Refrigerating effect, measurement

Capacity (Condensing Unit) - The refrigerating effect in Btu/h produced by the difference in total enthalpy between a refrigerant liquid leaving the unit and the total enthalpy of the refrigerant vapor entering it. Generally measured in tons or Btu/h. 

Several 1-kw helium refrigerators have been operated for sustained periods and their performance and operating characteristics have been determined. The measured refrigeration effect of these units has been approximately 10% below calculated and 25% below theoretical level. The discrepancy between the measured and the calculated has not, as yet, been... 

Operating data for the 1-kw refrigerator indicate a value of i , the work input per unit of refrigeration, of 70 with a conventional nonlubricated compressor. The average refrigeration effect per pound of circulated gas, J5, is 12.0. This compares to calculated values of 58 and 16 for E and B, respectively. These differences in the theoretical and measured parameters are due to reduced performance by the compressor, expander, and heat exchanger. The comparison is also affected by the values assumed for the thermodynamic properties of the helium. 

The coefficient of performance, COP, of a refrigeration cycle measures its performance. It is defined as the ratio of the heat absorbed from the cold reservoir (the refrigeration effect) to the work required ... 

Radiation effects, as well as combustion behavior, were measured. LNG and refrigerated liquid propane cloud fires exhibited similar surface emissive power values of about 173 kW/m. ... 

A micro supply curve of conserved energy for a large commercial refrigerator. Each step represents a conservation measure. The numbers above the steps are keyed to the measure descriptions in the legend. Note that measures 1-4 are cost-effective because the cost of conserved energy is less than the energy price. If energy prices rise, then measures 6 and 7 may also become cost-effective. 

Gaseous chemical compounds whose molecules contain chlorine and/or fluorine - such as refrigerants R12, R22 and R134a - will influence the emissions of alkali ions from a surface impregnated with a mixture of KOH and lron(lll)hydroxide and maintained at 800 °C to 900 °C by an external Pt heater. The released ions flow to a cathode where the ion current is measured and then amplified (halogen diode principle). This effect is so great that partial pressures for halogens can be measured down to 10 mbar. 

Effect of Sample Dilution. To determine the effect of sample dilution on impedance measurements, shrimp samples were stored at >2(y C or for 21 d. Frozen samples were used to mimic fr h shrimp while refrigerated samples were used to represent spoilage over time. Duplicate SO-g samples were removed from storage every 7 d and used for impedance analysis. Each sample was removed from the bags, boiled for 5 min, cooled to room temperature, then transferred to a tared blender jar and diluted either 1 1 or 1 10 with sterile deionized, demineralized water. Samples were homogenized for 2 min on high. Controls consisted of water alone. 

Pikal, M.J., Shah, S. The collapse temperature in freeze-drying dependence on measurement methodology and rate of water removal from the glassy phase. Int. J. Pharm. 62,165-186,1990 Thijssen, H.A.C., Rulkens, W.H. Effect of freezing rate on rate of sublimation and flavour retention in freeze-drying, pp. 99-114. International Institute of Refrigeration (HR) (Comm. X, Lausanne), 1969... 

Materials. Styrene (BDH Chemicals Ltd.) was stabilized with 0.002 % t-butyl catechol. The stabilizer was removed by washing successively with 10 % potassium hydroxide solution and water, drying over calcium chloride for 24 hr, and vacuum distilling. The monomer was kept in a refrigerator until required. Effective removal of inhibitor was checked by gas chromatography and by dilatometric measurement of the rate of bulk thermal polymerization at 60 °C this was 0.080 % hr which compares with a literature value (17) of 0.089 % hr . ... 

A thermodynamic measure of the quality of a low-temperature refrigeration and liquefaction system is its reversibility. The second law, or more precisely the entropy increase, is an effective guide to the degree of irreversibility associated with such a system. However, to obtain a clearer picture of what these entropy increases mean, it has become convenient to relate such an analysis to the additional work required to overcome these irreversibilities. The fundamental equation for such an analysis is... 

The effectiveness of a refrigeration cycle is measured by its coefficient of performance. For given values of Tc and TH, the highest possible value is attained by the Carnot refrigerator. The vapor-compression cycle with reversible compression and expansion approaches this upper limit. A vapor-compression cycle with expansion in a throttle valve has a somewhat lower value, and this is reduced further when compression is not isentropic. The following example provides an indication of the magnitudes of coefficients of performance. 

The cryogenic adsorption system was specially developed to measure adsorption isotherms of H2 and D2. This system is equipped with a closed helium cycle two-stage Gifford McMahon refrigerator to operate under cryogenic conditions. The adsorption temperature can be kept constant within 0.03 K at 20 K. Adsorption isotherms are obtained by gas adsorption manometry. This method is based on the measurement of the gas pressure in a calibrated, constant volume, at a known temperature. The dead space volume was calculated from a helium calibration measurement at the temperature of interest. Thermal transpiration effect was calibrated according to the work by Takaishi and Sensui [41]. 

Measurement of the steam or refrigerant flow can provide a good indication of heat duty. If there are multiple users, which cause disturbances to the utility, then a temperature to flow cascade control arrangement should be considered. In such a cascade arrangement, the temperature controller output provides the setpoint for the flow controller. The flow controller minimizes the effect of utility stream disturbances and hnearizes the temperature control loop. 

---