/e) ratios of 11, 18.6, 20, and 33.8 is found to be 134%, 87%, 57%, and 53%, respectively. An abrupt increase in test channel wall temperature is an indication of CHF occurring. CHF was observed at the top portion of the grooved channel and was found to be of departure from nucleate boiling type.

Steam inside the containment should be condensed to reduce the system pressure after severe accidents such as loss of coolant accident (LOCA) and main steam line break (MSLB). Due to the absence of an active coolant system, the passive containment cooling system (PCCS) can be used to improve safety by condensing the steam on a test section (coolant) tube surface. However, the steam condensation is degraded by the presence of non-condensable gases like air. The condensation heat transfer coefficient is dependent on operating parameters such as system pressure, air-mass fraction, and wall subcooling and geometric parameters such as tube diameter, tube length, and angle of orientation. In the present study, experiments are conducted on a vertical tube to estimate the condensation heat transfer coefficient in the presence of air. The system pressure ranges from 2 - 5.5 bar, air-mass fraction of 0.3 - 0.8 and wall subcooling of 27 - 80 degrees C. The influence of test section tube diameter (48.2 mm, 32 mm, 22 mm, and 16 mm) and inclination angles (90 degrees and 68 degrees from the horizontal) are investigated. Based on the experimental data, a correlation for condensation heat transfer coefficient in terms of system pressure, air-mass fraction, wall subcooling, tube diameter and angle of inclination is proposed. The condensation heat transfer coefficient increases with the increase in the system pressure and decreases with the increase in the air mass fraction, wall subcooling and condenser tube diameter. With the decrease in the diameter of the vertical condenser tube from 48.2 mm to 16 mm, an increase in the condensation heat transfer coefficient of 66% is observed. A non-dimensional correlation for condensate Nusselt number as a function of Grashof number, air-mass fraction and Jakob number is also proposed. This correlation predicts 80% and 90% experimental data within 20% and 30% uncertainty range, respectively. (c) 2023 Elsevier Ltd. All rights reserved.

The current study investigates the distribution of local heat transfer coefficient, measurement of pressure loss and CHF in a lobed horizontal channel for flow boiling. Lobed channels with different lobed depths of 2.3, 2.0 and 1.25 mm, each having three different channel lengths (400, 600, and 1000 mm), are used for the experiments. The working substance used is R-123 with different mass flux. The heat flux range used is from 14 to 375 kW/m(2). Pressure drop, critical heat flux, and local heat transfer coefficients of the lobed channel are compared with corresponding smooth horizontal tubes.

The accurate measurement of thermal properties of ferro siliceous sacrificial concrete (FSSC) is quite difficult but essential to study the radiation shielding behavior and molten core corium interaction (MCCI). The present study aims to propose a step-wise transient method based on a semi-infinite medium principle to measure the different thermal properties of FSSC using transient temperature measurement and a simple data processing approach. Various thermophysical properties such as specific heat, thermal conductivity, thermal diffusivity and thermal effusivity are determined, which can be helpful to understand the ablation behavior of the FSSC during molten core-corium interaction in nuclear power plants. The results of specific heat of the FSSC vary from 760 to 770 J/ kg.K, while the value of thermal conductivity lies in the range of 7.0-7.4 W/m.K. The average value of thermal diffusivity and thermal effusivity is found to be 2.51 x 10-6 m2/s and 3900.5 Jm-2K -1s-1/2,respectively. The specific heat obtained using semi-infinite assumptions is predicted well by the rule of mixture. The results of thermal conductivity obtained from the present model are compared with the results of the Serial, Parallel and Lichtnecker models available in the literature. These models under predict the value of thermal conductivity obtained from the experimental results.

We present a numerical study of inclined jet impingement on a heated flat surface. Previous research on such configuration focused on peak heat transfer rate and its location on the impingement surface. However, for the inclined jet, it is still unresolved whether the peak heat transfer rate location coincides with the stagnation point or not. Present investigation tries to resolve these locations, their importance, and their relevance to wall shear stress distribution and turbulence fluctuations. We carried out a numerical study using Scale Adaptive Simulation (SAS). Volume of Fluid (VOF) method was employed to capture the liquid–air interface. We used a circular pipe with an inner diameter of 6mm to produce a fully developed jet. The inclination angle varied from 45°to 0°(in the interval of 15°), where 0°is the orthogonal jet case. The numerical study was validated by comparing numerical findings with experimental data. It was found that locations of stagnation point and peak heat transfer locations are distinct. Shear stress distribution at the impingement surface is vital in determining peak heat transfer location. Also, increased turbulence fluctuations near the impact cause sharp variations in the Nu profile for the inclined jet.

Packed beds with diverging geometry find applications in packed bed reactors and converging geometry are used in the ethanol fermentation process. Experimental studies are conducted on pressure drop characteristics of converging and diverging packed beds with spheres of same diameter, spheres of different diameters, cylindrical inserts and mixing of spherical and cylindrical particles. The packing material spheres used is made up of stainless steel (SS304) having particle diameters 2.38 and 5 mm and cylinders of copper having 2 mm diameter and 4.6 mm height. The pressure drop is measured for a Reynolds number (based on particle diameter) range of 20-1200 with water as the working fluid. In this work, the effects of various converging and diverging angles of test section on the pressure drop in packed beds are studied. The pressure drop in packed beds with cylindrical inserts is higher as compared to pressure drop with packing of 2.38 and 5 mm spherical particles. The deviation in pressure drop for converging and diverging ducts at similar range of particle Reynolds number is less than 15% for majority of the cases. The pressure drop behavior for mixed packing of spheres and cylinders in converging and diverging channels are also explored in this work. The feasibility of using cylindrical packed bed correlation for very small differential elements of converging and diverging channels is examined in this study. The method used to calculate the pressure drop by using straight channel correlation is found to be applicable for both the converging and diverging channel packed beds.

An experimental study was performed to understand heat transfer characteristics of inclined liquid jet impingement on heated semi-cylindrical convex curved and flat surfaces in free surface configuration (unconfined). In experiments, curvature ratio of D/d = 7 along with the flat surface (D/d -> infinity) were considered, here d is the hydraulic diameter of the circular pipe used to produce a liquid jet, and D is the cylindrical surface's diameter. Jet to plate spacing (H) was held constant to 24 mm (H/d = 4). Results are presented for four different inclination angles [0 degrees (orthogonal jet), 15 degrees, 30 degrees, 45 degrees], and Reynolds numbers (17,036 to 42,590). Applicability of inclined jet impingement on a curved and flat surface, their advantage, disadvantages in terms of heat removal rate (Nusselt number) are discussed. A Parametric study was performed by varying Reynolds number, inclination angle, and curvature ratios (D/d) to understand these parameters' effect on heat transfer. Findings revealed that higher inclination angle cases (theta = 30 degrees and theta = 45 degrees) could give an overall high heat removal rate from the cylindrical surface as compared to the orthogonal jet case, especially for higher Reynolds numbers. However, there are no advantages in terms of the heat removal rate by using an inclined jet for lower Reynolds number cases.

Impinging jet studies are available in the literature, which involves air as a working fluid or water in the submerged jet configuration. However, literature is scarce for free surface liquid jet impingement. In this work, heat transfer characteristics of free surface water jet impingement on a convex uniformly heated semi-cylindrical curved surface is presented. In experiments, two different curvature ratios, Did are considered, where d is the inner diameter of circular nozzle pipe, and D is the outer diameter of the semi-cylindrical convex surface. Jet to surface distance was fixed to H/d = 4 (d = 6 mm). Reynolds number ranging from 17036 to 42590 were considered for experimental study. Nusselt number contours are presented for three different Reynolds numbers and two different curvature ratios, in which one case was D/d = infinity (flat surface). Present investigation revealed that surface curvature effects heat removal rate near the stagnation point. Heat transfer away from the impact in the circumferential direction is found to be affected by curvature, especially for higher Reynolds number (Re = 42590). (C) 2020 Elsevier Ltd. All rights reserved.

The accelerating growth of electricity demand necessitates looking for potential waste heat recovery solutions in production industries. Significant potential for efficient waste heat recovery is observed in the cement manufacturing industry. Based on the waste heat source temperatures in a cement plant, two potential candidates, the supercritical CO2 Brayton (S-CO2) cycle or the Organic Rankine cycle (ORC), promises low capital cost and enhanced thermodynamic performance. The current study focuses on modelling and optimization of the S-CO2 and ORC cycles for a 1 MTPA cement plant, with the raw-clinker preheater as the waste-heat source. The primary objective is to maximize the net-power output using genetic algorithms. A comparative performance analysis of the two ORCs with working fluids: R134a and Propane, the simply recuperated S-CO2 cycle (RC) and recompressed-recuperated S-CO2 cycle (RRC) configurations is presented with varying number of preheaters. For all cases, ORC-R134a yields more power than the ORC-Propane, RC, and RRC configurations. In terms of the waste heat recovered, ORC-Propane marginally outperforms ORC-R134a. The ORC configurations recover 32%–38% of the available heat, while the S-CO2 configurations recover, at maximum, 25%–30% of the available heat.

Packed beds are used at the laboratory scales to model and understand the phenomena of water flow through soil and rocks. The behaviour of local wall heat transfer coefficient with randomised packing of mono-dispersed spheres is examined in the present study. Under steady-state conditions, the high-resolution local wall temperature data is obtained by placing the infrared (IR) camera in close proximity to the test section. The local wall heat transfer coefficient is computed using the measured bulk fluid temperature, local wall temperature data and applied heat flux. Physical and numerical experiments were conducted for the narrow bed to particle diameter ratio of 1.25 using random packing of mono-dispersed (impermeable) glass spheres (diameter 6 mm) in order to be able to recreate similar geometry for numerical simulations of fluid flow and heat transfer. An attempt is made for recreation of the experimental narrow bed geometry by using the technique of method of gaps and computational fluid dynamics simulations were performed. The results of simulations are presented in appropriate velocity vectorial plots and flow stream lines revealing complex 3D mixing patterns inside void spaces of the narrow bed. Local variations of wall heat transfer coefficient are found along the packed bed and the numerical simulations of fluid flow and heat transfer reveal interesting complex flow patterns inside the bed.

During the free-surface circular water jet impingement cooling of a heated surface (250 degrees C-900 degrees C), rewetting is an important phenomenon that can be directly correlated with the measured surface temperature history and heat flux distribution. In the present work, an experimental study of water jet impingement cooling is done on a heated horizontal SS-304 plate of dimension 78 x 78 x 13 mm(3) instrumented with seven embedded thermocouples at two different depths of 1 and 3 mm from the top surface. An orthogonal free-surface circular water jet with nozzle diameter of 4 mm is used for the current study. The effect of variation in different parameters like water flow rate, initial plate temperature, nozzle-plate spacing, and so forth on rewetting and the wetting front growth during water jet cooling is analyzed. Experimental results and visual observations show that the wetting front growth rate increases with increase in water flow rate from 3 to 5 LPM and decreases with an increase in initial plate temperature (500 degrees C-900 degrees C), respectively. However, no significant effect is observed with the change in nozzle height beyond 100 mm.

Experimental and computational investigation is carried out to study heat transfer characteristics and to explain the underlying physics for the case of inclined free surface liquid jet impinging on a uniformly heated flat plate. Experimentally, four Reynolds number 17541, 26,311, 35,081, and 438,521 were considered while in the numerical study, Reynolds number of 17,541 and 26,311 were considered. In all the experiments, jet to surface spacing was fixed (H/d=4) and inclination angles of 45o, 30o, 30o and 0o (orthogonal jet) were considered. Local Nusselt number contours are presented for the above range of Reynolds number and inclination angle. Also, profiles of Nusselt number are analyzed and compared for different Reynolds numbers and inclination angles (θ). The numerical study was performed using SST-SAS model and VOF method was used to capture the liquid-air interface. The aim of the numerical study is to explain the underlying physics of heat transfer characteristics through flow dynamics. Streamlines, pressure, velocity, and turbulence intensity are calculated and plotted for a few cases. It is observed that with increasing inclination angle, the location of peak Nusselt number is shifted towards the compression side or uphill side, while the magnitude remains nearly the same. The point of maximum Nusselt number was found to be independent of Reynolds number.