Counter Flow Microchannel Heat Exchanger Research Articles

Numerical investigation for the effects of surface roughness in counter flow microchannel heat exchanger with different channels geometries

This article presents a numerical investigation focused on how roughness of surface affects the overall performance of a counter-flow microchannel heat exchanger (CFMCHE). The study examines various microchannel shapes, including triangles, squares, circles, and trapezoids, to evaluate their performance within the context of CFMCHE. Water with consistent properties flows through aluminum microchannels used as the working fluid. The analysis employs the roughness-viscosity method to assess how surface roughness influences the CFMCHE’s performance. The study’s findings emphasize that the trapezoidal channel shape exhibits the most favorable performance among the shapes investigated. Additionally, among the operational parameters considered, the hydraulic diameter emerges as the most influential factor in determining the most suitable characteristics for CFMCHE. The presence of surface roughness was found to marginally improve thermal performance while slightly reducing hydraulic efficiency. This research provides valuable insights into the intricate interplay between surface roughness and channel shape. Notably, the impact of roughness is more pronounced in the case of the trapezoidal shape compared to other geometries.

Comparative Study of Straight and Venturi Channel Cross-Sections of Microchannel Heat Exchangers

Abstract This study provides extensive research on fluid flow and heat transfer for 4-layered ceramic-compact counterflow microchannel heat exchangers (CFMCHE) using CFD-ACE®, a computational fluid dynamics (CFD) package. The goal is to build and expand upon previous studies in this area to identify a more efficient channel shape for better performance of the microchannel cross-section through numerical analysis under the same operating conditions. To develop the methodology for numerical analysis, a three-dimensional (3D) computational model of the CFMCHE was developed and validated with published and experimentally tested results with a percentage difference in outlet temperatures of 3-5% for hot fluids and 6-12% for cold fluids across the entire design of experiments (DoEs). Microchannel heat exchangers (MCHEs) exhibit high heat transfer rates and area-to-volume ratios, making them suitable for industrial applications. In this study, various design options for channel cross sections in a venturi shape were assessed numerically using a validated methodology in a segmented venturi CFMCHE to enhance performance. The steady-state performance of the Venturi CFMCHE was compared to that of the straight CFMCHE baseline design under the same bucket volume, area, and operating conditions. It was found that the venturi CFMCHE showed a ∼4-9% improvement as compared to the straight CFMCHE, but same time the pumping power was also 15-40% under the same operating conditions.

An In-Depth Comparison of Straight and Wavy Microchannel Heat Exchangers

Abstract This paper presents extensive fluid flow and Heat-Transfer studies conducted using a commercial computational fluid dynamics (CFD) package known as CFD-ACE® to elaborate and expand on the reference studies available for ceramic-compact counterflow microchannel heat exchangers (MCHEs). The computational 3D model was developed using an experimentally tested MCHE and validated with experimental data with 3–5% variation for hot fluid and 6–12% variation for cold fluid for the entire design of experiments (DoEs). This study aimed to identify the performance of novel microchannel shapes using numerical analysis. The MCHE has good heat exchange properties, a compact design at industrial throughput, and a lower inner volume. During the study and identification of novel channel shapes, the segmented wavy MCHE was evaluated. The results were compared with those of the same volume and area straight MCHE baseline design under various identical operating conditions. Although the performance in terms of effectiveness is increased up to ∼12–25% in wavy MCHE with respect to straight MCHE simultaneously, the pressure drop is also increased by ∼60–80% under the same operating conditions. Therefore, performance and trade-offs are required to make the correct decision regarding feasibility. The effectiveness of the heat-transfer enhancement was also evaluated by plotting the heat-transfer coefficient ratio with respect to the pressure ratio of the two designs under identical operating conditions. This numerical study clearly indicates that wavy channels are better from the thermal performance point of view, whereas straight channels are better from the pumping power point of view, and the quantitative values are presented in graphical form.

Investigation of Counterflow Microchannel Heat Exchanger with Hybrid Nanoparticles and PCM Suspension as a Coolant

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

Study the hydro and thermal performance of microchannel heat exchanger with hybrid suspension of nanoparticles and MEPCM particles

This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed

Evaluation of a counter-flow microchannel heat exchanger performance with air-water vapor mixture to liquid water

Given its configuration and operation conditions, the performance of a counter-flow microchannel heat exchanger (MCHX) is evaluated through detailed calculations. The fluids, both liquid water and air, are considered as continuum flow flowing in microchannels. The MCHX has 59 sheets, and each sheet has 48 microchannels. The microchannels for both fluids have the same cross section of 0.8mm×1mm and same length of 200mm. Log mean temperature difference method is adopted for this evaluation. Using appropriate equations, the properties of air-water vapor mixture are calculated based on that of the two components. Given the inlet temperature for liquid water(35℃) and air (170℃),the calculated outlet temperature for both fluids are 55.5℃ and 43.3℃, respectively. The results also show that the air at the outlet is saturated. The overall heat transfer coefficient reaches 100W/m2ꞏK, which is much higher than that of conventional heat exchanger with similar fluid combinations.

NUMERICAL INVESTIGATION OF ROUGNESS EFFECTS ON HYDERDYNMIC AND THERMAL PERFORMANCE OF COUNTER FLOW MICROCHANNEL HEAT EXCHANGER

In this paper the effect of surface roughness on the performance of counter flow microchannel heat exchanger has been numerically investigated. The studied Microchannel heat exchanger is a square shape and made of aluminum as substrate material with different values of hydraulic diameters (20, 50, 110, 150 ) μm. The working fluid used is water at constant properties. Roughness- viscosity model has been used to study the roughness effect with 0.14 ratio of roughness to hydraulic diameter. The results obtained indicate that pressure drop of (CFMCHX) increased with increasing surface roughness and decrease hydraulic diameter also the results showed that there is a slight increasing in thermal performance with increasing the surface roughness.

Heat transfer characteristics of Cu-based microchannel heat exchanger fabricated by multi-blade milling process

A Cu-based double-layer compact counter-flow microchannel heat exchanger has been designed, fabricated, and evaluated. A manufacturing method called multi-blade milling is used for cost-effective fabrication of rectangular microchannel with height of 0.5–2 mm, width of 0.2–0.8 mm and spacing of 0.4–1 mm. Theoretical analysis of structural characteristics of microchannels based on specific surface area is conducted. The experimental and numerical investigations on the effect of microchannel size on fluid flow and heat transfer characteristics for optimization of microchannel size and their implementation in heat exchanger are performed. Nusselt number and Poiseuille number at a range of Reynolds numbers are presented and compared using deionized water as the coolant. The velocity and temperature distribution through numerical simulation provide better understanding on the fluid flow and heat transfer characteristics. Based on the experimental and numerical results, the optimal geometric parameters of microchannel with height of 0.5 mm, width of 0.4–0.6 mm, and spacing of 0.4 mm are recommended to achieve the enhancement of heat transfer and the compactness of microchannel heat exchanger.

Investigation of heat transfer in a microchannel with same heat capacity rate

In this paper, a new experimental setup was proposed to realize the constant-heat-flux boundary condition based on a counter flow microchannel heat exchanger with the same heat capacity rate of the hot and cold streams. This approach provides a constant fluid temperature gradient along the surfaces. An analytical two-dimensional model was developed to describe the heat transfer processes in the hot stream and the cold stream, respectively. In the experiments, DI-water was employed as the working fluid. Laser induced fluorescence (LIF) method was used to measure the fluid temperature field within the microchannel. Different combinations of flow rates were studied to investigate the heat transfer characteristics in the microchannel. The measured mean temperature distribution matched well with the proposed analytical model. A correlation for Nusselt number (Nu) was proposed based on the experimental Reynolds number (Re < 1) and Prandtl number (Pr).

Performance Augmentation and Optimization of Aluminum Oxide-Water Nanofluid Flow in a Two-Fluid Microchannel Heat Exchanger

In this paper, laminar forced convection and entropy generation in a counter flow microchannel heat exchanger (CFMCHE) with two different working fluids in hot and cold channels, i.e., pure water and Al2O3–water nanofluid are investigated numerically using a three-dimensional conjugate heat transfer model. The temperature distribution, effectiveness, pumping power and performance index for various volume fractions between 0.01–0.04, three nanoparticles diameters, i.e., 29, 38.4, and 47 nm and a range of Reynolds number from 120 to 480 are given and discussed. According to second law of thermodynamics and entropy generation rate in the CFMCHE, the analysis of optimal volume fraction, particles size, Reynolds number as well as optimal placement of using nanoparticles in hot/cold channels is carried out. It is found that decreasing particles size and increasing nanoparticles concentration lead to higher effectiveness and pumping power as well as lower temperature in the solid phase of CFMCHE. Furthermore, the frictional contribution of entropy increases with decreasing particles size and increasing volume fractions while the trends for heat transfer contribution of entropy are reverse. Total entropy decreases as particles size decreases and volume fraction increases hence the maximum performance occurred at lower particles sizes and higher volume fractions. The Reynolds number has significant effect on performance of system and with decreasing it the effectiveness increases and heat transfer contribution of entropy decreases while the pumping power and frictional contribution of entropy decrease. Finally, it is seen that the capability of heat transfer of Al2O3–water nanofluids is higher when they are under heating conditions because the effectiveness of CFMCHE is higher when nanoparticles are used in cold channels.

Modeling non-adiabatic counter flow microchannel heat exchangers

This article presents a thermal model of counter flow microchannel heat exchangers that are subjected to thermal interaction with its surroundings (ambient or substrate or neighboring microdevices) due to its non-adiabatic outer wall. The thermal model consists of two governing equations, one for each of the fluids, describing the variation of temperature in the axial direction. Analytical solutions of the model can be used for determining the temperature at any axial location; it is used primarily for calculating the effectiveness with respect to each fluid. The effectiveness with respect to each fluid is found to depend on NTU, heat capacity ratios, surrounding temperatures and the thermal resistance between each of the fluid and the respective surrounding. When heat transfer is from the surrounding to the fluids the effectiveness based on the hot and cold fluid decreased and increased, respectively. For this scenario an optimal effectiveness exists for hot fluid but none exists for the cold fluid. The opposite is true in all aspects when heat transfer is from the fluids to the surroundings. Among the two operating possibilities associated with unbalanced flow condition of the counter flow microchannel heat exchanger the operating condition in which the cold fluid has the higher heat capacity, among the fluids, is found to be the best in terms of effectiveness of the fluids.

Experimental Validation of a Thermal Model of Counterflow Microchannel Heat Exchangers Subjected to External Heat Flux

The effect of uniform external heat flux on the effectiveness of counterflow microchannel heat exchangers is experimentally studied in this article for validating an existing thermal model. The model validated in this study is a one-dimensional model previously developed by the same authors. The model is validated to be independent of microchannel profile, hydraulic diameter, and heat capacity ratio. For studying the effect of microchannel profile, experiments are conducted under balanced flow conditions using trapezoidal and triangular microchannels with approximately equal hydraulic diameter of 278.5 μm and 279.8 μm, respectively. The influence of hydraulic diameter on the thermal model is studied using a trapezoidal microchannel with hydraulic diameter of 231 μm and 278.5 μm. Experiments are conducted under unbalanced flow conditions, with a heat capacity ratio of 0.5, using the trapezoidal microchannel of hydraulic diameter of 278.5 μm. Deionized water is used as the fluid in all experiments. The hot and cold fluid effectiveness is studied and the theoretical predictions and experimental results are found to be in excellent agreement. Thus, the model validated in this article can be used for accurately modeling microchannel heat exchangers irrespective of the microchannel hydraulic diameter, profile, and heat capacity ratio.

Performance of a Conceptual Counter-flow MCHE operated on CuO-Water Nanofluid: Influence of Geometry

Microchannel heat exchangers (MCHE) can be designed with different channel geometry such as circular, triangular, rectangular, square, trapezoidal and hexagonal. In this article, the influence of channel geometry on thermal, hydraulic and overall performance of counter flow MCHE operated on CuO-water nanofluid flow has been highlighted. Herein, Nusselt and Poiseuille number for different channel shapes and thermo-physical properties of CuO-water nanofluid (viz., thermal conductivity, viscosity…) have been designed either empirically or adopted from literature. Results of pumping power with trapezoidal geometry MCHE is found to be highly sensitive with nanofluid flow. Rectangular shape counter flow MCHE gives highest thermal effectiveness, while iso-triangular geometry gives best overall performance by converting the pressure energy into thermal energy.

Development of an adhesive-bonded counterflow microchannel heat exchanger

A low-temperature liquid-to-vapor counterflow microchannel heat exchanger has been redesigned and fabricated using a scalable, low-cost adhesive bonding process. Adhesive erosion concerns are mitigated with the use of sealing bosses. Performance has been tested using water and compressed air as test fluids. Results show greater effectiveness and higher heat transfer rates than the original heat exchanger due to relaxed design constraints afforded with adhesive bonding. A maximum effectiveness of 82.5% was achieved with good agreement between theoretical and experimental values. Although thermal performance was improved, higher pressure drops were noted. Pressure drops were predicted with a maximum error of 16% between theoretical and experimental values. Much of the pressure drop was found to be in the device manifold which can be improved in subsequent designs.

Effect of Partition Wall on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger

The effect of a partition wall on heat transfer characteristics of a two-stream gas-to-gas counterflow microchannel heat exchanger has been numerically investigated. The flow passages of the microchannel heat exchanger are plane channels of 100 μm in height and 20 mm in length. The material of the partition wall is assumed to be stainless steel. The computations were performed for a wide range of flow rate to investigate heat transfer characteristics of the microchannel heat exchanger. Moreover, computations for various partition wall thicknesses were conducted to investigate the effect of the wall thickness. The thickness ranged from 200 μm to 6 μm while the channel height was fixed at 100 μm. Numerical results show that heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger are affected by partition wall thickness. Computations for various partition wall thicknesses and thermal conductivities of the partition wall were performed. The results were compared with those of a single microchannel with constant wall temperature. Applicability of the assumption of constant wall temperature was revealed.

Investigation of a Counter Flow Microchannel Heat Exchanger Performance with Using Nanofluid as a Coolant

In this paper the performance of a counter flow microchannel heat exchanger (CFMCHE) is numerically investigated with a nanofluid as a cooling medium. Two types of nanofluids are used Cu-water and Al2O3-water. From the results obtained it’s found that thermal performance of CFMCHE increased with using the nanofluids as cooling medium with no extra increase in pressure drop due to the ultra fine solid particles and low volume fraction concentrations. The na-nofluids (Cu-water and Al2O3-water) volume fractions were in the range 1% to 5%. It’s also found that nanoflu-id-cooled CFMCHE could absorb more heat than water-cooled CFMCHE when the flow rate was low. For high flow rates the heat transfer was dominated by the volume flow rate and nanoparticles did not contribute to the extra heat absorption. Also the performance of CFMCHE can be increased considerably by using nanofluids with higher thermal conductivities.

Numerical investigation of counter flow microchannel heat exchanger with slip flow heat transfer

The rectangular microchannel heat exchanger performance is numerically investigated in this paper. Hydrodynamic and heat transfer characteristics in a laminar, 3-D, incompressible, slip flow, steady state and counter flow are proposed. The Navier–Stokes equations and energy equation for the hot and cold fluids are solved with the slip velocity and temperature jump conditions. The governing equations are discretized using finite-volume method-upwind differencing scheme, and then these are solved using SIMPLE algorithm method on staggered grid with FORTRAN code. From the obtained results it was found that the factors affecting the effectiveness are: Reynolds number Re, thermal conductivity ratio K r, Knudsen number Kn and aspect ratio α. Increasing of Re, Kn and α separately lead to decrease the effectiveness. While the effectiveness increases with increasing K r until it reach a certain optimal value which gives the maximum effectiveness at K r = 90. Also, it is found that Nusselt number decrease with increases Knudsen number. Increasing of Re and Kn separately lead to increase pressure drop.

Thermal and Hydraulic Performance of Counterflow Microchannel Heat Exchangers With and Without Nanofluids

Abstract This paper analyzes the thermal and hydraulic performance of a counterflow microchannel heat exchanger (CFMCHE) with and without nanofluid as working fluid. A 3D conjugate heat transfer simulation is carried out using a finite volume approach to evaluate the effects of inlet Reynolds number, Brownian motion, and volume fraction of nanoparticles on the pumping power, effectiveness, and performance index of CFMCHE. The accuracy of the code has been verified by comparing the results with those available in the literature. A single phase approach is used for the nanofluid modeling. The base fluid used in the analyses as a basis for comparison was pure water. Two types of nanofluids, namely, water-Al2O3 with a mean diameter of 47 nm and water-CuO with a mean diameter of 29 nm, each one with three different volume fractions, are utilized. In addition, two temperature dependent models for the thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion are used. Calculated results demonstrate that the effectiveness and performance index of CFMCHE decrease with increasing Reynolds number. Moreover, it is observed that the relative enhancements in the pumping power become more prominent for higher values of Reynolds numbers. It was also found that the performance index and pumping power are not sensitive to volume fraction at higher and lower Reynolds numbers, respectively.

The design, fabrication, and evaluation of a ceramic counter-flow microchannel heat exchanger

Abstract This paper reports the model-based design and experimental performance evaluation of an all-ceramic compact counter-flow microchannel heat exchanger. Ceramic materials enable high-temperature operation that can exceed the capabilities of comparable metal heat exchangers. Additionally, ceramics may enable operation in harsh chemical environments in which metals cannot be used. Although the internal manifolds and channel layouts can be complex, a unique fabrication process called Pressure Laminated Integrated Structures (PLIS) facilitates low-cost manufacturing. The heat exchangers are tested using inlet air heated up to 750 °C on the hot side, room-temperature inlet air on the cold side, and flow rates up to 3 × 10−3 kg s−1 (150 standard liters per minute of air). The paper reports measured performance of single units at the kilowatt scale for which heat-exchanger effectiveness up to 70% has been achieved.

Heat transfer characteristics of parallel and counter flow micro-channel heat exchangers with varying wall resistance

Thermal behaviours of parallel and counter flow micro-heat exchanger are investigated numerically, with emphasis on the role of wall resistance and thermal entry effects. The influence of different parameters, such as, thermal resistance (R), Knudsen number (Kn), effectiveness (e) and Number of Transfer Units (NTU) are investigated. It is found that the temperature jump at the walls increases with increasing R and Kn. On the other hand, the NTU increases with decreasing R and Kn. Furthermore, for counter flow, thermally fully developed flow may not exist over a large section of the heat exchanger due to the heat conduction in the separating wall and the entrance region.