High-efficiency Heat Research Articles

Effect of Swirl on the Performance of LPG Domestic Burner

In the present experimental work, an1 attempt is made to improve the heating efficiency of the of the conventional LPG burner with modifications. The LPG burners having the multiple fuel jets with an angle of 15°, 20° and 25° are used to create the swirl in the flame jets. The porous medium is also used the burner for the study. The performance of the conventional LPG burner (radial burner) is studied in terms of heating efficiency for the different thermal inputs (Wattages) and the results are compared with that of swirl burners. Water boiling test is conducted according to BIS. The maximum heating efficiency for the porous burner for 20° burner shows the highest heating efficiency of 68% % which is 17% higher than the conventional burner.

Analysis and optimization of the curved trapezoidal winglet geometry in a high-efficiency compact heat exchanger

The present work is undertaken to optimize the geometry of the curved trapezoidal winglet mounted over each cooling tube to enhance the overall performance of the heat exchanger. Before conducting the optimization study, the most critical geometric entities have been identified, and this has helped in significantly reducing the computational overheads. It has been found that the three most critical design parameters are the arc radius (R), the angle subtended (θ) and the winglet's leading-edge height (h1), and the same are chosen for optimization. To plan the experiment, we make use of the Latin hypercube sampling (LHS) scheme. The system responses viz. the Colburn factor (j) and the friction factor (f) ‒ for different combinations of the independent variables ‒ are computed using the numerical simulations together with the conjugate heat transfer approach. To get the best outcome from computations, both fluid and solid domains have been discretized using hexahedra. We make use of the Reynolds-averaged Navier-Stokes (RANS) approach ‒ with SST k–ω (a 2-equation) turbulence model as a closure to RANS ‒ for evaluating the dependent variables. The artificial neural network (ANN) is trained using the data from the DoE table to build the metamodel necessary for conducting the multiobjective optimization. The genetic algorithm (GA) is employed to generate the optimized data sets. The study reveals that the optimized HE variants outperform the baseline model not only at the on-design condition but also at the off-design conditions. The resulting Pareto front points reveal very interesting results, and these data would facilitate the designers to make choices over a wide range of the VG geometry of the heat exchanger.

A robust in vitro anticancer activity via magnetic hyperthermia mediated by colloidally stabilized mesoporous silica encapsulated La0.7Sr0.3MnO3 core- shell structure

In magnetic hyperthermia therapy (MHT), lanthanum strontium manganese oxide (LSMO) has drawn significant attention due to its ability to prevent overheating problems. However, heating efficiency, colloidal stability as well as cell viability imparted by LSMO has limited its application for clinical purpose. To circumvent the above issues, we report a strategy to encapsulate the LSMO within a mesoporous silica shell. The uniform mesoporous coating of silica on LSMO of thickness 9 nm is characterized by TEM. Moreover, the colloidal stability as well as cell viability are found to be significantly improved after silica coating on LSMO as demonstrated by the DLS measurement and MTT assay respectively. The heating efficiency of mesoporous silica encapsulated LSMO nanoparticles (MSLN) under an alternating magnetic field (AMF) of a frequency 350 kHz and amplitude of 14 kA/m is tested and found to have high heating efficiency (255 W/g) and intrinsic loss power found to be 3.7 nHm2/kg. Further linear response theory has been used to numerically evaluate the SAR value to validate the experimental values. In vitro biological characterization data using lung cancer cells (A549) revealed that MSLN resulted in approximately 80 % cell death at nanoparticle dose within the biosafety limit. Cell death pathway analysis showed apoptosis as the predominant mode of cell death at 43 °C. Therefore, the outcomes of this study warrant further testing of MSLN in in vivo models to test them for potential implications in the field of cancer therapy.

Stoichiometry and Orientation- and Shape-Mediated Switching Field Enhancement of the Heating Properties of Fe3O4 Circular Nanodiscs

The generation of topological magnetic vortex-domain structures in iron-oxide nanomaterials has promising applications in biomedical scenarios, such as heat generators for hyperthermia treatments. In this report we describe alternative kinds of magnetic-vortex nanoparticles, circular ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ nanodiscs (NDs), and dissect their heating properties by in-depth investigation of their shape and size, stoichiometry, orientations, and switching field ``${H}_{S}$'' behaviors, through experiments and theoretical simulation. We find that the stoichiometric NDs show better heating performance than nonstoichiometric materials because of the significant electron hopping between ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ ion. The higher heating efficiency (in terms of specific absorption rate, SAR) is observed only for the higher switching field regime, an effect that is associated with the parallel and perpendicular alignment of nanodiscs with respect to low and high ac magnetic field, respectively. A higher SAR of approximately 270 W/g is observed at a higher switching field (approximately 700 Oe) for NDs of diameter 770 nm, which increases by a factor of 4 at a switching field of approximately 360 Oe for NDs of diameter 200 nm. The reported results suggest that the heating efficiency in these systems can be enhanced by controlling the switching field, which is, in turn, tuned by size, shape, and orientation of circular magnetic vortex nanodiscs.

A novel dual-temperature ejector-compression heat pump cycle - exergetic and economic analyses

• Two dual-temperature air-source heat-pump systems are compared. • Different eco-friendly refrigerants are evaluated in the systems, and their effects are compared. • The DAHP-II outperforms the DAHP-I system significantly in terms of economic and exergy efficiency. • The refrigerant type shows slightly effect on system exergy efficiency, while affects the economic obvious. High-efficiency air source heat pumps are of great importance for energy saving and environmental protection, especially for the cold area in north China. In this study, the thermo-economic performance of the dual-temperature ejector-compression air-source heat-pump (DAHP) cycle, is conducted wherein R1234yf, R290, and R134a are used as refrigerants. Two configurations are examined: DAHP-I (without an ejector, conventional system for comparison) and DAHP-II (enhanced by an ejector). The effects of the principal operating parameters on the system performance, including the exergy destruction ( Ex d_tot ), exergy efficiency ( η ex _sys ) and economic, are investigated, and the two systems are compared. The results indicate that the DAHP-II significantly outperforms the DAHP-I in terms of Ex d_tot , η ex _sys and economic index, and the R290 is the most suitable refrigerant applied for the DAHP-II system. Compared with DAHP-I, the Ex d_tot for DAHP-II is reduced by 24.0%–54.8%. For DAHP-II, although the refrigerant type affects Ex d_tot and η ex _sys slightly, while the effect on economic is noticeable. Comparing with R1234yf, the system using the R134a and R290 as the working fluid, the total annual capital cost rate ( C ˙ t o t ) can be reduced by 6.2% and 11.0% respectively. Besides, the DAHP-II outperforms the DAHP-I system significantly with the R134a, R290 and R1234yf as refrigerant in terms of economic. The relative decrease ratio in total annual capital cost rate ( C ˙ t o t ) are 21.6%, 13.5% and 24.0% respectively. This study provides a basis for the application of DAHP system.

All‐MXene Cotton‐Based Supercapacitor‐Powered Human Body Thermal Management System

AbstractPersonal body thermal management (PBTM) has shown great potential in the application of artificial skin, smart clothing, and health care for the rapidly developed flexible electronics and “Internet of Things”. However, the heating efficiencies of the previously reported PBTM systems are relatively low with low response rate and high driving voltage, which are not satisfying for wearable devices. Here, we report a MXene‐coated cotton fabric (MCF)‐based PBTM system, which shows good water vapor permeability, air permeability, wear resistance, and wash stability. The optimal MCF shows high electron conductivity of 197 mS cm−2 and high heating efficiency, which could be heated up to 100 °C within 10 s under the low applied potential of 3 V. By applying a low voltage of 1.5 V, the MCF exhibited a high temperature of 45 °C, meeting the requirement of human body. In addition, serving as the electrode material of supercapacitors, the MCF exhibits high areal specific capacitance of 208 mF cm−2 at a scan rate of 5 mV s−1. The symmetric supercapacitor device could provide a high energy density of 2 μWh cm−2 and power density of 5.3 mW cm−2. Using the MCF‐based symmetric supercapacitor as the power source, the MCF could be heated and employed as a supercapacitor‐powered PBTM system, which indicates its significant potential for the application of wearable PBTM and beyond.

Modeling and determination of total heat exchange factor of regenerative reheating furnace based on instrumented slab trials

Regenerative heating furnace as a high-efficiency and energy-saving heating equipment is widely applied in iron and steel industry. Accurate knowledge of total heat exchange factor of regenerative heating furnace is of great significance to improve its on-line control performance. Therefore, determination of total heat exchange factor of regenerative reheating furnace is investigated in this work. A three-dimensional mathematical model of regenerative reheating furnace based on the analysis of heat transfer process is established. The zonal method is used to solve the temperatures of gas zone, slab surface zone and wall surface zone, in which the Monte Carlo method is used to compute the total radiant exchange areas of thermocouple to all other zones in the furnace. The total heat exchange factors of regenerative reheating furnace are determined and the effects of thermal and operational parameters, such as productivity, fuel consumption and slab hot charging temperature are analyzed. The results show that the total heat transfer factor increases with the decrease of fuel consumption or slab hot charging temperature, and increases with the increase of productivity. The present work is valuable for dynamical compensation of total heat exchange factor of the online control mathematical models in regenerative reheating furnace.

Analysis of refrigeration and heating efficiency of ground source heat pump

This paper studies the efficiency of ground source heat pump(GSHP) used in refrigeration and heating, comparing it with air source heat pump (ASHP) by means of theoretical analysis and experiment. The results were as follows, the cooling efficiency of GSHP in summer is higher than that of heating in winter because of the heat is transferred from high temperature to low temperature during cooling in summer, which can be compared to heat pipe; By calculating the power consumption of pump and fan, it is found that theoretically GSHP unit and system have higher heating efficiency than ASHP; The experiment shows that the daily average COP of the unit and the system is 4.22-4.62 and 3.26-3.55, respectively, both the unit COP and system COP of GSHP is higher than that of ASHP, which is consistent with the theoretical analysis.

Carbothermal Treated Iron Oxide Nanoparticles with Improving Magnetic Heating Efficiency for Hyperthermia

Iron oxide nanoparticles with high magnetic heating efficiency is highly desired for magnetic hyperthermia applications. In this paper, carbothermal treatments with graphene were used for improving the magnetic heating efficiency of iron oxide nanoparticles. With the increasing treatment temperature from 400°C to 700°C, the specific absorption rate (SAR) increased 2-7 folds. Oxygen vacancies resulted from carbon reduction process, along with the rapid grain growth (from 5.1 nm to 225.6 nm), improved eddy current loss. SAR calculations suggested that eddy current loss accounted up to 23.9%-78.5% of the total SAR after carbothermal treatments, which was the main factor for SAR improvements. This work may provide a methodological reference of preparing iron oxide nanoparticles for magnetic hyperthermia.

Preparation and Properties of Microwave-Absorbing Asphalt Mixtures Containing Graphite and Magnetite Powder

Abstract The concept of microwave-absorbing asphalt concrete has been proposed to create an asphalt mixture with high microwave heating efficiency. A mixture of 20 % graphite powder and 80 % magnetite powder was used as the microwave-absorbing composite to replace the common mineral filler in asphalt mixtures to improve its microwave absorption capacity. This study aimed to evaluate the effect of proposed absorbent composite on the properties and microwave heating efficiency of asphalt mixtures. The results indicate that the addition of graphite and magnetite powder exhibited an improvement in the microwave heating efficiency of asphalt mixtures. The heating rate of asphalt mastic was improved by more than 10 times, whereas the heating rate of asphalt mixtures containing the absorbent composite was improved by 47.8 %. The pavement performance test results show that the mechanical performances including the dynamic stability, bending strain, residual Marshall stability, and ratio of splitting tensile strength after and before the freeze-thaw cycle satisfy the relevant specification requirements.

Flame-retardant MXene/polyimide film with outstanding thermal and mechanical properties based on the secondary orientation strategy.

With the development of multifunction and miniaturization in modern electronics, polymeric films with strong mechanical performance and high thermal conductivity are urgently needed. Two-dimensional transition metal carbides and nitrides (MXenes) have attracted extensive attention due to their tunable surface chemistry, layered structure and charming properties. However, there are few studies on using MXenes as fillers to enhance polymer properties. In this paper, we fabricate a three-dimensional foam by the freeze-drying method to enhance the interfacial interaction between adjacent MXene sheets and polyimide (PI) macromolecules, and then a composite film with a dense and well-ordered layer-by-layer structure is produced by the hot-pressing process. Based on the secondary orientation strategy, the resultant MXene/PI film exhibits an enhanced thermal conductivity of 5.12 ± 0.37 W m−1 K−1 and tensile strength of 102 ± 3 MPa. Moreover, the composite film has good flexibility and flame retardancy owing to the synergistic effect of MXene sheets and PI chains. Hence, the MXene/PI composite film with the properties of flexibility, flame-retardancy, high mechanical strength and efficient heat transmission is expected to be used as the next thermal management material in a variety of applications.

Evaluation of Butt Joint Produced by a Hot-Wire CO2 Arc Welding Method

The purpose of this study was to develop a high-efficiency and low-heat-input CO2 arc-welding process using hot-wire feeding. A previous paper showed that the proposed hot-wire CO2 arc-welding process has the potential to simultaneously achieve both high efficiency and low heat input. This paper investigated the production of a sound joint with only two welding passes on a butt joint of 20mm-thick steel plates with no defects or unstable welding phenomena using the developed hot-wire CO2 arc-welding process. Welding condition optimization was investigated using high-speed imaging and cross-sectional observations. The optimized conditions, which were the combinations of the welding current and hot-wire feeding speed as 350A and 7.5m/min, 400A and 5m/min, 450A and 5m/min, 500A and 5m/min, derived to avoid the presence of defects and molten metal precedence, which achieved sound welded joints possessing adequate properties of strength and toughness.

Эффективность применения рабочих тел в цикле Ренкина в энергосберегающих системах транспортировки природного газа

In this paper, the application of various non-ozone-depleting low-boiling working fluids for the Rankine cycle is analyzed based on exergy efficiency. The Rankine cycle is used for high-efficiency waste heat recovery from flue gases generated in gas transport systems at natural gas compressor stations. The system was modelled based on calculations using the CHEMCAD software in conjunction with the “Energy unit” module compatible with the main program interface, which was used for assessing system energy efficiency. It was concluded that the neopentane Rankine cycle with a regenerator is more efficient. Preliminary economic analysis has shown that the proposed system has an acceptable payback period (up to 6 years).

Rapid tumor inhibition via magnetic hyperthermia regulated by caspase 3 with time-dependent clearance of iron oxide nanoparticles.

Among conventional cancer therapies, radio-frequency magnetic hyperthermia (MHT) has widely been investigated for use with magnetic nanoparticles (MNPs). However, the majority of in vivo biodistribution studies have tested very low MNP dosages (equivalent to magnetic resonance imaging (MRI) applications) to check for clearance rate; which is far below the clinical dose of MHT. Due to this poor validation in preclinical scenarios, quite a few MNPs already in clinical use were later discontinued, on grounds of unexpected clinical outcomes in terms of inflammation, and prolonged clearance in vivo. By exploiting an economical method of synthesis, we have developed chitosan-coated Fe3O4 nanoparticles with high heating efficiency performance. Their anti-tumor response was evaluated in an ectopic tumor model of C6 glioblastoma by MHT. The intratumoral injection of MNPs on days 1 and 7 resulted in rapid tumor inhibition rate of 69.4% within 8 days, with complete inhibition within 32 days, and no recurrence recorded over a 5-month follow-up. Notably, the MNP-mediated MHT therapy achieved the highest degree of therapeutic efficacy required for complete tumor ablation by combining controlled temperature range (<44 °C), reduced MNP dosage; much lower than in most reported studies, and AMF parameters (time of exposure and frequency) within the clinical safety limit. Periodic body weight measurements confirmed negligible adverse side effects in rats. The anti-tumor activity was validated by severe apoptosis (TUNEL, cleaved Caspase-3), reduced proliferation (Ki 67) and disrupted vasculature (CD 31) in the Fe3O4-MHT-treated group. Real-time gene expression of pro-inflammatory cytokines (IL-6, TNF-α, IL-1α, IL-1β) confirmed the intratumoral activation of IL-6, suggesting the role of immunomodulation in triggering the adaptive immune response for faster tumor regression in the treated group. In addition, the biodistribution and clearance rate of MNPs monitored using ICP-OES confirmed their time-dependent biodegradation via excretion (urine, feces), phagocytosis (liver) and circulatory system (blood), with negligible deposition in other major organs (kidney, heart, lungs). Although we could not show complete clearance of our MNPs within the time frame tested, future studies should focus on combining MHT with immunotherapy, and target tumors at a much-reduced iron dose, consequently improving in vivo clearance rate, and hence overcoming the limitations of MHT in clinical therapy.

Performance analysis of new structure heat exchanger based on field synergy and numerical simulation

High efficiency heat exchanger is always a hot topic, and field synergy theory is introduced as an important means to optimize the heat transfer efficiency. Based on the field synergy theory, a new type of heat exchanger is proposed in this paper, in which, the cold and hot fluid presents reverse cross flow law. Through the verification of the test and numerical simulation results, a reasonable numerical simulation model and method are obtained. Then, the flow and heat transfer conditions of the new structure heat exchanger are simulated by the verified numerical simulation technology. The conclusion is as follows: K-ε turbulence model and coupled heat transfer model can be effectively used in the numerical simulation of heat exchanger. And the reverse cross convection heat exchanger can effectively improve the uniformity of water temperature distribution in the heat exchanger.

A Study of Mesh Sheets of 3-kW Stirling Engine

In recent years, the interest in low-pollution and high-efficiency heat engines has been increasing due to the growing awareness of environmental protection, and power generation at relatively low temperatures, such as use of exhaust heat and sunlight, has been attracting attention. Compared with other heat engines, Stirling engine is very important because it can be driven by any heat source at low temperatures, such as exhaust heat, and it does not emit exhaust gas. In order to realize a more efficient Stirling engine, it is essential to design a heat exchange system that is suitable for each component. Performance measurement and analysis on a new mesh regenerator material at low temperature difference using a 2-piston alpha-type 3-kW Stirling engine, NS03T are carried out. Mesh sheets developed for high performance Stirling engines can be designed with CAD and CAM technologies by etching process. For this study, M5 and M7 mesh sheets which are thin sheets of stainless steel with square holes in a grid arrangement, are used. With nitrogen and helium as the working fluid, the engine performance is measured by changing the charge pressure, heating temperature, and engine speed to clarify the flow resistance and heat transfer characteristics of the M5 and M7.

Experimental performance of ammonia-charged micro heat pipe array for energy saving

Energy is required to be transported effectively during energy exploration, storage and utilization. Micro heat pipe array is a high efficient heat transfer device. Ammonia is promising working medium for micro heat pipe array due to its outstanding thermophysical parameters. However, there are no ammonia-charged micro heat pipe arrays being investigated up to now. In this paper, ammonia-charged micro heat pipe arrays were experimentally studied to enhance the heat transfer capability for energy saving and efficient utilization in practical applications. With dimensions of 520 mm × 20 mm × 2 mm, the micro heat pipe array reached a high heat transfer capability of 175 W, corresponding to an equivalent thermal conductivity of 7.06 × 105 W/(m∙K). Furthermore, the influence of the tilt angle of the micro heat pipe array on the heat transfer characteristics was studied and analyzed. With the increase of the tilt angle, it tended to achieve higher heat transfer capacity due to higher pressure head generated by gravity. Moreover, temperature tolerance test of a shorter micro heat pipe array was conducted and it could operate steadily and reliably under 120 °C, corresponding to a pressure of 92 bar. The experimental results demonstrated that ammonia could make great improvements for energy systems based on micro heat pipe arrays in various applications.

The effect of heat recovery on the optimal values of helicopter turboshaft engine parameters

Recent studies related to fuel economy in air transport conducted in our country and abroad show that the use of recuperative heat exchangers in aviation gas turbine engines can significantly, by up to 20...30%, reduce fuel consumption. Until recently, the use of cycles with heat recovery in aircraft gas turbine engines was restrained by a significant increase in the mass of the power plant due to the installation of a heat exchanger. Currently, there is a technological opportunity to create compact, light, high-efficiency heat exchangers for use on aircraft without compromising their performance. An important target in the design of engines with heat recovery is to select the parameters of the working process that provide maximum efficiency of the aircraft system. The article focused on setting of the optimization problem and the choice of rational parameters of the thermodynamic cycle parameters of a gas turbine engine with a recuperative heat exchanger. On the basis of the developed method of multi-criteria optimization the optimization of thermodynamic cycle parameters of a helicopter gas turbine engine with a ANSAT recuperative heat exchanger was carried out by means of numerical simulations according to such criteria as the total weight of the engine and fuel required for the flight, the specific fuel consumption of the aircraft for a ton- kilometer of the payload. The results of the optimization are presented in the article. The calculation of engine efficiency indicators was carried out on the basis of modeling the flight cycle of the helicopter, taking into account its aerodynamic characteristics. The developed mathematical model for calculating the mass of a compact heat exchanger, designed to solve optimization problems at the stage of conceptual design of the engine and simulation of the transport helicopter flight cycle is presented. The developed methods and models are implemented in the ASTRA program. It is shown that optimal parameters of the working process of a gas turbine engine with a free turbine and a recuperative heat exchanger depend significantly on the heat exchanger effectiveness. The possibility of increasing the efficiency of the engine due to heat regeneration is also shown.

Improving the efficiency of aviation turbofan engines by using an intercooler and a recuperative heat exchanger

Continuous improvement of fuel efficiency of aircraft engines is the main global trend in modern engine construction. To date, aviation gas turbine engines have reached a high degree of thermodynamic and design-and technology perfection. One of the promising ways to further improve their fuel efficiency is the use of complex thermodynamic cycles with turbine exhaust heat regeneration and with intermediate cooling in the process of air compression. Until recently, the use of cycles with a recuperative heat exchanger and an intercooler in aircraft gas turbine engines was restrained by a significant increase in the mass of the power plant due to the installation of heat exchangers. Currently, it has become technologically possible to create compact, light, high-efficiency heat exchangers for use on aircraft without compromising their performance. An important target in the design of engines with heat recovery is to select the parameters of the working process that provide maximum efficiency of the aircraft system. The article focuses on the statement of the task of optimization and choice of rational parameters of the working process of a bypass three-shaft turbojet engine with an intercooler and a recuperative heat exchanger. On the basis of the developed method multi-criteria optimization was carried out by means of numerical simulations. The results of optimization of thermodynamic cycle parameters of a bypass three-shaft turbojet engine with an intercooler and a recuperative heat exchanger in the aircraft system according to such criteria as the total weight of the engine and fuel required for the flight, and the aircraft specific fuel consumption per ton - kilometer of the payload are presented. A passenger aircraft of the Airbus A310-300 type was selected. The developed mathematical model for calculating the mass of a compact heat exchanger, designed to solve optimization problems at the stage of conceptual design of the engine is presented. The developed methods and models are implemented in the ASTRA program. The possibility of improving the efficiency of turbofan engines due to the use of complex thermodynamic cycles is shown.

High-Efficiency HVAC System with Defog/Dehumidification Function for Electric Vehicles

Electric vehicles (EVs) generally use an electric heating system to provide heat. However, the heating system consumes a large amount of energy, and therefore reduces the mileage of the vehicle. The energy consumption can be reduced by replacing the electric heating system with a heat pump air conditioning system. Such systems achieve an effective heating of the vehicle interior, but do not provide a defog or dehumidification function. Consequently, the inside surface of the windshield tends to fog in cold weather; leading to poor driver visibility and an impaired road safety. Accordingly, the present study proposes a novel high-efficiency heating, ventilation and air conditioning (HVAC) system with both heating and defog/dehumidification functions for electric vehicles. The effectiveness of the proposed system is investigated experimentally using a simulated cabin placed in a temperature and humidity-controlled test chamber. The experimental results confirm that the HVAC system achieves the required cooling, heating and defog/dehumidification functions and meets the corresponding standards. Moreover, the application of HVAC in EVs could lead to significant electrical power saving effect.