Effects of competitive interactions of different life forms submersed plants on biomass allocation in shallow lakes

Plant competition has been recognized as one of the most important factors influencing the soructure and function of lake ecosystems. Competition from plants of dissimilar growth form may have profound effects on shallow lakes＇. An experiment was conducted to investigate the effects of competitive interactions of submersed plants with dis- similar growth forms on the biomass allocations. Hydrilla verticitlata and Vallisneria natans were selected and were planted in a single-species monoculture and a mixed-species pattern, Results showed that the growth of E natans was＇ significantly affected by the tt, verticillata and caused a sharp reduction of biomass, but the root：shoot ratio of E ha- tans was not affected significantly and there was a minimal increase in mixture： while for H. verticillata, the biomass and the root：shoot ratio were not significantly changed by the competitive interactions ore natans, there was minimal increase of biomass and minimal decrease of the root：shoot ratio. These results may indicate that theplant which can develop a dense mat or canopy at the water surface would be a stronger competitor relative to the plant that depends more on light availability near the sediment.

Effects of soil compaction on growth variables in Cappadocian maple(Acer cappadocicum) seedlings

This study investigates the effects of increasing soil penetration resistance(SPR) on seedling morphology and seedling architecture. When seedlings of deciduous Cappadocian maple(Acer cappadocicum Gled.) were grown in a greenhouse in a loamy soil under a wide range of soil compactions, all morphological variables studied changed significantly with increasing SPR. The relationships between increasing SPR and all morphological responses except lateral root length followed a negative quadratic curve. All biomass variables except lateral root biomass showed a bell-shaped response with respect to SPR, with a maximum biomass variable between 0.6 and1.2 MPa, decreasing at higher soil compaction values. All allocation ratios were significantly affected by soil penetration resistance. Biomass allocation to roots was also affected by soil compaction. There was not a significant relationship between the specific stem length and increasing soil penetration resistance. The specific root length showed two trends to increasing SPR; it first decreased in response to the moderate compaction treatment(up to about 1.2 MPa), then increased significantly. We concluded that increasing soil compaction caused morphological changes to root and shoot sections of A.cappadocicum seedlings.

Performance and Optimization for a Ground-Coupled Liquid Loop Heat Recovery Ventilation System

Ground-coupled heat pumps(GCHP)are commonly used in residential heating system.To mitigate the boreholes temperature dropping with operating time,a new exhaust-air recharging system is developed.The new recharging system can be used in three operational modes.In this paper,a ground-coupled heat recovery ventilation(HRV)model is discussed.A thermal model is set up to find the optimal brine flow rate and heat transfer allocation ratio between exhaust and supply coils for maximum heat recovery efficiency.Contrary to the conventional liquid-loop HRV systems,the brine temperature entering the exhaust coil never goes blow zero(0℃),and hence defrosting is needless in the ground-coupled HRV system.This can make the ground-coupled HRV system over 20% more efficient than a conventional HRV system at low outdoor temperatures.

Study of Performance on Recharging the Borehole by Means of Exhaust-air Energy

In this paper,the performance analysis of recharging the borehole by means of exhaust-air energy is carried out.The results show that a vertical borehole used as heat source for a Ground Source Heat Pump(GSHP)can be recharged in high efficiency.With equal heat transfer capabilities of exhaust-air coil and borehole collector,the system provides a maximum overall efficiency.However,due to ground infinite capacity,the optimum brine flow rate is different from conventional two-exchanger system.The recharging system provides two peak overall efficiencies when the capacity ratio Cr=5 for laminar flow and Cr=15 for turbulent flow respectively.The overall efficiency is independent of exhaust-air temperature and undisturbed ground temperature,although the fluid properties depend on temperature.In practical system lower ethyl percentage brine should be chosen if the freezing point meets the system request,which can provide a higher overall efficiency.

Comparisons and optimization of two absorption chiller types by considering heat transfer area,exergy and economy as single-objective functions

Absorption cooling technology is an environmentally friendly method to generate continuous chilled water making use of multiple thermal sources,such as waste heat and renewable thermal energy.In this study,two absorption chillers(nominal capacity of 400 kW)with series and parallel connections are evaluated.To research the ideal configuration of chillers after thermodynamic analysis,the structures of the chillers are optimized using the particle swarm optimization algorithm by considering the heat transfer area(HTA),exergy efficiency and total annual cost as single-objective functions.The impact of temperature differences between external and internal flows,heat exchanger efficiencies and the solution allocation ratio is estimated.The optimized HTA,coefficient of perform-ance,exergy efficiency and total annual cost are 149.0 m^(2),1.56,29.44%and$229119 for the series-connected chiller,and 146.7 m^(2),1.59,31.45%and$234562 for the parallel-connected type,respectively.Under the lowest HTA condition,compared with the reference simulation results,the energy and exergy performances are improved,while the annual total cost is higher.The annual total cost is highest when maximizing the exergy efficiency,which is attributed to the increase in the HTA.The operating cost accounts for 27.42%(series type)and 26.54%(parallel type)when the annual cost is the lowest.