Experimental Evaluation of Cavitating Venturi as a Passive Flow Controller in Different Sizes

The paper presents an innovative method for smoothing fluctuations of heat flux, using the thermal energy storage unit (TES Unit) with phase change material and Artificial Neural Networks (ANN) control. The research was carried out on a pilot large-scale installation, of which the main component was the TES Unit with a heat capacity of 500 MJ. The main challenge was to smooth the heat flux fluctuations, resulting from variable heat source operation. For this purpose, a molten salt phase change material was used, for which melting occurs at nearly constant temperature. To enhance the smoothing effect, a classical control system based on PID controllers was supported by ANN. The TES Unit was supplied with steam at a constant temperature and variable mass flow rate, while a discharging side was cooled with water at constant mass flow rate. It was indicated that the operation of the TES Unit in the phase change temperature range allows to smooth the heat flux fluctuations by 56%. The tests have also shown that the application of artificial neural networks increases the smoothing effect by 84%.

Passive flow control in liquid-propellant rocket engines with cavitating venturi

Cavitating venturis are common as flow control devices in liquid rocket engines. The fact that cavitating venturi provide a constant flow rate under varying downstream pressure, they are particularly useful during the ignition transient when the downstream pressure in the combustion chamber rises rapidly. Pressure recovery is one of the key design issues for cavitating venturis. By using empirical relations a cavitating venturi can be designed with acceptable pressure recovery at a desired mass flow rate. However dimensionless parameters such as critical cavitation number and discharge coefficients are geometry and fluid dependent which cannot be achieved by the empirical relations. These parameters can be deduced from computational fluid dynamics simulations. Therefore, the aim of this study is to model cryogenic cavitating flows by using a commercially available flow solver ANSYS Fluent and validating the simulations with the experiments.

Performance and image analysis of a cavitating process in a small type venturi

Thermal modeling and development of characteristic equations of evacuated tubular collector (ETC)

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing supply systems. Cylindrical sintered bronze inserts featuring lengths, diameters and particle sizes commonly used in gas bearings and thrust pads were examined. The paper describes the test set-up and experimental results obtained for: a) Mass flow rate through single porous resistances at different upstream and downstream pressures; and b) Mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from set-up a) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from set-up b) were compared with those from set-up a) at the same pressure differentials across the insert.

An understanding of the potential environmental impacts of amine solvents used in Carbon Capture and Storage (CCS) is important as more of these technologies are moving to the pilot stage of development and will be more regularly operated. It is clear that solvents with otherwise promising performance may have challenges and considerable inherent problem due to by-product formation, of which often neglected. In this regard, it is also necessary to study the concentration profiles of the by-products formed in aid of treating liquid waste streams. The study also includes the chemistry and reaction mechanisms of amine transformation products. The studied quaternary systems in varying blends were generally written as CO2- amine-TEA-H2O, where amine could be MEA or DEA. TEA corresponds to triethanolamine, MEA to monoethanolamine, and DEA to diethanolamine. The simulation was done using Aspen Plus® v8.6 at different mass flow rates (kg/h): 500, 750, and 1,000; temperatures (oC): 25, 30, 35, 40, 45, and 50; and pressures (atm): 1, 2, and 3. The results shows direct proportionality between the efficiency and solvent’s flow rate, pressure, higher secondary amines ratio along with temperature in majority. At constant temperature, pressure, and mass flow rate, the highest removal efficiency was that of MEA-TEA (10-20 %wt) and the lowest was DEA-TEA (10-20 %wt). In addition, the results yield reasonable predictions on liquid-phase product concentration profiles. The components behave according to their expected trends and the results are very promising.

Vincristine has been proven promising regarding its safety and efficacy for the renal artery denervation both in experimental models and in humans. The aim of the study was to compare in an experimental model the efficacy of constant versus random flow rate delivery of vincristine on renal sympathetic denervation. We used 10 juvenile Landrace swine. After the introduction of a 7F sheath into the femoral artery, a guide wire was advanced into the distal part of the renal artery. Then the first delivery balloon catheter, which delivers vincristine in random flow rate, was advanced at the proximal part of the artery, and the balloon was inflated in order to locally deliver vincristine to the media of the renal artery. The process was repeated in the contralateral renal artery, with the use of the double balloon catheter that delivers vincristine with a constant flow rate. Euthanasia of the animals was performed at 28 days. All sections were processed for histological and immunohistochemical analysis. The delivery of vincristine with both catheters was successful and uncomplicated. Immunohistochemistry showed that the mean number of intact nerves in all sections was significantly lower in the group of vincristine delivered with constant flow catheter compared to the group that the delivery was performed in a random fashion. (1.48 ± 0.37 vs. 1.70 ± 0.41, p = 0.04). Chemical renal denervation with vincristine by a constant flow rate catheter is more effective compared to the denervation performed by a catheter that delivers vincristine in a random fashion.

Theoretical and empirical models for the gas void fraction (α) are reviewed. Simple rules are developed for obtaining rational bounds for the void fraction in two-phase flow. The lower bound is based on the separate cylinders formulation for turbulent-turbulent flow that uses the Blasius equation to predict the Fanning friction factor. The upper bound is based on the Butterworth relationship that represents well the Lockhart-Martinelli correlation. These two bounds are reversed in the case of liquid fraction (1−α). The bounds models are verified using published experimental data of void fraction versus mass quality at constant mass flow rate. The published data include different working fluids such as R-12 and R-22 at different pipe diameters, different pressures, and different mass flow rates. It is shown that the published data can be well bounded for a wide range of mass qualities, pipe diameters, pressures and mass flow rates. Further comparisons are made using the published experimental data of void fraction (α) and liquid fraction (1−α) versus the Lockhart-Martinelli parameter (X), for different working fluids such as R-12, R-22 and air-water mixtures.

Introducing glass fibre to polyurethane foams increases the foam stiffness without raising the isocyanate content. This allows glass fibre reinforced polyurethane foams to be used in structural applications. Glass fibre reinforced polyurethane foams can be manufactured on a large scale using a chopper gun spray system. The glass fibre is commonly supplied as a roving (long strands of fibre wound into a spool) and the chopper gun breaks the roving into equal length pieces, which delivers a stream of glass fibre at a constant mass flow rate. Residual natural fibre is cost-effective, abundant and renewable making it an ideal candidate to replace non-renewable glass fibre in reinforcing polyurethane foam. However, residual natural fibre are often supplied as loose tufts and require multiple steps to be made into roving. In this study, a novel concept was developed that can meter natural fibre at a constant mass flow rate. The concept has the potential for developing natural fibre reinforced polyurethane foams on a large scale, with uniform fibre dispersion and high fibre volume fractions. The concept is verified through mathematical simulations and a prototype.

A thermal energy storage medium must meet the requirements of a stable storage material with high heat capacity. Heat storage based on the sensible heating of media such as water, rock, and earth represents the first generation of solar energy storage subsystems and technology for their utilization is well developed. However, recently the heat storage based on the latent heat associated with a change in phase of a material offers many advantages over sensible heat storage. The most important characteristic of such a subsystem is its sufficient storage capacity. The PCM (phase change material) behavior is visualized by constructing an idealized model thermal capacitor subjected to simulated solar system environmental conditions which include thermal cycling utilizing the latent heat of paraffin for heating and cooling. The proposed model of the capacitor is of a flat plate geometry consisting of two panel compartments forming the body of the capacitor containing the paraffin, leaving at their inner surfaces a thin passage allowing the water flow. The whole structure is assumed to be insulated to minimize heat loss. Analysis solution is used to generate data about the temperature distribution, the melt thickness, and the heat stored in the PCM under two conditions of: (a) constant mass flow rate tests for various water inlet temperatures, and (b) constant water inlet temperature for various mass flow rates. A FORTRAN computer program is constructed to perform the analysis. It is found that water outlet temperature increases with time until it becomes nearly equal to the inlet temperature. Increasing the mass flow rate for a given inlet temperature, decreases the time required for outlet temperature to reach a given value. Increasing inlet temperature for a given mass flow rate gives a very rapid decrease in the time required for the outlet water temperature to reach a given value. Instantaneous rate of heat storage is determined from the inlet-to-exit temperature differential and measured flow rate. This rate is then integrated numerically to determine the cumulative total energy stored as a function of time. It is found that the instantaneous rate of heat storage decreases till reaching a nearly constant value. The total or cumulative heat storage as a function of time, showed a nearly linear trend in the mid-range time, and it increased with increasing inlet temperature.

Optimization of insulation thickness of double buried district heating pipes using the Eco-indicator method

Theoretical investigation of a humidification-dehumidification desalination system configured by a double-pass flat plate solar air heater

Flow-blurring (FB) is a twin-fluid atomization technique that generates fine sprays through internal turbulent mixing. This study presents a parametric computational investigation of an FB injector operating with air and various liquids at ambient pressure. A validated unsteady two-phase solver based on the Volume of Fluid (VOF) method is used to model the injector at different air-to-liquid mass flow rate ratios (ALRs). Parameters such as penetration length, volume fraction, static pressure, vorticity magnitude, and turbulent kinetic energy are analyzed to understand flow dynamics. The results identify three distinct flow regimes: air-dominant, liquid-dominant, and bubbly flow. Screening analysis of a full factorial design of 32 cases shows that liquid mass flow rate and dynamic viscosity are the most influential factors in penetration length. The resulting penetration length varies between 2 [mm] and 8.5 [mm] across the design space. A correlation analysis confirms these findings and reveals important two-way interactions between parameters, such as the positive effect of combined liquid and air mass flow rates. This insight offers a promising pathway for optimizing flow-blurring injectors in various applications.

This paper describes about the design, fabrication and flow simulation of a choked flow nozzle which is used to supply constant mass flow rate to the air heater which can provide supersonic conditions for Supersonic Engine Test Facilities. The test facility is considered to be capable of delivering working gas at 5-20 kg/s flow rate, stagnation temperature at 800-2200 K and stagnation pressure at 8-40 bar to the inlet of combustion chamber of the engine for specified duration. The outlet condition for the choked nozzle is considered to be known and the required inlet pressure for the nozzle has to be found out. This converging nozzle should be capable of providing constant mass flow rate.