scholarly journals A Flexible Top-Down Numerical Modeling of an Air-Cooled Finned-Tube CO2 Trans-Critical Gas Cooler

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7607
Author(s):  
Angelo Maiorino ◽  
Ciro Aprea ◽  
Manuel Gesù Del Del Duca
Keyword(s):  
Experimental Data ◽  
Carbon Dioxide ◽  
Numerical Models ◽  
Numerical Approach ◽  
Finned Tube ◽  
Outlet Temperature ◽  
Refrigeration System ◽  
Top Down ◽  
Viable Solution ◽  
Technical Solutions

Carbon dioxide trans-critical refrigeration systems have been deeply investigated over the last years, with the aim to improve their performance by using several possible technical solutions. However, most of them lead to a more complex and expensive system, and therefore a trade-off is always needed to identify the best viable solution. Therefore, many efforts have also been focused on the study of a critical component of the basic carbon dioxide trans-critical cycle, which is the gas cooler, especially by numerical simulations. This work shows a new flexible approach to numerically model an air-cooled finned-tube CO2 trans-critical gas cooler integrating a Top-Down methodology with a Finite Difference Method to solve the governing equation of the thermodynamic processes involved. The model was developed to reproduce the behavior of an experimental CO2 refrigeration system, which provided the experimental data used for its validation. In detail, the model showed a good agreement with the experimental data, with average deviations of 1 K (0.3%), 0.9 bar (1%) and 0.15 kW (2.8%) regarding the refrigerant outlet temperature, the refrigerant outlet pressure and the rejected heat, respectively. The Top-Down numerical approach slightly outperformed the performance of previous numerical models available in the literature. Furthermore, the analysis of the refrigerant temperature and pressure along the tubes and rows also shows that the model can reproduce their behavior consistently and accordingly to data reported in the literature. The proposed approach can be used for detailed thermo-economic analysis of the whole refrigeration system, with the aim to optimize the design of the gas cooler.

scholarly journals Numerical Approach for the Estimation of Throat Heat Flux in Liquid Rocket Engines

2020 ◽  
Author(s):  
P. Concio ◽  
M. T. Migliorino ◽  
F. Nasuti
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Numerical Models ◽  
Numerical Approach ◽  
Experimental Information ◽  
Correct Prediction ◽  
Rocket Engines ◽  
Liquid Rocket Engines ◽  
Liquid Rocket

Abstract The problem of prediction of heat flux at throat of liquid rocket engines still constitutes a challenge, because of the little experimental information. Such a problem is of obvious importance in general, and becomes even more important when considering reusable engines. Unfortunately, only few indirect experimental data are available for the validation of throat heat flux prediction. On the numerical side, a detailed solution would require a huge resolution and codes able to solve at the same time combustion, boundary layer with possible finite-rate reactions, expansion up to at least sonic speed, and in some cases radiative heat flux. Therefore, it is important to validate, with the few experimental data available in the literature, simplified CFD approaches whose aim is to predict heat flux in the nozzle in affordable times. Results obtained by different numerical models based on a RANS approach show the correctness and quality of the approximations made, indicating the main phenomena to be included in modeling for the correct prediction of throat heat flux.

scholarly journals Dynamic Model of a Transcritical CO2 Heat Pump for Residential Water Heating

2021 ◽  
Vol 13 (6) ◽  
pp. 3464
Author(s):  
Hélio A. G. Diniz ◽  
Tiago F. Paulino ◽  
Juan J. G. Pabon ◽  
Antônio A. T. Maia ◽  
Raphael N. Oliveira
Keyword(s):  
Experimental Data ◽  
Carbon Dioxide ◽  
Mathematical Model ◽  
Steady State ◽  
Mass Flow Rate ◽  
Heat Pump ◽  
Mass Flow ◽  
Flow Rate ◽  
Outlet Temperature ◽  
Time Step

This paper presents a distributed mathematical model for a carbon dioxide direct expansion solar-assisted heat pump used to heat bath water. The main components are a gas cooler, a needle valve, an evaporator/collector, and a compressor. To develop the heat exchange models, mass, energy, and momentum balances were used. The model was validated for transient as well as steady state conditions using experimental data. A reasonably good agreement was observed between the predicted temperatures and experimental data. The simulations showed that the time step required to demonstrate the behavior of the heat pump in the transient regime is greater than the time step required for the steady state. The results obtained with the mathematical model revealed that a reduction in the water mass flow rate results in an increase in the water outlet temperature. In addition, when the carbon dioxide mass flow rate is reduced, the compressor inlet and outlet temperatures increase as well as the water outlet temperature.

scholarly journals Modelling of CO2 storage in geological formations with DuMux, a free-open-source numerical framework. A possible tool to assess geological storage of carbon dioxide in Romania

2019 ◽  
Vol 85 ◽  
pp. 07002 ◽  
Author(s):  
Alexandru Tatomir ◽  
Alexandru-Nicolae Dimache ◽  
Iancu Iulian ◽  
Martin Sauter
Keyword(s):  
Carbon Dioxide ◽  
Open Source ◽  
Large Scale ◽  
Numerical Models ◽  
Co2 Storage ◽  
Geological Storage ◽  
Biological Phenomena ◽  
Viable Solution ◽  
Multi Phase Flow ◽  
Multi Phase

Geological storage of carbon dioxide represents a viable solution to reduce the greenhouse gases in the atmosphere. Romania has initiatives to build a large-scale integrated CO2 capture and storage demonstration project and find suitable on-shore and off-shore CO2 storage locations. Numerical simulators are essential tools helping the design process. These simulators are required to be capable to represent the complex thermo-hydro-mechanical-chemical and biological phenomena accompanying the geological CO2 storage such as, multi-phase flow, compositional effects due to dissolution of CO2 into the brine, non-isothermal effects due to cold CO2 injection, geomechanical effects, mineralization at the reservoir-scale. These processes can be simulated accurately and efficiently with DuMux (www.dumux.org), a free- and open-source simulator. This article presents and reviews briefly these mathematical and numerical models.

Simulation and Performance Evaluation of Finned Tube Gas Cooler for Trans-Critical CO2 Refrigeration System

2013 ◽  
Vol 281 ◽  
pp. 324-328 ◽  
Author(s):  
Dileep Kumar Gupta ◽  
Mani Shankar Dasgupta
Keyword(s):  
Carbon Dioxide ◽  
Mathematical Model ◽  
Performance Evaluation ◽  
Cost Effective ◽  
Finned Tube ◽  
Refrigeration System ◽  
Air Velocity ◽  
Time Performance ◽  
And Performance

Carbon dioxide is one of the rediscovered sustainable options, as CFCs and HFCs are now in the list of regulated substances, to be phased out in time bound way. There are however various challenges to the successful use of CO2 as refrigerant. Cost effective and widely acceptable technology is demand of the time. Performance of trans-critical CO2 refrigeration systems is found to be sensitive to the gas cooler design. In the present work a detailed mathematical model is developed for a finned tube air cooled gas cooler and the same is validated using published literature. Subsequently, to achieve the lowest possible approach temperature, the performance of the gas cooler is analyzed for various air velocity and alternate pipe arrangements. The effect of increase in size of gas cooler to its performance is also studied.

Identifying Physico-Chemical Laws from the Robotically Collected Data

2019 ◽  
Author(s):  
Liwei Cao ◽  
Danilo Russo ◽  
Vassilios S. Vassiliadis ◽  
Alexei Lapkin
Keyword(s):  
Experimental Data ◽  
Numerical Models ◽  
Predictor Variable ◽  
Physical Models ◽  
Training Data ◽  
Mixed Integer ◽  
Physico Chemical ◽  
Data Points ◽  
Future Work ◽  
The Relationship

<p>A mixed-integer nonlinear programming (MINLP) formulation for symbolic regression was proposed to identify physical models from noisy experimental data. The formulation was tested using numerical models and was found to be more efficient than the previous literature example with respect to the number of predictor variables and training data points. The globally optimal search was extended to identify physical models and to cope with noise in the experimental data predictor variable. The methodology was coupled with the collection of experimental data in an automated fashion, and was proven to be successful in identifying the correct physical models describing the relationship between the shear stress and shear rate for both Newtonian and non-Newtonian fluids, and simple kinetic laws of reactions. Future work will focus on addressing the limitations of the formulation presented in this work, by extending it to be able to address larger complex physical models.</p><p><br></p>

Analysis and Modeling of Defects in Unsupported Overhanging Features in Micro-Stereolithography

2016 ◽  
Author(s):  
Vito Basile ◽  
Francesco Modica ◽  
Irene Fassi
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Numerical Approach ◽  
Fe Analysis ◽  
Test Cases ◽  
Layer By Layer ◽  
Failure Condition ◽  
Micro Scale ◽  
Part Geometry ◽  
Shape Component

In the present paper, a numerical approach to model the layer-by-layer construction of cured material during the Additive Manufacturing (AM) process is proposed. The method is developed by a recursive mechanical finite element (FE) analysis and takes into account forces and pressures acting on the cured material during the process, in order to simulate the behavior and investigate the failure condition sources, which lead to defects in the final part geometry. The study is focused on the evaluation of the process capability Stereolithography (SLA), to build parts with challenging features in meso-micro scale without supports. Two test cases, a cantilever part and a bridge shape component, have been considered in order to evaluate the potentiality of the approach. Numerical models have been tuned by experimental test. The simulations are validated considering two test cases and briefly compared to the printed samples. Results show the potential of the approach adopted but also the difficulties on simulation settings.

Heat Transfer Analysis of Room-Temperature Finned-Tube Evaporator for Cryogenic Nitrogen

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Shun Ching Lee ◽  
Tzu-Min Chen
Keyword(s):  
Heat Flux ◽  
Room Temperature ◽  
Integrated Model ◽  
Finned Tube ◽  
Heat Transfer Analysis ◽  
Outlet Temperature ◽  
Ambient Conditions ◽  
Governing Equations ◽  
Initial Value ◽  
Two Phase

Abstract The behavior of cryogenic nitrogen in a room-temperature evaporator six meters long is analyzed. Trapezoid fins are employed to enhance the heat flux supplied by the environment. The steady-state governing equations specified by the mixed parameters are derived from the conservations of momentum and energy. The initial value problem is solved by space integration. The fixed ambient conditions are confirmed by way of the meltback effect. An integrated model is utilized to analyze the convective effect of two-phase flow, which dominates the evaporation behavior. Another integrated model is employed to determine the total heat flux from the environment to the wet surface of the evaporator. The foundation of the formation of an ice layer surrounding the evaporator is presented. If the fin height is shorter than 0.5 m, the whole evaporator is surrounded by ice layer. If the fin height is longer than 0.5 m, the total pressure drop of nitrogen in the tube is negligible. The outlet temperature is always within the range between −12 °C and 16 °C for the evaporator with the fin height of 1.0 m. For the evaporator with dry surface, the nitrogen has the outlet temperature less than the ambient temperature at least by 5 °C.

Hybrid Analysis of Gas Annular Seals With Energy Equation

2013 ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
William C. Witt ◽  
Neal R. Morgan ◽  
Houston G. Wood
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Energy Equation ◽  
Flow Analysis ◽  
Experimental Studies ◽  
Rotor System ◽  
Bulk Flow ◽  
Outlet Temperature ◽  
Cfd Analysis ◽  
Annular Seals

Annular seals are used in turbomachinery to reduce secondary flow between regions of high and low pressure. In a vibrating rotor system, the non-axisymmetric pressure field developed in the small clearance between the rotor and the seal generate reactionary forces that can affect the stability of the entire rotor system. Traditionally, two analyses have been used to study the fluid flow in seals, bulk-flow analysis and computational fluid dynamics (CFD). Bulk-flow methods are computational inexpensive, but solve simplified equations that rely on empirically derived coefficients and are moderately accurate. CFD analyses generally provide more accurate results than bulk-flow codes, but solution time can vary between days and weeks. For gas damper seals, these analyses have been developed with the assumption that the flow can be treated as isothermal. Some experimental studies show that the difference between the inlet and outlet temperature temperatures is less than 5% but initial CFD studies show that there can be a significant temperature change which can have an effect on the density field. Thus, a comprehensive analysis requires the solution of an energy equation. Recently, a new hybrid method that employs a CFD analysis for the base state, unperturbed flow and a bulk-flow analysis for the first order, perturbed flow has been developed. This method has shown to compare well with full CFD analysis and experimental data while being computationally efficient. In this study, the previously developed hybrid method is extended to include the effects of non-isothermal flow. The hybrid method with energy equation is then compared with the isothermal hybrid method and experimental data for several test cases of hole-pattern seals and the importance of the use of energy equation is studied.

Leakage Flow Investigations on a Through-Wall Crack Related to Thermal Fatigue of Nuclear Power Plant Piping

2017 ◽  
Author(s):  
Stefan Schmid ◽  
Rudi Kulenovic ◽  
Eckart Laurien
Keyword(s):  
Experimental Data ◽  
Nuclear Power ◽  
Numerical Models ◽  
Measurement Techniques ◽  
Experimental Investigations ◽  
Leakage Flow ◽  
Test Rig ◽  
Reduced Pressure ◽  
Flow Rates ◽  
Set Up

For the validation of empirical models to calculate leakage flow rates in through-wall cracks of piping, reliable experimental data are essential. In this context, the Leakage Flow (LF) test rig was built up at the IKE for measurements of leakage flow rates with reduced pressure (maximum 1 MPA) and temperature (maximum 170 °C) compared to real plant conditions. The design of the test rig enables experimental investigations of through-wall cracks with different geometries and orientations by means of circular blank sheets with integrated cracks which are installed in the tubular test section of the test rig. In the paper, the experimental LF set-up and used measurement techniques are explained in detail. Furthermore, first leakage flow measurement results for one through-wall crack geometry and different imposed fluid pressures at ambient temperature conditions are presented and discussed. As an additional aspect the experimental data are used for the determination of the flow resistance of the investigated leak channel. Finally, the experimental results are compared with numerical results of WinLeck calculations to prove specifically in WinLeck implemented numerical models.

Sign in / Sign up

Export Citation Format

Share Document