Comparison of single-stage refrigerator is a broad class of refrigerator, which can be applied to ice, air conditioning, food refrigeration and industrial processes and so on.Single-stage refrigeration cycle is the refrigerant in the refrigeration system have been compressed, condensation, throttling, the process of evaporation of four, will complete the cycle of single-stage cryocooler, which reached a cooling purposes.

By the refrigeration system evaporator, single-stage compressor, oil separator, condenser, ammonia storage device, ammonia liquid separation, the throttle valve, and other ancillary equipment and other components, with each other through the pipe connection into a closed system. Where the evaporator is cold transport equipment, liquid refrigerant evaporates absorbing the heat to achieve the object being cooled refrigeration; compressor is the heart of the system, play a suction, compression, transmission role of refrigerant vapor; oil separator for deposition separation of the compressed refrigerant vapor in the oil; condenser heat the compressor discharge refrigerant vapor condensing to become saturated; storage is used to store ammonia refrigerant condenser in the condensate liquid ammonia, adjusting between the condenser and evaporator liquid ammonia refrigerant supply and demand; ammonia liquid gravity separator for liquid ammonia system, the important ancillary equipment; throttle on the role of the refrigerant from the throttle control and regulation of both the refrigerant into the evaporator, the liquid flow, and the system high side and low side is divided into two parts.

2. two-stage refrigeration cycle

Two-stage ammonia refrigeration cycle is a single-stage refrigeration cycle developed on the basis, and its two-stage compression process, from the evaporator into the first low-pressure refrigerant vapor compression cylinder to the middle-class pressure, and then enter through the intermediate cooling high pressure stage cylinder, compressed into the condenser to the condensing pressure. General evaporating temperature -25 ℃ ~ -50 ℃, should be used for cooling two-stage compressor.

By the refrigeration system evaporator, two-stage compressor, oil separator, condenser, intercooler, ammonia storage device, ammonia liquid separation, the throttle valve, and other ancillary equipment and other components, with each other through the pipe connection into a closed system . Among them, the intermediate cooler refrigerant using a small amount of liquid under pressure in the middle of vaporization heat, the low-level discharge of superheated steam are cooled to reduce high levels of suction temperature, but also high-pressure liquid refrigerant to be cooled.

中文用户可以浏览：无油涡旋压缩机国内外研究现状

Scroll compress another efficient positive displacement compressor after reciprocating compressors, rotor compressor and screw compressor. It’s know as the most advanced continuous compressor. This kind of compressor are known for operating more efficiently and quietly than conventional compressors. Compared to pistons, its main component is only 10% of the former, the volume reduced about 40%, efficiency improved 10%, weight is only 85% of the former.

With the development of industry, clean air is needed in some particular field. At this time, oil free compressor become the major option. Because of the advantages of oil free scroll compressor, it becomes the focus in the resarch of compressor.

Oil free compressor was founded between 1920s and 1930s. Sulzer Brothers Ltd., from Swiss, first patented Labyrinth seal oil lubrication compressor. At the beginning of 1950s, first oil free compressor appeared on the market. Shenyang air compressor factory and Lanzhou Institute of Chemical Physics, CAS, are the two institutions which engaged in researching oil free compressor first in China.

The oil free compressor has very favorable prospect of development. The first factory, which produce oil free compressor , in China, estimated to make about 5 billion in after 2011 when it go into full operation.

However, research on oil free scroll compressor is still fairly few. It faces many shortages. How to seal and lubricate remains the big challenges in improving its efficient. Compared to compressors work with lubricant oil, the leakage is much bigger.

In order to lubricate without oil, we need to inlay self-lubricatingmaterial. The most popular self-lubricatingmaterial are PTFE, PEEK, PESF and PES.

The old experience and the traditional method of 2-D design remains the major methods for design and manufacture. But these two methods have the same shortage of inefficiency and long development cycle. So it can not meet the needs now. To find a new method becomes important.

中文用户可以查看中文版：无油润滑涡旋压缩机设计计算步骤

Disclaimer:

This calculation method is suit for designing a compressor that you know the compressor displacement Q_d (V³/min) and suction pressure p_s as well as the exhaust pressure p_d (MPa). And according to a Chinese paper “Choice of Bask Geometric Parameters and Structure Parameter,λ=h/Pt , on a Scroll Compressor” by Gu Zhaolin, published on “Compressor Technology”, 1996, we choose Pt、t and h as bask geometric parameters. So I modified the calculate steps to this method:

1. Calculate the indicated power of electromotor. P_i (Kw)

equation for calculating the indicated power of electromotor

You can find this equation in document [2] at page 62. In this book, it use  kgf/cm² as unit of pressure. So I made a small change in order to change the pressure unit to IU MPa.

2. Compute motor power P_e (Kw)

The leakage and friction factors concerned, shaft power Pz can be counted through this equation:

P_z=1.12P_e

Make sure there are about 5%～15% power reserve, the motor power Pe should be:

P_e=(1.05～1.15)P_z

3. Select motor speed n_w, it should be between 1000 and 4000r/min

4. Calculate the exhaust volume V_d (m³/r)

V_d=Q_d/(i*nw)

‘i’ in this equation is a parameter defined by the amount of compression chamber. If there is just one orbiting scroll and one fixed scroll, i should be 2. For compressor with Z orbiting scrolls and fixed scrolls, i should be 2*Z.

5. Calculate the suction volume V_s (m³/r)

Use a ideal gas model to simplify the calculation and assume the cycle as adiabatic. So:

pV^k=C

k is the adiabatic exponent of working medium or refrigerant. The adiabatic exponent is 1.4. The suction volume can be defined:

equation for calculating the suction volume of scroll compressor

6. Geometric interior volume specific ratio ε_v

ε_v=V_s/V_d

7. Select  scroll pitch P_t(mm), scroll width t (mm). t should be 2～6mm

8. The angle that the involute beginning α (rad)

α=pi*t/P_t

pi=3.1415926535 897932

9. The maximum angle of involute Φ_e(rad) and the exhaust angle θ_d(rad)

ε_v=(2*Φ_e-3pi)/[2(Φ_e-θ_d)-3pi]

equation 1 for calculating the maximum angle of involute Φe and the exhaust angle θd

equation 2 for calculating the maximum angle of involute Φe and the exhaust angle θd

You will get the answer by combine the three equation. You may need tools like Matlab to get the  result. http://www.zhangpeng.info/

10. Scroll height h (mm)

V_s*1000000=P_t(P_t/2-t)h(2Φ_e-3pi)

You should adjust your parameters to use unit of ‘m’ other than ‘mm’. But I defined all the distance use the unit of ‘mm’, so I plus a 1000000 to make the change.

11. Check λ=h/P_t if it appropriate

Some paper said λ should between 1.5 and 2.5. If the λ you gained exceed the limit, duplicate step 7-11.

12. Radius of basic circle R_b (mm)

R_b=P_t/2pi

13. Radius of shaft circle R_or (mm)

R_or=(P_t-2t)/2

14. Balanced design of orbiting scroll.

15. Choose a oil-free format and the self-lubricatingmaterial

References:

1、刘振国.涡旋式流体机械与涡旋压缩机[M].机械工业出版社. 2009

2、编写组.活塞式压缩机设计[M].机械工业出版社. 1974

3、Gu Zhaolin, Yu Yongzhang. 涡旋压缩机设计计算研究[J].流体机械. 1996.2

4、Gu Zhaolin. Investigation of Scroll Compressor Design[J].低温工程. 1996.1

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All these references are written in Chinese, you ask me if you have any question during reading these references.

Here you see an simple desiccant system .

desiccant system

At day , refrigerant turn to vapor and the pressure in absorber increase . Vapor flow to a condenser and then be cooled there . We store this liquid. www.zhangpeng.info

When the temperate of environment decrease and there are no enough radiation , absorb medium then absorb vapor . Pressure in evaporator decrease. According to heat transfer law, we know the left liquid will turn to vapor and the temperate goes down . We use this phenomenon to cool the air in the building.

To know more about desiccant system please see our PPT :

http://docs.google.com/Presentation?id=dhhmxwkj_3c6ckh4d9