Many heat transfer problems are often involved in petroleum, chemical, power, metallurgy, energy and other industrial sectors. Shell and tube heat exchangers are the most widely used heat transfer equipment in current industrial production. Compared with other types of heat exchangers, its main advantages are large heat transfer area per unit volume and good heat transfer effect. In addition, simple structure, wide range of materials required for manufacturing, and high flexibility in operation, etc., have been widely used in the field of chemical engineering.

According to the different use conditions and processing conditions of the heat exchanger, the connection methods are basically divided into three types: expansion joint, welding and expansion welding. Because the expansion joint method can withstand high pressure, it is especially suitable for materials with poor weldability and A situation in which the welding workload in the manufacturing plant is excessive. Therefore, this method is widely used in practical production. With the continuous development of technology, new technologies such as roller expansion, explosion expansion and hydraulic, liquid bag and rubber expansion have been developed successively. This paper intends to compare these several expansion processes, and provide a reference for choosing a reasonable expansion process for actual production.

Currently, Alfa Laval presents a new generation of heat exchangers: AXP10 and AXP14. Both heat exchangers are suitable for transcritical CO2 systems, are brazed and are compact. The new heat exchanger incorporates the latest technology, allowing it to achieve maximum heat recovery capacity with a high level of safety.

The purpose of Alfa Laval's design of products with high efficiency and reliability is to support the use of environmentally friendly and reliable CO2 refrigeration systems, especially in supermarkets. Applications of the new transcritical CO2 heat exchanger include heat pump hot water systems, supermarket refrigeration equipment and refrigerated transport. The basic features of AXP10 and AXP14 are: 1) Increased efficiency and increased COP; 2) Operating pressure greater than 140 bar; 3) Minimum and maximum operating temperatures are -196 °C and 225 °C, respectively; 4) AXP10 is mainly suitable for heat pump systems and refrigerated transportation; 5) AXP14 is mainly suitable for commercial refrigeration and heat pump systems; 6) The patented stainless steel structure can save space and reduce mass.

The principle of ground source heat pump technology and the characteristics of ground source heat pump technology The stored low temperature thermal energy. The ground source heat pump is a system that uses this low-temperature heat energy as the heating heat source of the heat pump and the cold source of the air conditioner, which can provide both heat and air conditioning. In winter, the heat pump takes/takes out the heat in the shallow surface layer to supply indoor heating; in summer, the heat pump takes out the indoor heat and releases it to the shallow layer on the surface. The characteristics of ground source heat pump are:

1. It belongs to renewable energy utilization technology. The superficial layer of the earth is like a huge solar collector, which collects 47% of the solar energy, which is more than 500 times the energy used by human beings every year. This near-infinite, low-enthalpy heat energy that is not limited by regions and resources is a clean and renewable energy that can be utilized by human beings. And geoenergy is not affected by climate like solar energy, nor is it limited by resources and geological structure like deep geothermal. In addition, when the ground source heat pump is used for heating in winter, it stores cold energy on the ground for summer use, and when air conditioning in summer, it stores heat for the ground energy for winter use. Therefore, the ground source heat pump is a renewable energy utilization technology.

2. High efficiency, energy saving and low operating costs. Because the ground source temperature is relatively stable throughout the year, it is higher than the ambient air temperature in winter and lower than the ambient air temperature in summer. It is a good heat pump heat source and air conditioning cold source △ Heating and heating network, this The temperature characteristics make the ground source heat pump 40% more efficient than the traditional air conditioning system, so it is necessary to save energy and operating costs by about 40%.

3. Significant environmental benefits It neither destroys groundwater resources nor pollutes it. It can be built in residential areas without combustion, smoke, or waste. It does not require a site for stacking fuel waste, and it does not need to transmit heat over long distances.

4. A dual-purpose ground source heat pump can provide heating and cooling throughout the year, saving investment and land occupation. Ground source heat pump, a renewable energy utilization technology, is highly efficient and energy-saving without any pollution. It conforms to the general trend of international energy development, and also conforms to my country's energy and environmental protection policies. It is a renewable energy utilization method worthy of research and vigorous development.

my country's commercial air conditioners set sail against the backdrop of the global market in 2013. In 2013, my country's commercial air-conditioning was affected by factors such as the relatively sluggish domestic real estate market and the continuous fluctuation of raw material prices, and its development faced many obstacles. However, from the perspective of the domestic market, many companies are optimistic about the commercial air conditioner market, actively adjust their own structure, adapt to the new development situation, establish development confidence, and view the current predicament with a positive attitude and long-term perspective.

Industry analysts pointed out that although the overall market growth of commercial air conditioners is slowing down, people are the focus of perfusion in the industry. Major enterprises have launched high-efficiency and energy-saving commercial air-conditioning products, and sales channels have further expanded to the third and fourth tier markets. Many small and medium-sized household appliance companies have combined their own advantages to actively explore market segments, and have taken the lead in gaining performance and the right to speak in these fields. The downturn of the commercial air-conditioning market is also a period of adjustment and layout for these companies. Regarding future market competitiveness, 2013 is also a year for them to deepen the market and actively adjust.

The development of the commercial air-conditioning market is inseparable from the support of policies. For the first time, the policy of energy saving and benefiting the people has injected a strong impetus into the development of the commercial air-conditioning industry. Major air-conditioning companies have also seized the development opportunities provided by national policies and sought their own development. With the implementation of the national energy-saving subsidy in the commercial air-conditioning industry, it has also added impetus to the development of air-conditioning for various enterprises. In the process of the market tending to recover, government procurement has become a warm tone that cannot be ignored in the cold and quiet market. Under the circumstance that the overall market of commercial air conditioners is not optimistic, the commercial air conditioner market purchased by the government has bucked the trend and the scale of purchases has grown steadily compared with the same period.

According to the survey, the market pressure of industry development is not only a challenge but also an opportunity, which has become an inflection point for the development of enterprises that are good at capturing development opportunities. From the perspective of the commercial air-conditioning industry in 2013, the market has undergone great changes.

It is very difficult to choose a suitable refrigerant replacement, many factors must be considered and a comprehensive evaluation must be carried out, not only to meet the requirements of ozone depletion potential (ODP), global warming potential (GWP), etc., but also to Consider thermal performance, toxicity, flammability, compatibility, investment and operating costs, etc. The application characteristics of R22 and R134a are analyzed as follows:

1. The global warming potential (GWP) of R134a is 0.25 and that of R22 is 0.36, both belonging to greenhouse gases.

With the emphasis on environmental protection, sewage source heat pump systems are more and more used in life, but the water quality of sewage is poor, so the use of sewage source heat pumps to exchange heat with sewage is often an indirect method. Therefore, the current common practice is not to let the sewage directly enter the heat pump unit, but to exchange the heat to the intermediate water through the sewage heat exchanger, and then the intermediate water to exchange the heat to the heat pump unit. Since the flow and heat transfer of sewage is very different from that of clean water, the previous design experience and parameters cannot be applied, and designers are faced with many new problems. However, in practice, many designers lack understanding of the particularity of sewage heat transfer, and directly apply the design parameters and methods for clean water, which is very dangerous for the quality of the project.