Heater Dimensions Research Articles

Optimization and comprehensive comparison of thermo-optic phase shifter with folded waveguide on SiN and SOI platforms

The thermo-optic phase shifter (TOPS) using metal heaters is widely used in various integrated photonics devices for its advantages of simple fabrication, low loss, and low cost. While folded waveguides are commonly employed to enhance the performance of these phase shifters, a comprehensive understanding of how varying the number of folds and the dimensions of heaters impact the device's performance is still lacking. In this paper, we conducted a comprehensive comparison and optimization into the impact of the number of folded waveguides and the width of heater on the performance of folded waveguide thermo-optic phase shifter (FW-TOPS) on silicon nitride (SiN) and silicon-on-insulator (SOI) platforms using the finite element method (FEM). The research has revealed that both the number of waveguides and the width of the heater exert a substantial influence on the performance of FW-TOPS, particularly on platforms with low refractive index contrast. In cases where the number of waveguides is the same, and the width of the heater electrode is identical, the comparison indicates that on the SiN platform, the FW-TOPS in waveguide Combination 2 (waveguide 1 is a single-mode waveguide, while waveguide 2 is a multi-mode waveguide) exhibits superior overall performance, compared to waveguide Combination 1 (both waveguide 1 and waveguide 2 are single-mode waveguides). However, on the SOI platform, FW-TOPS with waveguide Combination 1 demonstrates better overall performance compared to waveguide Combination 2. Furthermore, the simulation results indicate that although air trenches can significantly reduce the power consumption of the FW-TOPS, they also lead to a substantial decrease in the response speed. Therefore, on the 300 nm-thick SiN and 220 nm-thick SOI platforms, air trenches do not effectively enhance the overall performance of the FW-TOPS.

Design and analysis of extrusion-compression molding setup for processing of glass fiber reinforced polypropylene composites

The processing techniques play a vital role in the development of short fiber reinforced thermoplastic composites. The extrusion technique is used for the compounding of short fiber and polymer before compression molding, as short fibers tend to entangle with each other and cause fiber agglomeration. In this paper, a new extruder nozzle design is firstly proposed for the extrusion compounding process for short glass fiber reinforced polypropylene, which can be utilized to direct the compounded composite flow towards a heated mold and then processed in compression molding. For compression molding of composite, temperature uniformity across mold plays a vital role in achieving uniform properties of the processed composite. A simulation study is done to investigate the effects of cartridge heater dimensions on temperature uniformity across mold, for its potential use as a heating element. The results show different cartridge dimensions produce different temperature profiles across the defined points in the cavity. Dimensional uniformity in the extruded strands can be achieved through the new nozzle design. The proposed nozzle and mold heat setup can be used for the extrusion-compression molding technique for the development of short glass fiber reinforced polypropylene composite.

The effect of heater dimensions with different liquid penetration lengths to dry spots on critical heat flux

• Depending on heater dimension, CHF increased 106% for water and 46% for Novec TM 7100. • Growth and rewetting time scale of dry spot at the center are compared for the CHF. • Width, the shorter of two side lengths, affect the velocity within macrolayer. • The average velocitiy within macrolayer affect the rewetting velocity and CHF. The Critical Heat Flux (CHF) on different heater dimensions for two different working fluids were experimentally evaluated. For a given boiling surface (SiO 2 ), the CHF differences were 107% for water and 46% for NOVEC TM 7100 under different heater dimensions. These differences were not describable with previous studies correlating the CHF with the characteristic length for a given heater dimensions. To understand the effect of the heater dimensions on the CHF, we compared the dry-spot growth time-scale and rewetting time-scale of the dry spot created at the center of the heating surface. The analysis showed that the average velocity in the macrolayer depends on the liquid penetration length, which is the shortest flow path from the end to the center of the heater. The average velocity in macrolayer affect the rewetting velocity and finally the CHF. Based on the analysis considering the dry-spot rewetting phenomena, the dependence of CHF on heater dimension for two different working fluids was well described in this study.

Experimental evaluations of the critical heat flux in terms of the heater dimensions, orientation, and surface morphology

Pool boiling experiments to evaluate the critical heat flux (CHF) have been conducted for decades. Although experimental results for the analyses of a myriad of parameters affecting the CHF have been reported steadily, the CHF results have a large discrepancy between them. This study attempts to acquire reliable CHF data by improving the methodology for pool boiling experiments in a direct heating method. In particular, contact resistance is carefully managed to attain the reliable data in every case of experiments. The experiments are performed with various parameters, namely, heater dimensions, orientation and surface morphology. The dimension effect on the CHF is evaluated with stainless steel heaters with widths of 10, 30, and 50 mm and lengths of 10, 30, and 100 mm. With the suggested size of the heaters for the practical application to real industry, the CHF is evaluated considering a change in the surface process: polishing with sandpaper, wire brushing, and buffing. As a result, unique CHF trends are observed, including CHF deterioration, and surface analyses are conducted using surface analysis instruments. Last, the effects of orientation (0° ~ 180°) on the CHF are evaluated, and the results are compared with the extant correlations and experimental data.

Improved melting of latent heat storage via porous medium and uniform Joule heat generation

To enhance the rate of heat transfer in phase change materials (PCM), high conductivity porous materials have been widely used recently as a promising method. This study introduces a novel approach for improving melting of PCM by incorporating uniform Joule heat generation with the porous structure compared to central heat generation. Different cases based on the heater-in foam configuration under the same heat generation rate are numerically verified and compared with the case of using the central heating element, which the heat transfer in the domain enhances by the porous medium. The effects of pore density and rate of heat generation are explored using the thermal non-equilibrium model to better deal with the interstitial heat transfer between the internal heat-generated-in-foam and the PCM. For the case with the central heating element, the effects of heater dimensions as well as the rate of heat generation are also investigated. The results show that the uniform heat generation from the porous structure can substantially reduce the melting time. Applying 100 kW/m3 for the rate of heat generation reduces the melting time by 21% compared with the best case of the localised heater. Meanwhile, applying higher pore-density foam does not bring any significant effect due to the uniform distribution of the heat generation. The results also show a small effect of localized heater size on the melting time with the same rate of heat generation density from the porous structure. However, for an identical volumetric heat source power of the localised heater, the rate of heat generation per volume is more effective compared with the heating element size due to the presence of the porous medium.

A numerical study on the design of sorption cells for multistage compressors

A research on sorption compressors, for driving Joule-Thomson cryocoolers in space application, is conducted in our lab. Sorption compressors are thermally driven, and unlike mechanical compressors, they do not have moving parts, and therefore do not emit vibrations and are highly reliable. There exist different sorption compressor configurations for different operating conditions and various gases. The current research focuses on nitrogen-activated carbon systems, since nitrogen is usually used as the working fluid for cooling to temperatures between 80 and 100 K and activated carbons are the best adsorbent for this purpose. The objective of the research is to allow the design of sorption compressors for different purposes, such as maximum effectiveness, maximum specific power, maximum volumetric power, and maximum flow rate per adsorbent mass. A numerical one-dimensional heat and mass transfer model is developed to enable the investigation of different sorption cell configurations. The model provides the performance dependency on the heater dimensions, the maximum temperature of the cycle, the sorption cell volume, and the different compressor stages, at steady states. In addition, all the physical dimensions and material properties are parametric, hence, the investigation can include numerous options of design options. The numerical model allows the investigation of many working pairs (adsorbent-adsorbate), and for a variety of applications.

Energy consumption in greenhouses and selection of an optimized heating system with minimum energy consumption

AbstractIn this paper, heat loss is precisely computed by a proposed code considering different climates. Estimating the costs of different central heating system, unit heaters were selected as the most feasible system. Finally, considering the heating capacity and unit heater's dimensions a computational fluid dynamics model was developed to find the optimized configuration of unit heaters in a typical greenhouse. Using this model, the required thermal load for a greenhouse based on the daily temperature of Arak city in 2017 was computed with a smart control system. It was found that savings in energy consumption were approximately 5447 m3 of natural gas each year.

C-Band and O-Band Silicon Photonic Based Low-Power Variable Optical Attenuators

We propose and experimentally demonstrate low-power and broadband variable optical attenuators (VOAs) on the silicon photonics platform. The VOAs are based on a Mach–Zehnder interferometer structure. Different variations were fabricated using electron beam lithography using different input and output couplers, heater length and width, operating wavelength, and substrate undercut. Experimental results for the C-band VOA show that, including the substrate undercut, a 3X improvement can be achieved in the power consumption, at the expense of a reduction in electrical bandwidth, where 5- and 20-dB attenuation can be achieved using only 5.5 and 8 mW. Moreover, the VOA can operate over more than 80-nm optical bandwidth with ripples below 1 dB. Furthermore, we study the impact of the heater dimensions on the optical attenuation and VOA bandwidth. Finally, we present similar results for an O-band VOA design.

Performance enhancement of Pirani gauge on silicon-on-insulator wafer with simple fabrication process

A micro-Pirani gauge, operating in the range of vacuum to atmospheric pressure, is designed, fabricated and characterized. The proposed micro-Pirani gauge is fabricated on a commercially available silicon-on-insulator (SOI) wafer with a simple micromachining technique. Since the micro-Pirani gauge has one heater with triple heat sinks, a new mathematical model is developed and validated with the experimental results. By using the mathematical model, the design parameters—thickness, width, and length of the heater and the gaps between the heater and heat sinks—are optimized for attaining a wide operating range of 0.05–760Torr. The heater dimensions and gaps in the optimized micro-Pirani gauge are as follows: thickness of 1.5μm, width of 3μm, and length of 350μm for the heater, and gaps of 0.6 and 1μm in the lateral and vertical directions, respectively. The total area of the micro-Pirani gauge, including the four bond pads, is 950×700μm2.

Limits to Fourier theory in high thermal conductivity single crystals

We report the results of time-domain thermoreflectance (TDTR) experiments that examine the ability of Fourier theory to predict the thermal response in single crystals when heater dimensions are small. We performed TDTR measurements on Al-coated diamond, 6H-SiC, GaP, Ge, MgO, GaAs, and GaSb single crystals with a wide range of laser spot size radii, 0.7 μm < w0 < 12 μm. When the laser spot-size is large, w0 ≈ 12 μm, TDTR data for all crystals are in agreement with predictions of Fourier theory with bulk thermal conductivity values. When the laser spot-size is small, w0 < 2 μm, there are significant differences between the predictions of Fourier theory and TDTR data for all crystals except MgO.

Fast response integrated MEMS microheaters for ultra low power gas detection

Semiconducting metal oxide (SMO) gas sensors typically operate at a few hundred degrees Celsius and consume hundreds of milliwatts of power, limiting their application in battery-powered devices. An analytical model is presented for the optimization of the heater dimensions, which suggests the minimal power consumption is achieved when heat loss through air conduction and supporting beam conduction are equal. We demonstrate micromachined SMO sensors with optimized microheaters, which consume only ∼2mW of power when operated continuously at 300°C. We also measure an ultra-fast thermal response time of 33μs via a transient temperature–resistivity response method. The short response time allows the heaters to be operated in ultra-short pulsing mode decreasing the average power consumption to the μW level. These micromachined SMO sensors are used in proof-of-principle experiments as ultralow power hydrogen sulfide SMO gas sensors.

Heat Sinks for Miniature Thermoelectric Coolers: Selection and Characterization

The effect of heat sink (HS) thermal resistance on the performance of a thermoelectric cooler (TEC) has been studied. A method of HS characterization is proposed for the typical case of substantial mismatch in the dimensions of these components. This dimension mismatch causes significant heat spreading resistance in the HS base plate which is highly dependent on the lack of conformity of the components. In this study we investigated modern a HS whose thermal resistance Rd was determined experimentally by use of a dummy heater of fixed dimensions. An analytical method is proposed for predicting HS thermal resistance for arbitrary heater dimensions using the certified Rd value as sole reference point. The method is based on an HS thermal model with three-dimensional heat spread in its base plate. This theoretical approach was used for characterization of HS from Alpha Company, a manufacturer of HS for microelectronics. HS with low pressure drop were considered under conditions of natural and forced convection. It is shown that their thermal resistance, which depends on TEC dimensions, can differ substantially from the certified value.

Mixed Convection of Nanofluid Flows in a Square Lid-Driven Cavity Heated Partially From Both the Bottom and Side Walls

This article presents the results of a numerical study on mixed convection within a square lid-driven which was heated simultaneously by two finite heat sources on the bottom and side walls, and also filled with nanofluids. The results were presented for different nanofluids. The governing equations were solved using a finite volume approach by the SIMPLE algorithm. The effects of the Rayleigh number, Reynolds number, the solid volume fraction, the dimensions of heaters, and their locations on the streamlines and isotherms contours were investigated accurately. Also, the effects of the above parameters on the average Nusselt number along two heat sources were precisely presented. Moreover, variations of the average Nusselt number of two heaters were considered whenever one heater was fixed and the location of the other heater was varied along the wall. In addition, variations of the length of one heater on the average Nusselt number were also studied whenever the length of the other heater was fixed.

Scanning Thermal Microscopy for Fast Multiscale Imaging and Manipulation

Multiscale resolution imaging and manipulation are essential for applications ranging from defect screening in circuits to nanoscale manipulation, patterning, and lithography. In this paper, we introduce a variant of scanning thermal microscopy to image surfaces at both the micro- and nanoscale. Electrothermal imaging at the microscale is performed in a completely out-of-contact, i.e., “noncontact” or “off-contact,” mode with a microscale heater, followed by higher resolution nanoscale imaging in contact mode with a nanoscale probe tip. Using this methodology, the imaging and manipulation functions of a single probe can be decoupled completely. This off-contact imaging mode is useful for avoiding tip wear and can be performed safely at high velocities. We demonstrate imaging of microscale features at speeds of up to 2 mm/s. The lateral resolution is determined by the dimensions of the heater used for imaging. For the flying heights and heater dimensions used here, the 1-σ lateral spatial resolution limit in the off-contact mode is less than 10 μm for 10-nm-tall features. A silicon nanowire attached to microscale electrodes is imaged to demonstrate the efficacy of this scheme.

Design and Validation of a 6-Volatility Tandem Differential Mobility Analyzer (VTDMA)

A volatility tandem differential mobility analyzer (VTDMA) was developed to allow fast field measurement of the volatile fraction of atmospheric aerosol particles in the particle size range 20–500 nm. In this VTDMA the volatile compounds are evaporated by heating the aerosol to a temperature between 25°C and 300°C. The heating unit is equipped with six symmetric columns kept at different temperatures that allow the heating temperature to be rapidly changed so that a higher temporal resolution can be achieved compared to a regular VTDMA. This work first focuses on the design and calibration of the heating units for the conditioning of a selected aerosol sample while minimizing sample losses due to thermophoresis and diffusion. The design was based on the modeling of the profiles of temperature and velocity and the behavior of a monodisperse aerosol in the heating units, using Computational Fluid Dynamics (CFD) Flow Modeling Software. This allowed for initial estimations of the heater dimensions and also ca...

Life of thermal bubble on platinum microheater

When electrical current is supplied to a microline heater immersed in liquid, a microthermal bubble can be formed. The bubble grows until it becomes too large to adhere to a solid surface and finally departs into liquid completing its life. Here we report the experimental results associated with the life of a thermal bubble continuously heated by a platinum microheater. We investigated the effects of the heater dimensions on the nucleation temperature. It was found that a bubble nucleates at lower temperature as the heater gets wider. We also measured the departure diameter and frequency of thermal bubbles depending on the thermal conditions of the microheater and the ambient liquid. As the microheater temperature increases, both the departure diameter and frequency increase, showing different behaviors from those of macroscale boiling. However, as the ambient liquid temperature rises, the departure diameter decreases despite the increase of the departure frequency. Finally, the transient temperature profile of the microheater during bubble formation process was measured. Rapid drop and rise of the temperature were observed, which are attributed to the small-scale convection of cold ambient liquid.

Droplet ejection performance of a monolithic thermal inkjet print head

This paper presents a simulation study of the droplet ejection performance of a thermal inkjet print head. The geometry of the print head comprises a dome-shaped ink chamber, a nozzle guide and a ring-shaped heater integrated on each chamber. The design eliminates direct contact between the heater and the ink, thus minimizing heater burnout. The ink manifold, ink chamber and nozzle are aligned, thus facilitating higher nozzle density. The model simulates thermal bubble dynamics including nucleation and growth of thermal bubbles caused by a thermal pulse. The model was validated by comparing model predictions with experimental results for a previously reported print head design. Then, the model was used to simulate the droplet ejection performance of the proposed inkjet print head. Effects of print head geometry including nozzle diameter, nozzle length, chamber size, heater dimensions and location, thermal conductivity of the passivation layer, operating conditions including total thermal energy and pulse width, properties of the ink including density, viscosity and surface tension on the performance of the inkjet device are investigated. The influence of these parameters on the drop volume and velocity, threshold energy and tail length of the ejected droplets is studied.

Faults analysis for MSF plants

This work analyses the faults consequences in MSF plants. This analysis will help to design an optimal action plans in order to mitigate the faults effects. The nature of the faults consequences are studied at two levels: process level and mathematical level. At the first one, faults are grouped according its effects over the process state; at the second level, they are grouped according the mathematical features of its consequences analyzed as functions of time (i.e. signals). The study was carried out by using a dynamic simulator for MSF desalination plants. It takes into account the heaters and stages dynamic, hydraulic, standard instrumentation and control systems. This simulator was developed to study the effects of faults that may affect a MSF plant. In order to extend the results scope, the simulator allows the modification of topology and parameters into a wide range. Indeed, it is possible to change the number of stages belonging to the recovery and rejection sections, controllers’ parameters (set point, integral time and gain), valves size, pumps characteristics, sea water conditions, stages and heater dimensions, etc. Since faults simulation is the main simulator goal, the model and its resolution were carefully designed to enhance stability and speed. The user can select the fault to simulate among a set of possible faults (fault in controllers, sensors, pumps, etc.), and can specify the activating time (at which the fault starts), the developing time (time elapsed from the fault start up until the fault reaches its maximum magnitude) and the fault magnitude. Thus, it is possible to simulate step and ramp perturbations. The simulator was tested with data from real plants and it has shown a good performance.

Cost optimization of a conical electric heater

Electric heaters are used extensively in many industrial applications including air conditioning, water heating, and drying of crop and other materials. There are several interacting parameters that affect heater performance and contribute to its operating and manufacturing costs. The design parameters of interest included coil length, coil diameter, helix diameter, coil pitch, number of turns, coil emissivity, heater wall emissivity, applied voltage, air flow rate, air temperature at the heater outlet, insulation thickness, and the heater dimensions. An objective function for the heater cost was defined in terms of the total annual costs for energy usage and manufacturing. The manufacturing cost included the material cost of the heater, the cost of coating the heater coil, and the cost of insulating the heater. A detailed model describing the performance of a conical heater was utilized to evaluate and minimize the objective function. The optimization problem was completely defined by introducing fourteen inequality constraints, three equality constraints, and ten design variables. The univariate search was used to reduce the number of inequality constraints. The direct search and variable metric methods were used to optimize the objective function at different values of the applied power and air temperature at the heater outlet, leading to the same results. The optimization results indicate that the optimum heater design was found at the minimum values of the coil diameter, conical angle, coil emissivity, and the maximum value of coil temperature. The maximum operating temperature of the optimum heater design (a heater with a silver coated coil) is substantially lower than the maximum normal operating temperature so that longer life for the heating element is expected. The effect of varying the applied power on the objective function showed that as the applied power increases the objective function may increase or decrease, depending on the combined effect of increasing the coil length and heater efficiency and decreasing the insulation thickness. The effect of varying the air temperature at the heater outlet on the objective function indicated that as the air temperature increases the objective function increases. Copyright © 2005 John Wiley & Sons, Ltd.

Modelling and performance analysis of an electric heater

Electric heaters are used extensively in many industrial applications. There are several interacting parameters that affect heater performance and contribute to its cost. Such parameters are: coil length, coil diameter, helix diameter, coil pitch, number of turns, coil emissivity, heater wall emissivity, applied voltage, air flow rate, air temperature at the heater outlet, insulation thickness, and the heater dimensions. Three conical heater configurations were selected for preliminary optimization. A conical heater configuration with outer ring coils was found to give the highest heater efficiency, the easiest and least expensive to manufacture, and was selected for detailed modelling. In the simulation model, the heater wall was divided into four annular sections and the continuous heater coil was divided into four segments of four ring coils. Energy and heat transfer equations were written for each ring coil, each section of the wall, and the air past each ring coil. Equations for coil resistance and power, air properties, heater geometry, and configuration factors are added to form a system of 220 nonlinear equations. Engineering equation solver (EES) was used to solve the system of equations. The results were checked by comparing the heater efficiency based on the average inlet and outlet air temperatures, and the heater efficiency based on the heater losses. Both efficiencies matched well in all calculations. The effects of varying the identified heater parameters on the heater performance were studied and discussed. The results indicate that increasing the coil length and airflow rate, while reducing coil emissivity, wall emissivity, and wire diameter could improve heater performance. Copyright © 2004 John Wiley & Sons, Ltd.