Dynamic Heat Research Articles

SLUCM+BEM (v1.0): a simple parameterisation for dynamic anthropogenic heat and electricity consumption in WRF-Urban (v4.3.2)

Abstract. We propose a simple dynamic anthropogenic heat (QF) parameterisation for the Weather Research and Forecasting (WRF) single-layer urban canopy model (SLUCM). The SLUCM is a remarkable physically based urban canopy model that is widely used. However, a limitation of SLUCM is that it considers a statistically based diurnal pattern of QF. Consequently, QF is not affected by outdoor temperature changes, and the diurnal pattern of QF is constant throughout the simulation period. To address these limitations, based on the concept of a building-energy model (BEM), which has been officially introduced in WRF, we propose a parameterisation to dynamically and simply simulate QF from buildings (QFB) through a physically based calculation of the indoor heat load and input parameters for BEM and SLUCM. This method allows users to simulate the dynamic QF and the electricity consumption (EC) as the outdoor temperature, building insulation, and heating and air conditioning (HAC) performance change. This is achieved via the simple selection of certain QF options among the urban parameters of WRF. The new parameterisation, SLUCM+BEM, was shown to simulate temporal variations in QFB and EC for HAC (ECHAC) and broadly reproduce the ECHAC estimates of more sophisticated BEM and ECHAC observations in the world's largest metropolis, Tokyo.

Experimental study on dynamic flow and heat transfer performance of silicon-based microchannel under variable thermal load

The issue of high power density in chips has become one of the bottlenecks restricting the improvement of chip performance. Silicon-based microchannel heat sinks (Si-MCHS) can guide the cooling fluid close to the chip junction, significantly enhancing the cooling capability. Due to the rapid changes in chip power consumption, understanding the flow and heat transfer performance of Si-MCHS, especially their dynamic heat transfer performance, is crucial. This paper introduces the fabrication of Si-MCHS and experimentally tests its static and dynamic performance. The microchannels can handle a maximum thermal flux of 71.3 W/cm2. It was found that the temperature response process of Si-MCHS mirrors that of a first-order system’s step response or zero-input response. Upon a sudden change in power consumption, the thermal response can reach 90 % of the steady-state temperature difference (ΔT) within 4 s and 50 % ΔT within 1 s. Increasing the pump speed significantly reduces the response time, while different power step changes have minimal impact on the response time. Consequently, we have formulated a graded flow rate control strategy based on the flow and heat transfer performance of Si-MCHS, which achieves effective flow rate control.

Diffusion-thermo and thermo-diffusion of gravity-driven chemical reactive magneto-Casson fluid in vertical oscillatory porous media with inclined magnetic field: Finite Element Solution

An interest in enhancing heat transfer and industrial materials performance has propelled studies of diverse viscoelastic fluids with various conditions and geometries. Thus, this research examines the combined influences of diffusion-thermo and thermo-diffusion on the flow and thermal distribution characteristics of a gravity-driven chemically reacting magneto-Casson fluid in vertical oscillatory permeable media with an inclined magnetic field effect. The Casson liquid formulation is adopted for the liquid viscous behaviour, which is essential in different engineering and industrial usages. The formulated partial derivative model for the flow velocity, thermal, and reacting species is transformed via similarity variables into an invariant model and solved computationally via the Galerkin finite element method (GFEM). The results indicate that the inclined magnetic field impacts the fluid flow and heat distribution characteristics. The Soret and Dufour influences are critical in modifying the heat and species boundary layers, particularly in chemical reactions. Hence, the study offers perceptions into augmenting non-Newtonian fluids industrial processes with heat and mass transfer for chemical reactors, polymer processing, and oil recovery. Therefore, an inclusive study clarifies the interplay complexity between different physical phenomena governing the behaviour of hydromagnetic Casson fluids in porous oscillatory media is considered for dynamical heat transfer in engineered systems.

Dynamic heat transfer mechanisms of internal thermal mass: effects of thermal conductivity and diffusivity under varied temperature conditions

The appropriate use of internal thermal mass in buildings can reduce energy consumption while maintaining thermal comfort. A prerequisite for selecting suitable internal thermal mass is to establish its relationship with indoor air temperature and heat exchange. However, there is currently a lack of analytical models to describe this relationship. This study investigates the dynamic heat transfer performance of internal thermal mass under constant indoor air temperature, exponentially declining temperatures, and sinusoidal heating and cooling conditions. The results show that under constant indoor air temperature, materials with lower thermal conductivity (e.g., plywood with 0.17 W/m·°C) generate more thermal waves and experience faster surface temperature rises compared to materials with higher conductivity (e.g., reinforced concrete with 1.74 W/m·°C). In the case of exponentially declining indoor air temperature, heat exchange per unit area decreases with increasing thickness, with plywood (0.02 m) reaching its peak temperature at 6360 s, and reinforced concrete (0.2 m) at 9900 s. For sinusoidal temperature variations, the decrement factor for plywood and reinforced concrete decreases from 0.90 to 0.59 as thickness increases from 0.02 m to 0.06 m, while the time lag increases from 1.45 hours to 3.16 hours. The heat exchange is primarily related to the effective thermal capacity per unit area and the storage coefficient, which are determined by the physical properties of the internal thermal mass. These findings provide a quantitative basis for estimating the impact of internal thermal mass on indoor air temperature and heat exchange in the early stages of building design.

Predictive modeling for dynamic heat load in frigid railway roadbeds: An energy-efficient approach

This research presents an innovative approach to dynamic heat load prediction in railway roadbeds situated in cold climates by incorporating the concept of heat load, traditionally used in the building sector. The method facilitates a comprehensive evaluation and energy-efficient control of heating systems in these specialized transportation infrastructures. Utilizing an integrated building simulation toolkit (DeST), a computational model for roadbed micro-elements is established, integrating weather, radiation, and shading models to simulate pertinent environmental factors. Employing the state space method, a thermal module calculates the base temperature of these micro-elements. Subsequent calculations determine the roadbed’s target temperature and temporal heat load. Empirical data from the Harbin-Qiqihar high-speed railway validates the method, revealing strong alignment between computed and measured roadbed temperatures. Heat load peaks at 945 W/m and averages 335 W/m in freezing conditions. The method accounts for thermal hysteresis and variations related to roadbed orientation and depth. Regional statistics show a heat load range of 531 to 1,338 W/m and establish a direct correlation between heat load and latitude. The findings significantly enhance the ability to assess frost damage and design energy-efficient heating plans for railway roadbeds in frigid environments.

Thermal performance analysis of a deep coaxial borehole heat exchanger with a horizontal well based on a novel semi-analytical model

This study introduces a novel semi-analytical model for deep coaxial borehole heat exchanger with a horizontal well(H-DBHE), which incorporates the effects of formation stratification and transient heat conduction within the pipe walls. Initially, the model's validity was checked through a comparison with the results derived from the published numerical models. This semi-analytical approach significantly reduces computational time while ensuring calculation accuracy. Subsequently, the study quantitatively examined the influence of the operation parameters, structural characteristics and the thermal capacity within the borehole on the dynamic heat extraction of H-DBHE. The numerical results demonstrate that the thermal capacity within the borehole significantly influences the heat extraction performance during intermittent operations of H-DBHE. Based on this finding, the study further investigated the effects of intermittent operation and heating time on the heat recovery performance of the system. Additionally, the study compared the long-term operational performance and thermal attenuation between H-DBHE and deep coaxial borehole heat exchanger (DBHE) over a ten-year simulation period. This research introduces a novel semi-analytical model for H-DBHE, which is of significant theoretical guidance for accurately predicting the heat extraction performance of H-DBHE and scientifically designing geothermal utilization systems.

Simulation of dynamic heat dissipation energy optimization based on IoT and image recognition in low carbon building VR design process

With the global emphasis on low-carbon buildings, how to effectively optimize the thermal management of buildings has become a research hotspot. This article constructs a three-dimensional model of low-carbon buildings and implements real-time heat dissipation detection of buildings through image recognition to evaluate their heat dissipation performance. Then a heat load prediction model was proposed, which obtained the heat load prediction results of buildings under different environmental conditions through data analysis. Thus, it lays the foundation for the subsequent optimization of dynamic heat dissipation energy. The core of the research is to establish a dynamic heat dissipation optimization strategy. This article provides a detailed introduction to the principle of dynamic heat dissipation synergy, combined with the thermal network temperature compensation model and dynamic adjustment model, to achieve the expected energy efficiency improvement. Finally, the construction of a dynamic heat dissipation energy optimization control system based on the Internet of Things has strengthened the collection and analysis of real-time temperature data, and its effectiveness and reliability in practical applications have been verified through system testing.

Dynamic blade tip clearance control of aero-engine by the integration of cooling air with fuel thermal management system

In advanced aero-engines, the precise control of tip clearance and thermal management of the fuel system are two important measures to improve the transient performance of the aero-engine. In order to optimize the overall performance of an aero-engine during a full-flight mission, this paper proposed a novel architecture integrating active clearance control system and aero-engine fuel thermal management system, which utilizes fuel heat sink to achieve indirect regulation of the tip clearance. Furthermore, a set of critical optimization criteria for the new architecture was derived to achieve dynamic heat distribution in the fuel thermal management system. Subsequently, the transient performance was tested under a complete flight mission with a duration of 10,000 s. The calculation results indicate that the new architecture effectively raises the fuel temperature to its maximum allowable value during low thermal load phases, which increases heat dissipation capability of the system. The new architecture exhibits a significant effect on the control of the tip clearance during the ground idle, cruise, and engagement phases, resulting in a maximum increase of 1.86% in the relative efficiency of the high-pressure turbine. The new architecture also prevents the engine from experiencing excessively narrow tip clearance during acceleration. Ultimately, the new architecture achieves a 2.59% reduction in total fuel consumption compared to the original design. The new architecture has significant potential to improve engine efficiency and increase operational safety.

A thermofluid temperature modeling, prediction of closed-loop cooling system of roll grinder based on circulation differential equations

Roll grinders are essential in high-precision roll manufacturing. However, lubricant temperature fluctuations decrease the precision of grinders. The complicated dynamic heat transfer within the closed-loop cooling systems of roll grinders poses significant challenges to accurately modeling their thermal states. This study proposed a novel model based on circulation differential equations for the thermofluid temperatures in roll grinders. Based on thermodynamic principles, differential equations of each component within the closed-loop cooling system were derived. To improve model accuracy, a thermal resistance approach was utilized, and the thermal interaction between lubricant and hydrodynamic bearings under different speeds and the heat convection between hydraulic hoses and air are considered. To validate the proposed model, a series of experiments across a range of spindle speeds were carried out. The results showed the model could achieve prediction accuracy less than 5.27%. Subsequently, the influence of system design parameters on cooling performance was analyzed. The proposed temperature model better comprehends the thermodynamic interaction within closed-loop cooling systems featuring hydrodynamic bearings. The limitations and potential application in other industrial areas were discussed.

Investigation on Dynamic Properties and Heat Transfer Mechanism of Droplet Impact on the Heated Wall Under a Leidenfrost State

Investigation on Dynamic Properties and Heat Transfer Mechanism of Droplet Impact on the Heated Wall Under a Leidenfrost State

Dynamic magnetic properties and magnetocaloric effect of a nanotube encapsulated with X36

Abstract Using Monte Carlo simulation, the dynamic magnetic properties and magnetocaloric effect of a mixed-spin (3/2, 2) single-walled nanotube encapsulated with X36 was studied, where X denotes the magnetic atom. The effects of intrinsic parameters on dynamic order parameters, magnetic susceptibility, internal energy, and specific heat were considered. The phase diagrams were obtained. The results indicate that the critical temperature can be increased by decreasing the absolute values of the anisotropies (D a , D b ), increasing the exchange couplings (|J ab |, J bb ), and decreasing the amplitude h 0 and the period τ of the external magnetic field. And under the influence of these parameters, the magnetocaloric effect is generated.

Fully coupled thermal-structural-vibration characteristics of 3-axis machine tools with complex hybrid linear axis-spindle systems considering structural nonlinearities

For machine tools composed of functional components bonded by joints with structural nonlinearities, the load- and temperature-dependent nonlinear restoring force,stiffness, and frictional heat generationfrom the jointdetermine its complex dynamic fully coupled thermal-structural-vibration characteristics. In response, in this work, considering the vibration feedback dominated by the structural vibration and employing a partition-based closed-loop iterative algorithm, a fully coupled thermal-structural-vibration model that characterizes the nonlinear coupling between temperature and mechanical fields is developed with the joint as the link. The multi-body dynamics model of the whole machine tool, considering the flexibility of the screw shaft, spindle, and joint nonlinearity, characterizes the milling dynamics influenced by structural vibration and regeneration effects. The global thermal resistance network model with dynamic heat flux, viscosity-temperature effect, and time-varying thermal resistanceis establishedto characterize the thermal characteristics. The partition-based closed-loop iterative algorithm is employed to realize the multi-field coupling and consider the moving heat source and the load distribution change caused by the reciprocating moving joint. Considering the changes in contact angle and contact deformation caused by preload, dynamic load, and thermal effect, load- and temperature-dependent nonlinear joint restoring force and stiffnessare developed. Based on the viscosity-temperature effects and the change of contact friction caused by thermal expansion and dynamic load, the load- and temperature-dependent nonlinear joint frictional heat generation is calculated. The milling load from tool-workpiece interaction is calculated, and the influence of multi-field coupling on regenerative chatter is explored. The proposed model was experimentally verified, andthe effectof parameterswas numerically investigated. The results show that the dynamic milling load excites the whole machine tool vibration, and for every 10 μm increase in cutting depth, the radial amplitude of the tool nose increased by at least 1 μm. The nonlinear coupling between temperature and mechanical field significantly affects the system response, and the joint contact stiffness dominates the multi-field coupling behavior.

Optimal control of a model for dynamic district heating networks

In the present paper an optimal control problem for a concrete system of differential-algebraic equations (DAEs) is considered. This problem arises in the dynamic optimization of unsteady district heating networks. Based on the Carathéodory theory existence of a unique solution to the specific DAE system is proved using specific properties of the considered district heating network model. Moreover, it is shown that the optimal control problem possesses optimal solutions. For the numerical experiments different networks are considered including also data from a real district heating network.

Utilization of hydrogen fuel in reheating furnace and its effect on oxide scale formation of low-carbon steels

The transition from fossil-based fuel to hydrogen combustion in steel reheating furnaces is a possible way to decrease the process-originated CO2 emissions significantly. This potential change alters the furnace gas atmosphere’s composition, impacting the oxide scale formation of the slab surface. Dynamic heating tests are performed for three low-carbon steels using different simulated combustion atmospheres, including natural gas, coke oven gas, and hydrogen combustion in air, and hydrogen combustion in oxygen. Significant differences are found in the oxidation behavior of steel grades in the simulated hydrogen reheating scenario. A steel grade with low Mn content only has an 18% increase in oxidation between methane-air to hydrogen-oxygen methods, while it is 41% for a high Mn and Si steel grade and 65% for a high-Mn steel grade. Thus, in terms of material loss increase by oxidation, the transition of the heating method causes the least problems for the low-Mn steel grade.

Thermal nonreciprocity tuned by wrinkle patterns in graphene

Abstract Thermal nonreciprocity are typically realized by using nonlinear heat conductivity, external field bias or spatiotemporal modulation of thermal parameters, but these methods require specific material properties or accurate modulation means. Low-dimensional materials like graphene provides a platform to engineer heat transport characteristics at the molecular level. Here, by simply tuning graphene’s wrinkle morphol ogy, the approach to generate nonreciprocal heat transfer is reported, which applies to both static and dynamic heat signals. Such nonreciprocity is attributed to the tunable responses of thermal conductivity on both temperatures and wrinkles. Phonon density of states (PDOS) of the wrinkled graphene exhibit distinct spectra, especially at the low frequency (around 17 THz), which results in reduced temperature sensitivity of thermal conductivities and eventually induces thermal nonreciprocity. The findings provide insights into the physics of thermal transport in wrinkled graphene, and paves a new avenue for mechan ically modulating thermal nonreciprocity. Our method to obtain thermal nonreciprocity is reversible, tunable and controllable, meanwhile remains structural integrity, which benefits functional applications such as heat management in electronics.

The preparation of different types of reclaimed rubber and their applications in tire inner liner

AbstractIn this work, the application of reclaimed ground tire rubber (RGTR) and butyl reclaimed rubber (BRR) in the inner liner rubber were investigated. Carbon black dispersion, rheological, mechanical, tear strength, dynamic compression heat build‐up, aging performance, and gas barrier properties of tire inner liner were evaluated to analyze the effects of reclaimed rubbers on the tire application. It was found that RGTR improves carbon black dispersion and tear strength of tire inner liner, while maintaining comparable tensile strength, particularly with low amount of RGTR. Furthermore, compounds containing lower amounts of RGTR exhibit reduced heat build‐up during dynamic compression tests. Additionally, RGTR with higher reclamation degree demonstrates favorable aging performance, and has superior gas barrier properties at lower amount. These findings suggest promising opportunities for the application of reclaimed rubber to enhance the performance inner liner of Radial Engineering Tires and contribute to the waste management.

Innovative passive techniques and PCM integration in building envelopes for enhanced energy efficiency in desert regions

Rising energy demands in buildings for heating, cooling and operating appliances underscore the importance of implementing energy-efficient solutions. Passive cooling techniques provide a sustainable alternative to conventional, energy-intensive cooling systems, promising reduced energy consumption in buildings. Using a dynamic heat transfer model validated with ANSYS Fluent, this study examined three configurations: integrating phase change materials at the brick's centerline with cavities filled with air, EPS insulation, and emissivity coating. Additionally, the benefits of combining all three passive methods were evaluated. Results indicated that among the evaluated PCMs, capric acid demonstrated superior performance. While each passive method studied offers distinct advantages in enhancing thermal performance and achieving energy efficiency, assessing their combined effects revealed significant insights. Specifically, integrating capric acid at the brick's centerline, while simultaneously configuring EPS insulation in the upper cavities and emissivity coating in the lower cavities, yielded superior performance. This configuration significantly reduced inner surface temperature by approximately 6.6 °C and minimized heat flux by about 58.4 % compared to traditional bricks. Achieving energy savings of 56.24 %, this configuration shows potential to enhance both thermal comfort and energy efficiency in building applications.

Modeling of a metal hydride energy storage tank dynamics using hybrid numerical, experimental, and machine learning methods

This study presents an integrated analysis combining numerical simulations, experimental investigations, and machine learning models to simulate the performance of metal hydride systems for hydrogen storage under various conditions by using a LaNi5 metal hydride cylindrical tank of 500 NL capacity, with a focus on PCM thermal enhancements and surface water heating and cooling. Numerical simulations offer insights into thermal and reaction dynamics, while experimental data are used for model validation and supplemented with additional numerical data for training a FFNN model to predict dynamic hydrogen flow, surface temperature, and surface heat flux. The obtained mean RMSEs for charging/discharging experimental data is 2.8 SOC% for the state of charge and 0.3 °C for surface temperatures. The study compares the effectiveness of water cooling and heating in metal hydride surface across different temperatures, highlighting their impact on the efficiency of hydrogen absorption and desorption processes. Energy consumption is shown to be non-linear; during charging, heat flux peaks before decreases rapidly within around 0.2 h. During discharging, heat flux rises steadily. The study also explores the impact of adding copper fins to the PCM covering metal hydride system, revealing significant improvements in charging and discharging efficiency, specifically, the integration of 16 copper fins led to a notable decrease in complete charging time from approximately 6.5 h to just over 5.2 h, and in complete discharging time from around 4.5 h to under 3.96 h. Using PCM, the highest heat flux is 5 times less during charge and 2 times less during discharge than that for water cooling mode.

A real-time phase transition modeling of supercritical steam cycle and load variation rate enhancement of thermal power plants under deep peak shaving

The ambitious green revolution to renewable energy sources in global power grids necessitates massive integration of solar and wind energy, which involves intermittent and unpredictable challenges. Thermal power plants are crucial in stabilizing the grid and addressing these challenges through flexibility reformation including deep peak shaving and frequent load variations since the unsteady state energy transfer and thermal dynamics during combustion and heat transformation in thermodynamic processes vary significantly. These conditions lead to issues such as furnace instability and latent heat of phase transition. This study introduces a novel approach to modeling phase transitions of supercritical steam cycle, and investigatesthe length, position, temperature, and energy transfer of the working medium and components under normal and low operational states. Conducting and analyzing the thermal feasible region associating the security of components and working medium this study establishes a control strategy for dynamic heat transfer to reduce component degradation effects andenhance load variation rate under flexible operations. Simulation model of a supercritical power unit based on the proposed method demonstrates an accuracy of 97.94%. Results from the optimal approach in maximizing load variation rate show the effectiveness and achieve 1.2%p.e./min most under transition process.

Identification of position, size and dynamic heat power of chips embedded in a real electronic board

Temperature is a critical factor in the lifespan of electronic systems. Therefore, it is essential to control all thermal parameters. In certain applications, such as commercial off-the-shelf (COTS) components, manufacturers may not have precise knowledge of the composition of electronic boards. As a result, it is important for them to define the positions of heat-dissipating elements, and the power dissipated to better predict the final thermal behavior of the system. Some electronic boards today even have components integrated into their volume. Since components can now be located not only on the surface but also within the volume of electronic boards, manufacturers need to define volume-based methods for detecting these heat sources. In this article, we address the problem of detecting sources within a volume using surface temperature data. To achieve this goal, we develop a representative numerical model of the system that can be used for an inverse source identification procedure. In a first time, we present a numerical approach that demonstrates the feasibility of the identification procedure on a board containing several electronic chips. Secondly, the volume source identification method is applied to a real case, using surfaces temperatures measured by infrared cameras. The experimental results obtained are consistent and show that this technique is suitable for detecting volumetric sources within an electronic board.