Heat Balance Research Articles

Wpływ zmian klimatu na środowisko zabudowane

We are currently in the period of an intensive climate change, resulting from changes in the heat balance of the earth’s surface and causing an increase in the temperature of the lower troposphere levels. According to the latest IPCC report of 2021, it is human activity that has indisputably caused the increase in atmospheric concentrations of greenhouse gases, responsible for this process. The consequences of climate change under Polish conditions, apart from a rise in temperature especially in the spring and winter months, are also changes in the amount and distribution of precipitation totals. A slight increase in precipitation totals is observed, however heavy rainfall is significantly more frequent, interspersed with periods of droughts and heatwaves. Ground frost-free periods are prolonged, and a negative trend in the duration and thickness of snow cover is recorded in most parts of the country. Although extreme phenomena occurring in Poland are permanently inscribed in its climatic conditions, the threat of strong winds has been increasing in recent years, and the intense precipitation that often accompanies them is the cause of peak discharges and flooding. Forecasts for progressive climate change are not optimistic, either on a global scale or for the country in question. The article examines the impact of climate change on the design, construction and maintenance of engineering structures globally and for Poland. Changes in design standards, selected examples of disasters and solutions to adapt and build resilience to climate change have been analysed. For most building disasters, climatic factors were the direct cause of the disaster, although in the course of the analysis it has usually turned out that the disasters exposed human errors in the design, construction and, to a lesser extent, the improper maintenance of engineering structures. However, there is an increasing number of new approaches to creating a climate change resilient built environment, including the latest one, which proposes to use the grey infrastructure of cities to build resilience to climate change.

Condensation characteristics of flows in newly developed three-dimensional enhanced heat transfer tubes

Condensation heat transfer characteristics were studied experimentally in order to evaluate the heat transfer performance of horizontal copper heat transfer tubes (smooth and enhanced). Using R410A and R32 as refrigerants, condensation heat transfer experiments were carried out for a saturation temperature of 45 °C; inlet vapor quality of the tube was 0.8 and outlet quality was 0.2; refrigerant mass flow rate range was in the range from 68 to 371 kg/(m2·s). Single-phase heat balance verification found that the heat loss is less than 6 %, with the deviation between single-phase experimental results and various correlations being less than 15 %. The condensation heat transfer coefficient increases with an increase in mass flow; as the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient (HTC) increases. Experimental results determined that the performance factor ratio (enhanced tube/smooth tube) of the three-dimensional surfaces investigated here are greater than 1. Tubeside heat transfer enhancement factor (EF) of the HB/D tube is the highest (max 1.76); its performance is closely related to increasing fluid turbulence and improving drainage. Performance factor (PF) of the HB/D tube (max 1.38) is the highest for most of the flowrates. All this indicates excellent thermal performance. Flow model-based analysis was performed in order to develop a correlation for the condensation heat transfer coefficient and the pressure drop for the enhanced surface tubes. Both prediction models accurately predicted all data points within a limited margin of error.

Investigating the transient conditions of “Sabat” space and its influence on pedestrian sensations during thermal walks. Algiers’ Casbah case study

Cities are already witnessing the impacts of climate change. Prolonged heat exposure have a direct effect on pedestrians’ thermoregulatory system, causing serious heat-related issues in the form of fatigue and thermal exhaustion. While the human body is capable of maintaining heat balance, excessive heat exposure combined with increasing heat loads can deteriorate the thermoregulatory process which leads to discomfort. Walkability is one of the significant challenges for climate change mitigation. Balancing the dichotomy of walking to mitigate climate change, and mitigating climate change to walk emphasizes the importance of promoting resilient walkability. In this context, the term “resilience” is used to highlight the need to design urban spaces able to adapt to increased urban heat, enabling pedestrians to tolerate and recover from discomfort conditions. This study investigates the potential of the “Sabat”, a traditional semi-outdoor space with lift-up design, and its distribution in generating transient thermal aeraulic conditions, and reducing fatigue sensation, hence, supporting a positive walking experience. Thermal walks have been conducted in Casbah of Algiers during temperate and hot weather conditions, in the context of uphill walking. Results revealed the alliesthesial effect of cool-shaded and ventilated Sabats to reduce fatigue sensation, which was confirmed by the significant correlation at lag-(-1) (r = 0.504, p < 0.001). Findings shed light on the importance of maintaining dynamic alliesthesia to create modulated restorative opportunities and offer starting point for hypothesizing broader trends for future implementation of Sabat design in modern cities.

Thermal Efficiency in Steel Reheating Process

In this study, the energy consumption by theprocess of steel billet reheating in an industrial steel reheatfurnace at the Libya Iron and Steel Company (LISCO) isconsidered. It is known that in the steel industry, one of the processes requiring the most energy is the process ofreheating the steel prior to hot rolling. A comprehensivemass and heat balance was performed on the furnace, takinginto account all actual entering and exiting furnaceparameters. Furnace thermal efficiency was found to be lowand heat losses from different areas of the furnace wereconsiderable.

Estimating the income-related inequality aversion to energy limiting behavior in the United States

Distributive energy justice is measured by the degree to which, and whether, different members of society have equal share in the benefits and burdens of the energy system. One way to achieve distributional energy justice is to ensure all households, regardless of income, can use as much energy as they need to heat and cool their home to desired temperature. We define a household's cooling balance point (CBP) as the ideal set temperature at which the household desires to keep its living space in summer; the heating balance point (HBP) is defined as the ideal set temperature in winter. To quantify the extent to which balance points were disproportionately concentrated among certain income groups, we used the extended concentration index. This index has an inequality aversion parameter that reflects the value judgment of a society. If this parameter <1, the society is pro-rich; if this parameter >1, as it increases, the society becomes more pro-poor. We estimated the empirical value of the income-related inequality aversion in eight U.S. states and examined several effects of demographic characteristics on inequality aversion.In an online survey, 1066 (from four southern states) and 906 (from four Midwest states) participants made choices between energy policies leading to different distributions of CBP (southern) or HBP (Midwest) across five income groups in a hypothetical society. Participants showed a pro-poor propensity: the median inequality aversions were 1.37, 95% CI of [1.35, 1.39] (CBP) and 1.56, 95% CI of [1.56, 1.60] (HBP). For both CBP and HBP: younger participants were less averse to inequality. For CBP, blacks (vs. whites) and conservatives (vs. centrist) were less averse to inequality; for HBP, Hispanics (vs. whites), low (vs. high) education participants, and those whose homes were well insulated (vs. adequately and vs. poorly insulated) were less averse to inequality. Our findings provide insights into how the broader public values energy justice, which further provides important policymaking implications.

Research on the Heat Dissipation in Aviation-Integrated Communication Equipment Based on Graphene Films

Aviation-integrated communication equipment is integral to modern aircraft to ensure its performance and safety. The heat dissipation problems of equipment have become increasingly prominent for the high electronic integration and system power consumption. To solve the above problem, the heat dissipation performance of aviation-integrated communication equipment based on graphene films is deeply studied. This paper establishes a three-dimensional model of aviation-integrated communication equipment to simulate the distribution of temperature fields. The influence between aluminum alloy and graphene films on the surface of magnesium alloy on the heat dissipation performance of aviation-integrated communication equipment is studied. The simulation results show that the heat balance time of the equipment using graphene films on the surface of magnesium alloy is reduced from 3600 s to 800 s, representing an approximately 77.78% improvement; the measured equipment exhibited a reduction in its overall thermal equilibrium temperature, decreasing from 68.1 °C to 66.3 °C, representing an improvement of approximately 2.64%.

Parametric Sensitivity Analysis of Stability Margins of Holos-Quad Microreactor

An analysis of the stability margins of the innovative Holos-Quad microreactor design is presented. This high-temeprature gas-cooled reactor (HTGR) system is designed to operate fully autonomously with passive safety mechanisms. Therefore, the inherent stability of the reactor is of great importance. Using a point-reactor model, which couples point kinetics to thermal-hydraulic heat balance equations and includes reactivity feedback effects of the fuel and moderator temperatures, the closed-loop transfer function of the reactor is derived. Applying the approach of linear systems and control theory, both the gain and phase margins of the Holos-Quad design are obtained. The analysis demonstrates that the design is stable, with an infinite gain margin and a finite phase margin. A parametric uncertainty quantification study is also performed using a total Monte Carlo approach. The stability of the reactor for different power levels, such as during reactor startup or load-following transients, is also explored. Finally, two sensitivity analysis methods are applied, namely, multiple regression (deriving standardized regression coefficients) and variance-based sensitivity analysis (known as the Sobol method), to study the contribution of each of the parameters to the stability margins’ uncertainty. This analysis improves our understanding of the role of each of the parameters in the stability of the reactor.

Effects of Freezing Temperature Parameterization on Simulated Sea‐Ice Thickness Validated by MOSAiC Observations

AbstractFreezing temperature parameterization significantly impacts the heat balance at sea‐ice bottom and, consequently, the simulated sea‐ice thickness. Here, the single‐column model ICEPACK was used to investigate the impact of the freezing temperature parameterization on the simulated sea‐ice thermodynamic growth during the MOSAiC expedition from October 2019 to September 2020. It is shown that large model errors exist with the standard parameterization and that different formulations for calculating the freezing temperature impact the simulated sea‐ice thickness significantly. Considering the winter mixed layer temperature, a modified parameterization of the freezing point temperature based on Mushy scheme was developed. The mean absolute error (ratio) of simulating sea‐ice thickness for all buoys reduces from 7.4 cm (4.9%) with the “Millero” scheme, which performs the best among the existing schemes in the ICEPACK model, to 4.2 cm (2.9%) with the new developed scheme.

Adjustments in energy metabolism of brown adipose tissue in heat-acclimated Kunming mice

The thermogenic capacity of brown adipose tissue (BAT) in rodents decreases with prolonged heat exposure. However, the underlying mechanisms are not well understood. In this study, Kunming mice were acclimated at 23 ± 1 °C and 33 ± 1 °C for four weeks each to examine the body heat balance and BAT alterations. Results showed that heat-acclimated Kunming mice exhibited reduced body mass and elevated body temperature. Additionally, they displayed lower resting metabolic rates, diminished non-shivering thermogenesis, and reduced BAT thermogenic function. Metabolically, there was a significant reduction in several key metabolites involved in energy metabolism in BAT, including thiamine pyrophosphate, citric acid, cis-Aconitate, isocitric acid, oxoglutaric acid, succinate, fumarate, L-Malic acid, oxaloacetate, flavin mononucleotide, nicotinamide adenine dinucleotide, and adenosine 5′-triphosphate. These findings suggest that BAT adapts to heat acclimation by regulating pathways related to pyruvate oxidation, tricarboxylic acid cycle, and oxidative phosphorylation, which may help maintain thermal homeostasis in Kunming mice.

Simulation of urban surface temperature and surface heat balance in the Tokyo metropolitan area

This study aimed to propose a method for simulating ground surface temperature and surface heat balance using thermal infrared remote sensing and an urban surface heat balance model and to conduct a simulation in the Tokyo metropolitan area. Previous studies have typically employed ground surface temperatures obtained through satellite remote sensing to analyze urban thermal environments. However, these studies were limited to using surface temperature data available only at the time of satellite passage. Therefore, in this study, we conducted a simulation for the Tokyo metropolitan area by integrating a one-dimensional heat balance model with ground surface temperatures observed by satellites. The novelty of this study lies in the utilization of parameters related to heat balance obtained through calculations of physical processes, as opposed to relying on empirical formulas or parameters. Consequently, realistic ground surface characteristics, including parameters such as evaporation efficiency and thermal inertia essential for the simulation, were derived by this combined method. Furthermore, diurnal variations in ground surface temperature distributions were accurately represented by using realistic surface temperature data based on satellite remote sensing, considering the effect of heat storage in urban areas—an aspect challenging to reproduce using conventional local meteorological models.

Disaggregation of canopy photosynthesis among tree species in a mixed broadleaf forest.

Carbon dioxide sequestration from the atmosphere is commonly assessed using the eddy covariance method. Its net flux signal can be decomposed into gross primary production and ecosystem respiration components, but these have seldom been tested against independent methods. In addition, eddy covariance lacks the ability to partition carbon sequestration among individual trees or species within mixed forests. Therefore, we compared gross primary production from eddy covariance versus an independent method based on sap flow and water-use efficiency, as measured by the tissue heat balance method and δ13C of phloem contents, respectively. The latter measurements were conducted on individual trees throughout a growing season in a mixed broadleaf forest dominated by three tree species, namely English oak, narrow-leaved ash and common hornbeam (Quercus robur L., Fraxinus angustifolia Vahl, and Carpinus betulus L., respectively). In this context, we applied an alternative ecophysiological method aimed at verifying the accuracy of a state-of-the-art eddy covariance system while also offering a solution to the partitioning problem. We observed strong agreement in the ecosystem gross primary production estimates (R2=0.56; P<0.0001), with correlation being especially high and nearly on the 1:1 line in the period before the end of July (R2=0.85; P<0.0001). After this period, the estimates of gross primary production began to diverge. Possible reasons for the divergence are discussed, focusing especially on phenology and the limitation of the isotopic data. English oak showed the highest per-tree daily photosynthetic rates among tree species, but the smaller, more abundant common hornbeam contributed most to the stand-level summation, especially early in the spring. These findings provide a rigorous test of the methods and the species-level photosynthesis offers avenues for enhancing forest management aimed at carbon sequestration.

Experimental Study of Composite Heat Pipe Radiator in Thermal Management of Electronic Components

Conventional straight fin (SF) radiators have difficulties meeting the cooling requirements of high-power electronic components. Therefore, based on the structure and technology of the detachable fin radiator, this paper proposes a kind of radiator embedded in the heat pipe base and uses the roll-bond flat heat pipe (RBFHP) to replace the traditional fin. The radiator has the advantages of modularity, easy manufacturing, low cost and good heat balance. In this study, the heat pipes (HPs)-RBFHPs radiator was tested in natural convection and forced convection to mimic the actual application scenario and compared with the conventional aluminum radiator. Heating power, angle, wind speed and other aspects were studied. The results showed that the cooling performance of the HPs-RBFHPs radiator was improved by 10.7% to 55% compared with that of the SF radiator under different working conditions. The minimum total thermal resistance in the horizontal state was only 0.37 °C/W. The temperature equalization of the base played a dominant role in the performance of the radiator at a large angle, and the fin group could be ineffective when the angle was greater than 60°. Under the most economical conditions with an inclination of 0° and a wind speed of 2 m/s, the input power was 340 W, the heat source temperature of the HPs-RBFHPs was only 64.2 °C, and the heat dissipation performance was 55.4% higher than that of SFs.

Weather-dependency of the thermographic flow visualization of the laminar-turbulent transition on wind turbines

Abstract Analyzing the airflow around wind turbines during operation requires an in-process-capable measurement approach that functions without modification of the rotor blade. Infrared–thermographic flow visualization is such a measurement approach. However, its measurement capabilities on wind turbines in operation are highly weather-dependent. Therefore, to understand the expected flow visualization quality in non-laboratory conditions, the dependence of the achievable contrast and contrast-to-noise ratio (CNR) of the laminar-turbulent transition on solar radiation and air temperature is studied, respectively. A linear dependence of the contrast on the absorbed solar radiation is derived as a first estimation from a theoretical study of the heat balance. While the air temperature variations are shown to have no effect under certain conditions. The slope of the linear dependence of about 0.025 m2K W−1 was validated by experiments. To further study the fundamental measurability limit, only the camera noise with constant variance is here applied to determine the achievable CNR, which is thus directly proportional to the contrast. As a result, the achievable contrast and CNR for visualizing the laminar-turbulent flow transition over the year, over the day, and for different yaw angles of the wind turbine are determined. For this investigation, a wind turbine location near in northern Germany, is assumed as an example, and a maximal achievable contrast and CNR of 4.2 K and 122, respectively, are estimated, which agree with previous measurements. The presented method applies to any other wind turbine location and thus enables planning thermographic flow measurements on any wind turbine in the world.

Developments in scale-up procedures for industrial dryers

The aim of dryer scale-up is to increase batch size, or throughput of a continuous process, while maintaining final moisture content, product quality, end-use properties, safety and reliability. This article reviews and updates previously published material on scale-up processes of dryers in general and individual dryer types, particularly material from a Drying Technology special issue on scale-up in 1994. This is adapted to give a basic generic theory for scale-up, applying this to various dryers and noting specific exceptions. It is demonstrated that simplifying assumptions can often be reliably made for scale-up which reduce the level of complexity for modeling compared to equipment design and performance calculations. For example, prediction of drying rate and drying time in spray and flash dryers needs a kinetic model, but for scale-up a heat balance and scaling calculation usually suffices. Approximations such as a one-third power law for drying time are often effective. It is shown that there is some theoretical basis for empirical scale-up rules that have been used by dryer manufacturers. Scale-down is also important, selecting the most appropriate conditions for small-scale tests that will correspond to the desired performance at commercial scale. The individual concepts are not new, but they have not previously been unified into a simply stated general basis for scale-up.

Multi-objective optimization and evaluation of the building-integrated photovoltaic/thermal-energy pile ground source heat pump system

Building integrated photovoltaic thermal (BIPV/T)-energy pile ground source heat pump (GSHP) system effectively maintains the soil thermal balance and improves the photovoltaic efficiency by recovering the waste solar heat from the BIPV/T collector to charge the ground. However, due to the strict carbon emission restriction and economic consideration for system application, multi-objective optimization should be implemented for the system design to further enhance its overall performance. Therefore, a complete optimization framework is proposed in this paper, which is based on the NSGA-II algorithm and functions by coupling TRNSYS and jEPlus+EA. Using the proposed optimization frame, a comprehensive optimization is conducted for the system, which optimizes five main design variables and adopts the total power consumption (TPC), life cycle climate performance (LCCP), and life cycle cost (LCC) to reflect the system's energetic, environmental, and economic performances. Seven optimization cases are included in the optimization project to identify design schemes that meet all possible proposed performance requirements for the system application. The optimized results show that the system optimization improves its performance greatly compared to the design condition, with a range of 38.03% ∼ 50.05% for the TPC, 24.52% ∼ 25.86% for LCCP, and 56.74% ∼ 61.66% for LCC. The energetic, environmental and economic performances of the system can be maximized by minimizing the TPC to 357.29 MWh in Case 1, LCCP to 596.15 tCO2 in Case 2, and LCC to 17.03 × 104 CNY in Case 3. By breaking down the objective functions, it is found that the heat pump unit holds paramount importance in all aspects of system performance, and the BIPV/T collector proves advantageous in enhancing the system's long-term performance due to its massive electricity generation. Accordingly, one important finding is that it is advisable to incorporate as many BIPV/T collectors as feasible while maintaining soil heat balance. The optimal energy pile number varies among the seven optimization cases, resulting in different heating capacities for the heat pump unit. Research outcomes in this work offer references for designing the energy-pile GSHP system to enhance the penetration of renewable energy into buildings.

Spectroscopic assessment and quantitative analysis of the trace element composition of vegetable additives to meat products

In this scientific work, using the method of laser-induced breakdown spectroscopy (LIBS), the spectra of beef samples and impurities in meat products, namely, banana, pineapple, kiwi, bergamot, poria coconut, Chinese angelica, chicken blood vine, were measured by using developed experimental devices. The purpose of the research was to evaluate the qualitative characteristics of additives to meat semi-finished products for the potential formation of the desired properties of the products due to the analysis of the received spectrograms of trace elements of the samples when applying the LIBS method, quantitative analysis for processing the received information. The determined values of the electron temperature of the plasma, the electron density of the used raw material samples, and the assessment of the local heat balance were used as evaluation criteria. When processing the obtained data, the characteristics of the laser-induced plasma surface of the presented samples were analyzed; the electron temperature and electron density were determined, and a quantitative analysis of trace elements was carried out. LIBS technology allows rapid real-time monitoring and qualitative analysis of trace elements online and over long distances. During the research, it turned out that quantitative analysis requires further study and optimisation of experimental conditions, such as pre-treatment of samples. These conditions optimise defocusing, double laser pulse, and sample temperature, which increases the signal/noise ratio of all spectral lines. The combination of fluorescence spectroscopy and Raman technology enables higher detection sensitivity and better molecule control, creating a quantitative analysis method model that can reduce matrix effects and overcome the self-absorption effect. Among the difficulties of using LIBS technology, several elements can be noted online simultaneously, compared to Raman. The combination of spectroscopy and fluorescence spectroscopy can obtain more comprehensive information about the composition of materials, which can become a potential platform for monitoring trace elements in food products.

A Dynamic Tanks-in-Series Model for a High-Temperature PEM Fuel Cell

A dynamic tanks-in-series model has been developed for the coupled heat, mass, and charge transfer processes in a high-temperature proton exchange membrane fuel cell. The semi-empirical model includes the heat and mass balance equations in the gas channels and the membrane electrode assembly together with the charge balance at the electrode/membrane interfaces. The outputs of the tanks-in-series model are the concentration, the temperature, and the current density with a step change from tank to tank. The dynamic non-isothermal model is capable of predicting both the transient and steady-state behavior of the fuel cell and reproducing impedance data under harmonic perturbations of the cell potential together with a comprehensive interpretation of experimental data.

A computational analysis of effective R-values of buried ducts – the dynamic performance of buried ducts

This paper evaluates the thermal performance of ducts partially or fully buried in loose-fill attic insulation. The overall thermal resistance between the ducts and the attic is referred to as an effective R-value. This paper shows a strong dependency of assumed attic temperature on the effective R-value. Based on the results, the effective R-value can be about twice as much with an attic temperature of 130 °F [54.4 °C], compared to when the attic temperature is 80 °F [26.7 °C]. Thus, this paper provides a polynomial regression equation based on a large set of simulations to determine the effective R-value of buried ducts depending on attic temperature and whether the HVAC system runs in cooling or heating mode. Further, the work presented in this paper investigated the potential impact of convective airflow within the attic insulation, particularly around the ducts. The analysis was based on computational fluid dynamics (CFD) and indicated that convectional forces are presented around the exterior surface of the ducts, but with negligible impact on the overall heat balance between the duct and the attic space.

Analysis of the possibility of reducing the heating time of thick-walled cylindrical components with holes

Thermal power plants, both fossil-fuel-fired and nuclear power plants operating in a modern energy system with a high share of renewable energy sources, should be characterised by high flexibility, i.e. operate safely over a wide range of load variations as having short start-up and shutdown times. Many years of experience in power plants and stress calculations in power plant components have shown that thick-walled pressure parts with complex shapes or holes in the walls determine the maximum allowable raising or lowering of the working fluid temperature. A new method for determining the optimum fluid temperature variations in a cylindrical component with openings was developed. The optimum fluid temperature variation was determined from the condition that the sum of the circumferential stresses from thermal and pressure load is equal to the allowable stress at the edge of the opening. The optimum fluid temperature variation over time was determined at constant pressure and with a linear change in pressure over time using the Heat Balance Integral Method (HBIM). HBIM is preferred over other numerical and analytical methods because it can accurately determine temperature distribution at the beginning of optimum heating for very short times.

Infra-Red Emission for Heat Radiation from Micro-Cone Textured Metallic Sheet Device with Semi-Regular Alignment

Abstract A micro-cone textured copper sheet was fabricated as an emitter of electromagnetic waves in the near-infrared (IR) to the far-IR wave lengths. This micro-cone texture was aligned in semi-regular by varying the micro-cone size parameters. The micro-cone height (H) was varied from 0.5 µm to 4 µm in average. SEM analysis was utilized to characterize the microstructure of micro-cone textures and to measure the population of micro-cone height (H), its root diameter (B) and pitch (D) with aid of the picture processing and computational geometry. This height population P (H) was compared to the IR emission spectrum, which was measured by the FT-IR (Fourier Transformation IR). Even varying the average height of micro-cone textures, the IR-emission wavelength (λ) abided by the resonance condition by λ ~ 2 x H within the standard deviation of heights and wavelengths. Through the heat radiation experiment in vacuum, the emitted heat flux was estimated to be 58 W/m2 by the one-dimensional heat balance between the heating rate of objective body and the radiated heat flux.