Varmekonvertering

Varmekonvertering, or thermal conversion, denotes the set of processes and devices that transform thermal energy into other forms of energy or, conversely, move heat from a warmer region to a cooler one using external work. It encompasses methods that convert heat into mechanical work or electricity, as well as systems that transfer heat by applying energy input, such as heat pumps.

Fundamental principles: The conversion efficiency is limited by thermodynamics. For heat-to-work conversion in heat engines, the theoretical maximum efficiency is the Carnot efficiency, 1 minus the ratio of cold to hot reservoir temperatures. Real devices exhibit irreversibilities that reduce efficiency. For heat pumps and refrigerators, performance is described by the coefficient of performance (COP), which compares useful heating or cooling to supplied work.

Common technologies: Heat engines include steam turbines and gas turbines used in power plants, as well as smaller-scale engines like Stirling engines. The organic Rankine cycle extends steam-turbine concepts to lower temperatures. Thermoelectric generators convert temperature differences directly into electricity via the Seebeck effect. Thermophotovoltaic cells absorb thermal radiation and convert it to electricity. Heat pumps move heat instead of generating it, enabling space heating and hot water using electrical energy or other energy sources.

Applications and challenges: Varmekonvertering underpins power generation, industrial waste-heat recovery, and efficient heating and cooling in buildings. Key challenges are material durability at high temperatures, cost, and achieving favorable efficiency under real-world conditions. Ongoing research focuses on new cycles, better thermoelectric materials, and integrated systems that optimize overall energy use.