Waste heat refrigeration and magnetic refrigeration, let me get to know your true face!

Waste heat refrigeration and magnetic refrigeration, let me get to know your true face!

Many people who do air conditioners only know compressor refrigeration or adsorption refrigeration. Many people don’t know. In fact, there are many other refrigeration methods, such as solar refrigeration, thermoacoustic refrigeration, waste heat refrigeration, etc. Let us get to know them today. Waste heat refrigeration and magnetic refrigeration.

　　 waste heat cooling

　　 1. What is waste heat cooling?

　　 Waste heat refrigeration is a technology that uses gas or waste gas, waste liquid in the production process, and heat discharged from some power machinery as energy sources to drive compression or absorption refrigerators for refrigeration.

　　 2. What is the principle of waste heat cooling?

　　 It is a kind of absorption refrigeration. This kind of thermal energy is mainly low-level thermal energy, which is compensated by consuming thermal energy. It uses lithium bromide as a working fluid for absorption refrigeration. Lithium bromide solution is only an absorbent, of which water is the real refrigerant. It uses water to vaporize at a low boiling point under high vacuum and absorb heat to achieve the purpose of cooling.

Three, waste heat refrigeration classification

　　 There are many waste heat refrigeration methods. Take automobile preheating and refrigeration technology as an example: there are injection, absorption, hybrid and other methods.

　　 1. Absorption refrigeration technology:

The waste heat-driven absorption refrigeration device uses lithium bromide aqueous solution as the working medium. Each heat exchanger is independently installed under the floor of the carriage and located in the same plane. The specially designed connecting pipes are used to connect to form a closed circuit, and the limited space on the car is reasonably used to solve the problem. There is a problem that absorption refrigeration equipment driven by car engine waste heat cannot be applied to vehicles due to its large size and weight.

　　2, jet refrigeration:

　　 consists of steam ejector, evaporator and condenser (ie condenser) and other equipment, relying on the suction effect of steam ejector to maintain a certain vacuum in the evaporator, so that water evaporates and cools.

　　 4. Development and application of waste heat refrigeration

1.The waste heat recovery system of high and low temperature dual thermoelectric generators proposed by Chungbuk University in South Korea can improve fuel economy by more than 10%. Tests have proved that in an environment with a room temperature of 30°C, the 4 cm×4 cm Bi2Te3 thermoelectric module can generate 6.7 V/3.39 A; 1.44 to 5.68 W when the high temperature end of the 4 cm×4 cm Bi2Te3 thermoelectric module is at 100°C to 200°C. It has played a huge potential in improving fuel economy and research on hybrid vehicles.

2) Ford Motor Company designed a HVAC system (HVAC) using engine exhaust heat to generate electricity to improve the comfort of light vehicles and increase energy efficiency. The energy utilization coefficient of the system is set at the refrigeration system cop>1.3, the heat pump system cop>2.3, and the conversion figure ZT of the hot spot conversion material is optimized, which improves the hot spot conversion efficiency.

Application prospects and directions of waste heat refrigeration

At present, absorption/waste heat refrigeration is developing in the direction of miniaturization and high efficiency. The development and research of absorption technology in various countries mainly focus on combined cycle, waste heat utilization, absorption heat pump, absorption and generation process mechanism research, and heat exchange structure And heat exchange surface, surfactant and corrosion inhibitor, unit optimization design and economic analysis, system characteristic simulation, etc. Absorption refrigeration has become one of the main development directions of refrigeration technology and has a very broad prospect.

　Magnetic refrigeration

　 1. What is magnetic refrigeration?

　Refrigeration is the refrigeration using the magnetocaloric effect, also known as the magnetic card effect. The magnetocaloric effect means that the melting and refrigerating working medium releases heat to the outside during isothermal magnetization, while the temperature decreases during adiabatic demagnetization and absorbs heat from the outside. The refrigerant in the magnetic refrigeration technology is a solid magnetic material.

2. Basic advantages of magnetic refrigeration

　　 1. No environmental pollution.

Because the working fluid itself is a solid material and water can be used as a heat transfer medium, it eliminates the ozone layer destruction, toxic, leaky, flammable, explosive and other environmental damage caused by the use of Freon, ammonia, hydrocarbons and other refrigerants. Defects;

　　2, high efficiency and energy saving.

　　The efficiency of magnetic refrigeration can reach 30%~60% of Carnot cycle, while gas compression refrigeration is generally only 5%~10%, which has significant energy saving advantages;

　　3, easy to miniaturize.

　　 Since the magnetic working fluid is a solid, its entropy density is much greater than that of gas, so it is easy to be miniaturized;

　　 4. Stable and reliable.

　　 Because no compressor is needed, there are few moving parts and slow speed, greatly reducing vibration and noise, high reliability, long life, and easy maintenance.

　　 5. Its application range is wide.

Applicable from μK, m K to above room temperature; it has broad application prospects in low temperature (liquid nitrogen, liquid helium, liquid hydrogen production) and high temperature (especially near room temperature) fields;

3. Current status of magnetic refrigeration research

　　 In 2001, Astronautics Cooperation of America and Ames Laboratory successfully developed a rotary magnetic refrigerator that uses permanent magnets to provide a magnetic field, becoming the first room temperature magnetic refrigerator. At present, the research on magnetic refrigeration in the low temperature region (below 20 K) is relatively mature and practical. Magnetic refrigeration in the high temperature zone is still in the experimental research and development stage. At present, the magnetic refrigeration technology from 80 K to room temperature is a research hotspot.

　　 Researching low-cost materials with giant magnetic card effect and using permanent magnets such as NdFeB to generate external fields (without using complex and expensive superconducting magnets) are the keys to room temperature magnetic refrigeration.

Fourth, the main difficulties faced by magnetic refrigeration

　　 1. The temperature difference produced by each magnetic refrigeration cycle is not large enough, only 1～3 K, and the magnetic entropy of the magnetic material is too small;

　　2. The heat exchange speed is not fast enough, which prolongs the refrigeration cycle and reduces the efficiency of the entire cycle;

3. Under room temperature conditions, without using superconducting technology, but still using electromagnets or rare earth permanent magnetic materials to generate the magnetic field, there will always be an air gap between the two magnetic pole faces, and the magnetic refrigeration materials that enter the magnetic field are limited, which requires good thermal insulation. Floor.

　　 5. Application prospects of magnetic refrigeration

　　 Magnetic refrigeration technology has the characteristics of energy saving and environmental protection, and has great development potential. Therefore, it has broad application prospects and can be used for refrigeration in household, commercial, industrial production, automobile air conditioning, supermarkets, medical and health services and other purposes.

　　 For the magnetic refrigeration technology to be widely used, new breakthroughs need to be made in the development of high-performance magnetic materials, the design of magnets and magnetic field structures, the improvement of cold storage and heat exchange technology, and the design of magnetic refrigeration devices.

In the extremely low temperature and liquefied helium and other small devices, its high efficiency, pollution-free, noise-free and many other features make it full of expectations for future space development and civilian needs; when the refrigeration source equipment is required to be light in weight, vibration and noise , Convenient operation, high reliability, long working cycle, wide range of working temperature and cooling capacity also have good prospects in the national defense field.