Ceramic Wick Research Articles

Experimental study of a bilayer ceramic wick for the evaporator of a two-phase heat transfer device

In order to enhance the thermal performance of two-phase fluid loop devices, the purpose of this study is to investigate the benefit of using a bilayer wick in a capillary evaporator.In a homogenous wick, the porous structure characteristics present an intrinsic competition between increasing the capillary forces and reducing the pressure drop.Our investigation focuses on studying heat and mass transfer in uniform and bilayer ceramic wicks with the same porosity. The findings highlight the interest of a bilayer ceramic wick with a pore diameter gradient. This configuration exhibits heightened capillary pumping without compromising liquid pressure drop, leading to improved thermal performance in the evaporator.Our results demonstrate that opting for a bilayer ceramic with a pore diameter gradient can save up to 25 °C at the casing temperature and reach up to 1430 W/m²K−1 as heat transfer coefficient for a 70 W heat load value.

An in vitro toxicological assessment of two electronic cigarettes: E-liquid to aerosolisation

Interest in the toxicological assessment of iterations of e-cigarette devices, e-liquid formulations and flavour use is increasing. Here, we describe a multiple test matrix and invitro approach to assess the biological impact of differing e-cigarette activation mechanism (button vs. puff-activated) and heating technology (cotton vs. ceramic wick). The e-liquids selected for each device contained the same nicotine concentration and flavourings. We tested both e-liquid and aqueous extract of e-liquid aerosol using a high throughput cytotoxicity and genotoxicity screen. We also conducted whole aerosol assessment both in a reconstituted human airway lung tissue (MucilAir) with associated endpoint assessment (cytotoxicity, TEER, cilia beat frequency and active area) and an Ames whole aerosol assay with up to 900 consecutive undiluted puffs. Following this testing it is shown that the biological impact of these devices is similar, taking into consideration the limitations and capturing efficiencies of the different testing matrices. We have contextualised these responses against previous published reference cigarette data to establish the comparative reduction in response consistent with reduced risk potential of the e-cigarette products tested in this study as compared to conventional cigarettes.

Fabrication and capillary performance of multi-scale microgroove ceramic wicks via nanosecond laser irradiation for ultrathin ceramic heat pipes

Ultrathin ceramic heat pipes have great potential in solving the heat dissipation problems for power semiconductor devices with ever-increasing power density. Ceramic wick structures with superior capillary performance plays a decisive role in the heat transfer performance of the ceramic heat pipe. In the study, a multi-scale microgroove wick (MSMGW) prepared by laser irradiation is developed. The effects of laser scan pitch, laser fabrication parameters and ceramic material on the surface morphology, wettability and capillary performance of the MSMGW were investigated. The 66 μm thick ceramic wick proposed that consists of micron-sized microgrooves, nanoscale voids and material surface reconsolidation layers demonstrates remarkable capillary performance. The laser scan pitch, laser power, repetition frequency, and scanning speed have significant impacts on the surface morphology and capillary performance of MSMGW. The MSMGW with optimal parameters could reach capillary wicking height of 114 mm within 28 s and yield a capillary parameter (K/reff) of 1.49 μm. Moreover, MSMGW on the material of alumina with advantages of excellent machining property and technology maturity, and working fluid of DI water with high vaporization latent heat and wide operating temperature range, exhibits the maximum capillary performance, indicating its highly promising prospects for high-performance ultrathin ceramic heat pipes.

Experimental study on a dual compensation chamber loop heat pipe with a ceramic wick

The dual compensation chamber loop heat pipe (DCCLHP) has excellent application prospects in the future field of space thermal management. However, DCCLHP has some problems, such as startup difficulty with a small heat load and serious heat leakage from the back of the capillary pump. To ensure the reliable startup and efficient heat transfer of DCCLHP in the space microgravity environment, a kind of DCCLHP with an eccentric structure of silicon nitride capillary wick was manufactured and verified. The experimental results show that the DCCLHP can be started with a 2 W small heat load, with two different starting conditions. The heat transfer capacity exceeds 450 W in the 2.0 m heat transfer range. The starting temperature overshoot of DCCLHP presents an inverted “V” shape relationship with the heat load. The smaller the temperature difference between the two compensation chambers is, the heat transfer performance of DCCLHP will be promoted. This study has significant reference value for applying DCCLHP in space microgravity thermal management.

Chemical characterisation of the vapour emitted by an e-cigarette using a ceramic wick-based technology

Fourth-generation ‘pod’ e-cigarette devices have been driven by technological advances in electronic atomization of the e-liquid. Use of microporous ceramic as a wicking material improves heating efficiency, but how it affects the chemical emissions of these devices is unclear. We assessed the emissions of a pod e-cigarette with innovative ceramic wick-based technology and two flavoured e-liquids containing nicotine lactate and nicotine benzoate (57 and 18 mg mL−1 nicotine, respectively). Among the studied harmful and potentially harmful constituents (HPHCs) listed by the US FDA and/or WHO TobReg, only 5 (acetone, acetaldehyde, formaldehyde, naphthalene and nornicotine) were quantified at levels of 0.14 to 100 ng puff−1. In the combustible cigarette (Kentucky reference 1R6F), levels were from 0.131 to 168 µg puff−1. Nicotine levels ranged 0.10–0.32 mg puff−1 across the 3 study products. From the 19 proposed HPHCs specifically of concern in e-cigarettes, only 3 (glycerol, isoamyl acetate and propylene glycol) were quantified. The low/undetectable levels of HPHCs reflect not only the optimal operating conditions of the e-cigarette, including an efficient supply of e-liquid by the ceramic wick without overheating, but also the potential of the e-cigarettes to be used as an alternative to combustible cigarettes.

Experimental Study on Thermal Performance of a Loop Heat Pipe with Different Working Wick Materials

In loop heat pipes (LHPs), wick materials and their structures are important in achieving continuous heat transfer with a favorable distribution of the working fluid. This article introduces the characteristics of loop heat pipes with different wicks: (i) sintered stainless steel and (ii) ceramic. The evaporator has a flat-rectangular assembly under gravity-assisted conditions. Water was used as a working fluid, and the performance of the LHP was analyzed in terms of temperatures at different locations of the LHP and thermal resistance. As to the results, a stable operation can be maintained in the range of 50 to 520 W for the LHP with the stainless-steel wick, matching the desired limited temperature for electronics of 85 °C at the heater surface at 350 W (129.6 kW·m−2). Results using the ceramic wick showed that a heater surface temperature of below 85 °C could be obtained when operating at 54 W (20 kW·m−2).

Design and test of a flat capillary pump with ceramic wick

<p indent=0mm>A novel flat capillary pump was designed to solve the problem of heat leakage from the evaporator to the accumulator in flat capillary pumps. The materials used to obtain the porous wick and main shell were silicon nitride and low-thermal conductivity titanium alloy, respectively. The size of the resulting capillary pump was <sc>82.0 mm</sc> × <sc>53.0 mm</sc> × <sc>16.0 mm,</sc> and eight cylindrical silicon nitride porous wicks were arranged inside the pump. The pore size, porosity, and heat conductivity of the porous wick were <sc>0.5 µm,</sc> 70%, and 2.7 W/(m K), respectively. Experimental results showed that the flat evaporator loop heat pipe can be started quickly and that no obvious overheating occurs in the evaporator under a heat load in the range of <sc>5.0–20.0 W</sc> when the angle of the capillary pump is 0°. The time required to start the flat evaporator loop heat pipe remarkably increased and the temperature increment evidently increased under a <sc>5 W</sc> start load when the angle of the capillary pump was increased. However, when the start load was increased to <sc>20 W,</sc> the starting characteristics of the pipe improved. The heat-transfer ability of the flat evaporator loop heat pipe, equilibrium temperature of the accumulator, and thermal resistance of the pipe were subsequently tested, and results revealed that the heat transfer and heat flux limits are <sc>400.0 W</sc> and <sc>26.3 W/cm²,</sc> respectively. The equilibrium temperature of the accumulator changed with the heat sink and load, and this is consistent with the typical running characteristic of the loop heat pipe. The minimum thermal resistance tested was 0.018°C/W. Finally, the back heat leakage from the evaporator to the compensation chamber was estimated from the energy balance of the compensation chamber.

Design features and elemental/metal analysis of the atomizers in pod-style electronic cigarettes.

BackgroundThe atomizers of electronic cigarettes (ECs) contain metals that transfer to the aerosol upon heating and may present health hazards. This study analyzed 4th-generation EC pod atomizer design features and characterized their elemental/metal composition.MethodsEleven EC pods from six brands/manufacturers were purchased at local shops and online. Pods were dissected and imaged using a Canon EOS Rebel SL2 camera. Elemental analysis and mapping of atomizer components was done using a scanning electron microscope coupled with an energy dispersive x-ray spectrometer.ResultsEC pods varied in size and design. The internal atomizer components were similar across brands except for variations occurring mainly in the wicks and filaments of some products. The filaments were either Elinvar (nickel, iron, and chromium) (36.4%), nichrome (36.4%), iron-chromium (18.2%), or nickel (9%). Thick wires present in 55% of the atomizers were mainly nickel and were joined to filaments by brazing. Wire-connector joints were Elinvar. Metal air tubes were made of Elinvar (50%), nickel, zinc, copper, and tin (37.5%), and nickel and copper (12.5%). Most of the wick components were silica, except for two pods (PHIX and Mico), which were mainly ceramic. Connectors contained gold-plated nickel, iron-chromium multiple alloys of nickel, zinc, gold, iron, and copper. Wick chambers were made of Elinvar. Outer casings were either nickel, copper-tin, or nickel-copper alloys. Magnets were nickel with minor iron, copper, and sulfur. Some frequently occurring elements were high in relative abundance in atomizer components.ConclusionsThe atomizers of pods are similar to previous generations, with the introduction of ceramic wicks and magnets in the newer generations. The elements in EC atomizers may transfer into aerosols and adversely affect health and accumulate in the environment.

Optimization of A Loop Heat Pipe (LHP) with Wick Separated from Heating Surface

Abstract A novel LHP, in which the wick is separated from the heating surface, has been proposed. And then, a steam chamber is formed, which can effectively use the pressure head of evaporation. This work is to optimize the key parameters in order to further improve the performance of such a novel LHP. A mathematical model, based on the node analysis method, had been established, which was validated against the experimental data. The height of steam chamber, the type of working fluids, and the material of wick were identified as key parameters to be optimized. The heating surface temperature, which was the highest temperature, and the start-up time were selected as the key performance indicators. Results showed there existed an optimal height of steam chamber (3mm) and charging ratio (55%) to achieve the lowest heating surface temperature and the shortest start-up time. For different working fluids, ammonia showed the best performance, followed by acetone, ethanol, and water. And the ceramic wick, with low thermal conductivity, demonstrated a better performance than the steel-nickel wick and copper wick with high thermal conductivity.

Steady State Thermal Behaviour of Ceramic Wick Structure for Application in Two Phase Heat Transfer Devices

This work reports on results from two phase heat transfer devices assembled with ceramic capillary structure. It is firstly presented the manufacturing of the ceramic wick structures and afterwards the characterization of the morphological-and fluid-dynamical properties of these ceramic wick structures. As closing results, it is presented the thermal behaviour of two different two phase heat transfer devices, i.e. a Capillary Pumped Loop and a Loop Heat Pipe. The properties of the ceramic wick structure are within the desirable range for a correct functioning of these devices, e.g. porosity, pore size and permeability constants ranging from 40 to 60%, from 5 to 30μm and from 10-10 to 10-13m2, respectively. The thermal behaviour tests of the heat transfer devices used power heat load input in range from 10 to 20W and for all devices the evaporator temperature reached steady state condition. Thus, as a result, it can be claimed these ceramic wick structures as successful alternative for assembling capillary evaporator of CPL and LHP.

Sampling gaseous compounds from essential oils evaporation by solid phase microextraction devices

Needle trap samplers (NTS) are packed with 80–100 mesh divinylbenzene (DVB) particles to extract indoor volatile organic compounds (VOCs). This study compared extraction efficiency between an NTS and a commercially available 100 μm polydimethylsiloxane-solid phase microextration (PDMS-SPME) fiber sampler used to sample gaseous products in heated tea tree essential oil in different evaporation modes, which were evaporated respectively by free convection inside a glass evaporation dish at 27 °C, by evaporation diffuser at 60 °C, and by thermal ceramic wicks at 100 °C. The experimental results indicated that the NTS performed better than the SPME fiber samplers and that the NTS primarily adsorbed 5.7 ng ethylbenzene, 5.8 ng m/p-xylenes, 11.1 ng 1,2,3-trimethylbenzene, 12.4 ng 1,2,4-trimethylbenzene and 9.99 ng 1,4-diethylbenzene when thermal ceramic wicks were used to evaporate the tea tree essential oil during a 1-hr evaporation period. The experiment also indicated that the temperature used to heat the essential oils should be as low as possible to minimize irritant VOC by-products. If the evaporation temperature does not exceed 100 °C, the concentrations of main by-products trimethylbenzene and diethylbenzene are much lower than the threshold limit values recommended by the National Institute for Occupational Safety and Health (NIOSH).

Development of biporous Ti3AlC2 ceramic wicks for loop heat pipe

Novel Ti3AlC2 wicks with two distinguished characteristic pore sizes were successfully developed. The heat transfer performances of the loop heat pipes with monoporous and biporous Ti3AlC2 wicks were comparatively studied. Results show that Ti3AlC2 wicks exhibit increased porosity and reduced thermal conductivity by using salt leaching pore-forming and two kinds of pores can be found in one Ti3AlC2 wick. Moreover, the loop heat pipe with biporous Ti3AlC2 wick operates reliably under the heat load of 25W compared with that employing monoporous Ti3AlC2 wick. Biporous Ti3AlC2 wicks proved to be possible alternatives to metals and conventional ceramics for applications in LHP wicks.

Thermal performance and capillary limit of a ceramic wick applied to LHP and CPL

Abstract The performance of a ceramic wick working as a capillary evaporator of a Loop Heat Pipe (LHP) and a Capillary Pumped Loop (CPL) is analyzed. The LHP and the CPL have a capillary evaporator with 10 mm of inner diameter and 25 mm of length. The LHP compensation chamber has the same diameter as the evaporator and a length of 50 mm. The ceramic wick was sintered from alumina and mullite powders, achieving 50% of porosity, 1–3 μm pore size distribution and permeability of 35 × 10 −15 m 2 , and then machined to properly fit the evaporators. The performance tests were carried out using deionized water as the working fluid for power inputs of up to 30 W. The thermal performance, capillary limit and area-specific thermal resistance of these systems were analyzed with the support of basic heat transfer and fluid flow lumped models. The lowest area-specific thermal resistance values of 31.7 °C/W/cm 2 for CPL and 25.0 °C/W/cm 2 for LHP were reached when dissipating 3.18 W/cm 2 , while the highest values of 52.8 °C/W/cm 2 for CPL and 38.8 °C/W/cm 2 for LHP were reached while dissipating 0.53 W/cm 2 and 1.06 W/cm 2 , respectively. The analysis shows that the systems operate well at their capillary limit and their performance is equivalent to similar devices operating with acetone and ammonia reported in the literature.

Evaluation of permeability of ceramic wick structures for two phase heat transfer devices

This work reports on different approaches to predict the pressure drop in capillary structures for two phase heat transfer devices (TPHTD). For this purpose, several porous wick structures were produced by slip casting and characterized concerning their porosity, critical pore diameter, capillary pressure and permeability. The wick structures exhibited porosity in the range of 48–58%, pore diameter ranging from 1 μm to 4 μm, with capillary pressure of 80 and 22 kPa, respectively. Two expressions were developed to simulate the pressure drop permeabilities as a function of the heat load applied to the TPHTD evaporator. The prime target of this work is to evaluate the differences in predicting pressure drop just by using the Darcyan constant, k 1 , and both by using Darcyan and non-Darcyan constant, k 1 and k 2 . When k 1 was used only it was considered as Darcyan approach and when both constants were taken into account it was considered as Forchheimer approach. Additionally, ceramic wick structures have been tested as capillary evaporator in a TPHTD. The startup was successful after 20 min the inlet and outlet evaporator temperatures remain constant. It confirms that all applied heat load was transported to the condenser. ► We manufactured and characterized ceramic wick structures for CPL applications. ► We evaluated their permeability regarding Darcyan and non-Darcyan constants. ► The pressure drop in the CPL could be predicted by Darcyan and Forchheimer laws. ► We demonstrated a successful performance of a CPL at different operations conditions.

Development of LHPs with ceramic wick

Abstract The ceramic porous wick is proposed as an alternative to wicks made of metal and plastic for Loop Heat Pipes (LHP) applications. Performance tests of two LHPs using acetone and water as working fluids were carried out for power inputs up to 25 W. The evaporators have a stainless steel cylindrical assembly, with 80 mm of length and 10 mm of inner diameter. The ceramic porous wick has 50% of porosity, 1–3 μm of pore radius distribution and a permeability of about 35 × 10 −15 m 2 . The active zone length of the evaporators is 25 mm. For a limited operation temperature of 100 °C, the LHPs were able to transfer up to 25 and 15 W using acetone and water, respectively, at steady state condition. An operation analysis concerning the effects of the LHP inclination, the heat sink temperature and LHP thermal resistances is also presented. Despite the relative good performance of the LHPs, further researches are still required taking into account changes related to properties of the ceramic porous wick in particular and improvements in the whole LHP design in general.

마이크로 세라믹 윅을 사용한 루프 히트파이프의 특성 연구

This paper presents the experimental and simulation study of a loop heat pipe (LHP) that can be applied to present electronics, space missions and thermal control systems. The present experimental study was carried out employing sintered alumina ceramic wick ($d

Burning rate of liquid supplied through a wick

Liquid fuel supplied through ceramic or metallic wicks is commonly used as a simulant for burning of planar liquid or solid surfaces. When the liquid flow through the wick is at least partly controlled by capillarity, the partially exposed wick matrix at the burning surface changes the concentration distribution adjacent to this surface. Here we show that when the characteristic length of the exposed matrix is not significantly smaller than the convection boundary-layer thickness, the burning rate from the wick deviates (being smaller for low thermal conductivity wicks) from that for planar liquid surfaces. The study is guided by experiments using a ceramic wick, by a one-dimensional gas-side diffusion analysis, and by a wick-side two-phase flow and heat transfer analysis.

Completeness of Combustion for Laminar Wall Fires Using Several Alcohols Burning in Air

Abstract Steady, fully-burning wall fires were studied for several alcohols burning in air. Methanol, 1-propanol. and 1-butanol were burned using a vertically-oriented porous ceramic wick. Completeness of combustion was evaluated and accounting for its effect in numerical modeling, on characteristics of laminar wall fires was examined. Measurements of the concentration profiles in the free-convection boundary layers formed revealed that for each of the fuels more than 30% of fuel carbon was found present in product CO, as opposed to CO2. However, using a numerical model that employs a one-step overall reaction, the subsequent decrease in the effective heat of combustion in accounting for incomplete combustion did not lead to a substantial change in burning characteristics. For all of the alcohols, there was less than a 5% decrease in burning rates and less than a 150K drop in peak temperatures.

Comparison of Theoretical and Experimental Burning Rates for a Laminar Wall Fire

Laminar methyl methacrylate (MMA) wall fires were studied. The principal objective of the investigation was to obtain and compare theoretical and ex perimental burning rates. The wall fires were produced by burning MMA on a ceramic wick in an oxygen/nitrogen environment. Burning rate measurements were made for several values of ambient oxygen mass fraction, and it was found that a unique burning rate did not exist for a given ambient condition. For supply rates that were great enough to cause fuel to drip from the wick surface, the burning rate was found to increase slightly with supply rate. The burning rates in the limit of zero fuel dripping were chosen as characteristic values for comparison with theoretical results. Diffusion flame theory for laminar burning of a vertical fuel surface was used to predict burning rates. The effects of incomplete combustion were examined (using recently measured values of the effective heat of combustion), and are found to decrease the calculated burning rates by about 5 percent. The variation in the calculated burning rates due to our lack of knowledge of the effective Lewis number and flame emissivity were considered, and found to give an uncer tainty band of ± 12 percent. Comparison of the theoretical calculations with the measured results show a similar, small increase with increasing ambient oxygen concentration. The band of theoretical results, however, predicts burning rates which are at least 10 percent greater than the measured values.

Study of Efflorescence Produced on Ceramic Wicks by Masonry Mortars

Ceramic wicks (Efflorwicks) were partly embedded in cylinders of masonry mortars of various compositions, and the hardened mortars were alternately wetted and dried, which produced various amounts of efflorescence on the wicks. Portland cement in mortars contributed significantly to efflorescence. The alkaline material of the cementing substance of the mortars appeared to be an important source of the efflorescence.