Tube Heat Research Articles

Study on Shutter Heating Performance of Gas Turbine Intake System

Abstract Aiming at the anti-icing and de-icing requirements of gas turbine intake system, study the heating performance of a typical shutter vane, and compares and analyzes the influence of different ambient temperature and different electrothermal pipe heat generation rate on vane temperature distribution and heat transfer characteristics. The results show that the air convection at different positions on the blade surface of the louver leads to the difference in the temperature distribution of the upper and lower surfaces of the blade, as well as the leading edge and trailing edge of the blade, and the leading edge of the blade, as the area with the lowest overall temperature distribution of the blade, should be focused on in the design of anti-icing and de-icing systems. Increasing the heat production rate of the electric heating tube, there is more heat flow near the midline of the blade, which makes the temperature rise at this position the highest, and it is necessary to pay attention to the energy waste and blade damage caused by local overheating of the blade. Therefore, when the ambient temperature increases from 245.15 K to 318.15 K, the leaf temperature increases from 248.73 K to 322.74 K, and the temperature rise also increases from 3.58 K to 4.59 K. The electrothermal technology can be used to the anti-icing and de-icing of the intake system shutters on the basis of choosing the heat generation rate of the electrothermal tube reasonably.

Study on the mechanical properties of PES-HmA samples printed by selective laser sintering under various pre-heating conditions

The purpose of this study is to investigate the influence of pre-heating characteristics on the mechanical properties and forming process of selective laser sintering (SLS) printed PES-HmA samples. An experimental setup with four heating tubes was designed to study the pre-heating temperature distribution on the powder bed. The pre-heating temperature distribution on the powder bed was captured using a thermal imaging camera. A method for evaluating pre-heating temperature distribution based on the average and standard deviation of surface temperature was proposed. The heating tube installation position was optimized using a response surface experiment study based on the temperature distribution evaluation. By optimizing the installation position of the tubes, the temperature distribution on the powder bed tends to become uniform. The effect of pre-heating temperature value and distribution on the mechanical properties of the SLS printed PES-HmA samples was also experimentally investigated. The cross sectional microstructure of the printed samples were examined by scanning electron microscope to analyze the layer formation process at different pre-heating temperature. By increasing the pre-heating temperature from 70°C to 100°C, the material diffusion at the layers interface was improved, which made the tensile strength of sample increased by 376%, and the flexural strength increased by 224%.

Evaluation of heat transfer enhancement effect at the hot/cold end of a Stirling engine using performance improvement factor

The driving force of a Stirling engine comes from the heating expansion and cooling compression of working medium. The enhancement of heat transfer capacity of the hot/cold end is the key to improve the Stirling engine performance, while how to objectively evaluate the heat transfer enhancement effect is a precondition. Herein, a polytropic model of a Stirling engine thermal cycle process was firstly established. A method for evaluating the heat transfer enhancement performance under oscillating flow was proposed based on the efficiency and power improvement of a Stirling engine. This method was further used to evaluate the heat transfer enhancement effect of a novel four-leaf helical heating tube under oscillating flow, the efficiency and power improvement factor of which was reached 13.5 % and 6.1 %, respectively. The results show that the efficiency and power improvement evaluation criterion was more comprehensive and intuitive in evaluating the heat transfer enhancement performance under oscillating flow compared with the conventional evaluation indictor like performance evaluation criterion and equivalent tube length and tube number criterion.

Design, numerical optimisation and experimental validation of an innovative solar-powered tube heater with multiple air impingement jets

This research investigates a novel tube heater designed for the seamless integration of an innovative solar thermal system into the powder-based coating process to heat steel tube at a temperature of 240 °C. It incorporates a comprehensive numerical model developed and assessed using ANSYS FLUENT, concentrating on seven critical parameters that significantly influence the tube heater’s performance and size. These parameters include tube heater length, jets’ length, funnel height, Z/Djet, Y/Djet and X/Djet ratios, as well as jet diameter. The findings underline the critical role of tube heater length in enhancing heat transfer and maximising thermal efficiency, while reducing jet length and funnel height demonstrated negligible effects on thermal performance, promoting material economy. A lower Z/Djet ratio enhanced heat transfer uniformity, improving thermal performance, while optimal X/Djet and Y/Djet ratios were identified as 4 maintaining a balance between heat transfer rate and energy consumption. A smaller jet diameter proved beneficial since the potential core was not achieved, increasing heat transfer to the steel tubes. The experimental model, conducted to validate the novel tube heater’s performance, remarkably aligns with the numerical model, showing an R-squared value of 0.992. These results affirm the numerical setup’s accuracy and reliability in capturing the tube heater’s thermal behaviour. It is concluded that the novel tube heater stands as a highly efficient solution for the seamless integration of solar thermal systems into the powder-based coating process of steel tubes, promising significant emissions reduction.

Numerical simulation study of boiling heat transfer of R290 flow in horizontal microtubes

Abstract R290 is considered to be an excellent alternative refrigerant for domestic air conditioners in the future. In this paper, CFD numerical simulation was used to obtain the flow field distribution of R290 in a micro-fine circular tube with an inner diameter of 2mm under a specific range of working conditions, and the effects of saturation temperature, mass flow density, heat flow density and tube type on the boiling heat transfer characteristics of R290 tube were investigated. The results show that the boiling heat transfer coefficient increases with the increase of saturation temperature, and the maximum value of the heat transfer coefficient increases by 8.1% when the saturation temperature increases from 284K to 286K. The boiling heat transfer coefficient increases with the increase of mass flow density, and the maximum value appears in the medium dryness range. The boiling heat transfer coefficient in the tube increases and then decreases when the heat flow density increases from 10 kW/m2 to 20 kW/m2 and increases faster at high heat flow density conditions. In addition, compared with the circular tube, the boiling heat transfer coefficient in the elliptical tube with an aspect ratio of 1.56 increases by 2.78% for R290 under the same flow area.

Radiation model and thermal characteristics of OLED glass substrate using electric heating tube

Glass substrate (GS) heating is a fundamental but significant technology for organic light emitting diode (OLED), which is critical to OLED displaying quality and efficiency. A rapid and reliable theoretical model is intensely demanded to guide practical system design, simulation analysis and experimental research for GS heating, but present radiative models are improper or inconvenient. Therefore, this paper establishes a new and direct calculation model with the addition of correctional coefficient 0.5 to blackbody radiation power of electric heating tube (EHT) and the proposal of comprehensive angle coefficient X, which can solve single and multi-source radiation problems theoretically. The simulation and experiment are both conducted for comparison analysis. The temperature errors of theory and simulation for multi EHTs are all within 1 % when compared with experimental results, which well validates the reliability and accuracy of theoretical and simulation models. Large EHT radius r, small distance L between EHT and GS, and suitable EHT number n are suggested, which benefits to the improvement of radiation heating and temperature uniformity of GS. It is hoped that this study can provide a useful tool on thermal radiation analysis and also a valuable promotion for practical OLED heating technology.

Design of Small-Size Lithium-Battery-Based Electromagnetic Induction Heating Control System

This paper presents the design and optimization of a small-size electromagnetic induction heating control system powered by a 3.7 V–900 mAh lithium battery and featuring an LC series resonant full-bridge inverter circuit, which can be used for small metal material heating applications, such as micro medical devices. The effects of the resonant capacitance, inductor wire diameter, heating tube material, and wall thickness were studied to maximize the heating rate of the workpiece and simultaneously reduce the temperature rise of the NMOS transistor. The optimal circuit configuration meeting the design requirements was finally identified by comparing the operational parameters and NMOS transistor loss under different circuit conditions. Validation experiments were conducted on designed electromagnetic induction smoking devices. The results indicate that under an output current of 4.6 A, the heating tube can reach the temperature target of 250 °C within 11 s, and all NMOS transistors stay below 50 °C in a 5 min heating process.

Heat transfer characteristics of oil receiving and delivering process in crude oil storage tanks

The study used numerical simulation methods to investigate the influence of different oil receiving and delivering cases on the non-uniform physical field within the storage tank. The results showed that the evolution of the physical field can be divided into three stages: diffusion, suppression, and equilibrium. The computational domain was divided into three zones based on the crude oil heating rate: significant influence zone, indirect influence zone, and minimal influence zone, and the indirect influence zone exhibits the most pronounced variations in velocity and temperature. The process of receiving oil with high-flow rate and low-temperature was found to be more conducive to the full use of heat in the tank when the heat exchanging quantity per unit time was the same. The synergistic effect of tubular heating and oil receiving and delivering resulted in a 21 % higher average temperature increase rate than the sum of the two processes. Finally, the study quantitatively described the linear relationship between the average temperature in each region and factors such as oil inlet velocity, oil receiving temperature, oil receiving and delivering time, and heating tube temperature, providing theoretical guidance for process planning in actual oil storage tank receiving and delivering.

An adjoint Green’s function approach for thermoacoustic instabilities in a duct with mean flow

Thermoacoustic instabilities arise from the feedback between an acoustic field and the unsteady heat released in a burner, yielding self-sustained oscillations. A fundamental framework for modelling thermoacoustic instabilities in systems where a mean flow is present is introduced, based on the definition of the adjoint Green’s function which permits to convert the acoustic analogy equation into an integral equation. The adjoint Green’s problem produces sensitivity functions which quantify the response of the system to initial, boundary or other forcing terms. A simple one-dimensional system is examined; it includes a steady uniform mean flow and a nonlinear heat source with an amplitude-dependent time-delay heat release model. The versatility of the approach is demonstrated by applying it to two resonators characterized by different acoustic boundary conditions: a Rijke tube and a quarter-wave resonator. The control parameters are: heat source position, heater power and tube length. The results reveal that the proposed analytical framework successfully captures the limit cycles, triggering phenomena, hystereses, and Hopf bifurcations observed in experiments. We show that the mean flow velocity cannot be discarded in the study of such systems; by increasing it, a stabilization generally ensues, with a modification of the bistability characteristics of the system.

Associations between exposure to extreme ambient heat and neural tube defects in Georgia, USA: A population-based case-control study

IntroductionThe association between extreme ambient heat exposures during pregnancy and neural tube defects (NTDs) in offspring remains unclear. This study sought to estimate the association between exposure to extreme ambient heat during periconception and NTDs. MethodsThis population-based case-control study in Georgia, USA (1994–2017) included 825 isolated NTD cases (473 anencephaly, 352 spina bifida) and 3,300 controls matched 1:4 on county of residence and time period of delivery. Daily ambient temperature data were linked to fetal death and birth records by county of residence. Extreme ambient heat exposure was defined as the number of consecutive days the daily apparent temperature exceeded the county-specific 95th percentile (derived over 1980–2010) during an eight-week periconception period. We calculated adjusted odds ratios (aORs) and 95% confidence intervals (CI) using conditional logistic regression models adjusted for maternal age, education, and ethnicity and month and year of last menstrual period. ResultsThe aORs for NTDs were 1.09 (95% CI 1.01, 1.17), 1.18 (95% CI 1.03, 1.36), and 1.29 (95% CI 1.04, 1.58) for exposure to 1–2, 3–5, and 6 or more consecutive days with apparent ambient temperatures exceeding the county-specific 95th percentile during periconception, respectively, compared to no days of extreme ambient heat exposure. Weekly analysis of extreme heat exposure indicated consistently elevated odds of offspring NTDs during periconception. These results were largely driven by spina bifida cases. ConclusionsOur results highlight potential health threats posed by increasing global average temperatures for pregnant people with implications for increased risk of neural tube defects in their offspring.

Investigation on thermochemical heat charging and discharging behavior of Ca(OH)2/CaO in a fixed bed reactor

Thermochemical heat storage (TCHS) technology plays a crucial role in the energy system, essential for maintaining the balance between energy supply and demand. The Ca(OH)2/CaO system holds significant promise for TCHS thanks to its high energy storage density, cost-effectiveness, and minimal heat loss. However, further research is required to elucidate the coupling mechanisms of the various physicochemical processes involved and to optimize the overall system performance. This paper focuses on assessing and elucidating the multi-physics coupled transport rules during both the charging and discharging stages in a fixed-bed reactor based on the developed numerical model. Results manifest the bed temperature rapidly increases to around 950 K, then slows down as the endothermic reaction predominates, completing dehydration in 1,900 s. During discharging, hydration conversion advances in a “U”-shaped pattern from the vapor inlet and side wall to the outlet, driven by the high vapor content near the inlet and the lower temperature near the wall. Furthermore, a thorough sensitivity analysis of the main parameters such as thermal conductivity and porosity is conducted to determine how different operating conditions affect the charging and discharging processes. Finally, a new reactor structure is proposed, in which a gas-guide duct is added at the central axis of the reactor to improve mass transport and uniformly distributed finned heating tube bundles to enhance heat transfer. These two functions can shorten the charging period by 9 % and 16 % respectively. The results can aid in predicting thermochemical conversion behaviors and multi-physic coupling transport processes, while also providing a foundational reference for the design of TCHS systems.

Resonant peak reduction of a rotor system based on gradually variable stiffness of supports with shape memory alloy springs

A novel method for reducing the resonant peak of a flexible rotor at critical speeds based on control of the gradual variable stiffness of supports (GVSS) using shape memory alloy (SMA) springs is presented in this paper. The resonance peaks of a rotor structure can be attenuated through the design of GVSS law. Firstly, the impact of GVSS on the rotor's critical speeds was analyzed, and the mechanical mechanism of vibration reduction based on GVSS was identified. Secondly, a rotor system with a single critical speed was used for simulation analysis and it was founded that the starting time to change support stiffness and the change rate were two critical factors that affect vibration reduction. Then, a further simulation was undertaken on a test rig designed with dynamic similarity of an aeroengine rotor having multiple supports and multiple critical speeds. The range of the variable stiffness with SMA springs’ supports and the control strategy of GVSS were investigated. Afterwards, the test rig was manufactured and assembled for testing and validation. To achieve rapid temperature changes for variation of the support stiffness, an innovative design utilizing the carbon fiber heating tubes and the liquid nitrogen sprays for heating and cooling of shape memory alloy springs was carried out. The test results indicate that using gradually variable stiffness of supports with SMA Springs can effectively reduce the multiple resonance peaks of a rotor, with a maximum suppression rate of 52.3 %. This verifies the feasibility of the method. It also indicates the potential for further engineering applications.

Flow and heat transfer performance of reciprocating oscillatory flow in a Stirling engine compared to steady unidirectional flow

The driving force of a Stirling engine comes from the thermal expansion and cold compression of working gas under reciprocating oscillating flow, the flow and heat transfer performance of which is significantly different with that of steady state unidirectional flow. In this work, the performance differences in a heating tube for a Stirling engine under steady state unidirectional and reciprocating oscillating flows were studied. The results indicate that the temperature distribution was mainly dependent on the inlet velocity for a steady unidirectional flow. For a reciprocating oscillatory flow, the temperature distribution was greatly affected by the working gas state in the previous period besides the inlet velocity. Furthermore, a slightly weaker of heat transfer was obtained for reciprocating oscillatory flow, accompanying with a slightly stronger pressure consumption. The change time of pressure difference, velocity and heat transfer for the reciprocating oscillatory flow were earlier than, substantially equal to, and later than that of the steady unidirectional flow. Finally, the entry-return asymmetric insert was suggested to prioritize the heat transfer enhancement in entry process of a heating tube under reciprocating oscillatory flow to achieve the excellent overall performance for a Stirling engine.

Experimental study on nitrogen pulsating heat pipes with different heat transmission distances and configurations

The heat transfer performance of nitrogen PHPs with different heat transmission distances (100 mm and 500 mm) and tube configurations (single-loop and complex-loop) were experimentally investigated. Experiments were conducted in the vertical bottom heat mode with different filling ratios (15 %–70 %). The results showed that the maximum effective thermal conductivity increased proportionally with the heat transmission distance whereas the thermal resistance remained constant (0.2 K/W at a filling ratio of 31.8 %). This verified the outstanding long-distance heat transfer advantage of the nitrogen PHP. Experiments at different filling ratios showed that the maximum thermal conductivity decreased as the filling ratios increased. A filling ratio of 31.8 % was recommended. Under this operating condition, the PHP can load the maximum heat input while exhibiting relatively high effective thermal conductivity. Compared to the single-loop configuration, the complex-loop exhibited higher effective thermal conductivity, and this enhancement in thermal performance was more pronounced for the longer PHP.

Exploring the impact of parameters on flow boiling heat transfer in microchannels and coated microtubes: A comprehensive review

Abstract The aim of this study is to present a comprehensive review of the impact of various parameters on flow boiling heat transfer in microchannels and coated microtubes. The objectives of this study are to analyze the existing literature, identify the research methods employed, summarize the findings, and highlight the novelty and potential improvements in the field of microscale heat transfer. The review encompasses a wide range of parameters including fluid flow rate, wall heat flux, surface roughness, tube diameter, and tube coating. By examining these parameters, the study investigates their effects on the heat transfer performance in microchannels and coated microtubes. A systematic analysis is conducted to understand the relationships between these parameters and the heat transfer characteristics. The findings of this review contribute to the current state of knowledge in microscale heat transfer. The analysis reveals significant insights into the impact of various parameters on flow boiling heat transfer, providing valuable information for researchers and engineers in fields such as microelectronics cooling, energy conversion, and biomedical engineering. Moreover, this review identifies areas for further investigation and highlights the challenges and opportunities that lie ahead in this research domain. The novelty and improvement of this work lie in its comprehensive analysis of the interplay between different parameters and their effects on flow boiling heat transfer. By synthesizing the existing literature, this review serves as a valuable resource for researchers and engineers working on microscale heat transfer. It offers a deeper understanding of the subject matter and paves the way for future advancements in the design and optimization of microchannels and coated microtubes for enhanced heat transfer performance.

Design of New Heat Pump Dryer System: A Case Study in Drying Characteristics of Kitchen Waste

Existing kitchen waste treatment equipment primarily employs biological cultures for high-temperature fermentation of kitchen waste during the secondary decomposition stage. The temperature inside the fermentation chamber is mainly achieved by heating the air through electric heating tubes. However, this method of electric heating still possesses numerous shortcomings, such as high power consumption and significant energy loss. Given the aforementioned reasons, this article proposes a heat pump drying device specifically designed for the moisture removal process during the fermentation treatment of kitchen waste. This device effectively removes the moisture generated during the fermentation of kitchen waste and assists the electric heating unit in the biomass waste treatment equipment in heating the fermentation chamber, thereby reducing electricity consumption.The closed-loop heat pump drying system can continuously introduce hot, low-humidity air into the fermentation chamber through a circulating fan to remove moisture from kitchen waste.To investigate the dehumidification performance of this device, this article varies the airflow rate of the circulating fan in the heat pump drying system and the inlet water temperature of the plate heat exchanger, achieving changes in the airflow through the dehumidification evaporator and the condensation temperature of the system. Under experimental conditions, the range of the coefficient of performance (COP) achieved by the device is between 3.07 and 5.39; the specific moisture extraction rate (SMER) ranges from 0.62 to 1.81 Kg/(Kw·h), and the moisture removal rate (Mr) ranges from 1.9 Kg/h to 8.2 Kg/h.

Numerical simulation study on erosion characteristics of desulfurization slurry using shell-and-tube heat exchanger for low-grade waste heat utilization

The wet desulfurization yields slurry with a moderate temperature and stable supply and thus holds promise for waste heat utilization. However, the corrosive nature and solid particle content of desulfurization slurry from the wet desulfurization process pose potential erosion challenges in waste heat utilization heat exchangers, which is an aspect scarcely explored in the existing literature. The present study aimed to investigate the erosion characteristics in desulfurization slurry heat exchangers using numerical simulation approaches, which can offer crucial insights for practical application in low-grade energy recovery. The result identified slurry mass flow rate and composition as essential factors of erosion distribution. Higher mass flow rates enhance heat transfer efficiency. Still, paradoxically, lower flow rates lead to more pronounced erosion, with a slurry mass flow rate of 35 kg/s resulting in nearly double the erosion compared to the benchmark condition of 56 kg/s. This phenomenon is ascribed to lower fluid velocities in the heat tubes, where the influence of changed velocity diminishes, but slurry exhibits more stable flow at higher mass flow rates. Furthermore, it is also observed that both elevated solids content and particle size lead to an increase in erosion rates. The difference in erosion caused by solid particles with particle sizes in the range of 200–350 µm is marginal. The heat exchanger structure and arrangement also impact fluid flow and erosion. While the difference in fluid flow between vertically and horizontally arranged heat exchangers is negligible, the erosion was significantly reduced to 1/10 in the vertical arrangement. The no-tube-in-window heat exchangers, designed to minimize vibration, exhibit reduced heat transfer capacity alongside diminished and more uniform erosion. The augmentation of tube passes reduces overall erosion but focalizes severe erosion at the slurry inlet, which presents a potential design solution.

MATHEMATICAL MODELING OF THE AUTONOMOUS HEAT SUPPLY SYSTEM WITH TUBULAR GAS HEATERS IN BUILDING STRUCTURES WHEN OPERATING IN THE CONDENSATION MODE

Problem statement. The application of modern autonomous heat supply systems is one of the directions of reducing the consumption of natural energy resources. There are many different autonomous systems of heat supply of objects. One of the variants of such systems is the system with tubе gas heaters. A tube gas heater consists of a gas burner, a radiating tube and a fan. One of the technical solutions for such heat supply systems is a tubular heater located inside the building structure. Increase of the efficiency of gas equipment can be achieved by operating this equipment in the condensation mode. Therefore, the operation of tubular gas heaters in building structures in the condensation mode is quite interesting in terms of increasing the efficiency of utilisation of the thermal potential of gaseous fuel and ensuring its saving. For research and practical design of autonomous heat supply systems with gas tube heaters in building structures with regard to the condensation mode of operation it is essential to develop a mathematical model for calculating the thermal and hydraulic modes of the system. The purpose of the article is to develop a mathematical model of an autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode. Conclusion. The mathematical model of hydraulic and thermal modes of autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode was developed. It is presented in the form of differential equations. The model is based on the equations of conservation of mass, motion and energy for the gas-air mixture inside the canal in two-phase flow, the equation of heat transfer inside the building structure, the equation of heat transfer from the external surface of the heater to the environment. The mathematical model of hydraulic and thermal modes of autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode will be used to calculate and design such systems.

Heat transfer enhancement of a Stirling engine heating tube with three-pronged slant rods under oscillatory flow

Heaters are crucial components in Stirling engines, where the working medium adsorbed heat from an external heat source. Enhancing heat transfer within the heater is essential for boosting the operational efficiency of the Stirling engine. In this study, a tube equipped with three-pronged slant rods was employed to improve the heat transfer within the heater under conditions of oscillatory flow. Three pairs of dynamic longitudinal vortices were generated and exhibited regular movement patterns with distinct phase angles. In comparison to the smooth tube configuration, the enhanced tube outlet exhibited a notable increase in the average working-medium temperature by 62 K and 46 K during the entry and return stages, respectively. The degree of heat transfer enhancement was found to be contingent upon the pitch, height, and inclination angle of the slant rod. Optimal heat transfer enhancement was achieved with slant rods featuring a pitch of 26 mm, a height of 3.5 mm, and an inclination angle of 45°. The performance evaluation criterion ranged from 1.29 to 1.81 of enhanced tube compared to smooth tube. These findings underscore the effective enhancement of heat transfer facilitated by the three-pronged slant rods within the Stirling engine's heater.

Oxidation Damage Analysis of Ferritic Alloy Steel Heater Tubes in Catalytic Reforming Unit

Oxidation Damage Analysis of Ferritic Alloy Steel Heater Tubes in Catalytic Reforming Unit