1-D transient numerical modeling of counter-current two-phase stratified flow inside a medium temperature solar linear collector (original) (raw)
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MATEC Web of Conferences, 2014
Numerical simulations using CFD are conducted on a boiling two-phase flow in order to study the changes in flow patterns during evaporation. A model for heat and mass transfer at the tube inner wall and at the liquid-gas interface is presented. Transport of two custom scalars is solved: one stands for the enthalpy fields in the flow, the other represents a new dispersed vapor phase in the liquid. A correlation is used to model heat and mass transfer at the tube inner wall. The dispersed phase is created at the surface in the liquid and flows up to the liquid-vapor interface. There, it is transformed into actual vapor phase. The multiphase VOF model is validated for the creation of slugs in an horizontal tube for an adiabatic flow. Results are presented for a subcooled boiling flow in a bend.
Mathematical modelling and simulation of multiphase flow in a flat plate solar energy collector
Energy Conversion and Management, 2015
Non-conventional collectors where organic fluid or refrigerant experience a phase change have many advantages over conventional collectors which have either air or relatively high temperature boiling liquid. Increase in heat transfer coefficient and system efficiency, corrosion prevention and freeze protection are the main benefits of the first type. In this study, a detailed numerical model of a flat plate collector is developed to investigate the fluid mean temperature, useful heat gain and heat transfer coefficient along the collector tube. The refrigerant HFC-134a was used in the simulation as the working fluid of the collector. The model can both predict the location where the fluid undergoes a phase change in the tube and the state at the exit under given inlet conditions. The effect of boiling on the heat transfer coefficient of the fluid is also investigated. Simulations were performed at three different mass flow rates (0.001, 0.005 and 0.01 kg/s) and three different operating pressures (4, 6 and 8 bar) to be able to see the effect of mass flow rate and pressure on plate temperature, heat loss coefficient, efficiency of the collector and the heat transfer coefficient of the fluid. The simulation results indicate that the heat transfer coefficient of the fluid increases from 153.54 W/m 2 K to 610.27 W/m 2 K in multiphase flow region. In the liquid single phase region, the collector efficiency rises from 60.2% to 68.8% and the heat transfer coefficient of the fluid increases from 39.24 W/m 2 K to 392.31 W/m 2 K with an increased flow rate whereas the collector efficiency decreases from 72.5% to 62.3% as the operating pressure increases from 4 bar to 8 bar. In order to validate the simulation model an experimental test rig was built and the experiments were performed with HFE 7000 as working thermo-fluid. A new simulation model utilizing HFE 7000 has been developed and the outlet temperature of the fluid was compared with the measured outlet temperature. Both measured and simulated results have shown close conformity.
Thermal Science, 2019
Solar collector water heating system use solar thermal energy to provide hot water for domestic and industrial use. These systems are operated either as open-loop or closed-loop flow circuit. The former loop systems are not recommended for the cold climates having water freezing problem. Although previous studies on solar collectors have used closed-loop operation with water as the working fluid. However, it must have high boiling and low freezing points for the colder regions and thus arises the need for antifreeze mixtures of water. Another solution the same problem is the use of heat transfer oil as intermediate working fluids. In the present study, the energy and exergy analysis of a boiler supported vacuum tube solar collector system working with closed-loop in different working fluid-flow rates have been performed and evaluated. Heat transfer oil has been used as an intermediate working fluid in the closed loop system at different flow rates of 0.277 kg/s, 0.383 kg/s, and 0.49...
E3S Web of Conferences, 2020
Utilizing solar energy has received a giant activity by energy applications into distinctive states within the world. The sun is regarded strong supply providing uninterrupted coherent energy. In this research, simulation study has been done to estimate the performance of dual purpose solar collector (DPSC). Flat plate dual purpose solar collector with dimensions (194 cm length, 95 cm width and 14 cm thickness) has been used for heating the air and water for different using. Rectangular fins are used in air duct to increase heat transfer coefficient in air heater part. COMSOL Multiphysics 5.4 computer program has been used to calculate the theoretical results. Many parameters such as a different flow rate and temperatures for the inlet working fluids are investigated.
Solar energy generating systems based on parabolic trough collector (PTC) are the most proven and commercially available solar thermal technology for power generation. Direct Steam Generation (DSG) in parabolic trough solar collector has great potential to reduce the capital cost and improve the performance of the solar field as well as the power block, but the flow stratification in the receiver leads to dry spots and consequently higher circumferential thermal gradient in the absorber wall that induce thermal stress and deforms the receiver from the focal plane. Hence, it is important to predict the flow regimes in the absorber tube that can further help to analyze heat transfer rate, temperature variation in the circumference of the absorber wall and stability of the receiver tube. In this study, a detailed mathematical model for two-phase flow boiling has been developed and solved using MATLAB. Flow pattern maps and transition of flow regimes are presented that help to predict different types of flows in the absorber tube. The effect of mass flow rate and pressure on flow regimes in the receiver tube have been evaluated. It is observed that stratified flow and stratified wavy flow exist at low mass velocity whereas bubbly flow occurs at a very high mass velocity. It is also observed that to achieve the annular flow in a DSG collector, the mass velocity should be high. The mathematical model is based on the temperature of the absorber tube rather than the temperature of the fluid as it also helps to evaluate the performance of the collector for any working fluid other than water.
International Journal on Interactive Design and Manufacturing (IJIDeM), 2018
The use of simulation in order to substitute real-life experiments and tests is a growing trend in all the designing activity all over the world. When the studies involve a continuous change of conditions and materials this solution becomes almost mandatory. In this work, simulations performed with the finite element method are used to study and improve a concentrated photovoltaic-thermal collector manufactured by the SME Solarus AB. The work assesses the behaviour of a new collector configuration, which puts the cooling fluid (water in this case) in counterflow, and compares to the solution obtained in a previous work. Additionally, the time dependency of the irradiance is considered in a next step of the study. This is of crucial importance to understand if the dynamic aspects of all processes under analysis are respected in order to validate, or not, the results obtained for the stationary conditions.
World Journal of Advanced Research and Reviews, 2021
Little works considered the optimization of working fluids in solar systems. Engineers, designers and scientists are interested with the optimization problems, furthermore it is very important specially, for solar systems to improve the energetic behavior and increase their efficiencies as a conversion system of solar irradiance to a useful thermal power. According to the available literature, the criteria of optimization mainly relates to energetic and economic analysis (one of them or both). The analysis was based upon the maximum useful energy obtained from solar collector. Accordingly, the optimum mass flow rate was found aspires to infinity. The second analysis is based upon minimum cost of the unit of useful energy [$/W]. The optimum mass flow rate of solar air-heating flat-plate collector for the considered domestic solar heating system has been found 29 kg/h per square meters of solar collectors. This paper deals with a third criteria that is, the amount of the additional en...
2011 IEEE 1st Conference on Clean Energy and Technology, CET 2011, 2011
A numerical model is presented for the simulation of double-diffusive natural convection in a triangular solar collector. This design is encountered in greenhouse solar stills where vertical temperature and concentration gradients between the saline water and transparent cover induce flows in a confined space. This phenomenon plays an important function in the water distillation process and in the biological comfort. In this double-diffusion problem, the ratio Br of the relative magnitude thermal and compositional buoyancy and Rayleigh numbers are key parameters. Finite element technique is used to solve the governing equations. Numerical results are presented for the effect of the above-mentioned parameters on local heat and mass transfer rate. In addition, results for the average heat and mass transfer rate are offered and discussed for the mentioned parametric conditions. Some interesting results are found in this investigation.
Research concerning the field of Liquid Heating Collectors (SLHCs) cannot be directly transferred to the large area of applications for Solar Air Heating Collectors (SAHC). Larger cross sections for transporting the air are necessary. This results in rather complicated fluid distributions within the products. In this paper we combine simulation and experimental techniques providing a high level of detail. Highly resolved three dimensional fluid dynamic simulations contain all the relevant heat transfer mechanisms in a plate SAHC: Heat conduction, convection patterns and radiation are modelled in the two air gaps. In all solid materials of the collector only heat conduction has to be accounted for. For the exchange of heat between the two air zones the heat transfer through the absorber is modelled. Nevertheless careful simplification is needed to be able to concentrate on the important details. Furthermore we shed light on numerical instabilities observed in the air gap between absorber and glass in the simulated example.
Journal of Solar Energy Engineering-transactions of The Asme, 2017
Numerical simulation enables the optimization of a solar collector without the expense of building prototypes. This study details an approach using Computational Fluid Dynamics (CFD) to simulate the performance of a solar thermal collector. Inputs to the simulation include; heat loss coefficient, irradiance and ambient temperature. A simulated thermal efficiency was validated using experimental results by comparing the calculated heat removal factor. The validated methodology was then applied to5 different inlet configurations of a header-riser collector. The most efficient designs had uniform flow through the risers. The worst performing configurations had low flow rates in the risers that led to high surface temperatures and poor thermal efficiency. The calculated heat removal factor differed by between 4.2% for the serpentine model and 12.1% for the header riser. The discrepancies were attributed to differences in thermal contact between plate and tubes in the simulated and actual design. W fin Width of the fin [m]