reheat

Reheat is the act of heating something that has already been heated or cooked, typically to restore it to a safe or desired temperature. The term is used in several fields, notably culinary practice, thermodynamics and power generation, and building HVAC systems.

In cooking, reheating refers to warming leftovers or previously prepared dishes for serving. Common methods include microwave, oven, stovetop, and steam. Safety guidance emphasizes heating foods to a safe internal temperature, typically 165°F (74°C) for leftovers, and reheating only once. Perishable foods should be stored promptly and consumed within a safe time window.

In power generation, a reheater is a component of many steam turbine cycles. After partial expansion in high-pressure turbines, steam is routed through a reheater to raise its temperature before entering the next expansion stage. Reheating increases the average temperature of heat addition, which improves cycle efficiency and reduces moisture content at the final stages, aiding turbine blade life. Implementations require additional boiler or piping hardware and introduce pressure and temperature constraints, balancing gains in efficiency against cost and complexity.

In building services, reheat describes the practice of warming cooled air after it has been dehumidified or conditioned in an air-handling system. Used primarily in variable-air-volume systems, reheat coils (electric, hot-water, or steam) raise air to the desired zone temperature. While reheat supports comfort and humidity control, it adds energy use, so designers minimize reheat through system sizing, control strategies, and efficient equipment.