scholarly journals Heat Transfer Characteristics of Rotating Ceramic Regenerators: Numerical Solution Using a Hybrid Finite Difference/Laplace Transform Scheme

1991 ◽  
Author(s):  
Keiji Kawasaki ◽  
Tadaaki Matsuhisa ◽  
Itsuro Sakai ◽  
Kunio Hijikata
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Laplace Transform ◽  
Gas Turbines ◽  
Initial Conditions ◽  
Working Fluids ◽  
The Core ◽  
Temperature Distributions ◽  
Steady State Operation ◽  
Ceramic Honeycomb

A hybrid numerical method, combining finite differences with respect to space and a Laplace transform with respect to time, is proposed to determine the heat transfer in a rotary heat exchanger used as a rotating ceramic regenerator for automotive gas turbines. The temperature distributions of the core and of the working fluids are solved for given boundary and initial conditions of a rotary regenerator using this method. An advantage of the present method is that it can be applied when the core and the working fluids have dissimilar temperature distributions. The temperature change in the ceramic honeycomb core was determined from start up to periodic steady state operation. The heat exchanger effectiveness was obtained for an extruded ceramic core used in automotive gas turbine applications.

Evaluation of Numerical Methods to Predict Temperature Distributions of an Experimentally Investigated Convection-Cooled Gas-Turbine Blade

2017 ◽  
Author(s):  
E. Findeisen ◽  
B. Woerz ◽  
M. Wieler ◽  
P. Jeschke ◽  
M. Rabs
Keyword(s):  
Heat Transfer ◽  
Numerical Methods ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Cooling System ◽  
Fe Model ◽  
Gas Turbine Blade ◽  
Transfer Coefficients ◽  
Temperature Distributions

This paper presents two different numerical methods to predict the thermal load of a convection-cooled gas-turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas-turbine rotor blade equipped with an academic convection-cooling system and investigated at a cascade test-rig. It consists of three cooling channels, which are connected outside the blade, so allowing cooling air temperature measurements. Both methods use FE models to obtain the temperature distribution of the solid blade. The difference between these methods lies in the generation of the heat transfer coefficients along the cooling channel walls which serve as a boundary condition for the FE model. One method, referred to as the FEM1D method, uses empirical one-dimensional correlations known from the available literature. The other method, the FEM2D method, uses three-dimensional CFD simulations to obtain two-dimensional heat transfer coefficient distributions. The numerical results are compared to each other as well as to experimental data, so that the benefits and limitations of each method can be shown and validated. Overall, this paper provides an evaluation of the different methods which are used to predict temperature distributions in convection-cooled gas-turbines with regard to accuracy, numerical cost and the limitations of each method. The temperature profiles obtained in all methods generally show good agreement with the experiments. However, the more detailed methods produce more accurate results by causing higher numerical costs.

scholarly journals Expanded Microchannel Heat Exchanger: Finite Difference Modeling

Designs ◽  
2021 ◽  
Vol 5 (4) ◽  
pp. 58
Author(s):  
David Denkenberger ◽  
Joshua M. Pearce ◽  
Michael Brandemuehl ◽  
Mitchell Alverts ◽  
John Zhai
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Finite Difference ◽  
Flow Rate ◽  
Experimental Results ◽  
Low Flow ◽  
Difference Model ◽  
The Core ◽  
Finite Difference Model ◽  
Flow Maldistribution

A finite difference model of a heat exchanger (HX) considered maldistribution, axial conduction, heat leak, and the edge effect, all of which are needed to model a high effectiveness HX. An HX prototype was developed, and channel height data were obtained using a computerized tomography (CT) scan from previous work along with experimental results. This study used the core geometry data to model results with the finite difference model, and compared the modeled and experimental results to help improve the expanded microchannel HX (EMHX) prototype design. The root mean square (RMS) error was 3.8%. Manifold geometries were not put into the model because the data were not available, so impacts of the manifold were investigated by varying the temperature conditions at the inlet and exit of the core. Previous studies have not considered the influence of heat transfer in the manifold on the HX effectiveness when maldistribution is present. With no flow maldistribution, manifold heat transfer increases overall effectiveness roughly as would be expected by the greater heat transfer area in the manifolds. Manifold heat transfer coupled with flow maldistribution for the prototype, however, causes a decrease in the effectiveness at high flow rate, and an increase in effectiveness at low flow rate.

Vehicular Gas Turbine Periodic-Flow Heat Exchanger Solid and Fluid Temperature Distributions

1964 ◽  
Vol 86 (2) ◽  
pp. 121-126 ◽  
Author(s):  
J. R. Mondt
Keyword(s):  
Heat Exchanger ◽  
Gas Turbine ◽  
Heat Exchangers ◽  
Gas Turbines ◽  
General Motors ◽  
Periodic Flow ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Temperature Distributions ◽  
Flow Heat

Design, fabrication, and operation experience with periodic-flow heat exchangers used in General Motors regenerative vehicular gas turbines has indicated that analysis techniques available in published reports are too restrictive for accurate performance and thermal distortion calculations. The design usefulness of previously published analyses is somewhat limited because fluid and metal temperature distributions are not part of the calculated results. These distributions are required for primary seal matching and core and structural thermal stress calculations. A nodal analysis has been accomplished at the General Motors Research Laboratories and a type of finite difference solution obtained for the periodic-flow heat exchanger. This solution can be used to study the effects of longitudinal thermal conduction, variable heat-transfer coefficients, finite rotation, and provides temperature distributions as functions of time and space for transient as well as “steady-state.” This has been checked both with available solutions for more simplified cases and some experimental measured results for periodic flow heat exchangers designed and built as part of the General Motors vehicular regenerative gas turbine program. A brief outline of the calculation procedures, program capabilities, and some calculated results is presented. This includes temperature distributions for periodic-flow heat-exchanger parameters encountered in the vehicular regenerator application.

Mathematical theory of the flow of a gas in a porous solid and of the associated temperature distributions

1954 ◽  
Vol 221 (1144) ◽  
pp. 1-28 ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Gas Turbines ◽  
Axisymmetric Flow ◽  
Porous Solid ◽  
Perfect Gas ◽  
Continuity Equations ◽  
Temperature Distributions ◽  
Special Cases ◽  
Transfer Equations

This paper considers the flow of a gas through a porous solid, when temperature differences exist between gas and solid and heat is exchanged between them. It attempts to determine the velocity and both temperature distributions, all of which in general are interdependent, in the general case of three independent space variables and of one time variable. It postulates both a simple heat-transfer equation suggested by an experimental paper and a generalization of Darcy’s law, which states that the velocity of flow of the gas is proportional to the pressure gradient. In addition, it makes use of the perfect gas and continuity equations. The heat-transfer equations (25) are deduced. Some special cases are solved explicitly. In general, a numerical solution is necessary, and an example of such a solution is given for steady axisymmetric flow. A case of linear flow with the variables periodic in time is solved analytically. Two applications of this theory are ‘sweat cooling’, which is used in gas turbines, and the design of heat exchangers.

The Deduction of the Integral and the Estimation of the Local Core Rotation Ratio by Telemetric Pressure Measurements in a Two Cavity Test Rig

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Wieland Uffrecht ◽  
André Günther
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Operation Mode ◽  
Radial Pressure ◽  
Pressure Measurements ◽  
Test Rig ◽  
The Core ◽  
Rotating Cavity ◽  
Cavity System ◽  
Core Rotation

The heat transfer in rotating cavities, as found in the internal air system of gas turbines, is mainly governed by the flow passing through these specific machine structures. The core rotation ratio represents the circumferential velocity, and is thought to be an influential flow parameter for heat transfer in rotating cavities with radial flow-through. Therefore, this paper focuses on deducing the core rotation ratio and the estimation of its local distribution using telemetric pressure measurements. The local core rotation ratio depends on the radial pressure distribution in a rotating cavity system. Thus, an integral core rotation ratio can be determined from pressure measurements in the rotating cavity system. A flow structure-based approximation of the measurements allows an estimation of the radial distribution of the core rotation ratio in the rotating cavity. The results of the measurements with varied flow rates and revolving speeds are presented, as well as a discussion of the fit parameters and their dependency on the operation mode of the test rig.

Heat Transfer Experiments of Ethylene Glycol-Water Mixture in Multi-Port Serpentine Meso-Channel Heat Exchanger Slab

2010 ◽  
Author(s):  
Mesbah G. Khan ◽  
Amir Fartaj
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Ethylene Glycol ◽  
Test Fluid ◽  
Water Mixture ◽  
Micro Channel ◽  
Working Fluids ◽  
Micro Channels

In past few years, narrow diameter flow passages (≤3 mm) have attracted huge research attentions due to their several advantageous features over conventional tubes (≥6 mm) especially from the view points of higher heat transfer, lesser weight, and smaller device size. Several classifications of narrow channels, based on sizes, are proposed in the open literature from mini to meso and micro (3 mm to 100 μm). The meso- and micro-channels have not yet entered into the HVAC and automotive heat exchanger industries to the expected potentials to take the above-mentioned advantages. The reasons may be the limited availability of experimental data on pressure drop and heat transfer and the lack of consolidated design correlations as compared to what is established for compact heat exchangers. While a number of studies available on standalone single straight channels, works on multi-channel slab similar to those used as typical thermal heat exchanger core elements are inadequate, especially the research on multichannel serpentine slab are limited in the open literature. The 50% ethylene glycol and water mixture is widely used in heat exchanger industry as a heat transfer fluid. Studies of pressure drop and heat transfer on this commercially important fluid using narrow tube multi-channel slab is scarce and the availability of experimental data is rare in the open literature. Conducting research on various shapes of meso- and micro-channel heat exchanger cores using a variety working fluids are a definite needs as recommended and consistently urged in ongoing research publications in this promising area. Under present long-term project, an automated dynamic single-phase experimental infrastructure has been developed to carryout the fluid flow and heat transfer research in meso- and micro-channel test specimens and prototype microchannel heat exchanger using a variety of working fluids in air-to-liquid crossflow orientation. In the series, experiments have been conducted on 50% ethylene glycol and water solution in a serpentine meso-channel slab having 68 individual channels of 1 mm hydraulic diameter to obtain the heat transfer data and the general pressure drop nature of the test fluid. Current paper presents the heat transfer characteristics of ethylene glycol-water mixture and the Reynolds number effects on pressure drop, heat transfer rate, test specimen NTU and effectiveness, overall thermal resistance, and the Nusselt number.

Plate-Fin Surface Optimisation Using Direct-Sizing

2000 ◽  
Author(s):  
Eric M. Smith
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Design Procedure ◽  
Local Geometry ◽  
Flow Friction ◽  
The Core ◽  
Plate Spacing ◽  
Offset Strip Fin ◽  
Strip Length

Abstract The direct-sizing of heat exchangers applies to that class of heat exchanger in which the local geometry of the core is the same everywhere. Many of our best performing exchangers possess this property. Previous papers discussing this topic were published by Smith (1994, 1997a). Optimisation of rectangular offset strip-fin (ROSF) surfaces involves varying plate spacing b, cell pitch c, and strip-length x in a logical manner. The Manglik and Bergles correlations for flow-friction and heat transfer of ROSF surfaces permits such optimisation. The design procedure which follows applies to a two-stream contraflow exchanger assuming perfect gases.

scholarly journals Assessment of Methods for Performance Comparison of Pure and Zeotropic Working Fluids for Organic Rankine Cycle Power Systems

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1783 ◽  
Author(s):  
Jesper Graa Andreasen ◽  
Martin Ryhl Kærn ◽  
Fredrik Haglind
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Power Systems ◽  
Temperature Difference ◽  
Power Output ◽  
Heat Exchangers ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluids ◽  
Net Power Output

In this paper, we present an assessment of methods for estimating and comparing the thermodynamic performance of working fluids for organic Rankine cycle power systems. The analysis focused on how the estimated net power outputs of zeotropic mixtures compared to pure fluids are affected by the method used for specifying the performance of the heat exchangers. Four different methods were included in the assessment, which assumed that the organic Rankine cycle systems were characterized by the same values of: (1) the minimum pinch point temperature difference of the heat exchangers; (2) the mean temperature difference of the heat exchangers; (3) the heat exchanger thermal capacity ( U ¯ A ); or (4) the heat exchanger surface area for all the considered working fluids. The second and third methods took into account the temperature difference throughout the heat transfer process, and provided the insight that the advantages of mixtures are more pronounced when large heat exchangers are economically feasible to use. The first method was incapable of this, and deemed to result in optimistic estimations of the benefits of using zeotropic mixtures, while the second and third method were deemed to result in conservative estimations. The fourth method provided the additional benefit of accounting for the degradation of heat transfer performance of zeotropic mixtures. In a net power output based performance ranking of 30 working fluids, the first method estimates that the increase in the net power output of zeotropic mixtures compared to their best pure fluid components is up to 13.6%. On the other hand, the third method estimates that the increase in net power output is only up to 2.56% for zeotropic mixtures compared to their best pure fluid components.

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