Ovens forced-air convection

The films were then thermally cycled at tOO, 200 and 300°C for an hour at each temperature in a forced air convection oven to complete the cyclization. The solution imidization procedure has been further described by Summers, et. al. (42,43). A representative structure for the poly(imide siloxane) copolymers is depicted in Figure 5. 

C.2 Engineering Consideration. The primary engineering considerations in prebaking are the selection and maintenance of baking ovens. Several types of ovens such as forced air convection ovens, conduction ovens, and infrared heated ovens are commonly employed. The main requirements for baking hardware are ... 

After humidification, the samples into vials were hermetically sealed and stored at 70°C 1°C in a forced air-convection oven. 

The only disadvantage to the use of hydrogen as a carrier gas is the real or perceived explosion hazard from leaks within the column oven. Experience has shown that the conditions required for a catastrophic explosion may never be achieved in practice with forced air convection ovens. However, commercially available gas sensors will automatically switch off the column oven and carrier gas flow at air-hydrogen mixtures well below the explosion threshold limit. A considerable difference in the relative cost of helium in the USA and Europe has resulted in different preferences on the two continents. For open tubular columns helium is widely used in the USA for safety rather than theoretical considerations while hydrogen is commonly used in Europe. 

Jacketed molds heated with hot oil or salts were used in the past. The heat transfer efficiency of these systems was good but the maintenance problems have made these systems uncommon today. Modem machines employ forced air convection ovens to heat the molds. In the majority of industrial machines the ovens are heated by the combustion of a gas, while in smaller machines electricity is normally used. Ovens are provided with blowers and baffles to improve heat transfer. 

Formula PVC 100, Plasticizer 50, Ba Zn (s) stabilizer 2. Samples milled 171 C, Molded to 1 mm at 177°C. Samples aged 7 days at 100°C in a forced air convection oven with 150-250 air exchanges/hour. 

There are several heating schemes used in reflow ovens, the result of years of technological evolution. Focused infrared (IR) lamps have given way to secondary emission panel heaters and, finally, to the forced hot-air convective ovens that are the de facto industry standard today. 

A variant of this method is the convective IR oven. This technique also relies on radiant or panel IR heating, but the air in the oven is stirred by fans to enhance uniformity of heating. However, techniques such as IR lamp, IR emitter, and combination convective units have been largely supplanted by a more favorable method forced-air convection, where air is forced through the panel heaters at high velocity. This produces very even oven temperatures and rapid heating response and control. This method is the mainstay of oven reflow. 

Just as in the reflow soldering oven, there are multiple solder-wave preheater styles, but only two are in prevalent use radiant preheaters (direct and indirect IR) and forced-air convective preheaters. Both are effective and both have their advantages. In fact, the best configuration is a combination of the two. Some wave-soidering machines can be equipped with both top and bottom preheaters. This can be advantageous for thermally massive boards. 

The cage also confines the column such that it will not flop around in the column oven under the influence of forced-air convection currents. Before a column cage is mounted on the hanging bracket in the oven, the column should be examined to see if the coils are evenly spaced or distributed around the width of the cage with minimum overlap, a pertinent consideration for uniform heating of the column. It is also important that ends of the column extending from the cage for connection to the injector and detector do not contact any metallic parts of the oven where abrasion can erode the protective outer layer of polyimide on the column surface. 

Most gas ehromatographs have the capability to operate the column oven at subambient temperatures. An accessory kit is available for either liquid nitrogen (—99°C) or carbon dioxide (—40°C) as a coolant and includes a cryogenic valve that is mieroprocessor controlled. The valve opens and closes, depending on the demand for coolant. In the open position, coolant is sprayed into the oven, where it chills the oven down with assistance from forced-air convection. 

The acetone solvent is removed by running the paper through convection heat in a forced air oven at 110-120°C. The retention... 

Exploratory syntheses were accomplished in 15 ml Teflon-lined autoclaves which were statically heated at autogenous pressure in forced convection ovens. Larger autoclaves (300 ml, 600 ml, and above) have also been successfully employed. At specified times, the autoclaves were removed from the oven, quenched in cold water, and the pH of the contents measured. Product VPI-5 was recovered by slurrying the autoclave contents in water, decanting the supernatant liquid, filtering the white solid, and drying the crystals in ambient air. 

In a conventional oven, the air in the oven is first heated to the desired temperature by the electric or gas heating element. This preheating may take several minutes. The heat is then transferred from the air to the skin of the chicken by natural convection in older ovens or by forced convection in the nevrer convection ovens that utilize a fan. The air motion in convection ovens increases the convection heat transfer coefficient and thus decreases the cooking time. Heat is then conducted toward the inner parts of the chicken from its outer parts as in microwave ovens. 

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