varmeinput

Varmeinput, or heat input, is the amount of energy transferred to a system as heat. In thermodynamics it is not a state function but a process quantity; it can be measured as heat transfer rate Qdot (kW) or as total heat Q (kJ) over a period. In many technical contexts, heat input is used to assess energy balance, efficiency, and process conditions.

In welding technology, varmeinput refers to the energy delivered to the weld pool per unit length, shaping penetration and microstructure. It is commonly estimated by HI = (V × I × 60) / S, giving heat input in joules per centimeter (S is travel speed in cm/min). Usually an efficiency factor eta is included to account for electrical losses and arc inefficiency: HI ≈ eta × (V × I × 60) / S. Higher heat input generally yields deeper penetration but more distortion and broader heat-affected zones; lower heat input yields narrower welds and faster cooling, affecting mechanical properties.

In plant and boiler engineering, heat input refers to the rate at which energy is supplied as heat, for example Qdot_in = fuel energy rate minus losses, typically measured in kilowatts or megawatts. In this context heat input is a key variable for efficiency calculations and emissions.

Measurement and control: Heat input is determined from electrical measurements (voltage, current, speed) in welding; in thermal systems by calorimetry or heat flux sensors. Control aims to balance sufficient weld quality with minimized distortion, or to meet efficiency targets in furnaces and boilers.

See also heat transfer, welding, energy balance.