A Comparison of Simplified One-Dimensional and Two-Dimensional Analytical Models for Predicting Metallic Recuperator Performance

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Harshdeep Sharma ◽  
Varun Goel
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Flue Gas ◽  
Transfer Model ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Zone Method ◽  
Flow Rates ◽  
One Dimensional ◽  
Mass Flow Rates

Abstract The performance models for high-temperature metallic recuperators considering one and two-dimensional heat transfer are presented. In one-dimensional model, an explicit expression to represent the effect of both the temperature and product of partial pressure and mean beam length on the emissivity is developed using emissivity charts. The effect of upstream and downstream surroundings is neglected. A two-dimensional heat transfer model is developed using zone method along with sum-of-gray-gases approximation to study the effect of upstream and downstream surroundings on performance. The results from the two models are compared. For lower values of inlet flue gas temperatures and higher mass flow rates, one-dimensional model predicts results within 5% of two-dimensional model. One-dimensional model provides a simplified solution for the assessment of recuperator performance but predicts the surface temperature distribution on a relatively lower side for higher inlet flue gas temperatures and low mass flow rates.

scholarly journals Verification and Improving the Heat Transfer Model in Radiators in the Wide Change Operating Parameters

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6543
Author(s):  
Mieczysław Dzierzgowski
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Water Mass ◽  
Heat Transfer Model ◽  
Operating Conditions ◽  
Transfer Model ◽  
Flow Rates ◽  
Wide Range ◽  
Different Types ◽  
Mass Flow Rates

Laboratory measurements and analyses conducted in a wide range of changes of water temperature and mass flow rate for different types of radiators allowed to provides limitations and assessment of the current radiators heat transfer model according to EN 442. The inaccuracy to determinate the radiator heat output according to EN 442, in case of low water mass flow rates may achieve up to 22.3% A revised New Extended Heat Transfer Model in Radiators NEHTMiRmd is general and suitable for different types of radiators both new radiators and radiators existing after a certain period of operation is presented. The NEHTMiRmd with very high accuracy describes the heat transfer processes not only in the nominal conditions—in which the radiators are designed, but what is particularly important also in operating conditions when the radiators water mass flow differ significantly from the nominal value and at the same time the supply temperature changes in the whole range radiators operating during the heating season. In order to prove that the presented new model NEHTMiRmd is general, the article presents numerous calculation examples for various types of radiators currently used. Achieved the high compatibility of the results of the simulation calculations with the measurement results for different types of radiators: iron elements (not ribbed), plate radiators (medium degree ribbed), convectors (high degree ribbed) in a very wide range of changes in the water mass flow rates and the supply temperature indicates that a verified NEHTMiRmd can also be used in designing and simulating calculations of the central heating installations, for the rational conversion of existing installations and district heating systems into low temperature energy efficient systems as well as to directly determine the actual energy efficiency, also to improve the indications of the heat cost allocators. In addition, it may form the basis for the future modification of the European Standards for radiator testing.

Application of the Transient Heat Transfer Measurement Technique Using TLC in a Network Configuration With Intersecting Circular Passages

2018 ◽  
Author(s):  
Anika Steurer ◽  
Rico Poser ◽  
Jens von Wolfersdorf ◽  
Stefan Retzko
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Mass Flow ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Flow Network ◽  
Mass Flow Rates ◽  
Time Information

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20mm that intersect coplanar at an angle θ = 40°, the innermost in three, the outermost in one intersection level. Two additional non-intersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional RANS simulations using the SST turbulence model. The presented analysis uncouples local heat transfer coefficients from actually measured local temperatures but uses the time information of the thermocouples instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether heat transfer is locally enhanced due to higher mass flow rates or the intersection effects.

First and second thermodynamic law analyses applied to a solar dish collector

2014 ◽  
Vol 39 (4) ◽  
Author(s):  
Vahid Madadi ◽  
Touraj Tavakoli ◽  
Amir Rahimi
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Exergy Efficiency ◽  
Exergy Destruction ◽  
Flow Rates ◽  
Energy And Exergy ◽  
Mass Flow Rates

AbstractThe energy and exergy performance of a parabolic dish collector is investigated experimentally and theoretically. The effect of receiver type, inlet temperature and mass flow rate of heat transfer fluid (HTF), receiver temperature, receiver aspect ratio and solar radiation are investigated. To evaluate the effect of the receiver aperture area on the system performance, three aperture diameters are considered. It is deduced that the fully opened receivers have the greatest exergy and thermal efficiency. The cylindrical receiver has greater energy and exergy efficiency than the conical one due to less exergy destruction. It is found that the highest exergy destruction is due to heat transfer between the sun and the receivers and counts for 35 % to 60 % of the total wasted exergy. For three selected receiver aperture diameters, the exergy efficiency is minimum for a specified HTF mass flow rate. High solar radiation allows the system to work at higher HTF inlet temperatures. To use this system in applications that need high temperatures, in cylindrical and conical receivers, the HTF mass flow rates lower than 0.05 and 0.09 kg/s are suggested, respectively. For applications that need higher amounts of energy content, higher HTF mass flow rates than the above mentioned values are recommended.

Mass flow rate for nearly-free molecular slit flow

1969 ◽  
Vol 35 (3) ◽  
pp. 599-608 ◽  
Author(s):  
J. Daniel Stewart
Keyword(s):  
Mass Flow ◽  
Pressure Ratio ◽  
Molecular Flow ◽  
Two Dimensional ◽  
Flow Rates ◽  
Average Mass ◽  
Slit Flow ◽  
Mass Flow Rates ◽  
Flow Through ◽  
Tank Pressure

The local and average mass flow rates for nearly free molecular flow through a two-dimensional slit are determined for several tank pressure ratios. The equilibrium gas in the two tanks and the container walls are assumed to be at the same temperature and the Willis iterative method with the Bhatnager-Gross-Krook model is used for the analysis. The results for an infinite pressure ratio are also presented in order to illustrate the effects of a finite pressure ratio.

Numerical simulation of two-dimensional fins using the meshless local Petrov – Galerkin method

2020 ◽  
Vol 37 (8) ◽  
pp. 2913-2938
Author(s):  
Rajul Garg ◽  
Harishchandra Thakur ◽  
Brajesh Tripathi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Experimental Investigation ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Content Type ◽  
One Dimensional ◽  
Mlpg Method ◽  
Convection Model ◽  
Good Agreement

Purpose The study aims to highlight the behaviour of one-dimensional and two-dimensional fin models under the natural room conditions, considering the different values of dimensionless Biot number (Bi). The effect of convection and radiation on the heat transfer process has also been demonstrated using the meshless local Petrov–Galerkin (MLPG) approach. Design/methodology/approach It is true that MLPG method is time-consuming and expensive in terms of man-hours, as it is in the developing stage, but with the advent of computationally fast new-generation computers, there is a big possibility of the development of MLPG software, which will not only reduce the computational time and cost but also enhance the accuracy and precision in the results. Bi values of 0.01 and 0.10 have been taken for the experimental investigation of one-dimensional and two-dimensional rectangular fin models. The numerical simulation results obtained by the analytical method, benchmark numerical method and the MLPG method for both the models have been compared with that of the experimental investigation results for validation and found to be in good agreement. Performance of the fin has also been demonstrated. Findings The experimental and numerical investigations have been conducted for one-dimensional and two-dimensional linear and nonlinear fin models of rectangular shape. MLPG is used as a potential numerical method. Effect of radiation is also, implemented successfully. Results are found to be in good agreement with analytical solution, when one-dimensional steady problem is solved; however, two-dimensional results obtained by the MLPG method are compared with that of the finite element method and found that the proposed method is as accurate as the established method. It is also found that for higher Bi, the one-dimensional model is not appropriate, as it does not demonstrate the appreciated error; hence, a two-dimensional model is required to predict the performance of a fin. Radiative fin illustrates more heat transfer than the pure convective fin. The performance parameters show that as the Bi increases, the performance of fin decreases because of high thermal resistance. Research limitations/implications Though, best of the efforts have been put to showcase the behaviour of one-dimensional and two-dimensional fins under nonlinear conditions, at different Bi values, yet lot more is to be demonstrated. Nonlinearity, in the present paper, is exhibited by using the thermal and material properties as the function of temperature, but can be further demonstrated with their dependency on the area. Additionally, this paper can be made more elaborative by extending the research for transient problems, with different fin profiles. Natural convection model is adopted in the present study but it can also be studied by using forced convection model. Practical implications Fins are the most commonly used medium to enhance heat transfer from a hot primary surface. Heat transfer in its natural condition is nonlinear and hence been demonstrated. The outcome is practically viable, as it is applicable at large to the broad areas like automobile, aerospace and electronic and electrical devices. Originality/value As per the literature survey, lot of work has been done on fins using different numerical methods; but to the best of authors’ knowledge, this study is first in the area of nonlinear heat transfer of fins using dimensionless Bi by the truly meshfree MLPG method.

Experimental Investigation of Turbine Leakage Flows on the Three-Dimensional Flow Field and Endwall Heat Transfer

2006 ◽  
Vol 129 (3) ◽  
pp. 608-618 ◽  
Author(s):  
Hans-Jürgen Rehder ◽  
Axel Dannhauer
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Test Section ◽  
Flow Behavior ◽  
Leakage Flow ◽  
Flow Rates ◽  
Low Pressure Turbine ◽  
Mass Flow Rates

Within a European research project, the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Göttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline patterns (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D particle image velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer occur mainly when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horseshoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

Performance Analysis of Shell and Tube Heat Exchanger using Different Nanofluids

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
J. Thavamani
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Mass Flow ◽  
Base Fluid ◽  
Particle Diameter ◽  
Flow Rates ◽  
Tube Heat Exchanger ◽  
Cold Fluid ◽  
Mass Flow Rates ◽  
Shell And Tube

Heat exchanger is the most important function in industrial sector for transferring heat energy to useful work. Heat transfer occurs between the cold fluid and hot fluid or from hot fluid to cold fluid in conduction and convection mode of through a heat exchanger wall. If heat transfer medium has very low thermal conductivity, it would have limited the efficiency of heat exchanger. Whenever the system is subjected to increased heat load, cooling is the main technical challenge for industries. The main objective of this work is to evaluate the effectiveness of shell and tube heat exchanger experimentally and analyse the flow behaviours of different nanofluids. In our experimental analysis, various nanofluids which consist of water and one percentage volume concentration of Al2O3, CuO and SiO2 passing through tube side in the shell and tube heat exchanger. The nano particle diameter is 70nm. The three dissimilar mass flow rates are considered for the experiments and their results are continuously monitored. The enhancement of heat transfer performance of CuO, Al2O3, SiO2 is compared with the base fluid water. Reynolds number values are calculated with three different mass flow rates and compared with heat transfer characteristics (LMTD, Nusselt number and overall heat transfer coefficient). SEM analysis, energy dispersive spectroscopy, X-ray diffraction of CuO, Al2O3 and SiO2.are conducted. The heat transfer effectiveness is increased by 22.12%, 19.46% and 1.47% respectively for CuO, Al2O3 and SiO2 when compared to base fluid.

Comparative Study on Parabolic Trough Collector by using Different Heat Transfer Fluids

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
Krishna Mounica ◽  
Y.V. Hanumantha Rao ◽  
Vinay Atgur ◽  
G. Manavendra ◽  
B. Srinivasa Rao
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Thermal Model ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Flow Rates ◽  
Parabolic Trough Collector ◽  
Heat Transfer Fluids ◽  
Mass Flow Rates ◽  
Simulation Results

In this paper the use of Syltherm-800 and Therminol-55 thermal oils in parabolic trough collector (PTC) is investigated with inlet temperatures of 375.35 K, 424.15 K, 470.65 K and 523.85 K and for mass flow rates of 4, 4.5 and 5 kg/sec. Analysis has been carried out using a thermal model and validated using the simulation results. Therminol-55 gives better heat transfer coefficient compared to Syltherm-800. Since Therminol-55 has higher specific heat and viscosity when compared to Syltherm-800, the use of Syltherm-800 as a heat transfer fluid in PTC is preferred. Better results are observed for temperature of 375.35 K and mass flow rate of 4 kg/sec.

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