Arithmetic Mean Temperature Research Articles

The maximum coefficient of performance of internally irreversible refrigerators and heat pumps

A class of irreversible refrigeration cycles is investigated to determine the maximum coefficient of performance in the heat pump mode and the refrigerator mode. For the purpose of generality and simplicity of the results, finite-time heat transfer in the condenser and evaporator is expressed in terms of arithmetic mean temperature differences. The generic source of internal irreversibility is measured by a single irreversibility factor which transforms the Clausius inequality into an equality to simplify the cycle model. These optimum cycle performances are obtained as closed form analytical expressions in which the irreversibility factor has been shown to be simply related to the ratio of the actual and endoreversible cycle coefficients of performance.

Finite-time optimum refrigeration cycles

A class of conceptual optimum refrigeration cycles is considered with a fixed overall heat conductance and a specified refrigerant operating temperature range to bound the optimization problems. These cycles deal with maximum refrigeration power, maximum refrigeration load, and maximum heat rejection load for the case of a heat pump. The resulting one degree of freedom problems are solved with a variable arithmetic mean temperature difference in the heat exchangers. The maximum refrigeration power solution yields an analytical closed form optimality rule which constitutes a close lower bound solution to the maximum refrigeration load and maximum heat rejection load problems.

A HEAT TRANSFER CORRELATION FOR ROTARY STEAM‐COIL VACUUM EVAPORATION OF TOMATO PASTE

ABSTRACTThe rate of heat transfer is required in designing and sizing the heat transfer surface necessary for heat exchangers. A heat transfer correlation equation was determined for a rotary steam‐coil vacuum evaporator for concentrating tomato juice at the temperature difference of 120–130°F. A Nusselt‐type dimensionless equation was obtained as follows: hoDt/k = 0.60 XS‐2.5 1 (ρND2c/μ)0.6 2 (cpμ/k)1/3μ/μW)0,14 in which ho is the film coefficient for the product side of coil surface; Dc is the ouside diameter of rotary coil; Dt is the inside diameter of the mixing vessel; k is the thermal conductivity; XS is the solids content in decimal; ρ is the density; N is the speed of the rotary coil; μ is the viscosity; and cp is the specific heat. All fluid properties were evaluated at the arithmetic mean temperature of the bulk fluid and the wall except the μW which was evaluated at the wall temperature. The Reynolds number is in the range of 1–200 and solids content 20–50%.

Comparison of Canadian and Japanese Merchant-Ship Observations of Sea-Surface Temperature in the Vicinity of Present Ocean Weather Station "P," 1927–33

A comparison has been made of sea-surface temperatures obtained by Canadian and Japanese merchant vessels in the vicinity of present Ocean Weather Station "P" (50°N, 145°W) from 1927 through 1933. The Canadian data were obtained by thermograph, the presumably more numerous Japanese data by bucket sample. Both data sets clearly display an annual oscillation. Agreement between the sets is good in spite of differences in data density and in methods of observation and of processing. Characteristics (amplitude, phase) of the annual oscillation are more consistent between the sets than is the arithmetic-mean temperature for the period. Heating of water in the condenser intake is suggested as the cause of a slightly greater (0.3 C) mean for the Canadian observations.

Statistical Prediction Methods for North American Anticyclones

Statistical prediction methods of forecasting the 24-hr movement and change of central pressure of North American winter anticyclones are developed utilizing multiple linear regression analysis. The three predictands obtained are the 24-hr change in central pressure and the eastward and northward displacements. This report is similar in some respects to one conducted by Veigas and Ostby relating to U. S. east coast cyclones. The dependent data consist of observations of 150 anticyclones. A moving coordinate system is employed: the predictor information is measured at certain predetermined grid points relative to the system center rather than at fixed geographical positions. Readily measured meteorological parameters are selected for the input data. These include point values of surface pressure, surface temperature, 500-mb height and their 24-hr changes; and the arithmetic mean temperature of the layer from the surface to the 500-mb level. Several different sets of regression equations are obtained for each predictand by slight modifications in the predictor-selection criteria. These regression equations are tested on a sample of 50 independent equations, and the per cent reductions of variance resulting from each method are compared.

Investigation of heat transfer in the turbulent flow of liquid metals in tubes

Experiments were carried out on two different pieces of apparatus~ On one setup mercury was used, on the other lead and a eutectic lead--bismuth alloy (43.5%pb+ + 56, 5~ Bi). Experiments with Mercury. Before being put into the apparatus, P-3 type mercury (99.9% pure) was passed through a chamois filter. The experimental apparatus was a " tube-intube" type heat exchanger made from 1KhlSN9T steel. The mercury flowed inside a tube with diameter of 17 • 12.5 ram. The heat given off in the pump and loop was carried off from the mercury by water flowing in an annular space 4.5 mm wide. Heat exchange over a length of 760 mm between the mercury and water was realized on the counterflow principle, with the mercury moving from the bottom upward. Before entry into the working part of the tube, allowance w~as made for a hydrodynamic stabilization interval, equal to 40 diameters. To reduce heat losses over the parts of the tube prior to the heat exchanger" and after it, compensation heaters were mounted on those parts. The temperature of the heat-exchange surface between the mercury and water at the inlet and outlet were measured by thermocouples. The power of the heat exchanger was determined from the mass flow rate and cooling of the mercury and was controlled according to the mass flow rate and heating of the water. The arithmetic mean temperature, calculated from the readings of thermoeouples placed at the inlet and outlet of the heat exchanger, was assumed as the mean temperature of the mercury. The mean temperature of the heat-exchange surface was determined by planimetry of the temperature profile over the length of the heat exchanger, taking into account corrections for depth to which the thermocouples were built in.