Performance evaluation indexes for quick-freezers

The idea of evaluating refrigeration equipment and the practical performance evaluation indexes of quick-freezers, namely energy utilisation efficiency, efficiency of airflow organisation, and uniform coefficient of airflow organisation, were suggested to compare the performances and to diagnose the existing problems for freezers. Based on the measurement, the performance evaluation indexes were applied to the performance analysis and the improvement for LSJ1500 spiral quick-freezer, the problem with LSJ1500 spiral quick-freezer was detected and the improved spiral quick-freezer LSJ1500A with the higher performance was achieved. It was proved that the suggested evaluation indexes are the effective tools in the food refrigeration industry.     

Appraising the flammability hazards of hydrocarbon refrigerants using quantitative risk assessment model. Part II. Model evaluation and analysis

Hydrocarbon refrigerants present are fire and explosion hazards due to their flammability. This paper describes a quantitative risk assessment (QRA) model to evaluate the potential for ignition when hydrocarbons are employed in stationary refrigeration and air-conditioning equipment. QRA enables examination of the effects that design, installation of equipment and external conditions on the frequency of ignition of the refrigerant and its consequences. Part I of this study presents the modelling approach for ignition frequencies, sub-models for refrigerant leakage and development of flammable concentration, and the associated consequences, being overpressures and thermal radiation. Part II provides recommended empirical input data and example results generated from the model.     

Use of hydrocarbons as drop-in replacements for HCFC-22 in on-farm milk cooling equipment

Many refrigeration systems on New Zealand dairy farms use HCFC-22 which is being phased out by 2015. Both laboratory and on-farm trials were undertaken to investigate hydrocarbons as drop-in replacements to HCFC-22 in milk silo refrigeration systems. A mixture of propane and ethane (Care-50) reduced energy use by 6–8%, and had similar system cooling capacity relative to HCFC-22. With propane (Care-40), energy use decreased by 5% but cooling capacity was 9% lower. The retrofits were simple and low cost because no alterations to the systems other than change in refrigerant and appropriate safety labelling and documentation were made. For most farms, the outside refrigeration system location and small charge mean that hydrocarbons could meet NZ standards for safe use of refrigerants. The low retrofit cost, improved energy efficiency, low environmental impact, mineral oil compatibility, similar cooling capacity and controllable flammability risks mean that the propane–ethane mixture is an attractive replacement for HCFC-22 on NZ dairy farms.     

Equipment design and installation features to disperse refrigerant releases in rooms—part II: determination of procedures

There is always a risk of leakage of refrigerant into a room that refrigeration and air conditioning equipment occupies. Mitigation of build-up of flammable concentrations from leakage through appropriate equipment construction and installation criteria minimises the potential for ignition. This paper is the first part of an investigation into design and installation measures to disperse leaked flammable refrigerant. It mainly describes the experiments and provides an analysis of the data. The paper describes a purpose built test facility, which was used to carry out experiments to study the dispersion of carbon dioxide to simulate leaked refrigerant. By measuring carbon dioxide concentrations and making flow visualisation, the effects of parameters such as equipment airflow and installation height were observed. The observed trends provide guidance for designing refrigeration and air conditioning equipment, which helps to ensure rapid dispersion of flammable concentrations in the event of a leak of flammable refrigerant. A second paper (Part II) discussed the development of numerical correlations, which are used in the resulting design procedure.     

Comparison of R-290 and two HFC blends for walk-in refrigeration systems

To help provide a clear understanding of the relative performance potential of HFCs (R-404A and R-410A) as compared to R-290 for walk-in refrigeration systems representing direct expansion commercial refrigeration systems with small charge, an experimental evaluation of the three refrigerants was investigated. To compare the environmental impact of refrigerants over the entire life cycle of fluid and equipment, including power consumption, the life cycle climate performance (LCCP) of the three refrigerants were evaluated based on measured data. The estimated LCCPs at various emission rates indicate that the LCCP of R-290 is always lower than that of R-404A. The LCCP of R-410A is lower than that of R-290 as long as the annual emission is kept below 10%. It was concluded that R-410A has less or equivalent environmental impact as compared to R-290 when safety (toxicity and flammability), environmental impact (climate change), cost and performance (capacity and COP) are considered.     

Electronic energy saving in refrigeration equipment

Electronic technology is now available for use on most types of refrigeration equipment. Loss reduced motors (LRMs), using development of technologgy originally invented for the NASA space programme, tackle a major area of inefficiency. Refrigeration engineers are well aware of the inefficiency of running the compressor drive motor at part load, and in central plant have minimized the problem by using several motors with load switching to match the actual load requirement. However, in smaller single compressor equipment no solution has yet been proposed. LRMs can provide the solution and, moreover, are etremely cost-effective with installation paybacks well within two years.     

Experimental verification of a mathematical model for simulation of industrial refrigeration plants

A mathematical model, proposed for simulation of food refrigeration processes, was tested against experimental data collected in a New Zealand meat processing plant which had a total refrigeration capacity of 2.5 MW. Predicted air temperatures in freezing and chilling operations followed the same trends as measured data. Differences were shown to be more attributable to uncertainties in data than to deficiencies in the formulation of the mathematical model. The model is considered suitable for use in simulation of a wide range of food refrigeration processes. Such simulations provide useful information about plant performance that cannot be obtained by steady state analysis. Predictions were worst for short times immediately following step changes in plant operation; should more accurate simulation of these periods be required a different form of mathematical model is needed.     

Evaluation of standing-wave thermoacoustic cycles for cooling applications

The most promising applications for standing-wave thermoacoustic cooling were investigated from the perspective of the ratio of coefficient of performance (COP) to the reversible COP or COPR. A design optimization program based on the thermoacoustic simulation program known as DELTAE was developed. The program was applied to two standing-wave thermoacoustic cooler configurations in order to determine the best possible COPRs for various temperature spans between hot-side and cold-side stack-end temperatures. It was found that the COPR of standing-wave thermoacoustic coolers increases with temperature span and reaches a maximum for temperature lifts around 80 °C. Analysis of the results and the losses clearly shows that the efficiency of these systems may be good for refrigeration, but not for air-conditioning and cryogenic cooling. The COPRs determined from measurements for various thermoacoustic coolers developed so far show similar trends, and generally support the optimization results.     

Stress corrosion cracking in refrigeration systems

It is generally understood that stress corrosion cracking can occasionally affect the high pressure vessels in ammonia refrigeration systems, but the nature of the problem is often mis-represented in design codes, safety standards and textbooks and ways in which the initiation of stress corrosion can be prevented are ignored. It is also not appreciated that stress corrosion can also affect low pressure vessels and pipework in ammonia systems, and copper pipework in fluorocarbon refrigeration systems.This paper provides an overview of published literature on stress corrosion cracking and then presents some recent case study material illustrating various ways in which stress corrosion has arisen in practice. The conclusions will provide guidance for design engineers and equipment owners on eliminating stress corrosion cracking and on dealing with it if it arises.     

An experimental investigation on performance of bubble pump with lunate channel for absorption refrigeration system

An experimental research on the performance of the bubble pump for absorption refrigeration units was made. The bubble pump provides the drive for the absorption cycle and is a decisive component of the absorption refrigeration unit. The bubble pump's property determines the efficiency of the absorption refrigeration system. A continuous experimental system with different size of bubbles pumps were designed, constructed and successfully worked. The experiments were performed by changing some of the parameters affecting the bubble pump performance. The experimental results shows that the performance of the bubble pump depends mainly on the driving temperature, the solution head and the combining tube diameters. With the suitable size of section area of the pump tubes the net elevating height of solution is 2.5 times as high as the solution submergence. The lunate channel has several outstanding characteristics, such as low starting temperature (minimum 68 °C), wide operating temperature range and lower requirement for vacuum condition (under 10 kPa). Then the elevating capability of the bubble pump with lunate channel is much better than others currently. It would provide well foundation for practical applications.     

Real-time measurement of mixing ratio of refrigerant/refrigeration oil mixture

The mixing of refrigeration oil with refrigerant in a refrigeration cycle has great influence on cycle performance. A sampling method is the most general way to measure the mixing ratio of refrigerant and refrigeration oil. Since the sampling method is time-consuming and reduces the amount of refrigerant and oil in the cycle, a real-time measurement is desirable. In this study, a refractive index measurement was applied to measure the mixing ratio of refrigerant/oil mixture. A laser displacement sensor was used to detect any change in optical path which results from changes of the refractive index of refrigerant/oil mixture. For the practical application of real-time measurement of the oil circulation ratio (OCR) in the refrigeration cycle, a correlation between the refractive index and the mixing ratio was developed. In addition, the changes of the refractive index in a range of a few percentages of the oil concentration and under subcooled conditions were measured. Finally, a transient measurement of the OCR in a practically operating refrigeration cycle was carried out successfully.     

A theoretical study of a novel regenerative ejector refrigeration cycle

There has been a demand for developments of the ejector refrigeration systems using low grade thermal energy, such as solar energy and waste heat. In this paper, a novel regenerative ejector refrigeration cycle was described, which uses an auxiliary jet pump and a conventional regenerator to enhance the performance of the novel cycle. The theoretical analysis on the performance characteristics was carried out for the novel cycle with the refrigerant R141b. Compared with the conventional cycle, the simulation results show that the coefficient of performance (COP) of the novel cycle increases, respectively, by from 9.3 to 12.1% when generating temperature is in a range of 80–160 °C, the condensing temperature is in a range of 35–45 °C and the evaporating temperature is fixed at 10 °C. Especially due to the enhanced regeneration with increasing the pump outlet pressure, the improvement of COP of the novel cycle is approached to 17.8% compared with that in the conventional cycle under the operating condition that generating temperature is 100 °C, condensing temperature is 40 °C and evaporating temperature is 10 °C. Therefore, the characteristics of the novel cycle performance show its promise in using low grade thermal energy for the ejector refrigeration system.     

Discussion of the feasibility of the Einstein refrigeration cycle

A careful modelling of the thermodynamic properties of the water–ammonia–butane system, the working fluid mixture used in the Einstein cycle, with the Patel–Teja cubic equation of state is performed. Numerical simulation is used to investigate the feasibility limits of this refrigeration cycle. Two modified configurations of the cycle are considered. A conflict between the evaporator and the condenser/absorber operating conditions is noted. The condenser/absorber operation needs a higher system pressure, which limits the refrigeration temperature in the case of air-cooling. On the other hand, the condensation of ammonia and the presence of a small quantity of water in the evaporator limit also the refrigeration temperature. In the case of a water-cooled machine, with a condenser/absorber temperature of 30 °C, the cycle COP reaches 0.19 which is still low.     

A new three-parameter cubic equation of state for refrigeration engineering calculations

A new three-parameter cubic equation of state is proposed in which the repulsion pressure term of the semiempirical van der Waals equation has been modified based on the hard-sphere potential and a functional form similar to Redlich-Kwong attraction term is adopted for the attraction term. All three parameters are treated as functions of temperature. For the purpose of examining the applicability of the new equation, it was applied to describe the thermodynamic properties of difluoromethane (R-32) and pentafluoroethane (R-125). It has been found that the essential thermodynamic properties are represented by the new equation as accurately as a conventional far-complicated modified Benedict-Webb-Rubin equation in the working range of refrigeration equipment. The new cubic equation was also compared with the Peng-Robinson equation and the Carnahan-Starling-De Santis equation.     

Hydrocarbons as refrigerants in small heat pump and refrigeration systems – A review

Due to the concern for the effects of the release of HFC refrigerants on the global environment caused by the high global warming potential of these substances, there is a large interest in Europe and elsewhere for the use of hydrocarbons as refrigerants. This article presents a comparison of the properties and performance of hydrocarbons as refrigerants in small-size heat pump and refrigeration systems (<20 kW cooling). A listing of several commercially available systems is also presented. The designs, safety precautions and performances of some of these systems are described.As a general conclusion, it is shown that using hydrocarbons will result in COPs equal to, or higher than, those of similar HFC systems. It is also shown that components suitable for hydrocarbon systems are available on the market, even though the number of large-size hermetic compressors is limited. A major concern, which should not be taken lightly, is the safety issue. Reduced charge through indirect systems and compact heat exchangers, outdoor placing of the unit, hydrocarbon sensors and alarms and forced ventilation are all steps which may be applied to reduce the risks under normal operation.     

Performance of a metal hydride cooling system

The performance of a single-stage metal hydride cooling system working with the ZrMnFe/MmNi_4.5Al_0.5 pair has been evaluated based on heat transfer and reaction kinetics considerations. Results show that the initial and operating costs of the system have to be minimized by optimizing the bed thickness, effective thermal conductivity and overall heat transfer coefficients. Of the three operating temperatures (heat source, heat sink and refrigeration temperatures), refrigeration temperature has the greatest influence on system performance, as desorption during the refrigeration process normally controls the cycle time and specific alloy output. However, heat source and heat rejection temperatures assume importance at high refrigeration temperatures. The average COP of the above system lies between 0.45 and 0.50.     

Performance parameters for the design of a combined refrigeration and electrical power cogeneration system

This paper discusses the conservation of energy in a cogeneration system. A steam power cycle (Rankine) produces electrical power 2 MW and steam is bleeded off from the turbine at 7 bar to warm a factory or units of buildings during the winter or to supply a steam ejector refrigeration cycle to air-conditioning the same area during the summer. In the summer this system can be as alternative solution instead of absorption. Certainly the ejector refrigeration unit is more economical than absorption unit. The ratio of electrical power/heat is varied into the region (0.1–0.4) and the evaporator temperature of the ejector cycle is varied into the region (10–16 °C). A computer program has been developed for the study of performance parameters of the cogeneration system.     

Generalized model for the simulation of food refrigeration. Development and validation of the predictive numerical method

A generalized mathematical model was developed to simulate food refrigeration in air. The model takes into account surface water evaporation. It allows food physical properties to be considered as functions of temperature and/or composition, while providing means for including internal heat generation, composite materials (for instance, flesh and skin) and time-varying external temperature and humidity. Wetted surfaces and packaging can also be accounted for by the model, which can be used for spheres, infinite or finite cylinders, slabs. The numerical method was developed using the Crank-Nicolson scheme, and compared with exact analytical solutions as well as with experimental data on the refrigeration of various foods.     

Analysis of room temperature magnetic regenerative refrigeration

Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 °C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed.     

Simulation of a solar driven aqua-ammonia absorption refrigeration system Part 1: mathematical description and system optimization

A theoretical thermodynamic analysis was performed on an aqua-ammonia refrigeration (AAR) cycle coupled to a solar water heating system using CPC-collectors and augmented with auxialiary energy. Thirteen AAR cycles were considered in the search for the maximum coefficient of performance. Also investigated was the exergetic performance of the AAR cycle. The adopted temperature and mass flow rate control strategy on the storage tank-auxiliary heater-AAR generator loop ensured operation of the refrigeration systems at design conditions. Consequently, the ratio between the pumps' electrical power and the designed evaporator heat transfer rate was kept to a minimum.