Refrigerating Systems and Refrigerants

Refrigerants R13B1 and R502 were ideal for such low-temperature applications because they had low pressure ratios and low compressing final temperatures. 

When changing over to another refrigerant, as shown in Table 2.1, it is important to carry out the following  

Heldner et al. [2.9]show (Table 2.3) the temperatures that should be reached on the shelves and in the condenser and what can be attained with the different refrigerants. 

Isceon 69 L Rhone-Poulenc R290/ 0.03 3680 Alkyl benzol 

Haseley 2.4] differentiates between two categories of refrigerants The first group can be exchanged in compressor systems without changing the compressor itself, but changing the injection valves. The second group with no Ozone Depletion Potential (ODP). 

Because HP 80 and Isceon 69 contain R 22, the use of them in existing installations is only for a limited time. For new installations, hydrofluorcarbons (HFC) are available with ODP values at 0, e. g. 

These three refrigerants have a Coefficient of performance , which is I - to 25 times smaller than that of R 502. 

drying chamber 2, condenser 3, condenser coil 4, jet pump 5, heat exchanger 6, throttle valve 7, pressure controlled N2 outlet 8, LN inlet (from [2.6] page 342). 

The company AMSCO Finn-Aqua [2.8] shows a different possibility of saving LN2 and yet retain some of the advantages. In the condenser housing, besides the conventional coils, a LN2-cooled plate is installed, which will be only operated under two conditions  

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As with heat pumping, the grand composite curve is used to assess how much heat from the process needs to be extracted into the refrigeration system and where, if appropriate, the process can... 

The processes using physical absorption require a solvent circulation proportional to the quantity of process gas, inversely proportional to the pressure, and nearly independent of the carbon dioxide concentration. Therefore, high pressures could favor the use of these processes. The Recitsol process requires a refrigeration system and more equipment than the other processes. This process is primarily used in coal gasification for simultaneous removal of H2S, COS, and CO2. 

A stream of 100 gpm (379 1/min) liquid expanding from 1,000 psi (6,900 kN/m ) to 100 psi (690 kN/m ) if it does not flash will develop approximately 40 hp (29.9 kW). Flashing usually more than doubles the power. Although this is only a small fraetion of the total required refrigeration, it is near the eoldest point in the system and is valuable. A hundred hp is the equivalent to a quarter of a million Btu per hour (73.3 kW) of heat. This would vaporize 2,900 lb (1,315 kg) per hour of liquid nitrogen at an absolute pressure of 20 psi (138 kN/m ). 

The following table shows the three most used refrigeration systems and approximate temperature ranges. 

The facility stores ammonia to supply nearby fertilizer manufacturers. It is transported to the plant by ship, transferred and stored in the tank for transfer as needed. The facility mainly consists of a storage tank, a refrigeration system, a control system, and a pipe connecting the tank with the plants. Ammonia is transported and stored as a refrigerated liquid (-33 C) at atmospheric pressure. 

Automotive air conditioning systems using vapor compression refrigeration systems and CFC refriger-... 

Assume operating pressure is 700 psig, K = 1.35. Note that this same K value could have been achieved by lowering the operating temperature to -90 F. This is also not practical from the oil standpoint or even from the economics of operating the entire system and refiigeration system at this level, unless (1) the refrigeration is available and (2) a suitable oil is available. 

Assume that this load can be handled best in two units operating in parallel. In this scenario, if one condenser develops trouble, the entire refrigeration system, and con-sequendy the plant process, is not shut down. 

In mechanical systems, the temperature of the available water (or coolant) to condense the refrigerant from the compressor determines the pressure level of this part of the system. Generally speaking, it is less expensive to operate at as low a pressure level on the discharge as is consistent with the suction pressure and with the physical characteristics of the refrigerant. Sometimes the cost of the refrigerant and the cost of its replacement on loss dictate that the optimum situation is not determined by the system and refrigerant s physical properties. 

Each system and its particular requirements must be evaluated from a composite of the conditions affecting the refrigerant. After a refrigerant is selected, the accepted design procedure and materials of construction can be applied. 

Figure 12-118A. Common names associated with centrifugal fan components. (Used by permission ASHRAE Handbook and Product Directory, 1979, pp. 3.1. American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc. All rights reserved.) Also see 1996 Edition, HVAC Systems and Equipment.

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