Appliance Design - November 2008 - (Page 28)

GAS TECHNOLOGY The Fisher & Paykel CookSurface has retractable burners. When not in use, the burner retracts nearly flush to the surface (left). When in use, the burners and pan support pins rise up for cooking (right). In this case, the flame gets extinguished either because of inconsistent gas flow or because the flame was so small that ambient air blew it out. (Preventing flame out at lower settings is even a bigger challenge in ranges, where the opening and closing of an oven door can provide enough air disturbance to blow out a small flame.) Cooking appliance designers have come up with different ways to solve these problems, from using fans to improving burner designs. On Thermador’s spark-ignition Star Burners, for example, the design overcomes the problem of flame lifting with a small overhang on the burner cap that allows for air between the cap and the burner base. By creating this space, Thermador has allowed room for combustible air to exit and enter, creating the correct pressure to avoid flame lifting, says Malte Peters, product manager. Thermador and many other manufacturers offer a safety feature for when the flame goes out. Typically, this is a thermocouple sensor that senses the presence or absence of flame. Dacor cooktops feature the PermaFlame technology, which Simadiris says uses a “form of thermocouple.” The igniter’s tip not only sparks the gas to create the flame; it also acts as the flame sensor. The sensor is constantly checking the burner and if it senses the flame, it sends a signal to the ignition controller that a spark is not needed. If there is no flame, it sends a signal that a spark is needed. This automatic reignition takes less than three seconds. An alternative safety approach to reigntion is to simply shut off the gas if the flame goes out. This method can be found on the Siemens avantGarde™ 36-in ceramic glass “gas on glass” cooktop. In this case, the flame needs to be manually reignited. Over the years, most manufacturers have 28 applianceDESIGN November 2008 switched from open (atmospheric) burners to sealed burners, which are designed to eliminate the gap between the burner and the burner tray that is found on open burners. This gap can allow liquid spills to run into the interior of the cooktop, making it difficult to clean. The sealed burners also offer a more uniform and elegant design compared to an open burner that allows the user to see more of the cooktops less attractive interior, says Simadiris. However, atmospheric burners are not extinct, even at the upper end of the residential cooktop market. Companies such as Viking Range of Greenwood, Miss., offers open burners on their high-end appliances for consumers and kitchen designers who want open system burners. Both types of burners provide exceptional cooking performance, so the difference between them is not in performance, but in cleanability, says Jeff Clemson, chief engineer — cooking products for Viking. It may come down to how often spills occur. Most commercial kitchens, where spills can be frequent, use open burner ranges because they are easier to breakdown for cleaning and the same is true about the Viking open burner ranges. The grate supports and burner bowls remove for easy cleaning in the dishwasher or sink. However, some customers make less of a mess when cooking and prefer the sealed burner configuration as all spills are contained on the surface. Viking offers a one-piece tooled and porcelainized cooking surface for ease of cleaning on the sealed burner tops, he says. In addition, some believe that open burners burn hotter than sealed systems because of the additional air that surrounds an open system. (That may have been true at one time, though those that offer sealed burners say that new designs now optimize the distance from the burner ports to the grate to increase airflow and minimize or eliminate this consideration.) Sealed burners are also sometimes used to improve simmering. Viking for instance offers the VariSimmer system. When adjusted to the lowest possible setting, the VariSimmer™ system flame is actually underneath the burner cap, heating only the cap without any flame hitting the pan, says Clemson. This allows for a very gentle simmer because there is no direct flame on the cookware. The simmer setting is variable because the right amount of heat to simmer a 2-qt. saucepan is different than the amount of heat needed to simmer an 8 qt. stockpot, he says. Using the correct amount of heat, and having it uniformly distributed under a pot or pan is another key to today’s burner systems. Thermador was one of the first to address this with its unique five-point, star-shaped burner. Malte Peters, who in addition to working for Siemens also serves as the cooking product manager for Thermador, says this shape helps deliver 56 percent more heat evenly to the bottom of cookware as compared to traditional round burners. Fagor’s triple ring burner is another example of a burner configuration that improves heat distribution. The triple-crown burners, with its three concentric flame outputs, can be used at low, medium and high settings. When the burner is first turned on, the innermost burner ring ignites. This is useful for simmering and small cooking vessels. As more heat is needed, the knob is turned and the second ring lights. For the largest pans and the hottest cooking, all three burner rings can be activated. Fagor points to the ease of use and control of this burner. Human factors is another growing concern for manufacturers. For instance, on Fisher & Paykel’s CookSurface, the cooktop uses audio signals to alert the user that something requires attention or to impart other informawww.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - November 2008

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