Dynamic Thermal Response Research Articles

Dynamic thermal response modelling of turbulent fluid flow through pipelines with heat losses

The dynamic thermal behaviour of pipe systems is important in many heating, cooling and process systems and is further complicated where radial heat transfer and the thermal capacity of the pipe are significant. In this study, the ability of three forms of discretized one-dimensional models in prediction of the dynamic thermal response of pipelines considering the longitudinal dispersion of turbulent fluid flow were examined. Furthermore, a model is proposed combining features of plug-flow and discrete stirred tank representations that take into account the thermal capacitance of the pipe material as well as radial heat transfer. This combination enables the proposed model to simultaneously handle the simulation of momentum and energy balance as well as simulation of the longitudinal dispersion in pipelines. The proposed model is further compared to experimental measurements. The results elucidated that the proposed model is not only able to capture the outlet temperature changes due to a step change in the very good agreement against the measurement data but also offers advantages in reduced computational expense.

A COMBINED USE OF FDM AND DOE METHOD TO DERIVE A NEW TRANSIENT SIMPLIFIED SEMI-ANALYTICAL MODEL: A CASE STUDY OF ANHYDRITE RADIANT SLAB

Radiant floor heating systems (FHS) are considered as reliable heating systems since they ensure maintaining inside air temperature and reduce its fluctuations more efficiently than conventional heating systems. The presented study investigates the dynamic thermal response of an experimental FHS equipped with an anhydrite radiant slab. A new simplified model based on an analytical correlation is proposed to evaluate the heating radiant slab surface temperature and examine its thermal behavior under dynamic conditions. In order the validate the developed analytical model, an experimental scenario, under transient conditions, was performed in a monitored full-scale test cell. 2D and 3D numerical models were also developed to evaluate the accuracy of the analytical model. The method of Design of Experiments (DoE) was used to both derive meta-models, to analytically estimate the surface temperature, and perform a sensitivity study.

Thermal instability and dynamic response analysis of a tensioned carbon nanotube under moving uniformly distributed external pressure

Abstract Single-walled carbon nanotubes (SWCNTs) are receiving immense research attention due to their tremendous thermal, electrical, structural and mechanical properties. In this paper, an exact solution of the dynamic response of SWCNT with a moving uniformly distributed load is presented. The SWCNT is modelled via the theories of Bernoulli-Euler-thermal elasticity mechanics and solved using Integral transforms. The developed closed-form solution in the present work is compared with existing results and excellent agreements are established. The parametric studies show that as the magnitude of the pressure distribution at the surface increases, the deflection associated with the single walled nanotube increases at any mode whilst a corresponding increase in temperature and foundation parameter have an attenuating effect on deflection. Moreover, an increase in the Winkler parameter, as well as a decrease in the SWCNT mass increases its frequency of vibration. Furthermore, an increase in the speed of the external agent decreases the total external pressure as a result of the removal of dead loads. The present work is envisaged to improve the application of SWCNT as nanodevices for structural, electrical and mechanical systems.

Thermal performances study on a façade-built-in two-phase thermosyphon loop for passive thermo-activated building system

Pipe-embedded building envelopes, as a burgeoning active insulation technique that has its pipe circuits inside the building envelope, are of particular interest to architects and engineers due to their excellent performances and invisibility characteristic. However, performances of this pump-driven technique highly rely on long-term electricity consumption, resulting in degradation of system efficiency in building load reduction and supplementary heating. In the present study, a facade-built-in two-phase thermosyphon loop (TPTL) for passive thermo-activated building system (i.e. TPTL-embedded building envelope) is proposed to turn the pump-driven heat injection process of active insulation technique into non-pump-driven. Experiments on a prototype are conducted to explore operational characteristics of the TPTL whose condenser is operated in the thermal boundary of Dirichlet and dynamic thermal response characteristics of the composite building envelope after coupling TPTL at different heat loads and filling ratios. Results show that the filling ratio has a critical impact on thermal resistances and startup behavior of TPTL, and the optimal filling ratio (around 116%) is not a fixed value at different operating conditions. Besides, condenser thermal resistance occupies the largest proportion among the system thermal resistance due to the heat accumulation phenomenon, therefore, the interlayer material also has a great impact on heat injection and release of TPTL-embedded building envelope. In addition, reverse startup and operation under specific test condition are observed and discussed accordingly. Overall, these results and conclusions are useful for the system design, operation control, and further investigations on the façade-built-in TPTL and the TPTL-embedded building envelope.

A dynamic thermal response on thermal conductivity at different temperature and moisture levels of EPS insulation

In this work, the dynamic thermal effect of thermal conductivity, K-value, is investigated at different operating temperatures and moisture levels of polystyrene expanded insulation material (EPS) by using computational modelling of heat transport. In building energy analysis and assessment, the heat transfer through the building envelope usually considers a constant single K-value and neglects the effect of the moisture content within the insulation. In reality, the building envelope is subjected to the combined thermal and moisture gradients. Therefore, an accurate analysis requires a simultaneous calculation of both sensible and latent effects. The purpose of this paper is to analyze the dynamic thermal effect on the K-value of EPS by using the conduction finite difference (CondFD). The results of this research show a slight difference in the thermal conductivity value of EPS insulation at different operating temperatures for different densities of the material. However, a greater difference is observed at higher moisture contents compared with the dry sample when the K-value of the insulation is temperature dependent.

Temperature and material behaviour effects on dynamic responses of asphalt concrete trackbed

ABSTRACTDeveloping a simulation model for railway subgrades is an important initial step towards a reliable design for a dense-graded asphalt concrete trackbed. This paper presents a comparative simulation study of the dynamic responses in terms of tensile strains and vertical displacements of the elastic and viscoelastic subgrade surface materials affected by different thermal loadings using the finite element method. The simulations for all conditions were performed with a train speed of 350 km/h. The relationship between different thermal loads and dynamic responses of the railway track materials in terms of tensile strain and vertical displacement was defined. This relationship indicated that the resultant tensile strains and vertical displacements for the viscoelastic material were greater than those of the elastic material at the same thermal load.

Evolution of all-glass nearly Zero Energy Buildings with respect to the local climate and free-cooling techniques

This paper presents research on the nearly Zero Energy Buildings (nZEB) metrics of an all-glass office building with advanced multi-layer six-pane glass and building integrated photovoltaic (BIPV) façade structures in different climate conditions. The study was carried out in the following steps: i) development of a time series model of dynamic thermal response of multi-layer six-pane glass and BIPV façade structures on the basis of transient computational fluid dynamics simulations, ii) integration of the façade structure dynamic model into the building dynamic model by adapting TRNSYS software code, iii) determination of the final energy balance including heating, cooling, ventilation, lighting, and on-site electricity production, iv) nZEB metrics evaluation considering night-time cooling by ventilation, evaporation cooling and hybrid ventilation of case study office buildings. It is shown that energy need for the cooling of the studied office building is dominant in all considered climate conditions, although it can be decreased up to 23% in most favourable considered climate conditions by implementing free cooling techniques. The case study buildings with BIPV structures on their east and west façades meet more stringed nZEB criteria; in addition, final energy demand decreases by 17–37% in comparison to the reference all-glass building. In the case of all-BIPV buildings, the final energy demand is decreased by 36–48%. Such buildings can significantly contribute to the mitigation of global climate change, as BIPV electricity production exceeds the building's energy demand.

Thermal Management of Dynamic Operation of Solid Oxide Cell-Based Energy Storage System for 2 Renewable Electricity Scenarios

The increasing contribution of renewable energy sources (RES) to the power generation sector has motivated researchers to devise new methods for reliable energy storage systems. The significance of mechanisms for storing large amounts of electricity for longer time-scales is accentuated by the dynamics of renewable electricity generation that depend upon the season of the year, time of day, and the location. Conventional large-scale electricity storage technologies such as pumped-hydro and compressed-air storage systems are limited by geographical features (e.g., access to a cavern or high elevations). Traditional rechargeable batteries are limited by the fact that energy and power capacities do not scale independently. One of the promising and multipurpose techniques for storing electricity from these fluctuating renewable sources such as wind and solar, is conversion of the electric power to sustainable and carbon free gaseous fuel like hydrogen (power-to-gas (P2G)). In fact, owing to its diverse applications and worthwhile features such as high gravimetric energy density, hydrogen has become an attractive means of delivering renewable energy to many heavy-duty transport and industrial processes that are difficult to electrify. The renewable hydrogen produced from these zero emission electricity sources could be stored in caverns or injected into existing natural gas grids, initially at low concentrations as mixed with natural gas and ultimately piecewise replacing natural gas in the system. The stored hydrogen could be utilized in transportation for fuel cell electric vehicles (FCEV), in power generation for stationary fuel cells or in chemical industries as a feedstock for chemical synthesis of low-carbon fuels or other products, enabling the eventual decarbonization of all energy conversion. One of the efficient and cost-effective techniques for electrochemical conversion of electricity to hydrogen is steam electrolysis using solid oxide electrolysis cells (SOEC). The steam electrolysis reaction is intrinsically an endothermic reaction for which the required energy is to be supplied as electricity or heat or a combination of both. High temperature electrolyzers, such as SOEC, benefit from both lower energy required for the electrochemical reactions and an ability to provide part of the endothermic energy demand with the heat content of the inlet streams. At high current densities, SOEC can operate exothermically, meaning that the heat generation due to the losses and electricity supply are greater than the endothermic energy demand. When the SOEC systems are connected to intermittent renewable sources like solar or wind, the varying electricity profile will cause the SOEC operation to dynamically switch between endothermic to exothermic modes and all levels of endothermicity and exothermicity in between. This transient behavior of the electrolyzer could lead to highly dynamic thermal response that could have detrimental effects on thermal stress and degradation. In this work, an energy storage system (ESS) is designed in Matlab/Simulink which simulates the dynamic operation of an integrated SOEC system applied to an intermittent RES. The main focus of the research is the thermal management of the SOEC stack during highly dynamic operation throughout the entire operating regime from highly endothermic to thermo-neutral and to highly exothermic operation. An additional thermal management challenge is to keep the SOEC system hot during periods of non-operation (hot standby). These challenges are addressed in the current work by a novel system design that integrates a solid oxide fuel cell (SOFC) with the SOEC and combines several control strategies within the balance of plant (BoP). For thermal balance of the system the SOFC exothermicity is used to reduce the dependence of the system on electric heaters. The SOFC system oxidizes a fraction of the renewable hydrogen produced by SOEC and generates heat and electricity. A heat exchanger network is designed to convey the SOFC heat to the SOEC for a wide range of endothermic conditions. The main function of SOFC is to keep the SOEC warm when it is not operating or when it is operating in highly endothermic regions. The proposed configuration is integrated with 2 different patterns of electricity production from RES: one representing measured wind dominant RES such as that in Germany, and one representing solar dominant RES such as that in California. Dynamic analysis of the system in terms of the electric power generated by RES for these 2 conditions is presented. The response of different parameters in the system to keep the integrated system warm, self-sustaining, and within desired limits for lower thermal stress and degradation are presented. These parameters include required SOFC power, voltage and temperature profiles of both SOEC and SOFC, BoP parasitic consumption, system efficiencies, hydrogen production amounts, consumption, and storage levels during transient operation.

The dynamic thermal response model and energy performance of multi-layer glass and BIPV facade structures

Despite the great progress made in the energy performance of buildings in recent decades, buildings remain significant energy consumers. Many advanced technologies for increase of energy efficiency have been developed, and strong commitments to increasing the energy performance of buildings have been adopted. The most well-known is the Recast of Energy Performance of Buildings Directive (EPBD), which requires that planners design buildings as nearly zero energy buildings (nZEB), highly energy efficient buildings in which a large share of energy demand is covered by renewable energy sources. In the present article, the evaluation methods and energy performance of advance facade building structures are presented. The structure consists of six-pane multi-layer glass with optional photovoltaic cells integrated in the outer glass layer (BIPV). The method for the determination of the dynamic thermal response model is presented, and the model is validated with experiments. Three indicators were developed (average daily heat flux q˙24 at inner surface of the facade structure, the autonomy factor AUT, the and utility factor UTI) to evaluate the all-year energy performance of such advanced building structures according to the heating and cooling energy needs and electricity production. Examples are shown for facade building structures located in three climate regions.

Nonlinear Static and Dynamic Thermal Buckling Analysis of Spiral Stiffened Functionally Graded Cylindrical Shells with Elastic Foundation

In this paper, an analytical method is used to study the nonlinear static and dynamic thermal buckling analysis of imperfect spiral stiffened functionally graded (SSFG) cylindrical shells. The SSFG cylindrical shell is surrounded by a linear and nonlinear elastic foundation. The proposed linear model is based on the two-parameter elastic foundation (Winkler and Pasternak). A three-parameter elastic foundation with hardening/softening cubic nonlinearity is used for nonlinear model. The material properties are temperature dependent and assumed to be continuously graded in the thickness direction. Also, for thermal buckling analysis, the uniform and linear temperature distribution in thickness direction is considered. The SSFG cylindrical shells are considered with various angles for spiral stiffeners. The strain–displacement relations are obtained based on the von Kármán nonlinear equations and the classical plate theory of shells. The smeared stiffener technique and the Galerkin method are applied to solve the nonlinear problem. In order to find the nonlinear dynamic thermal buckling responses, the fourth-order Runge–Kutta method is used. To validate the results, comparisons are made with those available in literature and good agreements are shown. The effects of various geometrical and material parameters are investigated on the nonlinear static and dynamic thermal buckling response of SSFG cylindrical shells.

Test Rig for Emulation of Turbocharged SOFC Plants

This work is devoted to an emulator test rig designed for experimental analysis on SOFC-based plants pressurised by a turbocharger. The utilization of a turbocharger for SOFC pressurization aims to reduce the machine costs, due to the large mass production of this component. This emulator rig is an essential plant to perform tests on the component integration, dynamic operations, control system development and prevention of risky operative conditions (e.g. surge). These are essential issues to be solved before developing expensive complete prototypes and the related commercialization. This experimental plant is based on a pressure vessel for emulating the thermal (combustor and inert ceramic material) and fluid dynamic (the volume) responses. The vessel pressurisation is obtained with a turbocharger, where the exhaust flow operating in the turbine powers the compressor. The plant is also equipped with a recuperator and with different valves for control and flexibility reasons (bleed, compressor/turbine bypass, and recuperator bypass). Preliminary experimental results are included in this work focusing attention on the turbocharger choice and on the component constraints. In details, these are the necessary experiments for choosing the suitable machine for the rig (with a good surge margin for this component coupling).

Dynamic thermal response of low-energy residential buildings based on in-wall measurements

This study analysed the dynamic thermal response of a low-energy building using measurement data from an apartment block in Copenhagen, Denmark. Measurements were collected during February and July 2018 on space heating energy use, set-points, room air temperature and temperature from sensors integrated inside concrete elements, i.e. internal walls and ceiling, at different heights and depths. The heating system was controlled by the occupants. During February, there were unusually high set-points for some days and a regular heating pattern for some other days. Overheating was observed during July. A considerable effect of solar gain was observed both during winter and summer months. The room air temperature fluctuations were observed at a certain extent inside the concrete elements; higher in the non-load-bearing internal wall, followed by the load-bearing internal wall and lastly by the ceiling. The phenomenon of delayed thermal response of the concrete elements was observed. All internal concrete masses examined may be regarded as active elements and can contribute to the physically available heat storage potential of the building. The study provides deep insight into the thermal response of concrete elements in low-energy residential buildings, which should be considered when planning a flexible space heating energy use.

Will naturally ventilated dwellings remain safe during heatwaves?

Heatwaves are responsible for many deaths due to hot weather. Natural ventilation is promoted as a cooling solution to reduce the impacts of climate change because of its energy-saving potential.This paper addresses the prediction of heat-related health risk situations in naturally ventilated dwellings, where indoor thermal conditions depend on external climate and occupant behaviour. Thus, the operating limits of a dwelling vary according to its dynamic thermal response to indoor and outdoor stresses.To secure a building design, a method to improve the prediction of heat-related health risks is proposed that links predicted percentage dissatisfied (PPD) and wet-bulb globe temperature (WBGT) indicators to distinguish a moderately warm situation from a heat stress situation (WBGT > 29 °C). Simulations are performed for a dwelling during the 2015 heatwave in Paris (France) to test the method.In the example, natural ventilation was found to reduce the indoor temperature, but there remains ambiguity regarding the ability of natural ventilation to provide moderate conditions. According to the scope of the ergonomic standards, “moderate thermal environment” and “heat stress” temperature ranges are not contiguous. Bridging of this gap requires establishing thermal comfort ranges and heat stress thresholds adapted to people according to their acclimatisation level and their sensitivity to heat.

Fabrication and characterization of La0.8Sr0.2CrO3/In2O3 thin film thermocouple for high temperature sensing

La0.8Sr0.2CrO3/In2O3 ceramic-based thin film thermocouple (TFTC) was successfully fabricated by using radio frequency (RF) sputtering method. The phases structures and morphologies of La0.8Sr0.2CrO3 and In2O3 thin films were investigated by XRD and SEM, respectively. La0.8Sr0.2CrO3 thin film showed orthorhombic phase and shuttle structure through post-annealing. The crystalization properties of In2O3 thin film were enhanced with the post-annealing. At the same time, their electrical conductivities were improved with the post-annealing process. When the thermoelectric properties of La0.8Sr0.2CrO3 and In2O3 were investigated by coupling with Pt thin film electrodes, both of them showed good linear relationship with temperature difference. The TFTC fabricated by La0.8Sr0.2CrO3 and In2O3 thin films showed very good performance with good stable, reproducible thermoelectric voltage, and high sensitivity at higher temperature. The sensitivity of La0.8Sr0.2CrO3/In2O3 thin film thermocouple was 305.8 μV/oC. The dynamic thermal response of the TFTC demonstrated that it could monitor the real-time and in-situ temperature successfully.

A fast response, low heat generating activation method for LHe level sensors.

A superconducting liquid helium (LHe) level sensor of length 300 mm has been fabricated based on the principle of differential heat transfer characteristic in helium gas compared to that in liquid. The sensor wire used has a diameter of 38 μm, and the wire was obtained from a pack of multifilament wires. A full thermo-electrical characterisation of the sensor was carried out in a dedicated setup. Its dynamic thermal response was also studied to understand its timing characteristics at different liquid levels and excitation currents. Based on the sensor characterisation, a new level measurement technique is evaluated which can reduce the heat load going to LHe during sensor activation without compromising on its sensitivity or accuracy. The timing response with this technique will make the level detection faster compared to the conventional techniques.

Dynamic temperature prediction of electronic equipment under high altitude long endurance conditions

Unmanned Aerial Vehicle (UAV) is developing towards the direction of High Altitude Long Endurance (HALE). This will have an important influence on the stability of its airborne electronic equipment using passive thermal management. In this paper, a multi-node transient thermal model for airborne electronic equipment is set up based on the thermal network method to predict their dynamic temperature responses under high altitude and long flight time conditions. Some relevant factors are considered into this temperature prediction model including flight environment, radiation, convection, heat conduction, etc. An experimental chamber simulating a high altitude flight environment was set up to survey the dynamic thermal responses of airborne electronic equipment in a UAV. According to the experimental measurement results, the multi-node transient thermal model is verified without consideration of the effects of flight speed. Then, a modified way about outside flight speed is added into the model to improve the temperature prediction performance. Finally, the corresponding simulation code is developed based on the proposed model. It can realize the dynamic temperature prediction of airborne electronic equipment under HALE conditions.

Dynamic analysis of a micro CHP system based on flame fuel cells

Micro combined heat and power (CHP) systems based on flame fuel cells (FFCs) are promising technologies for residential applications due to their simple setup and rapid startup. A dynamic model was developed in this paper for a micro FFC-based CHP system which consists of an FFC and a heat exchanger. At first, the operation conditions at the design point (system AC power output is 1.1 kW) and the part-load point (system AC power output is 0.7 kW) were determined respectively at steady state. An exergy assessment was conducted for each component and the whole system. It is found that at the design point, the heat exchanger accounts for the majority of the exergy losses. Then, the transient responses of the system components as well as the electrical and heat dynamics of the whole system were investigated when the operation conditions of the system ramped from the values at the design point to those at the part-load point. The electrical dynamic response of the CHP system, in terms of the output AC power shows a time delay of less than 50 s, while the thermal dynamic response, in terms of the generated heat shows a time delay of 300 s. The electrical dynamic response of the system is limited by the dynamics of the gas supply process of the fuel-rich burner. The thermal settling time of the system is governed by the thermal settling time of both the SOFC stack and the heat exchanger. The relatively slow thermal response under a transient electrical demand indicates that an additional heat storage is necessary in the FFC-CHP system.

Dynamic interfacial mechanical-thermal characteristics of atomically thin two-dimensional crystals.

Owing to the flexible nanoelectronic applications of two-dimensional (2D) materials, further exploration of their nanoscale local mechanical properties and their coupled physical characteristics becomes extremely significant. The puckering effect is a typical micro/nanoscale local frictional characteristic generally in the tip-film-substrate system, which is simultaneously expected to be coupled with a dynamic thermal interfacial response. Here, applying scanning thermal microscopy (SThM), we observed a novel mechanical-thermal coupling effect in monolayer/bilayer MoS2 and WS2 films: puckering deformation can induce the enhancement of interfacial thermal resistance (TR). By the SThM method, the puckering effect was further proved to depend on the film thickness and the scan velocity. More importantly, the crystallographic orientation-dependent anisotropy of the puckering effect in atomically thin two-dimensional crystals was demonstrated by SThM. It is inferred that the puckering deformation of the film redistributes the in-plane stress, resulting in the isotropy breaking of the in-plane stiffness. Such new findings are of great significance to help optimize the nanoscale tribological/thermal design and dynamic mechanical-thermal management of 2D-materials in nanoelectronics.

Analysis of nonlinear thermal dynamic responses of sandwich functionally graded cylindrical shells containing fluid

Based on the classical shell theory, taking into account the nonlinear geometry of von Karman-Donnell, this article deals with the nonlinear dynamic analysis of Functionally Graded Material (Sandwich-FGM) cylindrical shells containing fluid under mechanical and thermal loads. By using the Galerkin method, the nonlinear dynamic equation is transformed into nonlinear differential equation in terms of time. The investigation of nonlinear dynamic response of sandwich-FGM cylindrical shells containing fluid is established. Numerical results show effect of temperature, fluid, geometric parameters of structure and material parameters (coefficient k) on the dynamic response of structure.

A DMA study of the interfacial changes on injection‐molded iPP/mica composites modified by a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene

ABSTRACTPresent work concerns to the study of the dynamic mechanical and thermal responses of selected polypropylene (iPP)/mica composites with a modified interface from the matrix side by using a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene, coming from a byproduct of industrial polymerization reactors. Thus, the study is mainly focused on the 75/25 iPP/mica ratio since it was identified in previous works as providing the maximum inter mica particle distance to assure they should participate in the overall process of dissipation of the mechanical energy supplied to the composites. Hence, the present dynamic mechanical analysis discussion tries to correlate the damping responses of the injection‐molded composites with those previously obtained but over compression molded composites as the basis of further studies all along the compositional iPP/mica map. Therefore, the latter let us, on the one hand, to follow how the main values of the different dynamic mechanical analysis parameters vary because of the interfacial modifier presence, and on the other, to develop a robust correlation between them and the corresponding macroscopic mechanical parameters. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45366.