Accurate Temperature Control Research Articles

A widely adaptable analytical method for thermal analysis of flexible electronics with complex heat source structures.

Flexible electronics, as a relatively new category of device, exhibit prodigious potential in many applications, especially in bio-integrated fields. It is critical to understand that thermal management of certain kinds of exothermic flexible electronics is a crucial issue, whether to avoid or to take advantage of the excessive temperature. A widely adaptable analytical method, validated by finite-element analysis and experiments, is conducted to investigate the thermal properties of exothermic flexible electronics with a heat source in complex shape or complex array layout. The main theoretical strategy to obtain the thermal field is through an integral along the complex curve source region. The results predicted by the analytical model enable accurate control of temperature and heat flow in the flexible electronics, which may help in the design and fabrication of flexible electronic devices in the future.

Smith predictor based fractional-order integral controller for robust temperature control in a steel slab reheating furnace

In this paper, a new strategy for robust control of temperature in a steel slab reheating furnace with large time delay uncertainty based on fractional-order controllers combined with a Smith predictor is proposed. A time delay model of the preheating zone of this process is used, obtained from an identification procedure applied in a real industrial furnace. It is shown that this process experiences very large time delay changes. A fractional-order integral controller embedded in a Smith predictor structure (FI-SP) is designed, which is robust to changes in such time delay. Simulated results of a standard Proportinal Integral Derivative (PID) controller, a PID controller embedded in a Smith predictor and the proposed FI-SP controller are compared. Six performance indexes have been used in this comparison. The analysis of these indexes shows that the designed FI-SP controller exhibits the most robust behavior (lowest indexes averaged in all the range of time delay variation) for ranges that include large time delays. Then the robustness features of the FI-SP controller outperform the other integer order controllers in the time responses both to set-point changes and to step disturbances. Therefore, this controller guarantees the best accuracy of temperature control. The designed FI-SP guarantees system stability and robust performance for a high range of plant time delay uncertainties.

Dynamic model for convective heating of a wet brick during energy characterisation of domestic electric ovens

Electric ovens usually represent a low-efficiency category among household appliances, influencing the overall environmental impact of buildings. The energy class of such devices is determined through a test procedure defined by the EN 60350 European standard, where a wet clay brick is heated under set conditions and accurate control of the air temperature during the test is required, which marks the importance of efficient control strategies. In this work a control-oriented dynamic model was devised to predict the transient thermal behaviour of the oven during energy consumption tests carried out in forced-convective mode, including the heat and mass transfer occurring between the wet brick and the cavity air. Model parameters were determined through an optimisation procedure based on experimental data. Comparisons with other sets of experimental data also allowed to validate the predictive capability of the model. The model predicts well the temperature of the cavity air, the Pt500 probe used as a temperature feedback and the core temperature of the brick with deviations lower than 10% after the heating phase of the cavity. The brick heating time and water loss are also captured by the model, with deviations lower than 6% for the former and 9% for the latter.

Improving the Consistency of Injection Molding Products by Intelligent Temperature Compensation Control

Temperature stability is critical to the consistency of product quality in the injection molding process, and it is very necessary to improve the temperature control accuracy under dynamic conditions. However, due to the large time delay, strong coupling, and the dynamic characteristics existing in the system, it is not an easy task to achieve precise temperature control in the injection molding process. In this paper, a new intelligent temperature compensation control strategy for the injection molding process under dynamic conditions is proposed in order to solve two key problems in the compensation control strategy: the compensation time and compensation quantity. A data-based feedforward iterative learning control (ILC) algorithm is designed to learn the optimal compensation time. Once the optimal compensation time is learned, a deep Q-learning algorithm which combined Q-learning with an artificial neural network (ANN) is proposed to learn the optimal compensation quantity. An experimental platform is designed to validate the superiority of the proposed method. Experimental results show that the proposed method can effectively improve temperature control accuracy under dynamic conditions. Meanwhile, the product consistency has also been improved.

An adaptive PID control method to improve the power tracking performance of solar photovoltaic air-conditioning systems

In order to increase the utilization of solar energy to lower the effect of photovoltaic power output fluctuations on power grids, an adaptive PID control method to improve the power tracking performance of solar photovoltaic air-conditioners is proposed in this paper. In this method, a dynamic temperature set point of the indoor zone is generated at each control time step based on the difference between the air-conditioning load and photovoltaic generation. The theoretical analysis shows that the proposed control is essentially a feedforward feedback control where the air-conditioning system can predictably adjust the compressor frequency based on the knowledge of how the solar radiation affects the cooling load. A case study in Shanghai shows that the proposed control method is able to significantly improve the power tracking performance of the photovoltaic air-conditioner, where the Solar Fraction (SF) and the Self-Consumption Ratio (SCR) are improved from 82.74% to 88.11% and from 70.12% to 74.42% respectively, without violating the indoor thermal comfort, where Mean Absolute Error (MAE) from the temperature set point is decreased from 0.197 to 0.168. The tuning of the power difference factor ko will lead to monotonic changes of SF &SCR and a minimum MAE. When ko is well tuned, the proposed control can realize desirable system improvements of both the power tracking ability and the indoor temperature control accuracy. The idea of this paper could be easily modified to benefit other solar cooling applications and conventional air-conditioners.

A proportional–integral (PI) law based variable speed technology for temperature control in indirect evaporative cooling system

The operation of indirect evaporative cooler (IEC) largely depends on the ambient temperature and humidity. To maintain stable indoor temperature, proper controller is essential. On-off control is a mature and stable control method used on constant speed fans. However, large fluctuation of indoor temperature can be observed because of limited control precision. To achieve better thermal comfort, a proportional–integral (PI) law based variable speed technology is proposed for accurate temperature control in an IEC system. This technology had been proved highly effective in central air-conditioning systems and direct expansion air-conditioners in terms of control precision and energy saving, but its techno-economic feasibility in IEC has not been investigated. In this study, annual dynamic simulation has been conducted to an IEC system based on the IEC model and control algorithm. Results show that indoor temperature can be controlled within ±0.5 °C around the setting point for 81.9% of time, while it is only 30.5% under on-off control. The PI based controller is well adapted to cooling loads in all seasons with good control precision, fast response speed and small overshoots. Response time of PI control is only 10 min in a disturbance rejection test, which is much shorter than 30 min under the on-off control. Annually, IEC with variable speed fans consume 50.0% less energy than that of on-off fans. At last, economic analysis shows that this technology is economically feasible only when the power of primary air fan is larger than 1.75 kW.

Experimental study on the temperature management behaviours of a controllable loop thermosyphon

The loop thermosyphon with active heat transfer control capability is a promising solution for the temperature management of the fresh food compartment of cool-storage refrigerators or other precise temperature control devices. However, the frequently start-stop operating mode of the loop thermosyphon has not received enough attention, its active temperature management behaviours still requires further investigation. In this study, a controllable loop thermosyphon used in the temperature control of a fresh food compartment is developed and its start-stop is controlled by the temperature controller with the assistance of two magnetic valves. The performances of the controllable loop thermosyphon in long-term and start-stop operating modes are tested. The controllable loop thermosyphon with 35% filling ratio present highest heat transfer rate, reliable heat transfer capability, and good stability for the varying temperatures in the fresh food compartment. Based on this filling ratio, the heat transfer rate remains higher than 40 W during the long-term operating test. When the controllable loop thermosyphon operates in the start-stop mode, the start-stop cycle decreases from 39.4 min to 27.2 min and the operating ratio increases from 12.6% to 53.7% as the temperature of the fresh food compartment rises. Particularly, when the start-stop cycle reduces from 42.6 min to 18.1 min, the temperature control accuracy is improved from 2.0 °C to 0.4 °C. The results demonstrate that the controllable loop thermosyphon is promising as a novel precise temperature management device and is qualified for the use in cool-storage refrigerators.

(Invited) Process Control of Advanced Cobalt Interconnect Plating Bath

Cobalt made an inevitable move into more and more applications as device features shrink. It has largely been replacing tungsten in prior forays: for encapsulating and for high-aspect-ratio fill. Cobalt now has a new target in its sights: copper interconnect [1]. Copper replaced aluminum about 20 years ago and had been successfully utilized in numerous semiconductor manufacturing nodes. However, when the IC industry moved beyond the 10 nm node, copper interconnects became more compact, causing an increase in the resistance-capacitance delay. One way to solve the problem is to utilize a cobalt metallization alternative that provides resistance benefits over conventional technology without compromising reliability and yield [2]. In this electroplating process, a super-filling relies on depletion of protons inside feature, leading to increased current efficiency for Cobalt. Depletion of protons in this case leads to reduction of suppression efficiency and further enhancement of cobalt deposition as compared to field [3, 4]. These publications agree that a successful super-filling requires tight pH control. This presentation reveals results of advanced method that allow to reach 0.005 pH repeatability required for electroplating process. While this cobalt plating process is maturing, tighter process control is required to provide more accurate and precise data as well as faster analysis data generation. Previously developed analytical methods [5, 6] had been refined and improved to address challenges of the modern industrial cobalt plating processes. New, efficient analytical techniques were also developed. These methods can also report additional properties of a plating solution (conductivity and pH) critical for bath performance. Fig 1. shows the electrochemical responses of different proprietary organic additives used in commercial cobalt plating baths. Optimized electroanalytical and hydrodynamic parameters enable the determination of a wide range of concentrations of organic additives without interference from other bath components, as well as from bath pH and temperature. Analysis of organic additives can be performed with relatively simple fluidics that include a single mini electrochemical cell with accurate temperature control. Typical analysis steps include fast electrode conditioning in support electrolyte, several or single injection of plating solution to determine changes in plating rate, and then subsequent calculation of the concentrations. One of the newly developed methods is non-reagent spectroscopic analysis of boric acid. This method can also be combined with non-reagent analysis of cobalt providing very fast analysis of both components. Fig. 2 shows correlation of obtained and expected values for wide range of boric acid concentrations. This presentation will provide more detailed information related to the electrochemical behavior of organic additives and inorganic components. The results of Electrochemical Impedance Spectroscopy investigations and Raman spectroscopy will also be presented. The presentation will be concluded with a discussion of analytical results for all bath components during electroplating process.

Research on the Theory and System for Testing Thermal Conductivity of Materials

Thermal conductivity is one of important indexes of material’s quality evaluation. This material’s thermal conductivity detection system was designed and made based on the least square support vector machine algorithm. The system hardware was made mainly by microcontroller ATmega64, the temperature detection circuit and heating and refrigeration circuit. The system software was based on virtual instrument development platform of Labwindows/CVI and the least square support vector machine algorithm, which has data collection and processing, and the results display and control functions. Application shows that this system has advantages of reliable operation, precise temperature control and high thermal conductivity detection accuracy.

Modular interface and experimental setup for in-vacuum operation of microfluidic devices.

We report on the design and operation of a world-to-chip microfluidic interface and experimental setup for fluidic micro- and nano-electromechanical systems. The central component of the interface is an engineered polyether ether ketone connector that brings fluid samples from a commercial syringe pump to the chip with the help of o-rings. In addition to that, the connector serves as an on-chip vacuum chamber. To confirm the adequate operation of our interface, we use complex microfluidic devices that were previously fabricated, suspended microchannel resonators, and demonstrate a fast exchange between fluids (on the scale of 130 s from isopropyl alcohol to water), in-vacuum operation of the devices (intrinsic damping regime), and accurate temperature control of the chip at different set points.

A Modelling and Control Approach for a Type of Mixed Logical Dynamical System Using in Chilled Water System of Refrigeration System

The chilled water system of central air conditioning is a typical hybrid system. The dynamic adjustment of cooling capacity based on hybrid system can achieve accurate temperature control and real-time energy saving. Mixed logical dynamical (MLD) systems have advantage for solving constrained optimization problems of this type of case by numerical methods. This paper proposes a novel modified type of MLD system, which enhances the model applicability and improves the switching flexibility and control effect for the framework. In order to meet the needs of cooling capacity and energy saving, the optimal control problem is transformed as MIQP problem by defined performance index. As a numeral example of application, the model and control method is used in pumps group control for variable water volume in chilled water system of central air conditioning. At last, the dynamic and energy-saving effects of the system are simulated, which shows the ideal control results.

Optical crystal temperature tuner based on feedforward-feedback compound control

To tune the output wavelength of the laser, the operating temperature of the optical crystal needs to be controlled precisely in a wide range. In this paper, a temperature tuning control method for optical crystals with high temperature control precision and large temperature control range based on semiconductor refrigerator (TEC) was studied. The operating characteristics of TEC,the thermal effects and heat transfer mechanisms of optical crystals were analyzed. A temperature-current double closed loop temperature control model was established. This temperature-current double closed loop control model takes control of both the electrical characteristic's variations of working TEC and the temperature variations of the optical crystal. To overcome the inherent hysteresis characteristic of feedback control, the feedforward compensation control based on the double closed loop control was introduced. The TEC driver module based on the ARM+FPGA architecture was designed to achieve the high-frequency and high-precision PWM drive control. In conclusion, an optical crystal temperature tuning system was completed. Experimental results show that the overall temperature control accuracy of this system is better than 0.002ºC and the system can quickly stabilize at any set point temperature in a wide temperature range of -30-130ºC, and it has good robustness to abnormal environment, which meets the requirements of tunable laser for temperature range and accuracy of optical crystal.

Improvement of Temperature Control Performance of Thermoelectric Dehumidifier Used Industry 4.0 by the SF-PI Controller

This paper proposes the series connected fuzzy-proportional integral (SF-PI) controller, which is composed of the fuzzy control and the PI controller to improve temperature control performance of dehumidifier using a thermoelectric element. The control of conventional PI controller usually uses fixed gain. For that reason, it is limited in achieving satisfactory control performance in both transient-state and steady-state. The fuzzy control within SF-PI controller adjusts the input value of PI controller according to operating condition. The PI controller within the SF-PI controller controls the temperature of the thermoelectric element using that value. The SF-PI controller can achieve more accurate temperature control than a conventional PI controller for that reason. The SF-PI controller has been tested for various indoor environmental conditions such as temperature and relative humidity conditions. The average temperature error of the SF-PI controller between the reference temperature and the thermoelectric element temperature is 22% of traditional PI’s value and consumption power is reduced by about 10%. Therefore, the SF-PI controller proposed in this paper can improved the performance of temperature control of dehumidifier using thermoelectric element. The power consumed by buildings accounts for a significant portion of the total power consumption, of which the air conditioner represents the largest energy consumer. In this paper, it is possible to reduce the energy consumption by improving the performance of the dehumidifier, one of the air conditioners, and it can be applied to various control fields in the future.

Focus on analytical equipment, sensors, and instrumentation

Focus on analytical equipment, sensors, and instrumentation

Rapid micro-assays for amylolytic activities determination: customization and validation of the tests

High-throughput function-based screening techniques remain the major bottleneck in the novel biocatalysts development pipeline. In the present study, we customized protocols for amylolytic activity determination (Somogyi-Nelson and starch-iodine tests) to micro-volume thermalcycler-based assays (linearity range 60–600 μM of reducing sugar, R2 = 0.9855; 0–2 mg/mL of starch, R2 = 0.9921, respectively). Exploitation of a thermalcycler enabled rapid and accurate temperature control, further reduction of reagents and samples volumes, and limited evaporation of the reaction mixtures, meeting several crucial requirements of an adequate enzymatic assay. In the optimized micro-volume Somogyi-Nelson protocol, we were able to reduce the time required for high-temperature heating sixfold (down to 5 min) and further increase sensitivity of the assay (tenfold), when compared to the previous MTP-based protocol. The optimized microassays have complementary scope of specificities: micro-starch-iodine test for endoglucanases, micro-Somogyi-Nelson test for exoglucanases. Due to rapid, micro-volume and high-throughput character, the methods can complement toolbox assisting development of novel biocatalysts and analysis of saccharides-containing samples.

Microwave-power-enabled tuning of NiCo double hydroxide nanostructures

Microwave heating has been widely used to enhance the fabricating rate of nanomaterials in the past few decades. However, the application of interaction between microwave and chemical reaction in tuning nanomaterials morphology is yet to be explored, while strategies to manipulate material nanostructures are of great importance for enhanced function. In this work, we demonstrate the potential of microwave in tuning the morphology of nanostructured NiCo DHs by accurate temperature control through the precise design of microwave reacting system. We find that 200-W microwave irradiation gives yield to unique flower-on-sheet hierarchical structure of NiCo DHs, while microspheres are derived from oil-bath heating. Microwave power is found to play a vital role in the tuning process. When microwave power decreases to 50 W, assembled nanoflakes are obtained; when microwave power increases to 300 W, microspheres are obtained. Further, fluid permittivity is monitored and field intensity in the reacting region is simulated and found to increase with time. Taken together, it is proposed that field-induced de-solvation possibly exists and is the main tuning mechanism. When tested as electrode materials in supercapacitor, products obtained from 200 W microwave treatment show enhanced storage capacities, especially at high current density.

An intelligent monitoring system for a pig breeding environment based on a wireless sensor network

The piggery environment is an important factor affecting health level, growth and development of pigs. To facilitate environmental monitoring for large-scale pig farms, an environmental monitoring system of air quality parameters for livestock breeding is developed based on a wireless sensor network (WSN). As the piggery environment is a multi-variable, non-linear and time-varying system, there are coupling effects among them. Fuzzy controllers are designed to control temperature and humidity, respectively. To reduce the coupling effect, a compensation decoupling controller is designed. Experimental results indicated that, compared with the data from an air quality analyser, measurement precision of temperature, humidity, ammonia and carbon dioxide in a WSN system was higher. Furthermore, the control accuracy of temperature and humidity was also higher. The monitoring system was used in Zhenjiang, Jiangsu Province, China, and it performed well, and it was demonstrated to be suitable for the intelligent monitoring and control in livestock breeding.

An intelligent monitoring system for a pig breeding environment based on a wireless sensor network

The piggery environment is an important factor affecting health level, growth and development of pigs. To facilitate environmental monitoring for large-scale pig farms, an environmental monitoring system of air quality parameters for livestock breeding is developed based on a wireless sensor network (WSN). As the piggery environment is a multi-variable, non-linear and time-varying system, there are coupling effects among them. Fuzzy controllers are designed to control temperature and humidity, respectively. To reduce the coupling effect, a compensation decoupling controller is designed. Experimental results indicated that, compared with the data from an air quality analyser, measurement precision of temperature, humidity, ammonia and carbon dioxide in a WSN system was higher. Furthermore, the control accuracy of temperature and humidity was also higher. The monitoring system was used in Zhenjiang, Jiangsu Province, China, and it performed well, and it was demonstrated to be suitable for the intelligent monitoring and control in livestock breeding.

高精度激光器电流驱动与交流温控系统设计

As an important part of the atomic magnetometer, the semiconductor laser's wavelength and power are mainly determined by current and temperature. However, the traditional DC temperature control system would cause magnetic field interference to the atomic magnetometer. Aiming at high-precision current control, temperature control and magnetic field interference, a laser constant current source driving system and Alternating Current(AC) temperature control system were developed. Firstly, a high-precision laser constant current source driving system based on power amplifier was designed. Secondly, the AC temperature modulation demodulation detection and AC heating drive system were designed. Finally, the STM32 controller, high-precision AD acquisition and DA output combined with temperature fuzzy adaptive PID control algorithm were used for high-precision temperature control. The experimental results show that the temperature control accuracy is 0.005℃ at 42℃, and the current stability is 0.5 A at 32 mA, which lays a foundation for laser optical power and wavelength stability.

Carbon nanotubes (CNT) market worth $9.84 bn by 2023

With carbon capture and utilization (CCU) technologies, it is possible to take CO2 from air and transform it into valuable carbon products, such as graphene and nanotubes. In this study, CO2 was reduced to solid carbon by molten lithium carbonate salt electrolysis. The reactor used for the electrolysis was a coaxial-type unit, where a cylindrical nickel cathode was placed inside a cylindrical stainless steel vessel; such a coaxial-type reactor has not been used before for molten salt electrochemical reduction of CO2. This reactor design allows studies of voltage-current characteristics, which have previously not been conducted for this specific process. As a result, voltage efficiency of this process could be determined along with effect of temperature to cell voltage. Based on these results it is evident that accurate temperature control is crucial in terms of energy efficiency of the process. Data monitoring revealed a high accuracy of temporal temperature control. Great temperature differences were observed spatially. Thermoneutral voltage from the process was determined to be 1.02 V. For this electrochemical process studied, carbon nano-onions (CNOs) were obtained as a main product. Identification of the product was carried out based on Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses. Results also showed that iron, chromium and nickel metals are released during electrolysis. Iron and chromium can only be released from the stainless steel anode, as nickel can come from anode or cathode.