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Lateral flow assays (LFAs), a popular point-of-care testing platform, have found widespread applications from laboratory to clinics. However, LFA-based testing is still subject to limited detection sensitivity, especially for classical gold nanoparticle-based LFAs. Inspired by traditional pen-based writing technologies, we developed a ball pen writing-without-ink method to amplify the detection signal of LFAs through controlling fluid flow rate. An enhancement of detection sensitivity by two times was obtained. Since the underlying mechanism of this method to improve detection sensitivity is to control the flow rate of the liquid on paper, it may be suitable for most paper-based platforms.

Liquid-filled porous materials exist widely in nature and engineering fields, with the diffusion of substances in them playing an important role in system functions. Although surface evaporation is often inevitable in practical scenarios, the evaporation effects on diffusion behavior in liquid-filled porous materials have not been well explored yet. In this work, we performed noninvasive diffusion imaging experiments to observe the diffusion process of erioglaucine disodium salt dye in a liquid-filled nitrocellulose membrane under a wide range of relative humidities (RHs). We found that evaporation can significantly accelerate the diffusion rate and alter concentration distribution compared with the case without evaporation. We explained the accelerated diffusion phenomenon by the mechanism that evaporation would induce a weak flow in liquid-filled porous materials, which leads to convective diffusion, i.e., evaporation-induced flow and diffusion (EIFD). Based on the EIFD mechanism, we proposed a convective diffusion model to quantitatively predict the diffusion process in liquid-filled porous materials under evaporation and experimentally validated the model. Introducing the dimensionless Peclet (Pe) number to measure the relative contribution of the evaporation effect to pure molecular diffusion, we demonstrated that even at a high RH of 95%, where the evaporation effect is usually assumed negligible in common sense, the evaporation-induced diffusion still overwhelms the molecular diffusion. The flow velocity induced by evaporation in liquid-filled porous materials was found to be 0.4–5 μm/s, comparable to flow in many biological and biomedical systems. The present analysis may help to explain the driving mechanism of tissue perfusion and provide quantitative analysis or inspire new control methods of flow and material exchange in numerous cutting-edge technologies, such as paper-based diagnostics, hydrogel-based flexible electronics, evaporation-induced electricity generation, and seawater purification.

One major conundrum that impedes the development and application of emerging soft and stretchable electronics lies in the integration of electronic components with soft substrates for rational combination of various device functionalities into a single wearable state, since the rigid, nondeformable electronics tend to detach from the deformable substrate under mechanical loadings like stretch. Modulating the stiffness of soft materials in a spatially controllable manner provides a promising solution to this rigid–soft coupling challenge, by shielding the local strain of rigid components while maintaining the stretchable properties of the soft substrates. Hydrogels with superb biocompatibility and skin-like mechanical features are ideal candidates for interfacing the human body and electronic functionalities for cutting-edge wearable uses, where there exists a challenge of spatially modulating the stiffness of hydrogels to meet the application demands. Herein, we develop a facile and straightforward method to locally stiffen a hydrogel (with an increased Young's modulus of one order of magnitude) via an additional crosslinking strategy. The locally stiffened site undergoes minimal strain (down to 12%) and the untreated area remains stretchable under external deformations (100% strain), which presents excellent and tunable strain shielding capability to prevent detachment of the electronic components from the substrate under strain levels up to 150%. We further demonstrate a multifunctional health sensing device based on a component-integrated locally stiffened hydrogel and its satisfactory performance in monitoring temperature, UV exposure and EMG signals unveils its brilliant prospects for wearable healthcare applications.

Fast nucleic acid (NA) amplification has found widespread biomedical applications, where high thermocycling rate is the key. The plasmon-driven nano-localized thermocycling around the gold nanorods (AuNRs) is a promising alternative, as the significantly reduced reaction volume enables a rapid temperature response. However, quantifying and adjusting the nano-localized temperature field remains challenging for now. Herein, a simple method is developed to quantify and adjust the nano-localized temperature field around AuNRs by combining experimental measurement and numerical simulation. An indirect method to measure the surface temperature of AuNRs is first developed by utilizing the temperature-dependent stability of Authiol bond. Meanwhile, the relationship of AuNRs' surface temperature with the AuNRs concentration and laser intensity, is also studied. In combination with thermal diffusion simulation, the nano-localized temperature field under the laser irradiation is obtained. The results show that the restricted reaction volume (≈aL level) enables ultrafast thermocycling rate (10

Background. Diarrhea-predominant irritable bowel syndrome (IBS-D) is a functional gastrointestinal disorder that severely affects patients’ life. Moxibustion is believed to be an effective way to treat IBS-D. However, the therapeutic effects and the underlying mechanisms in symptom management of IBS-D by different moxibustion therapies remain unclear. Methods. IBS-D model rats were divided into groups and treated with ginger-partitioned moxibustion (GPM), mild moxibustion (MM), and laser moxibustion (LM) at a temperature of 43°C, respectively. The temperature curves of acupoints were recorded during interventions. The therapeutic effects were evaluated on the basis of general condition, stool, and hematoxylin-eosin staining of the colon tissue. Moreover, the expression of transient receptor potential vanilloid 1 (TRPV1) receptors in both acupoint tissue and colon tissue was analyzed by immunohistochemistry. Results. After moxibustion treatment, the symptoms were improved. The expression of TRPV1 was increased in acupoint tissue and decreased in colon tissue. GPM and MM showed a more significant influence on IBS-D rats compared with LM. The temperature profile of GPM and MM was wave-like, while LM had an almost stable temperature curve. Conclusion. GPM, MM, and LM could improve the symptoms in IBS-D rats. Moxibustion might activate TRPV1 channels in the acupoint tissue and induce acupoint functions, which in turn inhibit the pathological activation state of the colon’s TRPV1, followed by improvements in abdominal pain and diarrheal symptoms. LM with stable temperature might lead to the desensitization of TRPV1 receptors and the tolerance of acupoint. GPM and MM provided dynamic and repetitive thermal stimulations that perhaps induced acupoint sensitization to increase efficacy. Therefore, dynamic and repetitive thermal stimulation is recommended in the application of moxibustion.

Coupled with detailed catalytic reaction mechanism, the exhaust reforming process in a fixed bed reactor was simulated using a porous media model to investigate the reforming characteristics under different initial conditions. The effects of gas hourly space velocity (GHSV), feed component, steam addition and wall temperature on the methane conversion rate, hydrogen yield and other characteristic parameters were analyzed. The simulation results show that the oxygen is consumed rapidly when the reforming gas enters the reaction zone and the steam reforming plays a dominant role in the latter part. The exhaust reforming process mainly involves oxidation reaction, steam reforming reaction and water gas shift reaction. The methane conversion and hydrogen production decrease with the rise of GHSV, while the molar ratio of H2 to CO first increases and then decreases and reaches its peak value when GHSV ranges from 30,000 h−1 to 35,000 h−1. As the ratio of methane to exhaust increases, a higher molar fraction of hydrogen at the outlet can be achieved owing to a bigger proportion of partial reforming reaction of methane, and methane conversion rate decreases. It also suggests that a modest steam addition is preferable for both the reforming performance and the life span of the fixed bed.

Cell aggregates represent the main format of cells existing in vivo and have been widely used as tissue and disease models in vitro. Nevertheless, the preservation of cell aggregates while maintaining their functionalities for off-the-shelf applications is still challenging. Among various preservation methods, droplet-based vitrification exhibits superior advantages for the cryopreservation of cell aggregates; however, the physical mechanisms underlying droplet-based vitrification of cell aggregate using this method remain elusive. To address this issue, we proposed a voronoi model to construct two-dimensional geometric morphologies of cell aggregates and established a coupled physical model to describe the diffusion, heat transfer and crystallization processes during vitrification. Based on these models, we performed a numerical study on the variation and distribution of cryoprotectant (CPA) concentration, temperature and crystallization in cell aggregates during droplet-based vitrification. The results show that although cell membrane is not an obvious barrier in heat transfer, it affects the diffusion of CPA remarkably as a biologic film and thus the following crystallization in cell aggregates. The effective protection of CPA during vitrification occurs during the initial stage of CPA diffusion, thus a longer CPA loading time does not necessarily lead to significant decrease in crystallization, but rather may induce more toxicity to cells.

This study reports on the effects of vane outlet angle on thermo-fluidic characteristics of curved vane brake discs via validated numerical models. Three vane outlet angles (45°, 90° and 135°) are considered. For a given rotational speed within the operating range of 200–1000 rpm, results show that increasing the outlet angle from 45° to 135° enhances the overall cooling performance by up to 16%. It is found that the increasing outlet angle enhances circumferential pressure difference, which intensifies secondary flow perpendicular to the mainstream and hence evidently enhances local heat transfer on inner disc surface. Further, the increase of outlet angle results in stronger flow impingement on pressure sides of the vanes and hence enhances local heat transfer. However, severe flow separation endows the brake disc having the outlet angle of 90° with the poorest heat transfer on suction sides of the vanes while those for the others are similar. In addition, local heat transfer variation on rubbing surface, inner rim surface and outer rim surface due to the variation of outlet angle has negligible effect on overall cooling performance. Comprehensive heat transfer enhancement mechanisms clarified in the present study are helpful to motivate further improved designs.

A novel cross-fin heat sink consisting of a series of long fins and a series of perpendicularly arranged short fins was proposed to enhance natural convective heat transfer. The design principle of the cross-fin heat sink was based on overcoming internal thermal fluid-flow defects in a conventional plate-fin heat sink. The thermal performance of the proposed heat sink was compared with a reference plate-fin heat sink in horizontal orientation. A numerical model considering both natural convection and radiation heat transfer was developed to obtain thermal fluid-flow distributions and heat transfer coefficients of both the cross- and plate-fin heat sinks. Corresponding experiments were performed to validate the model predictions. It was demonstrated that, compared to the reference plate-fin heat sink, the cross-fin heat sink enhanced the overall (including natural convection and radiation) and convective (excluding radiation) heat transfer coefficients by 11% and 15%, respectively. Importantly, the enhancement was achieved without increasing the overall volume, material consumption, and too much extra cost. The proposed cross-fin heat sink provides a practical alternative to the widely adopted plate-fin heat sinks.

Natural convection in metal foam heat sinks with open slots was investigated experimentally. The test sample was made in-house by attaching several foam strips having fixed width of 10 mm and length of 100 mm onto a substrate of 100 × 100 × 4 mm3 in size. A total of 29 test samples with different slot widths (s = 0/2.86/5/8/12.5/20 mm) and foam heights (H = 10/20/40/60/80 mm) were tested under both horizontal and vertical orientations for each sample. The zero width of open slots corresponds to a heat sink with a single foam block as considered in open literature, while the non-zero open slot width 2.86/5/8/12.5/20 mm corresponds to 8/7/6/5/4 foam strips in a heat sink, respectively. Compared to a single foam block, the foam with open slots are more permeable for air penetrating through the heat sink. More foam strips means more heat transfer area available but less permeation of the heat sink. Experimental results revealed that there exists an optimum open slot width (5–8 mm) for maximum heat transfer coefficient at given heat sink volume. With optimum open slot width, the heat transfer coefficient is enhanced by 14.9%, 21.3%, 37.6%, and 38.2% relative to single foam block (s = 0 mm) at the foam height of 10 mm, 20 mm, 40 mm, and 80 mm, respectively.

LED lightings have made significant contributions to global energy saving, where one major challenge is the overheating of LED chips since the light output and lifespan of LED chips decrease exponentially with increasing operating temperature. Restricted by cooling capacity, the power input and light output of a LED bulb is limited. At present the luminous flux of commercial LED bulbs (A19 size) is usually limited to 800 lm with the related power consumption within 9 W. Therefore, there is an urgent market need for high-lumen bulbs while maintaining the size and shape as conventional incandescent bulbs. We report herein a novel design which could make full use of the entire outer surface of LED bulb as heat dissipating surface under passive cooling conditions. The novel design contains a chimney inside the bulb and an external heat sink, enabling two parallel heat dissipating paths, i.e., chips - heat sink - environment and chips – chimney – lampshade - environment. In conventional design with an external heat sink for cooling, the lampshade functions only to transmit light rather than dissipate heat. However, in the novel design the chimney inside the bulb could thermally activate the lampshade to dissipate heat as well. Upon properly distributing thermal loads to the two heat dissipating paths, cooling capacity of the novel bulb was optimized. With this design strategy, the passive cooling capacity was significantly improved to be 1.57 times higher than the conventional design and the commercially available bulbs of the same size and shape. Most importantly, the design strategy may be extended to other passive cooling scenarios such as indoor small cells for 5G communication.

The performance and lifetime of a LED bulb are highly sensitive to its operating temperature. Due to size and shape constraints, thermal management of LED bulb is challenging. This paper presented a combined numerical, analytical, and experimental study on the thermal-fluid flow and optimization of a novel chimney-based LED bulb. A CFD model considering both natural convection and radiation heat transfer was established and validated by experiment. An analytical model based on thermal resistance analysis was developed and verified against the CFD model. Compared to conventional LED bulbs, the advantage of the chimney-based LED bulb is that it can utilize the lampshade surface for heat dissipation in addition to the conventional role for light guide. To improve natural convection inside the chimney-based LED bulb, a gas mixture was introduced in the bulb and its composition was optimized by using the analytical model. It was found that the temperature rise of a LED bulb filled with the optimum gas mixture (a mixture of 74% helium and 26% xenon) was 30.7% lower than that filled with air at the same power input. The optimized gas mixture and the optimization method may be extended to other applications for natural convection in enclosures.

Lateral flow assays (LFAs) have found widespread applications in biomedical fields, but improving their sensitivity remains challenging mainly due to the unclear convection-diffusion-reaction process. Therefore, we developed a 1D mathematical model to solve this process in LFAs. The model depicts the actual situation that one report particle may combine more than one target, which overcomes the deficiency of existing models where one report particle combines only one target. With this model, we studied the effect of report particle characteristics on LFAs, including binding site density, target analyte and report particle concentration. The model was qualitatively validated by reported experimental data and our designed experiments where the report particle with different accessible binding site (HIV-DP) densities is obtained by changing the ratio of HIV-DP and Dengue-DP in preparing AuNP-DP aggregates. The results indicate that a strong signal intensity can be obtained without consuming excess detector probe with the optimum binding site (N = 30). A maximum normalized target concentration of 120 is obtained to prevent the false-negative result, while a minimum normalized report particle concentration of 0.015 is recommended to produce a strong signal. The developed model would serve as a powerful tool for designing highly effective LFAs.

This numerical study presents a systematic comparison of the fluid flow and heat transfer characteristics between standard and cross-drilled ventilated brake discs incorporating pin-fins. To validate the numerical model, heat transfer measurement is performed for a commercially available standard brake disc. Within the representative operating range of 200–1000 rpm, results show that the introduction of cross-drilled holes on the rubbing discs enhances the overall cooling capacity of the pin-finned brake disc by 15–17%. As a result of axial pressure gradient, the low-momentum boundary-layer fluid near the rubbing surfaces is driven into the ventilated channel through the cross-drilled holes. Consequently, within radial spans of the cross-drilled holes, local heat transfer on the rubbing surfaces is evidently improved. In addition, the through-hole flow provides substantial heat removal from additional surface of the holes. However, the flow ejected from the cross-drilled holes blocks and interacts with the mainstream entered from the inlet of the ventilated channel, which ultimately reduces the effective flow area and increases resistance to the mainstream. Thus pumping capacity through the inlet of the ventilated channel decreases; and correspondingly, local heat transfer on other surfaces of the rubbing discs is slightly deteriorated. These mutually conflicting mechanisms are responsible for the superior overall cooling performance of the cross-drilled pin-finned brake disc.

We conducted analytical, numerical and experimental investigations on solidification of fluid saturated in highly porous metal foams with open cells. Based on pore-scale thermal equilibrium assumption, an analytical extension of the classical Neumann’s solution was made to predict phase change heat transfer in PCM-foam composites. To explore the heat transfer mechanisms underlying the phase change process and clarify the role of foam insertion, three-dimensional direct numerical simulations on periodically distributed tetrakaidecahedron cells were carried out. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. The phase interface was macroscopically flat via experimental visualization but microscopically irregular via pore-scale simulations. Temperature difference between the saturating PCM and metallic ligaments was negligible, so that local thermal equilibrium and one-equation model were applicable especially at low Ste numbers (e.g., 0.22). The present findings provide new insights to cold energy storage design, utilization and economic analysis in HVAC systems.

Lateral flow assays (LFAs) have found applications in clinical diagnostics, veterinary medicine, food safety, environmental monitoring, bio-defence, drug abuse, etc . However, conventional LFAs with single test zone for one analyte (sLFA) show qualitative, positive/negative results (that are usually not so accurate for decision-making) and suffer from the hook effect (that easily induces false negative results). In this study, a modified LFA with multiple test zones for one analyte (mLFA) is developed for detection of nucleic acid showing two methods to interpret assay results. One is the sum of detection signals of test zones, which exhibits a stable and broader detection range compared with sLFA. The other is the pattern of test zones that is presented is correlated to the concentration of analyte, facilitating semi-quantitative detection without the aid of a reader or analyzer.

As a kind of biomimetic materials, ultralight hierarchical porous structures possessing excellent mechanical properties such as load bearing, impact energy absorption, vibration reduction and noise attenuation have been exploited. Often, these porous structures exhibit continuous flow passages that allow for cooling fluids to pass through, thus enabling simultaneous load-bearing and active heat dissipation. This study investigated the convective cooling efficiency of a sandwich panel with hierarchical corrugated core subjected to heating from the face sheets and active cooling through the core. Built upon the classical fin approach, a theoretical model coupling wall heat conduction and fluid convection in the core was established for the hierarchical corrugated-core sandwich panel, covering the full range of fluid flow (from laminar, transition to turbulent). The theoretical model predictions were validated against full numerical simulations. Based on the theoretical model, an artificial intelligence optimization method (i.e., the ant colony algorithm) was adopted to find the optimal combination of key independent geometric parameters of the sandwich panel for maximized heat transfer performance. For the problem of multi-variables optimization, it was demonstrated that the ant colony algorithm is superior in terms of computational time to the traditional exhaustive search method. For a given pressure drop, a set of optimum geometric parameters corresponding to maximum cooling efficiency was found for the proposed hierarchical corrugated-core sandwich panel.

Lightweight sandwich panels with fluid-through cellular cores are promising for applications requiring simultaneous load-bearing and heat dissipation such as the combustion chamber of scramjet. While existing core topologies have exhibited good designability for specific thermal or mechanical requirements, the increasing demand for multifunctional attributes usually points to different core topology designs. Finding a single core topology that possesses excellent mechanical and thermal properties simultaneously remains challenging. To address the issue, the concept of a hybrid core (termed herein as the N core) that combines the conventional corrugated core with the web core was proposed to mitigate confliction between thermal and mechanical designs. Out-of-plane compressive characteristics of the hybrid cored sandwich panel was investigated theoretically, numerically and experimentally. An elastic–plastic analytical model was developed to predict the out-of-plane compressive behavior, with connection strength between facesheets and core as well as non-uniform strut thickness accounted for. For validation, test sample was fabricated using 3D-printing technology and tested under quasi-static out-of-plane compression. The validated model was then employed to exploit optimal configuration of the N core and maximum load capacity of the panel at minimal weight. It was demonstrated that, due to non-uniform strut thickness, the hybrid structure exhibited stepwise deformation, i.e., initial, subsequent and ultimate failures. Under the constraint of equal mass, the load capacity of either the hybrid or corrugated core is superior to the web core, while both the hybrid and web cores outperform the corrugated core in terms of active cooling capacity. For multifunctional applications, the proposed hybrid corrugated core possesses comprehensive thermal and mechanical advantages over conventional corrugated and web topologies.

We conduct both analytical and numerical investigations on the solidification behavior of fluid saturated in highly porous open-cell metallic foams. Based on the pore-scaled thermal equilibrium assumption, an analytical extension is made to the classical Neumann's solution to solidifying fluid as an interstitial into metallic foams. To underlying the heat transfer mechanisms for phase change process and the role of inserted foam, an idealized tetrakaidecahedron unit cell geometric model was reconstructed and direct numerical simulations were conducted. Showing good agreement with experimental results and direct numerical simulations, the developed model is verified, favoring the assumption of local thermal equilibrium. The numerical simulation results at pore scale qualitatively demonstrate that: i) the solidification interface is globally flat within a pore; ii) the local natural convection does exist and it contributes to the evolution of solidification interface (9% promotion).

In nucleic acid testing (NAT), gold nanoparticle (AuNP)-based lateral flow assays (LFAs) have received significant attention due to their cost-effectiveness, rapidity, and the ability to produce a simple colorimetric readout. However, the poor sensitivity of AuNP-based LFAs limits its widespread applications. Even though various efforts have been made to improve the assay sensitivity, most methods are inappropriate for integration into LFA for sample-to-answer NAT at the point-of-care (POC), usually due to the complicated fabrication processes or incompatible chemicals used. To address this, we propose a novel strategy of integrating a simple fluidic control strategy into LFA. The strategy involves incorporating a piece of paper-based shunt and a polydimethylsiloxane (PDMS) barrier to the strip to achieve optimum fluidic delays for LFA signal enhancement, resulting in 10-fold signal enhancement over unmodified LFA. The phenomena of fluidic delay were also evaluated by mathematical simulation, through which we found the movement of fluid throughout the shunt and the tortuosity effects in the presence of PDMS barrier, which significantly affect the detection sensitivity. To demonstrate the potential of integrating this strategy into a LFA with sample-in-answer-out capability, we further applied this strategy into our prototype sample-to-answer LFA to sensitively detect the Hepatitis B virus (HBV) in clinical blood samples. The proposed strategy offers great potential for highly sensitive detection of various targets for wide application in the near future.

Janus particles with asymmetric crystals show great importance in optoelectronics and photocatalysis, but their synthesis usually requires complicated procedures. Here, an unexpected Janus vitrification phenomenon is observed in a droplet caused by the Leidenfrost effect at a cryogenic temperature, which is commonly regarded as symmetric. The Leidenfrost phenomenon levitates the droplet when it comes in contact with liquid nitrogen causing different cooling conditions on the droplet's top and bottom surfaces. It induces asymmetric crystallization in the droplet, forming a Janus vitrified particle with an asymmetric crystallization borderline after cooling, as further evidenced by cryotransmission electron microscopy (cryo-TEM) experiments. Theoretical analysis and experimental study indicate that the position of the asymmetric crystallization borderline is determined by the droplet radius and density, and the observation window of asymmetric crystallization borderline is determined by the chemical concentration. The finding reveals the asymmetric crystallization phenomenon in droplet vitrification for the first time, and provides a new insight for creating Janus particles through the Leidenfrost phenomenon.

To improve the cooling performance of disc brake systems, cross-drilled holes penetrating across the rubbing discs are separately introduced into a commercial radial vane brake disc (as reference) and a novel X-lattice cored brake disc. Prototype samples of both the reference and cross-drilled brake discs are fabricated. A rotating test rig is designed and constructed to characterize and compare the cooling performance of the brake discs with infrared thermography. Within the typical operating range of a vehicle, e.g., 200–1000 rpm, the experimental results show that the introduction of cross-drilled holes can substantially enhance brake disc cooling. For the radial vane brake disc, the overall Nusselt number is enhanced by 31%–44%; for the X-lattice cored brake disc, the cross-drilled holes only lead to 9%–18% enhancement. As the radial vane brake disc and the X-lattice cored brake disc with cross-drilled holes exhibit similar cooling performance, flow through the cross-drilled holes has a more prominent effect on the former than the latter. Corresponding fluid flow and heat transfer mechanisms underlying the enhanced heat transfer by cross-drilled holes and the different effects of cross-drilled holes on the two distinct brake discs are explored. The experimental comparison and the thermo-fluidic physics presented in this paper are beneficial for engineers to further improve disc brake cooling.

Due to contrast deficiency and blurred details in some low-light images, this paper presents a low-light image enhancement method using multi-layer fusion and detail recovery. Firstly, V channel in HSV color space is copied to three layers: Retinex layer, brightness layer and detail layer. In Retinex layer, the combination of weighted guided image filtering and morphology eliminates halo phenomenon. Meanwhile brightness and details of images are enhanced by the improved Retinex. Adaptive normalization is adopted to enhance brightness further in brightness layer. In detail layer, the improved model of local linear is to obtain more details. Finally, a detail recovery based on pixel arrangement is performed to avoid partial fuzzy details caused fusion. Experimental results show that the proposed method can more effectively highlight image details and improve the contrast.

Lateral flow assays (LFAs) have been extensively explored in nucleic acid testing (NAT) for medical diagnostics, food safety analysis and environmental monitoring. However, the amount of target nucleic acid in a raw sample is usually too low to be directly detected by LFAs, necessitating the process of amplification. Even though cost-effective paper-based amplification techniques have been introduced, they have always been separately performed from LFAs, hence increasing the risk of reagent loss and cross-contaminations. To date, integrating paper-based nucleic acid amplification into colorimetric LFA in a simple, portable and cost-effective manner has not been introduced. Herein, we developed an integrated LFA with the aid of a specially designed handheld battery-powered system for effective amplification and detection of targets in resource-poor settings. Interestingly, using the integrated paper-based loop-mediated isothermal amplification (LAMP)-LFA, we successfully performed highly sensitive and specific target detection, achieving a detection limit of as low as 3 × 10(3) copies of target DNA, which is comparable to the conventional tube-based LAMP-LFA in an unintegrated format. The device may serve in conjunction with a simple paper-based sample preparation to create a fully integrated paper-based sample-to-answer diagnostic device for point-of-care testing (POCT) in the near future.

The melting process of phase change material (PCM) infiltrated in a finned metal foam was numerically investigated using two approaches: (a) pore-scale and (b) volume-averaged numerical simulations. The pore-scale simulation modeled the intricate geometry of the open-cell metal foam using sphere-centered tetrakaidecahedron and coupled the heat transfer in foam/fin solids with that in the PCM. The volume-averaged simulation used the Darcy–Brinkman–Forchheimer model to account for the motion of melt PCM as well as the one-temperature model based on local thermal equilibrium assumption. The volume-averaged simulation results were compared with the pore-scale simulation results which were used as the benchmark. Reasonable agreement between prediction results of the two approaches was observed. When using the volume-averaged method, the one-temperature model may be applicable without needing the more complicated two-temperature model. The thermal performance of the finned metal foam was compared with conventional plate-fin and metal foam structures, demonstrating its superiority as thermal conductivity enhancer of PCM.

Honeycomb structures, inspired from bee honeycombs, had found widespread applications in various fields, including architecture, transportation, mechanical engineering, chemical engineering, nanofabrication and, recently, biomedicine. A major challenge in this field is to understand the unique properties of honeycomb structures, which depended on their structures, scales and the materials used. In this article, we presented a state-of-the-art review of the interdisciplinary efforts to better understand the design principles for products with honeycomb structures, including their fabrication, performance (e.g., mechanical, thermal and acoustic properties) as well as optimization design. We described how these structural perspectives have led to new insights into the design of honeycomb structures ranging from macro-, micro- to nano-scales. We presented current scientific advances in micro- and nano-technologies that hold great promise for bioinspired honeycomb structures. We also discussed the emerging applications of honeycomb structures in biomedicine such as tissue engineering and regenerative medicine. Understanding the design principles underlying the creation of honeycomb structures as well as the related scientific discovery and technology development is critical for engineering bioinspired materials and devices designed based on honeycomb structures for a wide range of practical applications.

Objective: Moxibustion therapy achieves satisfactory therapeutic effects largely depending on the heat stimulation of burning moxa. Understanding the thermal characteristics of heating process is an effective way to reveal the underlying mechanisms of moxibustion therapy. Methods: This paper performs experimental study on temperature distributions of burning moxa sticks and fresh in vitro porcine abdominal tissue using an infrared camera and thermocouples. Meanwhile, a moxibustion model incorporating moxa stick burning model and tissue heat transfer model was established with consideration of radiation propagation and water evaporation. Results: The burning features of moxa sticks were acquired and the radiation energy generated by the burning moxa stick was absorbed and scattered in biological tissue, resulting in a large temperature gradient in the skin layer. And the water evaporation led to a mass loss and reduced skin surface temperature. The numerical model was verified by experimental results and the effects of moxibustion treatment distance and duration can be quantified based on model calculation. Conclusion: The detailed heat transfer process of moxibustion was obtained experimentally and numerically. During moxibustion, the radiation attenuation and water evaporation have a significant influence on the energy transport in biological tissue which cannot be ignored. The treatment distance of 3 cm is the recommended value to achieve the treatment efficacy without thermal damage and pain. Significance: This research would reveal the underlying mechanisms of moxibustion therapy. Besides, the developed models are expected to establish a guideline for moxibustion clinical treatment.

Forced convective heat transfer in lightweight sandwich-walled cylinders with quadrangle core (I type) and triangle cores (V, N, W and M type) was investigated experimentally, numerically and theoretically, targeting multifunctional applications (e.g., combustion chamber) requiring simultaneous load bearing and heat dissipation. Sandwich-walled cylinder with the N type core was fabricated using 3D-printing technology. Forced convection experiments were carried out to validate numerical simulation results and to reveal varying flow stages in the channels of the sandwich wall. Flow in these channels changed from laminar (Re 4100) as the Reynolds number was increased. With the total heat dissipation area fixed, the heat transfer performance of the quadrilateral core (I type) was better than triangular cores (V, N, W and M type). Among the triangular cores, those with homogeneous pore structure (V and N) exhibited superior heat transfer performance in comparison with the nonhomogeneous ones (W and M type). The optimal number of unit cells for each core type was determined using the theory of intersection-of-asymptotes. With the unit cell number optimized for each core, the I core exhibited the best heat dissipation performance while the M core had the worst. Under structural loading, however, the buckling resistance of the I core was not as good as the triangular ones. Thermal and mechanical synergy must be considered in the selection of sandwich core topology for multifunctional applications.

Nitrocellulose membrane (NC), as a paper-like matrix with microscale porous structures, has found widespread applications in biomedical fields due to its excellent biological features and physiochemical properties. In these biomedical applications, diffusion, convection, and binding reaction of biomolecules (e.g., acids and proteins) in NC through wicking flow is the fundamental physical process. However, the optimization of NC based biomedical devices has been limited by the lack of the understanding on the wicking flow behavior of NC membranes from the microstructural point of view. To address this, we experimentally and theoretically investigated the microstructural effects on the wicking flow behaviors (e.g., permeability, effective pore radius) of NC membrane and found that the wicking flow is highly dependent on the pore-morphology characterizing parameters (e.g., porosity and pore size). We further developed a theoretical model yielding a closed-form solution to predict the microstructure-permeability relation, which was validated by our experimental results. Our theoretical model would be a powerful tool for tailoring the wicking flow behavior of NC membranes through controlling the microstructural parameters, and thus for optimizing NC membrane-based biomedical devices from the view point of material design in the future.

A three-dimensional tubular exhaust reformer was investigated to study the effects of EGR ratio and the amount of the steam addition on the methane-exhaust gas reforming process under different excess air coefficients. The objective was to maximize hydrogen production economically, by regulating the amount of exhaust gas and the steam addition at the inlet of the reaction tube with the amount of methane addition fixed. Coupled with the detailed catalytic reaction mechanism based on Rh-Al2O3 catalyzer, the exhaust gas reforming process in a fixed bed reactor was simulated by using a porous media model. The results showed that, in the entry region of the reaction zone, oxidation reaction dominates with significant heat release; whilst after the entry region steam reforming reaction dominates with heat absorbing. The exhaust gas outside the reaction tube played the role of preheating the mixture before the reaction zone and heat preservation in the reaction zone. Results showed that with the methane addition fixed, there is an optimum M/O value (about 2) and W/M value (about 1.25) for maximum hydrogen production. In addition, the surface coverage ratio of coke deposit in the reaction bed decreases with the increase of EGR ratio and steam addition.

This paper presents a combined experimental and numerical study on finned metal foam (FMF) and metal foam (MF) heat sinks under impinging air jet cooling. Experiments were conducted on aluminum foams of 96.3% porosity and 8 PPI (pores per inch) with four 2 mm-thickness plate fins. Different foam heights were tested at varying Reynolds numbers. Experimental results show that under a given flow rate condition, as the foam height increases, the heat transfer of MF heat sinks decreases monotonously whilst that of FMF heat sinks first increases and then slightly decreases. Under a given pumping power condition, the heat transfer of MF heat sinks is insensitive to the foam height whilst that of FMF heat sinks increases as the foam height increases. Under either a given flow rate or a given pumping power condition, the heat transfer of FMF heat sinks can be 1.5–2.8 times that of the MF heat sinks having the same height. A numerical model was also developed to simulate the conjugated heat transfer between plate-fins and metal foams in FMF heat sinks. The influence of the bonding material between metal foams and plate-fins as well as the inlet thermal boundary condition were discussed in detail using the numerical model. Comparisons of experimental and numerical results reveal that using the laminar Darcy’s extended model can predict fairly both the heat transfer and pressure drop of MF and FMF heat sinks under high Reynolds numbers if the foam properties are given correctly.

PurposeThe purpose of this paper is to present a porous medium model for forced air convection in pin/plate‐fin heat sinks subjected to non‐uniform heating of a hot gas impinging jet. Parametric studies are performed to provide comparisons between inline square pin‐fin and plate‐fin heat sinks in terms of overall and local thermal performance for a fixed pressure drop.Design/methodology/approachHeat conduction in substrates is coupled with forced convection in the pin/plate‐fin flow channel. The forced convection is considered by employing the non‐Darcy model for fluid flow and the thermal non‐equilibrium model for heat transfer. A series of experiments is performed to validate the model for both the pin‐fin and plate‐fin heat sinks.FindingsThe present porous medium model is capable of capturing the presence of lateral heat spreading in the plate‐fins and the absence of lateral heat spreading in the pin‐fins under non‐uniform thermal boundary condition, attributing to the adoption of the orthotropic effective thermal conductivity for the solid phase in the energy equation. The present results show that the inline square pin‐fin heat sink has topological advantage over the plate‐fin heat sink, although the heat spreading through the plate‐fins on reducing the peak temperature on the substrate is pronounced.Originality/valueThis paper reports an original research on theoretical modeling of forced convection in pin/plate‐fin heat sinks subjected to the non‐uniform heating of an impinging jet.

The identification and quantification of chemicals play a vital role in evaluation and surveillance of environmental health and safety. However, current techniques usually depend on costly equipment, professional staff, and/or essential infrastructure, limiting their accessibility. In this work, we develop paper-based capacitive sensors (PCSs) that allow simple, rapid identification and quantification of various chemicals from microliter size samples with the aid of a handheld multimeter. PCSs are low-cost parallel-plate capacitors (~$0.01 per sensor) assembled from layers of aluminum foil and filter paper via double-sided tape. The developed PCSs can identify different kinds of fluids (e.g., organic chemicals) and quantify diverse concentrations of substances (e.g., heavy metal ions) based on differences in dielectric properties, including capacitance, frequency spectrum, and dielectric loss tangent. The PCS-based method enables chemical identification and quantification to take place much cheaply, simply, and quickly at the point-of-care (POC), holding great promise for environmental monitoring in resource-limited settings.

The Leidenfrost phenomenon of liquid droplets levitating and dancing when placed upon a hot plate due to propulsion of evaporative vapor has been extended to many self-propelled circumstances. However, such self-propelled Leidenfrost devices commonly need a high temperature for evaporation and a structured solid substrate for directional movements. Here we observed a “cold Leidenfrost phenomenon” when placing a dry ice device on the surface of room temperature water, based on which we developed a controllable self-propelled dry ice hovercraft. Due to the sublimated vapor, the hovercraft could float on water and move in a programmable manner through designed structures. As demonstrations, we showed that the hovercraft could be used as a cargo ship or a petroleum contamination collector without consuming external power. This phenomenon enables a novel way to utilize programmable self-propelled devices on top of room temperature water, holding great potential for applications in energy, chemical engineering and biology.

In recent years, paper-based point-of-care testing (POCT) has been widely used in medical diagnostics, food safety and environmental monitoring. However, a high-cost, time-consuming and equipment-dependent sample pretreatment technique is generally required for raw sample processing, which are impractical for low-resource and disease-endemic areas. Therefore, there is an escalating demand for a cost-effective, simple and portable pretreatment technique, to be coupled with the commonly used paper-based assay (e.g. lateral flow assay) in POCT. In this review, we focus on the importance of using paper as a platform for sample pretreatment. We firstly discuss the beneficial use of paper for sample pretreatment, including sample collection and storage, separation, extraction, and concentration. We highlight the working principle and fabrication of each sample pretreatment device, the existing challenges and the future perspectives for developing paper-based sample pretreatment technique.

This paper presents a combined experimental and theoretical study on the fundamental thermomechanical properties of high-porosity, wire-woven bulk Kagome (WBK) cellular cores fabricated using a newly developed technique. Particular focus is placed upon the influence of brazing on the strength, forced air convection characteristics, and effective thermal conductivity of thematerial. Upon uniaxial compressive loading, brazing of the WBK joints increases the core strength more than 10 times compared with that without brazing. Thermally, althoughbrazinghas no effect on the effective thermal conductivity, it leads to significantly enhanced heat dissipation under forced convection. In the absence of fluid flow, heat spreading along the lateral ligaments plays no part in conduction, whereas the tortuous ligaments along the direction of conduction act to reduce the effective conductivity. However, under forced convection, the activation of convection from the lateral ligaments as a result of brazing leads to pronounced enhancement of the overall heat dissipation capability.

A thermal resistance analysis for pin-fin heat sinks subjected to nonuniform flame impinging-jet heating is presented. Explicit analytical expression of the overall total resistance is obtained by evaluating each of the individual thermal resistances in the circuit, including the spreading resistance, the material resistance, the convective resistance, and the resistance due to fluid temperature rise. Upon modeling the nonuniform heat flux distribution over the entire upper surface of the substrate due to flame impinging-jet heating with an exponential function, the spreading resistance within a circular plate is obtained analytically. To verify the assumptions/approximations made in the analogy model, the results predicted by the thermal resistance analogy model are compared with those obtained from a three-dimensional numerical model, with overall good agreement achieved. The interaction of heat conduction in the substrate and heat convection in the fluid flow is then investigated using the analogy model. Obtained results demonstrate that increasing the rate of convection heat transfer decreases the spreading resistance in the substrate. Furthermore, an optimal substrate thickness is found to exist when the lateral spreading of heat in the substrate is balanced by that conducted through the thickness direction of the substrate.

The flow and temperature fields caused by a two-dimensional heating air jet obliquely impinging on a flat plate are experimentally characterized. Whilst the jet flow is discharged at Re Dh = 8.2 × 10 3 based on the hydraulic diameter of the orifice, D h , and the jet exit-to-plate spacing (separation distance) is fixed at 8 D h , the impingement angle (inclination) is systematically decreased from 90° (normal impinging) to 30° (oblique impinging). A separate experiment is carried out for a two-dimensional cooling jet obliquely impinging on a heated plate (constant heat flux). The results demonstrate that the response of local surface temperature to plate inclination behaves in a completely different manner. For impinging jet cooling, the inclination (from normal impinging position) reduces the local effective temperature values at corresponding points about actual stagnation point, inclusive of it. For impinging jet heating, the inclination causes, conversely, an increase in local surface temperature including the stagnation point temperature. However, the shifting of the actual stagnation point towards the uphill side of the plate is consistently observed for both hot and cold jet cases. This newly found feature for an obliquely impinging jet is attributed to the combined effects of asymmetric entrainment and momentum redistribution (i.e., thickening/thinning of hydraulic boundary layers on each side of the plate with respect to the actual stagnation point).