Optimum Mass Flow Research Articles

Design Verification of Heat Exchanger for Ballast Water Treatment

Using waste heat from ship’s engines is one of the methods considered for heat treatment of ballast water. For such a system harvesting the engine exhaust heat, a heat exchanger will be vital. Design optimisation of a heater employing exhaust gases of the engine as utility fluid and ballast sea water as the process fluid was achieved using Lagrangian methods, keeping the annual cost as the objective function. Costs for installation, maintenance as also costs for the utility and process fluids were considered. Heat balance data, specific fuel consumption values from a typical operational ship and current fuel costs were considered for the design. The thermodynamic and geometric designs were worked out using computer based software for comparing the designs. Costs were also computed using a different approach for all the designs. Since the amount of heat transferred was specified and the application was limited to a single process, direct cost method was used for the computation. The objective function values obtained from Lagrangian equations were compared with the values obtained from direct cost computations. From the optimal designs, choice was justified based on annual cost, optimum exit temperature of shell side fluid and optimum mass flow of tube side fluid..

Optimal operating conditions for maximum biogas production in anaerobic bioreactors

The objective of this paper is to demonstrate the existence of optimal residence time and substrate inlet mass flow rate for maximum methane production through numerical simulations performed with a general transient mathematical model of an anaerobic biodigester introduced in this study. It is herein suggested a simplified model with only the most important reaction steps which are carried out by a single type of microorganisms following Monod kinetics. The mathematical model was developed for a well mixed reactor (CSTR – Continuous Stirred-Tank Reactor), considering three main reaction steps: acidogenesis, with a μmax of 8.64 day−1 and a KS of 250 mg/L, acetogenesis, with a μmax of 2.64 day−1 and a KS of 32 mg/L, and methanogenesis, with a μmax of 1.392 day−1 and a KS of 100 mg/L. The yield coefficients were 0.1-g-dry-cells/g-pollymeric compound for acidogenesis, 0.1-g-dry-cells/g-propionic acid and 0.1-g-dry-cells/g-butyric acid for acetogenesis and 0.1 g-dry-cells/g-acetic acid for methanogenesis. The model describes both the transient and the steady-state regime for several different biodigester design and operating conditions. After model experimental validation, a parametric analysis was performed. It was found that biogas production is strongly dependent on the input polymeric substrate and fermentable monomer concentrations, but fairly independent of the input propionic, acetic and butyric acid concentrations. An optimisation study was then conducted and optimal residence time and substrate inlet mass flow rate were found for maximum methane production. The optima found were very sharp, showing a sudden drop of methane mass flow rate variation from the observed maximum to zero, within a 20% range around the optimal operating parameters, which stresses the importance of their identification, no matter how complex the actual bioreactor design may be. The model is therefore expected to be a useful tool for simulation, design, control and optimisation of anaerobic biodigesters.

Theoretical Study of New Configuration of Photovoltaic/Thermal Solar Collector (PV/T) Design

The combination of solar thermal and PV technologies leads to form a single module called PVT system. This system is able to produce heat and electricity simultaneously. In this paper, a new configuration and design of PV/T system are proposed, and a theoretical study of this system is evaluated. The PV/T consists of certain layers which are the glass, air gap, PV panel, absorber plate and insulating material layer. The monocrystalline PV and spiral flow absorber plate are used in this study. The results of the system performance under typical sunny climatic Malaysian condition are presented. The maximum thermal and electrical efficiencies obtained are 64.4 % and 12.13%, respectively. The effect of mass flow rate on the outlet water temperature is also evaluated. It is shown that the optimum mass flow rate for the designed system is between 0.005 and 0.075 kg/s.

Avoiding Compressor Surge During Emergency Shutdown Hybrid Turbine Systems

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide a means of quantifying risk mitigation strategies. An open-loop system analysis regarding the dynamic effect of bleed air, cold air bypass, and load bank is presented in order to evaluate the combination of these three main actuators during emergency shutdown. In the previous Hybrid control system architecture, catastrophic compressor failures were observed when the fuel and load bank were cut off during emergency shutdown strategy. Improvements were achieved using a nonlinear fuel valve ramp down when the load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shutdown activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.

Abrasive water-jet milling of aeronautic aluminum 2024-T3

The abrasive water jet is a 30-year old technology widely used to compete conventional machining capabilities. While it is mainly used for cutting applications, studies demonstrated its ability for milling, turning and micro-piercing. But as long as abrasive water jet issues are not clearly identified and analyzed, these processes can hardly be industrialized. This paper proposes an innovative methodology for studying abrasive water jet milling. Its main purpose is to consider the machined depth as an experimental factor and the feed rate as a product. A large-domain full-experimental-design on the pressure, the orifice diameter, abrasive mass flow rate, the milled depth and the feed rate on milling of aluminum 2024 T3 is presented. Finally, a mathematical model on the optimal abrasive mass flow rate and the milled depth are developed. The good correlation of these models within the large experimental domain suggests the pertinence of the proposed methodology.

Part load based thermo-economic optimization of the Organic Rankine Cycle (ORC) applied to a combined heat and power (CHP) system

The objective of this paper is to develop a thermo-economic design methodology for an Organic Rankine Cycle (ORC) based on the specific investment cost (SIC), taking into account changing operating conditions and part load behavior. ORCs typically work in changing operating conditions. Examples are solar, waste heat, and combined heat and power applications (CHP). The proposed design methodology consists of four steps. First an ORC is sized for fixed operating conditions. With this sizing the part load regime is modeled. The part load model is then used in a 1-year simulation to assess the actual power output. The last step comprises of selecting the optimal sizing. The usefulness of the model is illustrated by applying it to an actual CHP system. Electricity is produced by internal combustion engines while the hot engine water is used for the heating of nearby buildings. However, there is still hot engine water left which can be fed to an ORC. The results of a year simulation show that the net power output varies strongly over a year, which in turn affects the SIC. Consequently, in a thermo-economic analysis it is of key importance to take into account the part load behavior of the system components. The methodology presented in this paper allows selecting the optimal size of the heat exchangers (condenser and evaporator), the optimal mass flow rates and the maximal power of fans and pumps for an application specific ORC. Hence, it is very useful for design and optimization purposes.

Thermoeconomic design optimization of a thermo-electric energy storage system based on transcritical CO2 cycles

The conceptual design of a thermo-electric energy storage (TEES) system for large scale electricity storage is discussed in this work by showing the results of the thermoeconomic optimization of three different system configurations that were identified in previous works. The system is based on transcritical CO2 cycles, water storage and salt-water ice storage and is designed for a capacity of 2 h discharge and equal charge and discharge power of 50 MW. A two-step optimization procedure is used. The system intensive design parameters are optimized at the master level through a genetic algorithm. The optimal cycle mass flow rates are calculated in a nested linear programming step where the heat integration between the cycles is optimized subject to the heat transfer feasibility imposed through Pinch Analysis cascade calculations. The synthesis of the heat exchanger network and of the storage tank systems was solved through a set of heuristic rules. Equipment purchasing costs were estimated by means of cost functions that were built upon vendors quotations. The results are discussed by showing the Pareto fronts of the three optimization cases and the trends of the decision variables along each optimal front. Nine solutions are discussed in more detail by showing the values of the design parameters and the process flow diagrams including storage and heat exchanger layouts. Design guidelines are then formulated which can be used in future works for detail plant design. The topological features that are found to maximize the system performance at the minimum costs are: superheating before the CO2 heat pump, two independent systems of hot water storage tanks above and below the ambient temperature, and air cooling at the heat pump side. The design parameters that affect significantly the costs and performances are the cycle pressures. These are in fact directly associated with temperature differences both at the cold and hot storage sides which should be carefully optimized to obtain the best trade-off between exergy losses and costs for heat exchangers. Due to the change in specific heat of the supercritical CO2 along the temperature range of hot water storage, a system of multiple storage tanks was used. Intermediate storage tanks help reduce significantly the temperature differences at the hot storage side and therefore their number represent another critical design parameter that must be optimized to achieve the best trade-off between costs and performances.

The Theoretical Modelling and Optimization of a 10 KWP Photovoltaic Thermal System for a Student Hostel in Singapore

Current commercial photovoltaic (PV) conversion efficiency (flat plate modules) is about 6--20%, depending on the materials used for the module construction. Since only a small fraction (<10%) of the incident solar energy is reflected and/or transmitted, a large fraction of the solar radiation is converted into heat. If this heat can be harvested as well, the overall energy efficiency of such an integrated photovoltaic thermal (PVT) hybrid system will be greatly improved. At the same time, pumping water through the PV modules will cool (if Twater < Tmodule) the solar cells and improve their electricity production efficiency. This article describes the design and numerical simulation of a PVT system for producing electricity and hot water in a student hostel in Singapore. The nominal electrical power output is 10 kWp (kilowatt peak). Thermal models were developed based on basic energy balance equations and average climatic conditions for Singapore over a typical year were used. A survey of the hot water usage pattern over a typical week was carried out and used in the simulation. The optimum mass flow rate in the collectors is found to be 0.039 kg/(s m2) and the optimum storage tank capacity for hot water is 2500 kg for a showering load of around 6000 kg/day. The average thermal and electrical efficiency of the system are 43% and 12%, respectively. The requirement of auxiliary electric energy for water heating is predicted to be reduced by 94%.

Nonlinear modeling and simulation of waste energy harvesting system for hybrid engine: Fuzzy logic approach

Fuel consumption could be cut significantly if waste heat energy of internal combustion engine (ICE) is harvested. Currently, ICEs lose their 42% of energy to exhaust and 28% of energy to the coolant. Several methods for waste thermal energy recovery from ICE have been studied by using supercharger or turbocharger or combined. This study presents the modeling and simulation of coolant based waste energy harvesting system (weHS). The supercharger compressed air gains heat during passing through the inner duct of the weHS while the coolant releases heat. The heated supercharged air is forced to the engine cylinders. The energy harvesting system performance is simulated by varying the supercharged air mass flow rate by keeping constant the coolant mass flow rate and vice versa. The waste energy recovery from the coolant by using weHS is simulated for the coolant flow rate of 2.0 kg/s, 2.5 kg/s, and 3.0 kg/s. The simulations result shows that the waste energies that could be recovered by using weHS are 30.9% for 2.0 kg/s, 32.57% for 2.5 kg/s, and 35% for 3.0 kg/s of the energy that engine lost to the coolant. The efficiency of the engine is expected to increase significantly if weHS is equipped with the engine. The optimum mass flow rate of coolant and mass flow rate of supercharged air are identified by using the fuzzy logic model for the maximum supercharged air temperature of 120 °C.

Modeling and co-simulation of a parabolic trough solar plant for industrial process heat

In the present paper a tri-dimensional non-linear dynamic thermohydraulic model of a parabolic trough collector was developed in the high-level acausal object-oriented language Modelica and coupled to a solar industrial process heat plant modeled in TRNSYS. The integration is performed in an innovative co-simulation environment based on the TLK interconnect software connector middleware. A discrete Monte Carlo ray-tracing model was developed in SolTrace to compute the solar radiation heterogeneous local concentration ratio in the parabolic trough collector absorber outer surface. The obtained results show that the efficiency predicted by the model agrees well with experimental data with a root mean square error of 1.2%. The dynamic performance was validated with experimental data from the Acurex solar field, located at the Plataforma Solar de Almeria, South-East Spain, and presents a good agreement. An optimization of the IST collector mass flow rate was performed based on the minimization of an energy loss cost function showing an optimal mass flow rate of 0.22kg/sm2. A parametric analysis showed the influence on collector efficiency of several design properties, such as the absorber emittance and absorptance. Different parabolic trough solar field model structures were compared showing that, from a thermal point of view, the one-dimensional model performs close to the bi-dimensional. Co-simulations conducted on a reference industrial process heat scenario on a South European climate show an annual solar fraction of 67% for a solar plant consisting on a solar field of 1000m2, with thermal energy storage, coupled to a continuous industrial thermal demand of 100kW.

Design and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS)

The present study considers the design, performance analysis and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS). The optimum mass flow rate of the geothermal fluid for minimum pumping power and maximum extracted heat energy was determined. In addition, the coaxial pipes of the downhole heat exchanger were sized based on the optimum geothermal mass flow rate and steady-state operation. Transient effect or time-dependent cooling of the Earth underground, and the optimum amount and size of perforations at the inner pipe entrance region to regulate the flow of the geothermal fluid were disregarded to simplify the analysis. The paper consists of an analytical and numerical thermodynamic optimization of a downhole coaxial heat exchanger used to extract the maximum possible energy from the Earth's deep underground (2 km and deeper below the surface) for direct usage, and subject to a nearly linear increase in geothermal gradient with depth. The thermodynamic optimization process and entropy generation minimization (EGM) analysis were performed to minimize heat transfer and fluid friction irreversibilities. An optimum diameter ratio of the coaxial pipes for minimum pressure drop in both limits of the fully turbulent and laminar fully-developed flow regime was determined and observed to be nearly the same irrespective of the flow regime. Furthermore, an optimum geothermal mass flow rate and an optimum geometry of the downhole coaxial heat exchanger were determined for maximum net power output. Conducting an energetic and exergetic analysis to evaluate the performance of binary power cycle, higher Earth's temperature gradient and lower geofluid rejection temperatures were observed to yield maximum first- and second-law efficiencies.

Three-Dimensional Printing of Soy Protein Scaffolds for Tissue Regeneration

Fabricating three-dimensional (3D) porous scaffolds with controlled structure and geometry is crucial for tissue regeneration. To date, exploration in printing 3D natural protein scaffolds is limited. In this study, soy protein slurry was successfully printed using the 3D Bioplotter to form scaffolds. A method to verify the structural integrity of resulting scaffolds during printing was developed. This process involved measuring the mass extrusion flow rate of the slurry from the instrument, which was directly affected by the extrusion pressure and the soy protein slurry properties. The optimal mass flow rate for printing soy slurry at 27°C was 0.0072±0.0002 g/s. The addition of dithiothreitol to soy slurries demonstrated the importance of disulfide bonds in forming solid structures upon printing. Resulting Bioplotted soy protein scaffolds were cured using 95% ethanol and post-treated using dehydrothermal treatment (DHT), a combination of freeze-drying and DHT, and chemical crosslinking using 1-ethyl-3-(3 dimethylaminopropyl)carbodiimide (EDC) chemistry. Surface morphologies of the different treatment groups were characterized using scanning electron microscopy. Scaffold properties, including relative crosslink density, mass loss upon rinsing, and compressive modulus revealed that EDC crosslinked scaffolds were the most robust with moduli of approximately 4 kPa. Scaffold geometry (45° and 90° layer rotations) affected the mechanical properties for DHT and EDC crosslinked scaffolds. Seeding efficiency of human mesenchymal stem cells (hMSC) was highest for nontreated and thermally treated scaffolds, and all scaffolds supported hMSC viability over time.

Artificial Neural Network based control for PV/T panel to track optimum thermal and electrical power

As solar energy is intermittent, many algorithms and electronics have been developed to track the maximum power generation from photovoltaic and thermal panels. Following technological advances, these panels are gathered into one unit: PV/T system. PV/T delivers simultaneously two kinds of power: electrical power and thermal power. Nevertheless, no control systems have been developed in order to track maximum power generation from PV/T system. This paper suggests a PV/T control algorithm based on Artificial Neural Network (ANN) to detect the optimal power operating point (OPOP) by considering PV/T model behavior. The OPOP computes the optimum mass flow rate of PV/T for a considered irradiation and ambient temperature. Simulation results demonstrate great concordance between OPOP model based calculation and ANN outputs.

Thermodynamic optimization principle for open inverse Brayton cycle (refrigeration/heat pump cycle)

A thermodynamic model for an open inverse Brayton cycle (refrigeration or heat pump cycle) with pressure drop irreversibilities is established. There are seven flow resistances (or pressure drops) encountered by the working fluid stream for the inverse Brayton cycle. Two of these, the friction through the blades and vanes of the compressor and the expander, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet and outlet, heat exchanger inlets and outlets and expander inlet and outlet. The analytical formulae about the cooling load of refrigeration cycle, the heating load of heat pump cycle and other coefficients are derived, which indicate that the thermodynamic performance for open inverse Brayton cycle can be optimized by adjusting the mass flow rate (or the distribution of pressure losses along the flow path). It is shown that there are optimal air mass flow rates (or the distribution of pressure losses along the flow path) which maximize the cooling load of refrigeration cycle, and the optimal air mass flow rates are smaller than the one at the maximum power output of the direct Brayton cycle.

Thermodynamic optimization of an open cycle of an externally fired micro gas turbine. Part 2: Performance optimization

The power and efficiency of the open regenerative cycle of an externally fired micro gas turbine power plant without blade cooling with pressure drop irreversibilities are optimized based on the model established using thermodynamic optimization theory in Part 1 of this article by adjusting the mass flow rate (or the distribution of pressure losses along the flow path). It is shown that there are optimal air mass flow rates (or the distribution of pressure losses along the flow path) which maximize the net power output, and the maximum has an additional maximum with respect to the compressor pressure ratio. When the optimization is performed with the constraints of the fixed fuel flow and the plant size, the net power output and the thermal conversion efficiency of the cycle can be maximized again by properly allocating the fixed flow area among the compressor inlet and the power turbine outlet. The numerical examples show the effects of the design parameters on the power output and heat conversion efficiency and that both the power output and conversion efficiency increase with the increase in the effectiveness of the regenerator, which is different from the open cycle regenerator gas turbine power plant.

Study and optimization of a solar subcritical organic Rankine cycle

Abstract The theoretical and experimental studies presented in this paper show the potential of producing mechanical power by a system combining a solar thermal collector with an organic Rankine cycle (ORC). A theoretical model based on heat transfer equations was developed and predicted the thermal equilibrium state of a small-scale single glazed flat plate collector. Experiments conducted with a commercial collector validated the modeling predictions. The thermal performances of the commercial collector and improved double-glazed flat plate collector were then simulated for different operational conditions. A subcritical Rankine cycle was simulated for organic fluids R134a, R227ea and R365mfc operating between the solar collector and a fixed temperature sink. In order to establish the optimum configuration, a set of parametric studies was carried out. Special attention is given to the optimum mass flow rate and to the impact made by improving the thermal performance of the solar collector. The results show that the expected net mechanical power strongly depends on the fluid mass flow rate and the optimum flow is a linear function of the solar radiation. Reducing the collector heat losses appears as the most relevant solution before the choice of the working fluid to improve the overall installation performance. Finally, this configuration can produce net mechanical power with an optimum efficiency up to 11%.

Performance of cooling hot gas discharge spray cooler with flow parameters variation

Rockets with combustion chamber would reach 3500K to 3700K. For efficiency reasons and safe design of ejectors, after-cooler is interposed between the diffuser and ejector. This process is also operated at fairly high pressure 10 to 200 bar. Due to high temperature and pressure, thermal shocks generated are prevented by spraying water particles uniformly inside the gas cooler. In this paper, the significance of water spray characteristics is studied thoroughly. The water droplet evaporated into a flow of exhaust gases with a droplet size of 15 microns diameter increases the total surface area and is about 400 m2 . The spray cooler length is suggested as 7-9 m to reduce the component of unevaporated water for optimum mass flow rate of primary fluid. Water injection velocity and pressure are varied as using number of nozzles. The injection pressure is reduced 10 times (2.0 - 2.5 bar) by increasing the number of nozzles (about 2000) in quadruple. Keywords: Combustion chamber, Rocket, Injection pressure, Water spray

A Simulation Model for Predicting the Performance of Solar Domestic Hot Water System

The article deals with the modeling and simulation aspects of the performance improvement of a solar domestic hot water system. A mathematical model of this system is carried out to predict its operating performance under specified weather conditions of Jeju Island, Korea. The optimum mass flow rate through collector based on the relationship between the useful heat gain of solar collector and the electricity consumption of solar pump is investigated. Besides, the effect of various parameters such as solar collector area, initial water temperature and volume of storage tank is analyzed. The result of the simulation shows that the optimum mass flow rate was determined at kg/s with the new coefficient . At this value, the amount of useful heat gain slightly decreased about 84.3 (Wh) corresponds to 0.16% but the amount of electricity consumption strongly decreased about 227.8 (Wh) corresponds to 48.8% compares with kg/s ( ) was proposed by . Furthermore, the system performance is affected strongly by the change of collector area, initial water temperature and volume of storage tank.

Effect of flow distribution on the photovoltaic performance of a building integrated photovoltaic/thermal (BIPV/T) collector

The phenomenon of non-uniform flow distribution and its influence on thermal performance within a traditional solar thermal collector is well known. Its effect on the photovoltaic conversion of a hybrid photovoltaic/thermal (PV/T) collector however has received little attention. In this study an investigation has been carried out to determine what effect flow distribution will have on the photovoltaic yield of a BIPV/T collector of various size. A three step numerical analysis was conducted to model flow distribution, temperature variation, and photovoltaic yield for a PV/T collector of various design (manifold sizes), geometric shape (aspect ratio), and operating characteristics (mass flow rate and flow direction in manifolds) in order to vary flow uniformity within the collector. The results revealed that flow distribution within the collector will have a significant influence on the photovoltaic performance of a hybrid PV/T collector. For the scenario where flow distribution was most uniform, photovoltaic performance was improved by over 9% in comparison to a traditional photovoltaic (PV) collector operating under the same conditions. For poor flow however, performance was only improved by approximately 2%. Parameters found to influence flow distribution include the manifold to riser pipe ratio where a ratio of 4:1 was found to be ideal and that increasing to a 6:1 ratio offered negligible improvement. Additionally it was found that array geometry (characterised by its aspect ratio in this study) plays an important role on both flow distribution and photovoltaic yield. This study has identified that the optimal mass flow rate is dependent on the shape or aspect ratio of the array.

Shell side numerical analysis of a shell and tube heat exchanger considering the effects of baffle inclination angle on fluid flow using CFD

In this present study, attempts were made to investigate the impacts of various baffle inclination angles on fluid flow and the heat transfer characteristics of a shell-and-tube heat exchanger for three different baffle inclination angles namely 0°, 10°, and 20°. The simulation results for various shell and tube heat exchangers, one with segmental baffles perpendicular to fluid flow and two with segmental baffles inclined to the direction of fluid flow are compared for their performance. The shell side design has been investigated numerically by modeling a small shell-and-tube heat exchanger. The study is concerned with a single shell and single side pass parallel flow heat exchanger. The flow and temperature fields inside the shell are studied using non-commercial computational fluid dynamics software tool ANSYS CFX 12.1. For a given baffle cut of 36%, the heat exchanger performance is investigated by varying mass flow rate and baffle inclination angle. From the computational fluid dynamics simulation results, the shell side outlet temperature, pressure drop, re-circulation near the baffles, optimal mass flow rate and the optimum baffle inclination angle for the given heat exchanger geometry are determined.