Development of a new generation of low-temperature absorption refrigeration machines

Scientific-Engineering Center P.O.B. 3682, Ma’alot, 2 105 906, ISRAEL Phone: +972−50−8 509 416; Fax: +972−4-9 971 336 E-mail: naumir@yandex.ru

3R-Technology 108 840, Russia, Moscow, Troitsk Тел: +7−910−404−6904; +7−905−782−2040 E-mail: miily@yandex.ru; pd6@bk.ru

I.N. MIRMOV, Cand. tech. Sciences, miily@yandex.ru, Institute for Nuclear Research, Russian Academy of Sciences, Moscow;
N.I. MIRMOV, Dr. S., naumir@yandex.ru, Scientific Engineering Center, City Ma’alot, Israel;
S.A. SHIPPTSOV, pd6@bk.ru, PAO «InterRAO», Moscow

Development of a new generation of low-temperature absorption refrigeration machines

Abstract

A new low-temperature absorption refrigeration machine (AbRMS^m), which operates on the basis a salt solution in alcohol are proposed. The using as a working solution of lithium bromide + methyl alcohol (LiBr / CH₃OH) makes it possible to obtain a boiling point of a refrigerant (methanol) in the evaporator to -18ºС. In absorption refrigeration machines refrigerant vapor moves from the evaporator to the absorber due to the difference in concentration. At negative boiling points of the refrigerant in the evaporator, the pressure in the absorber is higher than in the evaporator. As a result to maintain a low pressure, and accordingly, the boiling point in the evaporator is impossible. To ensure a given negative boiling point of the evaporator, to overcome the pressure difference in the apparatus and to maintain normal operation of the refrigerating machine the evaporator and the absorber are interconnected by a hydrodynamic amplifier. The hydrodynamic amplifier (here and after the amplifier) belongs to the class of gas-liquid jet apparatuses. In the amplifier, a strong solution is used as the working fluid, which flows from the generator to the regenerative heat exchanger. Due to the kinetic energy of the flow of the working fluid (solid solution), the process of suction of methanol vapor from the evaporator proceeds and a given pressure and, accordingly, boiling point is maintained in it. It is necessary to install 2−3 or more hydrodynamic amplifiers when a capacity is 30 kW and above.

Taking into account the classification of refrigeration machines adopted in refrigeration engineering it is proposed to develop a model range of absorption refrigeration machines AbRMS^m 10−350 (10, 18, 35, 70, 120, 150, 200, 350 kW).

The absorption refrigeration machine consists of two assembly blocks (A) and (B). The assembly unit may have an absorber — evaporator and generator — condenser arrangement in a single housing or consist of separate apparatuses [fig. 1]. Absorption refrigeration machines with a capacity of 10 kW and 18 kW are made single-hull.

1. The main differences of the proposed refrigeration machine from the known analogues

1.1. The absorber and the evaporator are connected to each other by a hydrodynamic amplifier so that the suction chamber of the amplifier is fixed on the throat of the evaporator and the diffuser is located in the absorber.

1.2. The heat exchange tubes of the absorber, evaporator, generator and condenser are fixed in square or rectangular tube grids, which can significantly reduce the length of the tubes while maintaining the desired heat exchange surface.

1.3. Since the main process of absorption of refrigerant vapors takes place in a hydrodynamic amplifier, the length of the absorber tube bundle is much shorter, therefore, the dimensions of the absorber itself are 1.8−2.0 times smaller.

1.4. The absorption refrigeration machine contains a storage receiver in which a coil is installed to supercool a strong solution. The receiver is installed after the regenerative heat exchanger.

1.5. Also the absorption refrigeration machine contains a pump that is designed to supply a strong solution through the nozzle of a hydrodynamic amplifier to the absorber.

1.6. A variant of the construction of the unit (B), in which the evaporator and the absorber are located in the same housing. In this embodiment of the evaporator design, heat pipes or two-phase thermosyphons are used to cool the coolant.

2. Main technical parameters and advantages of the proposed refrigerating machine:

2.1. For the model range of absorption refrigeration machines under development the values given correspond to the nominal cooling capacity under the following specified operating conditions:

Values given

Working substance: methanol / LiBr;

Refrigerant boiling point (methanol) in the evaporator: −10°С and −12°С;

Refrigerant condensing temperature: 30−40°C;

Condensation pressure: 0.3−0.4 bar;

Coolant: an aqueous solution of ethylene glycol. Coolant temperature at the evaporator outlet: −6º… −8°С.

2.2. The absorption refrigeration machine consists of two assembly units, which reduces the weight and improves the conditions of service and repair.

2.3. The hydrodynamic amplifier provides a stable and uniform flow of refrigerant vapor from the evaporator to the absorberand also compensates for the pressure difference in the absorber and evaporator.

2.4. Hydrodynamic amplifier allows you to maintain a predetermined pressure and boiling point of the refrigerant in the evaporator;

2.5. The use of a hydrodynamic amplifier provides an intensive process of absorption of methanol vapor with a strong solution due to mixing in the mixing chamber and diffuser;

2.6. Prevention of possible crystallization of the solution is ensured by installing on the drain pipe between the evaporator and the absorber of the pump and the automatic solenoid valve

2.7. Using in the evaporator heat pipes or two-phase thermosyphons increases the reliability of the refrigerating machine at least 2 times.

3. Areas of using

The developed standard series of low-temperature absorption refrigeration machines can be used to obtain technological cold at the enterprises of the meat and dairy industry, in the food, chemical and oil and gas industry.This type of refrigerating machines can be used for air conditioning systems in shopping and entertainment centers, industrial and office buildings and in everyday life.

Using of absorption refrigeration machine as a high-temperature stage in a 2-stage machine makes it possible to use them for shock freezing of the products, the ice cream and biological products.

4. The economic feasibility of the use and manufacture of low-temperature absorption refrigeration machines

4.1. For the enterprise of the developer and the manufacturer, the economic efficiency is determined as follows:

4.1.1. Production of a single sample of AbRMS^m, for example, with a capacity of 120 kW will be € 150,000−160,000. The cost of a serial machine of the same cold capacity will be cheaper on 20−25%.

4.1.2. The developed range of absorption refrigeration machines closes almost the entire consumer market of absorption refrigeration machines for low-temperature cooling. The recoupment of investments for the development and manufacture of about 8−10 refrigerating machines during the year will not exceed 2 years.

4.1.3. Additional profit of the enterprise will be obtained through the organization of the chief-installation and implementation of commissioning works.

4.1.4. The developed absorption refrigeration machines will give great returns if it is used as a high-temperature stage in two-stage refrigeration machines.

4.1.5. The production of machines can be established in any country and in any region if the factory has a standard set of mechanical and welding equipment.

4.2. For a company or an enterprise that purchases a low-temperature absorption refrigeration machines, economic efficiency is made up of the following indicators:

4.2.1. AbRM work on waste (secondary) sources of thermal energy. The temperature of the heating source is about 68−75°C;

4.2.2. Electricity is spent only on the drive of the circulation pump. For example, for an AbRM with a capacity of 120 kW with given conditions, the power consumption is 6.2 kW. For the same compression refrigeration machines, the power of the installed electric motor is 58 kW, that is, it consumes 8.6 times less electricity.

4.2.3. In addition, developed the AbRM on 18−20% lighter than existing refrigeration machines of the lithium bromide / water.

4.2.4. The period of normal operation without additional maintenance is about 12−14 years.

4.2.5. The mechanical units in the refrigeration machine are two circulation pumps that only require regulatory servicing of pump and motor seals.

4.2.6. The use of an absorption refrigeration machine as a high-temperature stage in two-stage refrigeration machines extends the possibilities of obtaining temperatures in cooled objects from -50ºС… ̶ 70ºС. At the same time, energy saving reaches 40−43% compared to compression 2-step machines.

5. Intellectual property

The structural schemes of the low-temperature absorption refrigeration machines, designs features of the main elements of such machines are displayed in Israeli patent № 248 315 of 05.02.2018 «Absorption refrigeration machine with a working solution of methanol / lithium bromide» and the patent of the Russian Federation № 2 690 896 of 06.06.2019 «Low-temperature absorption refrigerating machine based on a solution of salt in alcohols» and also in scientific articles of specialized journals.

Notes:

1. Taking into account the development of the stand for filling refrigerating machines with the working solution, and the test bench, the duration of reaching the serial production of the model range should be about 28−32 months.

2. Approximate costs in the first year of work on the development and creation of two or three pilot samples of the refrigerating machine, test benches and filling stations are about 350,000−400,000 €.

3. The next year of work will provide an opportunity to reduce costs on 20−22%.