Wick Surface Research Articles

Visualization experimental study on the boiling characteristics of vapor chamber evaporator surface with different heat sources

The effective functioning of vapor chambers depends on the phase change of the working fluid at the wick surface. Given the prevalent role of vapor chambers in thermal management in the electronics industry, it is critical to study the boiling characteristics and thermal performance of vapor chambers, as well as the effect of heat source conditions. In this work, to observe phase change at the wick surface, the visualization confined chamber with wick (VCCW) is proposed and fabricated, which features a side window and a 2 mm thick wick sintered with aluminum powders. The working fluid used is acetone. The heat source is designed in three different sizes to heat the VCCW in either the middle or right position. The experimental results show that the boiling curve is divided into four stages. In the stage Ⅰ, the boiling curve is linear, and the visualization results reveal that the phase change phenomenon on the wick surface is evaporation. The Ⅱ stage is defined as ONB (Onset of Nucleate Boiling) for the vapor chamber evaporator surface. The boiling curve shows a turning, and bubbles were observed to appear and spread by visualization. In the Ⅲ and Ⅳ stages, the boiling curve remains linear. The stable nucleate boiling and intermittent local dryout is observed before and after the DNB (Departure from Nucleate Boiling). The slope of the boiling curve increases as the size of the heat source enlarges, which contributes to greater superheat and evaporation of the working fluid at smaller heat fluxes. Moreover, the position and size of the heat sources affect the ONB and DNB due to heat diffusion and capillary-driven supply of fluid.

Testing the performance of tubular solar still with flat basin, cords wick basin, and various angle of inclinations

Freshwater scarcity is a growing concern due to population expansion and industrial development. Solar stills offer a solution for generating potable water, although production volumes are limited. This research aims to address this challenge by improving the yield, thermal efficiency, and cost-effectiveness of freshwater production in tubular solar stills (TSS). We propose a novel approach that incorporates wick materials within the TSS design. This method involves creating a specific number of cuts (cracks) in a secondary basin liner positioned 2.5 cm above the original liner within the still. The upper liner is extended with wick, and wicking cords are suspended from edges and openings of this liner. These cords continuously remove saltwater, ensuring a consistently moist wick surface. The design of the wick cords optimizes water utilization and minimizes energy waste. The cords extract precisely the amount of saline water needed for evaporation, eliminating the loss or overflow of hot water. This approach maximizes wick efficiency without sacrificing freshwater production. The study investigates the performance of the TSS using 32 wick cords in conjunction with jute wick material. This modification to the conventional TSS offers a simple and cost-effective method to enhance productivity. Additionally, the glass cover of the still is tilted at an angle to facilitate the collection of distilled water droplets. ICWTSS was used as a code name for the modified TSS. After that, three distinct inclination angles (2°, 4°, and 6°) were examined, and the effectiveness of ICWTSS at each angle was contrasted with that of CSS. With a 6° angle of inclination, the ICWTSS showed a 67 % thermal efficiency and a 257 % increase in production over CSS.

Numerical simulation-based design of optimized surfaces for condensation heat transfer

Heat transfer enhancement is a well-established research topic due to its industrial relevance. The advent of 3D printing, also known as additive manufacturing, has opened up the pathway for the design of compact heat exchangers with innovative shapes, complex geometries and smaller size. In particular, additive manufacturing technologies speed up the transition from CAD models to physical prototypes and thus numerical simulation tools for two-phase heat transfer are expected in the future to play a key role for the design of heat exchangers. With regard to filmwise condensation, numerical methods capable to account for all the main forces involved (such as gravity, surface tension, vapor shear stress) must be considered for the optimization of the condensing surfaces. The present study is focused on the preliminary design of innovative shapes for enhancing the condensation heat transfer in a grooved wick heat pipe. Most of the condensation heat transfer studies available in the literature deal with vapor condensing inside tubes or over cylindrical/plain surfaces, while the condensation process occurring inside heat pipes has been less investigated. The grooved wick surfaces must be designed with the aim to promote the drainage of the condensate and minimize the thickness of the liquid film forming over the wick structures. In the present work, the behaviour of different surfaces is studied during condensation of refrigerants by performing Volume of Fluid (VOF) 2D numerical simulations with Ansys®Fluent. The numerical results allow to determine the liquid film thickness and the heat flux distribution along the grooves.

Enhanced capillary performance of nanostructures copper woven mesh wick for ultrathin heat pipes

Multiscale microstructure mesh wicks (MMWs) are widely used in the fabrication of ultrathin heat pipes (UTHPs) due to their excellent capillary properties. In this study, multiscale structures, including superhydrophilic nanosheet structures and microparticles, were prepared on copper meshes by a simple chemical etching method to enhance the capillary properties of wicks. The effects of chemical etching time on wick morphology, composition and capillary rise were investigated, and the effects of high-temperature sintering on the capillary performance of wicks were compared to provide application guidance for evaluating the heat transfer performance of UTHPs. The results indicated that the chemical etching caused the self-growth of superhydrophilic CuC2O4 nanosheet structures on the copper mesh surface compared with the untreated surface, and the maximum capillary rise velocity and the wicking coefficient could reach 8.4 mm/s and 404.457 mm2/s, respectively. After high-temperature sintering, the superhydrophilic CuC2O4 on the wick surface turns into CuO and Cu through reduction and pyrolysis reactions, and the nanosheet structure also turns into particle structure and bridges into microchannels at the dense particles. Due to the change of surface structure and chemical composition, the capillary performance of the wicks decreased, and the maximum capillary rise height could reach 80.6 mm and the maximum capillary performance parameter could reach 117.419 mm2/s, which were approximately 11.43% and 70.97% lower than that without high-temperature sintering, respectively.

Characterization of high-performance nanostructured wick for heat pipes

To investigate the best performance wick forms to support the design and fabrication of high-performance heat pipes. This paper investigates the comprehensive performance of wicks by nanosurface technology and experimental methods to predict heat pipe performance rapidly. In this paper, two kinds of nanostructured wick were prepared by the oxidation-reduction method. They are stainless steel fiber mat-type nanostructured and nickel foam-type nanostructured wicks. The effect of surface nanostructure on the wick performance was investigated by comparing the surface characteristics, capillary properties, permeability, and evaporation properties. In this study, the competitive relationship between the characteristic parameters of the wick is measured by the capillary performance factor M: K/reff, which is used as a measure of the comprehensive performance of the wick, and its maximum value is pursued industrially. The result shows that the nanostructured wick presented excellent super hydrophilic properties. A liquid-lift visualization experimental method for measuring the capillary performance factor M was proposed, and it was verified to be correct by the separation effect of the capillary pumping experiment under a vacuum environment. With the increasing oxidized degree, the densification of nanoparticles on the wick surface increased the capillary performance factor M from 8.68 μm to 13.81 μm, with a maximum enhancement of 59.1%. The effective capillary radius decreased from 47.0 μm to 40.1 μm, with a maximum reduction of 14.9%. The permeability increased from 433 μm2 to 583 μm2, with a maximum enhancement of 34.7%. The increase in porosity made the effective capillary radius dominate the competition for permeability, and the capillary performance factor decreased by 17.1%. The thermal resistance of the wick decreased with the enhancement of the capillary performance factor, which fell from 20.3 cm2·K/W to 12.6 cm2·K/W. The current study provides a reference for the future design and preparation of high-performance heat pipe wicks.

Investigating Near-Surface Hydrologic Connectivity in a Grass-Covered Inter-Row Area of a Hillslope Vineyard Using Field Monitoring and Numerical Simulations

The interplay of surface and shallow subsurface fluxes plays a critical role in controlling water movement in hillslope agroecosystems and impacting soil and plant health during prolonged dry periods, demonstrating a need for in-field monitoring. This study was conducted for two years (2021–2022) by combining field monitoring of the grass-covered inter-row area (passive wick lysimeter, surface runoff, and meteorological data), laboratory determination of soil hydraulic properties (SHPs), and numerical modeling with the aim to explore near-surface fluxes at the SUPREHILL Critical Zone Observatory (CZO) located on a hillslope vineyard. Additionally, sensitivity analysis for basic root water uptake (RWU) parameters was conducted. The model was evaluated (R2, RMSE, and NSE) with lysimeter (hillslope) and runoff (footslope) data, producing good agreement, but only after the inverse optimization of laboratory estimated hydraulic conductivity was conducted, demonstrating that adequate parameterization is required to capture the hydropedological response of erosion-affected soil systems. Results exhibit the dependence of runoff generation on hydraulic conductivity, rainfall, and soil moisture conditions. The data suggest different soil-rewetting scenarios based on temporal rainfall variability. Sensitivity analysis demonstrated that Leaf Area Index (LAI) was the most responsive parameter determining the RWU. The study offers an approach for the investigation of fluxes in the topsoil for similar sites and/or crops (and covers), presenting the methodology of self-constructed soil–water collection instruments.

Effects of surface nanotexturing on the wickability of microtextured metal surfaces

Hypothesis: Achieving spontaneous, rapid, and long-distance liquid transport is crucial for many practical applications such as phase change heat transfer and reactions at solid–liquid interfaces. Surface nanotexturing has been widely reported to improve the wickability of microtextured metal surfaces. Although surface nanotextures show high capillary pressure, the high fluid flow resistance through nanotextures prevents fluid transport. The underlying mechanisms responsible for the enhanced wickability of nanotextured surfaces are still unclear.Experiments: Herein, we prepared a variety of microtextures and nanotextures on copper surfaces by femtosecond laser micromachining and chemical oxidation, respectively. The wickability of these textured surfaces was quantitively compared by measuring wicking coefficient and capillary rise speed. We designed experiments to eliminate any possible effects of surface oxidation and metal composition on wickability. A theoretical model describing the vertical and horizontal capillary flow in V-shaped microgrooves was proposed and utilized to analyze the experimental results. The effects of time-dependent wettability on wickability were also examined.Findings: Surface nanotexturing can enhance surface wettability while altering the micrometer-scale structural characteristics. The greatly enhanced wickability of nanotextured surfaces can only be observed when the surface microtextures have a very small aspect ratio. Otherwise, for metal surfaces with fine microgrooves, the latter effect is more pronounced, and thus the surface wickability may deteriorate after preparing surface nanotextures; for surfaces with wide microgrooves, both effects are minimal, and the surface wickability enhances only marginally after surface nanotexturing. Furthermore, the wickability of microtextured surfaces will decay rapidly due to the adsorption of airborne organics, whereas adding surface nanotextures can significantly inhibit this degradation. The anti-contamination capability of surface nanotextures is considered likely to be a potential mechanism responsible for the greatly enhanced wickability of nanotextured surfaces noted in some studies.

Novel Design of Double Slope Solar Distiller with Prismatic Absorber Basin, Linen Wicks, and Dual Parallel Spraying Nozzles: Experimental Investigation and Energic–Exergic-Economic Analyses

Increasing the evaporation zone inside the solar distiller (SD) is a pivotal method for augmenting its freshwater production. Hence, in this work, a newly designed prismatic absorber basin covered by linen wicks was utilized instead of the conventional flat absorber basin to increase the surface area of the vaporization zone in a double-slope solar distiller (DSSD). Meanwhile, for further enhancement of modified DSSD performance, dual parallel spraying nozzles are incorporated underneath the glass cover as a saltwater feed supply to minimize the thickness of the saltwater film on the wick, which enhances the heating process of the wick surface and, consequently, the evaporation and condensation processes are improved. Two double slope distillers, namely a double slope solar distiller with wick prismatic basin and dual parallel spraying nozzles (DSSD-WPB&DPSN) and a traditional double slope solar distiller (TDSSD), are made and tested in the outdoor summer conditions of Tanta, Egypt (31° E and 30.5° N). A comparative energic–exergic-economic analysis of the two proposed solar stills is also conducted, in terms of the cumulative distillation yield, daily energy efficiency, daily exergy efficiency, and cost per liter of distilled yield. The present results show that the cumulative distillation yield of the DSSD-WPB&DPSN was 8.20 kg/m2·day, which is higher than that of the TDSSD by 49.64%. Furthermore, the energy and exergy efficiencies were increased by 48.51% and 118.10%, respectively, relative to TDSSD. Additionally, the life cost assessment reveals that the cost per liter of the distilled yield of the DSSD-WPB&DPSN is decreased by 11.13% compared to the TDSSD.

Analytic solutions of heat and mass transfer in flat heat pipes with porous wicks

Flat heat pipes have been used in cooling computer chips. However, previous models impose heat rate through the pipe as an input parameter, preventing optimization of heat transfer. We consider a horizontal flat heat pipe with an idealized porous wick on either one or both walls. A constant temperature difference is imposed across the two ends of the pipe, and we seek a steady-state solution. The pores in the wick are straight circular capillaries running along and across the wick, and are filled with a partially-wetting liquid. Its vapor fills the center region of the pipe and is connected to the liquid through circular pore openings on the wick surface. At the hot end, the liquid evaporates from the pore openings into vapor, which moves to the cold end where it condenses and the condensate flows in the wick to the hot end to complete a cycle. The mass evaporation rate at each pore opening on the wick surface is found from evaporation kinetics. This pore-level result is incorporated into pipe-level mass, momentum, and energy balances. The mass evaporation rate is found to depend only on the pipe temperature and is essentially independent of the vapor pressure. Consequently, the pipe behaves like a fin with evaporative cooling instead of convective cooling. Thus, the analytic fin solution holds for the pipe temperature and contains only one dimensionless number S (S2 is the ratio of evaporative to conductive heat rate through the pipe). It is observed that in heat pipes, S≫1 and thermal energy is chiefly transferred by vapor flow. Analytic solutions are subsequently found for the evaporation rate, the heat rate through the pipe, and the liquid and vapor flows along the pipe. Our idealized-wick parameters are converted to the porosity and permeability of a porous medium, so that we can compare directly with two published flat heat-pipe experiments. We analyze the effects of pipe length and wick thickness on the heat rate through the pipe, and provide guides for future design of flat heat pipes.

Overshoot temperature control on evaporator wall of loop heat pipe for space vehicle thermal control through bypass line under high thermal load

• The thermal performance of the heat pipe was able to be enhanced by the bypass line. • The thermal performance was significantly enhanced by the bypass line. • Bypass line is a passive means for start-up thermal performance control of loop heat pipe. This paper presents the experimental results of controlling an evaporator wall temperature overshoot problem under a high thermal load by applying a bypass line to the loop heat pipe (LHP). To solve the overshoot problem during the LHP start-up, any nucleation bubbles generated on the wick surface should be removed from the vapor channel as soon as possible. In special cases, a serious evaporator wall temperature overshoot problem at high thermal loads can cause start-up failure. The LHP must be operated stably within an appropriate temperature range during start-up because any sudden rise in the evaporator wall temperature may cause serious damage to the temperature control target. To control the evaporator wall temperature overshoot of the LHP with a flat evaporator and sintered metal wick, a bypass line was installed between the evaporator and the liquid reservoir. The bypass line was integrated into the LHP using a sintered metal wick and flat evaporator, of dimensions (width and length) 40 × 50 mm. The body of the LHP was made of stainless steel, and distilled water was used as the working fluid. The vapor generated in the evaporator was supplied to the vapor transport tube through inverted axial trapezoidal grooves. The inner diameters of the liquid and vapor transport tubes were 2 mm and 4 mm, respectively, and both tubes were 0.5 m long. The input thermal load ranged up to 270 W for a coolant temperature of 10°C. The LHP was aligned at a favorite tilt angle of 15°, where an evaporator wall temperature overshoot was observed. The experimental results demonstrated the ability of the bypass line to effectively control the evaporator wall temperature overshoot during start-up under high thermal loads.

Experimental investigation of nano-particle deposited wick Structure's heat transfer characteristics

Recently, nanotechnology attracts more and more attention in heat transfer system. Many studies have shown that using nanofluid as the working fluid can improve the thermal performance of the heat pipe. In this paper, the preliminary effort of applying nano-surface engineering on the heat pipe wick to fabricate the nano-structured wick structure has been carried out. Experimental investigation has been performed to determine the effect of the heat source power, mesh aperture and the wick surface structure on the total thermal resistance of the wick structure. When the heat source power increased from 20 W to 30 W, then to 50 W, the evaporation resistance decreases 25.9% and 13.7% respectively, while the conduction resistance increases 24.8% at first and then decreases 9.5%. The evaporation resistance is less with than without the wick structure, and it increases with the increase of mesh aperture. When the mesh aperture increases from 75 μm to 150 μm, then to 460 μm, the evaporation resistance increases 1.9% and 1.7% respectively. Whereas, the wick structure, as well as the mesh aperture have slight influence on the conduction resistance. The experimental results suggest that the nano structure on the surface can efficiently decrease the evaporation resistance but increase the conduction resistance at the same time. Compared to the wick structure with smooth surface, the evaporation resistance of nano-surface deposited by 0.01% TiO2 and 0.02% TiO2 has decreased 4.3% and 15.5%, respectively. This study provides a reference for the preparation of the heat pipe with greater performance in the future.

Physical mechanisms for delaying condensation freezing on grooved and sintered wicking surfaces

Heat pipes are passive heat transfer devices crucial for systems on spacecraft; however, they can freeze when exposed to extreme cold temperatures. The research on freezing mechanisms on wicked surfaces, such as those found in heat pipes, is limited. Surface characteristics, including surface topography, have been found to impact freezing. This work investigates freezing mechanisms on wicks during condensation freezing. Experiments were conducted in an environmental chamber at 22 °C and 60% relative humidity on three types of surfaces (i.e., plain copper, sintered heat pipe wicks, and grooved heat pipe wicks). The plain copper surface tended to freeze via ice bridging—consistent with other literature—before the grooved and sintered wicks at an average freezing time of 4.6 min with an average droplet diameter of 141.9 ± 58.1 μm at freezing. The grooved surface also froze via ice bridging but required, on average, almost double the length of time the plain copper surface took to freeze, 8.3 min with an average droplet diameter of 60.5 ± 27.9 μm at freezing. Bridges could not form between grooves, so initial freezing for each groove was stochastic. The sintered wick's surface could not propagate solely by ice bridging due to its topography, but also employed stochastic freezing and cascade freezing, which prompted more varied freezing times and an average of 10.9 min with an average droplet diameter of 97.4 ± 32.9 μm at freezing. The topography of the wicked surfaces influenced the location of droplet nucleation and, therefore, the ability for the droplet-to-droplet interaction during the freezing process.

Superior influence of surface wickability over surface morphology on critical heat flux enhancement during quenching in liquid nitrogen

Our group developed a surface modification technique suitable for polymeric materials, in which sacrificial sugar particles were sprayed to generate amplified surface roughening, successfully inducing prominent critical heat flux (CHF) enhancement under cryogenic conditions. In this study, we set out to further investigate the implications of our technique, by exploring the variation of the nozzle-to-sample distance and its effect on the surface profile created. It was found that as the spraying distance increased (up to 50 cm), the CHF from the generated surface increased to an optimal point (285%). By performing a thorough characterization of the surface, it was found that the roughness and wickability of these surfaces increased proportionally up to this point. Once the distance increased beyond the optimum, we observed a more complex phenomenon between the surface roughness and the wickability, which could be attributed to the topographical features of the surface generated as the distance increased. Considering these early findings, we intend to direct and motivate further studies into these phenomena that could eventually clarify the controversy regarding the attribution to either surface roughness or wickability as the main drivers of CHF enhancement.

Recent advancements in thermal performance of nano-fluids charged heat pipes used for thermal management applications: A comprehensive review

Heat pipes are highly effective compact heat exchanger systems used in wide areas of thermal devices. Previously, conventional working fluids have been used in heat pipes for effective heat transfer in various applications. In recent years, researchers have been looking at ways to improve heat transmission in heat pipes by employing nano-additives in base liquids known as nanofluids. Nanofluids have higher thermal performance and lower thermal resistance compared to conventional working fluids. This study aims to summarize the recent advancements in thermal performance of nanofluids charged heat pipes used for different thermal management applications. Also, this study highlights nanofluids' preparation, characterization, and stability enhancement methods. The findings of several studies found that the decrease in thermal resistance between (20–80%) is caused by the development of a porous coating on a wick surface. Also, experiments show that nanofluid-charged heat pipes perform best between a 50–70% filling ratio. Nanofluids increase heat pipes' heat transfer coefficient by 20–25% more than distilled water. Additionally, it discusses the mechanism of heat transfer that contribute to the change in thermal output of various heat pipes. The thermal efficiency of heat pipes is improved due to higher thermal conductivity and increased nucleation sites of nanofluids. The critical technical issues associated with nanofluids charged heat pipes and future recommendations are also highlighted in this study. This study will provide new insights to researchers from the scientific fraternity to understand the physics behind improving the thermal output of various nanofluids charged heat pipes compared to conventional fluids.

Performance assessment of a novel solar distiller with a double slope basin covered by coated wick with lanthanum cobalt oxide nanoparticles

Solar distillers are simple desalination systems used to produce freshwater from saline water by utilizing solar energy. The low water yield is the key drawback of solar distillers. In this work, a novel double slope wick type solar distiller (DSWSD) coated with lanthanum cobalt oxide (LaCoO 3 ) nanoparticles doped in black paint is experimentally investigated. The nano LaCoO 3 /black paint is uniformly speared on the jute wick surface to boost the absorption improvement of solar irradiance for effective desalination. The influence of water flow rate (namely; 0.050, 0.10, and 0.20 kg/min) on the internal mass and heat transfer of the proposed DSWSD is analyzed. The mass and heat transfer coefficients (HTCs) are computed using the experimental results and compared with those computed according to Dunkle’s correlations. Experiments have been conducted on the established DSWSD under climatic conditions of Vijayawada, Andhra Pradesh (16.4419° N, 80.6226° E), India. It is observed that there is an increase in the internal HTCs as well as distilled yield at low flow rates of saline water for the DSWSD. The daily productivity of the proposed DSWSD coated with and without 20 wt % LaCoO 3 /black paint is 5.40 and 3.85 kg/m 2 . day, respectively, at saline water flow rate of 0.05 kg/min. Moreover, the average values of evaporative and convective HTCs as well as energy efficiency are found higher by 11.20%, 17.54%, and 24.86%, respectively, than that of the solar distiller without LaCoO 3 /black paint.

Pool boiling heat transfer and bubble dynamics over V-shaped microchannels and micropyramids: Does high aspect ratio always benefit boiling?

Metallic microchannels have been widely applied in two-phase heat transfer devices to satisfy the high heat flux cooling requirements of compact devices, but the pool boiling heat transfer and bubble dynamics over metallic microchannels have been rarely reported. Herein, we investigate the pool boiling heat transfer and bubble dynamics over V-shaped open microchannels prepared on copper by ultrafast laser micromachining. The open microchannels are of various channel widths, 100 μm and 50 μm, and of depth-to-width ratios varying from 0.5 to 2. In addition to the conventional methods used for studying boiling, we utilized the captive bubble method and the capillary tube method to analyze the bubble dynamics and the surface wickability, respectively. We find that for the microchannels with a channel width of 100 μm, the critical heat flux (CHF) and the heat transfer coefficient (HTC) increase with the increase of depth-to-width ratio; but the opposite trend is observed for the microchannels with a channel width of 50 μm. We propose that the surface wickability affects the boiling heat transfer more significantly with the increase of heat flux. For narrow and deep V-shaped microchannels, there is a mismatch between the bubble removal rate and the liquid supplying rate and thus leading to the deteriorated boiling heat transfer. We also demonstrate that the wickability of pyramidal microstructures is much higher than V-shaped microchannels. The CHF and HTC of pyramidal microstructures increase by 5–40% and 35–157%, respectively, compared to the V-shaped microchannels with identical structural spacing and depth.

Superior Antidegeneration Hierarchical Nanoengineered Wicking Surfaces for Boiling Enhancement

AbstractMicro‐ and nano‐structured surfaces having high wicking capability enable excellent liquid transport efficiency and have great promise in water desalination, atmospheric water harvesting, biomedical device development, and electronics thermal management applications. However, the poorly understood degeneration of surface wickability during exposure to air represents the main hindrance to societal application of structured surfaces. Here, the authors investigate wicking degeneration on structured surfaces and elucidate the importance of environmental volatile organic compound adsorption from air. Based on their developed mechanistic understanding, the authors design a highly scalable, cost‐effective, and hierarchical structure having both superior wicking capability and antidegeneration performance. Year‐long continuous surface wickability measurements demonstrate a 4100% higher surface wickability durability of this structure when compared to widely used single‐tier surface structures. Pool boiling tests coupled with in situ and in‐liquid optical microscopy are used to characterize the effect of wicking degradation on boiling heat transfer performance. This work demonstrates the previously unidentified coexistence of several dry areas underneath individual bubbles during boiling on highly wicking structured surfaces, resulting in significant augmentation of the three‐phase contact line length. In addition, this work outlines design guidelines for the fabrication of surface wicking structures having high performance and durability.

Improving the performance of pyramid solar distiller using dangled cords of various wick materials: Novel working mechanism of wick

In this work, a new idea of using the wick material inside the solar distiller is provided. This paper introduces a new mechanism of using wick materials inside the solar stills. The main aim of the proposed mechanism is to improve the solar still productivity. This was achieved by creating specified number of cracks on a parallel upper basin liner with an offset of 3 cm from the original basin liner of the solar still. The basin saline water was kept at 2.5 cm over the original basin liner. Besides, the upper basin liner was covered by a wick material. Moreover, wick cords were dangled from the cracks and edges of the upper basin liner to withdraw the saline water and keep the wick surface wet all the time. This design prevents wasting energy and optimizes the use of wick inside the solar still because the wick cords withdraw an amount of saline water equals to the evaporated quantity without excessing or removing hot water. So, there is no loss of hot water. The tested parameters in this study were the different types of wick materials (cotton wick and jute wick) and different numbers of cracks/cords (9, 16, 25, and 35 cords). Experimental results obtained that the thermal performance of the cords wick solar still was superior than that of the conventional solar still. In addition, using the jute wick provided constantly better performance of cords wick solar still than the cotton wick material. Moreover, the best performance of cords wick solar still was obtained at 25 cords, where the increase in productivity of cords wick solar still over the conventional solar still was 122 and 118% when using jute and cotton wick, respectively. Also, the daily thermal efficiency of cords wick solar still was 53% (at 25 cords) compared to 34.5% for the conventional solar still.

Three-dimensional lattice Boltzmann investigation on pore scale liquid–vapor distribution patterns and heat transfer performance of a loop heat pipe heterogeneous porous wick evaporator

The pore scale numerical simulations on evaporation of a three-dimensional heterogeneous porous wick capillary evaporator used in a loop heat pipe (LHP) are realized through using a lattice Boltzmann method with liquid–vapor phase change. The dynamic liquid–vapor interface characteristics are obtained. The steady-state wick state and heat transfer performance as well as the influences of wick porosity and surface wettability are discussed. It is found that as heat flux increases, the wick state changes from the fully saturated state at low heat fluxes, to the partial dryout state at medium heat fluxes, and finally to the complete dryout state at high heat fluxes. The effective heat transfer coefficient of evaporator firstly grows slowly for the saturated wick, then increases rapidly and reaches a maximum value at partial dryout wick state, but afterwards drops sharply when the wick starts to be complete dryout. With the decreasing of wick porosity and contact angle, the heat flux to achieve the maximum effective heat transfer coefficient is increased and the complete dryout state is postponed. In the present range of parameters, the maximum effective heat transfer coefficient is improved by reducing wick porosity, while it is barely affected by contact angle.

Experimental study of solar still having variable slope tilted wick in the basin to enhance its daily yield

In this study, conventional solar still was modified by adding variable slope tilted wick in the basin so that day and night productivity of still can be enhanced. The tilted wick was constructed in such a way so that tilt angle can vary according to the incident angle of solar radiation i.e. from 0° to 45°. The experiments were conducted under similar weather conditions for several days. The depth of basin water of still was taken 3 cm for all set of experiments. Initially, the experiments were conducted on 30° tilted wick with different flow rate (0.10 g/m2/s, 0.20 g/m2/s, 0.30 g/m2/s) on the wick inside the basin of modified solar still. The range of flow rate was taken based on trial experiments so that wick don’t get dry throughout the day. The overall distillate of modified still with 30° tilted wick at 0.10 g/m2/s, 0.20 g/m2/s and 0.30 g/m2/s flow rate was found to be 3.51 kg/m2, 3.60 kg/m2 and 3.41 kg/m2 respectively. Further, the experiments with tilted wick were conducted at 0.20 g/m2/s flow rate and 3 cm water depth in the basin by varying angle of inclination of tilted wick at 0°, 15°, 30° and 45°. It have observed that the overall distillate at 0°, 15°, 30° and 45° angle of tilt of wick was found to be 3.1 kg/m2, 3.51 kg/m2, 3.60 kg/m2 and 3.41 kg/m2 respectively. The maximum distillate was observed at 30° which is almost equivalent to the latitude of the location and sunrays falls directly on the wick surface. It has been found that day and night distillate of modified still with 30° remains 37.17 % higher than that of conventional still. The maximum cumulative efficiency was found to be 43.16% for the modified still with tilted wick at 30°.