techdirections November 2012 : Page 22

Keep Laptop Cool with Simple Custom Riser By William Rynone rynone_eng@juno.com A Approaches to Addressing Temperature Concerns Reducing the temperature from the computer requires that the heat be removed, and there are different ways of accomplishing this. Heat is transferred by various means, two of which are conduction and convec-tion. To take the conduction approach to our computer-cooling project, we could place a metal sheet between the computer and table top. This sheet could be of various materials. Two good heat-conducting metals are copper and aluminum. Copper has one of the best heat-conducting characteristics and alu-minum has a heat conducting capac-William Rynone, Ph.D., P.E., is an engineer and engineering educator, Annapolis, MD. The easy-to-make netbook riser relies on convective cooling. 22 tech directions X NOVEMBER 2012 Photos by Richard Wilkinson LTHOUGH my netbook computer—a dimin-ished capacity laptop computer—uses less power than its big brother, when working with it on my lap, my thighs are roasted, even in the winter. When using the unit on a ﬂat surface, such as a table top, the bottom surface of the computer and table top become quite warm—and it is generally acknowledged that semi-conductor life is diminished by high operating temperatures. Many of your students may en-counter these concerns with laptops or netbooks of their own. This article offers a solution that they can easily make: a laptop (or netbook) riser. The second approach to cooling ity approximately 60% that of copper. the laptop is to elevate it from the Since aluminum is considerably less table surface and rely on air ﬂow to expensive than copper, that might provide convective cooling. This is give it considerable appeal. (Interest-the approach we take with the laptop ingly, there appears to be a correla-riser. tion between electrical conductivity and thermal conductivity. One notable exception is beryllium oxide which has an electrical resistance compa-rable to glass but the thermal conductivity of aluminum.) Next, with the metal sheet approach, this ques-tion arises: “What should the sheet dimensions be?” The heat-conducting properties for a sheet metal heat-sink are proportional to its thick-ness and surface area. So, the larger the better. At a minimum, in terms of surface area, the sheet should extend beyond the edges of the com-puter so that its superior heat conductivity can be enhanced The author’s netbook being kept cool atop by convective cooling. the custom-sized riser

Keep Laptop Cool with Simple Custom Riser

William Rynone

ALTHOUGH my netbook computer—a diminished capacity laptop computer—uses less power than its big brother, when working with it on my lap, my thighs are roasted, even in the winter. When using the unit on a flat surface, such as a table top, the bottom surface of the computer and table top become quite warm—and it is generally acknowledged that semiconductor life is diminished by high operating temperatures. Many of your students may encounter these concerns with laptops or netbooks of their own. This article offers a solution that they can easily make: a laptop (or netbook) riser. Approaches to Addressing Temperature Concerns Reducing the temperature from the computer requires that the heat be removed, and there are different ways of accomplishing this. Heat is transferred by various means, two of which are conduction and convection. To take the conduction approach to our computer-cooling project, we could place a metal sheet between the computer and table top. This sheet could be of various materials. Two good heat-conducting metals are copper and aluminum. Copper has one of the best heat-conducting characteristics and aluminum has a heat conducting capacity approximately 60% that of copper. Since aluminum is considerably less expensive than copper, that might give it considerable appeal. (Interestingly, there appears to be a correlation between electrical conductivity and thermal conductivity. One notable exception is beryllium oxide which has an electrical resistance comparable to glass but the thermal conductivity of aluminum.) Next, with the metal sheet approach, this question arises: “What should the sheet dimensions be?” The heat-conducting properties for a sheet metal heat-sink are proportional to its thickness and surface area. So, the larger the better. At a minimum, in terms of surface area, the sheet should extend beyond the edges of the computer so that its superior heat conductivity can be enhanced by convective cooling. The second approach to cooling the laptop is to elevate it from the table surface and rely on air flow to provide convective cooling. This is the approach we take with the laptop riser. Constructing the Laptop Riser Making the riser calls for suspending two lengths of 1/2" dia. tubing between two wooden endplates. To minimize cost, the end plates are short lengths of 1 * 2. To effect good heat conductivity, I used 1/2" hollow, brass rods (obtained from K&S Engineering, #139, or another source). Solid brass would be a better conductor but would weigh considerably more. If cost is a great concern, the rods could be made of 1/2" wood dowels, but this would diminish heat transfer. Students can adjust the side-to-side width of the assembly to suit the width of their computers. I adjusted the top-to-bottom inside spacing to be equal to computer height plus an additional 1/4" on the bottom and 1" on the top to accommodate the hinge space. Location of the dowel holes in the endplates should take into account clearance of any protuberances on the computer bottom such as feet. For typical dimensions, see Fig. 1. I finished the riser with a coat of clear polyurethane varnish on the wood. The copper in a brass alloy tends to cause a blue, copper sulfide coating to develop, so I also recommend applying a coat of clear Krylon to the tubes.

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