A numerical study on the internal heat leak mechanisms in a variable property three-stream heat exchanger

2021 ◽  
pp. 095765092110149
Author(s):  
Yasser Shafiei-alamooti ◽  
Ali Ashrafizadeh
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Heat Conduction ◽  
Heat Exchanger ◽  
Temperature Distribution ◽  
Heat Exchangers ◽  
Numerical Study ◽  
Internal Heat ◽  
Heat Leak ◽  
Maximum Heat

Heat leakage mechanisms need to be addressed in the thermal analysis of multi-stream heat exchangers due to their effects on the intended heat transfer between the streams. In this paper, multi-dimensional heat transfers between various fluid streams and also between the fluid and solid parts of a three-stream plate-fin heat exchanger is numerically modeled considering the variation of thermo-physical properties of both solid and fluid parts. All internal heat leak mechanisms, i.e. longitudinal heat conduction, transverse bypass through fins, and heat transfer reversal in a stream are taken into consideration. The distribution of longitudinal heat conduction along the stream’s separating plates (plates) is also explored. It is shown that the longitudinal heat conduction depends strongly on the variation of properties in some flow arrangements. For such cases, the plates experience areas with relatively low temperature, and a new longitudinal heat conduction, mainly induced by property variation, is identified and presented. This induced longitudinal conduction is close to 1% of the maximum heat exchange between the streams in this study. Another interesting result is that the longitudinal temperature distribution in the plates does not necessarily follow the temperature distribution along the nearby streams due to the entrance effects and unbalanced heat capacity rates. Numerical results show that property variations affect all of the thermal leakage phenomena and, therefore, need to be considered in the modeling and thermal analysis of multi-stream heat exchangers.

Numerical Investigation of Heat Transfer Enhancement Using Hybrid Vortex Generator Arrays in Fin-and-Tube Heat Exchangers

2016 ◽  
Vol 8 (3) ◽  
Author(s):  
Shubham Agarwal ◽  
R. P. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Numerical Study ◽  
Vortex Generator ◽  
Roll Angle ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Hybrid Configuration

This is a novel study for assessing the heat transfer enhancement in a multi-row inline-tube heat exchanger using hybrid vortex generator (VG) arrays, i.e., rectangular winglet pairs (RWPs) with different geometrical configurations installed in coherence for enhanced heat transfer. The three-dimensional numerical study uses a full scale seven-tube inline heat exchanger model. The effect of roll of rectangular winglet VG on heat transfer enhancement is analyzed and optimized roll angle is determined for maximum heat transfer enhancement. Four different configurations are analyzed and compared in this regard: (a) single RWP (no roll); (b) 3RWP-inline array(alternating tube row with no roll of VGs); (c) single RWP (with optimized roll angle VGs); and (d) 3RWP-inline array(alternating tube row with all VGs having optimized roll angle). It was found that the inward roll of VGs increased the heat transfer from the immediately downstream tube but reduced heat transfer enhancement capability of other VG pairs downstream. Further, four different hybrid configurations of VGs were analyzed and the optimum configuration was obtained. For the optimized hybrid configuration at Re = 670, RWP with optimized roll angle increased heat transfer by 17.5% from the tube it was installed on and by 42% from the immediately downstream tube. Increase in j/ƒ of 36.7% is obtained by use of hybrid VGs in the optimized hybrid configuration. The deductions from the current study are supposed to well enhance the performance of heat exchangers with different design configurations.

scholarly journals Numerical Study on Flow and Heat Transfer Mechanisms in the Heat Exchanger Channel with V-Orifice at Various Blockage Ratios, Gap Spacing Ratios, and Flow Directions

2019 ◽  
Vol 2019 ◽  
pp. 1-21 ◽  
Author(s):  
Amnart Boonloi ◽  
Withada Jedsadaratanachai
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Numerical Results ◽  
Blockage Ratio ◽  
Maximum Heat ◽  
Flow And Heat Transfer ◽  
Maximum Heat Transfer ◽  
Smooth Channel ◽  
Gap Spacing

Numerical assessments in the square channel heat exchanger installed with various parameters of V-orifices are presented. The V-orifice is installed in the heat exchanger channel with gap spacing between the upper-lower edges of the orifice and the channel wall. The purposes of the design are to reduce the pressure loss, increase the vortex strength, and increase the turbulent mixing of the flow. The influence of the blockage ratio and V-orifice arrangement is investigated. The blockage ratio, b/H, of the V-orifice is varied in the range 0.05–0.30. The V-tip of the V-orifice pointing downstream (V-downstream) is compared with the V-tip pointing upstream (V-upstream) by both flow and heat transfer. The numerical results are reported in terms of flow visualization and heat transfer pattern in the test section. The thermal performance assessments in terms of Nusselt number, friction factor, and thermal enhancement factor are also concluded. The numerical results reveal that the maximum heat transfer enhancement is found to be around 26.13 times higher than the smooth channel, while the optimum TEF is around 3.2. The suggested gap spacing for the present configuration of the V-orifice channel is around 5–10%.

The Effectiveness-NTU Relationship of Microchannel Counter Flow Heat Exchangers With Axial Heat Conduction

2007 ◽  
Author(s):  
B. Mathew ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Microchannel Heat Exchanger ◽  
Axial Temperature ◽  
Axial Heat ◽  
Relationship Of ◽  
End Wall ◽  
Axial Heat Conduction

In this paper the effect of axial heat conduction on the thermal performance of a microchannel heat exchanger with non-adiabatic end walls is studied. The two ends of the wall separating the coolant are assumed to be subjected to boundary condition of the first kind. As the end walls are not insulated heat transfer between the microchannel heat exchanger and its surroundings occur. Analytical equations have been formulated for predicting the axial temperature of the coolants and the wall as well as for determining the effectiveness of both fluids. The effectiveness of the fluids has been found to depend on the NTU, axial heat conduction parameter and end wall temperatures. The heat transfer through the end walls have been expressed in nondimensional terms. The nondimensional heat transfer from both ends of the wall also depends on the axial heat conduction parameter and temperature gradient at the end walls. A new parameter, performance factor, has been proposed for comparing the variation in effectiveness due to axial heat conduction coupled with heat transfer with the effectiveness without axial heat conduction. The effectiveness of both the hot and cold fluid for several cases of end wall temperatures and axial heat conduction parameter are analyzed in this paper for better understanding of heat transfer dynamics of microchannel heat exchangers.

scholarly journals Experimental Research and Simulation of Fin and Tube Heat Exchanger

2017 ◽  
Vol 9 (4) ◽  
pp. 451-461
Author(s):  
Artur Rubcov ◽  
Sabina Paulauskaitė ◽  
Violeta Misevičiūtė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Ventilation System ◽  
Experimental Tests ◽  
Maximum Heat ◽  
Tube Heat Exchanger ◽  
The Heat Transfer Coefficient

The paper provides the results of experimental and theoretical test of a wavy fin and tube heat exchanger used to cool air in a ventilation system when the wavy fin of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number applying LMTD-LMED methodology, determined the dependency of the heat transfer coefficient on the supplied air flow rate with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating and 6 heat exchangers in cooling mode. After processing the results of the experimental tests, empirical equation defining the characteristics of the heat transfer coefficient of all heat exchangers were derived. The maximum heat transfer coefficient deviation is 11.6 percent. The correction factor of the wet fin (Lewis number) depending on the number of Reynolds, which ranges from 0.75 to 1.1 also is determined. Maximum capacity deviation equals 3.7 percent. The obtained equations can only be applied to a certain group of heat exchangers (with the same shape of fins or the distance between the tubes). The results of the experimental test and simulation with ANSYS program are compared and the heat transfer coefficients vary from 6.5 to 11.4 percent.

Conjugate Heat and Mass Transfer in Metal Foams: A Numerical Study for Heat Exchangers Design

2010 ◽  
Vol 297-301 ◽  
pp. 960-965 ◽  
Author(s):  
Jean Michel Hugo ◽  
Emmanuel Brun ◽  
Frédéric Topin ◽  
Jérôme Vicente
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Effective Properties ◽  
Numerical Study ◽  
Pore Space ◽  
Solid Matrix ◽  
Metallic Foam ◽  
Computational Domain

This numerical study focuses on the determination of macroscopic (effective) properties from pore scale calculation. These results will be applied to heat exchangers design. The computational domain -representative of heat exchanger section- is a parallelepiped filled with metallic foam, heated on one face and crossed by a forced fluid flow. Conjugate heat transfer and fluid flow are computed using finite volume approach on the actual solid matrix and pore space topology obtained from X-ray tomograms. Calculated heat transfer coefficient and flow law parameters are in good agreement with literature data. An active foam length is defined and measured in order to provide optimal design characteristic for foamed heat exchanger.

scholarly journals Numerical Study of Compact Plate-Fin Heat Exchanger for Rotary-Vane Gas Refrigeration Machine

2017 ◽  
Vol 53 (2) ◽  
Author(s):  
V. V. Trandafilov ◽  
M. G. Khmelniuk
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Model ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Development Research ◽  
Aspen Hysys ◽  
Simulation Results ◽  
Refrigeration Machine

Plate-fin heat exchangers are widely used in refrigeration technique. They are popular because of their compactness and excellent heat transfer performance. Here we present a numerical model for the development, research and optimization of a plate-fin heat exchanger for a rotary-vane gas refrigeration machine. The method of analysis by graphic method of plate - fin heat exchanger is proposed. The model describes the effects of secondary parameters such as axial thermal conductivity through a metal matrix of the heat exchanger. The influence of geometric parameters and heat transfer coefficient is studied. Graphs of dependences of length, efficiency of a fin and pressure drop in a heat exchanger on the thickness of the fin and the number of fins per meter are obtained. To analyze the results of numerical simulation, the heat exchanger was designed in the Aspen HYSYS program. The simulation results show that the total deviation from the proposed numerical model is not more than 15%. 

Numerical analysis of compact plate-fin heat exchangers for aerospace applications

2018 ◽  
Vol 28 (2) ◽  
pp. 395-412 ◽  
Author(s):  
Ranganayakulu Chennu
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Design Data ◽  
Content Type ◽  
Compact Heat Exchangers ◽  
Performance Deterioration

Purpose The purpose of this study is to find the thermo-hydraulic performances of compact heat exchangers (CHE’s), which are strongly depending upon the prediction of performance of various types of heat transfer surfaces such as offset strip fins, wavy fins, rectangular fins, triangular fins, triangular and rectangular perforated fins in terms of Colburn “j” and Fanning friction “f” factors. Design/methodology/approach Numerical methods play a major role for analysis of compact plate-fin heat exchangers, which are cost-effective and fast. This paper presents the on-going research and work carried out earlier for single-phase steady-state heat transfer and pressure drop analysis on CHE passages and fins. An analysis of a cross-flow plate-fin compact heat exchanger, accounting for the individual effects of two-dimensional longitudinal heat conduction through the exchanger wall, inlet fluid flow maldistribution and inlet temperature non-uniformity are carried out using a Finite Element Method (FEM). Findings The performance deterioration of high-efficiency cross-flow plate-fin compact heat exchangers have been reviewed with the combined effects of wall longitudinal heat conduction and inlet fluid flow/temperature non-uniformity using a dedicated FEM analysis. It is found that the performance deterioration is quite significant in some typical applications due to the effects of wall longitudinal heat conduction and inlet fluid flow non-uniformity on cross-flow plate-fin heat exchangers. A Computational Fluid Dynamics (CFD) program FLUENT has been used to predict the design data in terms of “j” and “f” factors for plate-fin heat exchanger fins. The suitable design data are generated using CFD analysis covering the laminar, transition and turbulent flow regimes for various types of fins. Originality/value The correlations for the friction factor “f” and Colburn factor “j” have been found to be good. The correlations can be used by the heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications and types of fins.

Numerical Study and Optimization of Corrugation Height and Angle of Attack of Vortex Generator in the Wavy Fin-and-Tube Heat Exchanger

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Wei Li ◽  
Tariq Amin Khan ◽  
Weiyu Tang ◽  
W. J. Minkowycz
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Tube Heat Exchanger ◽  
Multi Objective ◽  
Maximum Heat Transfer

Wavy fins have been considered as an alternative of the straight fins in compact heat exchangers (CHEs) for better heat transfer performance, which can be augmented by considering vortex generators (VGs). This work is related to numerical investigation and optimization of corrugation height of fin and angle of attack of delta winglet type VGs in a wavy fin-and-tube heat exchanger. For this purpose, three-dimensional (3D) Reynolds-averaged Navier-Stokes analysis and a multi-objective genetic algorithm (MOGA) with surrogate modeling are performed. Numerical simulation is carried out to study the effect of delta winglets with varying the corrugation height of wavy fin in three rows of tubes with staggered tube arrangements. The corrugation height (H) and angle of attack (α) vary from 0.3 mm to 1.8 mm and 15 deg to 75 deg, respectively. Results are illustrated by investigating the flow structures and temperature contours. Results show that increasing the corrugation height of wavy fin and angle of attack of delta winglets enhances the heat transfer performance of heat exchanger while friction factor is also increased. Employing delta winglets has augmented the thermal performance for all corrugation heights and superior effect is observed at a higher corrugation. To achieve a maximum heat transfer enhancement and a minimum pressure drop, the optimal values of these parameters (H and α) are calculated using the Pareto optimal strategy. For this purpose, computational fluid dynamics (CFD) data, a surrogate model (neural network), and a multi-objective GA are combined. Results show that optimal orientation of delta winglets with respect to corrugation height can improve both the thermal and hydraulic performance of the heat exchanger.

Ultra-Compact Micro-Scale Heat Exchanger for Advanced Thermal Management in Data Centers

2021 ◽  
Author(s):  
Raffaele L. Amalfi ◽  
Todd Salamon ◽  
Filippo Cataldo ◽  
Jackson B. Marcinichen ◽  
John R. Thome
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Operating Conditions ◽  
Transfer Performance ◽  
Two Phase ◽  
Maximum Heat ◽  
Pressure Drops

Abstract The present study is focused on the experimental characterization of two-phase heat transfer performance and pressure drops within an ultra-compact heat exchanger (UCHE) suitable for electronics cooling applications. The UCHE is composed of a double-side-copper finned plate with an optimized geometry that enhances the heat transfer performance and flow stability, while minimizing the pressure drops. These features make the UCHE the ideal component for thermosyphon cooling systems, where low pressure drops are required to achieve high passive flow circulation rates and thus achieve high critical heat flux values. The UCHE's thermal-hydraulic performance is first evaluated in a pump-driven system at the Laboratory of Heat and Mass Transfer (LTCM-EPFL), where experiments include many configurations and operating conditions. Then, the UCHE is installed and tested as the condenser of a thermosyphon loop that rejects heat to a pumped refrigerant system at Nokia Bell Labs, in which both sides operate with refrigerants in phase change (condensation-to-boiling). Experimental results demonstrate high thermal performance with a maximum heat dissipation density of 5455 (kW/m3/K), which is significantly larger than conventional air-cooled heat exchangers and liquid-cooled small pressing depth brazed plate heat exchangers. Finally, a thermal performance analysis is presented that provides guidelines in terms of heat density dissipations at the server- and rack-level when using passive two-phase cooling.

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