Continuous Heat Research Articles

Effect of biochar on desiccation of marine soils under constant and cyclic temperatures

Biochar has recently been gaining increasing attention as a stable and sustainable soil amendment material. However, the effect of biochar amendment on the desiccation behaviour of coastal soils has not yet been examined. Consequently, the present study primarily investigated the effect of exposing biochar-amended marine soil (BAS) to constant and cyclic temperatures on its swell–shrink, evaporation and desiccation cracking characteristics. Biochar contents of 1%, 2%, 4% and particle size ranges of PS-1 (600 μm < D ≤ 2000 μm), PS-2 (300 μm < D ≤ 600 μm), PS-3 (D ≤ 75 μm) (D: biochar particle diameter) were employed. It was revealed that the absolute volumetric shrinkage of both unamended and biochar-amended specimens increased as the number of thermal cycles increased. Under continuous heat exposure, 4% (PS-3) BAS in compacted state achieved the maximum reduction in volumetric shrinkage which was 42%. Moreover, under continuous heat exposure, 2% (PS-1) BAS in slurry state achieved the highest reduction in desiccation cracking, which was 73%. The present study highlights the importance of identifying the most effective combination of biochar content and particle size required to achieve a desired outcome, in order to gain the maximum benefit of biochar as an amendment material at the lowest possible cost.

Multi-Scale Process Monitoring Based on Time-Frequency Analysis and Feature Fusion

Data-driven process monitoring is an important tool to ensure safe production and smooth operation. Generally, implicit information can be mined through data processing and analysis algorithms to detect process disturbances on the basis of historical production data. In industrial practice, signals with different sources of disturbance show different distribution patterns along with the time domain and frequency domain, that is, noise and pulse-type changes are usually contained in the high-frequency portion while most process dynamic is contained in the low-frequency portion. However, feature extraction is usually implemented at a single scale in traditional multivariate statistical algorithms. With this concern, a novel multi-scale process monitoring method is proposed in this work, by which wavelet packet decomposition is first employed for time-frequency analysis. After decomposition, multivariate statistical models are established for each scale to construct process statistics. For the high-frequency part, the classical principal component analysis (PCA) algorithm is adopted to construct squared prediction error (SPE) and Hotelling T2(T2) statistics. While for the low-frequency part, the slow feature analysis (SFA) algorithm is adopted to construct T2, Te2, S2 and Se2 statistics for the extraction of the long-term slowly changing trend. Then the monitoring statistics, obtained from each method at different scales, are integrated by a support vector data description (SVDD) method to give a final fault detection decision. The performance of the proposed method is verified on the benchmark Tennessee Eastman Process (TEP) and an industrial continuous catalytic reforming heat exchange unit by comparing with related multivariate statistical methods, which only focus on a single scale.

Single-band tunable metasurface for thermal emitters in 5G bands

In communications, controlling the absorptivity and emissivity of the metasurface emitters is a meaningful area of research. However, the reported emitters mainly employ a continuous external energy to support the operating state, resulting in continuous energy consumption. In this work, a metasurface thermal emitter based on phase-change material Ge2Sb2Te5 (GST) is proposed and verified. This thermal emitter shows selective emission performance independent of continuous external heat source in the 26–32 GHz. Since the GST array reveals crystalline and amorphous phases, this emitter achieves a maximum emission amplitude of 0.95 and a minimum emission amplitude of 0.17. Therefore, by switching the crystalline and amorphous states of the GST array, this emitter can achieve a maximum modulation depth of 0.78. The continuous modulation of the emission performance of this transmitter is achieved through varying the annealing temperature. At the same time, since the phase transition state of GST is thermally stable (the phase transition state can remain stable even if the external thermal conditions fail), the thermal emission performance of this thermal emitter does not require continuous energy consumption to maintain. This continuously tunable, switchable mode, and thermally stable metasurface emitter has potential applications in infrared imaging, thermophotovoltaics, 5G communications, radiative cooling, and more.

The effect of annular phase-change material layer on the thermal behavior of solar collector tube

The temperature of the Heat Transfer Fluid (HTF) in the solar collector tube is greatly affected by the instantaneous solar radiation and which usually causes the HTF temperature large fluctuations. To improve this performance, a novel solar collector tube integrated by annular phase-change material (PCM) layer and solar collector tube was proposed in this study, and the thermal behavior of the tube with 630 mm in length and 20/70 mm in diameter inside and outside has been studied. Solar Salt (60 wt% NaNO3 and 40 wt% KNO3) was applied as the PCM. Air was selected as HTF. The thermal characteristics of the novel and traditional solar collector tubes were experimentally and numerically investigated under different solar radiations and air flow rates. The results show that the temperature in the solar collector tube with PCM were 65.45–128.75 °C higher than that without PCM after cooling for 4 h in different solar radiations. The temperature in the solar collector tube decreased as the air flow rate increased. The average temperature falling rate with PCM were 35.6–76.4 °C/m·s−1 slower than that without PCM during the heat storage process, the solar collector tube with PCM shows more advantages at high flow rates. Within the measuring time of 300 min, the total thermal efficiency of the collector tube with PCM layer is higher than that of without PCM layer. The solar collector tube with PCM is better suited to create a stable mid-temperature and high-temperature environment in continuous solar radiation and heat extraction.

Carbonized bamboo parenchyma cells loaded with functional carbon nanotubes for preparation composite phase change materials with superior thermal conductivity and photo-thermal conversion efficiency

Phase change materials (PCMs) are widely used in the field of energy storage management owing to their store and release thermal energy ability through latent heat. However, organic PCMs have the problems of easy leakage, low thermal conductivity and photo-thermal conversion performance, which greatly prevent their practical application. In order to solve these defects, a novel shape stable composite PCMs was prepared by adding polyethylene glycol (PEG) into porous carbonized bamboo parenchyma cells (CPC) containing carbon nanotubes (CNTs). The supporting materials containing CNTs not only had unique three-dimensional porous structure, but also had continuous heat transfer network structure. Compared with pure PEG, the thermal conductivity (TC) of PEG/CPC-CNTs with 0.494 W/m·K was increased by 128%. The prepared composite PCMs had melting and crystallization latent heat with 149.4 J/g and 144.1 J/g. In terms of shape stability, the PEG encapsulation rate by CPC reached 80% which was better than that of untreated PC. Thermo-gravimetric (TG) analysis and thermal cycling experiments showed that PEG/CPC-CNTs had superior physical and chemical stability. More importantly, the matrix material composed of CPC and CNTs made the composite PCMs with a photo-thermal conversion efficiency up to 87.2%. So, PEG/CPC-CNTs composite PCMs with a simple preparation method have great application potential in the field of bamboo or wood based buildings materials such as wood plastic composite, particleboard, floor or roof panels and so on.

Experimental Cyclic Heat Stress on Intestinal Permeability, Bone Mineralization, Leukocyte Proportions and Meat Quality in Broiler Chickens.

Simple SummaryRecently, our laboratory published a heat stress model to induce gastrointestinal leakage in broiler chickens. Nevertheless, the model describes continuous heat stress (HS) conditions from day 21 until 42 days of age. The current brief report intends to present an alternative model (12 h/day), particularly more in accordance with real-world conditions, to evaluate nutraceuticals or products that can reduce the severity of HS under experimental conditions. Results of this study confirm what has been extensively reported by numerous scientists. Cyclic HS increased leaky gut, reduced performance, bone mineralization, and meat quality in broiler chickens.The goal of this research was to assess cyclic heat stress on gut permeability, bone mineralization, and meat quality in chickens. Two separate trials were directed. 320 day-of-hatch Cobb 500 male chicks were randomly assigned to four thermoneutral (TN) and four cyclic heat stress (HS) chambers with two pens each, providing eight replicates per treatment in each trial (n = 20 chicks/replicate). Environmental conditions in the TN group were established to simulate commercial production settings. Heat stress chickens were exposed to cyclic HS at 35 °C for 12 h/day from days 7–42. Performance parameters, intestinal permeability, bone parameters, meat quality, and leukocyte proportions were estimated. There was a significant (p < 0.05) reduction in body weight (BW), BW gain, and feed intake, but the feed conversion ratio increased in chickens under cyclic HS. Moreover, HS chickens had a significantly higher gut permeability, monocyte and basophil levels, but less bone mineralization than TN chickens. Nevertheless, the TN group had significant increases in breast yield, woody breast, and white striping in breast fillets compared to HS. These results present an alternative model to our previously published continuous HS model to better reflect commercial conditions to evaluate commercially available nutraceuticals or products with claims of reducing the severity of heat stress.

Numerical study of oblique fins under natural convection with experimental validation

3D numerical simulations are performed in order to investigate the thermofluids characteristics of the oblique fin heat sink under natural convection. Detailed parametric study is carried out on the effects of geometrical parameters, including main channel width, oblique channel width, fin length, fin width, offset ratio, and fin rotational angle. Through detailed sensitivity analysis, it is found that fin oblique angle and fin rotational angle are the most critical parameters affecting the performance of oblique fins; followed by the main channel width, fin length, and offset ratio. Yet, the effects of fin width and oblique channel width are very minor. Based on sensitivity analysis, an optimum oblique fin heat sink configuration is obtained and a novel symmetrical oblique fin is proposed and compared with the continuous fin heat sink. Subsequently, an experimental verification is made to validate the results of the optimum oblique fin heat sink. The simulation is in line with the experimental data, and the proposed oblique fin heat sink offers more than 3 °C reduction in the maximum heat sink temperature when compared to the continuous fin heat sink.

Thermodynamic Process and Analysis of Dilution Refrigerator

Thermodynamic analysis is essential for not only guiding the design of refrigerator, but also studying its operation mechanism. As the core component, the dilution unit plays an important role in deciding the performance of dilution refrigerator. In this study, a coupled thermodynamic model is established by analyzing each component separately for improving the operation of dilution refrigerator. And an optimization calculation based on that model is carried out to obtain some meaningful results on the dilution unit design. The optimal flow rate of the dilution refrigerator under different working conditions are pointed out. By considering the effect of viscous heat on the performance of the heat exchanger, the applicable conditions of the continuous heat exchanger and the methods to overcome the viscous heat are given.

Mathematical Model and Numerical Simulation of Coalbed Methane Migration Considering the Adsorption Expansion Effect

The influence of gas adsorption and desorption on the volumetric strain of coal was measured by a self-designed, fluid–solid coupling triaxial coal adsorption deformation experimental system. The experimental results show that coal deformation has a threshold value with an increase in gas content. Before the gas content reaches the threshold value, coal deformation is not obvious. When the gas content reaches the threshold value, the deformation will increase sharply. At the same time, coal volume strain changes with coal gas content in accordance with exponential law ε = ε0(eϒc-1). Based on the experimental results, considering the coupling effects of heat transfer, water seepage, coal and rock mass deformation, and coalbed methane desorption and seepage, a mathematical model of heat transfer–deformation–seepage coupling coalbed methane migration was established, and a numerical simulation study was carried out on the heat injection-enhanced coalbed methane mining project. The results show that (1) With continuous heat injection, the gas in the coal seam is rapidly desorbed, and the adsorbed gas content forms an elliptical funnel that extends from the extraction hole to the deep part of the coal body and takes the fracturing crack as the center to the upper and lower boundaries of the coal seam. At day 30, the adsorbed gas content in the whole drainage area has decreased to 0.1 m3/t within 2m from the fracture zone. (2) On the basis of considering the gas adsorption expansion effect, the strain of the coal body decreases from roof to floor. With the increase in the heat injection time, the strain value will also increase, and the strain increase will decrease. When the heat injection is 30 days, the maximum strain at the roof is 0.015. The research results have important guiding significance for predicting coal rock deformation and determining gas extraction efficiency in the process of heat injection-enhanced coalbed methane extraction.

Joule heat enabled efficient In-situ regeneration of carbon nanotubes as model adsorbents

Thermal-desorption has been considered as an environmentally friendly approach to regenerate the exhausted adsorbents to achieve a sustainable adsorption process. However, the traditional thermal desorption method suffers from the demanding contradiction between the desorption efficiency and energy consumption. Herein, we developed an efficient and economical thermal-desorption strategy based on the Joule heating by employing a three-dimensional carbon nanotubes (CNTs) film as the model adsorbent. The features of CNTs film with negative temperature coefficient endow the impressive heat production for the electrical resistance decreased from 341.0 Ω at 25.7 °C to 36.7 Ω at 76.5 °C. The desorption ratio of target pollutant (i.e., benzoic acid) in the continuous Joule heat induced thermal desorption process could be reached to 93.2% with the energy consumption of 0.25 kW h, which is two orders of magnitude lower than that in the indirect thermal desorption process for one ton of wastewater at the specified scale. This study proposed a green and energy-efficient strategy for thermal regeneration, and provide a method guidance for the development of green regeneration technology.

Statistical method based on dissimilarity of variable correlations for multimode chemical process monitoring with transitions

Chemical industrial processes are always accompanied by multiple operating conditions, which brings great challenges for multivariate statistical process monitoring methods to extract general characteristics from multimode data, especially for time-varying characteristics in transitions between two modes. In this work, a novel statistical process monitoring method based on the dissimilarity of process variable correlation (DISS-PVC) is proposed. The proposed method aims to monitor multiple stable modes and between-mode transitions simultaneously with no prior knowledge of the number of operating modes. Unlike traditional methods oriented to monitoring process variables, the proposed method is applied to monitor the correlation of process variables based on the idea that variable correlation should always conform to a certain process internal mechanism, no matter in which stable or transition mode. Mutual information is first employed to quantitate variable correlation with a moving-window approach. Cosine similarity between eigenvalues of mutual information matrices is selected as a dissimilarity index to evaluate the difference in variable correlation between two data sets and perform fault detection. The effectiveness of the proposed method is verified on the benchmark Tennessee Eastman (TE) process and an industrial continuous catalytic reforming heat exchange unit.

Design and optimization of a baffle-type phase-change heat storage electric heating device

Aiming at the phenomenon of excess power and large peak-valley power difference in various application areas, here we design a baffle-type phase change heat storage electric heating device. The device uses expanded graphite (EG)/paraffin (PA) as the heat storage medium, and encapsulates the EG/PA composite phase change materials (CPCM) in a rectangular slab that is directly heated using an electric heating slab. To investigate the impact of the number and thickness of the rectangular plates on the thermal storage and exothermic performance of the device, we perform three-dimensional numerical simulations. We further make performance comparisons with the commonly used shell-and-tube and concentric tube types. In addition, the designed device was optimized by adding fins using the orthogonal test method. To verify the heating effectiveness of the device, we also simulated the temperature field, PMV (Predicted Mean Vote), and PPD (Predicted Percentage Dissatisfied) of the heating room. Our investigations confirm continuous heat release of the device for 7 h during the day which meets home heating requirements. It is also shown that the heat storage and exothermic efficiency reach to 85.83% and 90.1%, respectively, after the device is optimized, the storage and exothermic efficiency increased by 8.15% and 6.43% respectively, and the real-time outlet temperature has increased by 4.98 °C compared with that before the optimization; the average indoor temperature of the heating room is 22.49 °C, PMV is 0.55, and PPD is 15.3% in line with the thermal comfort requirements. The device can realize heat storage and heating at the same time when the power is in the valley, during the peak period, the power supply is turned off and the heating is directly supplied by CPCM. compared with the direct electric heating systems can reduce users' electricity costs, and shift peaks and fill valleys and provide a broad commercialization prospect. The research results provide a reference for the design and optimization of heat storage devices and their application in practical engineering.

Construction of continuous heat conductive channel, a double harvest strategy to enhance thermal conductance and bending strength of C/SiC composites

The development of efficient and quick method to prepare structure-function integrative C/SiC composites is always a major challenge in this field. Herein, the thermal conductivity and bending strength of C/SiC composites were enhanced simultaneously via continuous high heat conductive channels constructed by continuous wave laser machining and pitch-based high thermal conductivity carbon fiber in thickness direction. Results revealed that the thermal conductivity of the modified C/SiC composites is three times higher than that of referential C/SiC composites due to its highly ordered heat conducive channel in the thickness direction. Importantly, the bending strength of modified C/SiC composites increased to 457 MPa. To better understand the enhance mechanism, the micro-structure for both the composites and heat conductive channel was systematically analyzed. The results demonstrated that the rivet effect of heat conductive channel and the formed two phases structure on the fibers dispersed partial of load and finally enhanced the property of the composites. In a word, this method holds a nice applicable future in constructing structure-function integrative C/SiC composites.

Relationship of heat stress with acute kidney disease and chronic kidney disease: A literature review

Introduction: Heat stress is a physical hazard and a potential health risk which can result in various conditions ranging from discomfort, headaches, psychological disorders, heat stroke and even death in extreme cases. Factors which cause heat stress include high ambient temperature, limited air movement, strenuous physical work and direct exposure to the heat of the engine/ sun. Continuous heat stress, exacerbated by dehydration, can lead to kidney disease. This study is a literature review conducted to explore factors that influence heat stress and the relationship of heat stress with acute kidney disease and chronic kidney disease. Methods: Literature search was conducted in September 2021. Research sources were taken from several databases, namely Science Direct, ProQuest, PubMed, and Google Scholar. From the databases, 23,316 articles were from Science Direct, 140,319 articles were from ProQuest, 670 articles were from PubMed, and 288,000 articles were from Google Scholars. Out of the total database only 24 articles met the inclusion criteria. The variables in this study were heat stress, acute kidney disease, and chronic kidney disease. Results: This literature review shows that several factors which can affect heat stress are heat exposure, workload, rehydration, and rest period arrangements. Heat stress experienced by workers can cause decreased kidney function and chronic kidney disease. Heat stress conditions that are continuously experienced by workers can cause chronic kidney disease. Conclusion: Heat stress can be experienced by workers due to heat exposure, heavy workload, poor rehydration, and poor rest period arrangements. Heat stress can cause acute kidney disease and chronic kidney disease.

Effects of Multi-Stage Split Injection on Efficiency and Emissions of Light-Duty Diesel Engine

The efficiency of light-duty diesel engines should be improved for further emissions regulation. Multi-stage split injection with five injection events was investigated for improvement in efficiency at low-load conditions. The injection timing and quantity were adjusted to achieve a smooth in-cylinder pressure rise and continuous heat release. The multi-stage split injection was compared to injection strategies involving two-pilot and single-main injections. A 0.5 L single-cylinder diesel engine experiment was conducted under low-load conditions. Two multi-stage split injection processes with different combustion phases were developed. The multi-stage split injections yielded a smooth in-cylinder pressure trace and a lower peak heat release rate than the two-pilot injection process. The combustion duration was shorter for multi-stage split injection with an advanced combustion phase, and the fuel consumption was reduced by 1.78% with lower heat transfer, exhaust heat, and combustion loss. The multi-stage split injection flame penetration was shorter than the two-pilot injections. The shorter flame penetration and lower tip velocity reduced the heat transfer to the combustion chamber. The PM emissions were also reduced by 30% under the same NOx emissions, because increased PM oxidation and divided fuel injection prevented flame diffusion and improved air utilization.

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Electron Heat Source Driven Heat Transport in GaN at Nanoscale: Electron-Phonon Monte Carlo Simulations and a Two Temperature Model.

The thermal energy transport in semiconductors is mostly determined by phonon transport. However in polar semiconductors like GaN electronic contribution to the thermal transport is non-negligible. In this paper, we use an electron–phonon Monte Carlo (MC) method to study temperature distribution and thermal properties in a two-dimensional GaN computational domain with a localized, steady and continuous electron heat source at one end. Overall, the domain mimics the two-dimensional electron gas (2DEG) channel of a typical GaN high electron mobility transistor (HEMT). High energy electrons entering the domain from the source interact with the phonons, and drift under the influence of an external electric field. Cases of the electric field being uniform and non-uniform are investigated separately. A two step/temperature analytical model is proposed to describe the electron as well as phonon temperature profiles and solved using the finite difference method (FDM). The FDM results are compared with the MC results and found to be in good agreement.

Heat extraction from hot dry rock by super-long gravity heat pipe: A field test

Recent theoretical studies dealing with the novel scheme for earth-deep hot dry rock geothermal energy extraction based on the use of a super-long heat pipe indicate its superior technical viability. The present work reports on a field test using a 3000-m heat pipe to extract hot dry rock geothermal energy conducted with the aim of demonstrating its practical feasibility. The in-house developed heat pipe uses deionized water as working fluid and produces steam with a maximum temperature of ∼90 °C, when the average underground formation temperature around the subsurface heat pipe is 95.6 °C. During the 30-day continuous heat mining process, the heat extraction rate achieved an average value of 190 kW with no obvious downward trend. After one month of continuous heat production, a one-week heat recovery can restore the system temperature to just slightly lower than the initial value. The thermal response of the system to different condensing temperatures was also tested. The results show that the heat extraction rate can be increased by decreasing the condensing temperature, but this improvement is insignificant when the condensing temperature is 55 °C or lower. Furthermore, the experimental results show overall good agreement with the model predictions, which indicates that the heat pipe is performing close to the desired operating conditions considered in the simulation model, in particular: no liquid accumulation, no local dry-out, and no vapor-liquid entrainment. This performance is a major departure from that of the typical heat pipes, and it makes the super-long gravity heat pipe a leading technological candidate for earth-deep geothermal heat extraction.

Thermal disturbance analysis in rock-soil induced by heat extraction from the abandoned well

Medium-deep geothermal energy has obvious advantages in building heating in cold regions. The abandoned oil well can be retrofitted into a closed-loop coaxial borehole heat exchanger to save costs. However, continuous heat extraction and recovery in long-term operation can cause potential deformation, and the thermal disturbance scope in the surrounding formation should be determined. In this study, the thermal process and disturbance induced by heat extraction are analyzed. The effects of heat load, flow rate, rock-soil thermal conductivity, outer pipe thermal conductivity, rock-soil density and depth for a single borehole are discussed. And the effects of distance for two boreholes on the thermal disturbance were evaluated. The results demonstrate that heat conduction between the circulating fluid and the formation is opposite at the shallow and deep depth, and the thermal process is enhanced at the bottom borehole. The thermal disturbance scope at the depth of 2000 m can exceed 40 m following 20 years of operation. The superimposed thermal process of the two boreholes induces more thermal disturbance. The thermal disturbance scope of each borehole was able to 75 m for the layout of the two boreholes. The results can provide a basis for layout of the coaxial borehole heat exchanger.

Thermal response of the two-directional high-thermal-conductive carbon fiber reinforced aluminum composites with low interface damage by a vacuum hot pressure diffusion method

A two directional high thermal conductive carbon fiber reinforced aluminum matrix composite with low interface damage is prepared by a vacuum hot-pressure diffusion method using the mesophase-pitch-based carbon fiber (CFMP) cloth as fast heat conduction channels. The fiber/matrix interface is composed of an amorphous gradient transition layer between aluminum matrix and CFMP rather than Al4C3 interface phase, thus endowing the continuous heat conduction channels in the composite. The composites deliver the high thermal conductivity of 305.5 W∙m−1∙K−1 in the X (Y) direction and the low volume density of only 2.53 g∙cm−3 when the fiber volume fraction reaches 30 vol%. The high thermal conductivity of the composite is attributed to the highly oriented fast heat transfer effect of the CFMP, the isotropic heat transfer effect of the aluminum matrix and the low-damage CFMP/aluminum interface. This study opens a new avenue to design and select the high thermal conductivity and lightweight thermal management materials for the aerospace field.