Mansoor Hameed Inayat

Numerical Simulation of Direct-contact Condensation from a Supersonic Steam Jet in Subcooled Water

Abstract The phenomenon of direct-contact condensation, used in steam driven jet injectors, nuclear reactor emergency core cooling systems and direct-contact heat exchangers, was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water. The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter. The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics (CFD) simulations were compared with the published experimental data and fairly good agreement was observed between the two, thus validating the condensation model. The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33, while the condensation heat transfer coefficient varies from 0.75-0.917 MW·(m 2 ·K) −1 for water temperature in the range of 293-343 K.

Study of axial mixing, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column using radiotracer technique.

Axial mixing, holdup and slip velocity of dispersed phase which are parameters of fundamental importance in the design and operation of liquid-liquid extraction pulsed sieve plate columns have been investigated. Experiments for residence time distribution (RTD) analysis have been carried out for a range of pulsation frequency and amplitude in a liquid-liquid extraction pulsed sieve plate column with water as dispersed and kerosene as continuous phase using radiotracer technique. The column was operated in emulsion region and (99m)Tc in the form of sodium pertechnetate eluted from a (99)Mo/(99m)Tc generator was used to trace the dispersed phase. Axial dispersed plug flow model with open-open boundary condition and two points measurement method was used to simulate the hydrodynamics of dispersed phase. It has been observed that the axial mixing and holdup of dispersed phase increases with increase in pulsation frequency and amplitude until a maximum value is achieved while slip velocity decreases with increase in pulsation frequency and amplitude until it approaches a minimum value. Short lived and low energy radiotracer (99m)Tc in the form of sodium pertechnetate was found to be a good water tracer to study the hydrodynamics of a liquid-liquid extraction pulsed sieve plate column operating with two immiscible liquids, water and kerosene. Axial dispersed plug flow model with open-open boundary condition was found to be a suitable model to describe the hydrodynamics of dispersed phase in the pulsed sieve plate extraction column.

Axial dispersion, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column by radiotracer residence time distribution analysis

Axial dispersion, holdup and slip velocity of dispersed phase have been investigated for a range of dispersed and continuous phase superficial velocities in a pulsed sieve plate extraction column using radiotracer residence time distribution (RTD) analysis. Axial dispersion model (ADM) was used to simulate the hydrodynamics of the system. It has been observed that increase in dispersed phase superficial velocity results in a decrease in its axial dispersion and increase in its slip velocity while its holdup increases till a maximum asymptotic value is achieved. An increase in superficial velocity of continuous phase increases the axial dispersion and holdup of dispersed phase until a maximum value is obtained, while slip velocity of dispersed phase is found to decrease in the beginning and then it increases with increase in superficial velocity of continuous phase.

Low cost indigenous particle imaging velocimetry

This study investigates the flow visualization using PIV technique. It is tried to indigenously develop PIV technique with the help of low power laser, ordinary camera, and available tracer particles. PIV results are obtained with the help of some open software. Flow patterns of water containing tracer particles are studied. Flows are induced by magnetic stirrer and rotor. Flow visualization study is very useful in finding velocity profiles of different flows. Instantaneous vector maps of flow field and calibration of velocities are presented. Further studies are under consideration in PIEAS to develop the mature PIV technique.

Comparative study of static and dynamic wetting properties of liquid-liquid phase in PMMA microfluidic T-shaped device

Microfluidics plays a vital role in modern technologies. Microfluidics has large and widespread applications especially in the field of bio-medical science, enhancing the reaction rates, chemical synthesis, electro chromatography and drug screening. The purpose of this research is to interrelate the wetting dynamic property at micro level in T-junction of a Poly methyl methacrylate (PMMA) channel to the static property at macro scale, as the dynamic property measurement at micro level is quite arduous. The experimental study of oil-water system was performed on micro and macro level. Formation of droplets were carried out in PMMA microchip using passive methodology and visualized with the help of camera mounted microscope. The sizes of these droplets were calculated by image processing. Fabrication of T junction microchip was performed by surface activation method. In the micro device the water droplet (dispersed medium) were formed in the vegetable oil (continuous medium) and the effect of different concentration of TWEEN 80 surfactant was studied. On the macro level the critical concentration of surfactant was measured by means of interfacial-tension between oil and water interface and contact-angle variation. While at micro level the effect of surfactant on droplet length was varied exponentially with its concentration then a breakeven point of surfactant amount was observed after which no significant change in wetting property was found. It was inferred that the wetting properties in microfluidic device can be characterized by the support of macro scale measurements.

Design a helical coil heat exchanger via CFD simulations

Helical coil heat exchangers are featured as compact and high heat transfer coefficient devices. Due to which the nuclear industry is focusing on efficient designs of helical coil steam generator to employ in advanced Small Modular Reactors (SMRs). In this work, CFD simulations have been carried out to study the heat transfer through helical coil heat exchanger by using a commercial code (Fluent). Constant heat flux boundary condition has been used in this work. Temperature distribution along its length and radial direction has been monitored. The significant effect of centrifugal forces has been visualized with the aid of contours of velocity distribution along radial direction. The analytical calculations have corroborated the simulations results.

Development of an inexpensive tensiometer for surface tension and contact angle measurements

In this paper we propose a low cost tensiometer that is easily reproducible with the requirement of minimal components and basic technical skills. It mainly uses a low cost Arduino microcontroller and a stepper motor to dispense the liquid. The calibration of the tensiometer was performed using the gravimetric method in order to test its accuracy and reliability. The tensiometer was mounted vertically in order to obtain a uniform shape of the droplet emerged from the tip of a blunt needle fitted at plastic (or glass) syringe which is suspended vertically under gravity. The droplet images were captured with CCD camera and analyzed in the image analysis software in order to calculate the drop shape factor which helps to evaluate the surface tension of the liquid using pendent drop method. The results were achieved within the range of 0.5–1 mN m−1 of literature values. Furthermore the sessile droplet method was used for measuring the water contact angle with the solid surface. The images were processed in the image analyzer software in order to measure the contact angle. It reveals that our laboratory made low cost tensiometer enable to measure the wetting properties and surface tension accurately. The accuracy of the instrument is found to be within the range of 1.0 percent in the determination of the surface tension of water.

Experimental study and CMFD modeling of transport processes in flow of two Immiscible liquids

Rectangular shaped sieve plate column was installed for study of transport parameters through high speed photography and image analysis. Two Immiscible liquids consisting of the dispersed phase (water) and continuous phase (kerosene oil) were introduced in countercurrent operation. Experiments were performed for dispersed and continuous phase superficial velocities 0.16-0.44 cm/sec and 0.37-0.47 cm/sec respectively, pulsation frequency 0.95 -1.72 rev/sec and pulsation amplitude 1cm. Upon increasing the superficial velocity of dispersed phase, its void fraction increases up to its asymptotic value and droplet velocity increase while the droplet size decreases. Upon increasing the pulsation frequency, its void fraction increases while the droplet size and droplet velocity decreases. A Computational Multi Fluid Dynamics simulation has been carried out in order to verify the experimental results using the FLUENT. The CMFD calculations for void fraction have been compared with the experimental results which have shown a maximum deviation of 2-3%.