Excessive Heat Loss Research Articles

Construction and insulation of agricultural buildings and structures

The article covers different application aspects of the products made of polyethylene foam within the scope of insulation systems of framed and frameless constructions used in the quality of storage premises, logistic objects, agricultural storage facilities and livestock facilities as well as framed residential buildings. Agricultural storage facilities, livestock facilities, covered parking areas for agricultural machinery and some types of storage premises represent the agricultural construction facilities which require the established protection systems against excessive heat losses as well as monitoring of the state of the internal environment - its temperature and humidity. These structures are built based on one of three schemes: frameless type, framed type with a rigid coating and framed type with a tent coating. The insulation of buildings constructed before 2010 is predominantly characterized by usage of mineral wool plates (with a protective facade covering) or sandwich panels. The main problem of suchlike coverings is the impossibility of creating an insulating coating without joints, seams or gapless junctions to the base. Mineral wool plates, in case of destruction of the waterproof coating, contact with water and firstly lose their thermal and physical properties, and then – come to the destruction themselves. Sandwich panels are more resistant to weather impacts, but create a coating with huge quantity of cold bridges and paths of convective air transfer through gaps or openings.

Enhanced Photothermal Conversion by Hot-Electron Effect in Ultrablack Carbon Aerogel for Solar Steam Generation.

Ecofriendly, highly effective, and low-cost solar steam generation has great potential in the applications of power generation, seawater desalination, and industry wastewater treatment. Solar steam generation requires an evaporator that has strong light absorption over a wide-frequency band (200-3000 nm), high photothermal conversion efficiency, and good thermal insulation to avoid excessive heat loss. Herein, foam-strengthened ultrablack carbon aerogels (CAs) with micropores, mesopores, and macropores were prepared using freeze drying. The small-size conductor effect in ultrablack CAs could increase the surface electron concentration, leading to the increase of light absorption and ultimately enhancing photothermal conversion efficiency. Consequently, under 1 sun illumination, dried CA-5 exhibited a fast temperature rise rate and the highest thermal equilibrium temperature of 87.6 °C among CAs, the equilibrium temperature is 20.8 °C higher than that of the foam. Besides, CA-5 exhibited a high water evaporation rate of 1.29 kg m-2 h-1 under only 1 sun illumination. To further increase the hot-electron effect, CO2 activation was implemented. The highest water evaporation rate among activated CAs (ACAs) was 1.37 kg m-2 h-1, which is about 2.85 times higher than that of pure water. The highest water evaporation efficiency was 87.51%, which is better than most of the previously reported evaporation efficiencies. Besides the hot-electron enhancement effect, ACAs with thermal insulation, mechanical strength, and thermal stability show great potential for producing fresh water from seawater, industrial wastewater, and even concentrated acidic or alkaline solutions.

Oral L-Tyrosine Supplementation Improves Core Temperature Maintenance in Older Adults.

During cold exposure, an increase in sympathetic nerve activity evokes vasoconstriction (VC) of cutaneous vessels to minimize heat loss. In older adults, this reflex VC response is impaired thereby increasing their susceptibility to excess heat loss and hypothermia. Because L-tyrosine, the amino acid substrate necessary for catecholamine production, has been shown to augment reflex VC in age skin, we hypothesize that oral ingestion of L-tyrosine will attenuate the decline in core temperature (Tc) during whole-body cooling in older adults. In a randomized, double-blind design, nine young (25 ± 3 yr) and nine older (72 ± 8 yr) participants ingested either 150 mg·kg of L-tyrosine or placebo before commencing 90 min of whole-body cooling to decrease skin temperature to approximately 29.5°C. Esophageal temperature and forearm laser Doppler flux (LDF) were measured continuously throughout the protocol to provide an index of Tc and skin blood flow, respectively. The change in esophageal temperature (ΔTES) was the difference in temperature at the end of cooling subtracted from baseline. Cutaneous vascular conductance (CVC) was calculated as CVC = LDF/mean arterial pressure and expressed as a percent change from baseline (%ΔCVCBASELINE). Oral tyrosine ingestion augmented the cutaneous VC response to cooling in older adults (placebo, 14.4 ± 2.0; tyrosine, 32.7% ± 1.7% ΔCVCBASELINE; P < 0.05). Additionally, tyrosine improved Tc maintenance throughout cooling in older adults (placebo, -0.29 ± 0.07; tyrosine, -0.07 ± 0.07 ΔTES; P < 0.05). Both the cutaneous VC and Tc during cooling were similar between young and older adults supplemented with tyrosine (P > 0.05). These results indicate that L-tyrosine supplementation improves Tc maintenance in response to acute cold exposure in an older population.

Severe Marine Weather Systems During Freeze-Up in the Chukchi Sea: Cold-Air Outbreak and Mesocyclone Case Studies From Satellite Multisensor Measurements and Reanalysis Datasets

In the present article, cold-air outbreak (CAO) and polar low (PL) events were examined over the Chukchi Sea during low sea ice extent of the basin in the November–December period, 2015. An analysis of weather events was performed using multisensor satellite measurements, the NCEP Climate Forecast System, version 2 (CFSv2), and Arctic System Reanalysis, version 2 (ASR2). The CFSv2 data showed that the most intense cold advection occurred at the 1000–900 hPa boundary layer. It was shown that CAO had been developing from November 30 to December 6 and was accompanied by the sea surface wind speed exceeding 20 m/s and rapid formation and drift of sea ice. Analysis of the sea ice response to the CAO showed fast freezing of the Chukchi Sea for seven days indicating excessive heat loss of the water basin. In addition, significant increase in the open and very open ice areas was observed. These areas could be exposed to excessive cold atmosphere, releasing heat into the atmosphere. PL events have been identified during intensive mesocyclogenesis over the sea during 15–17 November. Weather conditions were characterized by the values of wind speed reaching 15–17 m/s and dry air with total water vapor content (5–7 kg/m2). Analysis of the synthetic aperture radar image revealed the position and horizontal size of the meso-α-cyclone, the fine structure of the mesoscale frontal system of the PL forming meso-γ-vortices, and the wave-like line of the horizontal wind shear in the local convergence zone. The representation of PL events in sea level pressure and near-surface wind speed fields from the ASR2 and CFSv2 datasets was ambiguous. However, the satellite-based and CFSv2 wind speeds better agreed for high-wind conditions.

Development of a Thermal Environment Analysis Method for a Dwelling Containing a Colonnade Space through Coupled Energy Simulation and Computational Fluid Dynamics

In building design, several approaches have been proposed for coupling computational fluid dynamics (CFD) and energy simulation (ES) to perform analyses of thermal environments. The unsteady analysis of thermal environments within buildings containing offices and colonnade spaces is difficult to perform using an ES that represents the space with a single mass point, owing to excessive predictive heat loss; therefore, CFD has typically been used instead. Although it is possible to divide the space into zones using ES, it leads to excessive predicted heat loss and the prediction of heat movement due to the influence of strong air currents, such as those associated with air conditioners. This behavior is observed because these zones are not detailed mesh divisions. To solve these problems, we proposed a method for calculating the ratio of heat contribution to zones that were pre-divided using CFD followed by the distribution of the total thermal load calculated by ES. In this study, we proposed a method for coupling ES and CFD, which enabled the unsteady analysis of a thermal environment in a large space and verified its accuracy.

The Effect of In-Plane Thermocouple Dimension on the Performance of CMOS and BiCMOS Thermoelectric Generators

With the advances of thin-film process technology in foundry services, recent development is to design thermoelectric generator (TEG) with in-plane thermocouple of polysilicon or polycrystalline silicon germanium by complementary metal oxide semiconductor (CMOS) or BiCMOS process. However, the small thermal resistance and adversely large electrical resistance in a thermocouple of micron dimension lead to small temperature gradient and excessive heat loss, hence resulting in poor harvester performance. The optimal design of thermocouple dimension is therefore critical to the TEG performance. A model of the effect of thermocouple dimension on the TEG performance is developed. For the TEG design by TSMC CMOS process with P- and N-thermoleg of thickness $0.275~\mu \text{m}$ and $0.180~\mu \text{m}$ , respectively, the model shows that the optimal thermocouple is $60\,\,\mu \text {m} \times 2\,\,\mu \text{m}$ (length $\times $ width). For design by TSMC BiCMOS process with P- and N-thermoleg of thickness $0.380~\mu \text{m}$ and $0.200~\mu \text{m}$ , respectively, it is $45\,\,\mu \text {m} \times 2\,\,\mu \text{m}$ . The numerical simulation and experimental verification on the latter show that better TEG performance can be achieved by optimal thermocouple dimension to match the electrical and thermal resistances.

Measurement uncertainty and quenching phenomena in uniform heating rod bundle CHF tests

The uniform heated rod bundle Critical Heating Flux (CHF) tests have been often conducted as a part of mixing vane performance evaluation processes. Presently, several commercial CHF correlations were developed based on a large amount of rod bundle CHF data using axial uniformly heated rod bundles. With a uniformly heated test section, majority of CHF events are dominated by dry-out mechanism under high quality, high void fraction local conditions. Considering the inverse proportional relationship between the quality and CHF, for an axially uniformly heated test section, the CHF events should occur near the end of heating length (EOHL) where the void fraction/quality is the highest. However, the upstream shift of CHF location is often observed in the uniform heating tests, sometime as much as 250 mm or higher upstream from the EOHL.In the past, without any sufficient convincing proof, long dryout areas as well as “unknown” “mysteries” mixing effects from the mixing vane grid were often considered as the contributing factors for this type of upstream shift. Based on further and detailed examination, this paper offer analysis and evidence to demonstrate another most plausible explanation, exit quenching effect, which ultimately concludes that rod bundle CHF using uniform heated rods could have data with huge measurement uncertainty and as much as over 30% of non-conservatism due to heat lose and quenching effects at the exit of the heated length. The quenching effect at the exit of heater length is mainly due to reflood phenomena generated between the high void/low flow test section exit region and the relatively cold single phase coolant immediately above in the top plenum resulting from either excessive heat loss or operating transient condition.In this paper, system code and CFD modeling were utilized to simulate the quenching phenomena in both steady state and transient conditions. The significant void fraction drop near the exit of the test section due to quenching were clearly observed in these simulations and also evidenced by the various degrees of coloration of the heaters surface in the experiment. This exit reflood quenching phenomena may change the CHF location, suppress boiling, cool down the heated surface, and eventually lead to non-conservative high CHF values. Based on this analysis and experimental observation, it is concluded that the CHF correlations developed based on these type of data are potentially non-conservative in various degrees pending on local thermal-hydraulic conditions, which should be taken into consideration for their applications, especially for safety analysis in nuclear reactor.

Heavy oil mobilization from underground coal gasification in a contiguous coal seam

Underground coal gasification (UCG) is a process to convert coal in-situ to combustible gases which are of versatile end use from power generation to chemical synthesis. It extracts the energy of coals which are normally too deep/thin to recover with conventional technologies, thus increasing enormously the recoverable coal reserves worldwide. It is generally advised to operate UCG in a coal seam with a thickness no less than 2 m as excessive heat loss to the surrounding environment significantly undermines the gross thermal efficiency. However, UCG can still be attractive in a thin seam when a heavy oil reservoir adjoins. This paper aims to shed light upon the feasibility of mobilizing heavy oil with UCG in a contiguous thin coal seam. A 3-D UCG model was integrated into a heavy oil reservoir model. Modelling results showed that, with a creative layout of process wells, it is possible to grow a UCG fire in favour of mobilizing neighbouring heavy oil. UCG can mobilize significant oil due to a remarkable reduction in oil viscosity in a short time. The characteristics of production wells as well as the expansion of a thermal cavity were also studied. Furthermore, the effects of coal thickness, oil well deployment and solution gas in live oil were investigated with respect to thermal cavity propagation and oil production, which can serve as a guide in designing future reservoir development with UCG.

Computational Fluid Dynamics aided investigation and optimization of a tunnel-ventilated poultry house in China

Ventilation system is crucial for poultry houses to control the indoor climate and air quality. The tunnel ventilation system is widely applied for large-scale poultry buildings in China but only limited scientific researches regarding the flow pattern, temperature distribution and design criteria are available in the literature. Thanks to the fast development of computer technology, Computational Fluid Dynamics (CFD) techniques were used in present study to investigate the indoor air movement, air temperature and relatively humidity. A three-dimensional CFD model was built according to the real dimensions of a laying hen house and the model was validated by comparing the simulation results with the field measurements at 30 positions. Meanwhile, statistical analysis was performed to determine the differences between different boundary conditions regarding the agreement between measured and CFD simulated results. Optimization of air inlet configurations was performed by using the validated CFD model and it was found that the uniformity of indoor air movement could prevent excessive local convective heat losses and reduce the temperature at the end of the house. Furthermore, the air inlets placed at the middle of the side wall could significantly reduce the high temperature expected at the end of the building without using extra energy, which is especially important for large-scale poultry farms with long buildings. The performance of side-wall windows was also examined and preliminary guidance was provided to effectively regulate the indoor climate by using these windows with the help of environmental monitoring systems. The present study contributes to the understanding and design of the tunnel ventilation system used in poultry houses.

Experimental study and numerical analysis of the scaling effect on the flame stabilization of propane/air mixture in the micro-scale porous combustor

In order to investigate the effect of heat recirculation through the porous medium on the flame stabilization limits for different channel heights, micro-combustors with three different channel heights 3 mm, 2.5 mm and 2 mm are fabricated and tested. A three-dimensional numerical model is established to explain the inherent mechanisms for the experimental results. It is shown that the stable flame can be established inside the micro-scale porous combustor with the channel height 2 mm which is smaller than the quenching distance. The porous medium combustion limit remains nearly unchanged as the channel height decreases due to the enhanced heat recirculation through the porous medium and the solid wall. The extinction limit increases obviously with the decrease of channel height due to the excess heat loss. The simulation results show that the flame thickness becomes larger as the channel height decreases. With the decreasing channel height, the wall temperature increases due to the increase of inner-wall convection heat transfer coefficient. The thermal balance analysis shows that the decrease of channel height results in lower thermal efficiency. The 2 mm (ε = 4) height combustor is more suitable for the micro thermoelectric generator. Extra heat exchange channel is need to utilize the output energy sufficiently.

The effects of electrical and thermal boundary condition on the simulation of radiofrequency ablation of liver cancer for tumours located near to the liver boundary

Effects of different boundary conditions prescribed across the boundaries of radiofrequency ablation (RFA) models of liver cancer are investigated for the case where the tumour is at the liver boundary. Ground and Robin-type conditions (electrical field) and body temperature and thermal insulation (thermal field) conditions are examined. 3D models of the human liver based on publicly-available CT images of the liver are developed. An artificial tumour is placed inside the liver at the boundary. Simulations are carried out using the finite element method. The numerical results indicated that different electrical and thermal boundary conditions led to different predictions of the electrical potential, temperature and thermal coagulation distributions. Ground and body temperature conditions presented an unnatural physical conditions around the ablation site, which results in more intense Joule heating and excessive heat loss from the tissue. This led to thermal damage volumes that are smaller than the cases when the Robin type or the thermal insulation conditions are prescribed. The present study suggests that RFA simulations in the future must take into consideration the choice of the type of electrical and thermal boundary conditions to be prescribed in the case where the tumour is located near to the liver boundary.

An experimental comparative study of the stabilization mechanism of biogas-hydrogen diffusion flame

This work describes an experimental study of the effect of hydrogen addition on the stabilization characteristics of laminar biogas diffusion flame. The focus is to identify and compare various factors influencing the blowoff process. Three compositions of biogas, BG40, BG50 and BG60 were considered and the amount of hydrogen added was varied from 5% to 25% of the biogas by volume.With increasing hydrogen addition, the critical flow velocity beyond which the flame blows off increases faster than the laminar burning velocity (LBV) does, indicating that flame stabilization is not solely dependent on laminar burning velocity. An exponential relationship is observed between LBV and flame propagation speed. Therefore, both flame propagation speed and LBV, together with other factors, contribute to flame stabilization. The reason for no stable lift for either biogas or H2-biogas flame is analyze by Schmidt number calculation, and the results agree with the literature. Also found is that hydrogen added to biogas accelerates the fuel mass diffusion, which may play an important role for stabilization of the nozzle-attached flame.The CO2-C3H8 and BG60 flames were compared to exclude the possible dominant role played by insufficient heat release and/or excessive heat loss due to CO2 present in biogas. Tested on varied-size burners show that flame stabilization depends on burner pore size, where larger diameter allows better flame stability. The universal equation for predicting blowout/blowoff velocity in the literature was found to be invalid for H2-enriched biogas flame and a new scaling law was put forwards.

Thermal and sound insulation of lightweight steel-framed façade walls

Lightweight steel-framed (LSF) construction has the potential to reach high standards regarding the functional performance of buildings. Despite the benefits of this construction system, the effect of thermal bridges caused by the high thermal conductivity of the steel structure can be a disadvantage. Furthermore, because LSF buildings have low mass and the connections between the outer and the inner sheathing of the walls are usually rigid, provided by steel studs, some acoustic performance drawbacks are also possible. Excessive heat loss or poor sound insulation are related to the external envelope behavior of buildings. Although several studies can be found regarding the influence of the steel frame on the thermal or sound insulation performance of LSF façade walls, the study of this influence from both perspectives at the same time is not widespread. In this work, the influence of the steel frame on both the thermal and sound insulation performance of LSF façade walls is studied. The thermal behavior and sound insulation are assessed using specialized software, namely THERM and INSUL, respectively. With this work it is intended to provide guidelines which can contribute to an effective design of LSF façade walls, considering both functional performances.

Model predictive temperature control and ageing estimation for an insulated cool box

The transport of perishable goods in insulated cool boxes (ICB) is affected by strong disturbances and requires an effective temperature control scheme. Model predictive control (MPC) can provide such a performing control scheme, however, the strong disturbance of irradiation by the sun can be rarely measured. Furthermore, the ageing of the ICB’s insulation is a parameter of vital interest for logistic and economic planning although it cannot be directly measured. In this work a MPC and a custom disturbance observer is presented, which provide an estimate of the current irradiation and the ageing state, respectively. This is obtained by first estimating the excess heat loss of the ICB, and then splitting up this heat loss into an irradiation part and a part due to ageing of the ICB’s insulation. The ageing model is assumed to be parametric, and a nonlinear estimation scheme is employed for parameter tuning. A suitable MPC formulation guarantees offset-free tracking of the desired temperature. The performance of the overall concept is demonstrated in a simulation for the nominal case, for increasing measurement noise, and for an abrupt change in the ageing parameters. Additionally, a non-parametric estimate for the confidence interval of the end-of-life prediction of the ICB is given.

Influence of gap height and flow field on global stoichiometry and heat losses during opposed flow flame spread over thin fuels in simulated microgravity

This study characterizes thin fuel opposed flow flame spread in simulated microgravity for a range of gap heights and airflow velocities in a Narrow Channel Apparatus (NCA). One objective was to estimate gap heights that suppress buoyancy without promoting excessive heat losses to the channel walls. A corollary of this objective was to assess the dependence of heat losses on the channel height. A second objective was to determine the influence of global combustion stoichiometry on simulated microgravity flame spread in the NCA. Whatman 44 filter paper was used for NCA gap heights ranging from 6–20 mm (half-gap below and above sample) and average opposed flow velocities 1–40 cm/s. Flames at low flows were fuel rich when the forced flows were of the same magnitude as the diffusive flow. For thin fuels, a full gap of 10 mm (5 mm half-gap) provided a compromise between buoyancy suppression and heat loss. Calculations were made of flame stoichiometry and of the influence of the velocity profile on flame spread rates (comparing it with previous theory). This part of the analysis provided support for the velocity gradient theory of flame spread. The information provided in this work on the theoretical nature of opposed flow flame spread over thin fuels is based on experimental measurements in simulated microgravity conditions.

Variable Time Step Control for Six-Step Operation in Surface-Mounted Permanent Magnet Machine Drives

The six-step operation of surface-mounted permanent magnet machine drives in a flux weakening region has many advantages compared to the pulse width modulation mode, such as the reduced switching loss and fully utilized inverter output voltage. However, if the ratio of the sampling frequency to the fundamental frequency is low in fixed sampling system, the low-frequency oscillation in the current can be incurred in the six-step operation. The low-frequency current causes a system stability problem and reduces system efficiency due to an excessive heat and high power loss. Therefore, this paper proposes the variable time step controller for six-step operation. By updating an output voltage, sampling phase currents, and executing the digital controller synchronized with the variable sampling time, the turn on and off switch signals for six-step operation can be generated at the exact moment. As a result, the low-frequency oscillation in the phase current can be eliminated. In addition, the system transfer function of the proposed control method is discussed for the system stability and system dynamic analysis. The effectiveness of the proposed method is verified by the comparative simulation and experimental results.

Study of the required thermal insulation (IREQ) of clothing using infrared imaging

The sense of cold develops due to the increase in heat loss from a human body. Excessive cold can be a health hazard, since excessive heat loss from the body may result in hypothermia/frostbite. Decreased body temperature due to heat loss also affects the physical, manual and perceptive performance of individuals. Therefore, protective measures are taken through clothing that controls and regulates heat loss. Clothing is a protective means for thermal insulation. Clothing and garments used in cold climates should have sufficient insulation to maintain the thermal balance of the body. The required clothing insulation (IREQ) is calculated on the basis of the hypothesis concerning the heat flow by conduction, convection, radiation and evaporation. This term is well defined in standards such as BS-EN 342 and ISO 11079:2007 (E). This paper presents an experimental study of the use of state-of-the-art Infrared (IR) thermography to estimate IREQ values. However, real IREQ values are difficult to estimate, considering that parameters, such as individual metabolism, are unknown and subject to change. Therefore, relative IREQ (IREQ*) values are computed and compared. Experiments were also conducted to measure the relative IREQ of winter jackets, summer jackets, and sweaters. The infrared images were obtained using a FLIR® T1030sc camera and analyzed using FLIR® Researcher Max software. The experiments were performed under conditions of -20°C to -35°C in the cold room at UiT- The Arctic University of Norway.

Numerical investigation and experimental validation of the impacts of an inner radiation shield on parabolic trough solar receivers

Conventional parabolic trough solar receivers are widely used to harvest heat energy at temperatures ranging from 400 °C to 550 °C. However, high temperatures cause excessive heat loss in solar receivers. Two types of novel solar receivers with an inner metal radiation shield (RS), one with solar selective absorbing coating on the outer surface and one without, were proposed and constructed to improve the thermal performance of solar receivers. Experiments were conducted in an enthalpy difference lab, and mathematical models with spectral radiant distributions were established to predict the thermal performance of the solar receivers. A comparison between the simulated and experimental results showed satisfactory consistencies. Predictions were obtained using the models with the root mean square deviation of less than 6%. The novel solar receiver without solar selective absorbing coating on the outer surface of the RS showed superior performance at absorber temperatures exceeding 550 °C. At the absorber temperature of 600 °C, the percentage of heat loss reduction of the receiver with solar selective absorbing coating and of that without reached 23.4% and 24.2%, respectively.

МЕТОД ОПРЕДЕЛЕНИЯ РЕАЛЬНЫХ ТЕПЛОПОТЕРЬ СУЩЕСТВУЮЩИХ СТРОИТЕЛЬНЫХ ОБЪЕКТОВ

This article is dedicated to the issues of energy saving, in particular to the problems of improving energy efficiency of modern buildings by experimental studies of thermo physical properties (TPP) of materials in order to eliminate excessive heat losses through building envelope. Based on the analysis of the existing methods of determining the materials’ TPP, the authors developed an algorithm to de­termine the actual heat losses of a facility under study. Operation of an installation for determining the TPP (heat transfer coefficient, thermal resistance and specific heat characteristics) of the facility under study is described. The formulas required for the calculation of TPP are given. Experimental results of the study are provided. Main advantages of the developed installation are described.

A study of thermal destratification for large warehouse energy savings

Thermal stratification in large warehouses is a common phenomenon in winter, especially for cold climates. Buoyancy-driven warm air tends to move upwards towards ceilings creating vertical temperature gradients with upper higher temperatures, and consequently leading to excessive heat losses through roofs. These warehouses therefore require thermal destratification through certain air mixing strategies, the selection of which often relies on engineering rules of thumb and experiences but can be better determined through combined experimental and numerical approaches. This paper investigated different thermal destratification methods in two industrial warehouses based on field measurements and CFD simulations with the focus on the quantification of thermal stratification, and the suitable methods modeling air mixing devices, e.g. ceiling rotating fans and bucket fans. The numerical models were first validated by field measurements and then used to simulate different destratification strategies and to compare associated energy impacts. The CFD methods for modeling air mixing devices and their performances can be applied to other similar cases.