Development of refrigeration unit

Contents

INTRODUCTION

THEORETICAL PART

1.1 Refrigerating machine working substance

1.1.1 Overview of refrigerants

1.1.2 Problems of switching from R12 to alternative refrigerants

1.2 Classification of piston compressors

1.3 General Information

1.4 Perfect Compressor

1.4.1 Definition of "ideal compressor"

1.4.2 Ideal Compressor Indicator Diagram

1.4.3 Operation required to compress and move gas with an ideal compressor

1.5 Types of ideal compressors

1.5.1 Isothermal ideal compressor

1.5.2 Adiabat perfect compressor

1.5.3 Polytropic perfect compressor

1.6 Actual Piston Compressor

1.6.1 Differences Between a Real Compressor and a Perfect Compressor

1.6.2 Actual Compressor Indicator Diagram

1.6.3 Schematized indicator diagrams of the actual piston compressor

DESIGN PART

2 Calculation of basic thermodynamic parameters of refrigeration

Unit

2.1 Method of calculation of single-stage piston compressor of refrigerating machine

2.1.1Define refrigeration machine point parameters

2.2 Structural and thermal calculation of heat exchangers

2.2.1 Calculation of geometric parameters of capacitor

2.2.2 Calculation of geometric parameters of evaporator

PROCESS PART

1 Evaluation of processability of the assembly unit

2 Assembly Process

V LIFE SAFETY

Introduction

1Assay Hazardous and Harmful Factors

1.1 Physical hazards and hazards

1.2 Chemical Harmful Production Factors

2 Measures to prevent hazardous and harmful production

Faktorov

2.1 Basic Safety Rules for Assembly Works

3 Protection against noise sources

4 Industrial hygiene and sanitation

4.1 Lighting

4.2 Microclimate

4.3 Fire Safety

5 Safety Instructions

5.1 Safety requirements before starting operation

5.2 Requirements for performance of work and rest modes

5.3 Industrial Sanitation Requirements

5.4 Requirements for lighting of premises and workplaces with PC

5.5 Requirements for organization and equipment of workplaces with PC

V ECOLOGY

Introduction

1 Freons and the environment

2 Air pollution

3 Hydrosphere contamination

4 Solid waste

5 Output

V ECONOMIC PART

1 Cost of production. Justification and definition

2 Calculation of cooling unit main units cost

3 Output

V INFILTRATION

V Literature

X Appendix

X Appendix

Introduction

Recently, the problems of the ozone hole and global warming have been increasingly heard. Previously unprecedented phenomena like the ice cover in Antarctica, unprecedented tsunamis and floods all this, according to a number of scientists, is a consequence of the influence of the technosphere on the nature surrounding us.

These assertions have led the world community to identify and eradicate factors that have a negative impact on the environment of the planet.

The first step towards the use of environmentally sound refrigerants was the signing in the mid-1980s by the largest producing countries of the Montreal (at the place of adoption) protocol, which ordered the elimination of the use of the ozone-depleting Freon by 2000, 12 by 2030 from Freon R22, and Freon R134a was considered a long-term prospect.

However, by the mid-1990s, it turned out that there were no positive changes in the environment. In addition, they drew attention to the fact that R134a, although ozone-safe, has the so-called global warming potential thousands of times higher than the potential of basic carbon dioxide. This led to the implementation of a new agreement, which also introduced emission standards at R134a.

In Germany, under the patronage of Greenpeace, an action was held "for ozone-safe and climate-friendly refrigerants," which served as an impetus for the development of already forgotten hydrocarbon technology.

Initially, mixed refrigerant R290/R600a was used, which allowed

reset existing refrigeration equipment without replacement

compressor unit, but after development of technology and introduction of new

R600a models firmly took the lead. Today in

Germany and Scandinavian countries refrigeration equipment with refrigerant

R600a occupies up to 80% of the market. The R600a refrigerant, unlike R134a, does not need to be synthesized, as it is often the associated gas in oil production. It is only necessary to separate it from impurities and introduce the inhibitors necessary to reduce its corrosive activity. An important factor is also its unpretentiousness to lubricants and, after the addition of inhibitors, structural materials. Let me remind you that only expensive high-quality polyester oil was suitable for lubrication of compressors with refrigerant R134a.

Lower operating pressures result in lower compression energy costs and, as a result, higher unit cooling capacity, which is the main indicator of quality, owing to rising energy prices.

And the last, so far, step in solving world environmental problems was the adoption at the end of 2004 of the new Kyoto Protocol, according to which R134a is considered unacceptable and the use of technologies using it should be discontinued by 2008.

In view of the above, I believe that the topic is timely and relevant.

1.1 Refrigerating machine working substance

1.1.1 Overview of refrigerants

The working substance used in any refrigeration process to absorb heat as a cooling medium is called a refrigerant. Currently, about 3040 working substances are used, from which ammonia and various fluorochlorobromo derivatives of methane and ethane, as well as propane and butane, are obtained for practical use, except for water and air. Hydrocarbon derivatives are called freons or freons, denoted by the chemical formula or the letter R to which a number determining the number of atoms is added.

When choosing a refrigerant, it is important to take into account its poisonousness, flammability, the nature of the effect on lubricants and materials, cost, etc. At the same time, the choice of refrigerant is largely determined by the requirements of maximum cycle efficiency, compactness of the refrigerating machine and specific parts, the identification of which is possible when analyzing specific cycles of refrigerating machines,

However, one of the main sources of air pollution is the refrigerant used as the working medium of the refrigerator. A number of refrigerants, being in the atmosphere, create a greenhouse effect. More than 95% of the global production of chladones is accounted for by ozone-depleting refrigerants such as R11, R12, etc.

The chemical stability of chlorofluorocarbon compounds (R11, R12) is so high that the molecules of these substances do not break down in the troposphere (lower part of the atmosphere) and reach the stratosphere (upper part of the atmosphere from 16 to 45 km). Under the influence of ultraviolet radiation, freon molecules decay with the release of chlorine atoms, which contribute to the destruction of the ozone layer.

1.4 Perfect Compressor

1.4.1 Definition of "perfect compressor"

In an ideal compressor, only the main processes are considered. Taking a number of simplifications for an ideal compressor, you can describe all the main processes in it with simple dependencies borrowed from the course of technical thermodynamics. Having considered the necessary laws that are valid for an ideal compressor, and having drawn conclusions from them, it is believed that in the first approximation similar laws, and therefore the conclusions from them, will be with certain deviations allowed to evaluate the operation of the actual compressor. Such a study of the operation of the piston compressor is sufficient to solve many issues that arise in practice.

Thus, an ideal compressor is a simplified thought model of a real compressor that can be used as a tool in solving practical problems related to the operation of a piston compressor. To define an ideal compressor, consider its detailed description.

For an ideal piston compressor, the following assumptions, simplifications and assumptions are introduced.

1. There is no dead volume, that is, all gas is pushed out of the cylinder during the injection stroke, after which no compressed gas remains in the cylinder; thus, there is no reverse expansion, no performance loss.

2. There are no loopholes in the working cavity of the cylinder, i.e. in the process of compression we have a constant amount of gas; from this it follows that how much gas will be sucked, as much will be supplied to the discharge nozzle (by mass).

3. The thermal inertia of the cylinder walls is absent and does not affect the thermodynamic compression process, that is, the index of the compression polytrope is constant (const).

4. The gas parameters in the cylinder (temperature and pressure) remain constant (unchanged) throughout the suction and injection processes.

5. There is no hydraulic loss during gas flow in the valve channels and in the pipelines, that is, during suction and discharge, the gas in the cylinder will have the same pressure as in the STV and STN, respectively.

6. During suction, the gas is not heated to the hot parts of the compressor, that is, the gas temperature in the cylinder during suction is equal to the gas temperature in the STV.

7. During injection there is also no heat exchange between the gas and the walls of the working cavity of the cylinder and valves.

8. The suction valve is self-operating; it opens in VMT and closes in NMT.

9. The pressure valve is self-operating. It opens at the moment when the pressure in the cylinder is equal to the pressure in the delivery branch pipe and closes in the TDC.

10. There is no friction in mechanical units and contact points of friction pairs (piston - piston rings, piston rings - cylinder, piston - cylinder, etc.).

The combination of assumptions, assumptions and simplifications uniquely defines the concept of "ideal compressor."

1.6.1 Differences Between a Real Compressor and a Perfect Compressor

The actual piston compressor is very different from the ideal one. The main differences causing the deterioration of its volumetric and energy indicators are discussed below.

Dead volume in cylinder of actual compressor

When the piston moves inside the cylinder, the gas in the dead volume cannot be displaced from the working cavity of the cylinder. Thus, in the dead volume after the completion of the pumping process, part of the working substance remains under pressure exceeding the pumping pressure by the value of hydraulic losses in the pressure valve. In the reverse stroke of the piston, this working substance will expand, so that the pressure in the cylinder at which the suction valve can be opened will be reached only after the piston has passed a certain distance. As a result, suction occurs only on part of the piston stroke, which leads to a decrease in the volume productivity of the actual compressor compared to the ideal one.

Hydraulic losses

In actual compressor there are hydraulic resistances to working substance flow through valves and pipelines. Thus, the gas pressure in the cylinder during suction is lower than in the suction nozzle, which affects the compressor capacity. During injection due to pressure loss on the resistance in the pressure valves, the gas pressure in the cylinder will be greater than the pressure in the pressure nozzle. Hydraulic losses in suction and delivery valves and pipelines lead to an increase in the power consumed by the compressor.

Pressure losses on the hydraulic resistances in the valves will not be constant during the stroke of the piston, since the flow rate of the working substance through the valves due to the speed of movement of the piston in the cylinder is variable.

Working substance heating during suction

The working substance entering the cylinder during suction is heated, receiving heat first from the compressor housing, and then from the valves, cylinder and piston. Thus, the temperature of the working substance in the cylinder at the end of suction will be higher than the temperature of the working substance in the suction pipe. Naturally, the density of the substance in the cylinder at the end of suction will be less than if the suction heating were not present.

Heat exchange in cylinder

While in the cylinder, the working substance exchanges heat with the surrounding parts. At suction and at the beginning of compression, its temperature is lower than compression and at injection, the temperature of the working substance becomes higher than that of the surrounding parts, and the heat exchange process proceeds in the opposite direction. As a result, compression and reverse expansion processes go with variable values ​ ​ of the polytrope index.

Working substance fluctuations in compressor cavities

These occur due to the periodic nature of its operation, which is manifested in pressure and temperature pulsations at the inlet and outlet of the compressor. The frequency and amplitude of the pressure change are greatly affected by the volume and extent of the network - pipelines and devices connected to the compressor. Oscillatory processes of the working substance in the compressor system - the network can significantly affect the capacity and capacity of the compressor.

Leaks and leaks of working substance

They are due to the presence of gaps and loopholes between the compressor parts: cylinder liner and piston, in the locks of piston rings, seals, valves, etc. Leakage is the overflow of the working substance, leading to its loss for the process under consideration. For example, the flow of working substance from the cylinder to the crankcase of the throne compressor through the leaks in the cylinder-piston group or suction valve is a leak. Leakage is the flow of working substance from one cavity to another, which does not lead to its loss for this process. So, the flow of the working substance through the leaks of the delivery valve into the cylinder or through the leaks of the cylinder-piston group from one cavity of the double-acting cross-body compressor to another is a leakage. Leaks and leaks lead to a decrease in the productivity and energy efficiency of the compressor, as they are internally irreversible throttling processes.

Mechanical friction

In a real compressor, there is friction in movable pairs, to overcome which power is spent, called friction power. As a rule, it also includes the power spent on driving the oil pump and bubbling the oil in the compressor crankcase. Friction power changes to heat, some of which is transferred to the working substance, which affects the nature of the compressor working processes. The rest of the heat is transferred to the environment.

The Reality of Compressible Gas

In some types of piston compressors (refrigeration compressors, high pressure compressors), gases or vapors that differ in their properties from the ideal gas are compressed. Such gases (or vapors), unlike the ideal gas, are called real. The reality of the gases, that is, their difference from the ideal ones, affects the productivity of the compressor and the power consumed by it.

The influence of these factors leads to the fact that the indicator diagram of the actual compressor is significantly different from the ideal one.