Refrigerant capacity

It has over 40 hmes more refrigerating capacity per unit volume than liquid helium and more than three hmes that of liquid hydrogen. It is compact, inert, and is less expensive than helium when it meets refrigeration requirements. 

The standard unit of measure for refrigeration capacity is known as the refrigeration ton. It represents the amount of heat that must be removed from a short ton (909 kg) of water to form ice ia 24 h. Its value is 3.51 kWt (12,000 Btu/h(= 12.7 MJ/h)). It is conventional to designate a kilowatt of refrigeration as a thermal kilowatt (kWt) to distiaguish it from the amount of electricity (kWe) required to produce the refrigeration. 

The impact of cold GR-S was quite pronounced. The U.S. government edicted that all of the emulsion SBR plants switch to the cold process. This required addition of refrigeration capacity in these plants as well as other significant changes, such as insulation of reactors, improved vacuum to reduce oxygen that retards polymerization, and the heating of latex in blowdown tanks to aid in the disengagement of butadiene when transferred to the flash tanks. 

Positive-Displacement Compressors Reciprocating compressors are built in different sizes (up to about one megawatt refrigeration capacity per unit). Modern compressors are high-speed, mostly direct-coupled, single-ac ting, from one to mostly eight, and occasion-aUy up to sixteen c inders. 

Two characteristics of compressors for refrigeration are the most important refrigerating capacity and power. Typical characteristics are as presented in the Fig. 11-82. 

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

FIG. 11-84 Typical power-refrigeration capacity data for different types of compressors during partial, unloaded operation. 

Air-cooled condensers are used mostly in air-conditioning and for smaller-refrigeration capacities. The main advantage is avauability of cooling medium (air) but heat-transfer rates for the air side are far below values when water is used as a coohng medium. Condensation always occurs inside tubes, while the air side uses extended surface (fiusy... 

It is common that compressor manufacturers provide data for the ratio of the heat rejected at the condenser to the refrigeration capacity as shown in Fig. 11-89. The solid line represents data for the open compressors while the dotted hne represents the hermetic and accessible compresors. The difference between sohd and dotted line is due to all losses (mechanical and elec trical in the electrical motor). Condenser design is based on the value ... 

FIG. 11 89 Typical values of the heat-rejection ratio of the heat rejected at the condenser to the refrigerating capacity. 

Refrigeration capacity and power P curves for the reciprocating compressor are shown in Fig. 11-92. They are functions of temperatures of evaporation and condensation ... 

Condenser performance should be expressed as evaporating effect to enable matching with compressor and evaporator performance. Condenser evaporating effect is the refrigeration capacity of an evaporator served by a particular condenser. It is the function of the cycle, evaporating temperature, and the compressor. The evaporating effect could be calculated from the heat-rejection ratio qc / e -... 

The secondaiy ejector systems used for removing air require steam pressures of 2,5 bar or greater. When the available steam pressure is lower than this, an electrically driven vacuum pump is used for either the final secondaiy ejector or for the entire secondaiy group. The secondary ejectors normally require 0,2-0,3 kg/h of steam per kW of refrigeration capacity,... 

Despite very high adsorbed concentrations, R32 would appear to have a much lower adsorbed refrigeration capacity than ammonia. Butane has even less merit than R32. 

The condition of air or water entering or leaving a coil or heat exchanger Tons of refrigeration capacity Tons of refrigeration capacity extracted Tons refrigeration rejected (at final cooler)... 

Observations of external wet bulb and dry bulb air temperatures or similar assessment of other forms of load may be combined with simple observations of what the plant is doing. If it were using its refrigeration capacity under cold no-load conditions then clearly something is wrong. A common fault is finding the plant calling for... 

Operating costs can be estimated based on statistical analysis of operating costs in existing plants. Costs of waste disposal can be evaluated in the same way as costs for any chemical process since procedures for disposal include, in fact, unit chemical processes and operations. Costs of utilities and maintenance are best assessed based on the company data banks. Typical utility figures per m capacity of reactors in MPPs are 800-1100 kg steam/h, 60-80 kW power, and 7,000-8,000 kJ/h refrigeration capacity. 

One final parameter, occasionally encountered in the literature, is the refrigerant capacity [16], RC, given in Equation 9.5, where T1 and T2 are the positions of the full-width-half-maxima in the - ASM versus Field plots, where T2 < Tv and SM is the maximum value found. 

Refrigeration capacity of the compressors at 10 °C higher than the above minimum temperatures Specification of manufacturer ... 

The evaporator insert consists of a smooth, seamless, stainless steel pipe (AISI316L). The evaporator is divided into four separate refrigerant injection parts with the required refrigerating capacity. 

Fig. 2.29. Refrigerating capacity of liquid nitrogen at different temperatures.

Heat Loads in Cryogenic Systems. In any cryogenic system, the heat load transferred to the cold surface determines the refrigeration capacity required to maintain the low temperature. Analysis has shown that the thermal loads received by a surface at cryogenic temperatures are due to ... 

Single-stage cold heads are available with a refrigerating capacity of 50 W at 50 K. This application would require four such heads (and associated He compressors). From the point of view of both temperature and pumping speed, this is not an appropriate application for a liquid-cryogen-based cryopump. 

Example 9.1 A refrigerated space is maintained at 10(°F), and cooling water is available at 70(°F). The evaporator and condenser are of sufficient size that a 10(°F) minimum-temperature difference for heat transfer can be realized in each. The refrigeration capacity is 120,000(Btu)(hr) 1, and the refrigerant is Freon-12. 

---