Air Blower Research Articles

Clinical, Microbiological, and Microcomputed Tomography Evaluation of Silver Diamine Fluoride in Controlling Root Carious Lesions: An in Vivo Study.

Silver diamine fluoride (SDF) application without removing necrotic tissue is an applicable non-invasive measure to primary care practice and may reduce the burden of untreated root caries. This study aims to examine clinical feature change, root caries-related bacteria, and silver penetration of SDF in arresting root caries. Ten study participants with 16 root carious teeth were included in this study. The clinical characteristics of root caries lesions (plaque deposit, color, hardness, and sensitivity symptom) were recorded. Then root caries samples were collected using a spoon excavator before and 2 weeks after treated with 38% SDF. The amounts of Streptococcus mutans (S.mutans), Actinomyces naeslundii (A. naeslundii), and Lactobacillus casei (L. casei) were determined using real-time PCR. Any tooth sample scheduled for extraction was further analyzed using micro-CT, stereoscopic microscope, and FE-SEM/ EDX to determine the silver penetration. Most treated samples were darker in color, predominantly turning black (n =15, 93.8%), had increased surface hardness (n =11, 68.8%), were non-sensitive teeth (n=14, 87.5%), and were negative to air blowing (n =12, 75%). Only S.mutans had a significantly lower number of bacteria after 2 weeks (p-value = 0.041). The micro-CT analysis revealed that the silver increased the root carious lesion's density in proportion to its depth. According to a stereoscopic microscope study, silver penetration caused dark bands, appearing along the dentinal tubule toward the dental pulp. An FE-SEM analysis showed that silver was found to be densely deposited on the surface of the lesions and penetrated through the dentinal tubule into the dental pulp direction. EDX mapping confirmed that the increased density was related to silver. Based on clinical and microbiological profiles, this investigation indicated that SDF is beneficial for controlling root caries, particularly S.mutans reduction. Silver can also penetrate deep into the lesion. Key words:Microbiology, Root caries, Silver diamine fluoride, Silver ion, Streptococcus mutans, Actinomyces naeslundii, Lactobacillus casei.

Investigation of non-uniform temperature distribution in air-cooled proton exchange membrane fuel cells with multizone temperature measurement

ABSTRACT Open-cathode air-cooled proton exchange membrane fuel cell stack relies on air fans both for fuel supply and stack cooling. Inappropriate stack thermal management and non-uniform temperature distribution can lead to compromised stack performance, reduced lifespan, and even thermal runaway. Thus, temperature distribution measurement, investigation and analysis are essential for air-cooled PEMFC’s optimized operation and performance. This study uses a multi-zone temperature measurement approach to investigate the impact of air supply method, airflow, and output current on stack temperature distributions. The experimental results reveal that the highest stack temperature occurs at the cathode channel outlet, while the lowest temperature is near the hydrogen inlet. At a 75A load, the maximum temperature difference between the inlet and outlet is 17°C. Increasing fan speed from 4500 to 8800 r/min reduces temperature non-uniformity in cell 10, the most uneven among the 19 cells, by 11.2%. Comparing blowing and suction air supply modes, blowing enhances stack output performance by 2.1%, with smaller temperature differences. Specifically, cell 10 experiences a 7.5°C lower difference at 4500 r/min and a 3.6°C lower difference at 8800 r/min airflow. Under blowing air supply, temperature non-uniformity decreases by 36.95% at 4500 r/min and 29.2% at 8800 r/min.

Improving the reliability of the turbocharger seal assembly by optimizing the elements of the seal assembly

Currently, most power units using internal combustion engines are equipped with turbocharging and that is explained by the requirements for efficiency, environmental safety and specific power characteristics. At the same time, the turbocompressor (TCR) is one of the resource-determining elements of power units, which accounts for a significant number of failures. Studies conducted towards the analysis of turbocompressor failures have shown that the main reason for it lies in a malfunction of the seal assembly, which is a consequence of extremely unfavorable conditions for its operation, consisting in a high (up to 800 оС) exhaust temperature, aggressive environment, a high (up to 120.000 min-1) rotor speed, the sliding speeds of the mating parts, up to 150 m/s. Oil for lubrication and cooling of the TCR is supplied through floating plain bearings, while the cavities of the turbine and compressor are isolated by means of the seal assemblies. Violation of their operability leads to the ingress of oil in a cavity of the impellers, to the imbalance of a rotor and, ultimately, to a turbocompressor failure. The determining factor affecting the operability of the seal assembly is a heat density of its parts. This factor is especially manifested in operating under forced conditions and engine shutdown, when cooling of a turbine volute is stopped by blown air, and a bearing assembly is stopped by circulating oil. In this case, a large part of the thermal energy is transferred from a heated turbine volute to the seal assembly and to the bearing assembly. The focus is on the temperature influence on performance of the turbocompressors’ sealing rings.

Problems of operating heating boilers of increased environmental efficiency

Purpose. Ensuring reliable operation of heating heat-generating devices with recirculation and exhaust gas heat recovery. Methodology. The normative methods of thermal calculation for surface heat exchange devices and the software according to the requirements of regulatory methods for this type of equipment for processing the results of our own experimental studies on heat exchange during deep cooling of combustion products of gas-consuming boilers were used. Findings. Calculation studies on the thermal operation modes during the heating period under the conditions of recirculation and heat recovery of flue gases of gas-fired water-heating boiler plants not equipped with air heaters were carried out. The main characteristics were determined of the thermal and humidity operation state for the air-supply ducts of these installations under the conditions of recirculation of flue gases’ part into the blown air. Regularities of temperature and dew point changes in the mixture of admixed gases and air under the conditions of using traditional heat recovery technologies and without them in different boiler modes and with different parts of recirculated gases were established. Problems of ensuring the operability and reliability of such boiler plants are highlighted. It is shown that these problems are related to condensate formation on the internal surfaces of air ducts and their freezing in some operating modes during in the cold period of the heating season. It is also shown that an effective solution to existing problems can be the use of air heaters in heat recovery systems to preheat the blown air before its mixing with recirculation gases. Originality. For the first time, the thermal and humidity operation modes of the air-supply ducts of heating boiler plants with increased environmental efficiency, which is ensured by boiler exhaust gases recirculation into the blown air, have been investigated. Practical value. The obtained research results will be used in the design of systems of recirculation and heat recovery of heat-generating devices’ exhaust gases to improve their environmental and thermal efficiency.

Sustainable Manufacturing

Energy saving air blowers by ever-growing British firm Lontra have been manufactured with the help of green machine tools

Solution blow spinning mass production of mullite nanofiber from environment friendly aqueous Al–Si solutions

Achieving large-scale production of high-performance mullite ceramic nanofibers posed a formidable challenge. Herein, an air heating-solution blow spinning technique was designed for the mass fabrication of mullite nanofibers at high speeds, ranging from 6 to 60 ​ml/h. Spinnable aqueous Al–Si solution systems, employing various aluminum sources, were systematically investigated. The optimization of the solution blow spinning apparatus involved the incorporation of a hot air blow device capable of dispensing streams of hot, dry air. Comprehensive investigations were conducted to examine the impact of variables such as spinning solution viscosity, spinning rate, and spinning distance on the resulting mullite fiber diameter and morphology. Following sintering at 1200 ​°C, mullite fiber cotton was successfully synthesized, exhibiting diameters spanning from 500 ​nm to 5 ​μm. These mullite nanofiber cotton demonstrated exceptional attributes, including robust temperature stability (up to 1300 ​°C), remarkable thermal insulation properties and superior filtration efficiency.

Ceramic membrane filtration of water samples from Ain Fayda Lake and cement factory (Al‐Ain), United Arab Emirates

AbstractThis article presents a Ceramic Membrane‐based Produced Water Treatment Technology and its application to water samples from Al‐Ain (Abu Dhabi Emirate, United Arab Emirates). The samples were collected during the summer of 2022 from Ain Fayda (lake water) and Al‐Ain cement factory (groundwater). This study investigates the effectiveness of the ceramic membrane for treating water samples and removing solid particles. A dead‐end filtration mode with a filtration flux of 3 m3/m2/d was used. For the Ain Fayda Lake water sample, the transmembrane pressure during filtration reached 120 kPa (temperature adjusted to 25°C); air blowing was used to reduce the transmembrane pressure to around 70 kPa and Total Suspended Solids were reduced from 1.4 to <1 mg/L during 160 min of filtration. For the Al‐Ain cement factory water sample, the transmembrane pressure during filtration reached 160 kPa (temperature adjusted to 25°C); air blowing reduced the transmembrane pressure to around 65 kPa and the Total Suspended Solids from 9.1 to <1 mg/L during 130 min of filtration. Both water samples belong to the Na‐Cl water type. Overall, this work shows the effectiveness of the Ceramic Membrane‐based Produced Water Treatment Technology for reducing Total Suspended Solids in sampled waters; thus, we recommend this approach for treating surface waters in Al‐Ain to improve the environment and possible usage in agriculture.

Yakınsak-Konik Nozulların Giriş ve Çıkış Çaplarının İtme Kuvveti ve Hacimsel Debi Üzerindeki Etkisinin Teorik, Nümerik ve Deneysel İncelemesi

It is possible to see convergent conical type nozzles everywhere, from daily life to rocket science. They are utilized as the main part of the propulsion system in many applications such as air blow guns for spraying, steam turbines for compression, rockets for thrust generation, satellites for altitude control and so on. Although the convergent conical nozzle is a well-known nozzle, there are few studies on the effects of geometric changes by comparing more than one approach together. Therefore, this study investigates thrust and volumetric flow rate for different inlet and exit diameters of the convergent conical nozzles theoretically, numerically and experimentally. In this study, the quasi-one-dimensional Euler equations are defined for the theoretical investigation of convergent conical nozzles. However, in this approach, many important features such as viscous losses are neglected. In fact, nozzle flows have highly complex features including shock waves, turbulence, and boundary layers due to compressible effects. Thus, Computational Fluid Dynamic (CFD) simulations are performed with ANSYS Fluent for numerical investigation of the nozzle in this study. CFD simulations provide a better understanding and illustration of convergent conical type nozzle flows. For a third approach, the experimental investigation is conducted for thrust and volumetric flow rate measurements. Theoretical and numerical results are compared with the experimental results and similarity ratios are defined to find the closest to the experimental results.

Numerical simulation of using DBD plasma air blower for a proton exchange membrane fuel cell

In this study, a novel air blower by applying the DBD plasma actuator for a PEM fuel cell is proposed for reducing power consumption and air flow saving. For this purpose, the DBD plasma actuators are installed on the bottom surface of the cathode channel of a PEMFC. The impact of the application of DBD plasma and the number of DBDs on the air mass flow rate and performance of PEMFC were numerically investigated. Results show that in comparison to the conventional air blower model, using the DBD plasma air blower at the cathode channel of a PEMFC results in a reduction of velocity magnitude and uniform velocity distribution of airflow within the cathode channel. Also, results indicate that the DBD plasma air blower model with less air flow consumption provides almost the same current density and performance as the conventional model. Results illustrate that the DBD plasma air blower with 3 DBDs can be a suitable candidate to obtain the best design for the DBD plasma air blower. The robust advantages of using the DBD plasma air blower become more underscored when the findings present the 90.31% reduction in the average power consumption.

Case Study of Decreasing of Quality of Processed Waste at Sewage Treatment Plant to Contain Waste Disposal on Ship Mv. Ck Angie

Prevention of contamination by sewage on ships can be overcome by using an auxiliary sewage treatment plant, a sewage treatment plant is a liquid waste treatment installation which is generally intended for domestic waste in the form of feces and laundry residue containing detergents which are harmful to the environment by utilizing aerobic bacteria as waste decomposers and UV sterilizers as a neutralizer for waste parameters. However, in reality when the author and engineer 3 conducted regular tests on the processed water content of the sewage treatment plant from May 4 2021 to May 25 2021, the results of the waste parameters were not in accordance with the manual book. So, according to the test results above, the authors take 3 causes for the decline in the quality of processed water which is the background for writing this thesis, namely the operation of the aeration blower is ineffective, the UV sterilizer does not function properly and the accumulation of sludge or excessive solid residue in the separation tank section. The research method used is descriptive. The approach method used is a qualitative approach method with data collection techniques carried out by means of observation and documentation based on data analysis techniques carried out using root cause analysis (RCA) techniques carried out on the MV ship. CK ANGIE from 11 December 2020 to 24 January 2022. the operation of the aeration blower is ineffective, If the uv sterilizer does not function properly, the cause of the problem is the dirty blower air filter and dirty blower air inlet pipe and the uv sterilizer section is caused by the life of the uv lamp which has exceeded running hours and the uv jacket is dirty. And for engine cadets to pay attention to the exhaust air pressure from the aeration blower so that when the exhaust air pressure from the aeration blower starts to decrease, they can immediately report it to the engineer in charge. suggestions for maintaining the performance of the UV Sterilizer are to pay more attention to the usage period or running hours of the UV Lamp so that the effectiveness of the UV Lamp continues to function properly. And for the jacket section of the UV sterilizer to be cleaned regularly by implementing a regular planned maintenance system (PMS)..

Measuring Photosynthesis of Entire Tree Crowns and Pulse Label Trees in Large Closed Chamber with 13CO2 in the Field: Design and Testing

Measuring the photosynthesis of entire tree crowns and pulse labelling trees with 13CO2 are valuable approaches to study carbon acquisition, transfer, and allocation; however, it is challenging for trees in the field. The objective was to develop and field test large chambers (35 - 45 m3) that enclosed the entire crown of a tree, provided a reliable estimate of tree crown photosynthesis, and ensured efficient 13CO2 labelling. The chambers, made of transparent polyethylene film pulled tightly over a frame, were equipped with an air conditioner, fans, and air blowers. Air temperature, relative humidity, and photosynthetic photon flux density were measured outside and inside each chamber. Six of 4-year-old rubber trees (Hevea brasiliensis) were pulsed-labelled with 18 L of 13CO2 in June and October 2016. The mean air temperature inside the chambers was 1.2 °C higher and the relative humidity 8 % lower than the outside air. The crown photosynthesis, calculated from the decrease in the CO2 concentration inside the chamber, was in the range 140 - 249 µmol s–1 and was significantly related to photosynthetic photon flux density, total leaf area of the tree, and average net CO2 assimilation at leaf level. The labelling efficiency, estimated as the ratio of the amount of 13C recovered in the foliage immediately after labelling divided by the amount of 13C delivered to the tree, was in the range 43 - 68 %. The designed chamber was suitable to estimate crown photosynthesis and perform 13CO2 pulse labelling of 5-m-tall trees in the field. HIGHLIGHTS Measuring carbon acquisition, transfer, and allocation of entire trees in the field is a challenge The paper describes in detail the system including a 45 m3 chamber that was developed and tested to measure crown photosynthesis and to label trees 5 - 6 m tall with 13CO2 The system and methodology proved efficient in controlling the chamber temperature and providing appropriate conditions for leaf gas exchanges The rates of crown photosynthesis were consistent with measurements at the leaf and ecosystem levels, providing a clear relationship with photosynthetic photon flux density More than 1-half the injected 13CO2 was recovered in the leaves after the end of labelling, showing that the design of the chamber and the labelling protocol were effective for studying C allocation within the tree GRAPHICAL ABSTRACT

Improvement Undesirable Characteristics of the Switched Reluctance Motor With Triangular Rotor Structure

The conventional switched reluctance motors (CSRMs) confront two key challenges, including torque ripple (TR) and radial force (RF), which are the foundations of creating noise, vibration, and tension that limits the applications of the motor. In order to reduce inappropriate inherent effects of the CSRMs, optimizing via motor structure will be more comfortable and less costly than control methods. Due to its simplicity and being without coils in the rotor, this part will be a suitable candidate for improvement destinations. In this paper, a novel structure of the rotor is presented in order to reduce the TR and RF of this motor. The proposed structure is derived from the conventional one with a triangular shape in the middle of rotor, known as a Triangular Rotor Switched Reluctance Motor (TRSRM). Finding the best geometric of the proposed model fulfilled by sensitivity analysis (SA) alongside 3-D finite element analysis (3D-FEA) and the best configuration for comparison to the CSRM selected. Experimental and simulation results demonstrate that TRSRM diminishes RF and TR compared to the CRSRM while keeping the weight and volume fixed and also has a low cost and simple manufacturing. These features make the proposed structure suitable for continuous-operation applications such as air blowers in industrial devices.

Experimental Investigation of Temperature Distribution in a Laminar Boundary Layer over a Heated Flat Plate with Localized Transverse Cold Air Injections

This study presents an experimental investigation focused on the interaction between a transverse injection of cold air (blowing) and the boundary layer over a heated flat plate. The flat plate was equipped with a cylindrical coil heater positioned at its center along the flow direction. The constant heat flux was maintained using a variable resistance potentiometer. The flat plate with the heater was mounted inside a subsonic wind tunnel to sustain a constant laminar air flow. The primary objective of this research was to examine the effects of cold air injections through localized holes in the flat plate near the trailing edge on the thermal boundary layer thickness δt(x,Rex,Pr). The thermal boundary layer thickness was measured using K-type thermocouples and PT-100 RTD sensors, which are made to move precise, small distances using a specially constructed traversing mechanism. Cold air was injected using purposefully fabricated metal capillary tubes force-fitted into holes through the hot flat plate. The metal tubes were thermally insulated using class-F insulation, which is used in electric motor windings. The presented work focused on a fixed free-stream velocity and a fixed cold-injection velocity less than the free-stream velocity but for two-variable heat fluxes. The results show that the thermal boundary layer thickness generally increased due to the secondary cold flow.

Computational fluid dynamics model for a C-shaped sodium hydroxide freeze valve

Freeze valves are safety components implemented in molten salt reactor (MSR) designs that utilize a salt’s phase change to isolate two parts of a system from each other. The correct prediction of the behavior of a freeze valve is crucial to the safe operation of MSRs. A freeze valve made from a nickel (Ni-201) tube bent into a C-shape and filled with sodium hydroxide (NaOH) is studied experimentally at the MS1 loop facility at Seaborg Technologies. The molten salt initially fills the freeze valve and is cooled by means of an external air blower and solidifies to close the valve. A computational fluid dynamics code STAR-CCM+ is applied to model the thermodynamic and flow properties of the freeze valve. The model accounts for both conjugate and radiative heat transfer, utilizing a volume-of-fluid method with an enthalpy-porosity-based phase change numerical method. The influence of impurity content on the salt’s melting point is modelled. Experimental temperature measurements are used to determine the model parameters, and the simulation results show a good agreement with the experimental data. Correlation coefficients between the experimental and simulation data are above 0.996, with the average absolute value of their difference being approximately 5 °C. Our sensitivity analysis shows that the performance of the freeze valve is strongly dependent on the latent heat and the flowability threshold of the salt used by the software to model salt dynamics in the mushy zone.

Towards accurate stereo-video based free-surface reconstruction for wave tank experiments

Measuring accurately the shape of the free surface in medium-scale hydrodynamic testing facilities is challenging with conventional wave gauges. To overcome this problem, it is necessary to go towards higher resolution measurement systems. For this purpose, we investigate the ability of stereo-video acquisition systems to reconstruct free surface waves in laboratory conditions. This technique has been proven to give satisfactory results in open sea conditions, although it is dependent on the environmental conditions (weather, solar incidence angle). At sea, the stereo-video reconstruction algorithm makes profit of the short waves generated by the wind in order to correlate the points from the left and right images. The main challenge of adapting this technique to laboratory conditions, i.e. in absence of sun and wind, is to overcome the absence of texture on the free surface. This paper presents recent work aiming at developing a stereo-vision measurement system for laboratory conditions. Our efforts have been devoted to finding an adapted lighting system and generating a texture suitable for the reconstruction algorithm. Different lighting configurations have been tested in order to understand its impact on the reconstructions. For the texture generation, we have investigated different means of generating short surface waves (water droplets, air blowing, circulation current, underwater acoustic emissions) in different experimental facilities. Our conclusions show that it is possible to reconstruct the shape of surface gravity waves in the presence of short surface waves and that the effects of lighting and texture on the quality of the reconstruction are strongly coupled.

A directly charged thermal store for compressed air energy storage systems

This paper discusses the design of a heat storage unit with integrated heat exchangers (TES + HX), which is intended to work in a Compressed Air Energy Storage (CAES) system. The unit can be charged directly by the system's stream of pressurised air, eliminating the need for additional heat exchangers and reducing the number of heat transfer processes. Silica sand is used as the storage medium due to its high heat capacity, non-corrosivity and its ability to accommodate the thermal expansion of steel pipes.A medium-scale, medium-duration CAES system (250 kW/1MWh) is used as a case study. The heat storage subsystem comprises a packed-bed thermal store, three air-to-air heat exchangers and an ambient pressure air blower. Combined, this subsystem has an approximate cost of £147k and achieves an efficiency of ∼89 %, which translates into a levelized cost of ∼48.5 £/MWh. An integrated TES + HX unit can achieve a levelized cost of ∼35 £/MWh. The unit has an estimated cost of £38.5k and achieves an overall roundtrip exergy efficiency of ∼91.8 %. The integrated TES + HX unit not only offers a significant reduction in the capital cost of a CAES system and an efficiency improvement, but it also allows for a simpler overall architecture.

EFEKTIFITAS PEMANASAN KAMAR ASAP MELALUI DISTRIBUSI UDARA MASUK (FORCED DRIVE FAN/FDF) DAN UDARA KELUAR (INDUCED DRIVE FAN/IDF) PADA PENGOLAHAN KARET LEMBARAN (RIBBED SMOKE SHEET) : REVIEW

The smoke chamber used has a capacity of 3,420 kg with a rubber sheet smoking period of five days. Reducing the water content (moisture content) on the rubber sheet is used by heating it with a smoking system. For smoke chamber operations, the fumigation temperature used on the first day is 40 - 45°C, on the second day 45 - 50°C, on the third day 50 - 55°C, on the fourth day 55 - 60°C, and on the fifth day the smoking temperature was maintained at 60°C. FDF and IDF are two air distribution devices, where the FDF functions to blow the air into the smoke chamber and the IDF draws the air into the smoke chamber. The balance between exhaled air and that drawn out of the smoke chamber must be proportional. Too much airflow will collect in the smoke chamber and too much the air withdrawal will affect heat transfer. After installing the FDF and IDF tools, the smoking time is 4 (four) days, so the use of smoked wood (rubber stem wood) is reduced from 3.19 m3 (for 5 days of smoking) to 2.55 m3 (for 4 days of smoking). There is a saving of one operational day. Reducing the use of smoked wood has an impact on processing efficiency. Heat energy from smoking has also increased. Before the installation of the FDF and IDF devices, the amount of heat energy was 64,074 kcal/day (320,372 kcal in 5 days). After installing the FDF and IDF devices, they increase the amount of air / oxygen (O2) in the combustion process so that there is an additional heat energy of 9,461 kcal/day (47,305 kcal in 5 days). The total amount of heat energy produced is 367,677 kcal for 5 (five) days of smoking. FDF and IDF are two air blowers commonly known as blowers with their respective specifications: The FDF used has an electric power of 3 kilowatts (4 horsepower/hp) with a rotation of 1,420 rpm, while the IDF has an electric power of 7.5 kilowatts (10 horsepower/hp). hp) at 1,440 rpm.

Effects of air blower and pump failures on the performance of A2O processes for wastewater treatment

The unexpected failure of equipment such as pumps and fans in wastewater treatment plants can reduce wastewater treatment efficiency, leading to direct leakage of untreated wastewater into the environment. It is hence important to predict the possible consequences of equipment failure to minimize the leakage of harmful substances. This study examines the impacts of equipment shutdown on the performance and recovery time of a laboratory-scale anaerobic/anoxic/aerobic system with regard to reactor conditions and water quality. Two days after the air blowers are stopped, the concentrations of the soluble chemical oxygen demand, NH4–N, and PO4–P in the effluent of the settling tank increase to 122 mg/L, 23.8 mg/L, and 46.6 mg/L, respectively. These concentrations return to their initial values after 12, 24, and 48 h of restarting the air blowers. The concentrations of PO4–P and NO3–N in the effluent increase to 58 mg/L and 20 mg/L, respectively, about 24 h after stopping the return activated sludge and mixed liquor recirculation pumps, owing to the release of phosphates in the settling tank and inhibition of denitrification.

OPERATION FEATURES OF ENVIRONMENTALLY EFFICIENT BOILER PLANTS OF MUNICIPAL THERMAL POWER ENGINEERING

The work is devoted to research on the improvement of thermal energy production technologies in gas-consuming heating boiler installations while improving their environmental performance and increasing the operation reliability. The work purpose is to study the heat and humidity modes of the air-supply ducts of boiler plants with exhaust gases recirculation systems into the blown air. The main objectives of the study are: to determine the thermal parameters of a heating boiler with a 2 MW heating capacity with a exhaust gases recirculation system mixed with blown air into its furnace space under conditions of using heat recovery technologies and without them; determination and analysis the heat and humidity parameters of this mixture in different operating modes of boiler plants. Known thermal calculation methods of boiler plants and data from our own experimental studies of heat transfer during deep cooling of boiler plant exhaust gases were used. The thermal calculation results of the heating boiler with a system for exhaust gas recirculation into its furnace space mixed with blown air are presented. The regularities of changes in the adiabatic combustion temperature and heat-humidity characteristics of the above mixture depending on the boiler heat load in different its operation modes during the heating period and the share of flue gas recirculation from 10 to 20 % were established. The research results show that the introduction of recirculation gases leads to a decrease by 150 – 250 °С of the adiabatic combustion temperature tad due to the need to consume fuel heat for heating the introduced ballast and the greater of the recirculation share s the lower the level of the indicated temperature. The research results also showed that gas recirculation causes insignificant (in the range of 0.5 – 4.7 °С) changes in the temperature of the boiler exhaust gases. Based on the data obtained, the change regularities in the heat-humidity characteristics (temperature and dew point) of the mixture of recirculated gases and air in different boiler operating modes during the heating period and under the studied recirculation shares were established. It is shown that recirculation causes condensate formation on the surfaces of air ducts in all operating modes of boiler and in some modes their icing is possible. To prevent these negative phenomena, it is necessary to apply measures to increase the temperature of the gas-air mixture by a value not less than Δtsum = 15 – 35 °С.

The effect of an extra hydrophobic resin layer on the bond strength and durability of one-step universal adhesives used as a primer

ObjectivesTo determine the effect of an extra hydrophobic resin layer (EHL) on the bond strength and durability of three different pH one-step universal adhesives (UAs) utilized in self-etch (SE) mode, and to explore whether UAs can be used as a primer in two-step bonding system. MethodsThree different pH UAs were utilized: G-Premio Bond (GPB), Scotchbond Universal (SBU), All-Bond Universal (ABU), while the bonding agent of Clearfil SE Bond 2 (SE2) was selected as the EHL. For the EHL groups, EHL was applied after the air blow of each UA and before light curing. The microtensile bond strength (μTBS), fracture modes, interfacial structures and nanoleakage (NL) were evaluated after 24 h water storage and after 15,000 thermal cycling (TC). Elastic modulus (EM) and hardness (H) was tested by a nanoindenter after 24 h. ResultsSignificantly higher μTBS was achieved in the GPB+EHL group compared with GPB both at 24 h and after 15,000 TC, while the additional use of EHL did not improve the μTBS of SBU and ABU significantly both at 24 h and after 15,000 TC. GPB+EHL demonstrated lower NL than GPB. The mean EM and H of the adhesive layer in GPB+EHL was significantly decreased compared with GPB. ConclusionsThe results indicated that the bond strength and durability of low pH one-step UA (GPB) were significantly improved by additional application of EHL both at 24 h and after 15,000 TC, while no significant improvement was observed for ultra-mild one-step UAs (SBU and ABU). Clinical significanceThis study indicates that GPB can be used as a primer in a two-step bonding system, while SBU and ABU may not be as effective. These findings may help guide clinicians in selecting the appropriate UAs and bonding techniques for different clinical scenarios.