Dynamic Heat Balance Research Articles

Математическая модель теплоснабжения помещения как объекта динамического управления температурой

Energy saving issue in the process of administrative buildings heating is an important one. Dynamic control of room temperature depending on the schedule of its usage gives great opportunities. Dynamic control should meet the criteria of energy efficiency and ensure air temperature in the rooms at time intervals of their usage at the required level in terms of external impact on the building. Obviously, such control can only be implemented by an automatic system. To synthesize such a system, we need mathematical models of room heating as control objects. Consequently, the problem under consideration is relevant. Experimental data and numerical simulation methods are used to obtain mathematical models. Mathematical models are obtained in the state space and in the form of transfer functions for controlling and disturbing influences based on the equations of the dynamic heat balance of the room. Two types of mathematical model of the room are defined. They make it possible to synthesize the laws of qualitative and quantitative control of the heat supply of the building with a given accuracy and to determine schedules of temperature changes depending on the schedule of its use, optimal in terms of minimum energy consumption.

(Digital Presentation) Thermal Management for Liquid-Cooling PEMFC: From Temperature Control Scheme Towards Control Strategy Modeling

Efficiency and durability of Proton-exchange membrane fuel cells (PEMFCs) relies on different interacting and coupling factors. The comfort temperature level with good homogeneity is one of the prominent factor, which significantly affects the stack-level and even on-board integrated systems confronted with frequent load changes. Featured with low-grade reaction heat generation (60~80 °C) and high proportion (~50%) accounting for entire yield, liquid-cooling PEMFC stack considerably relies on the construction of thermal management scheme to achieve temperature dynamic heat balance. Similarly, to further improves the electrical efficiency and lifetime, coordinate operation of thermal management BOP components is expected to be fully activated by advanced control-oriented strategy with modeling algorithm. Hence, this review focus on the current status, challenges and future perspectives on extensive potentials for liquid-cooling thermal management system (TMS) in PEMFCs. Firstly, the fundamental temperature control configurations with dual-control targets are introduced, followed by the viewpoint of structure-based as well as material-based, i.e., the effects of cooling channel design (such as parallel, serpentine and wave flow field) and novel coolant adoption (including single metal particles nanofluids and hybrid particles-based nanofluids) upon stack temperature profile and heat transfer performance are reported in detail. Then, the current situation of primary thermal management schemes is supported with classic proportional-integral-differential (PID) feedback control strategy and analyzed to address the necessity of decoupling the temperature parameters to improve the dynamic response for the high-power PEMFC stack. Furthermore, novel control strategies with emerging modeling algorithms (like model reference adaptive control, sliding mode control), oriented for comfort temperature grade, the robust response against varying loads and high efficiency with lower parasitic power, are discussed to evaluate the feasibility and practicality for TMS further integrated into overall energy management architecture of PEMFC system. Finally, in conclusion and perspective, it is appreciated for advanced thermal control strategy to promote single passive temperature control towards proactive thermal management implementation, which is promising and beneficial to identify its substantial potential of low-grade heat recovery and utilization for on-board PEMFC system. Figure 1

An effective temperature derived from a mechanistic thermophysiological model for sows reared in hot climates

Increased metabolic heat production caused by breeding for higher productivity puts sows at a high risk of suffering from heat stress. To reasonably predict the actual thermal status of sows becomes essential for efficiently mitigating heat stress. However, the existing thermal indices for pigs neither have been verified by experimental data of sows nor consider the effect of the dynamic heat balance within sow's body. This study proposed an effective temperature for sows (ETS) in hot climates based on an existing 2-node mechanistic thermophysiological model. The ETS was verified to be able to reflect the thermal status of sows with desired level of confidence by using physiological parameters measured sow experiments. The relative humidity and airspeeds impact ETS and effective temperature (ET), which was predicted by other four ET models, at different levels. The impact of ambient temperature on ET could be well reflected by both ETS and the four ET models. In addition, the ETSs predicted under dynamic conditions with/without considering heat storage were comparable in temperate climate. However, the thermal status of sows in hot climate was predicted more precisely by ETS obtained from dynamic conditions considering heat accumulation in the body of the sow. Considering heat storage in dynamic simulations, ETS derived based on metabolic heat production predicted the thermal status of sows better than ETS derived based on total heat loss. • An effective temperature for sows (ETS) reared in hot climates derived. • Influences of relative humidity and airspeed on ETS investigated. • Impact of dynamic heat accumulation within sow's body on ETS revealed. • Dynamic ETS can better serve for the control of climatic conditions in pig houses.

Thermal management system for liquid-cooling PEMFC stack: From primary configuration to system control strategy

Of various interacting and coupling factors acting on efficiency and durability of PEM fuel cell (PEMFC), comfort temperature level with good homogeneity maintains a dominant role in stack-level, and even integrated system which confronted with load changes frequently. Featured with low-grade reaction heat generation (60–80 °C) and its high proportion (∼50%) accounting for entire yield, liquid-cooling PEMFC stack considerably relies on the construction of thermal management scheme to achieve dynamic heat balance. Furthermore, to improve the efficiency and lifetime goals, coordinate operation of thermal management components is highly activated by robust control-oriented strategy with advanced modeling algorithm. Hence, this review focus on thermal management system (TMS) for liquid-cooling PEMFC stack, from the perspectives of primary configuration and system control strategy. Firstly, temperature control configurations with dual-control targets of TMS are introduced, followed by the development status of cooling channel design and novel coolant adoption. Then, thermal management scheme with coupling architecture is analyzed and discussed in order to address the necessity of decoupling the temperature regulation to improve the dynamic response of TMS. Based on the current situation of typical robust non-PID feedback and feedforward control strategy, novel control strategies with emerging modeling algorithms are presented to show the feasibility targets of comfort temperature grade, the robust response against varying loads as well as high efficiency with lower parasitic power. Finally, in conclusion and perspectives, the guideline and outlook of TMS for liquid-cooling PEMFC are provided to highlight its extensive potentials in low-grade heat recovery of large-power and high-efficiency PEMFC-based powertrain or FCEVs. • Proper temperature with uniformity is critical for efficiency and durability of PEMFC stack. • Advanced TMS for temperature control of liquid-cooling PEMFC is emphasized. • Effects of cooling channel design and novel coolant adoption upon TMS are discussed. • Novel temperature control strategy modelling should be further weighed under practical test.

Resilient Operation of Electric Power Distribution Grids Under Progressive Wildfires

Wildfires have been growingly recognized as a prominent threat in regions with high temperatures during the summer. Power distribution systems, especially those passing through forest regions, are exposed and highly vulnerable to wildfires. This article provides a general formulation to enhance the operational resilience of power distribution networks equipped with renewable energy resources, e.g., wind and solar energy, micro turbines as well as energy storage systems when exposed to progressive wildfires. The wildfire incident is characterized comprehensively and the dynamic heat balance equations of power distribution branches are used to model the impacts of wildfires on overhead line conductors. A mixed-integer quadratic optimization formulation is applied to optimally operate and coordinate all local energy resources to reduce load outages and enhance the system resilience. The applied framework is evaluated on the IEEE 33-node test system. Comprehensive sensitivity analyses are conducted to assess the efficacy of the applied framework, where the numerical results reveal the resilient operation of power distribution networks in the face of wildfire emergencies.

Dynamic Heat Balance Modelling of Industrial Bioleaching Plant: Influence of Both Environment and Operating Conditions and Heat Management Improvement

Dynamic Heat Balance Modelling of Industrial Bioleaching Plant: Influence of Both Environment and Operating Conditions and Heat Management Improvement

A Proposal for the Optimisation of Algorithms for the Calculation of the Energy Demands of Residential Housing

In response to increased energy consumption and CO2 emissions, various energy efficiency policies, standards and housing certifications have emerged around the world. These aim to measure and quantify energy efficiency and endorse homes for meeting certain standards according to consistent categories that vary by continent or country. These energy rating systems correspond to a series of criteria and formulations that, through the calculation and combination of multiple variables, establish the classification values. In Chile, there is the Energy Rating System for Housing (CEV), which performs energy efficiency calculations using dynamic heat balance spreadsheets in Microsoft® Excel. When applied for everyday use and at a large scale, this system has the disadvantage of requiring a great deal of processing time for each simulation. This research proposes an improvement to the CEV energy demand calculation mechanism by generating a solution that takes advantage of the use of multiprocessors and implements the various algorithms in the C programming language. The results show that the CEV values obtained with the proposed calculation engine are equal to those of the current system but demonstrate a 76.5% improvement in their processing time.

Tanks-in-series model for an auto-thermal reforming reactor with a channeled monolith

A novel tanks-in-series-reactor (TSR) model has been developed for auto-thermal reforming of hydrocarbons in a monolithic reactor carrying microchannels. The model is based on the dynamic mass and heat balance equations defined for the channel and catalyst layer. The description of chemical reactions is based on a simplified multi-step surface reaction mechanism under the assumption of the rate-determining step. The predicted steady-state concentration profiles are consistent with experimental literature data.

Characterizing Variations in the Indoor Temperature and Humidity of Guest Rooms with an Occupancy-Based Climate Control Technology

This paper characterizes variations in the indoor temperature and humidity profiles of actual guest rooms equipped with Occupancy-Based Climate Control (OBCC) systems that were used to initiate a temperature setback to 15.6 °C in the winter and to 26.7 °C in the summer in the guest rooms. Empirical knowledge of these conditions can provide useful insights for an improved field demonstration and optimization of OBCC, as well as for a more realistic temperature and occupancy input for building simulations for hotel guest rooms. As a result, one year of one minute temperatures and humidity data was characterized against outdoor climate for three different occupancy modes, which was useful to identify the observed room-to-room variations in heat losses and resultant indoor temperatures during the heating season due to the different dynamic heat balance conditions of the guest rooms. This indicated potential discomfort in the rooms that appeared to have a stronger association between outdoor and indoor temperatures, which was also identified from the thermal comfort survey indicating thermostat-related discomfort sources. Interestingly enough, the guests who stayed in these rooms tended to set their thermostat at higher setpoint temperatures when they occupied the room, which appeared to compensate for the low balance-point temperatures of these rooms.

Experimental Study on Temperature Change and Crack Expansion of High Temperature Granite under Different Cooling Shock Treatments

It is valuable to observe the influence of different cooling methods on the exploitation of geothermal energy and breaking hard rocks in deep geo-engineering. In this work, the effects of different cooling shock treatments on high temperature granite are discussed. First, perforated 100-mm-side cubic biotite adamellite samples were heated to four targeted temperatures (150 °C, 350 °C, 550 °C, and 750 °C). Then, anti-freeze solutions were compounded to produce the different cooling shock effects (20 °C, 0 °C, and −30 °C) by adjusting the calcium chloride solution concentration, and these anti-freeze solutions were injected rapidly into the holes to reflect the rapid cooling shock of high-temperature granite. Finally, the temperature variations and crack expansions of high-temperature granite under different cooling shock treatments were analyzed and the cooling shock cracking mechanism is discussed briefly. The main results can be summarized as: (1) The high temperature granite exposed to the cooling shock exhibited a "rapid cooling + rapid heating" change during the first 5 min. Due to the cooling shock, the total temperature was significantly lower than the natural cooling until 120 min later. (2) Below 350 °C, the macrocracking effect was not significant, and the sample reflected a certain range of uniform microcracks around the injection hole, while the macrocracks tended to be obvious above 550 °C. Moreover, as the refrigerant temperature decreased, the local distribution characteristics of the macrocracking became more obvious. (3) Based on the analysis of the dynamic heat balance, the undulation and width of the cracks around the heat balance zone were stable, but the numbers and widths of cracks near the hole wall and the side of the sample were visibly increased. This study extends our understanding of the influence of cooling shock on granite cracking.

Development and optimization of a novel controller for regenerative indirect evaporative cooler

Abstract The main characteristic of an indirect evaporative cooler (IEC) is the high dependency on ambient air conditions. To ensure stable indoor temperature and provide better thermal comfort, proper control strategy is essential. However, very limited studies report the controller used in IEC. In this paper, a novel control scheme named high-low (H-L) is proposed for regenerative indirect evaporative cooler (RIEC). Under H-L control scheme, the fans would be switched between high speed and low speed rather than completely turned off. The H-L control adopts the multi-speed technology, providing energy saving potential compared with conventional on-off control and overcome the complexity and costly of variable speed technology. The annual performance of RIEC was simulated under H-L control based on the RIEC model and dynamic indoor heat and mass balance model. The influence of low speed to high speed ratio (L/H) is discussed in order to propose an optimal L/H by considering both the thermal comfort and annual energy consumption. The results show that the H-L control can provide stable indoor temperature and satisfactory thermal comfort with Predicted Mean Vote (PMV) in the range of -0.5 to 0.5 for 76.2% of time. The optimal L/H is found to be 0.25 to 0.33 because of high thermal comfort provided and lowest energy consumption.

Determination of the power transmission line ageing failure probability due to the impact of forest fire

With increased occurrences of a forest fire, the short-term reliability of power transmission lines needs to be re-evaluated considering the impact of forest fire on the ageing of transmission lines. How to include the impacts from a forest fire on line ageing in a comprehensive way becomes an important issue for the study of line failure probability. In this study, a method is proposed to evaluate the impact of forest fire on line ageing degree based on dynamic heat balance equation and Weibull distribution. The method will help maintenance staffs to assess the damage level of transmission lines. The method is tested by a contrast experiment and a case study with real meteorological data. Simulation results show that forest fire can greatly threaten the reliability of power transmission lines, while during this process flame characteristics, wind and load ratio could be the major factors that affect the line reliability. With the results obtained, this study also provides the system operator with valuable instructions on how to reduce the damages caused by fire to transmission lines.

Comparative study of on-off control and novel high-low control of regenerative indirect evaporative cooler (RIEC)

The main characteristic of an indirect evaporative cooler (IEC) is its dependency on ambient air conditions. To ensure stable indoor temperature and provide better thermal comfort for the occupants, proper control strategy is essential. However, very limited studies report the controller used in IEC. Therefore, two control schemes are comparatively studied for regenerative indirect evaporative cooler (RIEC) application, including conventional on-off control and newly proposed high-low (H-L) control. Under on-off control scheme, the fans are either in operation at constant rated speeds or turned off if the indoor temperature is satisfied. While under H-L control scheme, the fans would be switched between high speed and low speed rather than completely turned off. The annual performance of RIEC was simulated under the two control schemes based on the RIEC model and dynamic indoor heat and mass balance model. The results show that the H-L control is superior to on-off control by providing better thermal comfort, better indoor air quality and 11.3% less energy consumption annually. The advantages of H-L control are mainly reflected in transition seasons with smaller indoor temperature variation range, lower switch frequency of the fan speed, smaller predicted mean vote (PMV) variation and longer fresh air guarantee.

Heat Compensation Calorimeter as a Process Analytical Tool To Monitor and Control Bioprocess Systems

Biocalorimetry is a process analytical tool extensively employed to measure metabolic heat in order to track cellular activity. To eliminate the inherent demerits in conventional biocalorimeters, an advanced bench-scale heat compensation fermentation biocalorimeter was designed. Improvement in calorimetric signal sensitivity for bioprocess monitoring was achieved by ensuring isothermal condition in the reactor, by operating two independent proportional, integral, and derivative (PID) controls in tandem. Significant reduction in heat loss to the environment was accomplished by incorporating a secondary cascade loop into the cryostat controller. Nonbiological heat measured under different process conditions was calibrated and taken into account as part of the dynamic heat balance. Sensitivity of the system was further improved by incorporating two individual theromostating setups in the reactor housing, viz, a preheated bubble column and a circulating thermal bath fluid in the head plate. Sensitivity and stability of the calorimetric signal were improved to 6.73 mW/L and 0.43 mW/(L h), respectively. The performance of the developed calorimeter was evaluated via real-time monitoring of hyaluronic acid (HA) fermentation by S. zooepidemicus MTCC 3523 and aerobic growth of P. pastoris GSM 115, respectively. The calorimetric signals fingerprinted the changes in cellular metabolism and process behavior with viable precision. Experimentally determined oxy-calorific coefficients, for HA fermentation (684.4 kJ/mol) and P. pastoris growth (471.6 kJ/mol), were in good agreement with theoretical predictions, which validated the reliability and reproducibility of the developed application. Therefore, the developed high-sensitivity calorimeter offered a wide scope for its application as a process analytical technology (PAT) tool for bioprocess monitoring.

The influence of doping on flash sintering conditions in SrTi1−xFexO3−δ

Joule heating in flash sintering depends on the sample resistance, which is linked to the charged defects concentration. To study the contribution of defects on the flash sintering mechanism, this link should be untied. In SrTi1−xFexO3−δ (STFO) system, point defect concentration can be pinned while the resistance is influenced by the oxygen partial pressure (pO2). SrTi0.97Fe0.03O2.985 onset temperature at different pO2 was examined at constant oxygen vacancy concentration. The furnace onset temperature decreases with increasing pO2. The onset temperature of five STFO samples was predicted based on resistance-temperature dependency of the porous green ceramics in a dynamic heat balance simulation. High compatibility of model and experimental results showed reduction of onset temperature with increasing doping. Ex-situ impedance measurements of green samples reveal an overlapping Nyquist plots close to the sample onset temperature. This indicates that the onset is determined by the green body resistance regardless how it has been achieved.

Determination of formal kinetic constants of thermal decomposition of aqueous hydrogen peroxide solution in a mixture of magnetic powder, based on experimental thermogram, obtained in adiabatic conditions

Process of thermal decomposition of hydrogen peroxide aqueous solution with the addition of magnetic powder in the form of toner for printers and lanthanum manganite were considered. Obtained resulting from an experiment in the Dewar container conducted thermogram analyzed using mass balance equations and heat. Formal kinetic parameters determined, and conclude that the magnetic powder in the mixture does not have catalytic properties. The described technique is recommended as a rapid analysis of the kinetics of the various reactions to substances having predefined thermal and thermodynamic properties. Recently, it has been suggested to use fluids mixed with a fine powder to change the thermophysical features of coolants in order to increase the heat exchanger efficiency. Application of magnetic powders allows for additional control over unit operation using the magnetic field. An aqueous hydrogen peroxide solution is often suggested to be used as a coolant in a variety of heat exchangers (such as solar collectors). The aqueous hydrogen peroxide solution with additives of fine magnetic powder can significantly improve the efficiency of heat exchangers. To study the kinetics of thermal decomposition of hydrogen peroxide aqueous solution with added magnetic powder, series of experiments were done to determine the process thermogram in adiabatic conditions of Dewar vessels. Dynamic heat balance equation for the reaction of thermal decomposition of hydrogen peroxide aqueous solution, considering the presence of magnetic powder particles and the reaction of hydrogen peroxide thermal decomposition are recorded under the assumption of the process equilibrium within the entire time interval . During experiments the mixture temperature variations from the initial to final did not exceed 8.5K, which allows, according to the Hess's law, heat of reaction (qd,, J/mol) to be taken as constant. The thermodynamic system is a colloidal solution of hydrogen peroxide, oxygen in water (with current masses, respectively, mH2O2,mO2, mH2O) and fine magnetic powder, consisting of toner for printers and lanthanum manganite (LaySrMnO3−X( y< x)) of the total mass mmp. Specific heat components, respectively, cH2O2, cO2, cH2O & cmp are temperature functions for a general case. Heat from the

Dynamic On-Line Control of Stainless Steel Making in AOD

A new dynamic control model based on simultaneous mass transfer of C, Cr, and Mn and dynamic heat balance is developed. It allows dynamic adjustment of argon-oxygen ratio. The model is implemented through Level II control system. The total operating period of one heat is divided into five different stages: charge calculation, first blow period, second blow period, third blow period and, lastly, the reduction stage. The charge calculation model, based on heat balance, mass balance and the costs decided the optimum charge mix to start with. Both linear and non-linear regression models are used to predict the temperature and composition of bath at the end of first blow period. The second blow and the third blow periods use the dynamic models for predicting the chemical composition and temperature. In the model for reduction stage (final stage) the amount of reduction mixture is determined for obtaining maximum recovery of Cr and Mn from slag. On-line testing of the dynamic models was carried out on the shop floor. The integration of models with the Level II control system using Supervisory Control and Data Acquisition System (SCADA) are discussed. User friendly HMI are developed such that the operators can easily use it during the regular operation on shop-floor. This is the first time that a full dynamic control system was implemented in India for the AOD process.

Heat Transfer Coefficients and Dynamical Thermal Models for Variable Flow Rates in Pipes and Ducts

This study presents thermal models of pipes or ventilation ducts with variable flow rates. The models are based on dynamic thermodynamic heat balances, and much attention has been put into developing accurate heat transfer coefficients. MATLAB/Simulink environment has been used for modeling, but the model is however universal and can be implemented into any software. The model has been validated against measurement data, and found to be quite accurate for use in typical HVAC applications. Accuracy is particularly good if taking thermal damping into account. Thermal damping of pipe or duct mass has shown to be significant for dynamic performance. The model is suited for control simulations or accurate heat loss simulations, where dynamic conditions are important.

Falling film melt crystallization (I): Model development, experimental validation of crystal layer growth and impurity distribution process

This paper was concerned with the model development and experimental validation of the detailed crystal layer growth and multi-ions impurity distribution process in the falling film melt crystallization (FFMC) model. The phosphoric acid (PA) was separated and purified by FFMC to obtain a hyperpure phosphoric acid (HPA), which was a vital electronic chemical in IT industry. To establish a valid model, which offered an easy and convenient path of the simulation, dynamic heat and mass balance, approaches were adopted to describe the variation of crystal layer growth rate along the crystallizer. An impurity balance approach was adopted to describe the change of distribution coefficient for multi-ion impurity. A criterion was proposed to determine the formation of branched-porous (B–P) structure. The model was validated by experimental results with various equipments and operational conditions and a good agreement was obtained. The effective distribution coefficient Keff for multi-ion impurities were less than 0.2 (Na+), 0.25 (Fe3+) and 0.35 (Ca2+) with proper operation conditions. The resulting model was directly exploited to understand crystal layer growth and impurity distribution behaviors in FFMC from laboratory to industrial scale. More significantly, the model proposed a method for the separation effect evaluation and the key operational conditions (feed rate and cooling rate) determination which could readily develop optimal crystal layer growth route during industrial crystallization. In addition, the model was a vital base to describe the subsequent purification step of FFMC: sweating process.

Change of Temperature of Cotton and Polyester Fabrics in Wetting and Drying Process

The purpose of this study was to measure temperatures of cotton and polyester woven fabrics in wetting and drying process by thermocouples placed on them. It also discussed temperature distribution caused by difiusion and evaporation at difierent relative humidity. The measurement points of thermocouples were located at two concentric circles with radius of 3 cm and 6 cm. The temperatures were measured by covering the same fabric when a droplet of water dropped on the center of circle at 20%RH, 65%RH and 80%RH environmental moistures, respectively. The results showed that because of difiusion determined by distance, it was difierent of temperature changes of every point. As the center of circle, at difierent humidity, temperatures when reached dynamic heat balance were difierent. The drying process of cotton showed consistency with temperature recovery. At 20%RH, it is the shortest for temperature returning to environmental temperature because of difiusion speed caused by steam content of environment. It can be applied to performance assessment for fabrics that liquid water absorbing function is required. It also can be used for evaluation of discomfort of wet fabrics by temperature decline with the wetting.