Thermal Energy Balance Research Articles

Vertical air temperature gradients under the shade of two contrasting urban tree species during different types of summer days

Moderation of thermal energy balance through the canopies of urban trees is well known. However, a more functional and quantitative view of the heterogeneous urban environment and their influence on the below-canopy vertical air temperature gradients is largely missing. Throughout the summer 2016 we continuously measured air temperature at three different heights (at 1.5, 3 and 4.5m from the ground) under the canopies of two common but contrasting street tree species in respect of eco-physiology and morphology in Munich, Germany: Robinia pseudoacacia L. (ring porous) and Tilia cordata Mill. (diffuse porous). Along with air and surface temperature we also measured meteorological and edaphic variables and categorized summer time as cool, mild, summer and hot days. Global radiation, vapour pressure deficit and soil temperature increased as the days got warmer but precipitation, soil moisture and wind speed showed the reversed pattern. Overall, T. cordata trees with higher leaf area index and sap-wood area provided three times more transpiration than R. pseudoacacia. On an average air temperature gradient of outside to inside canopy dropped from 1.8°C to 1.3°C for T. cordata but from 1.5°C to only 0.5°C for R. pseudoacacia as the days got warmer. Vertical decline of air cooling effect was around 1°C from canopy to the near-ground (1.5m). Lower soil moisture but higher soil temperature suggested that cool air from the canopy mixed with a higher amount of sensible heat flux under the canopies of T. cordata compared to the R. pseudoacacia as the days got warmer. The study indicated a threshold for extreme hot days when grass surface evapotranspirational cooling will not be as effective and act like built surfaces rather deep shading from tree canopies will be important.

The physical foundation of the reconnection electric field

Magnetic reconnection is a key charged particle transport and energy conversion process in environments ranging from astrophysical systems to laboratory plasmas [Yamada et al., Rev. Mod. Phys. 82, 603–664 (2010)]. Magnetic reconnection facilitates plasma transport by establishing new connections of magnetic flux tubes, and it converts, often explosively, energy stored in the magnetic field to kinetic energy of charged particles [J. L. Burch and J. F. Drake, Am. Sci. 97, 392–299 (2009)]. The intensity of the magnetic reconnection process is measured by the reconnection electric field, which regulates the rate of flux tube connectivity changes. The change of magnetic connectivity occurs in the current layer of the diffusion zone, where the plasma transport is decoupled from the transport of magnetic flux. Here we report on computer simulations and analytic theory to provide a self-consistent understanding of the role of the reconnection electric field, which extends substantially beyond the simple change of magnetic connections. Rather, we find that the reconnection electric field is essential to maintain the current density in the diffusion region, which would otherwise be dissipated by a set of processes. Natural candidates for current dissipation are the average convection of current carriers away from the reconnection region by the outflow of accelerated particles, or the average rotation of the current density by the magnetic field reversal in the vicinity. Instead, we show here that the current dissipation is the result of thermal effects, underlying the statistical interaction of current-carrying particles with the adjacent magnetic field. We find that this interaction serves to redirect the directed acceleration of the reconnection electric field to thermal motion. This thermalization manifests itself in form of quasi-viscous terms in the thermal energy balance of the current layer. This collisionless viscosity, found in the pressure evolution equation, dominates near the x-line. These quasi-viscous terms act to increase the average thermal energy. Our predictions regarding current and thermal energy balance are readily amenable to exploration in the laboratory or by satellite missions, in particular, by NASA's Magnetospheric Multiscale mission.

Low carbon scenarios for higher thermal comfort in the residential building sector of South Eastern Europe

The paper presents the residential sector building typology, thermal energy balance, and scenarios prepared at several levels of sector segmentation to assist the design of low-carbon development policies for Albania, Serbia, and Montenegro. The research is breakthrough for developing Europe and could be replicated in its countries. The paper describes methodological steps and selected results. First, representative building types were identified; their energy performances by end-use, retrofit packages, as well as associated costs were assessed. Second, this information was inserted into a bottom-up simulation model prepared in the Long-range Energy Alternatives Planning System (LEAP) software. Using it, sector energy balances, the reference scenario, as well as moderate and advanced low-carbon high-thermal-comfort scenarios were prepared. The low-carbon scenarios assumed ambitious regulatory and financial policies. It was found that due to fuel poverty partial and intermittent heating is a typical situation; therefore, the thermal demand as predicted by the models applied to the different segments of the dwelling stock is much higher than its actual consumption. Also, actual consumption by energy source was found not fitting official energy balances because households use more wood and more heating systems than officially reported. In 2030, the moderate and ambitious scenarios lead to a reduction of CO2 emissions by 23–73% and 16–73% respectively versus the reference, offering however at the same time higher thermal comfort. The priority is to retrofit small buildings constructed after 1991 in Albania and those built in 1971–1990 in Montenegro and Serbia. Assuming the discount rate of 4% and counting saved energy costs as benefits, almost all scenarios are cost-effective as a whole on the country level, however not for many building categories. Therefore, not only saved energy costs but also other benefits should be monetized and compared to the scenario costs that present the next research opportunity.

Influence of Ash Ring on Lime Rotary Kiln Operation

This paper describes influence of ash ring on operation of lime rotary kiln in terms of process and energy consumption. Individual influences were described from perspective of combustion and change of process parameters from optimal parameters to limit operational conditions. Paper describes influence of ash ring formation on thermal energy balance during kiln operation from point of total thermal balance.

Analysis of thermal and electrical efficiency of photovoltaic/thermal – PV/T modules operating in moderate climate at microscale

The paper presents an application concept for PV/T - Photovoltaic Thermal Technology in moderate climates (such as the Polish climate), at a micro scale, i.e. for a single family house. The paper analyses the operation of a PV/T system applied to Domestic Hot Water – DHW heating and electricity production. A mathematical model of the system operation has been developed. The paper focuses on modeling thermal and electrical efficiency of photovoltaic/thermal - PV/T modules. It also briefly presents the governing equations for the thermal energy balance of a storage tank, where thermal stratification effects take place. Some selected results of the numerical simulation of the PV/T system operation are described. Daily distribution of hourly averaged thermal and electrical efficiency of the PV/T modules without cover and with one glazing are presented. The PV/T systems do not give significant thermal energy output in winter. PV/T modules without glazing do not supply heat at all for three winter months, their highest thermal efficiency is in summer and it can be nearly 15%. In the same period glazed modules have efficiency equal to nearly 24%. However, the unglazed modules can give much more electrical energy in summer than those with glazing, and the electrical efficiency can reach the levels of 11.4% and 9.4%, respectively. In winter the difference is smaller, i.e. for unglazed the efficiency is 12.2%, and for glazed 11.2%.

Renewable Energy from Thermal: Electrical Power Generation in Ceramic and Tile Industry

In recent years, global warming and environmental pollution caused a limitation of the use of natural energy and resource use has become more important Renewable resources. In the industrial sector, most of factories such as Ceramic tile production, glass, and cement of devices that are used for heat production of biofuel. After heat generation, thermal energy balance of heat production is wasted. Thermoelectric modules with exposure to ambient air temperature difference between the devices and electrical energy will generate. Ultra long life, lack of moving parts, quiet and relatively low price thermoelectric modules, they are a very attractive option for use in the field. Since the temperature above the ambient heat is transferred from wasted heat energy transferred to the surrounding environment can be used to produce electrical energy. In this study, a review of the development of Thermoelectric cooling briefly introduced first. Next, the Ceramic Tile Production Process has been summarized. To improve performance, have been described thermoelectric cooler modeling and numerical compact model. Finally, simulation results are presented. The electrical energy generated can be transmitted to electrical energy to the distribution network that the production process is simulated by MATLAB software.

Structural and material records of paleoearthquakes in terrigenous rocks: Analysis and interpretation

The results of an instrumental and analytical investigation of the products of mineral and textural transformations in the tectonic slickensides and fault gouge in the near-surface terrigenous sedimentary rocks (clays, arkose sandstones, shungites) which have undergone localized deformations in fault zones of presumably seismogenic origin are presented. Based on this, several peculiarities in the behavior of a dynamic slip in the upper transition horizon from aseismic to seismogenic mode of faulting in the Earth’s crust are elucidated. The changes in the mineral phase compositions of the fault facies against the protolith composition are estimated; the parameters of the temperature regime and thermal energy balance of deformational metamorphic reactions are determined. The probable causes of instability in the faults, the mechanisms of the loss of strength, the weakening and strengthening during seismogenic dynamic slip are considered. The role of tribochemical phenomena in the course of a rock’s transformation into a fault gouge and the related energy effects are discussed. An inventory of the possible energy costs on the processes of transforming material in dynamic slip zones is compiled.

Thermal analysis of a multistage active magnetic regenerator cycle for hydrogen liquefaction

The present paper deals with thermal analysis of cascade Active Magnetic Regenerator (AMR) cycle for the liquefaction of hydrogen starting from room temperature. For this purpose, the energy equations for fluid and solid within the regenerator bed of the AMR cycle have been considered. To solve the resulting mathematical model implicit finite difference method has been used. Thermal energy and mass balances are performed for several liquefaction systems composed of different number of cascade cycles. A simulation method using Hysys simulation commercial code has been presented. The multistage system operates with an ideal magnetic material as refrigerant and hydrogen gaseous as carrier fluid. First, the coefficient of performance (COP) of the AMR cycle and the required volume of magnetic material as functions of the number of cascades have been investigated. Then, the required volume is optimized by using the relationship between the COP and the volume. It has been found that a number of 6 AMR cycles operating in series is the optimal number of cascades required to liquefy 1 kg/h of hydrogen supplied at 25 °C. The system can operate between two volumes of magnetic material; namely, the minimum required volume (2.96 L) and the most efficient volume (7.44 L), corresponding to COP values of 1.23 and 4.7 respectively.

Discovery of massive star formation quenching by non-thermal effects in the centre of NGC 1097

Observations show that massive star formation quenches first at centers of galaxies. To understand quenching mechanisms, we investigate the thermal and nonthermal energy balance in the central kpc of NGC1097- a prototypical galaxy undergoing quenching- and present a systematic study of the nuclear star formation efficiency and its dependencies. This region is dominated by the nonthermal pressure from the magnetic field, cosmic rays, and turbulence. A comparison of the mass-to-magnetic flux ratio of the molecular clouds shows that most of them are magnetically critical or supported against gravitational collapse needed to form cores of massive stars. Moreover, the star formation efficiency of the clouds drops with the magnetic field strength. Such an anti-correlation holds with neither the turbulent nor the thermal pressure. Hence, a progressive built up of the magnetic field results in high-mass stars forming inefficiently, and it may be the cause of the low-mass stellar population in the bulges of galaxies.

A thermal energy balance optimization model of cutting space enabling environmentally benign dry hobbing

Dry hobbing is a well-known environmentally benign process for gears production by eliminating serious pollution and occupational health hazards in the shop floor. However, due to the absence of the cooling and lubrication of cutting oil, it requires quite accurate monitoring and adjustment of the accumulation of thermal energy within the cutting space to reduce the thermal deformation of machine tool. In this paper, an analytical method is proposed to reveal the mechanism of thermal energy accumulation in dry hobbing. And further, a thermal energy balance optimization model is developed to minimize the average temperature of cutting space by optimizing the heat-carrying efficiency of chips, the temperature of compressed air, and the mass flow rate of air filter. The comprehensive learning particle swarm optimization (CLPSO) based solution method is designed to search the optimal solutions of the proposed model. To verify the performance of the proposed thermal energy balance problem, a case study has been conducted and the experimental results showed that the maximum difference of the average temperature of cutting space reduced by 16.3%, and the M-value of hobbed gears was effectively controlled, which demonstrated the effectiveness of the proposed approach.

Tubular solar-energy collector integration: Performance enhancement of classical distillation unit

Abstract The current study discusses a new design regarding embedded simple distiller to a solar collector cylindrical shape. Investigating the performance improvement is based on solving transit thermal energy balance equations which can predict temperatures in different locations of the still. Introducing the pre–heater system was also modeled using a third ordinary differential equation for water as a working fluid. In order to validate the obtained findings, Dunkle's model was employed and outputs compared to previous works. Results demonstrated that the collector contributes appreciably in augmenting the basin water temperature higher than a simple still case and both couples of distillate amounts and instantaneous efficiencies were respectively (∼2.77 kg/m 2 , ∼4 kg/m 2 ) which an accorded enhancement of ∼31% and (∼40%, ∼80%) for the passive and active targets. The total cost of the collector materials was estimated to be about 63 US Dollars which represents a cheap price. Moreover, a critical issue was examined around heat losses of the proposed solar heater. At this stage, used empirical correlations available in literature enabling U L prediction (overall heat loss coefficient) of the former and flat–plate collector method has been performed. It was reached that the TSC can perform against a FPC with lower heat loss. Other parameters such as painted receiver, absorbtivity–emissivity effects and environmental circumstances have all influenced the TSC performance were also analyzed.

The Radial Temperature Gradient in the Gleeble® Hot-Torsion Test and Its Effect on the Interpretation of Plastic-Flow Behavior

The radial temperature gradient developed via direct-resistance heating of round-bar hot-torsion specimens in a Gleeble® machine and its effect on the interpretation of plastic-flow behavior were established using a suite of experimental, analytical, and numerical-simulation tools. Observations of the microstructure variation developed within a γ′-strengthened nickel-base superalloy were used to infer the temperature gradient as well as differences between the temperature at the outer diameter and that indicated by thermocouples welded to the surface. At temperatures of the order of 1375 K (1102 °C), the radial variation of temperature was typically ~20 K (~20 °C). Such variations were in agreement with an analytical heat-conduction model based on the balance of input thermal energy and radiation heat loss at the free surface. Using a constitutive model for LSHR, the effect of the radial temperature gradient on plastic flow during hot torsion was assessed via numerical integration of the torque as a function of radial position for such cases as well as that corresponding to a uniformly-heated sample. These calculations revealed that the torque generated in the non-uniform case is almost identical to that developed in a sample uniformly preheated to a temperature corresponding to that experienced at a fractional radial location of 0.8 in the former case.

An intermediate-scale model for thermal hydrology in low-relief permafrost-affected landscapes

Integrated surface/subsurface models for simulating the thermal hydrology of permafrost-affected regions in a warming climate have recently become available, but computational demands of those new process-rich simu- lation tools have thus far limited their applications to one-dimensional or small two-dimensional simulations. We present a mixed-dimensional model structure for efficiently simulating surface/subsurface thermal hydrology in low-relief permafrost regions at watershed scales. The approach replaces a full three-dimensional system with a two-dimensional overland thermal hydrology system and a family of one-dimensional vertical columns, where each column represents a fully coupled surface/subsurface thermal hydrology system without lateral flow. The system is then operator split, sequentially updating the overland flow system without sources and the one-dimensional columns without lateral flows. We show that the app- roach is highly scalable, supports subcycling of different processes, and compares well with the corresponding fully three-dimensional representation at significantly less computational cost. Those advances enable recently developed representations of freezing soil physics to be coupled with thermal overland flow and surface energy balance at scales of 100s of meters. Although developed and demonstrated for permafrost thermal hydrology, the mixed-dimensional model structure is applicable to integrated surface/subsurface thermal hydrology in general.

Simulation of coal permeability under non-isothermal CO<SUB align="right">2 injection

CO2 injection into coal seams is a non-isothermal process, which has significant impact on coal permeability but has not been well studied. In this paper, a non-isothermal model coupled with nonlinear gas flow and matrix deformation was developed. The effects of temperature change on each term of the effective strain during the CO2 injection scenarios, as well as the variations of fluid properties over a range of sub- and supercritical-thermodynamic conditions were investigated. This model involves the balance of thermal energy and the law of heat transfer. Two non-isothermal cases of CO2 injection were studied and compared with the isothermal case. The results show that CO2 injection into coal seams reduces coal permeability for all three cases. The coal matrix expands with temperature increase due to the thermal expansion and shrinks due to the decrease in adsorption amount. However, the final permeability with low-temperature CO2 injection remains lower than that with high-temperature gas injection since the effect of sorption-induced strain on permeability outweighs that of the thermal deformation. The increase in temperature leads to the reduction in coal swelling (with the decrease of CO2 adsorption capacity), resulting in larger cleat aperture and higher coal permeability for the cases studied in this work. [Received: November 29, 2015; Accepted: June 22, 2016]

Simulation of coal permeability under non-isothermal CO<SUB align="right">2 injection

CO2 injection into coal seams is a non-isothermal process, which has significant impact on coal permeability but has not been well studied. In this paper, a non-isothermal model coupled with nonlinear gas flow and matrix deformation was developed. The effects of temperature change on each term of the effective strain during the CO2 injection scenarios, as well as the variations of fluid properties over a range of sub- and supercritical-thermodynamic conditions were investigated. This model involves the balance of thermal energy and the law of heat transfer. Two non-isothermal cases of CO2 injection were studied and compared with the isothermal case. The results show that CO2 injection into coal seams reduces coal permeability for all three cases. The coal matrix expands with temperature increase due to the thermal expansion and shrinks due to the decrease in adsorption amount. However, the final permeability with low-temperature CO2 injection remains lower than that with high-temperature gas injection since the effect of sorption-induced strain on permeability outweighs that of the thermal deformation. The increase in temperature leads to the reduction in coal swelling (with the decrease of CO2 adsorption capacity), resulting in larger cleat aperture and higher coal permeability for the cases studied in this work. [Received: November 29, 2015; Accepted: June 22, 2016]

QUALITATIVE SCREENING METHOD FOR IMPACT ASSESSMENT OF UNCERTAIN BUILDING GEOMETRY ON THERMAL ENERGY DEMAND PREDICTIONS

Abstract. Virtual 3D models of cities are now being extensively employed for the estimation of thermal energy demand at varying spatial and temporal scales. Efforts in preparing and management of the datasets required for the simulations have reached an advanced stage. Thus allowing to perform city scale simulations using simplified thermal energy balance models. However, the uncertainty inherent in datasets and the reliability of their data sources are often not given due consideration. Such consideration to the uncertainty problem would need a paradigm shift in simulation practices from a single value assignment to uncertainty characterization followed by assessment of qualitative and quantitative impact on the simulation results. The proposed study establishes a mechanism to handle the uncertainty arising from the building geometry reconstruction process and its possible consequences on the thermal energy demand calculations.

Energy balance at the soil atmospheric interface

Soil atmospheric interactions play an important role within the thermal energy balance and seasonal temperature variations of the ground. This paper presents a formulation for the surface boundary conditions related to interactions between soil and atmosphere. The boundary condition formulated considers heat flow at the soil–atmosphere interface through mechanisms of shortwave radiation, long-wave radiation, sensible radiation and latent heat radiation. The effects of surface moisture flux on energy balance at the interface are explicitly included in the formulation. The developed boundary condition has been implemented in a numerical model for coupled thermal, hydraulic and mechanical behaviour of unsaturated soils. The evaporation component of the model is tested, and the results are compared with data from an experimental study at the surface of an area of agricultural land reported in the literature. The results of modelling have been found to compare favourably with the reported data set. The formulation developed for the soil atmospheric boundary condition allows climatic variables, including solar radiation, ambient air temperature, relative humidity, wind speed, rainfall and evaporation, to be incorporated in the long-term analysis of energy balance. This also enables a further detailed inspection of the climate’s role in ground thermal behaviour of ground source heat systems.

Transient temperature behavior and analysis of single-phase liquid-water geothermal reservoirs during drawdown and buildup tests: Part I. Theory, new analytical and approximate solutions

This work focuses on transient temperature responses of single-phase liquid-water geothermal reservoirs to constant-rate drawdown and buildup tests. New analytical and approximate solutions are presented for predicting drawdown and buildup sand-face transient temperature behaviors of a fully penetrating vertical well in an infinite-acting homogeneous reservoirs. The solutions account for the effects of Joule-Thomson (J-T) heating/cooling, transient adiabatic fluid expansion/compression, convection, and conduction. The solutions are compared and verified with the solutions from three different non-isothermal simulators that solve the mass and thermal energy balance equations rigorously and simultaneously. The impacts of various parameters such as wellbore storage, skin zone near the wellbore, thermal conductivity, and outer reservoir boundary conditions on the sand-face temperature responses are also investigated and discussed. Drawdown and buildup sand-face temperature data are shown to exhibit three infinite-acting radial flow (IARF) periods (represented by semi-log straight-line equations); early-time IARF reflecting the adiabatic expansion/compression effects in the skin zone if it exists, intermediate-time IARF reflecting the J-T effect in the skin zone, and late-time IARF reflecting the J-T effect in the non-skin zone. In an accompanying paper (Part II), we present an interpretation and analysis methodology based on the analytical solutions derived here for parameter estimation from temperature transient data jointly with pressure transient data.

Overall energy, exergy and carbon credit analysis of N partially covered Photovoltaic Thermal (PVT) concentrating collector connected in series

In this paper, overall thermal energy gain and exergy gain have been analyzed for four different cases (case (i) 25% PV coverage area, case (ii) 50% PV coverage area, case (iii) 75% PV coverage area and case (iv) 100% PV coverage area, on each collector) of N-numbers of partially covered Photovoltaic thermal (PVT)-compound parabolic concentrator (CPC) water collector connected in series. The analysis is computed by considering a, b, c and d type weather conditions for New Delhi climate condition, India. A transient model of N-PVT-CPC water collectors connected in series has been developed using basic thermal energy balance equations. Six collectors has been optimized for desired temperature range. An attempt has been taken to select an appropriate configured partially covered N-PVT-CPC water collector. On the demand of electrical and overall exergy, case (iv) has been found to be appropriate because net annually overall exergy is 752.77kWh and net annual electrical energy is 683.40kWh which is maximum. On the other hand, when the demand of thermal gain is needed, case (i) is first choice due to it has been given 5203.02kWh overall thermal energy gain which is five times greater than case (iv). The enviroeconomic study examines CO2 emission per annum is reduced by energy generation and how much money is saved. For case (i), 153.90$/annum on overall thermal energy basis and 22.25$/annum on the basis of overall exergy for case (iv).

The response of the temperature of cold‐point mesopause to solar activity based on SABER data set

AbstractThe thermal structure and energy balance of upper atmosphere are dominated by solar activity. The response of cold‐point mesopause (CPM) to solar activity is an important form. This article presents the response of the temperature of CPM (T‐CPM) to solar activity using 14 year Sounding of the Atmosphere using Broadband Emission Radiometry data series over 80°S–80°N regions. These regions are divided into 16 latitude zones with 10° interval, and the spatial areas of 80°S–80°N, 180°W–180°E are divided into 96 lattices with 10°(latitude) × 60°(longitude) grid. The annual‐mean values of T‐CPM and F10.7 are calculated. The least squares regression method and correlation analysis are applied to these annual‐mean series. First, the results show that the global T‐CPM is significantly correlated to solar activity at the 0.05 level of significance with correlation coefficient of 0.90. The global solar response of T‐CPM is 4.89 ± 0.67 K/100 solar flux unit. Then, for each latitude zone, the solar response of T‐CPM and its fluctuation are obtained. The solar response of T‐CPM becomes stronger with increasing latitude. The fluctuation ranges of solar response at middle‐latitude regions are smaller than those of the equator and high‐latitude regions, and the global distribution takes on W shape. The corelationship analysis shows that the T‐CPM is significantly correlated to solar activity at the 0.05 level of significance for each latitude zone. The correlation coefficients at middle‐latitude regions are higher than those of the equator and high‐latitude regions, and the global distribution takes on M shape. At last, for each grid cell, the response of T‐CPM to solar activity and their correlation coefficient are presented.