Apparatus for eco-refrigerants experimental investigations.

Pop, Horatiu ; Apostol, Valentin ; BARAN, Nicolae 等

1. INTRODUCTION

Lately, through the European environmental legislation aquis, issues concerning environmental protection have become a priority at European and national level (***, 2004). The strategy consists of drastically reducing the gas emissions that lead to ozone layer depletion, but, also, of those that lead to the greenhouse effect amplification. The majority of contemporary refrigerants are included in the last category (***, 2000). From this point of view, the goal is to gradually replace polluting refrigerants with eco-refrigerants synthetic or natural substances (Lorentzen & Pettersen, 1992; Lorentzen, 1995).

The substitution process of pollutants refrigerants with ecorefrigerants involves the following steps:

* establish the thermodynamic compatibility between the substitution refrigerants and pollutant refrigerants;

* establish the application range;

* monitor and solve the technical problems which occur when pollutant refrigerants are substituted with an ecorefrigerant in existing or in a new designed VCRS.

Some research activities of the Chair of Thermodynamics, Refrigeration and Thermal Systems of the Faculty of Mechanical Engineering and Mechatronics, University "Politehnica" of Bucharest (UPB) are part of this general framework. To achieve the objectives of the research in the field of refrigerants, in a dedicated laboratory an experimental arrangement which consists of a refrigeration chamber fitted by one stage VCRS, has been built. The experimental investigation allows the determination of the: cooling load, compressor energy consumption and heat exchangers fans, refrigerant mass flow rate, thermal operating regime and the cooling performance coefficient. The testing offers the possibility to compare the overall performance obtained when the system operates with various refrigerant types. In this context, experimental research is performed to find the most appropriate refrigerants to substitute the pollutants ones.

When a refrigerant is substituted with another one in an existing VCRS, the thermal parameters and system performances are changing. Therefore, problems may occur regarding the: compatibility with the compressor lubrication oil and with certain materials used in the VCRS construction, such as sealing elements (e.g. incompatibility with rubber--HFC or CO2) and the material of the compressor electromotor (e.g. incompatibility ammonia--copper). Also, changes of the refrigerant flow parameters through pipes occur, evidenced by speed variation. This can causes problems concerning oil returning to the compressor and, respectively, heat transfer worsening at the condenser and evaporator. The refrigerant substitution involves modification of refrigerants mass flow rate, cooling load and compressor power consumption. All of these can lead in the end to a different coefficient of performance. These changes need to be carefully tracked to determine the compatibility between the existing VCRS and alternative eco-refrigerants. After the first step of the experimental investigations compatibility, endurance and reliability tests must be performed (Marinescu et al, 2006).

To achieve these goals, as detailed below, the testing apparatus is equipped with devices for measuring and control (automation), but, also, with a data acquisition system that allows remote monitoring and controlling of the functional parameters through a network (e.g. INTERNET).

To ensure the validity of the experimental investigation results, the apparatus was designed to assure two experimental performance measurement methods, used in parallel (Tarlea et al, 2008), namely:

(i) direct method: measurement of liquid refrigerant mass flow using an electronic flow meter;

(ii) indirect method: determination of refrigerant mass flow rate based, on the VCRS thermodynamic cycle calculus and on the measurement of compressor energy consumption. Because this method combines measurements and calculus it will be improved by energy balance on the condenser.

2. EXPERIMENTAL APPARATUS DESCRIPTION

As can be seen in Fig. 1, the testing apparatus consists of: 1--refrigeration chamber; 2--condensing unit; 3--control panel; 4--electricity meter; 5--liquid refrigerant flow meter; 6--the link pipeline between the condensing unit and evaporator; 7--acquisition data console.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The inside refrigeration space of the refrigeration chamber is cooled, using a direct expansion method, by the evaporator of the VCRS. The refrigeration chamber is characterized by: a functional volume of 1 [m.sup.3], with a single access door and with sandwich polyurethane-plastic walls.

The condensing unit, showed in Fig. 2a, consists of: 1--sealed compressor, 2--condenser; 3--condenser fan, 4--liquid receiver; 5--electrical connections box; 6--high and low pressure controller, 7--suction line, 8--discharge line.

The control panel, whose picture is presented in Fig. 2b, consists of: 1 -temperature and relative humidity controller of the air, inside the refrigeration room, 2a--air temperature display at evaporator outlet; 3a--air temperature display at condenser inlet; 4a--air temperature display at condenser outlet; 5a--display of sub cooled refrigerant temperature (at the expansion valve inlet); 6a--display of overheated refrigerant temperature (at the compressor suction line); 7a--controller of compressor suction pressure; 8a--controller of condensing pressure; 9a--display of air temperature inside the refrigeration chamber near the evaporator, 10a--display of air temperature inside refrigeration chamber near the door, 11--switch, 12--damage light indicator.

Pressure and temperature measurements are done by of pressure and temperature transducers mounted at the cold circuit. Air temperature and air relative humidity inside the cooling chamber are measured through specialized probes. The electricity meter is used to measure the energy consumed by the compressor electromotor. The refrigerant electronic flow meter is mounted on the liquid refrigerant pipe which connects the condensing unit and evaporator. For flow meter operation is used a 24V source, DC voltage. Connecting pipeline between the condensing unit and the evaporator of VCRS is equipped with a dryer filter (Figs.1 and 2), mounted at the outlet of the liquid receiver, and with an electromagnetic valve (Fig 1). The dryer filter retains the moisture and any impurities, and the electromagnetic valve stops feeding the evaporator with liquid refrigerant, when the minimum set temperature has been reached. Also, on this pipeline the expansion valve is mounted.

Acquisition data console records and stores all data provided by the controllers, liquid refrigerant flow rate and electricity meter. Through dedicated software, the console can be configured to record data at a certain time interval. By remotely accessing the console (e.g. INTERNET), acquisition and functional parameters of the VCRS can be set up through the network.

3. CONCLUSIONS

The experimental apparatus presented in this paper is integrated in the Refrigeration Plants Laboratory of the Chair of Applied Thermodynamics, Thermal and Refrigeration Systems of the Faculty of Mechanical Engineering and Mechatronics, "Politehnica" University of Bucharest. It is use to complete, in good conditions, the activities of the research in the field of alternative refrigerants, which is a priority within the European environmental legislation aquis. The apparatus is based on a single stage vapor compression refrigeration system (VCRS), used to cool down a refrigeration chamber. It is provided with a control panel, enduring the measurement and the control of pressure, temperature, relative humidity, mass flow rate of refrigerant and the electric parameters of the compressor's electric motor. An acquisition data console records the data provided by all this specialized probes. The VCRS functional parameters and time acquisition can be set up through the network.

To ensure validity of experimental investigation results, the apparatus was designed to assure two experimental measurement methods, used in parallel: a direct method, which is a more accurate and an indirect method, which will be subjected to future improvements.

The experimental database obtained by using this apparatus allows: (i) to compare the overall performance obtained when the single stage VCRS operates with various types of refrigerants, (ii) to find the most appropriate refrigerants to sub stitute the pollutant ones, (iii) to point out the technical problems which may appear after the substitution process in an existing VCRS and also during the performance, endurance and reliability tests.

4. REFERENCES

Lorentzen, G. & Pettersen, J. (1992). New possibilities for nonCFC refrigeration, in Pettersen J. Editor, Proceedings of International Symposium on Refrigeration (IIR), Energy and Environment, Trondheim, Norway, pp 29-34

Lorentzen, G. (1995). The use of natural refrigerants: a complete solution to the CFC/HCFC predicament, International Journal of Refrigeration., Vol. 18(3), page 190-197, ISSN: 0140-7007

Marinescu C.; Popescu G. & Apostol V. (2006). New Ecorefrigerants Family, Research Report, Contract no. 1915/15.09.04, National Program RELANSIN'04, beneficiary AMCSIT--UPB, Bucharest. Available from: http://www.mecanica.pub.ro. Accessed: 2008-12-10

Tarlea, M.G., Popescu, G., Chiriac, F., Maracine, I., Apostol, V. & Sinca, O. (2006). Implementation of the European Union Environmental Aquis in Romania, eco-refrigerants, Research Report, Contract no. 214/20.07.2006, National Program CEEX'06, beneficiary AMCSIT--UPB, Bucharest Available from: http://www.mecanica.pub.ro. Accessed: 2008-12-10

*** (2004) MMGA, Update of Country Program for the Phaseout of Ozone Depleting Substances in Romania, http://www.mmediu.ro/arhiva.htm. Accessed on: 2006-0820

*** (2000) UNEP, OASIS: Ozone Action Strategy Information Systems 2nd Edition, ISBN: 9280718223, New York