Choosing heater power by tank volume alone often leads to poor results. The required duty is influenced by the mass of liquid, specific heat, temperature rise, heating time, process flow, vessel losses, pipe losses, insulation, ambient temperature, and any heat consumed by evaporation or chemical reaction. For a flowing liquid, the basic sensible-heat relationship is Q = mass flow x specific heat x temperature rise. For a batch, the same energy must be divided by the desired heat-up time, then adjusted for losses and operating margin.

A complete inquiry should state the liquid name and concentration, density and specific heat if available, viscosity at cold and hot conditions, inlet and target temperatures, minimum ambient temperature, tank volume or mass flow, desired heating time, operating and design pressure, available voltage and phase, and the hazardous-area classification. The customer should also identify whether the heater is installed directly in a tank, in a separate circulation vessel, or in an inline process pipe.

Watt density deserves special attention. Clean water can generally accept a higher surface loading than viscous oil, heat-sensitive chemicals, or fluids that can coke, polymerize, or form scale. Lower watt density reduces the temperature difference between the element sheath and the process fluid, helping protect the medium and limiting deposits. However, it requires more element surface area and may increase equipment size.

When process data are incomplete, Runkel can work from alternative information such as tank dimensions, estimated daily throughput, pump capacity, pipe size, current heat-up time, or the rating of an existing heater. Final selection should still be confirmed by the plant engineer. Correct sizing balances heat-up speed, control stability, equipment dimensions, electrical capacity, and lifecycle reliability.

Heat losses should be estimated realistically. An insulated indoor vessel may require only a modest allowance, while an outdoor tank in a cold or windy location can lose substantial heat through its shell, roof, supports, nozzles, and connected piping. If the process must maintain temperature continuously after warm-up, the holding duty should be calculated separately from the initial heat-up duty. This helps determine whether all stages are needed continuously or only during startup.

Electrical constraints can also influence the final configuration. A high calculated duty may exceed the available feeder capacity or create an undesirable step change when energized. Dividing the load into stages, lengthening the allowed heat-up time, improving insulation, or using circulation to improve heat transfer can produce a more practical system. A preliminary calculation should therefore be reviewed together with the plant’s electrical and mechanical limitations.

Call to Action

Discuss your application with Runkel. Send the medium or gas composition, flow or volume, inlet and target temperatures, pressure, voltage, installation dimensions, control requirements, and hazardous-area information to info@runkel.cn, or visit www.runkel.cn.