Non-heated Surface Research Articles

Multifunctional and recyclable aerogel/fiber building insulation composites with sandwich structure

Fire, electromagnetic (EM) pollution, and sustainability require building insulation with fire resistance, EM interference shielding, and recyclability. However, fewer building insulation materials can fulfill these multifunctional requirements. Here, we report a multifunctional building thermal insulation material with a sandwich structure that uses SiO2 aerogel powder as the insulating filler phase, α-Al2O3 fiber as the refractory reinforcing phase, and carbon fiber mat (CFF) as the electromagnetic interference shielding layer prepared by the mixing-pressing-drying method. The effects of different SiO2 aerogel power contents on fire resistance, thermal insulation, and hydrophobicity, the effects of different carbon fiber contents on EMI performance, and the effects of CFF as an interlayer on compressive strength and recyclability were investigated. The results demonstrated exceptional fire resistance properties and low thermal conductivity (0.0529 W/m·K) with a SiO2 aerogel powder content of 11.2 wt%. Specifically, the structure of the aerogel/fiber composite remains intact and the temperature of the non-heated surface is lower than 75.8 ℃ after 4 min of continuous flame combustion. It can achieve a commercial shielding standard of 20 dB at a carbon fiber content of 5 wt%. In addition, CFF as interlayers can effectively improve the compression strength of the material and solve the problem of difficult recycling of carbon fiber. In conclusion, this sandwich structure of multifunctional aerogel/fiber composites provides new ideas for the manufacture of fire resistance, energy-saving, EM-protection, and recyclable building insulation materials.

Determining the thermal-physical characteristics of a coke foam layer in the fire protection of cable articles with foaming coating

An issue related to using cable products for building structures is to ensure their stability and durability when operating within wide limits. Therefore, the object of research was a change in the properties of the polymer sheath of the cable during the formation of a swollen coating layer under the influence of high temperature. It is proved that in the process of thermal action on the flame retardant coating, the process of thermal insulation of the cable involves the formation of particulate products on the surface of the sample. Under the action of the burner flame, a temperature was reached on the surface of the sample, which led to a swelling of the coating of more than 16 mm. The measured temperature on the inverse surface of the sample was no more than 160 °C, which indicates the formation of a barrier for temperature. In this regard, a calculation and experimental method for determining thermal conductivity when using a flame retardant as a coating has been developed, which makes it possible to estimate the coefficients of temperature conductivity and thermal conductivity under high-temperature action. According to the experimental data and established dependences, the coefficients of temperature conductivity and thermal conductivity of wood were calculated, which are 214.4·10–6 m2/s and 0.62 W/(m∙K), respectively, due to the formation of a heat-insulating swollen layer. The maximum possible temperature penetration through the thickness of the coating was assessed. A temperature was created on the surface of the sample, which significantly exceeds the ignition temperature of the polymer sheath of the cable, and, on a non-heated surface, does not exceed 160 °C. Thus, there is reason to argue about the possibility of directed adjustment of the fire protection processes of an electrical cable by using coatings capable of forming a protective layer on the surface of the material, which inhibits the rate of heat transfer.

Defining patterns of heat transfer through the fire-protected fabric to wood

Under the thermal action on wood when applying a protective screen made from fire-retardant fabric, the process of temperature transfer is natural. It has been proven that depending on the thermal properties of the coating of fire-proof fabric, this could lead to varying degrees of heat transfer. Therefore, it becomes necessary to study the conditions for establishing low thermal conductivity and establishing a mechanism that inhibits heat transfer to wood. Given this, a mathematical model has been built of the process of heat transfer to wood when it is protected by a screen made of fire-proof fabric. According to the experimental data on determining the temperature on the non-heated surface of the fabric and the resulting dependences, the density of the heat flow transmitted to wood through fire-proof fabric was determined. Thus, with an increase in the temperature, the density of the heat flow to the surface of the wood through a protective screen made of fire-proof protected coating based on "Firewall-Attic" increases to a value above 16 kW/m2, which is not sufficient for ignition of wood. Instead, the density of the heat flow through the protective screen of fire-proof fabric protected by the "Firewall-Wood"-based coating did not exceed 14 kW/m2. This makes it possible to argue about the compliance of the detected mechanism of formation of heat-insulating properties in the protection of wood and the practical attractiveness of the proposed technological solutions. Thus, the peculiarities of inhibition of the process of heat transfer to wood through a protective screen made of fire-proof fabric under the action of a radiation panel imply the formation of a heat-insulating layer of coked cellular material when decomposing the coating. Thus, on the surface of the fire-proof fabric, a temperature above 280 °C was achieved and, on an untreated surface of the fabric, it did not exceed 220 °C, which is insufficient for the ignition of wood.

Effect of rheology and interfacial tension on spreading of emulsion drops impacting a solid surface

This paper presents an experimental and theoretical study of Newtonian and non-Newtonian (Bingham plastic) emulsion drop impact on a solid non-heated surface. The utilization of different emulsifiers at a constant concentration of continuous and dispersed phases in emulsions allows the considerable variation of the surface tension at the liquid–liquid interface. Our data for the maximum spreading diameter of water, n-decane, and emulsion drops impacting on a surface are compared with that predicted from the existing models for single-phase liquid drops. All selected models underpredict the experimental data. As a result, the importance of considering the capillary effects at the internal interfaces of the emulsion drops and the careful examination of all rheological properties in the case of Bingham plastic fluids is confirmed experimentally and is taken into account theoretically. The models of Pasandideh-Fard et al. [“Capillary effects during droplet impact on a solid surface,” Phys. Fluids 8, 650 (1996)] and Ukiwe and Kwok [“On the maximum spreading diameter of impacting droplets on well-prepared solid surfaces,” Langmuir 21, 666–673 (2005)] are modified and adapted to the emulsion drop by means of including the additional surface energy term at the liquid–liquid interface of the emulsion drop in the energy conservation equation and the non-Newtonian Reynolds number. The predictions of the maximum spreading diameter give good agreement with the measured one. Several constraints and future lines of research that relate to a specific behavior of the compound liquid drops at the impact on a solid surface are highlighted.

Thermophysical characteristics of the formed layer of foam coke when protecting fabric from fire by a formulation based on modified phosphorus-ammonium compounds

This paper reports the analysis of flame retardants for fabrics that has established that the meagerness of the data that explain and describe the process of fire protection, as well as the neglect of elastic coatings, leads to the combustion of structures made from fabrics under the influence of flame. The development of reliable methods to study the fire protection conditions for fabrics leads to the design of new types of fireproof materials. Therefore, it becomes necessary to define the conditions for the formation of a barrier for burning and flame propagation by a piece of fabric and for establishing a mechanism that would inhibit a temperature transfer to the material. To address this issue, an estimation-experimental method has been devised for determining thermal conductivity when using a fire protection agent as a coating, which makes it possible to assess the thermal conductivity coefficient under the effect of high temperature. Based on the experimental data and theoretical dependences, the coefficient of thermal conductivity for the fire-resistant layer of foam coke was calculated, 0.034 W/(m∙K), which, accordingly, ensures the heat resistance of the fabric. The study results have proven that the process of the thermal insulation of fabric involves the formation of soot-like products at the surface of the sample. The inhibition of the process of heat transfer to the material treated with a composition based on modified phosphorus-ammonium compounds is characterized by the formation of a heat-protective layer of coke at the surface of the fabric. The maximum possible penetration of temperature through the thickness of the coating has been estimated. At the surface of the sample, a temperature was generated that significantly exceeds the ignition temperature of the fabric, and, at the non-heated surface, does not exceed 150 °C. Thus, there is reason to assert the possibility of targeted adjustment of fire protection processes in the fabric by applying coatings that can form a protective layer on the surface of the material, which inhibits the rate of heat transfer

Heat and Fluid Flow Characteristics of Nanofluid in A Channel Baffled Opposite to The Heated Wall

In this paper, a nanofluid-based solar collector duct equipped with baffles is examined numerically. Baffles are located on the back plate to guide nanofluid flow toward absorber plate for heat transfer enhancement purposes. Cu-water nanofluid with fixed flow rate and concentration in the baffled duct are investigated for thermohydraulic mechanisms. Baffles with different inclination angles, heights and pitches are considered in this study. Numerical simulations are performed using Ansys fluent software with verified results compared to those of an experiment in the literature. The results show that the baffle angle 60° causes the lowest thermohydraulic performance. Because in the angle range of 30 to 60° the heat transfer is less variable while the pressure loss increases sharply. At the baffle pitch of 40 mm, there is no reattachment point at the non-heated surface. At the angle of 90°, three eddies are formed around a baffle. The slope linear regression analysis yields that baffle height has the strongest effects on thermohydraulic performance followed by baffle pitch and baffle angle. Nanofluid pressure loss respectively increases with baffle height and baffle angle at the rate of 0.463675 and 0.0049607 while absorber plate temperature respectively decreases with the baffle height and baffle angle at the rate of -0.176746 and -0.001377. Flow patterns and isotherms of all the cases examined are presented and analyzed in this study.

Computational fluid-dynamics-based simulation of heat transfer through vacuum glass

The heat transfer process of vacuum glass is very complicated. In particular, the heat transfer process of functional vacuum glass, which includes the coupling of heat conduction, convection, and radiation, does not have an exact mathematical solution. The most important parameter representing the thermal properties of vacuum glass, the heat transfer coefficient, is difficult to measure online because it increases over time, thereby decreasing the thermal-insulation performance. Thus, measuring it quickly and accurately for a vacuum glass in use is difficult. This study was conducted to develop an efficient method to simulate heat transfer through vacuum glass. To this end, based on advanced numerical-simulation technology, a computational fluid dynamics software was used to analyse the heat transfer process, and the simulation results applied to guide and analyse the non-steady-state test method. It was found that when a circular heating plate is used to heat the side of the vacuum glass, the ratio of the radius of the heating plate to the thickness of the vacuum glass should exceed three. This approach guarantees that the centre of the heating plate undergoes one-dimensional heat transfer, and the temperature measurement at the centre of the non-heated surface is of practical significance.

Vacuum-formed mouthguard fabrication to obtain proper fit using notched sheet.

Mouthguards should be provided with appropriate thickness and proper fit to exert their effects. However, mouthguard thickness becomes thinner after forming. The aim of this study was to examine the effect of using a notched mouthguard sheet and forming as the heated surface of the sheet contacts the surface of the working model. The material used was a 3.8-mm-thick Sports Mouthguard. Notches with a length of 90 and 80mm were cut into an ethylene vinyl acetate sheet 20mm from the anterior and posterior margins and 15mm from the right and left margins, respectively, and the sheet was compared with the original. The sheets were then formed using a vacuum former. Original and notched sheets were heated until the temperature of the sheet reached 80°C, and the non-heated surface of the sheet was sucked down over the model. Both sheets were also heated at first until the sheet temperature reached 80°C, then turned upside down, and the heated surface of the sheet was sucked down over the model. The thickness and fit of the mouthguard were measured at the central incisor and first molar. Differences in thickness and fit according to the measurement parts and the sheet conditions were analyzed by two-way ANOVA. The thickness of the mouthguard significantly differed by the measurement parts and the sheet conditions (P<0.01), and the notched sheet maintained the required thickness. Fit differed between the measurement parts and the sheet conditions (P<0.01), and the sheets formed as the heated surface contacted the working model showed better fit. These results suggest that the ideal mouthguard with appropriate thickness and proper fit can be fabricated by notching a sheet and contacting the heated surface of the sheet to the working model.

Self-Sorting of Bidispersed Colloidal Particles Near Contact Line of an Evaporating Sessile Droplet.

Here, we investigate deposit patterns and associated morphology formed after the evaporation of an aqueous droplet containing mono- and bidispersed colloidal particles. In particular, the combined effect of substrate heating and particle diameter is investigated. We employ high-speed visualization, optical microscopy, and scanning electron microscopy to characterize the evaporating droplets, particle motion, and deposit morphology, respectively. In the context of monodispersed colloidal particles, an inner deposit and a typical ring form for smaller and larger particles, respectively, on a nonheated surface. The formation of the inner deposit is attributed to early depinning of the contact line, explained by a mechanistic model based on the balance of several forces acting on a particle near the contact line. At larger substrate temperature, a thin ring with inner deposit forms, explained by the self-pinning of the contact line and advection of the particles from the contact line to the center of the droplet due to the Marangoni flow. In the context of bidispersed colloidal particles, self-sorting of the colloidal particles within the ring occurs at larger substrate temperature. The smaller particles deposit at the outermost edge compared to the larger particles, and this preferential deposition in a stagnation region near the contact line is due to the spatially varying height of the liquid-gas interface above the substrate. The sorting occurs at a smaller ratio of the diameters of the smaller and larger particles. At larger substrate temperature and larger ratio, the particles do not get sorted and mix into each other. Our measurements show that there exists a critical substrate temperature as well as a diameter ratio to achieve the sorting. We propose regime maps on substrate temperature-particle diameter and substrate temperature-diameter ratio plane for mono- and bidispersed solutions, respectively.

Simultaneous estimation of thermal properties of orthotropic material with non-intrusive measurement

This article presents a simple in-house laboratory experiment method for the simultaneous estimation of principal thermal conductivity and specific heat capacity of an orthotropic composite with non-intrusive temperature measurement. The principle of method involves in symmetrical heating of two identical samples with a planar heater sandwiched in-between them and measuring the temperature of non-heated surface non-intrusively using IR camera. The forward problem that mimics the heat conduction from heater to sample and then to ambient is a 3-D transient conduction equation which is solved using finite volume method whereas inverse problem is solved using Levenberg-Marquardt algorithm. At first numerical estimations are carried out with synthetic temperature data to decide upon the parameters to be identified/fixed as well as to find optimal experimental variables. Then, using measured temperature response of the non-heated surface, the thermal properties of unidirectional fiber reinforced carbon composite are estimated. Induced bias errors in the estimated parameters because of error in the fixed parameters are also approximately quantified. The estimated transverse thermal conductivity is found to be 0.72 W/m K whereas the in-plane conductivities parallel and perpendicular to fiber are 5.43 W/m K, 0.64 W/m K respectively. Also, the estimated specific heat capacity is found to be 1044 J/kg K. A maximum deviation of 10% from the absolute Guarded Hot Plate measurement is found in the estimated thermal conductivity parallel to fiber.

Patterns from dried water-butanol binary-based nanofluid drops

In this work, the behavior of evaporating binary-based nanofluid sessile droplets deposited on a smooth silicon substrate at different temperatures is explored. The formation of deposition patterns during the evaporation is studied by tracking particle clusters using optical microscopy. Similarly to evaporation of pure water-based nanofluid droplets, three distinctive deposition patterns are left behind the complete evaporation: a relatively uniform coverage pattern (on a nonheated surface); a “dual-ring” pattern at higher temperature, i.e., 81 °C; and a “stick-slip” pattern at 99 °C. Infrared thermography technique was employed to visualize the evolution of thermal patterns on the surface of the drying droplets. Thermal imaging shows that the evaporation of binary mixture droplets can be classified into three regimes. In the first regime, multiple convection vortices can be observed at the droplet interface, corresponding to the chaotic motion of nanoparticles captured by video microscopy. This flow regime is believed to be driven by surface tension gradients arising from local concentration gradients. As evaporation time proceeds, the number of convection vortices decreases in regime I, and a few numbers of those are left in the second regime. The flow slows down and a rapid transition (the second regime) occurs; this is followed by the last regime. At the two highest temperatures of 81 and 99 °C, the end of the transition regime is associated with the existence of two distinctive counter-rotating vortices. For the third regime, the results from both infrared thermography and video microscopy show identical behavior to those of water-based nanofluid droplets at the same substrate temperatures. This reveals that most of the more volatile component (not all) has evaporated after the first two regimes; hence, the solutal Marangoni driven by local concentration gradients is significantly weakened and has no further role in the flow structure in the last regime. Instead, the thermocapillary effect and continuity are the underlying reasons for the internal flow structure of the evaporating droplets during the last regime.

Optimal heating condition of mouthguard sheet in vacuum-pressure formation: part 3 styrene-based thermoplastic elastomer.

The aim of this study was to identify suitable heating conditions of polyolefin-polystyrene co-polymer sheets in vacuum-pressure formation, monitor the sheet temperature during molding, and examine the thickness of the fabricated mouthguard. Mouthguards were fabricated with polyolefin-polystyrene co-polymer sheets (4.0-mm thick) utilizing a vacuum/pressure-forming device, which was subjected to vacuum forming for 10 s and pressure molding for 2 min. Four heating conditions were compared, defined by the amount of sag distance of 5, 10, 15, or 20 mm from the center of the softened sheet below the clamp. The working model was trimmed to a height of 20 mm at the cutting edge of the maxillary central incisor and to a height of 15 mm at the mesiobuccal cusp of the maxillary first molar. The radiation thermometer was used to measure the sheet temperatures of the center of the heated and non-heated surfaces under each condition. The sheet thickness after fabrication was determined for the incisal and the molar portions, and dimensional measurements were obtained using a measuring device. The differences in the sheet thickness produced by the different heating conditions were analyzed by Games-Howell's multiple comparison tests. For condition of 5 mm sagged, the temperature on the non-heated surface did not reach a sufficient softening temperature and the thickness was smallest. Mouthguard thickness was largest in the order of 15 mm sagged condition, followed by 20 mm sagged condition and then by 10 mm sagged condition, but a statistical difference was not observed in the labial and the buccal surface among the three conditions. This study demonstrated that for sufficient softening, it was necessary to heat the sheet to obtain a sag of 10 mm or more, and that the mouthguard thickness decreased as the sag increased.

Heating methods for reducing unevenness softening of mouthguard sheets in vacuum-pressure formation.

Unevenness in softening of the plastic sheet leadsto a decrease in the mouthguard thickness during thermoforming. Inthis study, we examined the heating methods for reducing unevenness when softening mouthguard sheets during vacuum-pressure formation. Ethylene vinyl acetate mouthguard sheets and olefin copolymer sheets (thickness: 4.0mm) were used. The following three heating conditions were compared: condition A-the sheet was molded when it sagged 15mm from the sheet frame (under normal condition); condition B-the heater was turned off when the sheet sagged by 10mm from the frame, followed by the sheet molding when the sagging reached 15mm below the frame; and condition C-the sheet was inverted after heating when the sheet sagged 10mm and was molded when the sagging reached 15mm below the frame. The sheet was heated and pressed over the model using a vacuum-pressure machine; then, 10s of vacuum forming and 2min of pressure molding were applied. The sheet temperatures were measured using a radiation thermometer. Thickness of the fabricated sheets was determined for the incisal and the molar portion using a measuring device. Thickness data for each condition were analyzed by one-way anova followed by Bonferroni's multiple comparison tests. On both sheets, condition B was smallest for temperature difference between the heated and the non-heated surface, and thicknesses after molding were greatest at all measuring portions. By comparing changes in sheet temperatures at molding and variation in thicknesses when applying the heating method using a vacuum-pressure molding machine, we found that reduced unevenness in sheet softening occurred when the heater was turned off when the sag distance of the sheet was 5mm less than the conventional molding, and then, the sheet was pressed when the conventional sag distance was reached.

Method for effectively maintaining the thickness of mouthguards fabricated using EVA sheets and a circle tray: influence of grooved sheet and heating conditions.

The shapes of ethylene vinyl acetate (EVA) sheets are mainly square or round. The aim of this study was to elucidate a fabrication method that effectively maintains the thickness of the round sheet. Mouthguards were fabricated using EVA sheets (diameter 125 mm, thickness 4.0 mm) and a vacuum-forming machine. The sheet was pinched at the top and bottom and stabilized by the circle tray. Two heating conditions were compared: (i) the sheet was molded when it sagged 10 mm below the level of the sheet frame at the top of the post under normal conditions (N); and (ii) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use and molded when it sagged 10 mm from the sheet frame (L). Two EVA sheet shapes were compared: an ordinary sheet (O) and a sheet with a horizontal v-shaped groove 30 mm from the anterior end (G). The height of the working model was 20 mm at the incisor point and 15 mm at the first molar. The sheet temperatures of the heating and non-heated surface were measured by the radiation thermometer. Post-molding thickness was determined for the incisal and molar portion. Differences in the thickness were analyzed using two-way anova. The temperature difference among points was smaller under condition L than under condition N. Thickness after formation was higher in condition L than in condition N, and was higher in condition G than in condition O. At the labial surface and the cusp, L-G was thickest. With the present techniques, uneven softening during heating can be improved by lowering the sheet frame and consequently reducing the reduction in the thickness of the sheet. Additionally, the thickness reduction is reduced by creating a horizontal groove on the sheet, establishing the clinical efficacy of this method.

Droplet First and Second Consecutive Impacts and Droplet–Droplet Collision on a Hot Surface in the Film Boiling Region

We studied experimentally the behavior of a single cold water droplet that falls onto a hot horizontal flat solid surface in the film boiling region. We found that when the droplet hits the surface (for the first time), three different regimes may occur. These regimes depend on the ratio of fluid's inertia and its surface tension (the Weber number, indicated as We) and on the surface temperature. For relatively low We numbers or surface temperatures, the droplet completely bounces back from the surface and no breakup occurs. For intermediate We numbers or surface temperatures, the spreading stage is faster and the droplet undergoes spreading and partial recession before it breaks up into bouncing small secondary droplets that leap inward and successively coalesce above the surface to form a single droplet once again. For high We numbers or surface temperatures, the spreading velocity is higher, the contact area with the surface is greater, and the liquid film thickness is smaller. Thus, during the expansion of the spreading stage, the droplet breaks up into bouncing small secondary droplets that uninterruptedly leap outward and travel independently. We also present the limiting conditions differentiating between the different behaviors found. This work shows droplet film boiling behaviors that are essentially different than droplet levitation on top of a thin vapor layer, as mainly assumed in theoretical models. We also observed that when a droplet hits the surface for the second, consecutive time (and on), the droplet behaves somewhat differently due to its preheating, very low impact velocity, different shape, spin, orientation, and the surface temperature. At the second impact on the surface (and on), the droplet can continue its bounce in a unique and different manner than in the first impact or it can explode violently to small secondary droplets. Both are unique and differentiating mainly by the droplet's shape and orientation at the exact moment of impact on the surface. Additionally, a rare and unique view of droplet–droplet collision during film boiling is presented. This type of collision behaves in a different way than other droplet–droplet collisions and compared to the adiabatic case of droplet–droplet collision on a nonheated surface. The behaviors found, presented, and discussed in this study change our view of the droplet–surface and droplet–droplet interactions that occur in spray cooling in the film boiling region.

PIV Measurements and POD Analysis during Natural Convection with Protruded Heater in a Rectangular Enclosure

An extensive measurement using 2-D Particle Image Velocimetry (PIV) technique has been carried out during natural convection with a heating sources protruded on the non-heated lower surface of a rectangular enclosure. A time-resolved data series have been captured to analyse the effect of different Rayleigh number on flow fields for fluid of Prandtl number 0.71. A fast and efficient data analysis tool based on the Proper Orthogonal Decomposition (POD) technique has been used to create low dimensional approximations of high dimensional systems for predicting the dominant flow structures. This includes interpolating results at off-design parameters, along with knowledge about contours of different higher modes as well as obtaining information about the energy content in each specific mode. The mean non fluctuating mode showed maximum energy and the same decreased with increasing mode number. This allowed a clear detailed understanding about the complex non-linearities in the problem using a linear decomposition technique

Inertia effect on thermal shock by laser beam shot

A stress wave generates and propagates in a beam window, a target container and solid target plates of the target system for neutron spallation source because of a thermal shock induced by an injection of a high-intensity proton beam. In this study, a thermal shock experiment was carried out using a ruby laser to investigate the behavior of the stress wave propagation. Numerical analyses on the stress waves induced by the thermal shock were carried out. It was confirmed that tensile stress waves were generated at the border of the heated area because of the inertia effect of the propagation of compressive stresses to outside of the heated area associated with the thermal shock. Subsequently the tensile stress waves concentrate at the center of the non-heated surface to become large. These trends are adequately supported by the numerical results.

Numerical simulation of convective heat transfer to a radial free surface jet impinging on a hot solid

The convective heat transfer between a circular free surface impinging jet and a solid surface has been studied numerically. The thin liquid film formed on the surface has been assumed to be in non-turbulent free surface flow. The effects of surface tension, viscosity, gravity and heat transfer between the film flow and the solid surface have been taken into account. The flow structure on a non-heated surface has been investigated first. Next, the steady-state flow structure in the liquid film as well as the heat transfer has been examined. The predicted results have been compared with experimental data for the purpose of validating the analysis. The hydrodynamics of the liquid film and the heat transfer processes have been investigated numerically to understand the physics of the phenomena.

Loss of blood platelet adhesion after heating native and cultured human subendothelium to 100 Celcius

Balloon angioplasty produces mechanical vessel wall injury that leads to substantial blood platelet deposition at the angioplasty site. The aim of the study was to determine whether thermal angioplasty might, by contrast, reduce platelet adhesion by denaturation of subendothelial adhesive proteins. Native and cultured human subendothelium was briefly heated to greater than or equal to 100 degrees C by laser irradiation or to 50-100 degrees C by immersion in preheated phosphate buffered saline (PBS). Subsequently, the subendothelium was exposed for 5 min to flowing human blood at a shear rate of 1300 s-1. Blood platelet adhesion to the subendothelium was determined quantitatively. Human umbilical arteries were used and the subendothelial matrix derived from cultured umbilical vein endothelial cells. After heating arterial subendothelium by laser irradiation to greater than or equal to 100 degrees C, zero platelet adhesion was found v 36(SD 2)% adhesion to the non-heated surface (p less than 0.001). After laser heating of the subendothelial matrix to greater than or equal to 100 degrees C, platelet adhesion was absent in 10/10 experiments (p less than 0.01). After heating the matrix to 100 degrees C by immersion in PBS, platelet adhesion was reduced to 5(5)% v 31(7)% at 37 degrees C (p less than 0.001). These in vitro results, if extrapolated to catheter interventions, suggest that thermal injury to the vessel wall by laser angioplasty or other thermal angioplasty methods may provide a basic and clinically relevant advantage over mechanical angioplasty modalities, because of a potentially reduced risk of complications related to platelet adhesion.