Effect Of Preheating Temperature Research Articles

Analytical and experimental study of premixed methane–air flame propagation in narrow channels

This study investigates analytically and experimentally the influence of preheat temperature on flame propagation and extinction of premixed methane–air flame in single quartz tubes with inner tube diameters of 3.9, 3, 2 and 1 mm respectively. The effects of preheat temperature, tube diameter, equivalence ratio and mixture flow rate on the flame speed and extinction conditions are determined. The analytical results show that high preheat temperature of the mixture can effectively suppress flame quenching, and the occurrence of stable solution in the slow flame branch extends the flammability limit leading to possible flame propagation in mini channels. Experimental results confirm that the flame speed increases and the flammability limit shifts toward the fuel lean direction either through increasing the preheat temperature or decreasing the mixture flow rate, or both. Decrease of propagating flame speed is observed before the stoichiometric equivalence ratio at high preheat temperatures. The analytical model provides insights into how propagating flame in mini channels can be sustained; however, the model is only good at predicting flame speed near the fuel lean branch. Influence of Cu 2+ ions exchanged zeolite 13X catalyst on flame speed is also addressed. It is noted that the zeolite based catalyst can lower the preheat temperature requirement in order to sustain the flame propagation in narrow channels.

Effect of preheat temperature on the location of the minimum state of cure in a molded component

AbstractThe distribution of state of cure in a molded rubber component is usually nonuniform due to the slow heat transfer processes involved in the molding–cooling cycle. The minimum in the distribution usually occurs in the center of the rubber section. For large components, one method of reducing molding time is to preheat the uncured rubber prior to molding, thus carrying out a portion of the required heat transfer in a more favorable geometry than the molded shape. In this work, computation of the state of cure distribution in preheat–molding–cooling cycles for one‐dimensional rectangular geometry shows that as the preheat temperature is increased, the locus of the minimum state of cure will move outward from the center toward the surface of the component. This has important implications for the range of cure states existing in an article and calls into question the convention of removing samples for state of cure tests from the center of the component. The variables considered in this work are the preheat temperature, the component thickness, and the target state of cure of the rubber compound. A design curve is developed whereby the preheat temperature to optimize the distribution of the cure can be established. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25:195–207, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20070

Equivalent dose in quartz from young samples using the SAR protocol and the effect of preheat temperature

Major concerns in the dating of samples younger than a few hundred years by the optically stimulated luminescence (OSL) technique are thermal transfer and partial bleaching. Thermal transfer during preheating enhances the OSL signal due to the charge transfer from thermally sensitive, but light-insensitive, traps to optical centres of quartz and results in an overestimate in equivalent dose, especially for very young samples. In this study, the single-aliquot regenerative-dose protocol is used to obtain values of equivalent dose ( D e ) from young samples taken from various environments around Istanbul. Within this framework, we aim to investigate the effect of preheat temperature on equivalent dose from 150 to 300 ∘ C , the reproducibility of D e measurements for young deposits and the contribution from thermal transfer of charge to the equivalent dose estimation. It was observed that the measured dose is influenced significantly by preheat temperature and the increase in the D e is clearly due to thermal transfer of charge from deep thermally sensitive traps to OSL trap during preheating of the samples prior to the main OSL measurements.

A Study of the Effect of Process Variables on the Stamp Forming of Rectangular Cups Using Fibre-Metal Laminate Systems

The quality of the part and the robustness of the process in stamp-forming of sheet materials are determined by a number of variables. This study looks at the application of the stamping process to a Fibre-Metal Laminate (FML) material system and the effect of the process variables on the formability characteristics of these material systems. The effect of pre-heating temperature on the splitting and wrinkling behaviour has been investigated for two different FML systems. It has been found that different FML systems exhibit different failure modes.

Flame Entrainments Induced by a Turbulent Reacting Jet Using High-Temperature and Oxygen-Deficient Oxidizers

The entrainments of a turbulent jet in co-flow under high-temperature and oxygen-deficient oxidizers have been numerically and theoretical studied. By describing the chemical flame reaction, the entrainment induced by a turbulent reacting jet flame is calculated along the entire chemical flame length by mean of a flame entrainment ratio. The results in the near field of a reacting jet are verified by comparison with the results of published measurements. The effects of preheat temperature, the oxygen concentration of the oxidizer, the heat release, and buoyancy on the entrainment rate are investigated. The following results were obtained: (1) The uniformity of the heat release in reacting jets has a strong effect on the flame entrainment: the more uniform the heat release, the greater the entrainment. The effect of heat release reduces the entrainment in the near field of the reacting jets with the same factor of the characteristic ratio, which is r = (Tf/To)0.5. (2) The entrainment increases as the oxygen concentration is decreased. Furthermore, the entrainment is independent of the fuel flow rate and the preheat temperature of the oxidizer for the investigated temperature range (1073−1573 K). (3) The effect of the oxygen concentration and preheat temperature of the oxidizer on buoyancy was examined. A correction Richardson coordinate, which includes the effect of the oxygen concentration (stoichiometric ratio), was derived to describe the local influence of buoyancy force along the chemical flame length under the high-temperature and oxygen-deficient oxidizer conditions. It can be concluded that the buoyancy force increases with the reduction of the oxygen concentration in the oxidizer. (4) The global behavior of the entrainment was revealed. The entrainment of jet flames can be identified as two regimes: (i) the near field, where the entrainment coefficient is positive, and (ii) the far field, where the entrainment coefficient is negative. Corrections for the entrainment rates were derived in terms of a Froude number (Fr) for the momentum−buoyancy transition jet flame under the high-temperature and low-oxygen-concentration oxidizer conditions. Furthermore, the maximum entrainments along the flame length are estimated.

Optical dating of quartz from young samples and the effects of pre-heat temperature

The optically stimulated luminescence (OSL) signal within quartz may be enhanced by thermal transfer during pre-heating. This may occur via a thermally induced charge transfer from low temperature traps to the OSL traps. Thermal transfer may affect both natural and artificially irradiated samples. The effect, as empirically measured via recuperation tests, is typically observed to be negligible for old samples (<1% of natural signal). However, thermal transfer remains a major concern in the dating of young samples as thermal decay and transfers of geologically unstable traps (typically in the TL range 160–280°C) may be incomplete. Upon pre-heating such a sample might undergo thermal transfer to the dating trap and result in a D e overestimate. As a result, there has been a tendency for workers to adopt less rigorous pre-heats for young samples. We have investigated the pre-heat dependence of 23 young quartz samples from various depositional environments using pre-heats between 170°C and 300°C, employing the single aliquot regeneration (SAR) protocol. SAR D e's were also calculated for 25 additional young quartz samples of different depositional environments and compared with previous multiple aliquot additive dose (MAAD) data. Results demonstrate no significant D e dependence upon pre-heat temperatures. A close correspondence between MAAD data and the current SAR data for the samples tested is also illustrated.

Effect of preheat on welding of ductile cast iron

The effect of preheat temperature on the microstructure obtained in the heat-affected zone (HAZ) and the carbide zone in the weld metal adjacent to HAZ has been studied in multipass welds for the as-cast and ferritic ductile cast irons. The welding was carried out with manual shielded metal arc welding using ENiFe–CI filler metal. Ultrasonic, microhardness distribution, tensile and impact tests were conducted to evaluate the quality of welded joints.

Thermoluminescence and electron spin resonance properties of some travertines from Turkey

For the sake of dating certain calcite geological samples, the TL and ESR properties of travertines from Denizli (in the southwestern part of Turkey) were studied and the effects of pre-heating temperature and pre-heating time on the sensitivity of the samples to radiation evaluated. Heat treatment above 350°C increases the sensitivity of all radiation-induced TL peaks except the 330°C glow peak. Results of gamma-ray dose calibration in travertine (CaCO 3 crystal of trigonal symmetry) indicate that the 180 and 280°C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280°C glow peaks reasonably well. The Mn 2+ lines of the ESR spectra are used to investigate the thermal decomposition processes of travertine samples, showing very good agreement with those of thermogravimetry. Glow mechanisms of TL in travertine have also been studied using ESR analysis. The pre-heating and subsequent laboratory irradiation procedure is found to enhance the TL and ESR signals of CO 3 3− and CO 2 − centres. An isochronal thermal anneal sequence experiment showed that 180 and 280°C peaks in travertines are correlated with CO 3 3− and CO 2 − centres in the same way that the peak at 330°C is correlated with SO 2 − centres. A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements.

5590706 On-line fouling monitor for service water system heat exchangers

The effects of pre-heat temperature (65–95 °C) and holding time (5 and 25 s) on fouling of reconstituted skim milk at high-heat temperatures of 135–150 °C using a bench-top UHT plant were investigated. Fouling was monitored by observing the variation in overall heat transfer coefficient (OHTC) with time and consisted of an induction phase (non-fouling) and a decline phase (fouling). A significantly shorter run-time was obtained with pre-heating at 65 °C than with pre-heating at 75, 85 and 95 °C. A longer holding time (25 s) in the pre-heating section significantly increased the run-time of the plant compared with 5 s holding. The high-heat temperature also affected the OHTC and run-time; similar run-times were observed at 135, 140, 142 and 145 °C but at 150 °C there was no induction phase and fouling rapidly occurred. Overall, pre-heating at 85 °C or 95 °C for 25 s, combined with a high-heat temperature of 145 °C, and pre-heating at 95 °C for 25 s combined with high-heat temperatures of 142 °C, produced the longest run-times of the bench-top UHT plant.

Ca 2+ -induced gelation of whey protein isolate: effects of pre-heating

The combined effect of pre-heating temperature (70 °–90 °C) and Ca 2+ level (10–120 mM) on Ca 2+-induced gelation of whey protein isolates at room temperature was investigated. High pre-heating temperature produced clearer gels than low temperature, and high [CaCl 2] produced opaque gels. When protein suspensions were pre-heated to 70 °C (for 30 min), only the gel's clarity was affected by [CaCl 2]. Fracture and water holding properties were affected by [CaCl 2] only at pre-heat treatment ≥ 80 °C. High gel strength (determined as fracture force and work required to break the gel) was obtained when protein suspensions were pre-heated at high temperature and dialysed against high [CaC1 2]. High pre-heating temperature resulted in high water holding capacity and gel extensibility (after compression), whereas [CaC1 2] only affected gel extensibility but not water holding capacity.

Effect of preheat temperature on the orientation relationship of (Mn,Fe)Al 6 precipitates in an AA 5182 Aluminium—Magnesium alloy

The precipitation of the (Mn,Fe)Al 6 phase during preheating of a commercial AA 5182 Al Mg alloy was studied by means of scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. The existence of two different morphologies with low and high aspect ratio (called here rhomboidal and platelike) was confirmed. The influence of preheating parameters on the precipitation was found to be close to the one known for Al-Mn alloys. It was found that the platelike dispersoids bear orientation relationships with the matrix of type [100] m||[2¯10] pp and (0¯11) m||(001) pp, which are not yet reported in the literature. On the other hand it was shown that rhomboidal precipitates do not follow any orientation relationship with the matrix. The more harmful influence on recrystallization and hot ductility of the rhomboidal precipitates compared to the platelike ones is discussed.

The effect of preheat temperature and urea addition on the seasonal variation in the heat stability of skim-milk powder

SUMMARYThe manufacture of skim-milk powder with heat stable characteristics was investigated commercially during the course of 8 trials carried out over a 12-month period. Skim-milk was preheated to temperatures ranging from 110 to 130 °C with a 2-min holding time prior to evaporation and drying. The effect of added urea was also examined during each trial run. Heat coagulation times at 120 °C were determined upon reconstitution of the powders to 20% total solids. From February to April the heat stability of the skim-milk powders increased, with the more heat stable samples being obtained at the higher preheating temperatures. Addition of urea increased the heat stability, particularly so in those milks which had been preheated to 130 °C. The presence of added urea during preheating was not found to be necessary as an equal effect on heat stability was observed when urea was introduced at the concentrate stage before drying. Later in the season optimum heat coagulation times were obtained by maintaining preheating temperatures at 118–120 °C.

Heat‐stable milk powders

Many milk products are subject to high temperature heat treatments during the course of manufacture. However, when heating becomes severe, as in the cuse of sterilisation temperatures, there is an increased risk of milk coagulation, Examples of dried milks whose heat‐stable characteristics are of importance include heat‐stable skimmed milk powder which is used in the manufacture of recombined evaporated milk and also coffee whiteners.Factors that affect the heat stability of skimmed milk powder are discussed. These include milk composition as affected by seasonal change, processing factors such as the effect of preheat temperature, and the role of various additives which stabilise milk to heat treatment.

Second Paper: An Investigation into the Effects of Pre-Heat Temperature on Ductility in a Warm Heading Process

Two-stage warm heading operations were carried out on a mild steel and three high tensile bolt materials (types 1, 2 and 4 from B.S. 3111:1959) at pre-heat temperatures in the range from ambient up to 600°C. The tests were carried out in the form of a transfer process (approximately 2 seconds delay between stages) and also as an interrupted process (approximately 30 minutes delay between stages). Artificial surface defects of various depths were machined on the heading specimens to aid measurements of the change in ductility with increase in pre-heat temperature. The method consisted of estimating the critical depth of groove which would be just on the point of fracture at the end of a particular heading operation. The steels tested were found to have low ductility at pre-heat temperatures in the range from 200°C to 300°C; at a pre-heat temperature of 600°C the steels exhibited extremely high ductility. The results suggest that rolled bar of relatively poor surface quality could be warm headed at 600°C without fracturing. A solid film of colloidal graphite and a high chlorine oil were both found to be satisfactory lubricants at all specimen pre-heat temperatures up to 600°C.

The Keeping Quality of Whole Milk Powder. I. The Effect of Preheat Temperature of the Milk on the Development of Rancid, Oxidized and Stale Flavors with Different Storage Conditions

Summary Milk not preheated became rancid in the vacuum pan, and powder made from it was very rancid in taste. Preheating the milk to be dried at 140° F. or higher for 20 min. was sufficient to destroy lipase activity, as measured by flavor and free fatty acid development in powders stored at 45 and 85° F., including both air-packed and nitrogen-packed samples kept for periods of storage up to 8 mo. A slight progressive improvement was shown in the keeping quality of the resultant powders as the preheat temperature of the milk was increased from 140 to 160° F., and a large improvement was noted with an increase from 160 to 170° F. Double nitrogen packing prolongs keeping quality of powders in relation to preheat treatment but is not a substitute for adequate preheat treatment (170° F. for 20 min.). Double nitrogen packing will prevent oxidized flavor in powders with adequate preheat treatment but not a slight flat (chalky) flavor at 85° F. storage. Storage of powders with adequate preheat treatment at 45° F. largely prevented stale as well as oxidized flavor defects in air or nitrogen pack for the duration of the experiment (1 yr.).