Coursework on heat engineering

Contents

INTRODUCTION

HEAT EXCHANGERS

Shell and tube heat exchangers

Element (section) heat exchangers

Pipe-in-Pipe Double Tube Heat Exchangers

Twisted heat exchangers

Submersible heat exchangers

Irrigation heat exchangers

Ribbed heat exchangers

Spiral heat exchangers

Plate heat exchangers

Graphite heat exchangers

ASSIGNMENT FOR COURSE WORK

DECISION

1) THERMAL CALCULATION OF PLATE HEAT EXCHANGER:

2) HYDRAULIC CALCULATION OF PLATE HEAT EXCHANGER:

LIST OF LITERATURE

Heat exchangers

Heat exchange processes are of great importance in chemical, energy, metallurgical, food and other industries. In heat exchangers, heat transfer from one medium to another through the wall separating them is due to a number of factors and is a complex process that is usually divided into three elementary types of heat exchange: thermal conductivity, convection and thermal radiation. In practice, these phenomena are not isolated, are in some combination and occur simultaneously. For heat exchangers, convective heat exchange or heat transfer, which is carried out with the combined and simultaneous effect of thermal conductivity and convection, is of greatest importance. Heat exchange processes are carried out in heat exchangers of various types and structures.

According to heat transfer method heat exchangers are divided into surface and mixing ones. In surface apparatuses, working media exchange heat through walls of heat conducting material, and in mixing apparatuses, heat is transferred with direct mixing of working media.

Mixing heat exchangers are simpler in design than surface ones: heat is more fully used in them. But they are suitable only in cases when, according to technological conditions of production, mixing of working media is permissible.

Surface heat exchangers, in turn, are divided into recuperative and regenerative. In recuperative apparatuses, heat exchange between different heat carriers occurs through separation walls. At the same time, the heat flow at each point of the wall retains the same direction. In regenerative heat exchangers, heat exchangers alternately contact the same heating surface. In this case, the direction of heat flow at each point of the wall periodically changes. Consider the continuous recuperative surface heat exchangers most common in industry.

Submersible heat exchangers

Heat exchangers of this type consist of flat or cylindrical coils (similar to twisted coils) immersed in a vessel with a liquid working medium. Due to the low liquid wash rate and the low heat transfer outside the coil, submersible heat exchangers are not efficient enough. It is advisable to use them when the liquid working medium is in a boiling state or has mechanical inclusions, as well as if it is necessary to use a heating surface made of special materials (lead, ceramics, ferrosilide, etc.), for which the shape of the coil is most suitable.

Irrigation heat exchangers

Irrigation heat exchangers are a series of superimposed straight pipes irrigated from the outside with water. Pipes are connected by welding or on flanges by means of "rockers." Irrigation heat exchangers are mainly used as refrigerators for liquids and gases or as condensers. Irrigating water is uniformly supplied from above through a chute with serrated edges. The water irrigating the pipes is partially evaporated, so that its flow rate in the irrigation heat exchangers is slightly lower than in other types of refrigerators. Irrigation heat exchangers are rather bulky devices; they are characterized by low heat exchange intensity, but are easy to manufacture and operate. They are used when low productivity is required, as well as when cooling chemically aggressive media or the need to apply a heating surface from special materials (for example, acid cooling devices from acid-resistant ferrosilide, which is poorly treated, are used).

Ribbed heat exchangers

Ribbed heat exchangers are used to increase the heat exchange surface by finning on the side that has the greatest thermal resistance. Ribbed heat exchangers (heaters) are used, for example, in steam heating of air or gases. An important condition for the effective use of the ribs is their tight contact with the main pipe (lack of air interlayer), as well as the rational placement of the ribs.

Ribbed heat exchangers are widely used in drying plants, heating systems and as economizers.

Plate heat exchangers

Plate heat exchangers are heat exchangers designed to transfer heat from a higher temperature medium (heating medium) to a lower temperature medium (heated medium). Heat transfer via thin corrugated stainless steel plates 0.5mm thick

The design of the plate heat exchanger is quite simple. When bracing a stack of plates, a number of channels are formed through which liquids taking part in the heat exchange process flow. The plates of the plate heat exchanger are absolutely the same, they are turned towards each other by 180 degrees. Hot and cold channels in plate heat exchanger are arranged one after the other. To ensure the heat exchange process, the liquids in the plate heat exchanger move towards each other, and the heated liquid transfers heat through the wall of the plate of the cooled liquid. Rubber seal eliminates mixing of liquids. This design of the plate heat exchanger allows it to be modified rapidly, increasing the number of plates, and thereby increasing the power of the plate heat exchanger, and rubber seals or heat exchange plates can be easily replaced if necessary. Plates are available of different types and sizes. The high heat transfer coefficient of the plate heat exchanger leads to a decrease in the number of plates, and therefore to savings.

Plate heat exchangers arrangement

Plate heat exchangers consist of separate corrugated plates separated by rubber gaskets clamped by tie bolts between two steel plates. The plates are made of 0.5mm thick stainless steel sheet by cold stamping. Rubber gaskets for compaction are made of EPDM food heat-resistant rubber mixture. By means of two guides, the group of plates is set to the desired position and tightened with tightening bolts to the required size, the amount of which depends on the number of plates in the heat exchanger. The total power of the demountable plate heat exchanger also depends on the number of plates.

Advantages of plate heat exchanger

Firstly, they have compactness (the area during installation, maintenance and repair is less than 5-20 times). Secondly, they have a high heat transfer coefficient. Thirdly, they have low heat losses. Fourthly, they have low pressure losses. Fifthly, low costs for installation, insulation and repair works. It is also possible to disassemble the heat exchanger during cleaning, they have the ability to increase power by adding plates.

Due to its ease of installation, it can be installed directly on the floor at the heat point or on the supporting structure of the block heat point.

Applications of plate heat exchanger

Plate-type are used in heating, hot water supply (HVS), air conditioning systems (cottages, gardens, schools, pools, individual heating points (ITP) of residential buildings, central heating points (CTP) of a group of houses and microdistricts). Plate heat exchangers are widely used in the food industry. In addition, plate heat exchangers are used for various technological processes (oil cooling, etc.).

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