Rate Of Heat Loss Research Articles

Microwave plasma torches for solid waste treatment and vitrification.

Conventional thermal plasma technology used in the treatment of solid waste has a high demand for power and a high rate of heat loss during solid waste treatment. We developed a novel approach for treating and vitrifying solid waste with a low-power microwave plasma torch (MPT). Based on theoretical thermodynamic equilibrium calculations, we studied the melting temperature of the residual ash and achieved vitrification of the residual ash with an MPT by adding specified ratios of discarded glass scraps. Thermocouples and a gas analyzer were used to characterize the temperature variations and gas concentrations in the plasma treatment chambers, respectively. An organic elemental analyzer and X-ray fluorescence (XRF) analyses were used to determine the chemical proportions of the solid waste residues. The morphologies of the residues and vitreous material were analyzed using scanning electron microscopy (SEM). The results showed that the microwave plasma treatment process converted 96 wt.% of the solid wastes into nonpolluting gases, leaving a residue of pure carbon and inorganic powder. Through theoretical calculations and experiments, atmospheric MPTs with power levels less than 10kW were identified as realistic means for treating and vitrifying solid wastes.

Cyclic Supercritical Multi-Thermal Fluid Stimulation Process: A Novel Improved-Oil-Recovery Technique for Offshore Heavy Oil Reservoir

Cyclic supercritical multi-thermal fluid stimulation (CSMTFS) is a novel technology that can efficiently recover heavy oil, while the heating effect, production and heat loss characteristics of CSMTFS have not been discussed. In this study, a physical simulation experiment of CSMTFS is conducted with a three-dimensional experimental system. The results of the study indicate that the whole process of CSMTFS can be divided into four stages, namely, the preheating stage, production increase stage, production stable stage and production decline stage, of which the production stable stage is the main oil production stage, and the production decline stage is the secondary oil production stage. In the first two stages of the CSMTFS process, there is no supercritical multi-thermal fluid chamber, and only a relatively small supercritical multi-thermal fluid chamber is formed in the last stage of the CSMTFS process. Out of the supercritical multi-thermal fluid chamber, supercritical water in the thermal fluids condensates to hot water and flows downward to heat the subjacent oil layer. At the same time, the non-condensate gas in the thermal fluids accumulates to the upper part of the oil layer and reduces heat loss. The analysis of heat loss shows that the heat loss rate gradually increases at first and then tends to be stable. Compared with conventional thermal fluid, the CSMTFS can more effectively reduce heat loss. The enthalpy value of supercritical multi-thermal fluid is significantly increased compared with that of multi-thermal fluid, which effectively solves the problem of insufficient heat carrying capacity of multi-thermal fluid. Overall, cyclic supercritical multi-thermal fluid stimulation can effectively solve the problems of conventional heavy oil thermal recovery technology in offshore heavy oil recovery; it is indeed a new improved-oil-recovery technique for offshore heavy oil. The findings of this study can help in better understanding the cyclic supercritical multi-thermal fluid stimulation process. This study is significant and helpful for application of CSMTFS technology in heavy oil recovery.

Study on thermal storage performance of heat storage tank with phase change material balls

In order to promote the application of heat storage device using phase change material (PCM), a water tank filled with sodium acetate trihydrate ball was designed, and its performance was studied. The effects of inlet temperature, flow rate on the charging and discharging time, hot water supply, thermal storage efficiency of PCM tank were analyzed through experiments and simulations. A new concept “heat loss rate of the heat exchange blind area” was put forward, by which the impact of PCM ball position on the heat exchange blind area was analyzed. The results show that with the increase of inlet temperature and flow rate, the charging and discharging time decrease. The hot water supply and the thermal storage efficiency reaches their maximum value (28.3L/h, 78 %) at the flow rate of 25L/h and the inlet temperature of 80 °C. When the height of the bracket in PCM tank is 60 mm, the heat loss rate of heat exchange blind area decreases by 47 %. The best height of PCM balls is 90 mm, which increases the average temperature of heat exchange blind area by 1.8 %. The study has guided significance for the practical application of water tank with phase change thermal storage module.

Correlation of heat loss with quenching distance during transient flame-Wall interaction

Detailed numerical simulations of stoichiometric premixed methane/air flames have been conducted for a side-wall-quenching (SWQ) setup, in order to study the effect of transient motion of the flame on flame-wall interaction (FWI). A W-shaped plane-jet (2D) flame is considered, which is bounded in its lateral direction by walls. The left wall oscillates in its normal direction with pre-defined frequencies f and stroke lengths L (distance between the minimum and maximum wall locations), exciting the entire flow and resulting in an unsteady motion of the flame at the left and right wall. While the instantaneous flame contours near the moving and the stationary wall differ, the instantaneous quenching distance dq and wall heat flux q˙w at the walls yield a quasi-linear correlation in the case of low f and L. However, hysteresis loops with a weakened correlation for q˙w vs. dq have been detected for large f and L, which leads to a considerably increased time-averaged dq and decreased time-mean q˙w compared with results obtained from the steady-state solution. The reason is attributed to the delayed response of the flame to the rapidly varying temperature and flow fields caused by the transient motion of the flame with respect to the wall. In this case, the flame requires a relaxation time to perceive the heat flux to the wall and to adjust its dynamics. The results indicate an essential impact of the unsteady flow nature on FWI, which has to be considered for turbulent combustion modeling. A quasi-linear correlation between the volumetric heat loss rate caused by the wall and the time-mean dq has been proposed for a first-order estimate of the effect of FWI, which could be implemented into the energy balance as sink term for modeling turbulent flame propagation under the influence of a cold wall.

Solid oxide fuel cell–internal combustion engine hybrid system utilizing an internal combustion engine for anode off-gas recirculation, external reforming, and additional power generation

A solid oxide fuel cell (SOFC)–internal combustion engine (ICE) hybrid system is proposed and analyzed. Although the existing SOFC–ICE hybrid system improves the efficiency of the SOFC stand-alone system by deriving additional power from the anode off-gas in the ICE, the proposed hybrid system further increases the system efficiency by utilizing the ICE for anode off-gas recirculation, external reforming, and additional power generation. Accordingly, we developed models for the SOFC and ICE and performed simulations to understand the operational characteristics of the hybrid system. Through simulation, the influence of each control parameter was analyzed, and the system operable ranges were determined according to the rate of system heat loss. When the heat loss considered is the least, a gross system efficiency of 66.9% is achieved at the optimum point. Thus, this study developed a high-efficiency SOFC–ICE hybrid system by combining methods that utilize the ICE as a recirculation blower, reformer, and power generator.

Effect of asymmetric fuel injection on combustion characteristics and NOx emissions of a hydrogen opposed rotary piston engine

Opposed rotary piston engines have the characteristics of high-power density and simple mechanisms. The applications of hydrogen fuel to internal combustion engines significantly are without carbon dioxide emission, alleviating the global warming. In this paper, hydrogen fuel was asymmetrically injected into combustion chambers to increase hydrogen penetration distance via; in the meantime, the engine performance and nitrogen monoxide (NO) emission with different ignition timing are explored by numerical simulation method. The symmetrical fuel injection scenario was provided as a baseline. In the scenarios of asymmetrical fuel injection, the engine had the best hydrogen injector position and ignition timing. Peak in-cylinder pressure Pmax reached 56.0 bar under ignition timing ti of −14.2° CA before top dead centre (bTDC) and hydrogen injector position (θ2) of 60.5°; in the meantime, heat loss rate HL and heat release rate Qr reached maximum values. Compared with the symmetric fuel injection engine, the peak NO emission of the asymmetric fuel injection engine was reduced by 15%. The proportions of energy loss by cylinder walls of asymmetric fuel injection engine were low and showed low dependency on ignition timing and hydrogen injector layout. Additionally, the asymmetric hydrogen injection structure makes hydrogen distribute evenly in the combustion chamber.

Combustion Characteristics and Performance Evaluation of Modified Mesoscale Annular Combustor

ABSTRACT The combustion characteristics and performance of a cylindrical stagnation flow-type mesoscale annular combustor were evaluated. The combustor comprised inner and outer porous tubes made of stainless steel and nickel – chromium–iron alloy, respectively. A rich C3H8–air mixture and air were supplied to the inner and outer tubes, respectively. The cylindrical flame was formed around the inner tube; consequently, a petal-type flame was formed downstream of the cylindrical flame. Experiments were conducted by maintaining a constant flow rate q i of the rich C3H8–air mixture in the inner tube while varying the equivalence ratio φ i of the mixture and the airflow rate q o of the outer tube. To investigate the combustion characteristics, the temperature was measured inside and at the outlet of the combustion chamber. The burned gas compositions, O2, CO, and NO, were analyzed. The heat loss rate η hl and the exergy loss rate η ex,loss were evaluated from the obtained temperature data. The minimum values of η hl and η ex,loss were 0.06 at φ i = 1.5, φ all = 0.3, and 0.44 at φ i = 5.0, φ all = 0.8, respectively. The values of η hl and η ex,loss verified that the combustor offers high performance.

Control of Large‐Scale Single‐Phase Ni Silicide Formation from Reactive Multilayers

The Ni/Si reactive multilayer (RML) is full of application potentials including reactive joining, igniters, and power sources. Here, the Ni/Si RMLs with atomic ratios of Ni and Si (2:1, 1:1, and 1:2) are studied, where the bilayer thickness and the total thickness are controlled to be 53 nm and 2 μm, respectively. After laser ignition, a rapid explosive reaction is observed where there are two self‐propagation wavefronts and their velocities reach 7.20 and 11.93 m s−1. The uniform, small grains, and single‐phase Ni silicides are obtained and controlled by tuning growth parameters. From the understanding of the Gibbs free energy diagram, the first wavefront comes from the solid‐state amorphization reaction between the Ni and a‐Si. The formation of the final Ni silicide causes the second wavefront. The entire reaction is described by a transient heat transfer model. It proposes a key parameter called heat loss rate, which explains the importance of RML thickness and the thermal diffusivity of the substrate. It allows to accurately control the reaction rate, which masters the final silicide phase. Thus, the oxidation of samples downgrades the reliability as the self‐propagation velocity of the two wavefronts dropped to 1.34 and 1.91 m s−1 in samples after 200 h of oxidation.

Development and application of digital twin technology for integrated regional energy systems in smart cities

In order to study the development and application of digital twin technology in the integrated regional energy system of smart cities, this paper proposes a basic concept of digital twin, and gives the construction method and possible applications of the energy internet digital twin. Taking the energy internet plan as an example, the key problems solved by digital twin technology are detailed. Finally, CloudIEPS, an energy internet planning platform based on digital twin, is introduced, which further proves the important role of digital twin technology through energy internet planning cases. According to the case analysis, the one-time investment cost of the optimized solution is 3,231,400 yuan less than the original solution, and the annual operating cost increases by 217,000 yuan. Compared with the original scheme, the one-time investment cost of the optimized scheme is reduced by 3,231,400 yuan, and the annual operating cost is increased by 217,000 yuan. The average heat loss rate of the original scheme is 11.5% and the average cooling loss rate is 12.4%, while the average overheating rate of the optimized scheme is only 1.9% and the average cooling loss rate is 10.4%.

Vapor Bubbles and Velocity Control on the Cooling Rates of Lava and Pyroclasts During Submarine Eruptions

AbstractInvestigating the conditions behind the formation of pyroclast textures and lava flow morphologies is important to understand the dynamics of submarine volcanic eruptions, which are hard to observe. The development of clast textures and lava morphologies depends on the competing effects of their eruption rates and the rates of solidification. While eruption rates are governed by subsurface magmatic processes, the solidification timescales depend on the rate of heat loss from lava to the external water. However, the effect of the speed of lava flow or clast on their solidification timescales under two‐phase (liquid water and vapor bubbles) water boiling conditions is poorly constrained. Using laboratory experiments with remelted igneous rocks, we investigate the effect of the relative motion between lava and external water on its cooling timescale. We use a range of water speed (0–12.5 cm s−1) in our experiments while keeping our sample stationary to simulate a range of relative speed between lava and ambient water. Using transient heat transfer modeling, we find that heat flux from the surface of the sample to the external water overall increases with increasing water speed. We find heat transfer coefficients of up to ∼1.72 × 103 W m−2 K−1. The implications of high heat flux on the formation of solid lava crust under submarine conditions are discussed.

Energy and exergy analysis of a glazed solar preheating collector wall with non-uniform perforated corrugated plate

The solar preheating wall provides an effective solution to the conflict between the requirement for fresh air and the need for heat conservation in winter by preheating fresh ventilation air. In this paper, a study of the glazed solar preheating collector wall is carried out by numerical simulation with the aim of improving heat collection efficiency through structural optimization. The influence of the environment as well as its range of applications are investigated. The characteristics of the internal flow and temperature distribution are obtained to facilitate the structural analysis. The influence of air volume and structural parameters on thermal efficiency is investigated, providing a good reference for structural design optimization. In addition, it is observed that the exergy efficiency of the optimized design is 1.3 times higher than that of the conventional solar wall, while the thermal efficiency is 15% higher than traditional ones. The heat loss rate is reduced by 40% in high wind and extremely cold regions compared to that of the unglazed one. The maximum supply percentage can reach 69.4% and the temperature rise is approximately 20 °C. Finally, a parametric investigation is carried out on different functional buildings, and an optimal structure in Xi'an is given as a reference. The energy collection and transfer efficiency increase with the increase of air volume, but the energy saving rate decreases. The results indicate that this solar wall is ideal for buildings with low fresh air demand, such as single residences and small offices. It also has a considerable preheating effect on high fresh air demand ones.

Crystalline TiO2 shell microcapsules modified by Co3O4/GO nanocomposites for thermal energy storage and photocatalysis

Modified microcapsule is devised to achieve the integration of thermal energy storage and light energy conversion of solar energy. This composite structure integrates the nanomaterial composed of graphene oxide (GO) and Co3O4 nanoparticles, on the microencapsulated paraffin coated by crystalline TiO2 shell. Compared with TiO2@paraffin microcapsules, introducing a thermal conductivity improved element of Co3O4/GO substantially increased the thermal conductivity by 57.7% and retained specific heat capacity of 2.154 J·g−1·K−1 and latent heat above 140 J·g−1. Microcapsules exhibited full-spectrum sunlight absorption ability, and the photothermal conversion efficiency was increased by 88.9%. Microcapsules are connected to the oxygen-containing functional groups on the flat of Co3O4/GO via hydrogen bonds and shared electron pairs, constituting a highly efficient Z-scheme heterojunction. By synergistic catalysis of photothermal, synergetic effects of semiconductor, and plasma resonance, the degradation rate of MB increased by 70.75%. This sophisticated multilevel structure of microcapsule possessed outstanding thermal cycling stability, which retains high thermal conductivity and specific heat capacity for microcapsule, while the latent heat loss rate was only 1.26%. This research implies a new insight for the field of energy storage microcapsules modification and multifunctional utilization of solar energy.

Role of self-generated magnetic fields in the inertial fusion ignition threshold

Magnetic fields spontaneously grow at unstable interfaces around hot-spot asymmetries during inertial confinement fusion implosions. Although difficult to measure, theoretical considerations and numerical simulations predict field strengths exceeding 5 kT in current National Ignition Facility experiments. Magnetic confinement of electrons then reduces the rate of hot-spot heat loss by >5%. We demonstrate this via magnetic post-processing of two-dimensional xRAGE hydrodynamic simulation data at bang time. We then derive a model for the self-magnetization, finding that it varies with the square of the hot-spot temperature and inversely with the areal density. The self-magnetized Lawson analysis then gives a slightly reduced ignition threshold. Time-dependent hot-spot energy balance models corroborate this finding, with the magnetic field quadrupling the fusion yield for near-threshold parameters. The inclusion of magnetized multi-dimensional fluid instabilities could further alter the ignition threshold and will be the subject of future work.

Steam Cavity Expansion Model for Steam Flooding in Deep Heavy Oil Reservoirs

Steam flooding is crucial for the development of heavy oil reservoirs, and the development of the steam cavity significantly determines the efficiency of steam flooding. Previous studies have elucidated the concept of steam overburden and pseudomobility ratio; however, the thermal energy loss in deep heavy oil reservoirs during steam injection needs further investigation. Therefore, in this study, the vapour–liquid interface theory and mathematical integration were used to establish a steam cavity expansion model. The wellbore heat loss rate coefficient, steam overlay, and pseudomobility ratio were used to accurately describe the development of the steam cavity in deep heavy oil reservoirs. The proposed model was experimentally validated, and it was observed that the model could accurately reflect the actual mine conditions. In addition, the pressure gradient distribution of the steam belt and the heat dissipation areas of the top and bottom layers of the steam cavity were evaluated. The results showed that the influence of the wellbore heat loss rate coefficient on the pressure gradient of the oil layer was primarily in the range of 5–20 m away from the steam injection well. Furthermore, it was observed that the pseudomobility ratio is inversely proportional to the development of the steam cavity. As the wellbore heat loss rate coefficient increased, the wellbore heat loss increased. The larger the area ratio, the more pronounced the steam overlay phenomenon, and the large area ratio does not meet the development requirements of the steam chamber. The research closely combines theory with production, and the results of this study can help actual mines by providing theoretical support for the development of deep heavy oil reservoirs.

Influence of thermal effects on the breakup of thin films of nanometric thickness

We apply a previously developed asymptotic model (J. Fluid. Mech. 915, A133 (2021)) to study instabilities of free surface films of nanometric thickness on thermally conductive substrates in two and three spatial dimensions. While the specific focus is on metal films exposed to laser heating, the model itself applies to any setup involving films on the nanoscale whose material parameters are temperature-dependent. For the particular case of metal films heated from above, an important aspect is that the considered heating is volumetric, since the absorption length of the applied laser pulse is comparable to the film thickness. In such a setup, absorption of thermal energy and film evolution are closely correlated and must be considered self-consistently. The asymptotic model allows for a significant simplification, which is crucial from both modeling and computational points of view, since it allows for asymptotically correct averaging of the temperature over the film thickness. We find that the properties of the thermally conductive substrate -- in particular its thickness and rate of heat loss -- play a critical role in controlling the film temperature and dynamics. The film evolution is simulated using efficient GPU-based simulations which, when combined with the developed asymptotic model, allow for fully nonlinear time-dependent simulations in large three-dimensional computational domains. In addition to uncovering the role of the substrate and its properties in determining the film evolution, one important finding is that, at least for the considered range of material parameters, strong in-plane thermal diffusion in the film results in negligible spatial variations of temperature, and the film evolution is predominantly influenced by temporal variation of film viscosity and surface tension (dictated by average film temperature), as well as thermal conductivity of the substrate.

A method for assessing heat losses in developing countries with a focus on operational data of a district heating (DH) system

The goal hereof was to propose a new method to estimate heat loss rates and find out how either the weather conditions of the serviced area or the available operational data affect each of the heat loss rate components. A linear regression function was used to describe the correlation between heat production and outdoor temperatures. Monthly measurements are used to estimate onsite heat loss in pipes in Russia. However, model coefficients can be adjusted to make it applicable to any European city, and the simulated behavior of the system is realistic in terms of the temperature profiles and heat losses for any DH system. The proposed model is more accurate than the conventional method with respect to the heat loss difference attributable to the variance in outdoor, supply, return, and ground soil temperatures. The difference between actual heat losses and heat losses projected by this new method varies from 0.4% to 1.2% with an average error of 0.65%. The results also show how the measurements state-of-the-art DH systems provide can help improve daily operation and maintenance to promote data-driven approaches. Technologies can be combined to further improve the performance.

Heat transfer performance of deep borehole heat exchanger with different operation modes

The deep borehole heat exchanger (DBHE) is an essential component of medium-depth geothermal heat pump systems (MD-GHPs). Compared with the conventional borehole heat exchanger, the DBHE has the advantages of minimal land area need, good seasonal heat storage performance and high efficiency in winter. However, most current DBHE research is focused on a single operation mode, and few studies on multiple operation modes. In this study, a DBHE heat transfer model is developed and its governing equations are discretized using the Finite Difference Method (FDM). The model is then validated using measured data from a real-world engineering project. This is followed by an analysis of the outlet water temperature, heat loss rate, maximum heat affected radius, and rock and soil heat recovery characteristics of DBHE with a variety of run-stop ratios (i.e., the ratio of the running time to the intermission time in a day). The following are the key findings: thermal recovery of rock and soil, as well as DBHE operation stability, are negatively correlated with the run-stop ratio, but DBHE heat loss rate is positively correlated with the run-stop ratio; when the run-stop ratio is 24:0 after 15 years of operation, the heat affected radius of DBHE on the surrounding rock and soil is 91.36 m; the other three run-stop ratios (i.e., 16:8,12:12 and 8:16) maybe reduced by 9.07%, 17.34% and 24.86%, respectively. The results of this study have implications for the design of DBHE with different operation modes.

Radiative Cooling Nanofabric for Personal Thermal Management.

A wearable textile that is engineered to reflect incoming sunlight and allow the transmission of mid-infrared radiation simultaneously would have a great impact on the human body's thermal regulation in an outdoor environment. However, developing such a textile is a tough challenge. Using nanoparticle-doped polymer (zinc oxide and polyethylene) materials and electrospinning technology, we have developed a nanofabric with the desired optical properties and good applicability. The nanofabric offers a cool fibrous structure with outstanding solar reflectivity (91%) and mid-infrared transmissivity (81%). In an outdoor field test under exposure of direct sunlight, the nanofabric was demonstrated to reduce the simulated skin temperature by 9 °C when compared to skin covered by a cotton textile. A heat-transfer model is also established to numerically assess the cooling performance of the nanofabric as a function of various climate factors, including solar intensity, ambient air temperature, atmospheric emission, wind speed, and parasitic heat loss rate. The results indicate that the nanofabric can completely release the human body from unwanted heat stress in most conditions, providing an additional cooling effect as well as demonstrating worldwide feasibility. Even in some extreme conditions, the nanofabric can also reduce the human body's cooling demand compared with traditional cotton textile, proving this material as a feasible solution for better thermoregulation of the human body. The facile fabrication of such textiles paves the way for the mass adoption of energy-free personal cooling technology in daily life, which meets the growing demand for healthcare, climate change, and sustainability.

Critical Role of Layer Thickness in Frontal Polymerization.

Thermal frontal polymerization (FP) is a chemical process during which a cold monomer-initiator mixture is converted into a hot polymer as a polymerization front propagates in the system due to the interplay between heat diffusion and the exothermicity of the reaction. The theoretical description of FP generally focuses on one-dimensional (1D) reaction-diffusion (RD) models where the effect of heat losses is encoded into an effective parameter in the heat equation. We show here the limits of such 1D models to describe FP under nonadiabatic conditions. To do so, the propagation of a polymerization front is analyzed both analytically and numerically in a rectangular two-dimensional (2D) layer. The layer thickness is shown to control the dynamics of the front and to determine its very existence. We find that for given heat losses, a minimum thickness is required for front propagation as recently observed in FP experiments of 2D thin films on wood. Moreover, when the thickness exceeds a critical value, the front is observed to survive independently of the rate of heat losses. This result cannot be predicted with 1D models where front extinction is always possible. A scaling analysis is proposed to highlight the physical interpretation of such a front survival. The influence of dimensionality on thermal instabilities is also analyzed, with a focus on the differences with the 1D predictions.

Assessment of the operation safety margin of the HL-LHC superconducting recombination Dipole D2 in case of helium filling failure

After the successful completion of the cryogenic performance tests of the He II heat exchanger prototype for the D2 recombination dipole of the future HL-LHC project at CERN, specific measurements were performed to determine the operation safety margin in case of abnormal operating conditions. This is particularly relevant in case of the failure of liquid helium supply in the He II cold source. For nominal operation, the liquid level is regulated at a constant value and it is not necessary to know its value very accurately. However, in case of a partial drying of the heat exchanger due to discontinuation of the helium liquid supply, it is essential to monitor the absolute value of the liquid level to anticipate any cooling malfunction. This paper describes the procedure for an accurate in-situ He II level measurement as well as for the heat loss and mass flow rate estimates in a He II phase separator. The operation safety margins of the He II heat exchanger prototype for the D2 magnet are then analyzed for the different operating conditions considered during the HL-LHC runs in case of non-nominal liquid level in the He II cold source.