Heat Temperature Control Research Articles

An Application of the Fractal Theory in the Design of Heat Sink for Precision Measurement Instrument

Temperature variation on accuracy and stability in measurement instruments is an important issue. High performance and miniaturized instruments have rigorous requirements on temperature. Heat transfer and temperature control are important in instruments design. For laser interferometer, temperature variation will adversely affect the frequency stability of the laser and the measuring precision. In order to effectively stabilize the frequency, a simple and effective heat sink design for laser interferometer is presented. It is based on the fractal theory and the heat transfer characteristics to allow higher dissipation for temperature control to generate higher heat transfer area in a finite space. Experimental results in frequency stabilization clearly show that this method is effective.

Fischer–Tropsch synthesis on monolithic catalysts with oil circulation

Monolithic catalysts made of cordierite and γ-Al 2O 3 have been prepared and tested for the Fischer–Tropsch (FT) synthesis. When operated without oil circulation, washcoated cordierite monoliths have previously been shown to be as active and selective as the corresponding powder catalyst provided that the monoliths have low washcoat loadings. Two-phase operation, i.e. with oil/product circulation during reaction, resulted in improved heat removal and temperature control, in lower apparent activity and faster deactivation, but the C 5+ selectivity was equal to or even better than without oil circulation. The lower apparent activities obtained with oil circulation seem to be a combination of catalyst deactivation and flow-related problems in the present experimental set-up.

Die life considering the deviation of the preheating billet temperature in hot forging process

Two estimating methods are proposed for predicting the die life due to wear or plastic deformation during hot forging considering the deviation of the preheating temperature of the billet. The characteristics of the billet during electroplating or induction heating are very complex in the preheating process. Therefore, an induction heating of billet has become increasingly important as a means of reducing the heating time and an effective control of heating temperature. In this paper, to calculate the temperature distribution of the billet in the preheating process according to the parameters such as heating time, frequency and current density in high-frequency induction heating, an induction heating program has been developed. Then, FE-simulation with the proposed wear and the plastic deformation models has been carried out for the hot forging sequence of a spindle part widely used in the present continuous hot forging die. The results showed that die life is greatly affected by the wear under the conditions that exist in a given deformation process and the maximum wear occurs at the corner of the finisher die. These proposed methods of the die life could be used effectively for quantitative prediction of the die life in the hot forging process. These results might also be extended further for the study of optimization of the die change schedule to grind the die.

Islet isolation under cGMP conditions: replacing the coil

Introduction Clinical islet transplantation is increasingly regulated, with isolation standards defined under current good manufacturing practices (cGMPs). cGMP requires validation of equipment cleaning and sterilization. The automated process for islet isolation requires rapid thermal exchange during processing, manipulating a metal coil containing cellular product into and out of chilled/heated waterbaths. We recognize challenges of validating cleaning and sterilization of this coil and propose replacement with a disposable blood warming system. Our specific aims were to assess the system's ability to accommodate flow rates utilized during various phases of pancreatic digestion and to assess its efficiency of heat exchange and temperature control. Methods In a pancreas digestion circuit, heat exchange occurred via the coil in a digital water bath, or Warmflo blood warming bag in a digital warming unit. Temperature within the digestion chamber was assessed using an inserted thermocouple. Time to achieve 37°C was measured for set heating element temperatures 38.5°C to 41°C. Circuit temperature maintenance characteristics were also recorded. Results The Warmflo bloodbag easily accommodated flows of 150 and 300 mL/min. At all set temperatures, the bag resulted in shorter or equivalent time to 37°C than the coil. Maintenance of 37°C was also equivalent. We have utilized this system for four human islet isolations with mean time to 37°C of 5.5 minutes, without difference in digestion quality. Conclusions Use of a disposable blood warming system in place of the coil during islet isolation provides adequate flow characteristics, heat exchange, and temperature control and may facilitate evolution of islet isolation toward cGMP compliance.

Development and characterization of induction heating–electrothermal vaporization (IH-ETV) sample introduction for inductively coupled plasma spectrometry

A general study of performance attributes was conducted for a prototypical electrothermal vaporization (ETV) sample introduction system, in which induction heating (IH) was used to facilitate the drying, pyrolysis, and vaporization of samples from long, undercut graphite cup probes in a radio-frequency (RF) induction field. In the first part of this study, experiments were carried out to determine the heating characteristics and temperature control aspects of an IH-ETV arrangement. Using a remote-sensing infrared thermocouple, it was determined that a 3/8-inch (9.53-mm) outer diameter graphite cup sample probe could be heated to a maximum temperature of 1860°C in the induction field of the IH-ETV under full forward power (1.5 kW). The IH-ETV device was found to have a rapid heating response (1/ e time-constant of 2.0±0.2 s) that was independent of the initial/final temperatures chosen. Linear temperature control was possible by regulating either the DC voltage applied to the plate or the current flowing to the grid of the RF generator oscillator tube. The second part of this work consisted of studies to establish benchmarks, such as limits of detection (LOD) with inductively coupled plasma optical emission spectrometry (ICP-OES) and transport efficiency for analyte vaporization under several x–Ar mixed gas atmospheres [where x=15% N 2, 10% O 2, HCl (sparged), or 15% SF 6 (v/v)]. In general, reproducible transient signals with evolution times of 5–15 s were seen for the vaporization of most elements studied, with peak area intensity and reproducibility generally being the best with SF 6–Ar. A 10-fold increase in transport efficiency was seen for refractory carbide-forming analytes (Cr, V) when vaporization was conducted in a halogenous ( x=HCl, SF 6) versus non-halogenous ( x=N 2, O 2) environment, with a two-fold improvement being observed for most other non-refractory elements (Cd, Cu, Fe, Mn, Ni, Pb, Zn). The transport of arsenic proved to be a special case unto itself, with its transport efficiency increasing to 90% when vaporized in the presence of SF 6 (a three-fold improvement over all other carrier mixtures) due to the formation of volatile AsF 5. Using the concept of transport-independent analyte sensitivity, the introduction of the aforementioned x–Ar mixtures into the center channel of the plasma appeared to not have any appreciable effect on plasma excitation conditions, with N 2 being the only exception (a 70% reduction in transport-independent sensitivity was observed). Detection limits ranged from 0.08 to 70 ng absolute and were highly dependent on the analyte studied and the vaporization atmosphere used. Based on the above information, the feasibility of an induction heating arrangement for thermal sample introduction was evaluated, with recommendations being made for the future design of IH-ETV instrumentation.

Temperature controlled CO(2) laser welding of soft tissues: urinary bladder welding in different animal models (rats, rabbits, and cats).

Laser welding of tissues is a method of closure of surgical incisions that, in principle, may have advantages over conventional closure methods. It is a noncontact technique that introduces no foreign body, the closure is continuous and watertight, and the procedure is faster and requires less skill to master. However, in practice, there have been difficulties in obtaining strong and reliable welding. We assumed that the quality of the weld depends on the ability to monitor and control the surface temperature of the welded zone during the procedure. Our objective was to develop a "smart" fiberoptic laser system for controlled temperature welding. We have developed a welding system based on a CO(2) laser and on infrared transmitting AgClBr fibers. This fiberoptic system plays a double role: transmitting laser power for tissue heating and noncontact (radiometric) temperature monitoring and control. The "true" temperature of the heated tissue was determined by using an improved calibration method. We carried out long-studies of CO(2) laser welding of urinary bladders in various animal models. Cystotomies were performed on the animals, and complete closure of the bladder was obtained with a surface temperature of 55 +/- 5 degrees C at the welding site. In early experiments on 31 rats, the success rate was 73%. In later experiments with 10 rabbits and 3 cats, there was an 80% and a 100% success rate, respectively. The success rate in these preliminary experiments and the quality of the weld, as determined histologically, demonstrate that temperature controlled CO(2) laser welding can produce effective welding of tissues. The fiberoptic system can be adapted for endoscopic laser welding.

Robust temperature control for microwave heating of ceramics

This paper presents results on the development of an automatic feedback control system for controlling the temperature of ceramic samples being heated by microwave energy. Design of the temperature controller is presented, and experimental results from heating experiments are given. The temperature control system is evaluated in terms of its robustness to parameter variations in the linearized model and in terms of its performance in actual experiments.

96/06526 Proportional and integral room temperature control for building heating and cooling

96/06526 Proportional and integral room temperature control for building heating and cooling

Automated growing of large single crystals controlled by melt level sensor

AbstractThe process of single crystal pulling is considered with simultaneous starting material make‐up into the melt and heater temperature control in response to a signal generated by the electronic contact melt level sensor, viz.: (i) conditions ensuring the radial broadening steadiness; (ii) effect of melt level displacement, melt temperature changes, changes of solid/liquid interface shape, melt evaporation on the growing crystal diameter; (iii) conditions of crystal purification from impurities and uniform distribution of dopant.

Intracranial microwave hyperthermia: heat induction and temperature control.

Malignant brain tumors cannot be effectively managed with conventional therapeutic modalities. The unique anatomical characteristics of the brain, the ease of lesion localization, and the dismal prognosis for this disease offer a viable (although quite formidable) proving ground for the development and tcsting of hyperthermal therapy. This paper deals with three of the four basic problems underlying the administration of intracranial hyperthermia-heat induction, temperature measurement, and temperature control. The fourth, and as yet unsolved, problem of predicting spatial temperature distributions is discussed.

Heat Transfer and Temperature Control in an Annealing Lehr for Float Glass

This paper presents an analytical model of a float glass annealing lehr, considering radiation between the moving ribbon and its enclosure and the convection of gas in a flue system. Results illustrate the use of mathematical modeling to improve design and operation. A linear algorithm, verified by “computer experiments,” is proposed for on‐line temperature control.

The heat exchange and temperature control system of the 2-metre liquid hydrogen bubble chamber

The heat exchange and temperature control system of the 2-metre liquid hydrogen bubble chamber

Experimental Techniques in Low‐Temperature Physics

This book is written chiefly to help those physicists, physical chemists, metallurgists and engineers who need to carry out investigations at low temperatures. It deals with the production and measurement of low temperatures, the handlng of liquified gases on the laboratory scale, the principles and some details of the design of experimental cryostats, including the problems of heat transfer and temperature control. Physical data on heat capacities, expansion coefficients, and the electrical and thermal conductivities of materials used in making low-temperature equipment are given.