Thermo-hydro-mechanical modelling study of heat extraction and flow processes in enhanced geothermal systems

Enhanced Geothermal Systems (EGS) are widely used in the development and application of geothermal energy production. They usually consist of two deep boreholes (well doublet) circulation systems, with hot water being abstracted, passed through a heat exchanger, and reinjected into the geothermal reservoir. Recently, simple analytical solutions have been proposed to estimate water pressure at the abstraction borehole. Nevertheless, these methods do not consider the influence of complex geometrical fracture patterns and the effects of the coupled thermal and mechanical processes. In this study, we implemented a coupled thermo-hydro-mechanical (THM) model to simulate the processes of heat extraction, reservoir deformation, and groundwater flow in the fractured rock reservoir. The THM model is validated with analytical solutions and existing published results. The results from the systems of single fracture zone and multi-fracture zones are investigated and compared. It shows that the growth of the number and spacing of fracture zones can effectively decrease the pore pressure difference between injection and abstraction wells; it also increases the production temperature at the abstraction, the service life-spans, and heat production rate of the geothermal reservoirs. Furthermore, the sensitivity analysis on the flow rate is also implemented. It is observed that a larger flow rate leads to a higher abstraction temperature and heat production rate at the end of the simulation, but the pressure difference may become lower.

Array modified PdAg/Al2O3 catalyst for selective acetylene hydrogenation: Kinetics and thermal effect optimization

Aiming at the low surface area of high-temperature-calculated alumina limits the dispersion of active metals, an in-situ growth method is applied to fabricate the alumina array modified spherical alumina. Taking the modified alumina as support, the highly dispersed PdAg catalyst for selective acetylene hydrogenation is synthesized, which exhibits a remarkable enhanced intrinsic activity. Moreover, when the acetylene conversion reached 90%, the ethylene selectivity remains 89%. Preferred selectivity is assigned to more isolated Pd sites and high electronic density, which facilitates the desorption of the resulting ethylene. More importantly, the modified catalyst exhibits good structural stability and resistance to carbon deposition. From one aspect, the decrease of heat production rate over active site is conducive to reduce the reaction heat accumulation, thereby avoiding the formation of hot-spots over the catalyst. From another point of view, the outer opening pore structure of the modified alumina are benefit for the heat transfer.

Total, average and marginal rates of basal heat production during human growth

<abstract> <p>Our goal was to examine how total, average (heat production rate per unit mass) and marginal (the increase in the heat production rate per unit increase in mass) rates of basal heat production changed as mass increased in growing humans. Specifically, our hypotheses were that the marginal basal heat production rate did not decrease monotonically as humans grew; and that an energetically optimal mass, one at which the average basal heat production rate of a growing human was minimal, existed. Marginal rates of heat production were estimated and six potential models to describe the effect of mass during human growth on basal heat production rate were evaluated using a large, meticulously curated, dataset from the literature. Marginal rates of heat production were quadratically related to body mass during growth; they declined initially, reached a minimum, and then increased. This suggested that the relationship between basal heat production rate and mass was cubic. Of the six potential models evaluated, a three-parameter cubic polynomial best described the data. Marginal rates of heat production were minimal for 56-kg females and 62-kg males. Basal heat production rates per unit mass of a growing human were minimal (i.e., energetically optimal) for 83-kg females and 93-kg males; the average masses of U.S. adults have been increasing and approaching these optima over the last 60 yr.</p> </abstract>

Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat

It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [ n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF ( n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (−2.5 ± 1.1 vs. −1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses ( P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (−0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group ( P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF. NEW & NOTEWORTHY This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated.

Fluid ingestion is more effective in preventing hyperthermia in aerobically trained than untrained individuals during exercise in the heat

It is unclear if fluid ingestion during exercise in the heat alleviates the thermoregulatory and cardiovascular strain similarly in aerobically trained and untrained individuals. It is also unknown at what exercise intensity the effects of rehydration are greater. Ten aerobically trained (T) and 10 healthy untrained (UT) subjects ([Formula: see text]O2peak, 60 ± 6 vs. 44 ± 3 mL O2·kg−1·min−1, respectively; P < 0.05) pedalled in a hot, dry environment (36 ± 1 °C; 25% ± 2% relative humidity; airflow, 2.5 m·s−1) at 40%, 60%, and 80% [Formula: see text]O2peak while ingesting fluids (Fluid). The results were compared with those from our previous study [Mora-Rodriguez et al., Eur. J. Appl. Physiol. 109(5): 973–981 (2010)] with no fluid ingestion (No Fluid). Subjects were not heat-acclimated. At 40% [Formula: see text]O2peak, Fluid reduced rectal temperature (TRE) in T and UT (0.31 ± 0.08 and 0.32 ± 0.07 °C; respectively). At 60% [Formula: see text]O2peak, Fluid reduced TRE in T more than in UT (0.30 ± 0.10 °C vs. 0.18 ± 0.10 °C; P < 0.05) but had no effect at 80% [Formula: see text]O2peak in any group. At similar relative intensity, heart rates (HR) were similar between groups. Fluid lowered heart rate (i.e., HR) similarly in the T and UT at 40% and 60% [Formula: see text]O2peak (11% and 6%, respectively; P < 0.05) but not at 80% [Formula: see text]O2peak (P > 0.05). At similar metabolic heat production (i.e., 60% for T vs. 80% [Formula: see text]O2peak for UT), Fluid lowered TRE only in the T individuals (P < 0.05). In summary, rehydration during low- and moderate-intensity exercise reduces TRE and HR more than during high-intensity exercise (80% [Formula: see text]O2peak) in T and UT subjects. Fluid replacement is more effective on preventing the rise in TRE in T than in UT individuals during moderate-intensity exercise (60% [Formula: see text]O2peak), as well as when exercising at a similar heat production rate.

Anthropogenic Heat Release Into the Environment

This work is intended to systematically study an inventory of the anthropogenic heat produced. This research strives to present a better estimate of the energy generated by humans and human activities, and compare this estimate to the significant energy quantity with respect to climate change. Because the Top of Atmosphere (TOA) net energy flux was found to be 0.85±0.15 W/m2 the planet is out of energy balance, as studied by the group from NASA in 2005. The Earth is estimated to gain 431 TW from this energy imbalance. This number is the significant heat quantity to consider when studying global climate change, and not the 78,300 TW, the absorbed part of the primary solar radiation reaching the Earth’s surface, as commonly cited and used at present in the literature. Based on energy supplied to the boilers (in the Rankine cycle) of at least 13 TW, body energy dissipated by 7 billion people and their domestic animals, the value of the total world anthropogenic heat production rate is 15.26 TW or 3.5% of the energy gain by the Earth. Based on world energy consumption and the energy dissipated by 7 billion people and their domestic animals, the value of the total world anthropogenic heat production rate is 19.7 TW or about 5% of the energy gain by the Earth. These numbers are significantly different from 13 TW. More importantly, the figures are 3.5 to 5% of the net energy gained by the Earth, and hence significant. The quantity is not 0.017% of the absorbed part of the main solar radiation reaching the Earth’s surface and negligible.

Anthropogenic Heat Release Into the Environment

This work is intended to systematically study an inventory of the anthropogenic heat produced. This research strives to present a better estimate of the energy generated by humans and human activities, and compare this estimate to the significant energy quantity with respect to climate change. Because the top of atmosphere (TOA) net energy flux was found to be 0.85 ± 0.15 W/m2 the planet is out of energy balance, as studied by the group from NASA in 2005. The Earth is estimated to gain 431 terawatts (TW) from this energy imbalance. This number is the significant heat quantity to consider when studying global climate change, and not the 78,300 TW, the absorbed part of the primary solar radiation reaching the Earth's surface, as commonly cited and used at present in the literature. Based on energy supplied to the boilers (in the Rankine cycle) of at least 13 TW, body energy dissipated by 7 × 109 people and their domestic animals, the value of the total world anthropogenic heat production rate is 15.26 TW or 3.5% of the energy gain by the Earth. Based on world energy consumption and the energy dissipated by 7 × 109 people and their domestic animals, the value of the total world anthropogenic heat production rate is 19.7 TW or about 5% of the energy gain by the Earth. These numbers are significantly different from 13 TW. More importantly, the figures are 3.5–5% of the net energy gained by the Earth, and hence significant. The quantity is not 0.017% of the absorbed part of the main solar radiation reaching the Earth's surface and negligible.