A. Koyfman, M. Jelinek, A. Levy, & I. Borde
Mechanical Engineering Department, Ben-Gurion University of the Negev,
P.O. box 653, Beer-Sheva 84105, Israel

EQUILIBRIUM TEMPERATURES AND PERFORMANCE OF TRIPLE EFFECT SERIES FLOW WATER-LITHIUM BROMIDE ABSORPTION REFRIGERATION SYSTEM

A.A. Dhas and M.P. Maiya
Refrigeration and Air Conditioning Laboratory, Department of Mechanical Engineering
Indian Institute of Technology Madras, Chennai – 600 036, India

The engineering profession demands more energy efficient systems and the triple effect water-lithium bromide vapour absorption refrigeration system is under active development which is expected to be about 25% more efficient than that of the double effect system. The equilibrium temperatures at low and medium pressure generators are obtained by energy balance and simultaneously the system performance is also predicted. The equilibrium temperatures and performance maps are generated for varying operating conditions. Both the equilibrium temperatures are found to increase with increase in supply heat and condensing temperatures, and decrease in heat exchanger effectiveness. Sub-optimal performances are observed at off-design conditions. The analysis is useful in guiding the absorption system to obtain the best performance at all operating conditions.

H. Yanagi¹, H. Suzuki¹, K. Iwase¹, N. Ishizuka¹, F. Komatsu¹, and K. Sengoku¹
M. Kanamori² and M. Hiramatsu^2
1  Advanced Tech. lab., Mayekawa Mfg. Co., Ltd., 2000 Tatsuzawa,
Moriya-Machi, Kitasooma-Gun, Ibaraki-Pref. 302-0118, Japan
²  Electrical Eng. Dept., The Chubu Electric Power Co., Inc,
20-1 Kitasekiyama, Ohtaka -Machi, Midori-Ku, Nagoya-Shi, Japan

M. Izquierdo¹, M. Venegas², M. de Vega² and P. Rodriguez^2
1 Instituto de Ciencias de la Construcción Eduardo Torroja (CSIC).
C/ Serrano Galvache s/n, 28033 Madrid
² Unidad Asociada de Investigación en Energia y Medioambiente del CSIC y la UC3M,
Avda. Universidad 30, 28911 Leganés, Madrid

The use of low temperature heat (belween 50°C and 90°C) is studied to operate absorption machines in two different applications : refrigeration and heat pump. A double stage absorption machine is modelled and simulated. Results are compared for two different absorbent-refrigerant pairs : H2O-NH3 and LiNO3-NH3, in order to determine which one is the more adequate for both applications. The results obtained show that in the refrigeration cycle, evaporating at –15°C, condensing at 40°C and generating refrigerant vapour at 90°C, the H2O-NH3 solution operates with a COP of 0.29 and the LiNO3-NH3 so/ution with a COP of 0.32. The results are presented for evaporator temperatures varying belween –5°C and –40°C and condensation temperatures ranging from 15°C to 45°C. For the absorption machine operating as a heat pump, condensing at 50°C, evaporating at O°C, and generating refrigerant vapour at 90°C, the LiNO3-NH3 solution reaches a COP of 1.32 and the H]O-NH3 so/ution a COP of 1.24. For the heat pump cycle the results are presented for evaporator temperatures belween O°C and 15°C. The minimum temperature required in the generators for both cycles, refrigeration and heat pump. are also shown.

H.M. Sabir
School of Engineering, Kingston University, Friars Avenue, London SW15 3DW, UK

The paper describes a novel heat driven refrigeration/heat pump cycle. The cycle marries the Vapour Resorption cycle and the GAX cycle. Detailed technical description of the combined GAX-R cycle is given and the expected COP is calculated to first approximation. The cycle reduces irreversible losses and offers improved performance in a single effect architecture.

Vikas Patnaik
Engineering Technology & Quality, The Trane Company, La Crosse, WI 54601, USA

A preliminary stage in the design of chillers is allocation of heat and mass transfer surface area between the various components. The allocation is based upon transport performance, pressure drop, component size and, last but not least, cost considerations. This paper presents a technique to optimize the area distribution, using a variation of dynamic programming. Absorption chillers with shell-and-tube components are considered for illustrative purposes, but the technique can be applied to any power or refrigeration system and component configuration.

Ch. Mostofizadeh, D. Bohne, Ch. Mergardt
Institut für Energie- und Verfahrenstechnik, An der Karlstadt 6, 27568 Bremerhaven, Germany

The possibility of using district heating for cold production for lower cold capacities was investigated. A function model with a cold capacity of 50 kW was set up which operates according to the principle of single-effect absorption and manages with low supply temperatures (80°C). A compact layout was achieved by installing plate packages. Numerous measurements show that the layout examined displays a stable operating behaviour and achieves a COP factor of about 0.8. At part-load >20% the COP factor is on the order of magnitude of 0.6.

ENERGY ANALYSIS OF INDUSTRIAL AMMONIA/WATER ABSORPTION REFRIGERATION PLANTS USING DATA VALIDATION

J.C. Bruno, M. Bourouis and A. Coronas
CREVER, Universitat Rovira i Virgili, Autovia de Salou, s/n, 43006 Tarragona, Spain

The objective of this paper is to propose a methodology to analyse the performance of existing industrial absorption refrigeration plants in order to determine its working conditions and evaluate its performance. To achieve this objective it is necessary to overcome the lack of the suitable instrumentation for energy analysis and to treat the raw data.
The proposed methodology to face these problems is basically based in three steps. First, the considered refrigeration plant is analysed to decide about the variables that are need to be known. The second step, is to collect online data from the selected and additionally installed measuring devices taking advantage of the new possibilities that offers the bus communication technology. In a third step, the collected data is treated using a Data Validation program developed in our research group. This software is used for data reconciliation and to detect gross errors using a procedure based on the MIMT method. For the data reconciliation purpose, the refrigeration plant is modelled as a non-linear problem defined by mass and energy balances solved using a Sequential Quadratic Programming approach. Finally, the performance of the plant is calculated using the validated data and in terms of COP, effectiveness and energy transferred in each component.
The proposed methodology has been validated in a refrigeration plant of 1 MW integrated in a gas engine based cogeneration system of a food industry situated in the north of Catalunya (Spain). The results highlight the suitability of the proposed combined data acquisition and validation system approach specifically devoted to absorption refrigeration plants to evaluate its performance.

Fredrik Setterwall, Dmitrey Glebov, Bo Wikensten
Dep. Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, Sweden

A 1,15 MW absorption chiller utilizing down to 70^oC hot water from district heating system have been developed and installed at Chalmers Technical University in Gothenburg, Sweden. The main features of the chiller is that the chiller is flexible with respect the geometrical configuration thus being adaptable to the conditions of the customer. The surfaces for heat and mass transfer are of lamella type instead of the commonly used tubular heat exchangers. As heat transfer additive 2-methyl-pentanol is used instead of 2-ethyl-hexanol.
The projected cooling demand is met whereas the coefficient of performance (COP) is lower than expected. The reason for this is the high rate of circulation of lithiumbromide solution between absorber and generator. Also the solution heat exchanger plays an important role for the low efficiency.
During the cooling season 2001 an optimization of the chiller will be performed. It is assumed that this will lead to higher COP and still sufficiently high cooling capacity of the chiller.

Lei Wang¹, Zhen Lu^2
1 Dong Hua University, Environment Science and Engineering Institute, Shanghai, 200051
² Shanghai Jiaotong University, Institute of refrigeration and cryogenics, Shanghai, 200030

Part load is a usual operation condition. It is somehow difficult in adjusting load when a small scale direct fired absorption chiller has only one burner. A part load operation by turning on and off the burner intermittently is an effective method for a small scale direct fired absorption chiller. The dynamic performance of the system and some components has been investigated. The coupling relationship between pressure, temperature and concentration of the lithium bromide solution have been analyzed. The result obtained indicates that the pressure of the high pressure generator and the temperature of the exhausted smoke are the most sensitive parameters. It is also found that the Transitional time from a full load to a part load condition is quite long, and the relative cooling capacity of a part load is almost near to the intermittent running time ratio and oil consumption ratio.

B. Cerkvenik¹, D. Stitou³, F. Storkenmaier², F. Ziegler^2
1 University of Ljubljana, Faculty of Mechanical Engineering, Askerceva 6, SI-1000 Ljubljana, Slovenia
² Bavarian Center for Applied Energy Research (ZAE Bayern), Walther-Meißner-Str. 6, D-85748 Garching, Germany
³ Institut for Science and Engineering of Materials and Processing, University of Perpignan, Rambla de la Thermodynamique, Technosud, F-66100 Perpignan, France

Due to their periodic operation, reaction cooling devices are more restricted in use than conventional absorption cooling devices. In addition, a higher heat of reaction as compared to the heat of absorption contributes to a lower theoretical COP of such devices. Despite of that, there are some niches, e.g. cascading sorption cycles, where reaction devices can be used for cooling and in parallel for heating purposes and have a chance to be competitive.
In this paper, experimental results of a device, working with two reactors in counter-phase, will be presented. The device has been built and tested as a part of a cascading triple-effect sorption device, with the function of increasing the COP of the cooling system. As working pair the reversible reaction between NH3 and NiCl2(NH3)2/6 has been used.
In this paper we will restrict ourselves to the discussion of the experimental results of the reaction device only. The cyclic operation of the device will be presented in detail. In addition, the COP of the device will be discussed. It is about 0,17, which is much higher than the COP of similar experimental devices with the same working pair. Still there are some irreversibilities, e.g., in form of heat losses, which have to be taken into the consideration for the design of the next generation of reaction cooling devices.