Electric Heating Elements Research Articles

Evaluation of a newly developed monitor of deep body temperature.

In 1971, Fox and Solman [1] first described the use of an electronic servocontrolled system to achieve almost complete thermal insulation. The temperature measuring probe has two thermistors separated by a thermal insulator, with an electrical heating element mounted at the rear of the probe. The temperatures on the two sides of the insulating layer, as detected by the thermistors, are compared by a differential amplifier. The error signal is used to control the heater current in such a way as to achieve a situation in which no temperature gradient arises across the insulating layer and thus no heat flows out through this layer. This technique is called the “zero-heat-flow” method. As long as a zero-heat-flow condition is maintained, the probe is equivalent to an ideal thermal insulator; i.e., heat loss from the skin surface beneath the probe is prevented and, after a sufficient time, the skin surface temperature will equilibrate with the deep tissue temperature. Monitoring of deep body temperature, especially from the forehead, is now often used in cardiac surgery in Japan. Deep temperature monitoring has also been used in intensive care units [2] and for monitoring of circulatory failure [3]. Although the monitoring of deep body temperature is noninvasive, clinical application of the monitor is limited by the slow initial response time and the slow response time for rapid internal temperature changes. The initial response time of a deep temperature thermometer, extending from the time when the probe is placed on the body surface to the time when the measured temperature become stable, seems to be long. The

ALLEGHENY LUDLUM TYPE 334

Abstract Allegheny Ludlum Type 334 is an austenitic stainless steel with alloying elements of aluminum and titanium. These additions, along with its higher chromium and nickel levels, give the alloy excellent strength and oxidation resistance, especially when compared to Type 304 stainless steel. Applications include sheathing for electric heating elements. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-833. Producer or source: Allegheny Ludlum Corporation.

Thermal Insulation Systems for Bioremediation in Cold Regions

Bioremediation of petroleum-contaminated soils in cold regions is hampered by low temperatures, frozen soils, and short summers. Extreme environmental conditions limit remedial efforts to a few technologies. Bioventing and combined air-sparging and soil vapor extraction have shown promise in subarctic regions. Expensive thermal desorption or encapsulation of organically contaminated soil is practiced in arctic Alaska and Canada, in lieu of successful bioremediation. Thermal insulation systems have recently been developed for innovative bioremediation efforts in cold regions. Commercially available insulation, electrical heating elements, and construction materials have been uniquely packaged to enhance bioremediation at two petroleum-contaminated sites in Alaska. Thermally enhanced bioventing successfully remediated hydrocarbon contamination in the vadose zone at a subarctic site within two years. Preliminary results from an oxygenated and fertilized biopile, actively warmed and covered with a thermal insulation system, shows promise at an arctic site. A guide for thermal insulation system design for bioremediation application in cold regions is developed.

Experimental study of a heat-driven/solar thermoacoustic refrigerator

This work reports the design and testing of a prototype thermoacoustic refrigerator optimized by the code DeltaE. The key functional feature of this quarter-wavelength resonator is its dual power input capability electric heating elements and the sun. These can be utilized independently or complimentarily to benefit all-weather operation. The machine operates near 270 Hz with helium (60%)–argon (40%) mixture at two bars mean pressure. Heat from either heat source is transported from the high-temperature end to the prime mover stack via thin copper plates that also serve as the hot-end heat exchanger. Both stacks utilize an uncoated automobile catalytic converter ceramic structure with 1.3-mm cell-to-cell square openings and 74% porosity. The ceramic structure provides a strong and easy-to-implement stack with minimal heat conduction. Both middle- and cold-end heat exchangers use simple copper fin design, with the middle heat exchanger using circulating water cooling. DeltaE results predict a 30<th>°C temperature drop across the heat pump stack at no-load condition with 30 W heating, 363<th>°C across the prime mover stack (work=4.0 W) and pressure fluctuation level equal to 6.2%. Results from the effects of working fluid, changing pressure, heating temperature, and cooling load will be discussed.

Defrosting of automotive windshields: progress and challenges

Climate control applications are of great interest to the automotive industry. The issue of windshield defrosting has received, and continues to receive, considerable attention from various investigators around the world. This paper presents an up-to-date assessment of our knowledge base on defrosting. It documents a comprehensive literature review covering experimental as well as computational efforts, accompanied by utilisation of electric heating elements, conducting films, and heat storage devices. The paper also presents a list of measurement methods for airflow and thermal patterns pertinent to defrosting. It concludes with an example on quick detection of a defroster system performance, recommends a defroster system development sequence, and addresses relevant future challenges.

FEASIBILITY OF AN ELECTRICAL RADIATIVE HEATING SYSTEM IN GREENHOUSES

Electrical heating elements were tested for their possible use as a radiative heating system in greenhouses and to find out whether these elements - despite the high cost of electrical energy - could economically be used for the prevention of frost damage in those greenhouses where conventional heating systems cannot be considered because of their high capital cost. The performance of the heating elements was studied in, an unheated plastic tunnel and in a single glazed glasshouse heated to 5 degrees C by means of a conventional pipe heating system. Heating elements were spaced 1, 1.5, and 2 m apart and the effect on vegetation temperature was followed. To simulate the maximal performance of the radiative heating elements, a simple steady state model describing vegetation and element temperatures as a function of inside climate, temperature of the surroundings and power input into the elements was built. From the experiments it was found that the radiative heating system could not be used successfully in the tunnel: the vegetation temperature almost equalled the outside air temperature. In the glasshouse the use of the radiative elements resulted only in a slight increase of the vegetation temperature. Comparison between experimental and simulated results showed that only 40% of the maximally achievable vegetation temperature increase was really obtained. Since even the maximum vegetation temperature increase at rather high electrical energy inputs (100 W.m(-2) greenhouse floor area) was too low, it was concluded that the system was not beneficial from both a technical and economic point of view.

On the Measurement of Residual Stresses in Aluminum Alloy Parts Fabricated by Precision Metal Mold Casting

One of the main causes of unwanted dimensional changes in precision metal mold casting parts is excessive and irregular residual stresses induced by temperature gradients and plastic deformation in the solidifying shell. Residual stresses can also cause stress cracking, and lower the fatigue life and fracture strength of the casting parts. In the present study, aluminum alloy casting system with metal mold equipped with electrical heating elements and water cooling units was designed and the casting specimens were produced to quantify the effects of different cooling conditions on the development of residual stresses. The layer removal method was used to measure the biaxial residual stresses in casting specimens produced from the experiments. The experimental results agreed with Tien-Richmond's theoretical model for thermal stress development for the solidifying metal plate.

The Corrosion Behavior of TiN Coated and Uncoated Incoloy 800 Alloy

Incoloy alloy 800 is used in a variety of applications in industry as well as in domestic appliances for sheeting on electric heating elements. The composition of the alloy enables it to resist deterioration in many corrosive environments. However, resistance of the alloy to corrosion in aqueous media needs to be further examined. The present study examines the corrosion properties of Incoloy 800 alloy of both coated and uncoated workpieces obtained in a 0.1N H2SO4 + 0.05N NaCl solution. TiN coating is achieved using a physical vapor deposition (PVD) technique while corrosion tests are carried out using electrochemical polarization methods. Moreover, in order to examine the influence of hydrogen diffusion, reduction of hydrogen at the Incoloy 800 surface is carried out in a solution of 0.1N HNO3 + 1 g/L thiourea. Tensile tests are conducted on the workpieces to determine the influence of hydrogen embrittlement on the resulting mechanical properties of the substrate. To examine the pit formation and stress induced microcracking, scanning electron microscope (SEM) analysis is carried out. The results show that the corrosion resistance of the alloy improves after TiN coating. In addition, no specific pattern or differentiation on the pit geometry is observed. The pitting rate and its size reduce considerably for TiN coated workpieces.

Radiative heat transfer in low-emissivity ovens

Low-emissivity ovens have linings of ε e<0.1 that enhance the thermal radiation exchange between sheathed electrical heating elements (that are exposed within the cavity) and the thermal load(s). These ovens are a quick and energy-efficient alternative to conventional ovens; however, due to the high levels of thermal radiation, they must be carefully designed and controlled so that uneven radiation distributions over loads are minimised. In this paper, a Monte Carlo ray-tracing model was employed to undertake a parametric analysis of low-emissivity ovens. The factors that influence the magnitudes and uniformities of radiation distributions occurring over loads are identified, and recommendations for optimal heating configurations and control algorithms are presented.

Simulation of a cold-stressed finger including the effects of wind, gloves, and cold-induced vasodilatation.

The thermal response of fingers exposed to cold weather conditions has been simulated. Energy balance equations were formulated, in a former study, for the tissue layers and the arterial, venous, and capillary blood vessels. The equations were solved by a finite difference scheme using the Thomas algorithm and the method of alternating directions. At this stage of development the model does not include any autonomic control functions. Model simulations assumed an electrical heating element to be embedded in the glove layers applied on the finger. A 1.3 W power input was calculated for maintaining finger temperatures at their pre-cold exposure level in a 0 degree C environment. Alternate assumptions of nutritional (low) and basal (high) blood flows in the finger demonstrated the dominance of this factor in maintaining finger temperatures at comfortable levels. Simulated exposures to still and windy air, at 4.17 m/s (15 km/h), indicated the profound chilling effects of wind on fingers in cold environments. Finally, the effects of variable blood flow in the finger, known as "cold-induced vasodilatation," were also investigated. Blood flow variations were assumed to be represented by periodic, symmetric triangular waves allowing for gradual opening-closing cycles of blood supply to the tip of the finger. Results of this part of the simulation were compared with measured records of bare finger temperatures. Good conformity was obtained for a plausible pattern of change in blood flow, which was assumed to be provided in its entirety to the tip of the finger alone.

Silicon carbide heating elements

Silicon carbide is widely used as an electrical heating element because of its excellent thermal and mechanical properties and its electrical resistivity. However, the increase of the electrical resistivity with running time and temperature limits the industrial development of the SiC heating elements. The processes responsible for ageing are not well understood, but it is generally assumed that this phenomena is primarily associated with the oxidation. The present work is a review of the substantial effort that has been made to determine and understand the effects of oxidation with respect to the properties, performance and durability of various commercialized silicon carbide heating elements. This review encompasses measurements of the main characteristics (crystalline phases, composition, density, porosity, flexural strength, thermal conductivity, oxidation and electrical resistivity).

Field Performance of Photovoltaic Solar Water Heating Systems

Energy consumed for water heating accounts for approximately 17.9 EJ of the energy consumed by residential and commercial buildings. Although there are over 90 million water heaters currently in use within the United States (Zogg and Barbour, 1996), durability and installation issues as well as initial cost have limited the sales of solar water heaters to less than 1 million units. Durability issues have included freeze and fluid leakage problems, failure of pumps and their associated controllers, the loss of heat transfer fluids under stagnation conditions, and heat exchanger fouling. The installation of solar water heating systems has often proved difficult, requiring roof penetrations for the piping that transports fluid to and from the solar collectors. Fanney and Dougherty have recently proposed and patented a solar water heating system that eliminates the durability and installation problems associated with current solar water heating systems. The system employs photovoltaic modules to generate electrical energy which is dissipated in multiple electric heating elements. A microprocessor controller is used to match the electrical resistance of the load to the operating characteristics of the photovoltaic modules. Although currently more expensive than existing solar hot water systems, photovoltaic solar water heaters offer the promise of being less expensive than solar thermal systems within the next decade. To date, photovoltaic solar water heating systems have been installed at the National Institute of Standards and Technology in Gaithersburg, MD and the Florida Solar Energy Center in Cocoa, FL. This paper will review the technology employed, describe the two photovoltaic solar water heating systems, and present measured performance data.

A continuous-purge pulsed valve suitable for high-temperature applications

A continuous-purge pulsed valve has been designed to introduce supersonic jet samples into a vacuum chamber. The new valve design separates the heated sampling and transfer lines from the solenoid coils with a long metal valve stem, which is kept cool with annular cooling fins. The valve is heated using electrical heating elements wrapped around the valve stem. A precision-machined stainless steel plunger maintains a metal-to-metal seal at the valve orifice, which is broken when the induced magnetic field from the solenoid pulls the plunger upward. Stable gas pulse widths were obtained down to 200 μs, which compares favorably with the 165 μs value for the commercial unit which uses a small Teflon poppet instead of the metal plunger.

5606641 Device for thermal regulation of a circulating fluid comprising a stacked corrugated plate heat exchanger with heat transfer and cooling paths and electrical heating element therebetween

5606641 Device for thermal regulation of a circulating fluid comprising a stacked corrugated plate heat exchanger with heat transfer and cooling paths and electrical heating element therebetween

A Photovoltaic Solar Water Heating System

A novel solar water heating system was patented in 1994. This system uses photovoltaic cells to generate electrical energy that is subsequently dissipated in multiple electric resistive heating elements. A microprocessor controller continually selects the appropriate heating elements such that the resistive load causes the photovoltaic array to operate at or near maximum power. Unlike other residential photovoltaic systems, the photovoltaic solar water heating system does not require an inverter to convert the direct current supplied by the photovoltaic array to an alternating current or a battery system for storage. It uses the direct current supplied by the photovoltaic array and the inherent storage capabilities of a residential water heater. A photovoltaic solar hot water system eliminates the components most often associated with the failures of solar thermal hot water systems. Although currently more expensive than a solar thermal hot water system, the continued decline of photovoltaic cell prices is likely to make this system competitive with solar thermal hot water systems within the next decade. This paper describes the system, discusses the advantages and disadvantages relative to solar thermal water heating systems, reviews the various control strategies which have been considered, and presents experimental results for two full-scale prototype systems.

Development of improved electrical-substitution radiometers at the National Research Council of Canada

We describe the development of a third generation of electrical-substitution radiometers (ESR's) at the National Research Council of Canada. The new ESR's follow the same general design as before, but incorporate improved thermopiles and electrical heating elements. The ESR's have a responsivity between 0.6 and 1.0 VW(-1), a time constant of approximately 2.0 s, a uniformity of 0.1% over a 6-mm-diameter region, and a noise level of approximately 6 nW. Performance characteristics of the new ESR's are discussed. It is shown that calibrations performed with these ESR's agree with those made with the previous generation of ESR's to better than 0.05%.

A New Cryosurgical Device for Controlled Freezing: I. Setup and Validation Tests

A new cryosurgical device utilizing liquid nitrogen, which is a modification of an existing commercial system, was developed. In the new computer-controlled cryodevice the temperature of the cryoprobe is controlled by means of an electrical heating element. The desired temperature-forcing function is calculated to ensure a specified constant cooling rate at the freezing front. The new device facilitates real-time data processing, and, in particular, simulation of the heat transfer processes. A series of tests was performed to study the characteristics of the cryodevice and to validate the underlying assumptions. These tests were performed using organic tissue, i.e., potatoes, as anin vivosimulating medium of biological tissue. The differences between experimental data and computed results were found to be within ±0.5°C, which falls within the uncertainty range of the experimental temperature measurements. A typical control error of the new device is within ±0.3°C, prior to the formation of the freezing front, and ±0.6°C thereafter, which is of the same order of magnitude as the uncertainty range of the temperature measurements. The new device is capable of producing maximal cooling rates of 50°C/min down to temperatures of −165°C and a maximal heating rate of 300°C/min. The maximal cooling power of the cryoprobe, due to LN2boiling, is 80 W; the maximal electrical heating power of the cryoprobe is 160 W. Precooling of the device requires about 30 min, and it can be operated continuously for about 3 h. Initial results of experimentalin vivocryosurgery performed on rabbit hindlimbs, including histological observations and thermal analysis, are presented in the second part of this study.

A model of the domestic hot water load

The electrical load required to supply domestic hot water is an important load for two reasons: (1) it represents a large portion (30 to 50%) of the domestic load; and (2) it is a load which can easily be controlled by the consumer or the supplier, because the use of the hot water need not coincide with the heating of hot water. A model representing the power system load due to hot water consumption from storage water heaters is provided. Variable parameters include the average amount of water used, the mean and deviation of distributions of usage times, thermostat settings, inlet water temperature and electrical heating element ratings. These parameters are used to estimate the after diversity electricity demand profile, and were verified for accuracy by comparison with measurements. This model enables the prediction of the effects of load control, examples of which are given in this paper. The model is also useful for evaluation of the response which could be expected from demand-side management options. These include changing the size of heating elements, reduction in water consumption and reduction in thermostat settings.

Controlling a nonlinear process with variable dead-time: A computer-based laboratory experiment

In process control, nonlinearities and dead-time often play a significant role in the unsuccessful implementation of control systems. This is due to variations in operating conditions and process behaviour affecting controller performance within the stability limitations of the feedback loop. In a laboratory experiment, where a liquid is heated by means of submerged electrical heating elements, temperature control of liquid in a tank by means of a feedback control loop can be investigated. The relationship between the manipulated variable and the tank temperature is non-linear. The loop was designed to contain significant dead-time, dependent on the variable flowrate of liquid through the system. By means of experimentally obtained open loop process reaction curves and by continously measuring the volumetric flowrate, enough information about the process can be obtained to develop a process model compensating for the presence of dead-time and to take the nonlinear behaviour of the process into account. Using a digital measurement and control system, an algorithm was developed which can be used for accurate control of the process. In this paper emphasis is placed on the current ability of computing equipment to apply theoretical concepts which had been known for a long time.

95/05964 Laboratory preparation of sorbents from chars

In this paper, an ash-free sampling device of coal-fired flue gas has been developed, including the U-shaped sampling probe, electric heating element and thermostat, sampling ports, porous ceramic filter, which can not only be used for low-ash flue gas sampling and measurement, but also be able to achieve high-ash flue gas measurement. The developed ash-free sampling device can work at a wide temperature range from 120 ∼ 650°C. It is adopted to conduct the field-testing at a coal-fired power station to measure mercury in the coal-fired derived flue gas, and the attained date are satisfactory and can reflect the actual power plant flue gas emissions level and speciation of mercury. The developed ash-free sampling device is with simple configuration and efficient function, providing an effective method and tool for mercury and other pollution emission measurement and their control.