Refrigeration Machine Research Articles

Oil Concentration Measurement In Saturated Liquid Refrigerant Flowing Inside A Refrigeration Machine

An ultrasonic device was calibrated to measure in situ and in real time the polyol ester oil (POE) concentration of the refrigerant liquid R 410A. The first part of this paper is devoted to the properties of the mixture, to the effects of the presence of oil on the speed of sound in the liquid phase and to the calibration and validation procedures carried out with a saturated liquid refrigerant. In order to have a number of calibration points that is not too large, it is necessary to maintain the mixture as close as possible to saturation conditions, which constrains the choice of the location of the sensor on the installation investigated. In the second part, the first results obtained on this installation are presented. It appears that the speed of sound in the POE / R 410A mixture is a strong function of the temperature and oil concentration, as was expected, but it also significantly depends on the pressure. Consequently, if the use of a sensor in a sub-cooled area is considered, additional calibration and validation procedures are necessary. This paper was presented at the ECOS'00 Conference in Enschede, July 5-7, 2000

Experimental investigation on a three-fluid absorption refrigeration machine

This paper investigates the performance of a domestic-size three-fluid absorption refrigeration system. The boiler, lift tube, vapour-liquid separator and the heat exchanger were modified, while maintaining the same principle of operation. The unit was charged with a recommended concentration of 34 per cent aqueous ammonia solution containing the right amounts of sodium dichromate and caustic soda. Hydrogen was charged, the pressure of which was increased from the lowest of 7.5 bar to the highest of 27.5 bar in steps of 2.5 bar. For each of these hydrogen pressures, data were recorded using different power supplies of 260, 315 and 370 W. The data recorded were in the form of total pressure in the system and temperatures taken from strategic points on the unit. The data collected from the experiment are shown in the form of temperature response graphs to facilitate easy comparison within the various working conditions. Although there are no performance characteristics available from the manufacturer, it is believed that the modified components have improved the time response of the unit.

00/01072 Technico-economic simulation and optimization of a compression refrigerating machine

00/01072 Technico-economic simulation and optimization of a compression refrigerating machine

Some Observations on Carnot Cycle as the Genesis of the Heat Pipe and Thermosyphon

The purpose of this article is to show that the limiting case of the Carnot vapor cycle with a temperature difference of only a few degrees between hot and cold reservoirs, can be interpreted as the idealized heat pipe (Carnot heat pipe) for transporting heat, utilizing the boiling condensation processes. The observation of the basic relationship (definition of absolute temperature) Q1/ Q2 = T1/ T2 for Carnot cycle reveals that the Carnot heat engine becomes a heat transfer device when the temperature difference is very small. The Clapeyron—Clausius equation for the infinitesimal (differential) Carnot vapour cycle becomes the genesis for the operating principle of the heat pipe and two-phase thermosyphon. The Carnot heat pipe is independent of the system and working fluid. Within the context of the idealized Carnot heat pipe, it is shown that thermodynamics, fluid mechanics and heat transfer (thermal sciences) are closely coupled in heat pipe operation. The present observation is based on various expositions of classical thermodynamics available in the historical literature. It is of interest to note that the Carnot vapor cycle provides the basic principle for heat pipe and two-phase thermosyphon in addition to the classical cases of heat engine, refrigeration machine and heat pump.

Performance Characteristics of Hybrid Cycle Combined Absorption Heat Transformer and Absorption Refrigerating Machine

Performance Characteristics of Hybrid Cycle Combined Absorption Heat Transformer and Absorption Refrigerating Machine

An irreversible-thermodynamic model for solar-powered absorption cooling systems

The ideal three-heat-reservoir cycle with constant internal irreversibilities and external heat transfer irreversibilities is used to model the absorption refrigeration machine of a solar operated absorption cooling system. Analytical expressions are obtained for the variation of the entropy transfer with storage tank temperature and the variation of the coefficient of performance (COP) with the cooling capacity of the plant. These expressions give the operating points for the maximum cooling capacity and the maximum COP. The results for ideal irreversible cycles are compared with those obtained by detailed simulation of the absorption cooling system. The effect of internal and external irreversibilities on the second-law efficiency of the plant is examined. The ideal cycles that include internal and external irreversibilities are found to give realistic limits and trends for the cooling capacity and the COP of solar powered absorption cooling systems.

An air and refrigeration machine oil console fire

An incident due to the ignition of a fire at the top of an oil console of air and refrigeration compressors caused the shut down of an ammonia plant for five days. The cause: failure of refrigeration compressor seals resulted in the lowering of the oil level in the console. This caused cavitation in the oil pump suction resulting in high vibration in the pump discharge piping which led to the snapping of a 3/4'' diameter interconnection line weld joint. Oil splashing from the snapped joint to the nearby steam header with improper insulation caused a serious fire above the oil console.

Technico-economic simulation and optimization of a compression refrigerating machine

This study is among the several works conducted by the authors with regard to technico-economic optimization of refrigerating machines. The most difficult part is the gathering of technico-economical data and the development of cost correlations. The tool presented in this work will be used for an optimization based on irreversibilities and cost minimization, since irreversibilities have a direct impact on the operating cost.

Flammability Measurements of Difluoromethane

Abstract Difluoromethane (CH2F2, or R-32) is a candidate to replace ozone-depleting chlorofluorocarbon refrigerants. Because CH2F2 is flammable, it is necessary to assess the hazard posed by a leak in a refrigeration machine. The currently accepted method for determining flammability, ASTM E 681 has difficulty discerning the flammability boundary for weak fuels such as CH2F2. This article describes an alternative approach to identify the limits of flammability, using a twin, premixed counterflow flame. By using the extinction of an already established flame, the point dividing flammable from nonflammable becomes unambiguous. The limiting extinction mixture changes with stretch rate, so it is convenient to report the flammability limit as the value extrapolated to a zero stretch condition. In the burner, contoured nozzles with outlet diameters of 12 mm are aligned counter to each other and spaced 12 mm apart. The lean flammability limit of CH2F2 in dry air at room temperature was previously reported by the authors to be a mole fraction of 0.14, using the twin counterflow flame method. In the current study, relative humidity was not found to affect the lean limit. Increasing the temperature of the premixed fuel and air to 100°C is shown to extend the flammability limit in the lean direction to 0.13. The rich limit of CH2F2 found using the counterflow method is around 0.27. The uncertainties of the measurements are presented and the results compared to data in the literature. [S0022-1481(00)02501-9]

An experimental study of an ejector cycle refrigeration machine operating on R113: Etude expérimentale d'une machine frigorifique à éjecteur au R113

This paper discusses an ejector cycle refrigeration machine that can use a wide range of refrigerants including halocarbons. The feature of such a system is the possibility of using a low grade heat source such as solar energy and waste heat to operate the system. A theoretical analysis was carried out to select a suitable refrigerant for the system. The influence of boiler, condenser and evaporator temperatures on system heat transfer is investigated experimentally under different operating conditions. The experimental machine uses R113 as a working refrigerant.

98/04155 P-h and enthalpy-concentration charts for quantitative evaluation of working fluids of absorption type refrigeration machines

98/04155 P-h and enthalpy-concentration charts for quantitative evaluation of working fluids of absorption type refrigeration machines

Experimental investigation of solar concentrating collectors in a refrigerant ejector refrigeration machine

This paper presents an experimental study of energy output and efficiency of solar collectors in a refrigerant ejector refrigeration machine using R113 as the refrigerant. Based on a theoretical study, the oil transformer is used as a working fluid in the solar system. The concentrating collectors show encouraging results for operating the system. The maximum collector efficiency was 20%. The system can be used for both cooling and heating purposes. © 1997 John Wiley & Sons, Ltd.

Thermodynamic analysis of combined diesel engine and absorption refrigeration unit—naturally aspirated engine with precooling

A procedure is presented for the thermodynamic analysis of a combined naturally aspirated diesel engine with precooling and absorption refrigeration machine. With the aid of the laws of thermodynamics, the amount of net work, efficiency and the temperature of the exhaust gases of a diesel engine (ideal cycle) as a function of pressure ratio and temperature ratio of the cycle have been calculated. The amount of energy required for precooling and the amount of cooling capacity available which can be used for air-conditioning purposes are calculated.

Characteristics of Voorhees refrigerating machine with hermetic piston compressor producing refrigeration at one or two temperature levels

Research on the operation of the refrigerating machine working on the Voorhees cycle which permits two-stage compression in a single-cylinder compressor has been carried out. The purpose of this research was to study the possibilities of using the Voorhees machine in a domestic refrigerator for production of refrigeration at one or two temperature levels. The experiments were carried out on the basis of a small hermetic lubricated compressor with a low refrigerating capacity operating on a commonly used R12 and natural refrigerant isobutane R600a. The improved refrigerating capacity in the Voorhees cycle with isobutane makes the latter an alternative substitute for conventional refrigerants. Some peculiarities in the operation of a hermetic piston compressor as part of the Voorhees refrigerating machine have been revealed. They require the use of a compressor developed specially for the Voorhees cycle. The method of optimizing the cycle parameters for a one temperature refrigerating system is suggested in this paper. The research carried out proved that the optimum intermediate pressures of the Voorhees refrigerating machine producing refrigeration either at one or two temperature levels are different.

Thermodynamic analysis of combined diesel engine and absorption unit—turbocharged engine

This paper describes the effects of pressure ratio and temperature ratio of the turbocharged diesel engine on the amount of net work and efficiency of the engine, and also the amount of energy available in the exhaust gases, which can be used to drive an absorption refrigeration machine. For an ideal cycle, the combined cycle is examined based on thermodynamic laws and the acceptance envelope identified. Then, based on the correlations derived, graphs have been plotted for the net work, efficiency and the amount of cooling load available in exhaust gases as a function of pressure ratio and temperature ratio of the cycle.

Thermodynamic analysis of combined diesel engine and absorption unit-turbocharged engine with intercooling

Large diesel engines are well suited for power generation in remote areas, their high thermal efficiency and relative insensitivity to high ambient temperatures make them suitable for use in desert and tropical climates. The exhaust gases from such installations represent a significant amount of thermal energy that can be put to beneficial use. This paper explores the utilisation of the exhaust gases from a turbocharged and intercooled engine as an energy input to a vapour absorption refrigeration machine that is used primarily to cool the engine charge air in an intercooler. The influence of the engine configuration and performance parameters on the performance of an ideal system is investigated.

Influence of the new refrigerant thermodynamic properties on some refrigerating turbocompressor characteristics

Comparison of the main geometrical and operating parameters of centrifugal compressors working with various refrigerants is realised in this paper. The interdependence between the centrifugal compressor pressure ratio, compression work, impeller peripheral speed, Mach number, compressor capacity, impeller diameter and width, speed of rotation, and refrigerant molecular mass, normal boiling temperature and specific volumetric cooling capacity for various refrigerants are shown and discussed. The flow phenomena in the turbocompressor flow field, caused by high Mach number and high pressure ratio, are analysed. Some theoretical observations for the influence of the substitute of the refrigerant on the turbocompressor performance characteristics are presented. The possibilities for the replacement of the refrigerant in the existing refrigerating machines are discussed.

Flow and thermodynamic characteristics of energy separation in a double-circuit vortex tube — An experimental investigation

Experimental investigations were made into the vortex energy separation effect of gas flux in tubes known as the Ranque effect. Technical applications of the results are considered. Unlike traditional energy separation tubes, so-called double-circuit vortex tubes were chosen that allowed the creation of a refrigeration device with high thermodynamic efficiency. Different thermodynamic and gas dynamical aspects of the processes taking place in the scheme developed are discussed taking into account the modern vortex interaction hypothesis. The possibility of constructing a double-circuit vortex tube refrigeration machine as efficient as a gas expansion system is demonstrated.

Experimental report on the reliability of ammonia-water absorption chillers

The analysis of a large amount of data on the failures of absorption refrigeration machines of the ammonia-water type was carried out. The data derive from the records of a 10-year maintenance contract under which every machine was installed. The records were computerized for the period 1989–1992, and they refer to sales starting from 1980 (i.e. to 73 778 machines). The failures are classified, identifying the most serious (generator and solution pump). The rate of early failures is rather high, but the failures are generally minor and easily repaired. The production quality was not constant, with a very bad year in 1984. The failure rate is evaluated for the first 10 years of life of the equipment. In general terms, one machine in two does not require any intervention during that period.

Performance limits of absorption cycles with external heat-transfer irreversibilities

Heat-transfer irreversibilities are included in the analysis of the ideal absorption refrigeration cycle working with three heat reservoirs. Expressions arc obtained for the COP at a given cooling capacity and the COP at the maximum cooling capacity in terms of four non-dimensional design and operating variables. The condition for the maximum cooling capacity depends only on the temperature ratios. The predictions of the model are compared with data obtained by detailed computer simulation of single-stage and double-stage absorption refrigeration machines. The predicted variation of the maximum cooling capacity with reservoir temperatures follows the same linear variation obtained by computer simulation. The COPs of single-stage and double-stage machines lie between the predicted COP at the maximum cooling capacity and the COP at the given cooling capacity. The COPs of real machines are much closer to the predicted values than to the COP of the reversible cycle operating between the same three heat reservoirs.