Both manual and automatic heat presses are widely available. A new style of press that is semi-automatic has entered the market as well, allowing for a manual closing process with an automatic opening. Digital technology in newer machines enables precise control of heat and pressure levels and timing. The most common types of heat press employ a flat platen to apply heat and pressure to the substrate. In the "clamshell" design, the upper heat element in the press opens like a clamshell, while in the "swing-away" design, the heat platen swings away from the lower platen. Another design type a "draw style press" allows for the bottom platen to be pulled out like a drawer away from the heat for preparation of the graphic. Vacuum presses utilise air pressure to provide the necessary force and can achieve high psi ratings.
Most heat presses currently on the market use an aluminum upper-heating element with a heat rod cast into the aluminum or a heating wire attached to the element. For high-volume operations involving the continuous imprinting of items, automatic shuttle transfer presses are used. The substrates to be imprinted are continuously loaded onto the lower platen and shuttled under the heat platen, which then applies the necessary heat and pressure. A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power production, and chemical processing. One common example of a heat exchanger is the radiator in a car, in which the hot radiator fluid is cooled by the flow of air over the radiator surface.
Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions and in cross flow the fluids move at right angles to each other. The common constructions for heat exchanger include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate. More information on heat exchanger flows and arrangements can be found in the heat exchanger article.
When engineers calculate the theoretical heat transfer in a heat exchanger, they must contend with the fact that the driving temperature difference between the two fluids varies with position. To account for this in simple systems, the log mean temperature difference (LMTD) is often used as an 'average' temperature. In more complex systems, direct knowledge of the LMTD is not available and the number of transfer units (NTU) method can be used instead.
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