Large-scale Heat Exchanger Research Articles

A monogenetic algorithm for optimal design of large-scale heat exchanger networks

The optimal design of large-scale heat exchanger networks is a quite difficult task not only due to its non-linear characteristics but also due to a great number of local optima in its solution space. An explicit analytical solution of stream temperatures for the superstructure heat exchanger networks was developed, which reduces number of decision variables significantly. Based on this solution, a mathematical model for synthesis of heat exchanger networks was formulated for searching the optimal configuration of a heat recovery system by a hybrid genetic algorithm. For large-scale heat exchanger networks, a monogenetic algorithm based on the optimization of sub-networks is proposed. In the first step of the optimization, the hybrid genetic algorithm is applied to the synthesis of the whole heat exchanger network for finding the functional groups (sub-networks) rather than the chromosomes (positions of the heat exchangers and splits of the streams) and genes (areas and heat capacity flow rates). Then the monogenetic algorithm for evolution of the functional groups is carried out to improve the HEN. This procedure was applied to examples taken from literature and better results were obtained.

Synthesis of Large-scale Multistream Heat Exchanger Networks Based on Stream Pseudo Temperature

Effective temperature level of stream, namely stream pseudo temperature, is determined by its actual temperature and heat transfer temperature difference contribution value. Heat transfer temperature difference contribution value of a stream depends on its heat transfer film coefficient, cost per unit heat transfer area, actual temperature, and so on. In the determination of the suitable heat transfer temperature difference contribution values of the stream, the total annual cost of multistream heat exchanger network (MSHEN) is regarded as an objective function, and genetic/simulated annealing algorithm (GA/SA) is adopted for optimizing the heat transfer temperature difference contribution values of the stream. The stream pseudo temperatures are subsequently obtained. On the basis of stream pseudo temperature, optimized MSHEN can be attained by the temperature-enthalpy ( T-H) diagram method. This approach is characterized with fewer decision variables and higher feasibility of solutions. The calculation efficiency of GA/SA can be remarkably enhanced by this approach and more probability is shown in searching the global optimum solution. Hence this approach is presented for solving industrial-sized MSHEN which is difficult to deal by traditional algorithm. Moreover, in the optimization of stream heat transfer temperature difference contribution values, the effects of the stream temperature, the heat transfer film coefficient, and the construction material of heat exchangers are considered, therefore this approach can be used to optimize and design heat exchanger network (HEN) with unequal heat transfer film coefficients and different of construction materials. The performance of the proposed approach has been demonstrated with three examples and the obtained solutions are compared with those available in literatures. The results show that the large-scale MSHEN synthesis problems can be solved to obtain good solutions with the modest computational effort.

06/00311 Solving large-scale retrofit heat exchanger network synthesis problems with mathematical optimization methods: Björk, K.-M. and Nordman, R. Chemical Engineering and Processing,2005, 44, (8), 869–876

06/00311 Solving large-scale retrofit heat exchanger network synthesis problems with mathematical optimization methods: Björk, K.-M. and Nordman, R. Chemical Engineering and Processing,2005, 44, (8), 869–876

Synthesis of large-scale heat exchanger networks using a sequential match reduction approach

In this paper, a sequential approach is outlined which generates networks for industrial sized heat exchanger network synthesis (HENS) problems. The proposed match reduction approach solves a sequence of subproblems, posed as transportation problems, successively reducing the set of matches that are considered in the next stage. The terms involved in the objective function are included at each step with increasing accuracy, until a final design is obtained. One of the subproblems identifies subsets of matches that can be designed separately. Due to the sequential approach, the final design is an approximating solution. Two examples are presented to illustrate the potential of the proposed method. The results show that large HENS problems can be solved to good solutions with modest computational effort. The obtained solutions are in fact, better than the results reported earlier in the literature.

Solving large-scale retrofit heat exchanger network synthesis problems with mathematical optimization methods

Heat exchanger network optimization is a standard problem in process design. Various mathematical models and heuristics have been developed to help the designer in constructing the network. Different target procedures, like the pinch analysis, are widely used both in academia and industry. Another approach to find cost optimal network structures is to use mathematical programming methods. The advantage with mathematical programming methods is that a rigorous optimization of the structure, sizes of heat exchangers and utility usage can be carried out, whereas the designer makes these decisions if purely pinch-based tools are used. Even if much effort has been put on research within this area, many of the mathematical models consider only grassroot design, whereas most practical cases today seem to be retrofit situations. In addition, these models are likely to be either rigorous but not solvable for bigger (large-scale, real life examples) or deficient and solvable for large-scale problems. This paper takes an attempt to address these problems simultaneously and to develop a rigorous optimization framework based on both a genetic algorithm and a deterministic MINLP-approach and to present an extended model for large-scale retrofit heat exchanger network design problems.

Effect of fence thickness on pressure drop and heat transfer in a perforated-fenced channel

This note is concerned with the heat transfer/performance in a channel with perforated fences which may be used in the application of large-scale heat exchangers

Les remontées d'eau active dans la piscine du réacteur Osiris

The Osiris swimming pool type reactor has been in operation at the Nuclear Research Centre at Saclay since 1966. With its rated output of 50 MW and equipment it is the most irnportant irradiation research facility in France and one of the best-equipped in Europe, especially by virtue of a number of original hydraulic design features. The authors briefly describe the general problems encountered in designing the circulation pattern for this type of reactor and draw particular attention to the special arrangements proviclecl for. The hydraulic research and tests which confirmed the validity of the proposed schemes are gone into in some detail. Due to the site background, the only reasonable way to achieve the clesirecl 501MW rated output was by designing for rising How in the core, which also meant taking steps to counter the following possible undesirable efi'ects :- (i) Excessive pool temperature rise due to large-scale heat exchange behveen the hot core outf1cnv and the colder water in the pool; (ii) Unacceptable activity on the pool surface, which would impair case of operation enabling convenient direct access to the core, which is one of the main advantages of this kind of reactor. The proposed design reduces the upflow of warm water from the core in the pool to a minimum with the least possible adverse effect on flexible peactor operation. The tests canied out on a 1:3 scale model at SOGREAH Grenoble comprised the two following phases:- (i) A constant-temperature geometrical study in which the Reynolds number varieel but remained high enongh to ensure that the modelwas representative of real conditions; (ii) A study of the effect of temperature gradients in c ausing density differences conducive to an upward flow of active water. These etrects were reproduced to Fronde scale, with non-uniform salt wat·er concentrations in the model. A number of tricky scale problems in phase (ii) made it necessary to coyer a fairly wide range of Reynolds and Froude numbers. The tests established that pool pollution rates remained at an acceptable level. It is interesting to compare these results with the data observed when the actual Osiris reactor was put into service, which showed fairly close agreement. This is important as it confirms the reliahility of the scale model approach to mixed convection problems provised certain scale requirements are closely complied with.