Hierarchic modeling of heat exchanger thermal hydraulics (original) (raw)
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Hierarchic modeling of heat transfer processes in heat exchangers
An alternate approach based on hierarchic modeling is proposed to simulate fluid and heat flow in heat exchangers. On the first level, the direct simulations have been performed for the geometry that is similar to a segment of the examined heat sink. Based on the obtained results, the Reynolds number dependencies of the scaling factors f and St Pr^0.66 have been established. On the second level, the integral model of the whole heat sink has been built using the volume averaging technique (VAT). The averaging of the transport equations leads to a closure problem. The direct model Reynolds number dependencies f and St Pr^0.66 have been used to calculate the local values of the drag coefficient and the heat transfer coefficient, which are needed in the integral model. The example calculations have been performed for 14 different pressure drops across the aluminum heat sink. The whole-section drag coefficient and Nusselt number have been calculated and compared with the experimental data. A good agreement between the modeling results and the experiment data has been reached with same discrepancies in the transitional regime. The constructed computational algorithm offers possibilities for geometry improvements and optimization, to achieve higher thermal effectiveness.
Thermo-hydraulic analysis of multi-row cross-flow heat exchangers
International Journal of Heat and Mass Transfer, 2018
This paper presents thermal hydraulic analysis of the cross-flow finned tube heat exchangers for an outdoor unit in residential airconditioning and heat pump applications. Performance of heat exchangers affect significantly the system energy efficiency and size of the airconditioning and heat pumps. The Navier-Stokes equations and the energy equation are solved for the three dimensional computation domain that encompasses multiple rows of the fin-tube heat exchangers. Rather than solving the flow and temperature fields for the outdoor heat exchanger directly, the fin-tube array has been approximated by the porous medium of equivalent permeability, which is estimated from a three dimensional finite volume solution for the periodic fin element. This information is essential and time-effective in carrying out the global flow field calculation which, in turn, provides the face velocity for the microscopic temperature-field calculation of the heat exchanger. The flow field and associated heat transfer for a wide range of face velocity and fin-tube arrangements are examined and the results are presented compared with experimental data. The predicted pressure drop and heat transfer rate for various inlet velocities are in excellent agreement with the measured data.
Advances in Numerical Modeling of Heat Exchanger Related Fluid Flow and Heat Transfer
2014
The rapid development of numerical solution methods for non-linear differential equations and advances in computers during recent years have gradually enabled predictions of flow and temperature fields as well as associated heat fluxes and stresses in engineering applications. However, turbulence modeling still presents a problem as accurate reliable predictions of flow separation; reattaching, impinging and recirculating flow regions are required. In addition, experimental investigations are needed to verify the computations. In several circumstances numerical investigations might be useful supplements to experimental testing methods, e.g., in providing details of local phenomena and fundamental mechanisms. For heat exchangers for both laminar and turbulent flows are of important and in addition the geometry is commonly more or less complex and sometimes of small dimensions. This paper considers current CFD methods including turbulence modeling, associated problems and limitations ...
Development on an integral computer code for simulation of heat exchangers
Heat exchangers are one of the basic installations in power and process industries. The present guidelines provide an ad-hoc solution to certain design problems. A unified approach based on simultaneous modeling of thermal-hydraulics and structural behavior does not exist. The present paper describes the development of integral numerical code for simulation of heat exchangers. The code is based on Volume Averaging Technique (VAT) for porous media flow modeling. The calculated values of the whole-section drag and heat transfer coefficients show an excellent agreement with already published values. The matching results prove the correctness of the selected approach and verify the developed numerical code used for this calculation.
Numerical Analysis of Thermal Hydraulic Performance of Heat Exchanger Tube with Inserts
Asian Journal of Applied Science and Technology (AJAST) , 2024
A heat exchanger is a device which is used to transfer heat between two or more fluids at different temperatures. To increase the rate of heat, transfer between two fluids, passive techniques are used, which changes the fluid flow behaviour inside the heat exchanger tube by using inserts. For the present study an Anchor shaped geometry is attached to a ball is used as inserts. This inserts embedded heat exchanger tube is numerically investigated at a wide range of Reynolds number (Re) i.e. 4000-22000. The geometrical parameters of the inserts are pitch (P = 70, 90, 110, and 130 mm), length of Anchor shape (lp = 7 mm, 6 mm, and 5 mm), diameter of ball (d = 10 mm, 12 mm, and 14 mm). The complete heat exchanger model and its parameters are analyzed and shown as results (Nusselt number and contours of fluid) of design model with all variations in its parameters is determined by Ansys workbench (Computational fluid dynamics). These variations are pretended to enhance the thermal performance, and observed 329.53% increment of heat transfer as compared to smooth tube, and found maximum thermal performance of 2.160 at Re = 22000, d = 12 mm, lp = 6 mm) and p = 90 mm.
Fluid Flow and Heat Transfer Numerical Prediction of Cross Flow Heat Exchanger
2016
Heat exchangers design is a major challenge problem in the process industry today. Heat exchanger applies to all equipment used to transfer thermal energy between two streams. Namely equipments in which two process streams exchange heat with each other. One of these equipments -cross flow heat exchanger-, used in numerous industry processes, uses as heat exchanger a normal flow to arrays of circular tubes arranged in staggered or in-line formation. These configurations, for instance, are typical in heat exchanger designs used in fossil-fuel and nuclear power plants and, indeed, over many other sectors of thermal and process engineering. Cross flow heat exchangers are designed based on experimental correlations. Depending on which correlation is used -and on the Reynolds number- , however, the heat exchanger area can vary from 30 to 50 percentage. According to the turbulence modeling technique and other details of the simulation, numerical prediction can be a useful tool for improving de...
Numerical Analysis of a Multi-Row Multi-Column Compact Heat Exchanger
Journal of Physics: Conference Series, 2012
In the present study we carry out three-dimensional fluid flow and heat transfer simulations on the external side of a compact heat exchanger to analyze the interaction between the fluid and its geometry. The overall objective is to use the resulting information for the design of more compact devices. The type of heat exchanger considered here is the common plain-fin and tube, with air flowing over the tubes and water as the inner-tube fluid. Two heat exchanger configurations, in which the tube arrangement is either in-line or staggered, conform the basic geometries. The size of the heat exchanger -regardless of the type of arrangementwhich serves as the baseline for the parametric analysis, is defined by fixing its length; i.e., the number of rows in the flow direction. For the two heat exchanger configurations examined here, the dimensional form of the governing equations, along with the corresponding boundary conditions, are solved under specific flow and temperature values using a finite element method to compute the velocity, pressure and temperature fields. From these, the heat transfer rate and pressure drop are then calculated. The computations are performed for a range in the values of the Reynolds number within the laminar regime. For all cases considered, results from this investigation indicate that the geometrical arrangement plays a major role in the amount of heat being exchanged and that, for a given device, the length needed to exchange 99% of the corresponding amount of energy that may be transferred by the baseline model, is confined to less than 30% of the size of the original device.
Computational Fluid Dynamics and Heat Transfer Analysis for a Novel Heat Exchanger
Journal of Heat Transfer, 2015
Computational fluid dynamics (CFD) and heat transfer simulations are conducted for a novel heat exchanger. The heat exchanger consists of semi-circle cross-sectioned tubes that create narrow slots oriented in the streamwise direction. Numerical simulations are conducted for Reynolds numbers (Re) ranging from 700 to 30,000. Three-dimensional turbulent flows and heat transfer characteristics in the tube bank region are modeled by the k-e Reynolds-averaged Navier-Stokes (RANS) method. The flow structure predicted by the two-dimensional and three-dimensional simulations is compared against that observed by the particle image velocimetry (PIV) for Re of 1500 and 4000. The adequate agreement between the predicted and observed flow characteristics validates the numerical method and the turbulent model employed here. The three-dimensional and the twodimensional steady flow simulations are compared to determine the effects of the wall on the flow structure. The wall influences the spatial structure of the vortices formed in the wake of the tubes and near the exit of the slots. The heat transfer coefficient of the slotted tubes improved by more than 40% compare to the traditional nonslotted tubes.
International Journal of Heat and Mass Transfer, 1992
for heat transfer and flow friction coefficients are provided for plane parallel piates and offset strip-fin plates over the ranges used in compact heat exchangers. Closed form expressions have been used to present these correlations. The proposed correlations allow one to adequately predict experimental data available for the heat exchanged and pressure losses in compact plate-type heat exchangers, The correlations cover continuously the full range from laminar to turbulent flow, for both short and long pipes. Suggestions to extend the correlations to other flow conditions are provided.
This work determines the thermo hydraulics behavior of smooth configuration surface for a compact heat exchanger by means of numerical simulation. The objective is to use the results as baseline for research in the enhancement of heat transfer and drag reduction, directed to reduce the energy consumption and diminish the environmental impact. The fin tube heat exchanger model is described. The constraints used in the implementation of the equation solver are announced. The average heat transfer coefficient and pressure drop obtained from numerical simulation are compare to experimental results presented in literature for models with the same dimensions and configuration. A good agreement between numerical and experimental results is reached. Local mechanisms responsible for the heat transfer and pressure drop are detailed. The study is conducted inside the laminar regime for frontal velocities ranging between 0.5 and 6 m/s.