Electric heating is the process of converting electrical energy into thermal energy. Since the discovery that electric current can produce thermal effects through conductors, many inventors around the world have been engaged in the research and manufacturing of various electric heating appliances. The development and widespread application of electric heating, like other industries, follows this pattern: from advanced
Electric Heater
Electric Heater
countries gradually spreading to the rest of the world; from cities gradually developing to rural areas; from collective use to household use, and then to personal use; products evolving from low-end to high-end. In the 19th century, electric heating appliances in their infancy were mostly crude. The earliest electric heating appliances were used in daily life. In 1893, the prototype of the electric iron first appeared and was used in the United States. Then in 1909, the use of electric stoves emerged, where electric heaters were placed in the stove, meaning heating shifted from firewood to electricity, i.e., from electrical energy to thermal energy. However, the rapid development of the electric heating appliance industry truly began after the invention of nickel-chromium alloys used as heating elements. In 1910, the United States first successfully developed an electric iron using nickel-chromium alloy heating wire, which fundamentally improved the structure of the iron and led to its rapid popularization. By 1925, products with heating elements installed in pots in Japan became the prototype of modern electric rice cookers. During this period, industrial electric heating products such as laboratory electric furnaces, glue melters, and heaters also emerged. The period from 1910 to 1925 was a major development stage in the history of electric heating appliances. In both household and industrial sectors, the emergence and widespread application of various electric heating appliances experienced rapid development, especially in households. Therefore, the invention of nickel-chromium alloys laid the foundation for the development of the electric heating appliance industry.
After the 1920s, there were fewer new application developments compared to the previous period, but during this stage, all kinds of electric heating appliances were redesigned and continuously improved, marking a stage of enhancement in the history of electric heating appliances. In household electric heating appliances, various devices were designed to be more aesthetically pleasing, durable, and robust, and most were equipped with automatic temperature and time control.
Measurement Units
1. Power: W, Kw 1Kw = 3.412 BTU/hr = 1.36 (horsepower) = 864 Kcal/hr
2. Weight: kg: 1Kg = 2.20462 lb (pound)
3. Flow velocity: m/min
4. Flow rate: m3/min, kg/h
5. Specific heat: Kcal/(kg℃): 1Kcal/(Kg℃) = 1BTU/hr.°F = 4186.8 J/(Kg℃)
6. Power density: W/cm2: 1W/cm2 = 6.4516 W/in2
7. Pressure: Mpa
8. Thermal conductivity: W/(m℃): 1 W/(m℃) = 0.01 J/(cm s℃) = 0.578 Btu/(ft.h.F)
9. Temperature: ℃: 1F = 9/5℃ + 32, 1R = 9/5℃ + 491.67, 1K = 1℃ + 273.15
Power Calculation
The calculation of heating power includes the following three aspects:
Power during operation
Power during startup
Heat loss in the system
All calculations should consider the worst-case conditions:
Lowest ambient temperature
Shortest operating cycle
Highest operating temperature
Maximum weight of the heating medium (maximum flow rate for flowing media)
Steps for calculating heater power:
Based on the process, draw a process flow diagram for heating (without involving material forms and specifications).
Calculate the heat required for the process.
Calculate the heat required for system startup and the time.
Redraw the heating process flow diagram, consider an appropriate safety factor, and determine the total power of the heater.
Determine the sheath material and power density of the heating element.
Determine the form, size, and quantity of the heater.
Determine the power supply and control system of the heater.
Working Principle
The fluid explosion-proof electric heater is a device that consumes electrical energy and converts it into thermal energy to heat the required materials. During operation, the low-temperature fluid medium enters the input port under pressure through the pipeline, flows along the specific heat exchange channels inside the electric heating container, following a path designed based on fluid thermodynamics principles, and carries away the high-temperature thermal energy generated by the electric heating elements during operation, thereby raising the temperature of the heated medium. The outlet of the electric heater provides the high-temperature medium required by the process. The internal control system of the electric heater automatically adjusts the output power of the electric heater based on the temperature sensor signal at the outlet, ensuring uniform temperature of the medium at the outlet. When the heating element overheats, the independent overheat protection device of the heating element immediately cuts off the heating power supply, preventing the heated material from overheating, coking, deteriorating, or carbonizing, and in severe cases, preventing the heating element from burning out, effectively extending the service life of the electric heater.
Application Scope
Typical application scenarios of fluid explosion-proof electric heaters mainly include:
1. Heating and raising the temperature of chemical materials in the chemical industry, drying some powders under certain pressure, chemical processes, and spray drying.
2. Heating hydrocarbons, including crude oil, heavy oil, fuel oil, thermal oil, lubricating oil, paraffin, etc.
3. Heating process water, superheated steam, molten salt, nitrogen (air), water gas, and other fluids that need to be heated.
4. Due to the advanced explosion-proof structure, the equipment can be widely used in chemical, petroleum, natural gas, offshore platforms, ships, mining areas, and other places requiring explosion-proof measures.
Functional Features
Explosion-Proof Electric Heater
Explosion-Proof Electric Heater
1. Small size, high power: The heater mainly uses clustered tubular electric heating elements.
2. Fast thermal response, high temperature control accuracy, high overall thermal efficiency.
3. High heating temperature: The heater is designed with a maximum working temperature of up to 850°C.
4. Uniform outlet medium temperature, high temperature control accuracy.
5. Wide application range, strong adaptability: The heater can be used in explosion-proof or ordinary environments, with explosion-proof grade up to dⅡB and C, and pressure resistance up to 20MPa.
6. Long life, high reliability: The heater is made of special electric heating materials, designed with low surface power load, and equipped with multiple protections, greatly enhancing the safety and lifespan of the electric heater.
7. Fully automatic control: According to requirements, through the heater circuit design, automatic control of parameters such as outlet temperature, flow rate, and pressure can be easily achieved, and it can be networked with computers.
8. Significant energy-saving effect: Almost 100% of the electrical energy is converted into heat and transferred to the heating medium.
Converting electrical energy into thermal energy to heat objects is a form of electrical energy utilization. Compared with general fuel heating, electric heating can achieve higher temperatures (e.g., arc heating can reach temperatures above 3000°C), and it is easy to achieve automatic temperature control and remote control (e.g., vehicle-mounted electric heating cups). It can maintain a certain temperature distribution of the heated object as needed. Electric heating can generate heat directly inside the heated object, resulting in high thermal efficiency and fast heating speed. According to the heating process requirements, it can achieve uniform overall heating or local heating (including surface heating), and it is easy to achieve vacuum heating and controlled atmosphere heating. During the electric heating process, there is less waste gas, residue, and dust, keeping the heated object clean and not polluting the environment. Therefore, electric heating is widely used in production, scientific research, and experiments. Especially in the manufacturing of single crystals and transistors, mechanical parts and surface quenching, ferroalloy smelting, and artificial graphite manufacturing, electric heating methods are adopted.
According to different methods of electrical energy conversion, electric heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and dielectric heating.
Heating Methods Edit
Resistance Heating
Using the Joule effect of electric current to convert electrical energy into thermal energy to heat objects. It is usually divided into direct resistance heating and indirect resistance heating. In the former, the power supply voltage is directly applied to the heated object, and when current flows, the heated object itself (e.g., electric ironing machine) generates heat. Objects that can be directly resistance heated must be conductors but with high resistivity. Since heat is generated inside the heated object itself, it is internal heating with high thermal efficiency. Indirect resistance heating requires special alloy materials or non-metallic materials to make heating elements, which generate heat and transfer it to the heated object through radiation, convection, and conduction. Since the heated object and the heating element are separate, the type of heated object is generally not restricted, and operation is simple.
The materials used for heating elements in indirect resistance heating generally require high resistivity, low temperature coefficient of resistance, minimal deformation at high temperatures, and resistance to embrittlement. Commonly used materials include metal materials such as iron-chromium-aluminum alloys and nickel-chromium alloys, and non-metallic materials such as silicon carbide and molybdenum disilicide. The maximum working temperature of metal heating elements can reach 1000–1500°C depending on the material type; non-metallic heating elements can reach 1500–1700°C. The latter are easy to install and can be replaced while hot, but they require a voltage regulation device during operation and have a shorter lifespan than alloy heating elements. They are generally used in high-temperature furnaces, places where the temperature exceeds the maximum allowable working temperature of metal material heating elements, and certain special occasions.
