Evaporative Heat Research Articles

기화열을 고려한 콘크리트의 온도평가시스템 개발

기화열을 고려한 콘크리트의 온도평가시스템 개발

Comparison of the Catalyzed Evaporation of Bio-oils From the Co-pyrolysis of Rice Husk and Waste Tires

The thermal behavior of the bio-oils produced from pyrolyzing the mixture of different proportional rice husk and waste tires and its kinetics of evaporation have been studied using thermogravimetry at a heating rate of 10 K min−1, with N2 at 1 atm. As a comparison, the thermal behavior of diesel 0# was also investigated. It shows that the kinetic equation obtained by Achar’s differential method and Coal-Redfern’s integral method are satisfied to explain the oil properties and quite agreed with the experimental data. The mean value of initial and final temperature of mass loss of the oils, which was produced by pyrolyzing the mixture of 50 wt% rice husk and 50 wt% waste tires with SBA-15 as catalyst, is equal to that of diesel 0#. Through established kinetic equations of the evaporation process, the pre-exponential factor and evaporation of heat (ΔvapH) for the oils are provided. It shows that ΔvapH of oils, which is in the range of 67.7 and 120 kJ/mol are lower than that of diesel 0# being 136.1 kJ/mol.

A saturated-interface-volume phase change model for simulating flow boiling

High-fidelity simulation of flow boiling in microchannels remains a challenging problem, but the increasing interest in applications of microscale two-phase transport highlights its importance. In this paper, a volume of fluid (VOF)-based flow boiling model is proposed with features that enable cost-effective simulation of two-phase flow and heat transfer in realistic geometries. The vapor and liquid phases are distinguished using a color function which represents the local volume fraction of the tracked phase. Mass conservation is satisfied by solving the transport equations for both phases with a finite-volume approach. In order to predict phase change at the liquid–vapor interface, evaporative heat and mass source terms are calculated using a novel, saturated-interface-volume phase change model. This phase change model is formulated to anchor the interfacial temperature at saturation within each iteration, and thereby acts as a robust constant-temperature boundary condition. Unlike other available phase-change models, the source terms are coupled with the local temperature explicitly; therefore, numerical oscillations around the interface temperature are not observed during iterations within a time step, which reduces the numerical cost. In addition, the reference frame is set to move with the vapor slug to artificially increase the local velocity magnitude in the thin liquid film region in the relative frame. This reduces the influence of numerical errors resulting from calculation of the surface tension force, and thus suppresses the development of spurious currents. As a result, non-uniform meshes may be used which can efficiently resolve high-aspect-ratio geometries and flow features. The overall numerical expense is significantly reduced. The proposed saturated-interface-volume model is first validated against a one-dimensional Stefan problem, and then used to simulate the growth of a vapor bubble flowing in a heated, 2D axisymmetric microchannel. The bubble motion, bubble growth rate, liquid film thickness, and local heat transfer coefficient along the wall are compared against previous numerical studies. A three-dimensional flow boiling problem is studied to demonstrate the cost effectiveness of the present approach and to highlight the transport mechanisms it can reveal in more complex domains.

Studies on combined cooling and drying of agro products using air cooled internal heat recovered vapour absorption system

The objective of this study is to develop an energy efficient heat pump combined storage and drying technology for agricultural products, to reduce the net energy consumption compared to conventional storage and drying systems. An experimental study of an improved air cooled condenser and absorber in ammonia–water vapour absorption refrigeration system and using more internal heat recovery by generator absorber heat exchangers is carried out simultaneously using the generated hot air for drying and better storage of the agricultural product. Vertical annulus radial grain bin dryer of 5 kg/h capacity is adopted to suit 10.5 kW for cold storage ammonia absorption refrigeration. The effect of heat sink and evaporator temperatures on the coefficient of performance (COP) of the system and the heat rejected from condenser and absorber for drying applications are studied. The temperature of the air at the outlet of the condenser/absorber is around 43–53 °C for various atmospheric conditions and is used for drying of the selected agro product (nylon sago) in the bin dryer. The drying characteristics of nylon sago, heat pump capacity and combined COP of the system are presented with descriptions. It is found that the combined COP of the system varies from 1.8 to 1.4 when the heat rejection temperature is between 53 °C and 43 °C respectively under actual operating conditions.

A new approach to enhance the heat and mass transfer of liquid desiccant dehumidification with a titanium dioxide superhydrophilic self-cleaning coating

The cooling system with liquid desiccant dehumidification is an energy-efficient and eco-friendly solution for the ever-increasing energy consumption and environmental impact of modern buildings. By significantly influencing the wetted area, the contact angle of the liquid–air interface is critical to the performance of desiccant dehumidification. In this study, to enhance heat and mass transfer performance, a new approach was developed with a titanium dioxide superhydrophilic self-cleaning coating on the dehumidifier surfaces that was made of a highly dispersed paste with nanoscale titanium dioxide particles and activated with ultraviolet light. We first tested the effect of the coatings on samples made of three commonly used materials, SUS304, SUS316, and SUS410, with a 30% LiBr solution and deionized water. Results show that the contact angle on the coated samples dramatically decreased to only 1/7 for water and 1/6 for the LiBr solution compared to uncoated samples. The durability of the coatings was studied experimentally by repeatedly immersing the samples in 30% LiBr, exposing them for 2 months, and reactivating them. It was found that the angle changed slightly for SUS304/316 samples with good anticorrosion performance, whereas the angle increased by 10°–20° for SUS410 samples due to the accelerated catalytic oxidization of the Titanium dioxide coating, which could possibly be solved by precoating an SiO2 compact layer. Furthermore, we found numerically that the wetted area during desiccant dehumidification could be effectively increased by 5–7 times with the coating. Accordingly, the heat exchange rate and moisture removal rate between the air and the desiccant could be increased by 1.2 and 2 times, respectively. Therefore, by dramatically reducing the desiccant contact angle on dehumidifier surfaces and enlarging the wetted area accordingly, the titanium dioxide self-cleaning coating could significantly improve the heat and mass transfer performance of liquid desiccant dehumidification, especially the mass transfer performance. The coatings' manufacture is cheap and facile for industrialization. This measure can be considered an effective and economic way to improve the performance of a dehumidifier and also has other applications in heat exchangers, evaporators, and absorption towers.

Фізична природа водневого зв’язку

The physical nature and the correct definition of hydrogen bond (H-bond) are considered.\,\,The influence of H-bonds on the thermodynamic, kinetic, and spectroscopic properties of water is analyzed.\,\,The conventional model of H-bonds as sharply directed and saturated bridges between water molecules is incompatible with the behavior of the specific volume, evaporation heat, and self-diffusion and kinematic shear viscosity coefficients of water. On the other hand, it is shown that the variation of the dipole moment of a water molecule and the frequency shift of valence vibrations of a hydroxyl group can be totally explained in the framework of the electrostatic model of H-bond.\,\,At the same time, the temperature dependences of the heat capacity of water in the liquid and vapor states clearly testify to the existence of weak H-bonds.\,\,The analysis of a water dimer shows that the contribution of weak H-bonds to its ground state energy is approximately 4--5 times lower in comparison with the energy of electrostatic interaction between water molecules.\,\,A conclusion is made that H-bonds have the same nature in all other cases where they occur.

가열과 비가열 상황에서 증발과 끓음 개념에 대한 초등교사들의 분류 기준에 대한 생각

The purpose of this study was to survey the elementary school teachers' thoughts of the classification criteria for evaporation and boiling concept in the heating and non-heating conditions. For this purpose, we conducted a survey and interviews with 37 elementary school teachers. When the heating conditions were presented, many teachers thought evapora- tion phenomena as boiling. In opposite condition, many teachers thought boiling phenomena as evaporation. This means that teachers' thought of boiling phenomena was connected with heating conditions and evaporation phenomena with non-heating conditions. In addition, the classification criteria to distinguish evaporation and boiling phenomena depending on the heating and non-heating conditions were not coherent. In this study, we suggested that a various cases beyond the typical case must be presented in the textbooks and teaching in order to avoid confusion of thoughts related to evaporation and boiling concepts.

Voltammetric detection and profiling of isoprenoid quinones hydrophobically transferred from bacterial cells.

We have developed a novel bacterial detection technique by desiccating a bacterial suspension deposited on an electrode. It was also found that the use of an indium-tin-oxide (ITO) electrode dramatically improved the resolution of the voltammogram, allowing us to observe two pairs of redox peaks, each assigned to the adsorption of isoprenoid ubiquinone (UQn) and menaquinone (MKn), which were present in the bacterial cell envelopes, giving midpeak potentials of -0.015 and -0.25 V versus Ag|AgCl|saturated KCl| at pH 7.0, respectively. Most of the microorganisms classified in both the Gram-negative and -positive bacteria gave well-defined redox peaks, demonstrating that this procedure made the detection of the quinones possible without solvent extraction. It has been demonstrated that the present technique can be used not only for the detection of bacteria, but also for profiling of the isoprenoid quinones, which play important roles in electron and proton transfer in microorganisms. In this respect, the present technique provides a much more straightforward way than the solvent extraction in that one sample can be prepared in 1 min by heat evaporation of a suspension containing the targeted bacteria, which has been applied on the ITO electrode.

Prospective systems and technologies for the treatment of wastewater containing oil substances

The article describes the research and subsequent application of the electric coagulating agents and galvanic coagulating agents. These may be used in order to raise the standard of the treatment of wastewater containing oil substances. A method of desalination of natural waters and wastewater by means of a dialyzer with a multilayer liquid membrane was designed. Our research obtained by the new way of filtration of oil substances and suspended substances has been designed for an ultra-gentle treatment of water. In comparison with already familiar methods like ultra-filtration and reverse osmosis, this new way has certain advantages. The function of materials will be examined in this article. Based on the research, we have found that the main advantages of the method using the coagulating agent are treatment efficiency, simple installation, etc. Agents can be used to increase the level of treatment of wastewater containing crude oil substances. We found and have demonstrated that, compared to usual methods used in the industry, e.g. heating (evaporation), ion exchange and other methods of demineralization (desalination) of wastewater, the presented way has several advantages like decreasing energy losses.

The Long-Term Field Experiment Observatory and Preliminary Analysis of Land-Atmosphere Interaction over Hilly Zone in the Subtropical Monsoon Region of Southern China

AbstractTo improve current understanding of the water cycle, energy partitioning and CO2 exchange over hilly zone vegetative land surfaces in the subtropical monsoon environment of southern China, a long-term field experiment observatory was set up at Ningxiang, eastern Hunan Province. This paper presents a preliminary analysis of the field observations at the observatory collected from August to November 2012. Results show that significant diurnal variations in soil temperature occur only in shallow soil layers (0.05, 0.10, and 0.20 m), and that heavy rainfall affects soil moisture in the deep layers (≥ 0.40 m). During the experimental period, significant diurnal variations in albedo, radiation components, energy components, and CO2 flux were observed, but little seasonal variation. Strong photosynthesis in the vegetation canopy enhanced the CO2 absorption and the latent heat released in daylight hours; Latent heat of evaporation was the main consumer of available energy in late summer. Because the field...

Theoretical investigations on combined power and ejector cooling system powered by low-grade energy source

A combined power and cooling system is proposed for cogeneration, which integrates the ejector cooling cycle with the Rankine cycle. Low-temperature heat source such as industrial waste heat or solar energy can be used to drive the Rankine cycle. This system will provide electricity and cooling effect simultaneously without consuming primary energy. The partially expanded vapor (from low-grade energy) will be bleed off and enter into ejector's primary nozzle, which achieves cooling effect. Simulations have been carried out to analyze the effects of various working conditions on the overall system performance, on ejector entrainment ratio and turbine power output. Five different refrigerants HFE7100, HFE7000, methanol, ethanol and water have been selected, and the above three parameters were compared, respectively. The simulation results indicated that turbine expansion ratio, heat source temperature, condenser temperature and evaporator temperature play significant roles on the turbine power output, ejector entrainment ratio and the overall thermal efficiency of the system. At a heat source temperature of 1208C, evaporator temperature of 108C and condenser temperature of 358C, methanol showed the highest thermal efficiency (0.195), followed by ethanol and water (0.173). It is recommended that the evaporator temperature and the appropriate working fluid should be selected according to the different working cooling requirements, and the turbine power output can then be determined accordingly.

A new potentiometric SO₂ sensor based on Li₃PO₄ electrolyte film and its response characteristics.

A potentiometric SO2 gas sensor based on Li3PO4 solid electrolyte has been developed using Au as the reference electrode and Li2SO4/V2O5 as the sensing electrode. The Li3PO4 film was deposited on Al2O3 substrate by resistance heating evaporation. Two Au films with designed patterns were formed on the Li3PO4 film by micro-fabrication technologies. The sensing electrode covers one electrode partly using thick-film technology. The electromotive force values between the sensing electrode and the reference electrode were measured and various characteristics were studied including sensitivity, response characteristics, and stability and selectivity. According to the results, we conclude that an optimal working temperature of the SO2 sensor is 500 °C, the measurement range is 0-100 ppm, the sensitivity is about 32.47 mV/dec, the response and the recovery time is about 5 min and 10 min, respectively. And the stability and the selectivity of the sensor are good, making it have potential in SO2 measurement of living environment.

Impacts of extreme 2013–2014 winter conditions on Lake Michigan's fall heat content, surface temperature, and evaporation

AbstractSince the late 1990s, the Laurentian Great Lakes have experienced persistent low water levels and above average over‐lake evaporation rates. During the winter of 2013–2014, the lakes endured the most persistent, lowest temperatures and highest ice cover in recent history, fostering speculation that over‐lake evaporation rates might decrease and that water levels might rise. To address this speculation, we examined interseasonal relationships in Lake Michigan's thermal regime. We find pronounced relationships between winter conditions and subsequent fall heat content, modest relationships with fall surface temperature, but essentially no correlation with fall evaporation rates. Our findings suggest that the extreme winter conditions of 2013–2014 may have induced a shift in Lake Michigan's thermal regime and that this shift coincides with a recent (and ongoing) rise in Great Lakes water levels. If the shift persists, it could (assuming precipitation rates remain relatively constant) represent a return to thermal and hydrologic conditions not observed on Lake Michigan in over 15 years.

Delivery of unprecedented amounts of perfluoroalkyl substances towards the deep-sea

The finding of perfluoroalkyl substances (PFASs) in particles sinking to the deep northwestern Mediterranean Sea confirms the role of the latter as ballast for the transfer of pollutants to the deep sea. The transfer of particulate matter down to the deep is enhanced during atmosphere-driven, high-energy physical oceanographic processes like dense shelf water cascading (DSWC), which is caused by winter surface heat losses and evaporation. Here we present data from samples collected during winter 2012, when dense shelf water formation and subsequent cascading triggered the flushing of large amounts of PFASs through a submarine canyon to depths in excess of 1000m. The finding of quantifiable concentrations of long-chain PFOA, PFOS and PFNA substances and significantly high concentrations of the short-chain substances PFHxA and PFBA indicates that these compounds, sorbed onto particulate matter, are quickly and directly transferred to the ocean's interior, thus highlighting the role of DSWC in removing those pollutants from the coastal ocean. Eventually, uncertainties about our results arising from the limited number of samples available are counterbalanced by their intrinsic value as intense DSWC events, like the one in 2012, occur only every 5–7years in the study area, which seriously restricts sampling opportunities. Our results add PFASs to the list of persistent organic pollutants like polychlorinated biphenyls, chlorobenzenes or polycyclic aromatic hydrocarbons known to be conveyed to the deep marine environment.

The Effects of Different Mechanical Turning Regimes on Heat Changes and Evaporation During Sewage Sludge Biodrying

Biodrying can be improved by understanding the changes in heat and moisture with different turning regimes. The aim was to investigate the drying effect of turning and to optimize the turning regime. Control technology based on in situ temperature and vapor sensors was applied. Turning in the temperature-increasing phase was the least effective strategy. Turning once in the later stage of the first thermophilic phase and twice after the first thermophilic phase produced the highest bioheat (1.641 MJ kg−1 initial biodrying material), achieved the highest evaporation (0.379 kg kg−1 initial biodrying material), and achieved a 58.1% heat utilization rate.

Heat transfer experimental research at evaporation of alternative refrigerants R407C and R410A at conditions of free convection

Aim of the work was the influence of regime parameters on heat transfer at evaporation of refrigerants R407C and R410 research. To achieve this aim the experimental stand was designed and made. The article contains results of visual observations for the evaporation process of different refrigerants on horizontal tube in big volume, the connection between heat transfer coefficient and regime parameters, heat flux density and evaporation pressure, was determined.

Total Heat Loss of Firefighters’ Protective Clothing

We examined the total heat loss, which is the summation of heat loss and evaporation loss, for the firefighters’ protective clothing and the combined clothing samples which were prepared from the firefighters’ protective clothing, the working wear clothing and the commercial T-shirts as determined by a test method specified in ASTM F 1868 part C. We compare the total heat loss, heat loss and evaporation loss obtained from firefighters’ protective clothing and combined clothing samples with those of the commercial T-shirts and a working wear using in a fire station. We confirmed that the total heat loss of firefighters’ protective clothing and combined clothing samples were approximately 2.5 times less and approximately 2.9 times less than those of clothing materials such as T-shirts and working wear clothing, respectively. It was found that very strong correlation existed between total heat loss and evaporation loss. We suggested that the total heat loss determined according to ASTM F 1868 part C could be estimated from the values of evaporation loss.

Method for Increasing the Efficiency of Automatic Fire Extinguish System at Objects Of Power

Operation of energy facilities requires compliance with all safety standards, and especially fire safety. Emergency situations that arise when operated the power equipment damage not only the objects of the technosphere but also the environment. In recent years, can be noted a trend of quite intensive development of technological bases of technology water mist fire extinguishing. Using the methods of optical panoramic imaging PIV, IPI and the method of high-speed video recording were performed the experimental studies of the characteristics of evaporation of large single water droplets as they pass through the flames of oil and oil products with varying parameters of the processes (the initial size of 2–6 mm, the rate of 2–4 m/s and the temperature of water drops 290–300 K, the temperature of the combustion products 185–2073 K). Was established decisive influence droplet size, velocities at which droplets enter the gaseous medium, the initial water temperature on heating rate and evaporation of droplets in a stream of high-temperature combustion products.

On heat transfer and evaporation characteristics in the growth process of a bubble with microlayer structure during nucleate boiling

We have previously observed and experimentally measured a microlayer formed beneath a growing bubble during nucleate pool boiling. The initial microlayer thickness was of micrometer order and increased linearly with distance from the bubble inception site. The quantitative degree of contribution of the microlayer evaporation to bubble growth was still not elucidated, although a large number of experimental studies have been conducted on the distribution and evaporation characteristics of the microlayer. To clarify the heat transfer characteristics, especially the contribution of microlayer evaporation in nucleate pool boiling, numerical simulations are performed here for two phase vapor–liquid flow induced by the growth of a single bubble using the volume of fluid method. Furthermore, a special model is proposed to combine the microlayer and bulk liquid regions, the scales of which are extremely different in the simulations. The microlayer was neglected in the volume fraction calculation, while the evaporation from the microlayer was included by applying the source terms of the basic equations for the presence of a virtual microlayer. Similar tendencies were observed between the calculated and experimental results on the variations in the microlayer radius and bubble volume. The proportion of microlayer evaporation to total bubble volume was generally in agreement with the previous results, and the ratio of microlayer evaporation to the change in the total bubble volume was approximately 40 percent.

Theoretical analysis of screened heat pipes for medium and high temperature solar applications

A mathematical model is applied to study the cylindrical heat pipes (HPs) behaviour when it is exposed to higher heat input at the evaporator for solar collector applications. The steady state analytical model includes two-dimensional heat conduction in the wall, the liquid flow in the wick and vapour hydrodynamics, and can be used to evaluate the working limits and to optimize the HP. The results of the analytical model are compared with numerical and experimental results available in literature, with good agreement. The effects of heat transfer coefficient, power input, evaporator length, pipe diameter, wick thickness and effective pore radius on the vapour temperature, maximum pressure drop and maximum heat transfer capability (HTC) of the HP are studied. The analysis shows that wick thickness plays an important role in the enhancement of HTC. Results show that it is possible to improve HTC of a HP by selecting the appropriate wick thickness, effective pore radius, and evaporator length. The parametric investigations are aimed to determine working limits and thermal performance of HP for medium temperature solar collector application.