Impacts of hydrogeological characters of fractured rock on thermodynamic performance of ground-coupled heat pump

Ground-coupled heat pump (GCHP) is used to recovery shallow geothermal energy, a widely distributed green energy source. Due to the imbalance between heat rejection and extraction, heat buildup underground is commonly associated with the long-term operation of GCHPs, which undermine system performance. Heat buildup intrinsically results the irreversibilities (entropy production) in subsurface heat sink, in which thermodynamic and transport properties are largely influenced by hydrogeologic properties, especially the existence of fractures and groundwater. This study investigates the influence of water flow in fractures on the thermodynamic performance of a single borehole heat exchanger (BHX) and heat buildup in the underground heat exchange zone (UHXZ). Potential influence factors were screened out, and new terms were proposed to quantify the scale of fractures and available heat and cold in the heat sink. Governing equations were established to calculate the impacts of vertical and horizontal fractures on the heat exchange rate in BHX as well as on the heat flow across the UHXZ. The analysis results show that water flow in fractures can significantly enhance heat transfer, reduce required number of boreholes, mitigate heat buildup and reduce irreversibilities underground. The results also suggest that the role of fracture scales and water velocity in GCHP operation should be carefully evaluated. Therefore, detailed hydrogeological survey is necessary. The study results provide a guide on more accurately evaluating the risk of heat buildup and how to take advantage of hydrogeological characters to improve the performance of GCHPs.

How Much Space Does My Shade Tree Need? Planting Space Recommendations for Medium and Large Trees in Florida Cities

Trees provide urban landscapes with shade, beauty, and habitat. They can also help lessen the effects of flooding and urban heat buildup while storing carbon dioxide, a major greenhouse gas. When planted in the wrong place, however, trees can damage urban infrastructure. To maximize the benefits provided by urban trees, we need better-informed tree selection and larger planting spaces with the capacity to support big-canopy trees. This new 8-page fact sheet is intended to help arborists, urban foresters, landscape designers, landscapers, and anyone else responsible for the planting of trees in developed areas make informed decisions regarding the planting width requirements of the trees they select. Written by Deborah R. Hilbert, Andrew K. Koeser, Brooke L. Moffis, JuWanda G. Rowell, and Drew C. McLean, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep592

Performance Comparison of Fixed and Tracking Type Solar Plants

Solar energy, which is essential for all on earth, is clean and plentiful and can be transformed into electrical energy using photovoltaic (PV) systems. The generation of energy using different types of PV solar panel mountings viz. fixed, tracking, and adjustable, depends on a variety of factors such as sun intensity, relative humidity, cloud cover, and heat buildup. This paper reviews the various parameters which influence the performance of solar power plants. Further, the performance comparison of fixed and tracking PV systems shows that in comparison to the classical fixed-position PV systems, the tracking type of PV systems capture much more solar energy and thus produce substantially higher output power. Furthermore, consideration is also given to design variables which should be taken into account during the initial stage of engineering of a plant to achieve better performances and outcomes from the generation of a solar power plant.

Selection and techno-economic analysis of hybrid ground source heat pumps used in karst regions

In order to take advantage of different forms of heat pumps and to mitigate thermal imbalance underground caused by long-term operation of ground source heat pumps, hybrid ground source heat pump systems have received an increasing attention. In this research, based on the fact that abundant groundwater resources are commonly available in karst regions, a new strategy is introduced for selecting and determining hybrid ground source heat pump capacity. Five scenarios of hybrid ground source heat pump system coupling groundwater source heat pumps with other supplementary heat pumps are proposed in this article to provide appropriate options to eliminate heat buildup under different hydrogeologic conditions. Methodologies for sizing and selection are established. Then, a case study of techno-economic analysis was performed for a project in the karst region in South China. The results showed that these scenarios can effectively mitigate heat buildup, and under the hydrogeologic condition in the case study. Compared to the solo ground-coupled heat pump solution, the optimal solution (Solution 4 in this study) can reduce the annual costs by 16.10% and reduce the capital investment by 60%. Methodologies developed in this study are beneficial for selecting appropriate approaches to mitigate heat buildup and enhance competitiveness of ground source heat pumps.

Investigation of Epoxidized Palm Oils as Green Processing Aids and Activators in Rubber Composites

Epoxidized palm oil (EPO) is environmentally friendly, biodegradable, and a relatively less costly processing aid. In this study, we investigated the suitability of EPO in place of aromatic processing oils in styrene butadiene rubber. The curing properties, mechanical properties, abrasion resistance, and heat buildup properties of rubber composites with EPO were compared with those of the standard with aromatic oils. The rubber composites with EPO showed enhanced mechanical properties including modulus, tensile strength, and elongation at break. This is ascribed to the improved dispersion of fillers in the rubber matrix and interaction between the filler and the polymer. Furthermore, EPO in the rubber matrix showed remarkable abrasion resistance, rebound resilience, and heat buildup at low loadings. EPO in a rubber composite presents feasibility as a renewable raw material that can serve as an alternative to petrochemical oils in various applications.

Tire tread rubber compounds with ternary system filler based on carbon black, silica, and metakaolin: Contribution of silica/metakaolin content on the final properties

Carbon black and high performance silica have been widely employed as binary system filler in tire tread formulations. This study evaluated the total and partial substitution of silica by metakaolin (MK) on the properties of tread rubber composites. Dynamic mechanical thermal analysis and abrasion tests were conducted as typical assessments of tire tread performance: rolling resistance (fuel consumption), wet traction (safety), and abrasion (durability). Further the energy spent by the equipment during the processing of formulations was also analyzed, as well as rheological and mechanical properties. A significant reduction of rolling resistance was obtained with 75% and 100% of silica substitution by MK, which could lead to lower heat buildup in tire tread applications, without showing negative effects on wet traction, although abrasion showed undesired results. The substitution of silica by MK also lowered energy demanded for processing. No major changes were observed in vulcanization parameters and mechanical properties, which is interesting considering the fact that MK is nonreinforce filler.

Influence of graphene oxide and multiwalled carbon nanotubes on the dynamic mechanical properties and heat buildup of natural rubber/carbon black composites

In this study, graphene oxide (GO) and multiwalled carbon nanotubes (MWNTs) were incorporated into natural rubber (NR) to study the influence of each of these materials when substituted for carbon black (CB) on the structure and properties of NR/CB composites. The influence of stirring time on the composites used to prepare the masterbatch was also studied. Morphological observations revealed that the dispersion of the filler was improved by partially substituting GO and MWNTs for CB. Improvements in the static mechanical properties and dynamic properties were achieved when the concentration of GO or MWNTs was 1 phr. The highest modulus and hardness was found in the composites with a short stirring time used for the preparation of the masterbatch. When compared to CB-filled vulcanizates, composites with GO had a greater tensile strength and equivalent heat buildup, which is mainly attributed to the larger cross-link density. In this article, compared with the MWNTs, GO is more beneficial to the preparation of rubber composite with high mechanical properties and low heat buildup. This is mainly due to the common functional groups carboxyl, hydroxyl, and epoxide in the GO can improve the dispersion of GO within a matrix.

PROPERTIES OF SBR FILLED WITH CARBON BLACK AND ARAMID PULP HYBRID FILLER: COMPARISON BETWEEN PREDISPERSED ARAMID PULP AND CONVENTIONAL ARAMID PULP

ABSTRACT Compounds of SBR incorporated with hybrid filler of carbon black (CB) and aramid pulp were prepared. The ratio of CB to aramid pulp was varied and its effects on viscoelastic and mechanical properties of the rubber were investigated. Two aramid pulp types were used in this study: conventional aramid pulp (CAP) and the predispersed aramid pulp (PAP). The rubber–filler interaction as indicated by bound rubber content decreases with increasing aramid pulp loading, regardless of the aramid pulp type. This results in a decrease in tensile and abrasion properties with increasing fiber loading. The energy dissipation properties of the hybrid composites are also poorer than those of the CB/SBR composite, as reflected by the heat buildup values. Use of predispersed aramid fiber resulted in improved dispersion of the fiber in SBR. Thus, Mooney viscosities of the PAP-filled systems are lower than those of the CAP-filled systems, but the percentages of elongation at breaks are higher. The distinct feature of aramid fiber/CB hybrid SBR composites is their high moduli over an extended range of temperatures up to 80°C that is unattainable with the use of CB alone.