Circuit Heat Research Articles

Investigation on oxygen vacancy regulation mechanism of ZnO gas sensors under temperature modulation mode to distinguish alcohol homologue gases

Homologous gases are difficult to be detected due to their similar chemical properties, especially for metal oxide semiconductor gas sensors whose selectivity has always been a significant challenge. Dynamic temperature modulation method with periodically changing operating temperature was used to detect alcohol homologous gases. However, there are still problems with the deviceization of heating control circuits. In this paper, dynamic temperature modulated method which needs a simple heating circuit is used to distinguish alcohol homologous gases in combination with oxygen vacancy modulation of ZnO gas sensors. Ethyl alcohol, n-propyl alcohol, isopropyl alcohol and n-butyl alcohol were measured by ZnO gas sensors with different oxygen vacancies content ratios under rectangular wave with a voltage range of 2–6 V. It was found that the greatest difference among the response curves when the material calcined at 600°C which has the largest oxygen vacancies content ratio. Finally, the recognition of the four homologue gases measured by ZnO-600 sensor was achieved by dynamic time warping and the recognition accuracy is 99.33 %.

Development of a Prototype Hydraulic Damping Device for Hot Water Heating Circuit in Pulse Mode

This paper provides a comprehensive exploration into the design and implementation of the hydraulic damping device within a pulse mode hot water heating loop. It outlines a systematic approach aimed at optimizing system performance, detailing the operational principles of the pulse mode heating circuit and presenting a structured construction scheme for the hydraulic damping apparatus. Accompanying this analysis is a simplified diagram illustrating the hydraulic damping system, offering a clear visual representation of its integration within the heating circuit. Through mathematical transformations, essential parameters such as complex impedance, frequency function, and vibration frequency characteristics are derived, providing valuable insights into the dynamic behavior of the system. Culminating this investigation, the paper constructs the frequency response of the circuit, offering a comprehensive understanding of its dynamic behavior across varying frequencies. This synthesis of theoretical frameworks and practical applications advances our understanding of pulse mode hot water heating technology, paving the way for enhanced efficiency and performance in heating systems.

Development of a Prototype Non-volatile Heating Circuit with Pulsating Mode

The emergence of global energy crisis makes energy saving technology become the key technology of sustainable development. Enhanced heat transfer technology can improve the efficiency of various heat transfer equipment and reduce the weight and volume, which plays a vital role in energy saving and sustainable economic development. In recent years, based on theoretical and experimental research, Chinese researchers and technicians have developed many new technologies to strengthen heat transfer, such as cross-scaled elliptic tube, discontinuous double-inclined inner rib tube, spiral groove tube, spiral groove tube, inner fin tube, twisted elliptic tube and so on. Among them, the pulsating heat transfer technology is an efficient and energy-saving means that can significantly strengthen the convective transport operation and improve the heat transfer effect. Through fluid pulsation or the vibration of the heat transfer pipe, the technology can remove the dirt deposited on the heat exchange surface, reduce the thermal resistance of the dirt, and improve the performance and life of the heat exchanger. It is widely used in the cooling of electronic components, automobile turbines, and the utilization of atomic energy in Marine environment. Firstly, the construction scheme of the experimental device is proposed, and the working principle of the experimental device is described in detail. The complex impedance, frequency function, amplitude-frequency characteristic and phase-frequency characteristic are obtained by mathematical transformation of power supply circuit. Finally, the frequency response of the circuit is constructed.

P‐178: Improve the response time of LCD and expand applications at low temperature

With the requirements for applications in extremely cold environments, LCD (Liquid Crystal Display) technology, limited by the properties of liquid crystal materials, exhibits poor image quality, especially when displaying rapidly changing images at low temperatures. Therefore, improving the response time at low temperatures is a key issue. In this paper, we have designed a heating circuit for the LCD. This circuit is controlled by an internal sensor, which improves the LCD's performance at low temperatures. Experimental results show that the internal sensor can provide feedback within a range of ‐50℃ to 150℃. The Gray‐ to‐Gray (GtoG) response time can reach 100ms at ‐40℃, greatly enhancing the competitiveness of LCD technology.

Experimental Studies and Performance Characteristics Analysis of a Variable-Volume Heat Pump in a Ventilation System

Air-to-air heat pumps are used in today’s ventilation systems increasingly often as they provide heating and cooling for buildings. The energy transformation modes of these units are subject to constant change due to the varying outdoor air state, including temperature and humidity. When choosing how to operate and control energy transformers, it is important to be able to adapt effectively to the changing outside air conditions. Nowadays, modern commercial heat pumps offer two levels of control flexibility: a compressor with a variable speed and an electronic expansion valve. This combination of control elements has boosted the seasonal energy efficiency of heat pumps. For a long time, cycle control possibilities have been dominated by electronic controls. The authors of this paper aim to present an additional element to the traditional heat pump controls, which provides a third level of control over the cycle. To achieve the objective, experimental investigations of a heat pump integrated into a ventilation unit have been carried out under real-life conditions. The experiments involved varying the operating modes of the unit by adjusting the compressor speed, the position of the expansion valve, and the volume of the system loop. The study examined the performance characteristics of the heat pump and found that the performance of a variable-volume heat pump is comparable to that of a conventionally operated typical constant-volume heat pump system. In addition, the study found that by adding a third level of volume control to the active heating circuit, in combination with conventional controls, the heat pump’s heat output range could be extended by 69.62%. The study determined the variation of the heat pump cycle in the p-h diagram with the variation of the loop volume. The benefits and drawbacks of a heat pump with a variable-volume loop are discussed in this study.

Model predictive control of heating in a low energy single-family house

This paper presents a control scheme that uses a Model Predictive Control (MPC) approach to manage the heating system of a low-energy single-family house. The house is equipped with an air-to-water Heat Pump (HP) and individually controlled hydronic underfloor heating circuits for each of its 11 heating zones. The MPC scheme is designed to maintain individual room comfort levels in each zone, while incorporating weather forecasts and following a heating reference to allow for load shifting for periods with low energy prices and high Photovoltaic (PV) production calculated by an upper level in a hierarchical control scheme. The focus of the design has been the model structure that allows for fast solutions to the MPC optimisation problem, while still capturing the high complexity, non-linear dynamics of the building. The controller is tested on a high-fidelity simulation model of the house, achieving disturbance rejection and system stabilisation. The rapid solving time makes repeated experiments and longer simulations feasible.

Inline induction heating for high-pressure fuel-based testing applications

Induction heating offers numerous advantages over conventional methods for heating high-pressure fluids in hydraulic testing applications. It simplifies complex processes, mitigates the risks associated with high-pressure environments, and enhances overall safety. The design of an efficient induction heating system requires a clear understanding of its key components, including the resonant tank circuit, impedance matching and isolation stage, high-frequency inverter, driver circuitry, and controller. The configuration of the resonant circuit plays a crucial role in device ratings and control methods. To meet the demanding requirements of switching devices like IGBTs, the driver circuit must ensure high immunity to interferences and failure. Effective system design allows the heating circuit to operate close to resonant switching, minimizing switching losses and cooling requirements. This paper presents the design and development of a 4-kW induction heater specifically tailored for inline heating of aviation fuel under high pressure. The system aims to achieve a precise temperature profile for testing line-replaceable units (LRUs) used in aircraft. The design methodology encompasses the selection of the resonant tank circuit configuration, impedance matching and isolation stage, high-frequency inverter, driver circuitry, and control strategies. Through extensive simulations in LTspice and experimental measurements, power losses in different components of the power conversion circuits are assessed, and overall system efficiency is evaluated. The results demonstrate the proposed induction heating system’s remarkable energy efficiency, reduced switching losses, and improved reliability. Furthermore, a comprehensive comparison with existing designs and industry norms is presented, highlighting the distinct advantages of the proposed system in terms of cost-effectiveness, energy efficiency, material utilization, and processing time. This research contributes valuable insights into the design and optimization of induction heating systems for high-pressure fluid heating applications, providing a practical and efficient solution for the aviation industry.

Turbulence suppression by cardiac-cycle-inspired driving of pipe flow.

Flows through pipes and channels are, in practice, almost always turbulent, and the multiscale eddying motion is responsible for a major part of the encountered friction losses and pumping costs1. Conversely, for pulsatile flows, in particular for aortic blood flow, turbulence levels remain low despite relatively large peak velocities. For aortic blood flow, high turbulence levels are intolerable as they would damage the shear-sensitive endothelial cell layer2-5. Here we show that turbulence in ordinary pipe flow is diminished if the flow is driven in a pulsatile mode that incorporates all the key features of the cardiac waveform. At Reynolds numbers comparable to those of aortic blood flow, turbulence is largely inhibited, whereas at much higher speeds, the turbulent drag is reduced by more than 25%. This specific operation mode is more efficient when compared with steady driving, which is the present situation for virtually all fluid transport processes ranging from heating circuits to water, gas and oil pipelines.

Retrofit of a standard split-type air conditioner into an air-to-water heat pump

In the context of the rising prices of energy and especially of natural gas, the interest in heat pumps has grown steadily over the last period, as they are a very convenient alternative to low and medium power thermal plants. Although the price of heat pumps has dropped a lot recently, these systems are still very expensive compared to the wall-mounted natural gas fuelled power plants found in the vast majority of residential buildings in Romania. In this context, the authors proposed the conversion of an inverter type air conditioner into an air-water heat pump with minimal costs, maintaining and even improving the global performance of the system. The newly made heat pump was tested at variable regimes in the Cogeneration Trigeneration Laboratory of the Faculty of Mechanical Engineering of Iasi. The external unit was inserted into a climatic chamber capable of simulating variable climatic conditions for any region in Europe. Later, the same heat pump was tested in real operating conditions, being inserted in the heating circuit of a medium-sized house in the Iasi area. Its operation was then monitored during an entire winter season, being instrumented to measure the energetic balance and determine the coefficient of performance (COP) continuously throughout the season, in accordance with the weather conditions and also to measure the seasonal coefficient of performance (SCOP).

Modelling of Floor Heating and Cooling in Residential Districts

In this study, a method is proposed to expand the utilization of an existing calculation model for a floor heat exchanger (HX) from room scale to small district scale. The model, namely Trnsys Type 653, is typically employed for the simulation of single or simultaneously controlled parallel heating circuits. It uses a simplified approach to calculate the heat exchange between fluid and screed, taking the HX effectiveness as an input. In order to calculate the effectiveness based on the HX design, fluid properties and mass flow rate, a Python model is developed to be coupled with Type 653. The results are compared to a reference finite element model set up in COMSOL® and depend on the HX design. The highest deviations range from over 1 K for 35 min to over 2 K for 175 min, while the lowest deviations range from below 0.5 K to below 1 K. Furthermore, the simplification of the floor HX model is analyzed by summarizing heating circuits from single rooms to a whole flat and from single flats to a whole floor. This approach results in deviations of approximately 2 and 4%, respectively, in the overall transferred heat over longer periods of time, while the switch-on frequency of the controller in an exemplary day is halved. While further analysis is required, the described simplifications seem promising for detailed district simulations with relatively low computational effort.

Experimental study and numerical simulation of a floor heating system in a three-dimensional model: Parametric study and improvement

In recent years, the installation of underfloor heating systems has increased considerably in many countries, due to their ability to be connected to a solar thermal collector in order to benefit from clean and renewable energy. This promising technology allows for reduced energy consumption, achieves a higher level of comfort, and ensures a more homogeneous temperature distribution than conventional heating systems. A huge loophole is detected in research works concerning the three-dimensional numerical modelling of the thermal behavior of underfloor heating by COMSOL Multiphysics software. The present study aims to reduce these knowledge gaps and to analyze the thermal behavior of the direct solar floor numerically and experimentally under the specific climatic conditions of Casablanca, Morocco. Visualize the thermal behavior of the underfloor heating system and the heating circuit as a 3D model using COMSOL Multiphysics software, based on the finite element method by investigating the influence of various design and operational parameters to select the best parameters that guarantee thermal comfort in the case of installing this heating system in traditional bathrooms.The results obtained by numerical simulation are then compared with those of the experimental measurements in order to verify the validity of the numerical model. The average deviation between the simulated and measured surface temperatures is approximately 1.04%, while the deviation in pipe temperature is around 3.13%, which shows a very good agreement between the numerical and experimental results. In addition, the results of the parametric study indicate that the key elements for enhancing the floor heating system are primarily a floor covered by tile with a minimum thickness of 5 mm, a pipe spacing of approximately 15 cm, a PER pipe diameter of 16/20 mm, and a thermal insulation layer with a thickness of 50 mm made of XPS or polystyrene. The incorporation of these improvements in the standard model ensures a surface temperature within the thermal comfort range of a less warm bathroom, approximately 34.13 °C, and a high heat flux emitted at the surface around 502.07 W compared to the standard model. In the literature, it was found that the comparison of architectural characteristics of direct solar floors receives minimal attention, with most studies only comparing systems in terms of thermal comfort or energy efficiency. In this study, the analysis and interpretation of the results obtained can be used to help engineers and designers select the type and dimensions of the best materials for heating floors installed in traditional bathrooms in Morocco.

Temperature- and Pressure-Reducing Regimes in the Growth Cell of HPHT Diamonds, Optimal for Preserving Crystal Integrity after Growth Completion

With its exceptional strength characteristics, diamond has some mechanical drawbacks, significant brittleness being among them. In particular, some HPHT-grown diamonds crack when the extreme parameters inherent to the diamond growth process gradually decrease. The cracking is caused by excessive stress due to the poor plastic properties of the diamond growth catalytic medium at certain stages of reducing the pressure and the temperature. An insulating container with the growth cell and heating circuit fragment inside can also make a significant contribution to the probability of cracking. This paper considers the possibility of minimizing the mechanical stress in the growth cell and, consequently, in the diamond crystal by choosing the optimal trajectory for the decrease in the pressure and temperature from diamond growth conditions to normal conditions.

Energy efficiency of circulating pumps when using non-freezing heat transfer fluids

Introduction. The article considers the issues of operation of circulating pumps of autonomous heat supply systems when the heating circuit is filled with antifreezing coolants. It is possible to remotely start up a heating system cooled down to –15 °С. Ethylene glycol and propylene glycol antifreeze have been studied as antifreeze carriers. Flow-rate characteristics, power efficiency coefficients are studied for “wet rotor” circulation pumps in versions of electric motors of asynchronous type with constant rotor speed and energy-saving pumps on permanent magnets.
 Materials and methods. The research was carried out on test stands. Wall-mounted gas boilers and electric boilers witha rated capacity up to 24 kW were used as heat generators. Circulation motors, control hydraulic valves, part of the pipes with a length of 6 meters were located in a separate freezer. The pumps and parts of the heating circuit were kept at subzero temperatures for 2 hours before the system was started up
 Results. Pressure and flow characteristics of two types of pumps, energy efficiency coefficients were obtained, comparisons with water coolant are provided, the influence of electric network voltage on the investigated parameters was determined.
 Conclusions. The research has shown the possibility of starting circulating pumps in a refrigerated condition with a temperature of –15 °С. Remote start of the cooled heating system with circulation circuit filling with antifreeze when using hydrocarbon fuel boilers is not possible. Operation of heating systems with non-freezing coolants in the operation temperature ranges of 20–80 °C requires changing in settings of the combustion process and a significant increase inthe circulation pump head in comparison with the coolant water.

Chemiresistors with In2O3 Nanostructured Sensitive Films Used for Ozone Detection at Room Temperature.

Detection of greenhouse gases is essential because harmful gases in the air diffuse rapidly over large areas in a short period of time, causing air pollution that will induce climate change with catastrophic consequences over time. Among the materials with favorable morphologies for gas detection (nanofibers, nanorods, nanosheets), large specific surfaces, high sensitivity and low production costs, we chose nanostructured porous films of In2O3 obtained by the sol-gel method, deposited on alumina transducers, with gold (Au) interdigitated electrodes (IDE) and platinum (Pt) heating circuits. Sensitive films contained 10 deposited layers, involving intermediate and final thermal treatments to stabilize the sensitive film. The fabricated sensor was characterized using AFM, SEM, EDX and XRD. The film morphology is complex, containing fibrillar formations and some quasi-spherical conglomerates. The deposited sensitive films are rough, thus favoring gas adsorption. Ozone sensing tests were performed at different temperatures. The highest response of the ozone sensor was recorded at room temperature, considered to be the working temperature for this specific sensor.

Stretchable conductive hydrogel with super resistance-strain stability and ultrahigh durability enabled by specificity crosslinking strategy for high-performance flexible electronics

Stretchable ionic conductive hydrogels (SICHs) are regarded as one of the indispensable components for flexible electronics desirable to provide stable signal transmission and functional reproducibility. However, the state-of-the-art SICHs demonstrate a narrow resistance-stability range and poor cyclical fatigue reliability due to ion migration limitations and the absence of the molecular design regime. Herein, we present a novel synthetic strategy that utilizes the dynamic Zn-carboxyl physical bonding, adjacent to B-hydroxyl chemical bonding, to realize the “specificity” cross-linking in pectin polymeric networks. This approach significantly extends the resistance-stability range of SICHs, while also providing remarkable longevity. Via “specificity” crosslinking design, the Zn-carboxyl physical bonding, bearing thermodynamically stable and dynamic exchange character, can break the resistance-strain dependence of ionic conductive hydrogel, offering an unprecedented resistance-stability under largely applied strain (300%). Moreover, the B-hydroxyl chemical bonding effectively overcomes the conductivity and mechanical strength trade-off dilemma due to its strong but dynamic feature, realizing the high durability of SICHs. In addition, the extraordinary tolerate harsh environment capacity was achieved by introducing glycerin to form rich hydrogen bonds in the SICHs network, which is crucial for the avoidance of congelation at subzero temperatures and dehydration resulting from the circuit heat. As a stretchable conductive component of deformable electronic devices, the SICH demonstrates extraordinary long life and stable operation. These observations reveal fresh stretchable conductive materials.

ZnO based NOx gas and VOC detection sensor fabrication techniques and materials

Nano- or micro-nano gas sensors have attracted a lot of attention since they have the potential for several applications. Utilizing a coplanar integrated design of the microheater and the inter-digitated electrode, a chemo resistive ethanol gas sensor with a thin layer of zinc oxide (ZnO) as a sensing layer has been examined (IDE). The article's conclusion offers potential future paths and research opportunities for improved sensitivity and selectivity for these sensors. SnO2-based sensors have received a lot of attention in the field of hazardous gas detection because of their extraordinary sensitivity. ZnO thin films are created using a chemical method. Gas sensors must have reduced packaging because they are essential in modern industry for managing environmental concerns. Since the gas sensor must operate at temperatures higher than ambient temperature, using the heater is necessary. The heating mechanism for the detecting layer in the various gas sensors that have recently been developed is either external or incorporates additional layers. The suggested architecture might be helpful in cutting down on the number of layers that must be deposited for the sensor and additional heating circuits. A new architecture with a coplanar microheater and IDEs has been created to analyse the gas response. The ongoing work is built on the coplanar microheater with IDEs produced for the ethanol sensor. Additionally, studies have been conducted to examine how the sensor's sensing capabilities are impacted by the integrated architecture. The sensor detects a layer thickness of 430 nm with a sensing response of 110 the sensing layer is active over the substrate. The study's major goal is to show how an integrated coplanar microheater and IDE architecture may be used with ethanol sensor based on ZnO.

Highly Sensitive Tunable Magnetometer Based on Superconducting Quantum Interference Device

In the present article, experimental results regarding fully integrated superconducting quantum interference devices (SQUID), including a circuit to tune and optimize the main sensor device characteristics, are reported. We show the possibility of modifying the critical current of a SQUID magnetometer in liquid helium by means of a suitable heating circuit. This allows us to improve the characteristics of the SQUID sensor and in particular to optimize the voltage-magnetic flux characteristic and the relative transfer factor (responsivity) and consequently to also improve the flux and magnetic field noise. It is also possible to reset the SQUID sensor in case of entrapment of magnetic flux, avoiding taking it out of the helium bath. These results are very useful in view of most SQUID applications such as those requiring large multichannel systems in which it is desirable to optimize and eventually reset the magnetic sensors in a simple and effective way.

Model of the combi boiler appliance in TRNSYS for domestic hot water circuit: Experimental and numerical validations of economic mode simulations

Combi boiler type heating appliances are used nearly in every residential building for both space and domestic hot water (DHW) heating functions. There are challenging targets regarding both of these functions. Since there is a huge laboratory testing procedure behind each appliance design and the structural or operational changes on the regular designs, simulation models could be established for the initial evaluations of the appliance testing. Therefore, due to the estimations from the preliminary results of the simulations, the number of the laboratory tests could be decreased with cost, time, and energy savings. In this study, the main objective is modelling DHW heating circuit of a combi boiler appliance with the help of Transient System Simulation Tool (TRNSYS 18) to calculate DHW outlet temperature under various operating conditions. The TRNSYS model is validated experimentally and compared with the previous works of the authors. A good agreement is achieved in both transient and steady-state regions and the TRNSYS model is found superior when compared to the previously established one-dimensional model of the authors. DHW circuit model is validated only for economic (eco) working mode simulations in this study. Mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE) values are compared for the outcomes of the previously constructed one-dimensional model and currently established TRNSYS model with reference to the experimental data. TRNSYS model decreases all of these errors calculated according to the overall temperature profiles including the transient region for the central heating water at the heat cell inlet, central heating water at the heat cell outlet, and the inlet and outlet temperature difference of DHW at the experimentally investigated DHW flow rates of 5 l/min, 7 l/min, and 8.7 l/min.

Multimodal health monitoring via a hierarchical and ultrastretchable all-in-one electronic textile

Wearable electronics with conductive yet stretchable bio-interfaces, multimodal health regulating capabilities, and strong weather resistance are especially expected by athletes and outdoor workers, yet conventional rigid, impermeable, and monofunctional wearables can hardly meet these requirements simultaneously. Here, a hierarchical and ultrastretchable all-in-one health-regulating electronic textile (AIO E-textile) with robust superhydrophobic and antibacterial surfaces is developed through electrospin-assisted layer-by-layer assembly and liquid metal (LM) printing. Skin-like and bio-compatible styrene-ethylene-butylene-styrene (SEBS) nonwoven textile is employed as a breathable matrix for the layered E-textile, in which an electrophysiological recording circuit, a strain-sensing circuit, and a Joule heating circuit are successively patterned using EGaIn. To ensure human skin health and weather resistance of the device, antibacterial and waterproof surfaces are respectively installed on both sides of the electronic textile via anchoring functionalized nanoparticles. Thus, this ultrastretchable (1141 %) AIO E-textile shows favorable moisture permeability (1300 g m−2 day), exceptional water repellency, remarkable antibacterial efficacy (>99.99 %) against E-coli, and low-watt Joule heating ability, which even exhibits accurate under-water motion detection capability, and high-definition acquiring of bioelectrical signals (electrocardiogram (ECG) and surface electromyography (sEMG)) when used as flexible epidermal bioelectrode. This work opens up a new avenue for daily applicable and multifunctional on-skin electronics.

Performance analysis of a thermochemical energy storage system for battery preheating in electric vehicles

• A thermochemical energy storage system for battery preheating of electric vehicles. • 2-D numerical model for Potassium Carbonate salt hydrate-based energy storage bed. • The performance of the energy storage bed is studied by parametric analysis. • Ambient temperature has significant impact on the system performance. • Heating rate of 0.43 °C min-1 is achievable for battery preheating of electric car. For a sustainable future, electric vehicles (EVs) are expected to offer a superior alternative to conventional fossil fuel-based vehicles. However, the performance of lithium-ion batteries used in EVs is known to deteriorate at low temperatures. Hence, preheating of EV batteries becomes imperative in cold climates. In the present paper, a potassium carbonate salt hydrate-based Thermochemical Energy Storage System (TESS) is proposed for battery preheating. The Energy Storage Bed (ESB) is a reactor of this system in which hydration-dehydration reactions take place. The ESB is envisioned as a modular design that presents the advantage of scalability for different EV variants and ambient conditions. A 2-D model of ESB is developed and its performance is analysed by various parametric studies. The proposed TESS achieves cycle efficiency of 47.1 %, volumetric energy storage density of 153.4 kWh m -3 , and specific heating power of 88.6 W kg -1 . Further, the analysis is extended to study the temporal variation in the battery temperature of an electric car by the addition of the proposed TESS to the existing heating architecture. The effect of various parameters associated with the heating circuit, on the evolution of battery temperature is also studied. Using the proposed TESS, a heating rate of 0.43 °C min -1 can be achieved for battery preheating of a typical electric passenger car.