Evaporation Area Research Articles

Effects of nanoparticle concentration and peclet number on nanofluid droplet evaporation behavior

Effects of droplet parameters are reported using model simulations on the evaporation characteristics of droplets containing insoluble nanoparticles and related to the formation of shells of particles. The droplet parameters are initial droplet diameter (do), initial particle mass fraction (Yvo), and the Peclet number (Pe) based on the fluid evaporation rate constant (K) to particle diffusivity in the fluid (Dpl). Time-dependent phenomena of the instantaneous droplet size (d), d2 vs time (for example, following the d2-law or the deviation from it), instantaneous evaporation efficiency (i.e., effective area of evaporation due to particle inclusion on the droplet surface compared to a pure fluid droplet) are reported. Analytical expression of shell parameters at shell formation such as time to shell formation, shell size, and evaporation efficiency are derived using the initial droplet parameters and compared with the computational results. It is found that the evaporation behavior of droplets containing insoluble nanoparticles, including the deviation from d2-law, is independent of do but is strongly influenced by the product of Pe·Yvo.

Performance enhancement of a v-corrugated basin hemispherical solar distiller combined with reversed solar collector: An experimental approach

The low freshwater production of the solar distillers is one of the most crucial obstacles to their effective use in distillation applications. In this work, an attempt has been made to ameliorate the distilled yield of the hemispherical solar distiller. This was fulfilled by using a v-corrugated basin and reversed solar collector in order to augment the evaporation area and assist in reflecting more solar irradiance onto the outer surface of the v-corrugated basin. Two hemispherical solar distillers, namely; v-corrugated basin hemispherical distiller integrated with a reversed solar collector (VBHD-RSC) and traditional flat basin hemispherical distiller (TFBHD) were designed and examined at the same outdoors conditions of El-Oued (33°27′N, 7°11′E), Algeria. Moreover, a comparative energic-economic analysis of the two proposed hemispherical distillers has been conducted in terms of freshwater productivity, daily energy efficiency, and freshwater distillate cost. The results show that the daily accumulative yield of the VBHD-RSC was 7.85 kg/m2.day which was higher than that of TFBHD by 68.82%. Moreover, the daily energy efficiency was obtained to be 59.70% and 35.52% for VBHD-RSC and TFBHD, respectively. Furthermore, the economic assessment indicates that the usage of a v-corrugated basin embedded with a reversed solar collector was more cost-efficient as it reduces the cost of freshwater production by 27.12% compared to TFBHD.

Estimating Evapotranspiration over Heterogeneous Surface with Sentinel-2 and Sentinel-3 Data: A Case Study in Heihe River Basin

Evapotranspiration (ET) is an important part of surface–atmosphere interactions, connecting the transfer of matter and energy. Land surface heterogeneity is a natural attribute of the Earth’s surface and is an inevitable problem in calculating ET with coarse resolution remote sensing data, which results in significant error in the ET estimation. This study aims to explore the effect and applicability of the evaporative fraction and area fraction (EFAF) method for correcting 1 km coarse resolution ET. In this study we use the input parameter upscaling (IPUS) algorithm to estimate energy fluxes and the EFAF method to correct ET estimates. Five ground stations in the midstream and downstream regions of the Heihe River Basin (HRB) were used to validate the latent heat flux (LE) calculated by the IPUS algorithm and EFAF method. The evaluation results show that the performance of the EFAF method is superior to that of the IPUS algorithm, with the coefficient of determination (R2) increasing, the root mean square error (RMSE) decreasing, and the mean bias error (MBE) decreasing by 17 W/m2 on average. In general, the EFAF method is suitable for correcting the deviation in LE estimated based on Sentinel data caused by land surface heterogeneity and can be applied to obtain accurate estimates of ET.

Ultrablack Poly(vinyl alcohol)‐Graphite Composite Xerogel with Vertically Arranged Pores for Highly Efficient Solar Steam Generation and Desalination

Ultrablack materials have attracted wide attention due to their high light absorbance and efficient photothermal conversion used in the field of solar steam generation to alleviate the drinking water crisis. Herein, ultrablack and low‐cost poly(vinyl alcohol)‐graphite composite xerogels (PGCXs) that have vertically arranged pores and high thermal conductivities are fabricated. The PGCX‐50% shows high light absorbance (95.44%), good wettability, and a water evaporation rate of 1.24 kg m−2 h−1 under 1 sun illumination when coupled in a two dimensional (2D) evaporator. To further improve the solar steam generation performance, the PGCX‐50% is switched to a three dimensional (3D) evaporator by rotating it. Under 1 sun illumination, the 3D evaporator has a highest water evaporation rate of 3.80 kg m−2 h−1, which is 3.07 times that of the 2D evaporator, due to its larger evaporation area and higher surface area at subambient temperature. Finally, a heatsink‐like 3D evaporator is designed and a water evaporation rate of up to 9.54 kg m−2 h−1 is achieved when coupled with wind energy. The high water evaporation rates of the PGCX even in concentrated brines ensure its great potential for drinking water production and seawater desalination.

Design and Investigation of an Effective Solar Still Applicable to Remote Islands

Most remote islands are characterized by small populations, many of whom live under the poverty line, poor geographical accessibility and lack of electricity. As such, the solar still, which has a low capital cost, easy operation and less need of maintenance, is recommended to be used in remote islands possessing rich solar irradiance. Against this backdrop, the present study aimed to design and fabricate an effective solar still suitable for application in the remote islands with low freshwater sources but easy access to sea water and rich solar irradiance. Integrating a conventional passive double-slope solar still with an evacuated solar water heater, fins and wick material improves the heat transfer rate through the brine in the basin and increases effective evaporative surface area. Experiments were conducted using batch mode operation during the periods September to October 2021 for the passive solar stills and November 2021 for the active solar still. Experimental results reveal that the augmentation of fins, wicks and a solar water heater influences the overall distillate output of the solar still. The combined use of fins, wicks and a solar water heater increases the average daily productivity by 147% and the average daytime hourly productivity by 245% compared to the conventional passive solar still under similar average solar radiation levels. Using the present design, the active solar still under the solar environment of the testing location can provide 4.4 L of potable water per day. However, to achieve the minimum requirement of 7.5 L/day per person set by WHO, the present design should be modified by increasing the absorber area of the active solar still by 63% and adding eight more evacuated tubes to the solar water heater. The estimated cost per liter of potable water generated by the active (modified) solar still showed that bottled water sold in a typical remote county (Penghu) in Taiwan was 117–283% more expensive than the water generated by the still.

Impact of deforestation on moisture evaporation from soil and canopy for the territory of Ukraine based on data of numerical experiment LUMIP

The study presents results of analysis of the impact of partial deforestation on spatio-temporal distribution of the outflow part of water balance, namely evaporation from soil and canopy. The data of 6 Global climate models of theoretical experiment Land Use Model Intercomparison Project (LUMIP) was used in the research. The aim of this experiment is to reveal the influence of global deforestation with further replacement by grass cover on distribution of climate characteristics. It was done for the period 1850—1929, where the first part 1850—1899 refers to the pre-industrial period or period with minimal mostly constant anthropogenic influence; the second part is the next 30 years — 1900—1929. During the pre-industrial period 1850—1899 land cover was reduced globally with a trend of 400 thousand km2 per year and during 1900—1929 it was stable. Defining the impact of deforestation, the normalization over the first 20 years (1850—1869) was performed and there were found anomalies of climatic characteristics as difference to this basic period. Deforestation with further replacement of the forest cover by grass causes an increase in soil evaporation with the trend up to 1.6 mm/10 years in the warm season with more significant changes in April —July, as deforestation reveals more of the soil. Thus, the correlation was −0.8 ...−0.4 between forest cover and soil evaporation with maximal changes in April. It can be connected with grass being sparse in this period but later on covering more soil and preventing intensive evaporation. On the contrary, evaporation from canopy in global climate models is reduced with deforestation as the evaporation area is shrunk. This effect was revealed during all seasons in most grid points, where deforestation occurs. But the biggest change is found in spring and summer months with values up to −0.8 mm/10 years and correlation r = 0.4 ... 0.9 depending on the model and the season. Thus, we found an effect of increasing evaporation from soil while decreasing evaporation from canopy in climate modeling as the effect of partial deforestation on the territory of Ukraine. These changes can cause redistribution in water balance components of the territory and have consequences for hydrological regime, agrometeorology etc. In particular, the increase in soil evaporation due to deforestation can provoke more intensive soil aridization and degradation. The influence of deforestation on total soil moisture and regime of precipitation will be presented in the next publication.

Experimental study on boiling heat transfer in negative-pressure flowing water in a vertical annular tube

To study energy recovery from low temperature wastewater during industrial production, a water-boiling heat transfer experimental device was built. A casing evaporator with a length of 1450 mm, an inner tube diameter of 30 mm, and an annular space gap of 14.2 mm is taken as the main research object. The boiling heat transfer characteristics of water in the annular tube area of the casing evaporator were experimentally studied by adjusting the inlet temperature (60? 85?C) of hot water and the pressure in the annular tube (12.1-57.6 kPa). The results show that, as the pressure of the system decreases, the boiling phenomenon in the annular tube becomes more intense and the convective heat transfer coeffi-cient increases. The boiling flow and average surface convective heat transfer enhancement rates, ? , were 2.2 and 1.5 when an initial pressure of 1 kPa was used. When the flow rate of the working medium in the annular tube was 1.69 kg?m2/s, the convective heat transfer coefficient gradually increased with the temperature and then stabilized when the inlet temperature reached between 80?C and 85?C. These results reveal the characteristics of boiling-water heat transfer in an annular tube and aid in the design of heat pipe systems for waste-heat recovery.

Effect of transparent glass cover material on double slope solar still productivity

Solar water distillation apparatus has been developed for the Thoothukudi coastal people in Tamilnadu, India, where drinking water is rare. This analysis focused on the possibility of employing stretched transparency PVC cover instead of usual clear glass sheet for solar distillation equipment. To increase the evaporative surface area, black cotton cloths with enlarged fibres were placed on the bottoms of stills. When the angle of inclination (13°) was equivalent to that of a glass sheet-covered still, more distilled water was recovered from the clear PVC sheet covered still. The solar still's collector received less sunlight than it might have because of an accumulation of water droplets sticking to the PVC lid. A plastic sheet material with reduced water surface adhesion is the ideal choice, or an anti-water surface adhesion chemical should be sought. Until this is achievable, the preferable cover material will remain traditional glass-covered solar distillation machines.

Economic analysis of conventional single slope solar distillation plant for different climates in India

The solar distillation system offers a sustainable tool for freshwater production. However, the lower production output is one of the barriers to the non-commercialization of solar distillation systems. Although for small-scale production, solar distillation is still considered to be an economical and reliable option. To test the viability and affordability of a solar distillation system, techno-economic investigation of a single slope small-scale distillation plant of capacity 100–400 L/day has been conducted for three different climates in India viz. hot and dry, hot and humid, and composite. Annual distillate output is numerically computed for three different cities corresponding to respective climatic zones. The average and maximum evaporation area of still required to fulfill the requirement for drinking water is computed. It is seen that the climate of Chennai has a maximum annual yield of 1319.6 L/m2, whereas the composite climate of Delhi has a minimum yield of 1120.4 L/m2. The yearly distillate of Jodhpur's climate is 1164.6 L/m2. Water cost is computed in terms of water produced in liters (cost/L) and energy output from solar still (cost/kW h). It is seen that the cost/L and cost/kW h of water produced for the different climatic zone in India is in between Rs. 0.73/L to Rs. 0.87/L (0.010USD/L to 0.012USD/L) and Rs 1.13/kW h to Rs 1.33/kW h (0.016USD/L to 0.019USD/L). Payback time to recover the distillation plant's investment cost for different climates is between 99 days and 116 days. (1USD = Rs70/–).

Design, fabrication, investigation and analysis of a novel flat evaporator loop heat pipe for cooling high heat flux server chips

• A novel LHP with a flat evaporator has been proposed and tested. • SEM, porosity, and capillary rise of different sintered powder size are measured. • The heat transfer performance of the novel LHP is studied at heat loads from 50 to 750 W. • The performance comparison of the novel LHP is presented. A novel loop heat pipe (LHP) with a flat evaporator has been proposed to meet the heat dissipation requirement of high heat flux server CPU. The sintered porous copper wick was provided with a double arrayed vapor channels to increase the evaporation area. And a 1 mm thick smaller particle size copper powder embedded with two 0.5 mm thick stainless steel rings was sintered on the inner surface of the compensation chamber to enhance the strength, and increase the working fluid into the porous wick such that the liquid saturation was enhanced and the dry zone was reduced at high heat flux. Additionally, a dual layer structure condenser was presented to increase the cooling area of the condenser. In this study, the systematic experimental studies were carried out mainly focusing on the optimization of powder size, heat transfer performance of the novel LHP and performance comparison of the novel LHP. The results demonstrated that the sintered copper powder of the 106–150 μm particle size shown the best capillary performance in comparison with other powder sizes. More importantly, in the heat load range of 500–750 W, the novel LHP of filling ratio of 46.1% exhibited better operating thermal characteristics. The minimum values of the LHP thermal resistance and the total system thermal resistance at the heat load of 750 W were 0.040 °C/W and 0.090 °C/W, respectively. Compared with the conventional LHP and the simple water block, the novel flat evaporator LHP was a more promising option when the heat load was higher than 250 W.

Highly‐Efficient Solar Steam Generation with Real Time Salinity Monitoring for Seawater Desalination

AbstractSolar steam generation (SSG) has attracted increasing interest due to its huge potential in seawater desalination. However, SSG performance is not yet satisfactory due to limited photothermal efficiency and crude thermal management. In addition, real‐time salinity monitoring is still lacking. Herein, inspired by the transpiration of trees, an umbrella‐shaped 3D structure is designed for high‐performance SSG. The water evaporation rate under one sun irradiation is as high as 2.17 kg m−2 h−1, outcompeting most previous work. The high evaporation rate is primarily attributed to the excellent photothermal effect and maximized utilization of the heat via enhancing water transport and enlarging the effective evaporation area. Due to the existence of an air gap between the umbrella cover and the bulk water, an extra thermal insulator is not needed. Thus, the SSG device is more compact and stable. Moreover, a flexible photonic crystal membrane is constructed to in situ monitor the salinity by the structural color via a visualization method. This SSG device keeps high evaporation rates in seawater desalination, showing great prospects for practical applications.

Constructing a Solar Evaporator with Salt-Collecting Paper by Stacking Hydrophilic Sponges for Freshwater Production and Salt Collection.

Solar water evaporation is universally considered as an effective method to alleviate the freshwater shortage worldwide. A series of three-dimensional, salt-resistant evaporators have been brought out to improve the evaporation performance. However, little attention was paid to the collection of salt from seawater and high salinity brine. In this work, a carbon black polyvinyl alcohol (PVA) sponge was prepared to harvest light using a physical adsorption method to load carbon black on the PVA sponge. The experimental results showed that optimal light absorption (97.8%) and evaporation rate (1.60 kg m-2 h-1) were achieved when the carbon black PVA sponge was produced at a carbon black concentration of 1 g L-1. Moreover, we stacked PVA sponges beneath the carbon black PVA sponge to construct a non-photothermal evaporation area. It was seen that the evaporator with an eight-layer PVA sponge had an excellent evaporation rate as high as 2.35 kg m-2 h-1. In addition, the salt-collecting paper, all-black printed by a laser printer, was inserted between the stacked PVA sponges for salt collection, and the eight-layer PVA sponge evaporator with the salt-collecting paper at the fourth floor was tested in a 2 h desalination experiment. The outcome indicated that a square meter of this evaporator can produce about 7.03 L of freshwater and 206 g of salt per day from 10 wt % NaCl solution. As a result, the solar evaporator developed in this work is capable of collecting salt and maintaining a high evaporation rate, which is of great competence in the fields of freshwater production and salt collection.

A bio-based 3D evaporator nanocomposite for highly efficient solar desalination

Interfacial solar desalination (ISD) is one of the best approaches to mitigate drinkable water shortages. However, finding an optimum ISD structure having high evaporation rate, high efficiency, low-cost, biocompatibility, self-floatable and salt rejecter, is still a challenging area. Here, a 3D modified bio-based floatable assembly (3D-MBFA) is reported which separates the evaporation area from bulk water. A superhydrophilic wicking fabric was chosen as both porous substrate for solar absorber and water transporter to evaporation area. The wicking fabric was modified by nanocomposite of cross-linked calcium alginate having Au nanoparticles. Thereafter, the modified wicking fabric was fixed on the piece of sunflower stem. The sunflower stem with its fantastic characteristics, such as low thermal conductivity, water transportation by micro-vessels and self-floatability, can guarantee the heat localization, surface water supply and high evaporation efficiency of the 3D-MBFA for solar steam generation. The fabricated 3D-MBFA solar steam generator demonstrates a very high evaporation rate, 3.2 kg m−2h−1, and evaporation efficiency under 1 Sun (1000 W m−2) illumination. Additionally, the 3D-MBFA shows excellent salt rejection property that is necessary for continually working without salt accumulation.

Microwave-induced spray evaporation process for separation intensification of azeotropic system

The microwave-induced film evaporation process has recently been reported as a promising method for separation intensification of polar/nonpolar mixtures. However, the relatively low separation efficiency and evaporation amount caused by massive intermolecular heat transfer with limited evaporation area restrict its industrial application. To this end, an innovative microwave-induced spray evaporator was developed to overcome the current defects. Furthermore, the experiments demonstrated an excellent separation efficiency of alcohol-water azeotropic systems are achieved via microwave-induced spray evaporator (such as the relative volatility of EtOH was more doubled). Moreover, the experiments of several mixtures with different permittivity and dielectric loss were performed to elucidate the mechanism of microwave-induced relative volatility change (MIRVC). The experimental results revealed that the increase of high dielectric loss components in the vapor phase under microwave heating in comparative experiments verifies the inference that dielectric loss determines the direction of MIRVC.

Morphological variability of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) cones in the context of seed extraction

In the paper generating curves given by fourth-degree polynomials were used to model the shape of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) cones from the Polish Forest Districts of Kołaczyce (one batch) and Opole (two batches), and to calculate the surface area and volume of individual cones. However, it was not possible to construct generalized equations for the surface area and volume of Douglas fir cones due to the high variability of empirical coefficients. The surface area and volume of the cones were also calculated from their length and diameter based on formulas for a cylinder and a barrel corrected by constants k1 and k2. The mean surface area of closed Douglas fir cones determined for the first, second, and third batch using the generating function was 4,348.4 mm2, 3,857.0 mm2, and 2,844.7 mm2, and the volume was 27,212.4 mm3, 21,012.9 mm3, and 12,844.4 mm3, respectively. The corresponding values calculated from the geometric formulas for solids were 4,332.0 mm2, 3,838.0 mm2, and 2,862.9 mm2 for the surface area and 27,366.0 mm3, 20,648.9 mm3, and 13,375.3 mm3 for the volume. The evaporation area of open cones was found to be five times greater than that of closed cones, with the difference being statistically significant. The outer and inner surfaces of scales taken from the middle segment of Douglas fir cones were photographed using a Quanta 200 scanning microscope (FEIC). The characteristic elements of scale morphology were evaluated by means of MultiScan Base software package. The outer and inner surfaces of Douglas fir scales were found to differ in some important ways, similarly as it has been reported in the literature for the Scots pine, silver fir, European larch, and black alder. The outer surface of scales is formed by thick-walled cells with marked protrusions, while the inner surface reveals cells with thin, frayed walls in the region adjacent to the seeds and wings. Knowledge of the geometry of Douglas fir cones and the morphology of their scales may be helpful in optimizing seed extraction parameters for those cones. Key words: seed extraction, model, shape curve, surface area, volume, scanning electron microscope

Performance evaluation of a solar still using hybrid nanofluid glass cooling-CFD simulation and environmental analysis

The use of nanopowders in the base fluids dramatically impacts the performance of cooling and heating systems. Nanoparticles enhance thermal conductivity by altering the thermal properties of the base fluid. The purpose of this paper is to numerically evaluate the glass cooling of a double-slope solar still using a hybrid nanofluid (Al2O3-TiO2) at a concentration of 0.4%. The hybrid nanofluid (Al2O3-TiO2) glass cooling flows over the glass to decrease the cover temperature and raise the freshwater generation using a pump. Hybrid nanofluid cover cooling raises the temperature difference between evaporation and condensation areas. The use of hybrid nanofluid glass cooling increases the natural convection heat transfer inside the solar still. The convective heat transfer coefficient and constant temperature are considered as boundary conditions of the glass cover and water surfaces of the solar still, respectively. The simulation results revealed that solar desalination's freshwater yield and energy efficiency increased by 11.09% and 28.21%, respectively, when hybrid nanofluid glass cooling is used compared to solar desalination without hybrid nanofluid. The optimal value of nanoparticle concentration was 0.45%, as estimated by the CFD simulation. Also, a new model for estimating the freshwater productivity of solar desalination with hybrid nanofluid glass cooling was developed and verified. Moreover, the environmental and exergoenvironmental parameters in solar desalination with hybrid nanofluid glass cooling were enhanced by 12.45% and 3.71 times, respectively.

Experimental and Theoretical Investigations of a Modified Single-Slope Solar Still with an External Solar Water Heater

One of the key impediments to the wide utilization of solar water desalination systems is limited production. Hence, this study aims at increasing the thermal performance of a single-slope solar still by increasing the surface area of evaporation and absorption exposed to sunlight. A hollow rotating cylinder was installed inside the still structure; this modified system was then joined with an outside solar water heater for productivity improvement. The obtained results show that a 0.5 rpm rotational speed ensured that the cylinder’s surface was kept wet. A mathematical model has been formulated using the finite difference method and the Fortran 90 programming language to assess the thermal performance productivity of two solar stills (conventional solar still (CSS) and modified solar still (MSS)) modelled under different conditions. The experimental and theoretical results are well agreed, with an error of 6.14%. The obtained results show that the maximum productivity recorded in July 2019 was about 11.1 L/m2 from the MSS and 2.8 L/m2 from the CSS, with an improvement rate ranging between 286% and 300% during June, July, August, and September 2019. The production cost per liter of distilled water from the modified and conventional solar stills was 0.0302 USD/L and 0.0312 USD/L, respectively, which indicates a noticeable reduction in the cost of distillate water production.

Interfacial Solar Evaporation by a 3D Graphene Oxide Stalk for Highly Concentrated Brine Treatment.

In this work, we demonstrate a 3-dimensional graphene oxide (3D GO) stalk that operates near the capillary wicking limit to achieve an evaporation flux of 34.7 kg m-2 h-1 under 1 sun conditions (1 kW/m2). This flux represents nearly a 100 times enhancement over a conventional solar evaporation pond. Interfacial solar evaporation traditionally uses 2D evaporators to vaporize water using sunlight, but their low evaporative water flux limits their practical applicability for desalination. Some recent studies using 3D evaporators demonstrate potential for more efficient water transfer, but the flux improvement has been marginal because of a low evaporation area index (EAI), which is defined as the ratio of the total evaporative surface area to the projected ground area. By using a 3D GO stalk with an ultrahigh EAI of 70, we achieved nearly a 20-fold enhancement over a 2D GO evaporator. The 3D GO stalk also exhibited additional advantages including omnidirectional sunlight utilization, a high evaporation flux under dark conditions from more efficient utilization of ambient heating, a dramatic increase of the evaporation rate by introducing wind, and scaling resistance in evaporating brines with a salt content of up to 17.5 wt %. This performance makes the 3D GO stalk well suited for the development of a low-cost, reduced footprint technology for zero liquid discharge in brine management applications.

A novel membrane-promoted crystallization process integrating water recovery and salt production for brine management

Brine management is one of the global challenges nowadays. Herein, by taking advantage of capillary forces and low-grade heat (50 °C), we propose a novel ceramic membrane-promoted crystallization (MPC) process for brine management. The MPC process simplifies the traditional multiple energy-intensive steps and dispenses the use of expensive anticorrosive equipment via adopting three hierarchical layers (α-Al2O3 substrate, γ-Al2O3 interlayer, and SiO2 top layer). The hydrophilic mesoporous SiO2 top layer provides continuous driving force for brine solution transport from the inner shell of the membrane toward the outer surface, where heterogenous nucleation and secondary nucleation occur to form numerous long needle-like salt whiskers. The growth kinetics of salt whiskers accelerates with time as the formed salt whiskers provide extra evaporation area to intensify water evaporation. Template-directing molecules P123 significantly enhance the specific surface area, pore volume, pore size, and pore regularity of the SiO2 top layer, thereby promoting both water recovery and salt production. The optimized membrane displays high water recovery (790.3 g m−2) and salt production (194.6 g m−2) for high-salinity brine (20 wt%). Moreover, the MPC process demonstrates high performance, mechanical stability and thermal durability during the long-term test. It is expected that the MPC process would provide an innovative zero-liquid discharge approach for the efficient and low-cost brine management.

Flow Pattern Analysis and Heat Transfer Characteristics During Subcooled Flow Boiling in a Rectangular Microchannel on ZnO Microrod Surface

Abstract The combination of microstructured surface and microchannel flow boiling is expected to solve the thermal management problems of high-heat-flux devices. In this study, the experimental investigation of subcooled flow boiling in a high aspect ratio, one-sided heating rectangular microchannel was conducted with de-ionized water as the working fluid. ZnO microrods were synthesized on the titanium surface to be used as the heated surface compared with the bare titanium surface. A facile image tool is utilized to process the flow patterns photographed by a high-speed camera, which is analyzed with the heat transfer characteristics. The flow pattern of isolated bubbly flow reveals the large number of nucleation sites formed on the microrod surface but the heat transfer performance deteriorates with increasing mass flux because of the smaller bubble area and weaker nucleation. With increasing heat flux, the flow pattern changes from isolated bubbly flow to alternating bubbly/slug flow and alternating slug/annular flow. The latter flow pattern is confirmed to bring a higher heat transfer coefficient due to the larger area of thin-film evaporation. Compared with the bare surface, a higher heat transfer coefficient is achieved on the ZnO microrod surface for up to 37% due to the more nucleate sites and strengthened convective evaporation. Therefore, this surface might be suitable for heat dissipation in the watercraft or aerospace industry considering the low density, strong intensity, and corrosion resistance of titanium.