Dynamic Heat Load Research Articles

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.

Dynamic simulation of ITER cryo-distribution system using Aspen HYSYS

The ITER cryogenic system consists of the Liquid Helium (LHe) plant, the Cryo-Distribution (CD) system, and the cryo-lines. The Auxiliary Cold Boxes (ACBs) dedicated to cooling the superconducting (SC) magnet system and the Cryoplant Termination Cold Box (CTCB) of the ITER CD system are in the factory acceptance phase. The internal components of ACBs, e.g., cryogenic valves, a cold compressor (CCp), heat exchangers, and a cold circulator (CCr), have been sized and assembled, ensuring their functionality. The interdependency of the functional parameters of one component over the others needs to be assessed, as their integrated performance under the dynamic heat load deposition from the SC magnets may impact the overall operation of the ITER cryogenic system. The ACBs are equipped with two helium baths having ∼ 1200 kg of He inventory and situated inside the Tokamak building. These baths act as a thermal buffer for the LHe plant, situated in the cryoplant building, allowing it to operate at a quasi-steady state despite heat load variation from the applications. Such a large helium inventory can challenge the secondary confinement system of ITER due to helium ingress accidental events and thus needs to be optimized. The integrated system-level simulation is therefore necessary for the safe and reliable operation of the cryogenic system under such demanding requirements. The present study summarizes the results obtained for ACBs dedicated to the magnet system, including CTCB for the enhanced ITER operation modes, and confirms the integrated performance of the system. The results show that the LHe baths inside the ACBs can be used as a thermal buffer with the proposed limit of initial filling and by keeping a constant opening of the respective J-T valves upstream of the LHe baths. The study outcome and the proposed recommendations would be beneficial to mitigate the pulsed heat load to the LHe plant while minimizing the helium inventory.

The first cooldown of SCL3 cryogenic system

RAON, Rare isotope Accelerator complex for ON-line experiments, is the first superconducting linear accelerators in S. Korea. It will have three linear accelerators (Linac), SCL1, SCL2, and SCL3. Now, construction of the SCL3, the third superconducting Linac was finished in the middle of 2022 and the commissioning of its cryogenic system was done July, 2022. The first cooldown of the Linac with the cryogenic system was started from September, 2022 and their temperature was reached at 2.05 K in January, 2023. The first cooldown was successfully completed and the static and dynamic heat loads of the Linac were measured. This paper shows the results of the first cooldown and the heat load tests.

A predictive model of long-term performance assessment of Ground Source Heat Pump (GSHP) systems in Japanese regions

This study predicts the long-term performance of ground source heat pump (GSHP) systems in different climatic regions of Japan. The research model calculates the dynamic heat load of a typical Japanese building in various cities using their meteorological data, considering different schedules for heating and cooling seasons. The model aims to analyze the performance degradation of the GSHP system after 15 years of operation due to the imbalanced heating and cooling loads. Additionally, it compares ground temperature changes, coefficient of performance (COP) variations, and annual operation times based on different thermal imbalance ratios (TIR) for the case studies. The results demonstrate that TIR serves as an appropriate factor for comprehensively evaluating system aspects, including GHE length, ground temperature, and COP degradation, across various climates. It was found that ground temperatures increased by a maximum of up to 4 °C in cooling-dominated regions due to higher thermal imbalance accumulative loads, while it decreased to around 1 °C in heating-dominated regions. The model also revealed that the COP decreased in the dominant operation for each case study due to induced thermal imbalance and soil temperature change. The thermal imbalance caused the system cooling COP decreased by 0.015/year in the worst case (Okinawa City) and 0.006/year in average for other cases.

Operation of 2 K cryogenic system with cold compressors for the SHINE test facility

The Shanghai high repetition rate X-ray free electron laser (XFEL) and extreme light facility (SHINE), a quasi-continuous wave hard XFEL facility, is currently under construction. In order to test all the superconducting components, assembled cryomodules and undulators, the SHINE test facility that consists of various test benches has been built. A superfluid cryoplant with 1 kW@2K was installed, commissioned, acceptance tested and turned into operation to support the cryogenic tests. The plant consists not only of a standard compressor system and cold box but also of a process vacuum system for 2 K operation. In the 2 K cryogenic system, three-stage cold compressors are firstly used to compress helium vapor at a mass flow of up to 50 g/s from 28 mbar to about 400 mbar. Afterwards, the sub-atmospheric helium is continually pressurize to the suction pressure of the warm compressors by five parallel process vacuum pumps. During the first eight months of 2 K operations, the tuning of the cold compressor regulation has been implemented to adapt the different static and dynamic heat loads. A helium pressure stability of superconducting cavities better than ±0.15 mbar at 31 mbar was achieved inside the vertical test bench with additional heating power of 160 W. In this paper, the pump down procedure and the operation results of cryogenic system at 2 K will be described.

Preparations of QWR superconducting cavities for beam commissioning

Quarter-wave resonator (QWR) cavities are prepared for beam commissioning. RF conditioning is performed for each QWR cavity. The total heat load, including static and dynamic heat loads, is measured for each cavity. The helium pressure fluctuation is reduced by changing the flow rate, supply pressure, return pressure, cryogenic valve control, etc. The cavity pressure is monitored during RF preparation. The amplitude and phase of the QWR cavity are stably controlled for beam commissioning.

LHC low-beta quadrupole magnets: cryogenic refrigeration capacity and improved controls for luminosity optimization

The LHC low-β quadrupole magnets, also known as “Inner Triplets”, are the final focusing magnets located on each side of LHC interaction points. The current LHC Inner triplets are NbTi superconducting magnets operated in superfluid helium at 1.9 K and use a bayonet heat exchanger to extract the heat deposited by the secondary particles coming from the proton collisions. The dynamic heat loads in Inner Triplet are consequently proportional to the LHC luminosity and due to the recent upgrades of LHC and its injectors, the cryogenic capacity limit can be reached around ATLAS and CMS experiments where the luminosity can go slightly beyond the LHC ultimate luminosity. First, this paper summarizes the history of the Inner Triplet cryogenics with the different tests performed in the past to assess their cooling capacity. Then, the different techniques implemented in the cryogenic control system to handle the luminosity transients are detailed and finally, a new control interaction between the cryogenic system and the LHC luminosity server is detailed to optimize online the LHC luminosity.

Multiphysics Simulation of a Novel Self-Adaptive Chip Cooling with a Temperature-Regulated Metal Pillar Array in Microfluidic Channels

Conventional liquid cooling techniques may provide effective chip cooling but at the expense of high pumping power consumption. Considering that there is dynamic heat load in practice, a self-adaptive cooling technique is desired to reduce operational costs while preserving inherent cooling effectiveness. In this work, a novel self-adaptive cooling strategy is presented to balance the thermal and flow efficiency in accordance with the dynamic thermal load, based on temperature-regulated movement of the metal pillar array in a microfluidic channel. With an illustrative device, the effectiveness of such a strategy is investigated using multiphysics modeling and simulation. As a case study, the device is considered to be initiated with a chip power of 5 W and an inlet coolant velocity of 0.3 m/s. It is shown that the temperature-regulated movement of the metal pillar heat sink will be activated rapidly and equilibrate within 30 s. Parts of the metal pillars immerse into the coolant flow, resulting in significantly improved heat transfer efficiency. The diminished thermal resistance leads to a reduction in chip temperature rise from 225 K (without structural adaptation) to 91.86 K (with structural adaption). Meanwhile, the immersion of metal pillars into the coolant also causes an increased flow resistance in the microfluidic channel (i.e., pressure drop increases from 859.27 Pa to 915.98 Pa). Nevertheless, the flow resistance decreases spontaneously when the working power of the chip decreases. Comprehensive simulation has demonstrated that the temperature-regulated structure works well under various conditions. Therefore, it is believed that the presented self-adaptive cooling strategy offers simple and cost-effective thermal management for modern electronics with dynamic heat fluxes.

New formulations and experimental validation of non-stationary convolutions for the fast simulation of time-variant flowrates in ground heat exchangers

Flowrate control can have a significant positive impact on the thermal performance and economic profitability of ground-source heat pump systems. Including dynamic advective processes in the design phase, however, remains a challenging task, as few computationally efficient modeling tools allow for their adequate and accurate representation. The present work addresses this issue by presenting new formulations of non-stationary convolutions, an efficient simulation algorithm that relies on the theory of linear time-variant systems for predicting the thermal response of a ground heat exchanger to both dynamic heat loads and flow rates. First, the new original formulations are presented, which include (1) a simple time-domain expression and (2) a fast frequency-domain expression. Then, the efficiency and validity of the new formulations are verified using experimental multi-flowrate thermal response tests involving dynamic circulation, pumping and bleed flow rates in closed-loop and standing column well ground heat exchangers. Results show that the new formulations can reproduce the outlet fluid temperature of both experimental test cases with good accuracy ( MAE = 0.06 ∘ C and 0.26 ∘ C , respectively). At last, the high efficiency of the new frequency-domain expression is demonstrated, with the computing times ( 0.04 s and 0.01 s ) being 100 and 8 times faster than the original formulation in both scenarios.

Design and development of vacuum chamber for superconducting undulator at IHEP

Superconducting undulators (SCUs) are crucial components for advanced photon sources and have broad applications. IHEP is currently developing SCU, which requires a vacuum chamber to provide a beam path and protect the superconducting magnets from image currents induced by the beams. However, due to the narrow magnetic gap and low temperature of the SCU, designing and processing its vacuum chamber presents challenges in terms of mechanical design, positioning, and intercepting synchrotron radiation that could damage the sensitive superconducting magnets. The SCU vacuum chamber is divided into three parts based on location and function: chamber inside the cryostat as well as upstream and downstream chambers outside it. The complex fit of the constant aperture vacuum chamber inside the cryostat with both magnets and cryostat ensures high-current operation while also safely managing dynamic heat loads imposed by beams. Using an SCU operating on HEPS as an example shows how smooth transitions between upstream/downstream and storage ring chambers effectively absorb synchrotron radiation to protect magnets and downstream equipment from damage caused by synchrotron radiation exposure. Simulations are performed to check the possible effects of synchrotron radiation on the mechanical properties, the ultimate vacuum of these chambers and to calculate the beam impedance. Finally, two solutions for using the vacuum chamber as a channel for measuring the magnetic field of the SCU in the operating state are discussed.

Transient temperature distribution in a multilayer semiconductor device with dynamic thermal load and non-uniform thermal contact resistance between layers

The thermal management challenge in microelectronic chips is exacerbated by their multilayer architecture and manufacturing processes that introduce non-uniform thermal contact resistance between adjacent layers. Most of the past work on development of thermal models to predict temperature distribution in microelectronic chips either does not account for such thermal contact resistance at all, or simply assumes it to be spatially uniform. This work presents an exact analytical solution for the transient temperature distribution in a multilayer chip with non-uniform thermal contact resistance between layers as well as dynamic, non-uniform heat generation. The problem is solved by first carrying out a Laplace transformation and then implementing a series solution, the coefficients of which are determined by solving a set of algebraic equations derived from the non-uniform thermal contact resistances between adjacent layers. While the problem is solved for a general M-layered chip, the solution for the practical case of a two-layer chip is also provided. Results indicate that the temperature distribution and its evolution over time is determined by the nature of the non-linear thermal contact resistance, and its overlap with the dynamic heat loads imposed on the chip. The impact of these and other relevant parameters is examined in detail. Results presented here improve the fundamental understanding of thermal transport modeling in multilayer semiconductor chips, with possible applications in other multilayer engineering systems as well.

Physics-guided LSTM model for heat load prediction of buildings

The thermal process of heating buildings is characterized by the multivariable, nonlinear, and large time lag. Accurately predicting building heat loads is crucial for regulating building heating systems. However, the current black-box method of heat load prediction has challenges such as extensive data usage and weak integration with the building's heat transfer process. To address these challenges, a physics-guided long short-term memory (LSTM) model for dynamic heat load prediction in the next seven days based on data-driven and mechanism analysis was proposed. The data for the model were collected from in-situ measurement and numerical simulation. Specifically, the thermal mechanism was introduced to the training loss function of LSTM and the selection of input variables. The influence of the adaptive data time step on prediction accuracy was investigated. The main conclusions obtained from the current data in this paper are drawn as follows. 1) Refining solar radiation intensity calculation for each orientation reduced mean absolute percentage error (MAPE) of heat load prediction results by 0.02%–1.8% compared to horizontal solar radiation intensity. 2) Improving the training loss function decreased MAPE of heat load prediction results by 0.04%–0.43% compared with the original loss function. 3) Adaptive data time step lowered the MAPE of heat load prediction results by 0.08%–1.8% compared with fixed time step. 4) Mean absolute errors corresponding to those three aspects decreased by 25 kJ–558 kJ, 6 kJ–157 kJ, and 41 kJ–1881 kJ. In the future, wider promotion and application of the prediction model will lead to better performance and be more beneficial to energy saving and carbon reduction of the heating system.

A temperature and vent opening couple model in solar greenhouses for vegetable cultivation based on dynamic solar heat load using computational fluid dynamics simulations

AbstractThe application of microclimate control technology in solar greenhouses under a dynamic solar heat load is of great significance for current research on energy consumption and clean efficiency in greenhouses. In particular, solar greenhouses use natural ventilation for the rapid exchange of energy and heat inside and outside the greenhouse. In this study, we proposed a coupling between the natural ventilation model and the computational fluid dynamics (CFD) model to investigate the relationship between ventilation and temperature in solar greenhouses, thus providing a more in‐depth understanding of greenhouse ventilation demands. The influence of vents on the greenhouse microclimate was simulated under dynamic solar thermal loads using CFD to propose a coupling between the natural ventilation model and the CFD model to investigate the relationship between ventilation and temperature in solar greenhouses. Furthermore, we analyzed the daily and annual greenhouse micro‐climates to provide a more in‐depth understanding of greenhouse ventilation demands. Results highlighted the impact of the outdoor wind speed and vent opening on greenhouse ventilation rates and temperatures, with a linear relationship between greenhouse ventilation rates and outdoor wind speed. The outdoor wind speed had little effect on the ventilation rate for reduced vent openings, while the indoor temperature decreased as outdoor wind speed increased. The average temperature in the greenhouse was observed to be greatly affected by wind speeds less than 3 m/s. Simultaneously, opening the greenhouse vent resulted in a fall in indoor temperatures, with openings less than 60% causing the greatest reduction, (the maximum temperature drift was determined as 9.33%).Practical ApplicationsWith the ability to conserve energy and reduce pollution, solar greenhouses are crucial to China's contribution and the global agricultural industry. Moreover, they are associated with improvements in the competitiveness of modern agriculture, particularly in the current era of rapidly increasing costs and pollution from fossil fuels and traditional energy. This study provides a basic reference for the natural ventilation of vents in the control of indoor air temperatures under dynamic solar thermal loads. The results can be used as a theoretical basis for the production management of solar greenhouses, and have an important practical significance for the subsequent automation and intelligent control of greenhouse environments.

Experimental research on dynamic characteristics and control strategy of the pump-driven two-phase loop with dual evaporators

The pump-driven two-phase loop is a promising thermal management technology for avionics, but its dynamic characteristics and control strategy are not clear. A prototype of a pump-driven two-phase loop with a single/dual evaporator for cooling of avionics was developed and its dynamic characteristic under different heat loads and flow rates were studied. It was found that after the evaporator outlet reached saturation, increasing the flow rate would instead reduce the performance, due to the increasing flow resistance of the gas tube and pump power consumption. Based on this, a control strategy of controlling the vapor quality at the evaporator outlet to 0.9–0.95, by adjusting the speed of the pump, was proposed and verified under dynamic heat loads. The results showed that this control strategy ensured optimal system heat transfer performance while reduced the power consumption of the pump. In the experiments of the pump-driven two-phase loop with dual evaporators, it was found that the branch with the larger heat load had a lower flow rate, and was more likely to be superheated. Therefore, in the control of a pump-driven two-phase loop with multiple evaporators, the branch with the maximum heat load should be taken as the control object.

Evaluating Variable-Emissivity Surfaces for Radiative Thermal Control

Variable-emissivity materials enable “adaptive radiators” to control heat flow and regulate the temperature of spacecraft. Although most variable-emissivity engineering efforts focus on achieving the maximum emissivity contrast (a design variable), the radiator performance is ultimately determined by the resulting temperature profile of the system (the objective function). Here, these temperatures are used to define, evaluate, and optimize the variable-emissivity design space for adaptive radiators that produce desired temperature profiles under prescribed dynamic heat loads. Rather than iterating toward the asymptotic emissivity targets of zero and unity, many quasi-steady and transient systems can achieve optimized thermal control under more relaxed emissivity targets that simplify the radiator design. Examples of thermochromic radiators in dynamic operational environments are considered, where the temperature dependence of the total, hemispherical emissivity is derived from both spectrally engineered metasurfaces and phase-change materials. This reimagination of adaptive radiators shifts the design and optimization of variable-emissivity materials away from simple emissivity extrema and toward system-tailored thermal performance.

Heat loads measurements at the XFEL cold linac

The European X-Ray Free Electron Laser (EuXFEL) at DESY is in operation since the beginning of 2017. The free electron laser is based on a superconducting linear accelerator that delivers electrons to the undulator section with beam energy up to 17.5 GeV. The linear accelerator consists of 96 cryomodules; each 12 m long module is an assembly of 8 superconducting cavities and one superconducting magnet. This paper focusses on the measurement of the static and dynamic heat loads of the cryomodules assembled in the linac. Heat loads are an important parameter to evaluate the efficiency of the refrigerator system, the quality of the cryomodule assembly and installation and the accelerating cavity performances, being the dynamic heat loads proportional to the cavity quality factor (Q0, the ratio of the stored energy to the dissipated energy). The paper describes at first the procedure to measure the static heat load without beam energy and the dynamic heat loads at different beam energy levels. The measurement results are then summarized and compared with the XFEL design values.

Optimization of a traveling wave superconducting rf cavity for upgrading the International Linear Collider

The Standing Wave (SW) TESLA niobium-based superconducting radio frequency structure is limited to an accelerating gradient of about 50 MV/m by the critical RF magnetic field. To break through this barrier, we explore the option of niobium-based traveling wave (TW) structures. Optimization of TW structures was done considering experimentally known limiting electric and magnetic fields. It is shown that a TW structure can have an accelerating gradient above 70 MeV/m that is about 1.5 times higher than contemporary standing wave structures with the same critical magnetic field. The other benefit of TW structures shown is R/Q about 2 times higher than TESLA structure that reduces the dynamic heat load by a factor of 2. A method is proposed how to make TW structures multipactor-free. Some design proposals are offered to facilitate fabrication. Further increase of the real-estate gradient (equivalent to 80 MV/m active gradient) is also possible by increasing the length of the accelerating structure because of higher group velocity and cell-to-cell coupling. Realization of this work opens paths to ILC energy upgrades beyond 1 TeV to 3 TeV in competition with CLIC. The paper will discuss corresponding opportunities and challenges.

Cryostat for HECRAL Superconducting Magnet

In order to support the normal operation of HECRAL (Hybrid superconducting Electron Cyclotron Resonance ion source with Advance in Lanzhou) superconducting magnet, a cryostat in the form of immersed in liquid helium was designed, which integrated two two-stage GM (Gifford-McMahon) cryocoolers, helium vessel, thermal shield, outer Dewar, suspension structures, service turret, binary current leads, corresponding monitoring and diagnosis system. The 1st cold head of the two-stage cryocoolers were used to cool the thermal shield and HTS (High Temperature Superconducting) current leads. Enough cooling capacity in the temperature region of 4.2K was supplied by the 2nd cold head to condense the saturated helium vapor evaporated by heat load (including static heat load and dynamic heat load), to realize the “0” liquid helium evaporation operation of the superconducting magnet. The corresponding heat load of the designed cryostat was analyzed, and the WST (Western Superconducting Technologies Co., Ltd.) was commissioned to install the cryostat and carried out cryogenic excitation test. The cryostat is now operated in IMP (Institute of Modern Physics, Chinese Academy of Sciences) and all parts of the magnet and cryostat are working normally, which ensures proper operation of the ion source.

Thermal analysis for fundamental power coupler of HALF 499.8 MHz superconducting cavity

The preliminary research work of Hefei Advanced Light Facility (HALF), a fourth generation diffraction limit storage ring, is in progress. Two 499.8 MHz superconducting cavities may be used in the HALF RF system. RF power will be feed into each cavity through a coaxial fundamental power coupler (FPC). Thermal design of the coupler is very important because of the large power losses on the coupler will cause overheating. Accurate and fast thermal analysis is a challenge in the thermal design. In this paper, two thermal analysis methods for evaluating the cooling effect of the coupler were compared. Computational Fluid Dynamics (CFD) code is used to perform thermal-fluid coupled analysis for the coupler in the first method, which is quite accurate but time-consuming. In the second method, average convective heat transfer coefficient calculated by correlation equations based on experimental results is used to evaluate the heat transfer between the fluid and the cooling pipe wall. The calculation time of the first method is about four times that of the second method. The simulation results of the two methods are consistent well at high flow rate, especially for turbulent flow. Therefore, the second method was used to perform thermal simulation under different cooling conditions and RF power levels. The influence of thermal radiation on the heat load to the cryogenic environment was also given in this paper. Simulation results show that thermal radiation has a slight impact on the heat load. When the copper emissivity equal to 0.02, the total static and dynamic heat load to 4.5 K are 0.833 W and 2.614 W at the power level of 200 kW, and the heat load to 4.5 K cryogenic environment caused by thermal radiation is 0.065 W.

A Preliminary Thermal Model of the LHe-Based SCAPE Cryostat

The SCAPE (SuperConducting Arbitrarily Polarizing Emitter) undulator is under development at the Advanced Photon Source (APS). This new undulator requires a cryostat that will be designed based on expected heat loads. For instance, the expected heating of the beam chamber by electron beam is estimated to be at a level of 182 W - much higher than in planar SCUs. This and other challenges require careful thermal analysis of the LHe-based SCAPE cryostat. A detailed thermal model of the LHe-based SCAPE cryostat has been created in ANSYS. This paper presents calculated cooling capacity and temperatures of the SCAPE cryostat for the static and dynamic heat loads.