Multiport Minichannel Research Articles

Heat transfer performance of a multiport mini-channel loop thermosyphon for cooling miniaturized electronic devices

Multiport mini-channel thermosyphon with hydraulic diameters less than 2 mm undergoes a severe entrainment problem both in vapor and liquid regions, impeding the flow and affecting the performance characteristics. To address this issue, a novel multiport mini-channel loop thermosyphon (MPMC-LT) design is proposed. This design separates the vapor and liquid flow paths, reducing entrainment and enhancing the performance characteristics. Tests are conducted with heat loads ranging from 5 to 45W at four inclinations (0°, 30°, 60°, and 90°) relative to the horizontal plane. Results revealed that the MPMC-LT design extends the entrainment limit by 10.6 times compared to conventional designs, reducing the interaction between the vapor and condensed working fluid. Additionally, the total entropy and thermal resistance drops by 20.7 % and 19.9 %, respectively at an optimum inclination angle of 30°. It is also noted that the effective thermal conductivity at the optimal inclination is 5.8 times higher compared to the conventional multiport thermosyphon designs. The design effectivity uses the buoyancy, inertial and surface tension forces to reduce resistance in the fluid flow, thereby enhancing the heat transfer characteristics. These results highlight that MPMC-LT is a suitable thermal management device for power electronic systems.

Flow condensation inside a multiport mini channel and a rectangular mini channel with pin fin array

In this paper, an experimental study of flow condensation was carried out of R134a in a multiport mini channel and a mini channel with pin fin array. The former comprised 20 parallel rectangular channels with an equivalent diameter of 0.64 mm. The latter is a narrow rectangular mini channel containing 10 rows of diamond pin fins with a staggered configuration, and height and longitudinal/transverse pitch of 0.5 mm and 2 mm respectively. To acquire the local value of heat flux and heat transfer coefficient, air jet impingement cooling devices were adopted to condense the vapor of refrigerants. The effects of vapor quality, mass flux, heat flux, and saturation pressure on flow condensation heat transfer coefficient were investigated with the operating conditions: vapor quality from 1 to 0, mass flux from 160 to 450 kg/(m2s), heat flux from 10.0 to 39.8 kW/m2, and saturation pressure from 600 to 1500 kPa. The experimental results indicated that the pin fin array significantly improves the condensation heat transfer coefficient up to nearly 186 % compared to the multiport mini channel in the high vapor quality region. For both channels, the local heat transfer coefficient increases with an increase in vapor quality, mass flux, and heat flux whereas decreases with increase in saturation pressure. The influence of heat flux and mass flux on heat transfer coefficient was more pronounced in the high vapor quality region than in the low vapor quality region. A sensitivity analysis was performed at different vapor quality levels. The most influential parameters in the smooth channel and the pin fin array are saturation pressure and mass flux, respectively. The relative contribution of heat flux is more obvious in the high vapor quality region. Some of the existing correlations have good prediction performance for the smooth channel experimental data in this paper, and the corresponding MAD is within 20 %. However, their deviations are much greater for the applications of pin fin array.

Predictive modeling for the boiling heat transfer coefficient of R1234yf inside a multiport minichannel tube

Existing prediction models of flow boiling heat transfer coefficient, such as the well-known superposition, asymptotic, and flow pattern models, provide an applicable method to attain the closest to the true value of the heat transfer coefficient in specific ranges. In this study, heat transfer coefficient data are collected through an experimental study of R1234yf inside a multiport minichannel tube within a mass flux of 50–500 kg/m2s, heat flux of 3–12 kW/m2, saturation temperature of 6 °C, and vapor quality up to 1. The assessment of the heat transfer coefficient is conducted by comparing the heat transfer coefficient of each model with that of R1234yf. In addition, a machine-learning prediction model is proposed to improve the prediction accuracy of the heat transfer coefficient. A machine-learning method could provide an accurate prediction result for the heat transfer coefficient by feeding the program with a factor from heat transfer coefficient data (e.g., a dimensionless number). Therefore, an alternative prediction method could be applied to predict the heat transfer coefficient with the lowest error by providing the setting parameter that fits the pattern of heat transfer coefficient data. In addition, a heat transfer coefficient correlation is proposed to define the only-value result of the machine-learning model.

Flow boiling pressure drop and flow patterns of R-600a in a multiport minichannels

This study experimentally investigated the flow boiling pressure drop and flow patterns of R-600a in a horizontal multiport extruded tube with 1.47 mm ID. The experiments were carried out with mass flux between 35 and 165 kgm−2s−1 and heat flux ranging from 4.5 to 18.5 kWm−2 at a saturation temperature of 24 °C. Flow patterns and void fraction distribution amongst channels were observed with a high-speed camera in a visualization section. The influence of mass flux and vapour quality on pressure drop was verified. The flow patterns identified during tests were plug, slug churn and wavy-annular, differently distributed along the channels. The results were also compared with eight different correlations proposed in the literature. Results indicate the dependence of pressure drop on both mass and heat fluxes.

A New Two-Phase Multiplier for Flow Pressure Drop in Multiport Minichannel Condensers and Evaporators

Due to flow maldistribution, the condensation and evaporation flow patterns in multiport minichannels are considerably different from single minichannels or macrochannels. This article compiled the friction pressure drop data from experimental phase-change investigations in multiport minichannel condensers and evaporators over the past two decades. The data was reduced to friction pressure gradients, and a new two-phase multiplier was proposed for estimating the phase-change pressure drop in multiport condensers and evaporators. Thirteen hundred and forty-four condensation pressure drop and six hundred and twenty-three evaporation pressure drop data from twenty-nine studies were correlated to yield four predictive two-phase multiplier equations in the laminar and turbulent flow regimes. The predictive correlations fit 67% of the laminar condensation and 80% of the turbulent pressure drop data within ±50%. Further, 57% of the laminar evaporation and 100% of the turbulent evaporation pressure drop data were fit within ±50%. The correlations were compared with widely published correlations and were a significant improvement. Meta-analysis revealed that multiport minichannels are most effective for reducing turbulent flow condensation pressure drop and laminar flow evaporation pressure drop. The compiled data and presented correlations and analysis should be helpful to the process, electronics packaging, aviation, and aerospace industries designing compact, lightweight, and high-efficiency condensers, and evaporators.

Heat Transfer in Multiport Minichannel Condensers and Evaporators: Correlation Development and Meta-Analysis

Condensers and evaporators are widely deployed as surface phase-change heat exchangers in power plants, desalination plants, and large refrigeration systems. Surface condensers and evaporators or shell and tube heat exchangers are frequently used in the process industry. However, compact condensers and evaporators such as multiport minichannel condensers and evaporators are evolving as compact, lightweight, high heat flux, and highly efficient alternatives to the bulky, space-consuming, and relatively less efficient shell and tube designs. This article reports regression analysis and new correlation development from experimental data compiled from horizontal, multiport minichannel condensers and evaporators in the past two decades. Thermo-hydraulic parameters such as the Reynolds number, Prandtl number, boiling number, Martinelli parameter, hydraulic diameter, and other variables were considered to predict the Nusselt number in such condensers and evaporators. Meta-analysis yielded statistically significant results and strongly suggested that multiport minichannels were more suitable for evaporation than condensation.

Experimental Investigation of Two-Phase Flow Boiling Heat Transfer Coefficient and Pressure Drop of R448A inside Multiport Mini-Channel Tube

Regulations and restrictions against high global warming potential (GWP) refrigerants have been introduced to encourage the adoption of environmentally friendly refrigerants and mitigate the environmental impact of the HVAC industry. R448A, a zeotropic blend with a GWP of 1390, has recently been proposed as a drop-in replacement for R404A and R410A in commercial systems. In this study, the heat transfer coefficient and pressure drop characteristics of R448A within a multiport mini-channel tube were experimentally investigated. The experimental ranges of the mass and heat fluxes were 100 to 500 kg/(m2s) and 3–15 kW/m2, respectively. Additionally, the range of quality from 0 to 1 was considered at two fixed saturated temperatures of 3 and 6 °C. The heat transfer coefficient increased with mass flux. Under low mass flux condition, the heat flux increased the heat transfer coefficient, but there was no noticeable effect of the saturated temperature on the heat transfer coefficient. At high mass flux, heat flux had no major effect on heat transfer, while a decrease in the saturated temperature was found to increase the heat transfer coefficient. Moreover, the pressure drop increased with an increase in the mass flux and vapor quality, whereas the heat flux did not affect the pressure drop. The heat transfer coefficient and pressure drop performance of R448A was compared with that of R410A inside the same tube. Finally, correlations for heat transfer coefficient and pressure drop were proposed for the prediction of heat transfer coefficient and pressure drop in practical applications.

Mini-channel heat exchanger optimization using genetic algorithm and multiple-criteria decision making

This study aims to apply an integrated optimization approach that combines Multi-objective Optimization (MOO) and Multiple-criteria Decision-making (MCDM) to optimize a multiport mini-channel having 2D sawtooth micro fins under laminar, transitional, and turbulent flow conditions. Water was considered as working fluid. The Reynolds number (Re), fin height (Hf), fin width (Wf), the number of micro-fins in each mini-channel (N), and the distance between the successive fins (S1) were selected as design and flow parameters and the Nusselt number (Nu) and the Poiseuille number (Po) were selected as objective functions. A Genetic Algorithm based MOO study was conducted using the correlations available in the literature aiming to find the optimum values of design and flow parameters that maximize Nu and minimize Po. Then, the VIsekriterijumska Optimizacija I Kompromisno Resenje (VIKOR) method was employed to help designers to select an optimum design among the Pareto optimal solution set which is the output of MOO. Finally, the optimization results obtained were compared with those obtained by the 1st Law of Thermodynamics based Performance Evaluation Criteria (PEC). The advantages and disadvantages of these methods were discussed in detail. It is revealed that the integrated approach is a more comprehensive and flexible approach that also covers the results of PEC.

Effect of confluence length on the heat transport capability of ultra-thin multiport minichannel thermosyphon

Effect of confluence lengths (Colen = 0 mm, 5 mm and 10 mm), heat loads (10–90 W), filling ratios (FR = 40% to 60%) and inclination angles (IA = 30°, 45°, 60° and 90°) on the heat transport capability of a multiport minichannel (MPMC) thermosyphon with hydraulic diameter of 1.18 mm and having Acetone as the working fluid is experimentally investigated. Enhancement of 33% in the heat transport capability (up to 90 W) was observed for MPMC thermosyphon with optimum Colen = 5 mm, whereas it was only 60 W at Colen = 0 mm. Reduction of 42.4% and 18.3% in thermal resistance (Rt) and evaporator wall temperature (Te,w) and enhancement of 19.5% in evaporator heat transfer coefficient (heva) are respectively observed for MPMC thermosyphon with optimum Colen = 5 mm and inclination angle (IA = 90°) when compared with Colen = 0 mm. Combination of reduced entrainment effect causing faster circulation of working fluid at optimum Colen, surface tension effect which pulls the bulk condensate to the corners and the thin film at flat sides of multiports are found to be the major reasons for enhancement in the heat transport capability of MPMC thermosyphon.

Experimental study on the thermal and flow characteristics of ZnO/water nanofluid in mini-channels integrated with GA-optimized ANN prediction and CFD simulation

The thermal and flow characteristics of ZnO/water nanofluid in two multiport mini-channels were experimentally and numerically studied. Nanofluids with volumetric concentrations of 0.75 and 1.5% were used. Experimentally, the influences of concentration, Reynolds number (100–3750) and channel size (1.22 and 1.42 mm) on performance were identified. A novel Genetic Algorithm-optimized Backpropagation-Artificial Neural Network (GA-optimized BP-ANN) was proposed for Nusselt number prediction. Numerically, the performance using single-phase and mixture model with different turbulence models were evaluated. Results reveal that the nanofluids show better heat transfer performance and higher pressure drop than that of water. Additionally, the improvement is more obvious in laminar/turbulent transition region at a higher concentration. A better heat transfer performance is observed in a smaller channel after laminar flow region. For thermal performance factor, enhancement only appears at higher Reynolds numbers after flow transition. The most remarkable enhancements are nearly 1.3 and 1.48 for the two channels at the Reynolds numbers of 1600 and 1430, respectively. The developed GA-optimized BP-ANN shows an extremely high prediction accuracy with a Mean Absolute Relative Deviation (MARD) of 2.70%. Numerically, the single-phase model combined with the Lam-Bremhorst model exhibits better simulation results for nanofluid in mini-channel with a MARD of 9.0% than the mixture model.

Heat and mass transfer analysis on multiport mini channel shelf heat exchanger for freeze-drying application

An experimental study on heat transfer characteristics of shelf heat exchangers, which are used in small-scale freeze dryers, is presented in this paper. The proposed heat exchanger consists of the multiport mini-channel flow paths, and a comparison with a conventional serpentine is carried out based on uniformity of the product temperature achieved. The experimental results indicate that the mini-channel shelf has better temperature uniformity than the latter. Skimmed milk is used as the test fluid. In the freezing and drying process, the product temperature variation is minimal in the mini-channel heat exchanger, with a variation of 12.5 % and 25%, respectively, and the heat transfer coefficient is found to be from 140 to 267 Wm−2 K−1. The moisture content in the product reduces to 50 % in 2 hours, and the drying rate is higher at 0.032 kg hr−1 after 1 hour of the drying process. The redesign of the heat exchanger will be an essential tool to improve the performance with uniform temperature distribution on the product and to improve the product quality.

Experimental study and CFD modelling on the thermal and flow behavior of EG/water ZnO nanofluid in multiport mini channels

Nanofluid and mini channel are two promising approaches to enhance the heat transfer performance. The present study combined these two techniques together and investigated the heat transfer and flow behavior of ZnO ethylene glycol (EG)/water nanofluid inside two multiport mini channels with the hydraulic diameters of 1.22 mm and 1.42 mm. ZnO nanoparticles with an average diameter of 30 nm were dispersed into 40%/60% EG/water solution to get nanofluids with 0.75% and 1.5% volume concentration. The heat transfer and flow performance under various operational conditions were identified by both experiments and CFD simulation. Experimentally, it reveals that the Nusselt numbers are averagely improved by 6.7% and 9.8% for nanofluids with 0.75% and 1.5% concentration respectively. However, the friction factors are also enlarged by 4.6% and 8.6% correspondingly, which results to a various thermal performance factor ranging from 0.94 to 1.31 with the average values of 1.05 and 1.07. The decrement of channel diameter leads to greater heat transfer coefficients, pressure drop, friction factor but nearly the same Nusselt number. A new correlation is developed to predict the Nusselt number for ZnO nanofluid flow in multiport mini channels with a MARD of 9.2%. Numerically, single-phase model gives better predictions for both Nusselt number and friction factor with the average relative deviations of nearly 16% and 19.1% correspondingly. Mixture model severely overestimates the Nusselt number but shows a reasonable friction factor prediction. The present study is expected to give some guidance for the study of nanofluid in mini channels.

Investigation on the thermal properties, heat transfer and flow performance of a highly self-dispersion TiO2 nanofluid in a multiport mini channel

The present study experimentally investigated the single-phase convective heat transfer and pressure drop characteristics of a highly self-dispersion TiO2 nanofluid inside a multiport mini channel with 1.22 mm hydraulic diameter. Nanofluids with volume concentrations of 0.5% and 1% were used. Thermal properties for the nanofluid were measured and compared with correlations. Results indicate that the adding of nanoparticles not only enlarges the thermal conductivity by 4.2% averagely but also significantly increases the viscosity by 14.9% for the 1% nanofluid. Besides the viscosity, the thermal conductivity and density can be predicted well by correlations. Compared with water flow, the nanofluid flow presents an earlier laminar-turbulent transition. Before the transition, the nanofluid has roughly the same performance but slightly smaller Nusselt numbers with water. After the transition, it shows better heat transfer performance and greater friction factors. Moreover, the thermal performance factor is greater than 1 for Reynolds number of 1500–2200 and the maximum of 1.57 occurs at the Reynolds of 1800. Outside this range, its value is close to 1 or even slightly smaller than 1. Finally, the exiting correlations for Nusselt number were evaluated. The present study provides a practical candidate and experimental data for the selection and design of nanofluid based heat exchanger.

Feasibility of using multiport minichannel as thermosyphon for cooling of miniaturized electronic devices

AbstractThe feasibility of using multiport minichannel (MPMC) as thermosyphon for cooling miniaturized electronic products is experimentally investigated with acetone as the working fluid. A detailed analysis on thermal performance and entropy generation due to heat transfer and pressure drop with the effects of heat load (10‐50 W), filling ratio (FR; 40%, 50%, and 60%), and inclination angle (45°, 60°, and 90°) has been carried out. The results showed a reduction of 22.2% and 9.31% in thermal resistance and evaporator wall temperature at optimum filling ratio (OFR) of 50%. Reduction in entropy generation due to heat transfer and pressure drop of 16.6% and 12.3%, respectively, was observed at OFR. Internal fins in MPMC increase the surface area and evaporation rate by enhancing heat transfer leading to a decrease in the rate of entropy generation. Multiport increases surface tension of condensate at right angles to the flow direction along with the effects of gravity and enhancing rate of condensation. A new correlation is developed to predict evaporator wall temperature as a function of heat load and FR. The proposed correlation agrees well with a deviation of ±20% with present experimental results and also with the published literature. Thus, the obtained results will be useful in cooling miniaturized electronic devices.

Condensation heat transfer characteristics and pressure drops of R410A, R22, R32, and R290 in a multiport rectangular channel

Experiments on the two-phase flow condensation heat transfer of R410A, R22, R32, and R290 (propane) inside a multiport minichannel tube are investigated in this study. The experiments are conducted with heat fluxes in the range of 3 to 15 kW/m2, working fluids mass fluxes in the range of 50 to 500 kg/m2s, and vapor quality up to 1.0, at a fixed saturation temperature of 48 °C. The test section is an aluminum multiport minichannel tube with a hydraulic diameter equal to 0.83 mm and 18 rectangular channels. The effects of mass flux, heat flux, and thermal properties of refrigerants on the heat transfer performance and pressure drop are illustrated and analyzed. The experimental heat transfer coefficients are compared with well-known correlations. Finally, from the experimental data, a new condensation heat transfer coefficient correlation for all refrigerants is proposed.

Cooling of high heat flux electronic devices using ultra-thin multiport minichannel thermosyphon

Studying multiport minichannels as thermosyphons are considered to be of great interest compared to cylindrical and flat shaped ones with single ports. In this study, a novel multiport minichannel (MPMC) thermosyphon (hydraulic diameter of 1.18 mm, length of 200 mm with 10 internal ports with thickness 0.1 mm each) with acetone as working fluid is experimentally investigated for cooling high heat flux electronic devices. Effect of heat load (10–50 W), filling ratio (40%, 50%, and 60%) and tilt angles (45°, 60° and 90°) on thermal resistance, convective heat transfer coefficients of evaporator and condenser, vapour velocity, flooding, sonic, boiling limits and efficiency are experimentally studied. Results showed 9.31% and 22.2% reduction in evaporator wall temperature and thermal resistance at optimum filling ratio (OFR) of 50%. Enhancement in evaporator heat transfer coefficient and thermal efficiency of 30.7% and 89.8% are respectively observed at OFR. Multiports present in minichannel acts as internal fins and increases the surface area and evaporation rate. Further multiports increases surface tension of condensate at right angles to the flow direction along with the effects of gravity enhancing the rate of condensation. Thus, the obtained experimental results will be useful in cooling of miniaturized high heat flux electronic devices..

Evaporation heat transfer coefficient and pressure drop of n-pentane inside parallel multiport mini channel

This paper investigates experimentally heat transfer during evaporation of n-pentane inside a parallel multiport mini-channel. The experimental tests are conducted in a test section within five rectangular stainless steel minichannels. The local heat transfer coefficient is measured for different testing conditions to study the influence of mass flux (G = 113–187 kg/m2·s) and heat flux (200 W–320 W). For low vapor quality region [0–0.4], the domination of nucleate boiling is significant while the forced convective boiling is obtained for high vapor quality region. A comparison of the experimental results with existing correlations is carried out by calculating mean absolute deviation which led to some diverging correlations >100% while others present a good estimation around 30%. Thus, a new correlation is developed to predict local heat transfer with MAE of 22% based on the experimental results. A considerable attention is also paid to pressure drop effects by measuring experimentally pressure drop in the minichannels and develop a new correlation to evaluate frictional pressure drop.

Flow boiling in horizontal multiport tube: Development of new heat transfer model for rectangular minichannels

The flow boiling characteristics of R32 and R1234ze(E) were investigated in a horizontal multiport tube with rectangular minichannels. The local heat transfer coefficient and frictional pressure drop were measured under mass fluxes of 50–400 kg m−2 s−1 at a saturation temperature of 15 °C. The heat transfer was characterized by forced convection in the region with a low heat flux, high mass flux, and high vapor quality; the heat transfer was characterized by nucleate boiling in the region with a high heat flux and a low vapor quality. Moreover, the heat transfer was characterized by the thin liquid film formed around the elongated vapor plugs with a low mass flux and low heat flux. These heat transfer mechanisms were also confirmed based on the visualization results of the flow boiling. The heat transfer deteriorated in the plug and slug-annular flows due to the occurrence of dry patches. A new heat transfer model for multiport rectangular minichannels was developed that considered forced convection, nucleate boiling, and thin liquid film evaporation. Moreover, this new heat transfer model considered flow patterns inside the multiport minichannels, heat transfer deterioration due to dry patches, and dryout inception quality. The newly model can predict the heat transfer characteristics in multiport rectangular minichannels for a mean deviation of less than approximately 15%. The frictional pressure drop of R32 was smaller than that of R1234ze(E) under the same mass flux and vapor quality conditions and compared with previous correlations.

Fabrication of Ti3SiC2/SiCp multiport minichannel plates for high-temperature applications

An innovative method for fabricating ceramic multiport minichannel plates (MMP) has been developed. The essence of the method is the combustion synthesis of Ti3SiC2/SiCp ceramic matrix composite using sandwich assembly of titanium metal items, viz. rods and sheets, and tape-cast rubber films filled with SiC particles and TiC additive. The fabrication route consists of hot pressing of starting materials at 100 °C under 60 MPa in air into a single integrated unit followed by heat treatment at 1400 °C in a vacuum hot press furnace under small uniaxial load of 80 N. It is shown that the one-dimensional titanium metal items act as both reactants and channel-forming templates. The MMP prepared by the proposed method contains primarily of 45 vol.% Ti3SiC2 and 44 vol.% SiC, as well 11 vol.% TiSi2 minor component. The material exhibits a composite microstructure consisting of a dense Ti3SiC2-based matrix and SiC particles uniformly embedded in it. The sample contains parallel-aligned hollow cylindrical channels of 0.8 mm in diameter distributed with a center-to-center spacing of 1.3 mm. The volume fracture of the channels is estimated to be about 19%.

Flow condensation heat transfer characteristics of R134a in multiport mini-channel by jet impingement cooling

The flow condensation heat transfer of refrigerant R134a inside a multiport mini-channel having a hydraulic diameter of 0.63 mm is experimentally investigated in the present study by jet impingement cooling. Experiments were performed under the operating states of refrigerant vapor quality 0–1, heat flux 10–46 kW/m2, mass flux 115–290 kg/(m2·s), and saturation pressure 0.38–0.51 MPa. The effects of these factors on condensation heat transfer are quantitatively studied. The results indicate that the local heat transfer coefficient is seldom affected by the mass flux and vapor quality of the refrigerant but is closely related with heat flux and saturation pressure. The prediction accuracies of the existing correlations are assessed, and a new formula is proposed. This study on flow condensation heat transfer in a multiport mini-channel is meaningful for the investigation and design of a two-phase mini-channel condenser.