scholarly journals Experimental performance comparison between circular and elliptical tubes in evaporative condensers

2021 ◽  
Author(s):  
Giuseppe Starace ◽  
Lorenzo Falcicchia ◽  
Pierpaolo Panico ◽  
Maria Fiorentino ◽  
Gianpiero Colangelo
Keyword(s):  
Heat Transfer ◽  
Experimental Approach ◽  
Fluid Dynamic ◽  
Major Axis ◽  
Performance Comparison ◽  
Operating Conditions ◽  
Condensation Temperature ◽  
Air Cooled Condensers ◽  
Reduced Scale ◽  
Dynamic Phenomena

AbstractIn refrigeration systems, evaporative condensers have two main advantages compared to other condensation heat exchangers: They operate at lower condensation temperature than traditional air-cooled condensers and require a lower quantity of water and pumping power compared to evaporative towers. The heat and mass transfer that occur on tube batteries are difficult to study. The aim of this work is to apply an experimental approach to investigate the performance of an evaporative condenser on a reduced scale by means of a test bench, consisting of a transparent duct with a rectangular test section in which electric heaters, inside elliptical pipes (major axis 32 mm, minor axis 23 mm), simulate the presence of the refrigerant during condensation. By keeping the water conditions fixed and constant, the operating conditions of the air and the inclination of the heat transfer geometry were varied, and this allowed to carry out a sensitivity analysis, depending on some of the main parameters that influence the thermo-fluid dynamic phenomena, as well as a performance comparison. The results showed that the heat transfer increases with the tube surface exposed directly to the air as a result of the increase in their inclination, that has been varied in the range 0–20°. For the investigated conditions, the average increase, resulting by the inclination, is 28%.

Heat Transfer Analysis of Human Cell Culture Under RF Exposure

2005 ◽  
Author(s):  
Muhammad Khalid ◽  
Chenn Zhou ◽  
Ashish Bassi ◽  
San Ming Wang ◽  
Howard Gerber ◽  
...  
Keyword(s):  
Gene Expression ◽  
Heat Transfer ◽  
Electric Field ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Heat Shock Gene ◽  
Exposure System ◽  
Finite Element Software ◽  
Rf Exposure

A 2.45 GHz radio frequency (RF) exposure system was designed and used to study the RF effects on the genome-wide gene expression in cultured human cells. In this system, a T-25 culture flask, which contains 10 × 106 cells in a 10ml medium, is placed in a WR 340 waveguide. The waveguide serves as an environmental chamber. The source is a pulsed magnetron for obtaining a high electric field with the specific absorption rate (SAR) at approximately 10 W/kg. In order to ensure the non-thermal effect, the system was designed to maintain a temperature of 37°C. In this research, the heat transfer analysis of the system was conducted using the computational fluid dynamic (CFD) software FLUENT® coupled with the finite element software, High Frequency Structural Simulation (HFSS) by Ansoft. The electric field was first analyzed by using HFSS to calculate the SAR distribution as a heat source input for CFD calculations. The fluid flow and temperature distributions within the flask were then analyzed using FLUENT®. The results were validated experimentally by measuring the temperatures with fluoroptic thermometer probes as well as by examining the level of heat shock gene expression. These results provide useful information for a better understanding and controlling of the operating conditions of the system.

Thermo Fluid Dynamic Analysis of a Gas Turbine Transition-Piece

2014 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Antonio Andreini ◽  
Lorenzo Mazzei ◽  
Giovanni Riccio ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Fluid Dynamic ◽  
Gas Turbine Engine ◽  
Operating Conditions ◽  
Thermal Loads ◽  
Turbine Engine ◽  
Transition Piece

The transition-piece of a gas turbine engine is subjected to high thermal loads as it collects high temperature combustion products from the gas generator to a turbine. This generally produces high thermal stress levels in the casing of the transition piece, strongly limiting its life expectations and making it one of the most critical components of the entire engine. The reliable prediction of such thermal loads is hence a crucial aspect to increase the transition-piece life span and to assure safe operations. The present study aims to investigate the aero-thermal behaviour of a gas turbine engine transition-piece and in particular to evaluate working temperatures of the casing in relation to the flow and heat transfer situation inside and outside the transition-piece. Typical operating conditions are considered to determine the amount of heat transfer from the gas to the casing by means of CFD. Both conjugate approach and wall fixed temperature have been considered to compute the heat transfer coefficient, and more in general, the transition-piece thermal loads. Finally a discussion on the most convenient heat transfer coefficient expression is provided.

Time-Resolved Heat Transfer and Fluid Dynamic Analysis of Natural Convection From Isothermal Horizontal Cylinders

2010 ◽  
Author(s):  
Tim Persoons ◽  
Ian M. O. Gorman ◽  
Gerry Byrne ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fluid Dynamic ◽  
Vertical Cylinder ◽  
Local Heat Transfer ◽  
Temporal Analysis ◽  
Local Heat ◽  
Operating Conditions ◽  
Thermal Plume ◽  
Horizontal Cylinders

This paper discusses the close coupling between fluid dynamics and local natural convection heat transfer rates from a pair of isothermally heated horizontal cylinders submerged in water. The presence of a second heated cylinder induces heat transfer enhancements of up to 10%, and strong fluctuations in local heat transfer rate. Therefore specific attention is focused on how the local heat transfer characteristics of the upper cylinder are affected by buoyancy induced fluid flow from the lower cylinder. The paper investigates a range of Rayleigh number between 2·106 and 6·106, and a vertical cylinder spacing between 2D and 4D. Simultaneous local heat flux measurements and flow velocity measurements using particle image velocimetry reveal oscillatory behaviour of the thermal plume, depending on operating conditions. A joint temporal analysis of the data has provided new insights into the governing mechanisms, which enables further optimisation of the heat transfer performance.

scholarly journals Performance Evaluation of Wire Cloth Micro Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 715 ◽  
Author(s):  
Hannes Fugmann ◽  
Sebastian Martens ◽  
Richard Balzer ◽  
Martin Brenner ◽  
Lena Schnabel ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Fluid Dynamic ◽  
Relative Difference ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Hydraulic Simulation ◽  
Pressure Drops ◽  
Wire Cloth ◽  
Good Agreement

The purpose of this study is to validate a thermal-hydraulic simulation model for a new type of heat exchanger for mass, volume, and coolant/refrigerant charge reduction. The new heat exchanger consists of tubes with diameters in the range of 1 m m and wires in the range of 100 m , woven together to form a 200 × 200 × 80 m m 3 wire cloth heat exchanger. Performance of the heat exchanger has been experimentally evaluated using water as inner and air as outer heat transfer medium. A computational thermal and fluid dynamic model has been implemented in OpenFOAM®. The model allows variation of geometry and operating conditions. The validation of the model is based on one single geometry with an opaque fabric and air-side velocities between 1 and 7 m / s . The simulated and measured pressure drops are found to be in good agreement with a relative difference of less than 16%. For the investigated cases, the effective heat transfer coefficients are in very good agreement (less than 5%) when adapting the contact resistance between tubes and wires. The numerical model describes the fluid flow and heat transfer of the tested heat exchanger with adequate precision and can be used for future wire cloth heat exchanger dimensioning for a variety of applications.

scholarly journals Comparison between R134a and R1234ze(E) during Flow Boiling in Microfin Tubes

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 417
Author(s):  
Andrea Lucchini ◽  
Igor M. Carraretto ◽  
Thanh N. Phan ◽  
Paola G. Pittoni ◽  
Luigi P. M. Colombo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Fluid Dynamic ◽  
Saturation Temperature ◽  
Operating Conditions ◽  
Two Fluids ◽  
The Heat Transfer Coefficient

Environmental concerns are forcing the replacement of commonly used refrigerants, and finding new fluids is a top priority. Soon the R134a will be banned, and the hydro-fluoro-olefin (HFO) R1234ze(E) has been indicated as an alternative due to its smaller global warming potential (GWP) and shorter atmospheric lifetime. Nevertheless, for an optimal replacement, its thermo-fluid-dynamic characteristics have to be assessed. Flow boiling experiments (saturation temperature Tsat = 5 °C, mass flux G = 65 ÷ 222 kg·m−2·s−1, mean quality xm = 0.15 ÷ 0.95, quality changes ∆x = 0.06 ÷ 0.6) inside a microfin tube were performed to compare the pressure drop per unit length and the heat transfer coefficient provided by the two fluids. The results were benchmarked for some correlations. In commonly adopted operating conditions, the two fluids show a very similar behavior, while benchmark showed that some correlations are available to properly predict the pressure drop for both fluids. However, only one is satisfactory for the heat transfer coefficient. In conclusion, R1234ze(E) proved to be a suitable drop-in replacement for the R134a, whereas further efforts are recommended to refine and adapt the available predictive models.

Large Eddy Simulation of a Transonic Linear Cascade With Synthetic Inlet Turbulence

2020 ◽  
Author(s):  
Ettore Bertolini ◽  
Paul Pieringer ◽  
Wolfgang Sanz
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Boundary Layer Transition ◽  
Turbine Cascade ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbulence Decay ◽  
Large Eddy

Abstract The aim of this work is to predict the boundary layer transition and the heat transfer on a highly loaded transonic turbine cascade using Large Eddy Simulations (LESs) with prescribed inlet synthetic turbulence. The numerical simulations were performed for the flow in a linear turbine cascade tested at the von Karman Institute for Fluid Dynamic (MUR test case). For the numerical case, two operating conditions with two different levels of free-stream turbulence intensity are evaluated. For the lower turbulence level case (Tu = 0.8%, MUR132) a laminar inflow is used for the LES simulations whereas for the higher one (Tu = 6%, MUR237) the inlet turbulence is prescribed by using the Synthetic Eddy Method (SEM) of Jarrin. The first part of this work deals with the LES setup. The standard Smagorinsky model was used as closure model. A value of the Smagorinsky constant CS = 0.05 was chosen whereas the turbulent viscosity was reduced in the region closest to the wall by changing the definition of the Smagorinsky length scale. To handle the strong fluctuations in the flow field the cell fluxes are computed using the WENO-P scheme. In the second part, precursor RANS and LES simulations are used to set the optimal values of the SEM parameters and to guarantee the correct level of turbulence at the blade leading edge. The turbulence decay of the synthetic turbulence is compared with the one of the RANS κ–ωSST model. Finally, a comparison between experimental and numerical results is done and the ability of LES to predict the boundary layer transition and the heat transfer on the blade surface is evaluated for the two different inflow conditions.

scholarly journals Impingement Density Analysis on Heat Transfer and the Appearance of Edge Cracks in Conventional Slab Using Hydraulic Nozzles

Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 108
Author(s):  
Alfonso Ruiz-Pineda ◽  
Alicia Aguilar-Corona ◽  
Constantin Alberto Hernández-Bocanegra ◽  
José Ángel Ramos-Banderas ◽  
Gildardo Solorio-Díaz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Continuous Casting Machine ◽  
Casting Machine ◽  
Major Axis ◽  
Operating Conditions ◽  
Heat Extraction ◽  
Opening Angle ◽  
Operating Pressure ◽  
Density Maps ◽  
Edge Cracks

In this work, the fluid dynamics and heat transfer of two hydraulic nozzles used in the secondary cooling of the conventional slab continuous casting machine were analyzed. Impingement density maps, the jet opening angle and heat flux associated with different operating conditions (impingement distance, pressure) were experimentally determined. The opening angle and impingement density footprint were found to vary considerably in shape and magnitude with varying operating pressure and distances. Finally, it was found that when short operating distances are used, a greater heat extraction gradient occurs in the major axis of the impingement footprint, which promotes edge-cracks in the slab in plant.

scholarly journals CFD Simulation of a Temperature Control System for Galvanizing Line of Metal Band Based on Jet Cooling Heat Transfer

2020 ◽  
Vol 10 (15) ◽  
pp. 5248
Author(s):  
Giovanni Carozzo ◽  
Carlo Cravero ◽  
Martino Marini ◽  
Matteo Mazza
Keyword(s):  
Heat Transfer ◽  
Cfd Simulation ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Jet Impingement ◽  
Operating Conditions ◽  
Temperature Control System ◽  
System Component ◽  
Jet Cooling ◽  
Dynamic Simulation Model

The work focuses on the development of a thermo-fluid dynamic simulation model of a section of close cooling, called a jet cooler, inserted in the galvanizing line of metal band production. Two models of increasing accuracy have been tested and calibrated by experimental data. Special attention to turbulence modeling and boundary conditions has been given. A literature survey was focused on the jet impingement process (the reference heat transfer mechanism for the system component) and on available correlations to predict the heat exchange coefficient. The numerical simulation of jet impingement has been applied to a module of an actual industrial cooler for steel band production. The operation of the jet cooler was simulated in real operating conditions to get a detailed insight into the jet impingement mechanism in order to optimize the heat transfer and reduce, as far as possible, the cooling fluid mass flow rate. The comparison of heat transfer correlations, used in industrial preliminary design, with detailed CFD results is discussed.

Heat Transfer in Rotating Passages With Smooth Walls and Radial Outward Flow

1989 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
T. J. Hajek
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Fluid Dynamic ◽  
Density Ratio ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Turbine Engine ◽  
Heat Transfer Coefficients ◽  
Streamwise Location

Experiments were conducted to determine the effects of rotation on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a smooth wall, large scale heat transfer model. The objective was to obtain the heat transfer data base required to develop heat transfer correlations and to assess computational fluid dynamic techniques for rotating coolant passages. An analysis of the governing equations showed that four parameters influence the heat transfer in rotating passages (coolant density ratio, Rossby number, Reynolds number and radius ratio). These four parameters were varied over ranges which exceed the ranges of current open literature results, but which are typical of current and advanced gas turbine engine operating conditions. Rotation affected the heat transfer coefficients differently for different locations in the coolant passage. For example, heat transfer at some locations increased with rotation, but decreased and then increased again at other locations. Heat transfer coefficients varied by as much as a factor of 5 between the leading and trailing surfaces for the same test condition and streamwise location. Comparisons with previous results are presented.

Heat Transfer in Rotating Passages With Smooth Walls and Radial Outward Flow

1991 ◽  
Vol 113 (1) ◽  
pp. 42-51 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
T. J. Hajek
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Fluid Dynamic ◽  
Density Ratio ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Turbine Engine ◽  
Heat Transfer Coefficients ◽  
Streamwise Location

Experiments were conducted to determine the effects of rotation on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a smooth wall, large-scale heat transfer model. The objective was to obtain the heat transfer data base required to develop heat transfer correlations and to assess computational fluid dynamic techniques for rotating coolant passages. An analysis of the governing equations showed that four parameters influence the heat transfer in rotating passages (coolant density ratio, Rossby number, Reynolds number, and radius ratio). These four parameters were varied over ranges that exceed the ranges of current open literature results, but that are typical of current and advanced gas turbine engine operating conditions. Rotation affected the heat transfer coefficients differently for different locations in the coolant passage. For example, heat transfer at some locations increased with rotation, but decreased and then increased again at other locations. Heat transfer coefficients varied by as much as a factor of five between the leading and trailing surfaces for the same test condition and streamwise location. Comparisons with previous results are presented.

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