Increase In Heat Transfer Coefficient Research Articles

Numerical Investigation of Heat Transfer Enhancement of Al2O3 Nanofluid in Microchannel Heat Sink

This study focusses on using computational fluid dynamics (CFD) to study the enhancement of heat transfer from the use of AL2O3 nanofluid in a microchannel heat sink (MCHS) to develop a more efficient cooling device for high-power integrated circuits. The objective is to investigate the heat transfer performance, parameters, and enhancement rate using Ansys Fluent software, and to compare the results with experiments to show the effectiveness of this method. This study will also focus on the relationship between the friction fraction and nanoparticles volume fraction to improve the heat transfer enhancement in the MCHS. The temperature, pressure, heat transfer coefficient, Nusselt number, and friction coefficient are analysed in this study. The results showed that an increase in the volume fraction of the nanofluid leads to an increase in the average heat transfer coefficient. The results showed that for 4% nanofluid volume concentration, the Nusselt Number has improved by 10% compared to pure water. However, an increase in volume concentration also resulted in an increase in pressure drop.

Numerical Investigation of Electro-Thermal Field Distribution Law of Busbar under Different Operating Conditions

The electro-thermal state of a busbar system of electrolysis cells for aluminum production represents the main factor affecting hydromagnetic stability and current distribution. Based on the busbar system of a 500 kA aluminum electrolytic cell, an overall busbar electro-thermal field coupling calculation model was established based on ANSYS. The characteristics of busbar temperature, current density, and voltage drop distribution were analyzed. In addition, the electro-thermal distribution of the busbar system was simulated under different current intensities, ambient temperatures, and heat transfer coefficients. The results show that the temperature distribution of the riser busbar and the cathode busbar is higher in the middle location and tends to decrease along the two sides. Differences in heat conduction and heat dissipation environment are the main factors affecting the distribution of the busbar system’s electro-thermal field, while the Joule heat of the current is not the major factor. Increasing the current intensity will increase the average temperature and average voltage drop of the busbar. With an increase in the ambient temperature, the average busbar temperature increases significantly, and the voltage drop of the busbar also increases. With an increase in heat transfer coefficient, the average temperature and voltage drop of the busbar decreases.

Experimental study on the ash deposition and heat transfer characteristics of a heat pipe air preheater

In this paper, a scaled-down air preheater for a heat pipe is prepared and a visualization experiment system for ash deposition is established. The local and global characteristics of ash deposition and the heat transfer performance of the air preheater are investigated, and the effects of parameters including the gas velocity and the ash concentration are discussed. Experimental results show that a loose ash deposition is formed on the fin of the heat pipe with test time. The ash deposition mass has a maximum at Row #2 and a secondary peak at Row #6 due to the enhanced flow disturbance. With increasing gas velocity, the mass of ash deposition on the windward side gradually decreases, but there is a mass peak on the leeward side. The effect of gas velocity on the mass of ash deposition in the heat pipe fins is severe on the windward side. When the gas velocity reaches or exceeds 10 m/s, the ash deposition mass on the fin is mainly concentrated on the leeward side (>80.1%). Furthermore, as the gas velocity increases or the ash concentration decreases, the total ash deposition mass in the preheater decreases, and the overall heat transfer coefficient increases. The descending range of the heat transfer coefficient over the test time decreases from 10.0% to 4.3% as the gas velocity increases from 6 m/s to 12 m/s and increases from 3.2% to 7.8% as the ash concentration increases from 23 g/m3 to 38 g/m3.

Experimental and numerical analysis of convective heat transfer and entropy generation of graphene/water nanofluid in AEAOT heat exchanger

BackgroundEffective utilization of nanofluid's potential and optimal heat exchanger design is paramount in addition to heat transfer enhancement. A novel alternate elliptical tube is fabricated, and graphene nanofluids are chosen to enhance the convective heat transfer characteristics. MethodsThe experimental setup is validated with circular pipe results before conducting graphene nanofluid experiments. The finite volume method was adopted to conduct simulation results, and its validation was done with the experimental results. The results of numerical simulations are compared with experiments, and the obtained mean percentage error (MPE) is 1.17%, 8.71%, 8.05% and 8.85% for water, G0.05%, G0.1% and G0.2%, respectively. Experiments are conducted at different mass flow rates and inlet temperatures of nanofluid. Significant findingsThe oval tube in an alternate direction improves the secondary flow region with a high swirl, leading to a smaller thermal boundary layer thickness. Nusselt number enhances as an average of 10.3%, 29.2% and 39.1% for graphene nanofluids prepared using weight concentrations 0.05%, 0.1% and 0.2%, respectively, at 80 °C. The effect of inlet temperature reveals heat transfer coefficient and Nusselt number increase and 1.57, 1.88, 2.16 times than water is observed for G0.05%, G0.1% and G0.2%, respectively. Pertinent to entropy generation, Bejan number (Be) decrease with graphene nanoparticle concentration; as inlet temperature increases, corresponding fluid friction irreversibilities are observed as 18.4%, 24.6% and 36.4% for G0.05%, G0.1% and G0.2% nanofluids, respectively. The present work caters for the importance of AEAOT design which prompts heat transfer enhancement; indeed, optimization of transition length and aspect ratio are essential to overcome the pressure loss cost.

Influence of cell size and its gradient on thermo-hydraulic characteristics of triply periodic minimal surface heat exchangers

The thermal performance of the triply periodic minimal surface (TPMS) structured heat exchangers (HEs) is highly related to their cell morphology. Unfortunately, current research on the TPMS structured heat exchangers are usually limited to performance comparison between different types of TPMS structures and the objects they researched mainly focused on a single unit or array units with a fixed morphology. In this work, we conduct the first experimental study on the effect of TPMS cell size and its gradient on thermo-hydraulic characteristics of additive manufactured (AMed) pure copper heat exchangers. Geometry measurement shows that the fabricated walls are about 26% thicker than the designed value. The simulation results show that the eccentric flow pattern goes through the entire HE velocity field and presents a rotation tendency. The temperature distribution in the main body presents a certain trend. The smaller the cell size, the more uniform the temperature distribution. The experimental results demonstrate that the effectiveness of cell size = 4 outperforms that of others. As the flow rate increases, the overall heat transfer coefficient and pressure drop increase, while the total thermal resistance decreases. The smaller the cell size, the higher the overall heat transfer coefficient and pressure drop, and the lower the total thermal resistance. The cell size = 6 has the advantage in PEC due to the lowest pressure drop. The cell size = 4 has a greater volume-based power density but also consumes a larger pressure drop per unit length. This study is expected to provide useful design guidelines for the future development of AMed heat exchangers with TPMS structures.

Numerical study on the heat transfer characteristics of a microchannel heat exchanger with liquid lead–bismuth eutectic and supercritical CO2 as working fluids

The Lead-cooled Fast Reactor (LFR) is a promising option for fourth-generation nuclear energy systems, with the supercritical carbon dioxide (sCO2) Brayton cycle being the preferred power cycle for future nuclear energy systems. Lead-bismuth eutectic (LBE) is a more suitable reactor coolant than lead due to its lower melting point. High-efficiency microchannel heat exchanger (MCHE) may be an ideal choice for the intermediate heat exchanger (IHX) in liquid lead–bismuth fast reactors. To prevent the channels of MCHE from being blocked by liquid LBE, a new structure of MCHE is proposed, in which the liquid LBE flow channel has a large equivalent diameter and corresponds to two sCO2 microchannels. In this study, the heat transfer characteristics of conventional and new structures of MCHE were investigated using numerical simulation. The results indicate that the temperature change at the inlet of the liquid LBE channel enhances the heat transfer of both liquid LBE and sCO2. Under constant temperature and pressure, the velocity of sCO2 has a significant effect on the convective heat transfer of sCO2, but has little effect on liquid LBE. Based on the reliability of equipment operation, this study recommends the use of the heat exchanger form in case 5. Compared with case 3, altering the velocity of liquid LBE results in a 7.1–8.3% increase in the convective heat transfer coefficient of liquid LBE, and a ∼38% increase in the convective heat transfer coefficient of sCO2. Similarly, changing the velocity of sCO2 leads to a 6.1–7.5% increase in the convective heat transfer coefficient of liquid LBE, and a 32.8–38.0% increase in the convective heat transfer coefficient of sCO2. For sCO2 heat transfer calculation, Yoon's heat transfer correlation is recommended, while Kirillov's heat transfer correlation is suggested for liquid LBE heat transfer calculation. The deviation between numerical calculation results and correlations is less than 18.1% and 12.7%, respectively.

Hydrocarbon Fuel Flow and Heat Transfer Investigation in Rotating Channels

Ram air turbines are used in the power generation systems of hypersonic vehicles, which can address the problem of the high power consumption of weapon systems. However, high incoming air temperatures can cause the turbine blades of power generation to ablate. At this point, the incoming air can no longer be used as a cooling source to cool the turbine blades. To prevent the ablation of the turbine blades of the hypersonic vehicle power generation, hydrocarbon fuel carried by the hypersonic vehicle itself is used to cool the turbine blades. Hence, hydrocarbon fuels under rotating conditions are investigated. The results show that the rotation leads to a strong pressure gradient that causes the density and dynamic viscosity of hydrocarbon fuel to increase dramatically. Compared to the static condition, the density and dynamic viscosity of the hydrocarbon fuel increase by a maximum of 65.1% and 405%, respectively, under the rotating condition. This leads to an obvious reduction in velocity. The comprehensive influence of the physical properties of the fuel, centrifugal force, and Coriolis force causes the convective heat transfer coefficient and Nusselt number of the channel to first increase and then decrease with the increase in the rotational speed. Compared to the static condition, the convective heat transfer coefficient and Nusselt number increase by a maximum of 69.7% and 45.6%, respectively, under the rotating condition. The critical rotational speed of the Nusselt number from rise to fall is 20,000 rpm for different inlet temperature conditions.

Experimental performance evaluation of a solar parabolic dish collector using spiral flow path receiver

The solar receiver design plays a crucial role in the performance and efficiency of a parabolic dish solar collector. This experimental study examines a finned spiral flow path receiver in a 16 m2 parabolic dish collector to enhance heat transfer from the receiver surface to the heat transfer fluid. The solar receiver is evaluated outdoors at water flow rates of 0.04 kg/s, 0.05 kg/s, 0.06 kg/s, and 0.12 kg/s. At water flow rates of 0.04 kg/s, 0.05 kg/s, and 0.06 kg/s, the receiver's average energy efficiency was 31.27 %, 44.34 %, and 50.69 %, respectively. At water flow rates of 0.12 kg/s, the peak energy and exergy efficiency are around 65.81 % and 6.85 %, respectively. The proposed solar receiver shows an increased heat transfer coefficient from the receiver surface to the fluid with more fluid residence time due to the spiral flow path and fins. The economic evaluation demonstrates that the solar receiver with a flow rate of 0.12 kg/s produces the most significant economic outcomes compared to other selected water flow rates. The proposed solar receiver's estimated levelized cost of energy, net present value, benefit-to-cost ratio, and payback period values are 0.18 ($/kWh), 925.61 $, 8.40 and 1.62 years. Thus, the finned spiral flow path receiver with a flow rate of 0.12 kg/s produces optimal performance among the selected water flow rates. The significant results benefit the solar community in designing an effective finned solar receiver for concentrated solar collectors.

Steam condensation on a circular tube in the presence of non-condensables (air) in passive containment cooling system

Steam inside the containment should be condensed to reduce the system pressure after severe accidents such as loss of coolant accident (LOCA) and main steam line break (MSLB). Due to the absence of an active coolant system, the passive containment cooling system (PCCS) can be used to improve safety by condensing the steam on a test section (coolant) tube surface. However, the steam condensation is degraded by the presence of non-condensable gases like air. The condensation heat transfer coefficient is dependent on operating parameters such as system pressure, air-mass fraction, and wall subcooling and geometric parameters such as tube diameter, tube length, and angle of orientation.In the present study, experiments are conducted on a vertical tube to estimate the condensation heat transfer coefficient in the presence of air. The system pressure ranges from 2 - 5.5 bar, air-mass fraction of 0.3 - 0.8 and wall subcooling of 27 - 80°C. The influence of test section tube diameter (48.2 mm, 32 mm, 22 mm, and 16 mm) and inclination angles (90° and 68° from the horizontal) are investigated. Based on the experimental data, a correlation for condensation heat transfer coefficient in terms of system pressure, air-mass fraction, wall subcooling, tube diameter and angle of inclination is proposed. The condensation heat transfer coefficient increases with the increase in the system pressure and decreases with the increase in the air mass fraction, wall subcooling and condenser tube diameter. With the decrease in the diameter of the vertical condenser tube from 48.2 mm to 16 mm, an increase in the condensation heat transfer coefficient of 66% is observed. A non-dimensional correlation for condensate Nusselt number as a function of Grashof number, air-mass fraction and Jakob number is also proposed. This correlation predicts 80% and 90% experimental data within 20% and 30% uncertainty range, respectively.

A novel convective heat transfer enhancement method based on precise control of Gyroid-type TPMS lattice structure

Innovative single-phase flow heat transfer enhancement technologies can improve heat dissipation efficiency and reduce the weight and volume of heat dissipation equipment. Triply Periodic Minimal Surfaces (TPMS) hold promise as a outstanding single-phase heat transfer enhancement structure. To further improve the convective heat transfer performance of TPMS, this study independently presents a novel lattice structure control method specifically designed for Gyroid-type TPMS, along with the corresponding mathematical equation. By adjusting the parameter “α” in the equation, the Gyroid lattice geometry can be controlled. This study named “α” as the “Lattice deformation control parameter of Gyroid”. Numerical simulations indicate that increasing α from 0 to 0.25 within the Reynolds number range of 282–2579 can lead to a 19.9–28.9% increase in the average convective heat transfer coefficient (h¯) of the Gyroid, a 0.3%-4.5% increase in the Nusselt number (Nu), and a 13.0%-20.3% decrease in the average friction factor (f¯). The research results suggest that optimizing α is a promising new technology for enhancing convective heat transfer of Gyroid-type TPMS, as it not only improves its heat transfer performance but also reduces its flow resistance. The main reason for the convective heat transfer enhancement of Gyroid-type TPMS with increasing α is the increase in the heat transfer area, while the reduction of flow resistance is mainly due to the formation of the “flow-guiding structure” inside the Gyroid.

Experimental study on wet gas condensation heat transfer and flow resistance in horizontal intensified tube

The heat transfer and flow resistance characteristics of in-tube vapor condensation with high content non-condensable gas is significant for designing waste heat recovery devices of gas-fired boilers. In this paper, the forced convection condensation of wet gas in the horizontal tube is experimentally investigated with a non-condensable gas mass fraction of 83–95%. The condensation heat transfer coefficient, thermal resistance and pressure drop are compared between bare tube and two intensified tubes, i.e., the corrugated and spiral tube, under various Reynolds number, wall subcooling degree and inlet humidity. The results show that the in-tube condensation heat transfer coefficient increases with increasing Reynolds number and inlet humidity, but decreases with increasing wall subcooling degree. Compared with the bare tube, the heat transfer coefficient and pressure drop increase up to 47.13% and 16.00% respectively for the spiral tube, and 116.04% and 88.48% respectively for the corrugated tube. When combing the heat transfer and flow resistance factors, the maximum comprehensive performance coefficients are 1.71 and 1.44 for corrugated tube and spiral tube respectively. The superiority of corrugated tube in the wet gas condensation is benefit from effective breaking the non-condensable gas film and promoting the vapor diffusion on the interface.

Performance evaluation of a solar air heater with staggered/longitudinal finned absorber plate integrated with aluminium sponge porous medium

Solar air heaters are used to heat air for drying and space heating applications, however, the low heat transfer between air and absorber plate accounts for its low efficiency. In this paper, an experimental study of a staggered/longitudinal finned plate solar air heater (SLFPSAH) with a built-in aluminium sponge porous media as a sensible heat storage material is presented. The fins with the direction of airflow are arranged in a staggered manner by covering a length of 1.25 m, while the remaining 0.75 m is arranged with longitudinal fins. The parameters influencing the performance of the SLFPSAH are investigated with and without using a porous medium. These parameters include solar irradiance, the temperature difference of air through the heater, air temperature ratio, convective heat transfer coefficient, useful heat gain, daily energy efficiency, and exergy efficiency. Experiments are conducted under different air mass flow rates; namely, 0.0078, 0.01, 0.02, and 0.049 kg/s. The results revealed that the implementation of an aluminium sponge porous media over the absorber plate significantly increases the energetic and exergetic performances of the SLFPSAH. It is found that the average air temperature ratio, daily exergetic efficiency, and daily exergy efficiency of the SLFPSAH integrated aluminium sponge porous medium are about 11.52%, 3.97%, and 45.61% greater than that without the aluminium sponge porous medium, at airflow rate of 0.02, 0.049 kg/s, respectively. Moreover, the maximal increase in the convective heat transfer coefficient of the SLFPSAH integrated with aluminium sponge porous medium is more than 1.62 times that obtained with the SLFPSAH without porous media, at the same conditions. Thus, the SLFPSAH with an integrated aluminium sponge porous medium is an effective way to enhance the exergetic and energetic performances of solar air collectors for solar drying applications.

Combined effect of solar intensity and air mass flow rate on inline spherical dimple based solar air heater during summer season

Experimental investigation was done in this study to compare the effectiveness of flat and inline spherical dimple engraved absorber plates solar air heater (SAH). During the summer, a SAH with a single glass cover, one pass, and two different types of absorber plates was evaluated on alternating days by taking readings from 9.30 a.m to 2.00p.m at an interval of 30 min. In order to conduct the investigation, the air mass flow rate (Ma) was raised from 0.0098 kg/s to 0.0520 kg/s (corresponding Re: 1861–10218) while solar intensities varied throughout the days. By increasing the Ma, various parameters were measured and different thermal characteristics were examined, such as the convective heat transfer coefficient, the blower’s power consumption, extracted power, effective power, efficiency, the heat gain factor, the heat loss factor, the SAH-efficiency factor, the averaged Nusselt number (Nu), and the averaged friction factor (f). The investigation reveals that with an increase in Ma, both flat and dimpled roughened SAH exhibit an increase in convective heat transfer coefficient, extracted power, instantaneous efficiency, heat gain factor, heat loss factor, and SAH-efficiency factor. However, the enhancement rate of inline dimple plate-solar air heater (IDP-SAH) due to engraved dimples is always higher than the flat plate-solar air heater (FP-SAH). Up to a particular Ma, both types of SAH have higher effective efficiencies. Thereafter effective efficiency decreases due to a significant increase in required pumping power. Comparing IDP-SAH to FP-SAH, the averaged Nu and the averaged f of IDP-SAH is 83.42% and 176.51% greater, respectively. In addition, the effective efficiency of IDP-SAH is 31.24% higher than the FP-SAH. The friction factor (f) starts to decline as the Ma increases. Even though the IDP-SAH and FP-SAH performance analyses were conducted on different days during the summer, IDP-SAH outperformed FP-SAH. The indentation of dimple on absorber plate helps in increasing surface area as well as helps in changing flow structure which is responsible for augmentation of heat transfer rate.

Cooling enhancement for light-emitting diode using plasma-activated water

We exploit the two-phase heat transfer enhancement using plasma-activated water for application in LED cooling. Within the steady-state LED temperature 80 °C ≤TLED≤ 110 °C, up to 73% increase in heat transfer coefficient can be achieved by replacing deionized water with plasma-activated water; concomitantly, we observe up to 14% increase in illuminance. This enhancement can be attributed to the presence of reactive oxygen and nitrogen species in the plasma-activated water that reduces surface tension, and, quite unexpectedly, minimizes the oxidation of the copper (heat source) surface. Specifically, the lower surface tension of plasma-activated water can lead to smaller vapor bubbles as well as reduction in their residence times on the heated surface. On the other hand, by increasing the electrical conductivity of plasma-activated water, i.e., higher concentrations of reactive oxygen and nitrogen species, we observe significant reductions in surface oxidation on the copper (heat source) surface. Peculiarly, unlike the copper surface oxidized by deionized water, for the plasma-activated water, we observe isolated oxidized islands that consist of nanosphere structures; these islands are hydrophobic and can lead to significantly shorter residence times of vapor bubbles. Since plasma-activated water can be produced easily via the corona discharge plasma, these promising results highlight its potential to be used in two-phase cooling systems.

Experimental Investigation of Heat Transfer Enhancement in a Double Pipe Heat Exchanger Using Compound Technique of Transverse Vibration and Inclination Angle

Numerous tests are recently conducted to assess vibration's role in accelerating the heat transfer rate in various heat exchangers. In this work, the enhancement of heat transfer by the effect of transfer vibration and inclination angles on the surface of a double pipe heat exchanger experimentally has been investigated. A data acquisition system is applied to record the data of temperatures, flow rates, and frequencies over the tests. A compound technique was adopted, including the application of a set of inclination angles of (0°, 10°, 20°, and 30°) under the effect of frequency of vibration ranging from sub-resonance to over-resonance frequencies. The results showed that the overall heat transfer coefficient enhances by applying the compound technique at all the working fluid's temperatures and flow rate ranges. The maximum increase in overall heat transfer coefficient occurs at an angle of 30° and the resonance frequency. Moreover, the effectiveness of the double pipe heat exchanger gradually expanded when temperature, inclination angles, and vibration amplitude rosed. But the effectiveness value declined as the hot working flow rate increased considerably. Finally, the enhancement factor demonstrated that the combined strategy (vibration frequencies and inclination angles) had been the most effective technique in improving and enhancing heat transfer and was superior to the other ways. Additionally, the extremes improvement in overall heat transfer coefficient, effectiveness, and enhancement factor are 183.4, 191, and 164.4 %. The improvement was situated at the resonance frequency with a 30° inclination angle.

A hyperbaric aerodynamic levitator for containerless materials research.

A hyperbaric aerodynamic levitator has been developed for containerless materials research at specimen temperatures exceeding 2000 °C and pressures up to 10.3 MPa (1500 psi). This report describes the prototype instrument design and observations of the influence of specimen size, density, pressure, and flow rate on levitation behavior. The effect of pressure on heat transfer was also assessed by studying the heating and cooling behavior of levitated Al2O3 liquids. A threefold increase in the convective heat transfer coefficient was estimated as pressure increased to 10.3 MPa. The results demonstrate that hyperbaric aerodynamic levitation is a promising technique for containerless materials research at high gas pressures.

Experimental Investigation of Tube-in-Tube Nanocomposite Coated Heat Exchanger

In this paper, heat transfer performance is investigated for plain and nanoparticle coated tube-in-tube heat exchangers. Four types of tubes, i.e. bare copper tube, bare aluminium tube, Cu-Al2O3 nanoparticle coated tube and anodized aluminium tubes are used for performing the experimental investigation. The coating thickness of Cu-Al2O3 nanocomposite surface and anodized aluminium tube varies from 10, 25 and 30 micrometres to 15, 20 and 30 micrometres respectively. The surface is found to be hydrophilic in nature as the contact angle changes from 79.82deg to 55.47deg. The prepared surfaces are characterized by FESEM, EDS and FTIR. By adjusting the hot and cold fluids relative mass flow rates, one may calculate not only the overall heat transfer coefficient but also the efficiency of the tube-in-tube heat exchanger. The Cu-Al2O3 nanocomposite coated surface has the highest overall heat transfer coefficient and efficiency, followed by an anodized aluminium surface, bare copper surface and bare aluminium surface. The aluminium anodic oxide (AAO) surface also exhibits an increased heat transfer coefficient, but to a lesser extent than the nanocomposite coating.

Numerical investigations on a triple fluid heat exchanger with helical and sinusoidal coils

A modification is made in the existing concentric heat exchanger design to enhance its heat duty. A standard concentric tube heat exchanger is modified by considering two inner tubes with a combination of helical and sinusoidal coils. Numerical studies are performed in this triple fluid heat exchanger to assess its thermal performance by taking into account mass flow rate, fluid temperatures, heat transfer, which are governed by fundamental heat transfer equations. Computational fluid dynamics simulation methodology together with local and element-by-element method is applied with a MatLab computer code. Hot water and milk fluids are used as working fluids in helical and sinusoidal coils, respectively. Cooling water is used as shell side fluid. The attainment of high heat-load-per-unit-area and high surface-area-to-volume ratio is used as optimizing parameter in the simulations. The helical coil provides an increase in heat transfer rate and overall heat transfer coefficient increases by a percentage 13% for varying hot fluid flow rates, when it is compared with the sinusoidal coil. The pressure drop for the helical coil increases, exponentially compared to the sinusoidal coil, thereby it shows a higher pumping power for the helical coil.

Computational fluid dynamics study of hydrogen production by sorption enhanced steam ethanol reforming process in fluidized bed

As a renewable resource, hydrogen plays a pivotal role in the energy transition of the current world. A promising route for hydrogen production is the sorption enhanced steam ethanol reforming (SE-SER), which is characterized by the complex multi-scale characteristics. This paper aims to explore the hydrodynamic (e.g., gas and solid flux, solid dispersion and velocity) and thermodynamic (e.g., particle temperature and heat transfer coefficient) characteristics on the micro-level together with the effect of operating parameters on the SE-SER performance. Accordingly, the reactive multiphase particle-in-cell (MP-PIC) model has been developed under the Lagrangian manner for studying the SE-SER process in the bubbling fluidized bed. In this model, it is assumed that uniform temperature appears inside the particle, and particles with similar properties are packed into a parcel to reduce computational cost. This model has been well validated with experimental data. The results indicate that along the bed height, the solid temperature decreases while the heat transfer coefficient increases. H2 and CO2 have similar distribution in the bed, mainly accumulating in the upper part of the reactor. Enlarging the ratio of H2O to C2H6O in the gas mixture promotes the yields of H2 and CO2. The relationships between key particle variables are explored. It is found that increasing the slip velocity enlarges the particle heat transfer coefficient, and large particle Reynolds number mainly appears with small solid volume fraction. The explored results provide valuable insights into deeply understanding complex multiphase flow and optimizing actual operation of the SE-SER field.

Enhanced internal condensation of R1233zd(E) on micro- and nanostructured copper and aluminum surfaces

In-tube condensation of refrigerants is an important process which affects thermal efficiency in many applications, ranging from refrigeration and air conditioning to electronics thermal management. In-tube heat transfer and pressure drop are important to heat exchanger sizing and design. In this work, micro- and nanostructured surfaces are applied to the internal wetted areas of copper and aluminum mini-channels to enhance the condensation heat transfer coefficient of hydrofluorocarbon R1233zd(E) refrigerant. To achieve scalable nanomanufacturing, surfaces were uniformly structured by relying on hydrochloric acid etching of aluminum and chemical oxidation of copper. The etched aluminum surfaces exhibited a 150% increase in heat transfer coefficient compared to smooth aluminum channels at specific qualities, with a 66% heat transfer coefficient improvement for complete phase change from saturated vapor to saturated liquid. Copper oxide structures showed no discernable difference in thermal-hydraulic performance when compared to smooth copper channels. Critical dimensionless parameters governing the heat transfer enhancement were identified by varying the tube internal diameter (2.3 mm to 4.7 mm), refrigerant mass flux (50 to 300 kg/(m2·s)), and refrigerant quality (0 to 1). The dimensionless parameters include the Bond number normalized to the condensate film thickness, and the Weber number modified by the vapor friction factor. The relatively small increase in pressure drop (< 10%) associated with these surface enhancements further supports the promise of this method. The scalable and cost-effective techniques used to create these aluminum microstructures may reduce manufacturing cost when compared with current enhancement approaches such as extrusion, drawing, and welding.