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• Four different heat pump systems (CVI-1S, CVI-SR, CVI-2S and CVI-3S) are analyzed. • The COP of each heat pump is maximized by optimizing the heat pump design. • The optimizations involve 167 fluids as possible refrigerants in the heat pumps. • The optimal fluids and the maximal COP are reported in charts. • The refrigerants dme, r161, r40, cf3i, r435a, r510a are among the best fluids. In this paper, numerical optimization analyses are performed for four distinct heat pump systems, namely, the CVI-1S, CVI-SR, CVI-2S and CVI-3S systems. These analyses are performed for various combinations of hot side and cold side temperature values (i.e., for hot side temperatures ranging from 25 °C to 60 °C, and for cold side temperatures ranging from -40 °C to 10 °C). A total of 167 fluids are compared in order to obtain the highest COP value, for each temperature combination investigated. A robustness analysis is also achieved so as to identify the fluids that provide a COP value larger than 95% of the maximal COP value. Results are presented as charts that allow identifying the best fluids and the most robust fluids for each heat pump system. The results show that heat pump systems involving more equipment or including separators are more efficient than the others. Moreover, the results show that the refrigerants dme, r161, r40, cf3i, r435a and r510a are among the most robust fluids for all heat pump systems investigated. [ABSTRACT FROM AUTHOR]

In this paper, the objective is to develop new graphical tools that allow straightforward identification of the optimal design of a Rankine cycle that uses LNG being regasified as a heat sink. To achieve that objective, a numerical model is developed in order to predict the value of the specific work output produced by the system. Then, numerical optimizations are performed and the results are reported in a graphical form. These new figures provide the values of the maximal specific work (objective function) for a wide range of operating conditions. These figures also provide the corresponding values of the four optimized design variables. The main result is that ethylene is the best working fluid for most of the operating conditions considered. Furthermore, a sub-optimal analysis is performed for each fluid investigated and the resulting figures allow to identify the fluids that can provide a specific work output close to that provided by the best working fluids. Finally, optimal designs identified in this paper are compared with optimal designs of the direct expansion (DE) and of the double direct expansion (D2E) systems. • A numerical model is used to optimize the Rankine-LNG design. • The specific work output is maximized, and the working fluid is optimized. • Among the 10 fluids studied, Ethylene provided the best results. • The optimized Rankine-LNG system is compared to optimized Direct Expansion systems. • Charts provided in this paper allow straightforward design of Rankine-LNG systems. [ABSTRACT FROM AUTHOR]

In this paper, a new theoretical method for upscaling the thermal conduction equation in periodic composite materials is presented. That method is named “the method of quasiperiodic fields”, and it is based on the assumption that the temperature field is quasiperiodic at the small scale. More specifically, that method allows to predict the form of the averaged governing equations, and the values of the effective transport coefficients. The new methodology involves four steps: (i) a first level averaging, (ii) the statement of a quasiperiodic problem, (iii) the development of factorized quasiperiodic problems, and (iv) the development of the closed form of the averaged thermal conduction equation. The values of the effective thermal conductivity obtained with that new method were compared with values reported in literature, and also with values obtained from direct numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, a new theoretical method for smoothing the diffusion equation in periodic porous media is presented. That strategy is named ‘the method of quasiperiodic fields’ because it is based on the postulate that the concentration is a quasiperiodic field throughout the porous medium. The method proceeds in four steps: (i) a first level averaging of the diffusion equation, (ii) the statement of a quasiperiodic problem, (iii) the statement of factorized quasiperiodic problems, and (iv) the development of a closed form for the averaged diffusion equation. A first application of these four steps on the initial diffusion equation in a periodic porous medium provides an averaged diffusion equation in which the effective diffusion coefficient varies periodically at the small scale. A second application of the four steps provides a smoothed diffusion equation in which the effective diffusion coefficient is constant. The final smoothed diffusion equation is stated in terms of the double average of the concentration field. [ABSTRACT FROM AUTHOR]

In this paper, the design of an Organic Rankine Cycle (ORC) is optimized by means of numerical simulations. The systems of interest are the subcritical and transcritical thermodynamic cycles. Optimizations are performed with the objective of determining the design that maximizes the specific power output. The design variables include the operating parameters (pressures, mass flow rates), and the best working fluid is determined by comparing the performance of 36 refrigerants. Optimization runs are performed for a wide range of geofluid temperatures (from 80 to 180 °C), and for a wide range of condenser temperature (from 0.1 to 50 °C). The results are summarized in charts that may be used as efficient tools for designing optimal geothermal power plants. Finally, an approximate analysis allowed to develop a new correlation for predicting the maximal specific power output of an ORC. [ABSTRACT FROM AUTHOR]

In this paper, three different modifications of the basic Rankine thermodynamic cycle are proposed. The objective is to increase the thermal efficiency of power systems based on Rankine cycles. The three new systems are named “Rankine-1SCR”, “Rankine-2SCR”, and “Rankine-3SCR” cycles, and they consist of linking a refrigeration cycle to the basic Rankine cycle. The idea is to use the refrigeration cycle to create a low temperature heat sink for the Rankine cycle. These three new power plant configurations are modeled and optimized with numerical tools, and then they are compared with the basic Rankine cycle. The objective function is the thermal efficiency of the systems (i.e., net power output (kW) divided by heat rate (kW) entering the system), and the design variables are the operating temperatures within the systems. Among the 84 × 84 (i.e., 7056) possible combinations of working and cooling fluids investigated in this paper, it is shown that: (i) the Rankine-1SCR system is advantageous for 1338 different fluid combinations, (ii) the Rankine-2SCR system is advantageous for 772 different fluid combinations, and (iii) the Rankine-3SCR system is advantageous for 768 different fluid combinations. [ABSTRACT FROM AUTHOR]

In this paper, six different modifications of the Double-Flash power plants are proposed. These modifications are named “interstage heating” and consist of additional heat exchangers properly located in the system. The six interstage heating designs are analysed, optimized and then compared to an optimized Double-Flash reference power plant. The objective function is the power plant specific output (kJ/kg), and the design variables are the separator temperatures (°C) and the split fraction. Optimizations are performed for a wide range of reservoir temperatures (i.e., from 140 °C to 240 °C). Results show that interstage heating processes may increase the specific output of the plant by about 5%, decrease the liquid content in the low pressure turbine by about 50%, and decrease the required cooling capacity of the plant by about 10%. On the other hand, the analysis showed that the new designs proposed have negligible influence on the high pressure turbine liquid content or on the silica saturation coefficient. [ABSTRACT FROM AUTHOR]

Abstract: The equations that govern the various transport phenomena occurring in a polymer electrolyte membrane fuel cell (PEMFC) were formulated and implemented in a commercial finite element software, in order to predict the fuel cell current density with respect to the operating conditions. The numerical model showed polarization curves in accordance with literature. The catalyst utilization was then improved by optimizing the platinum distribution (design variable) in the fuel cell, so as to maximize current density (objective function) for a fixed total amount of platinum (constraint). The first analysis showed that, for equal anode and cathode catalyst layer thicknesses, maximal current density was achieved by placing more catalyst in the cathode than in the anode. The second analysis showed that, for equal anode and cathode catalyst layer density, maximal current density was achieved by using a catalyst layer that is thicker on the cathode side than that on the anode side. Finally, a topological optimization of the platinum density within the cathode catalyst layer was performed with a gradient based algorithm, and the results showed that at a high stoichiometric ratio, the best design has most of its platinum placed where the reaction rate is the highest, i.e., close to the membrane layer. [Copyright &y& Elsevier]

Highlights: [•] The Self-Superheating (SSH) process is a modification of geothermal Flash cycles. [•] Self-Superheating provides 5% more specific work than Flash cycles. [•] Self-Superheating reduces the turbines moisture content by 20–40%. [•] Optimal separator temperature of SSH cycles is 5°C lower than those of Flash cycles. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the dimensionless reaction rate density of a two-dimensional channel with catalyst on its boundary was maximized by optimizing its aspect ratio H/L. Order of magnitude expressions in the limit of small H/L and in the limit of large H/L were developed and then intersected to predict the optimal aspect ratio and maximum reaction rate. Numerical simulations were performed and the results corroborated very well with the scale analysis. The results showed that the optimal design of microreactors depends on the Schmidt number (Sc), the Bejan number (Be) and the Catalyst number (Ct). Correlations based on those numbers are proposed. The analysis was performed for steady-state laminar flows, using the dilute species assumption and a first order kinetic expression. [Copyright &y& Elsevier]

Abstract: In this paper, we address the fundamental problem of maximizing the reaction rate of a channel reactor with catalyst on its boundaries by varying its aspect ratio L/H. The volume, pressure drop, amount of catalyst and catalyst surface density of the channels were constrained. The expression of the reaction rate in the limits of small, moderate and large L/H values were obtained by scale analysis. A distinct behaviour appeared for each of these three geometrical limits: a kinetic controlled regime, an external diffusion controlled regime, and a regime limited by fluid flow rates. From this scale analysis, we predicted analytically that the length can be varied so as to increase the rate of reaction of a catalytic channel, up to a threshold value from which further change of the geometry does not alter significantly the reaction rate. Intersections of the three reaction rate expressions provided estimates for the maximal reaction rate and for the threshold lengths, as a function of the Bejan number, the Schmidt number and a catalyst number. Finally, CFD simulations of the channel reactors were performed, and numerical parametric studies agreed well with the estimated equations for the threshold L/H values. Correlations based on the numerical data are proposed for the design of catalytic channel reactors. [Copyright &y& Elsevier]

Abstract: The thermal inertia of building internal components may be used to shift the irradiation (solar) heat load, which could result in substantial energy saving. In this paper, a numerical model was implemented to determine the thermal performance of internal surfaces including Phase Change Materials (PCM). The model was exploited to compare a typical concrete floor with a floor with PCM. Thermal performance was defined by three different objective functions, each pinpointing different thermal characteristics of the heat load. First, parametric studies were performed to understand the influence of the thickness of a typical concrete floor. Then, the optimization of the melting temperature, thickness and position of a PCM layer included in a floor was performed. These analyses used either simplified or real weather conditions (for Québec City). Results showed that the thickness of the concrete floor could be optimized based on the three criteria retained. Also, the floor performance may be enhanced by the inclusion of a PCM layer. It was shown that the gain of performance brought by the internal surfaces thermal mass strongly depends on the weather conditions considered. This paper provides a fundamental understanding of PCM influence on internal surfaces. [ABSTRACT FROM AUTHOR]

Abstract: A numerical model is presented to determine the thermal shielding performance of an exterior wall (e.g., building envelope) containing layers of PCMs. The model is exploited to perform a parametric study to assess the influence of the position and melting temperature of one PCM layer. Results showed that benefits are to be expected when the interior and exterior temperatures are close. Then, the wall composition has been optimized with a genetic algorithm based on a yearly analysis with the possibility of including several PCM layers. Idealized weather conditions and measured weather conditions (including solar radiation) have been considered. Results showed that for Québec City, optimal south-facing wall includes one PCM layer when real weather data are considered. Its effect is to shield the heat transfer in the summer. This paper provides a fundamental understanding of multilayer walls with PCMs. [Copyright &y& Elsevier]

A straightforward procedure is developed to determine dissipation fields (e.g., exergy destruction in conduction, pumping power, Joule heating) from the linear boundary conditions applied on their associated linear diffusion problem (e.g., heat conduction, Darcy flow, electrical flow). The mathematical tool proposed in this article takes advantage of the quadratic (nonlinear) behavior that comes with dissipative fields equations. The first objective of this article is to build a mathematical formulation expressing any dissipation field as a combination of fundamental dissipative fields resulting from decomposed boundary conditions, similarly to linear problems where fundamental solutions may be added with the superposition principle. The second objective is to demonstrate the numerical advantage of this formulation when applied to heat transfer and fluid flow optimization problems. Application of the mathematical tool proposed in this article to boundary control problems provided significant computational time reductions. [ABSTRACT FROM AUTHOR]

Abstract: The objectives of this paper are two: (i) propose an evolutionary algorithm for optimizing the topology of a heat-generating area cooled by a high thermal conductivity material in contact with a heat sink, and (ii) compare the evolutionary procedure and optimal structures found to the ones predicted by constructal theory. The evolutionary algorithm starts with an initial random topology, for which control volumes are repositioned based on temperature and heat flux information in order to minimize the hot spot temperature. Significant diminution of the hot spot temperatures have been achieved by the algorithm. Results revealed three families of geometrical configurations for the optimal conductive pathways generated by our algorithm, depending on the values of the conductivity ratio and amount of high thermal conductivity material: few radial blades growing on the heat sink, tree-shaped networks, and networks with loops. The optimal structures are compared with the heat tree architectures generated by constructal theory, and several similarities in terms of performances and geometries are revealed. [Copyright &y& Elsevier]

Falcipennis canadensis (Spruce Grouse) are a habitat specialist of coniferous forest in North America and typically have large home ranges (≈ 25 ha, range = 22-75 ha). Although this species is sensitive to logging, few studies report abundance and population trends in relation to habitat loss and fragmentation. In early May of 1997 to 1999. we surveyed Spruce Grouse in 21 riparian and 27 upland residual forest strips (width = 51-132 m) located within six clear-cut landscapes (23-256 km²) of southcentral Québec, Canada. We also surveyed five control sites in uncut continuous forest surrounding one landscape. Contrary to our prediction that Spruce Grouse would not be observed from such narrow strips, they were detected in 24 of the 48 strips. Both types of strips had similar occurrence rates and abundance indices (2.01 ± 0.46 [SE] males/10 stations in riparian strips, 1.29 ± 0.35 males/10 stations in upland strips). Because of the age of adjacent cuts (mean = 4.2 years. range = 2-8 years), crowding of grouse that were present at logging time into forest strips does not adequately explain the numbers of Spruce Grouse in these structures. Therefore, we conclude that Spruce Grouse observed in forest strips have either immigrated from outside or were local recruits. Despite persistence of Spruce Grouse in residual forests of logged landscapes, we suggest a cautious approach to forest management since the species' long-term persistence could be jeopardized if residual forest strips are harvested. [ABSTRACT FROM AUTHOR]

The snowshoe hare (Lepus americanus Erxleben) is an important prey for many predators in the boreal forest. In this biome, clear-cut landscapes are generally large and consist of aggregated cutting blocks separated by narrow forest strips (typically 60–100 m wide). To identify attributes of forest strips that are important for snowshoe hares, we measured the use of strips using track counts over two winters in six clear-cut landscapes (23–256 km2) in south-central Quebec. Surveys were conducted in 20 riparian strips (RS), 20 upland strips (US), and 15 control sites (CO) at the periphery of clear-cut landscapes. Overall, 392 signs of hare presence were recorded along 50 km of transects. Snowshoe hares were present in one-third of the strips surveyed and were five times less abundant in US and RS than in CO. The species avoided strip edges. Hares were more common in the wider strips (>100 m), in the strips adjacent to residual forest patches (≥25 ha), or in those having a denser shrub canopy, which is often associated with a greater basal area in balsam fir (Abies balsamea (L.) Mill.). To maintain snowshoe hare at moderate densities in large clear-cut landscapes, we suggest leaving uncut forest strips >100 m wide in areas having a good shrub cover with presence of balsam fir. [ABSTRACT FROM AUTHOR]

We evaluated the accuracy of 2 aerial survey techniques over 4 large enclosures (6.0-29.4 km2) where the deer (Odocoileus virginianus) population was reconstructed using hunting harvest and winter mortality data. We conducted surveys (n=8) along equally spaced parallel lines. Six surveys using the double-count technique involved 2 independent observers located on the same side of a helicopter who simultaneously counted animals over narrow plots (60-m width). Four of these surveys yielded deer densities 64-83% of assumed densities (based on the reconstructed population). The 2 other surveys had accuracies of 37 and 46%, respectively, and were judged unreliable because the sighting probability of the front observer was <0.40. We conducted 2 surveys with a thermal infrared sensor. One survey had the highest accuracy (89%) among all surveys while the other gave poor results (54% accuracy). We concluded that when sighting probabilities of observers exceed 0.45 of deer groups, double-count surveys provided valid estimations of densities for management purposes, although 1 deer out of 4 was missed on average. Because of closed forest canopy, thermal infrared sensing of deer along systematic survey lines was not a reliable technique. [ABSTRACT FROM AUTHOR]

We studied the response of beaver (Castor canadensis Kuhl), moose (Alces alces L.), and snowshoe hare (Lepus americanus Erxl.) to clear-cutting in three blocks that had been logged 10 years ago. In a previous study, these species had been surveyed in the same blocks 2 years before and 2 years after logging. We also surveyed an uncut block of the initial experimental design that was logged more recently. Over the 10-year period, the shrub layer and available browse have improved markedly in clear-cut areas. As compared with logged coniferous stands, logged mixed stands had higher lateral cover (62% vs. ≍55%) and taller regeneration (>4 m vs. <3 m). Beaver density did not change over the period because its feeding habitat remained unchanged in the riparian forest strips. Moose densities increased 54%–87% in two harvested blocks as a result of both logging and stricter hunting regulations (selective hunting). Based on the rate of increase observed in a control block, we estimate that a 25% density increase in the mixed forest block can be related to logging, while selective hunting can solely be responsible for the change in the coniferous forest block. Snowshoe hare have started to reoccupy logged coniferous stands, but their relative density still remained less than half that of uncut stands. We conclude that, after 10 years, logged mixed stands already offer good habitat conditions for moose and snowshoe hare. Conversely, in logged black spruce (Picea mariana (Mill.) BSP) stands, habitat conditions still remain poor for snowshoe hare because of a lack of cover. [ABSTRACT FROM AUTHOR]

Aerial surveys can provide direct density estimates for ungulates over large areas such as hunting zones, a prerequisite for intensive management. In 1991 Québec implemented double-count aerial surveys as part of its white-tailed deer (Odocoileus virginianus) management program, on a hunting-zone basis. This technique involves 2 independent observers located on the same side of an aircraft who simultaneously count animals in sample plots. Two 5-year survey plans have been successfully completed for the whole province. Deer densities for most zones could be estimated with a ±20% CI (P = 0.90), while the survey provided less precise evaluations for subunits or individual wintering areas. A typical survey for a hunting zone with 200 plots (5 km x 60 m) required approximately 30-40 helicopter hours and cost $43,000 Canadian, including salaries and travel expenses. The technique offers great potential for a variety of landscapes as part of deer management programs. [ABSTRACT FROM AUTHOR]

Determining at what scale to operate and how much cover is needed are important questions for winter habitat management of white-tailed deer, Odocoileus virginianus (Zimmermann, 1780), through logging. We used binary cover maps (reclassified forest vegetation maps) and windows of different sizes (0 .2 km × 0.2 km, 0.5 km × 0.5 km, 1 km × 1 km, 2 km × 2 km, and 3 km × 3 km) to describe the relationship between deer density from an aerial survey and the proportion of balsam fir, Abies balsamea (L.) P. Mill., forest (BF) cover in a 270-km2 block on Anticosti Island, Quebec. Maximum white-tailed deer densities reached were quite similar (31–34 deer/km2) irrespective of window size, except for the 3 km × 3 km window for which maximum density remained half lower. Density increased with the amount of BF cover and then reached a plateau above 60% or 70% (two smaller windows) or decreased above 50% or 60% (1 km × 1 km and 2 km × 2 km windows). Results confirm goals previously used for habitat management of deeryards. This new method allows greater flexibility in research applications for describing density–cover relationships because both scale and proportion of cover can be analysed simultaneously. [ABSTRACT FROM AUTHOR]

Winter aerial surveys of moose (Alces alces) were completed on 14 landscapes (10–256 km²) formed of aggregated black spruce (Picea mariana) clear-cuts logged 3–9 years ago in southcentral Québec. Moose were present in 8 landscapes (11 yards) and had a mean density of 0.20 moose/10 km², which was 50% of the density observed in the same hunting zone with a similar forest composition. Based on previous work, effects of variability in hunting pressure and time since cutting were assumed not to influence distribution and abundance of moose. Browse density did not increase with age of cuts. Moose density was not related to the size of the clear-cut landscapes or the proportion of residual forest (18–40%) within each landscape (P = 0.14). Moose yards were not located close to uncut forest surrounding the landscapes and did not have a greater proportion of residual forest than clear-cut landscapes. Moose yards had a denser shrub layer and more browse available than random sites selected in the same landscapes. The presence of moose in large clear-cut black spruce landscapes is related to vegetation characteristics and not the spatial pattern of the forest. The authors propose two strategies to maintain moose populations and moose hunting activity in this type of forest after harvesting. [ABSTRACT FROM AUTHOR]

Habitat-selection analysis involves a comparison between the proportions of different cover types that are used by the animal and the proportions that are available. Telemetry locations or animal occurrences (e.g., from aerial surveys) can provide information on habitat utilization. With telemetry data, a classical approach involves computing habitat use at the individual location sites or inside fixed circle buffers applied to the sites. We used this approach (200 m radius circles) on data from a systematic aerial survey on Anticosti Island, where 260 groups of white-tailed deer (Odocoileus virginianus) (374 animals) were counted in a 270-km² block. We compared the selection indices obtained from site occurrences with those of two approaches that define areas of high intensity (animal concentrations): 50% fixed kernels (0.5-2 km bandwidth) and the local K function (0.5-2 km distance). The results were very consistent among the three sets of approaches, with the same cover types generally identified as those having the highest or lowest indices. White-tailed deer preferred forest stands where balsam fir (Abies balsamea) was present as high regeneration or was dominant in the tree layer (>50% basal area) and stands at the regeneration stage. In the studied landscape, there seems to be a wide range of spatial scales where the selection process can be analyzed from aerial survey data. [ABSTRACT FROM AUTHOR]

To describe the forest mosaic suitable for marten ( Martes americana) in a clearcut boreal landscape, we studied habitat selection in an area (123 km2) located in western Québec, in which black spruce ( Picea mariana) was the predominant forest type. This block had been recently clearcut with the protection of regeneration cutting technique, a logging method that employs equally spaced harvesting trails. The resulting landscape had a center dominated by a cutover matrix (60% of the block) and surrounded by contiguous uncut forest. Over 2 years, 20 marten equipped with radio collars provided enough locations to delineate their winter home range. Habitat composition and spatial configuration were measured at both stand and landscape scales by means of a geographic information system database that included telemetry locations and home ranges, forest maps, and limits of clearcut areas. Inside their winter home ranges, animals avoided open regenerating stands composed mostly of recent clearcuts with sparse regeneration. They did not select coniferous stands, even those that were mature or overmature, but preferred deciduous and mixed stands, a large proportion of which had a dense coniferous shrub layer as a result of a spruce budworm (Choristoneura fumiferana) epidemic 15–20 years ago. At the landscape scale, winter home ranges differed from random mosaics because they had a larger proportion of uncut forest (>30 years), a smaller proportion of open regenerating stands, larger core area in forest habitat, and less edge between open regenerating stands and forest. Winter home ranges usually contained <30–35% open or closed regenerating stands and> 40–50% uncut forest. We conclude that marten and clearcutting may be compatible, provided that forest logging is adapted to that species at the landscape level. Where the objective is to maintain marten at a local scale in black spruce forest, we suggest that ≥50% uncut forest be... [ABSTRACT FROM AUTHOR]

• Dual pressure transcritical ORC is usually the best in the range of conditions tested. • Specific work output between 5 and 70 kJ/kg were obtained from simulations. • Five fluids (R218, R115, R227ea, RC318, RE245cb2) stand out in the optimization. • Optimal values of cooling tower range are lower at colder brine and hotter cold sink. • Parasitic loads (pumps, cooling) range from 15 to 45% of the gross power produced. Four variants of the Organic Rankine Cycle (ORC) applied to geothermal power plants are optimized by means of numerical tools. These variants are: (i) the subcritical ORC with single-pressure heater (ORC/S/SC), (ii) the transcritical ORC with single-pressure heater (ORC/S/TC), (iii) the subcritical ORC with dual-pressure heater (ORC/D/SC), and (iv) the transcritical ORC with dual-pressure heater (ORC/D/TC). All the systems are recuperative and include a wet cooling tower. The objective function is the specific work output and design variables include operating pressures, mass flow ratios between the brine and the working fluid, superheaters effectiveness and cooling tower range. The systems are optimized for 20 different potential working fluids. The optimization is performed for inlet brine temperatures from 80 to 180 °C, and for ambient air wet bulb temperatures from 10 to 32 °C. The results show: (i) the superiority of ORC/D/TC for most of the cases, (ii) the relevance of using a dual-pressure heater at high sink temperature and low brine temperature, and (iii) the importance of choosing the right cooling tower range for an optimal power plant design. [ABSTRACT FROM AUTHOR]

Abstract: This review presents when and how Genetic Algorithms (GAs) have been used over the last 15 years in the field of heat transfer. GAs are an optimization tool based on Darwinian evolution. They have been developed in the 1970s, but their utilization in heat transfer problems is more recent. In particular, the last couple of years have seen a sharp increase of interest in GAs for heat transfer related optimization problems. Three main families of heat transfer problems using GAs have been identified: (i) thermal systems design problems, (ii) inverse heat transfer problems, and (iii) development of heat transfer correlations. We present here the main features of the problems addressed with GAs including the modeling, number of variables, and GA settings. This information is useful for future use of GAs in heat transfer. Future possibilities and accomplishments of GAs in heat transfer are also drawn. [Copyright &y& Elsevier]

1. The density of large herbivores is a major driver of forest ecosystem structure and function in conjunction with episodic disturbances, especially in forests with a regeneration strategy based on shade-tolerant seedlings capable of re-establishing canopy dominance (advance regeneration). Yet, uncertainty about the relationships between forest regeneration, herbivore density and other disturbances makes it difficult to set population goals. Using an innovative controlled browsing experiment, we investigated the relationships between the regeneration dynamics of balsam fir Abies balsamea, the density of white-tailed deer Odocoileus virginianus and timber harvesting. 2. We hypothesize that advance tree regeneration either: (i) recovers approximately linearly as deer density is reduced; (ii) recovers exponentially; or (iii) does not recover because factors other than browsing control advance regeneration. We tested these alternatives through manipulation of deer densities (0, 7·5, 15 deer km−2 and in situ local densities) and forest cover (clearcut and uncut forest). 3. Balsam fir seedling mortality decreased exponentially with decreasing deer density in clearcut and approximately linearly in uncut forest. Independently of deer density, the recruitment of seedlings in clearcut dropped from 56 ± 5% to 7 ± 1% within 3 years. 4. Seedling growth increased exponentially with decreasing deer density in clearcut whereas no height growth was observed in uncut forest. 5. Overall, the abundance of fir saplings recovered exponentially in clearcut but remained low and independent of deer density in uncut forest. The abundance of spruce Picea spp. saplings was unrelated to deer density and increased with time. 6. Synthesis and applications. Forest disturbance from selective browsing at high deer densities over an extended period of time leads to recruitment failure following a canopy disturbance such as a clearcut. Indirect competitive advantage given to species resistant to browsing can shift forest composition. Nonlinear relationships between fir regeneration and deer densities imply that the level of culling required to reach herbivore densities compatible with natural regeneration of native forest is larger than expected if tree regeneration was proportional to deer density. In the boreal forest of Anticosti Island, local densities < 15 deer km−2 achieved within 3 years following clearcut are compatible with the maintenance of native forest. [ABSTRACT FROM AUTHOR]

The early responses of the field layer to changes in biotic and abiotic conditions are key determinants of the future composition and structure of forests where sustained heavy browsing pressure has depauperated the shrub understory. We investigated the relationships between white-tailed deer density and field layer plant community dynamics in boreal forests managed for wildlife and timber production. We hypothesized that the growth and reproduction of field layer plants are either: (H1) directly proportional to deer density, or (H2) related to deer density through nonlinear relationships or (H3) through nonlinear relationships with thresholds. We tested these hypotheses using data from a controlled browsing experiment involving a gradient of deer densities (0, 7.5, 15, 27 and 56 deer km−2) in interaction with timber harvesting conducted on Anticosti Island, Canada. In recent clearcuts, the dominant responses of the field layer plants were exponential recovery in growth and reproduction with decreasing deer densities. The abundance of browse-tolerant species such as grasses was positively related to deer density, suggesting an apparent competitive gain. These results support the prediction from our second hypothesis, although the presence of ecological thresholds should not be ruled out. Rapid changes in the early successional stages have potentially long-term consequences on successional patterns through processes such as the modulation of germination and early establishment success of seedlings from later successional species. Quantitative data as those presented here are essential for the development of ecosystem management prescriptions. On Anticosti Island, reduction of local deer densities to levels <15–7.5 deer km−2 in the first 3 years following timber harvesting appears to be compatible with the regeneration dynamics of this system although lower levels of deer densities may be required for the conservation of browse-sensitive plant species. [ABSTRACT FROM AUTHOR]

Forest maps are widely available and can provide an inexpensive way to analyse ecological phenomena at a landscape level. This paper presents a case study whose objective was to help manage the deer herd and associated habitat on Anticosti Island. The selection by deer of winter habitat was analysed spatially using aerial survey data and a forest map produced by interpretation of aerial photographs. Initially, it was demonstrated that the spatial distr ibution of deer across the landscape could not be considered random. Grid cells of two different sizes—500 m×500 m and 1 km×1 km—were extracted from the forest map, and landscape indices thought to be relevant were calculated for each to characterize the key landscape features on which deer select their winter habitat. To do this, the landscape indices were correlated with the number of deer found in grid cells of a given size. It was found that deer preferred areas on which balsam fir was present, and areas in which there was a relatively high concentration of regeneration/dense forest edge. Correlations were better for the larger grid cell size suggesting that deer on Anticosti Island selected habitat based on an area larger than 500 m×500 m. However, it is noted that this result is probably also due in part to the modifiable areal unit problem (MAUP) whereby larger window sizes tend to provide better correlations between two variables. The location of the grid cells within the study area also affected the results slightly. [Copyright &y& Elsevier]

Habitat selection by moose was studied over 4 years in two large sectors subject to intensive forest harvesting using a two-scale approach. At the coarser scale, i.e. location of the home range within the landscape, habitat selection did not appear to be influenced by the presence of clear-cuts. In one sector, moose preferred mature mixed stands, young coniferous, and mature coniferous stands. In the second sector, the highest preference was noted for cut areas and mature deciduous stands. Moose home ranges were located in areas with higher edge and interspersion among habitat patches. Home range size for females was positively related to the proportion of cuts, but movements were not. Habitat selection was more pronounced at the finer scale (animal locations within home range) and did not differ between sectors. Mixed stands were preferred in all seasons. Mature conifer stands were preferred in summer and in early winter while young conifer stands were preferred in late winter. Clear-cuts were avoided except in early winter. Moose were located in areas closer to edge between food and cover stands than were random locations, especially in late winter. A marked decrease in movements also was noted in late winter. This study shows differences in habitat selection pattern between the coarser and finer scales. For example, clear-cuts did not seem to markedly influence home range location at a coarser scale, and adaptations to minimize their impact seemed to operate at a finer scale. Coarser scale habitat selection was probably linked to a trade-off between predator avoidance and browse availability, whereas seasonal changes suggest behavioural adaptations of moose to maximize energy gain and counteract predation and other adverse environmental conditions at the finer scale. [ABSTRACT FROM AUTHOR]

The heat contained in internal combustion engine exhaust gases can be converted into mechanical energy by using an Inverted Brayton Cycle (IBC). In this paper, five different IBC versions are numerically modeled and optimized to maximize their specific work output: (i) basic IBC, (ii) IBC with liquid water drainage (IBC/D), (iii) IBC with liquid water drainage and a steam turbine (IBC/D/S), (iv) IBC with liquid water drainage and a refrigeration cycle (IBC/D/R), and (v) IBC with liquid water drainage, a steam turbine and a refrigeration cycle (IBC/D/S/R). The three latter cycles are presented for the first time in literature. The optimization is performed for a wide range of inlet gases temperatures (600–1200 K) and heat sink temperatures (280–340 K). Among the five IBCs, the IBC/D/S/R has the highest specific work output for the whole range of operating temperatures. A comparison with the subcritical Rankine cycle and Organic Rankine Cycles using isobutane and benzene shows that an IBC system might be a better choice for specific operating temperatures. Liquid water addition in the IBC/D/S/R leads to optimized designs using only the steam turbine at high inlet gas temperatures, indicating that a Rankine cycle is better suited for these conditions. • The inverted Brayton cycle is a good candidate for heat recovery from exhaust gases. • It is best combined with water drainage, vapor-compression and open Rankine cycles. • Work output of 270 kJ per kg of exhaust at 1200 K can be reached with 280 K cold sink. • It outperforms ORC and Rankine cycle for certain hot and cold source temperatures. [ABSTRACT FROM AUTHOR]