EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency, in order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result, it can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.

Does hydrological fluctuation alter impacts of species richness on biomass in wetland plant communities?

Aims The diversity-productivity relationship is one of the most critical questions in ecology and can be altered by environmental factors.Hydrological fluctuation affects growth of wetland plants,and such effects vary with plant species.Therefore,we hypothesized that hydrological fluctuation changes effects of species richness on productivity of wetland plant communities.Methods We constructed wetland plant communities consisting of three or six wetland plant species and subjected them to hydrological fluctuation(i.e.gradually changing water level)of two frequencies and two ranges,with unchanged water level as the control.We measured height,root and shoot dry mass of each plant at harvest.Important Findings Hydrological fluctuation significantly decreased biomass of wetland plant communities,which was due to impacts of fluctuation range,but not those of fluctuation frequency.Community biomass was significantly higher when species richness was higher,and such an effect did not depend on hydrological fluctuation.Therefore,hydrological fluctuation can decrease the productivity of wetland plant communities but may not alter the diversity-productivity relationship.

Experimental evidence for root competition effects on community evenness in one of two phytometer species

Aims Plant-plant interactions,being positive or negative,are rec-ognized to be key factors in structuring plant communities.However,it is thought that root competition may be less impor-tant than shoot competition due to greater size symmetry below-ground.Because direct experimental tests on the importance of root competition are scarce,we aim at elucidating whether root competition may have direct or indirect effects on commu-nity structure.Indirect effects may occur by altering the overall size asymmetry of competition through root-shoot competitive interactions.Methods We used a phytometer approach to examine the effects of root,shoot and total competition intensity and importance on evenness of experimental plant communities.Thereby two different phytom-eter species,Festuca brevipila and Dianthus carthusianorum,were grown in small communities of six grassland species over three levels of light and water availability,interacting with neighbouring shoots,roots,both or not at all.Important Findings We found variation in community evenness to be best explained if root and shoot(but not total)competition were considered.However,the effects were species specific:in Dianthus communities increasing root competition increased plant community evenness,while in Festuca communities shoot competition was the driving force of this evenness response.Competition intensities were influenced by environmental conditions in Dianthus,but not in Festuca phytometer plants.While we found no evidence for root-shoot interactions for neither phytom-eter species root competition in Dianthus communities led to increased allocation to shoots,thereby increasing the potential ability to perform in size-asymmetric competition for light.Our experiment demonstrates the potential role of root competition in structuring plant communities.