According to Zhihu's inquiry, the heating principle of Haier drum washing machine is mainly realized by electric heating tube. Electric heating tube is a kind of equipment which can convert electric energy into heat energy, and it is made of nickel-chromium alloy or stainless steel. When the washing machine needs to be heated, the electric heating tube is electrified, and the current generates heat through the electric heating tube to heat water. Haier drum washing machine has built-in temperature sensor, which can control the working temperature of electric heating tube and keep the water temperature in the washing machine within a suitable range.