Significant Heat Loss Research Articles

Monitoring body temperature during moderate intensity exercise and inactive recovery in the cold: a pilot study

Exposure to cold ambient conditions during outdoor recreation can lead to significant heat loss. It is unknown how fast body temperature decreases or how fast a person could become hypothermic in cold temperatures. We present a series of pilot tests involving moderate intensity exercise and inactive recovery in the cold to monitor how body temperature changes with exposure to -10°C. The primary aim of this pilot study was to test the feasibility of the proposed protocol with the intention to design a main study. The primary questions were: (i) to what degree does body temperature increase or decrease with this protocol, (ii) whether epitympanic temperature is a suitable measure of core temperature using a recently developed, non-invasive device and (iii) if participants are able to tolerate the cold during inactive recovery. This pilot series included seven participants. After an acclimatization phase (15 minutes), participants exercised at 60% peak heart rate (20 minutes) followed by a seated, inactive recovery phase (15 minutes) in the cold. The mean ambient conditions were -10.0±0.4°C and 66.1±8.6% relative humidity and no wind. The primary findings based on the feasibility criteria were that body temperature increased while exercising at an intensity of 60% HRpeak and decreased during inactive recovery by -0.3±0.1°C (epitympanic temperature). Secondly, the agreement between epitympanic and esophageal temperature (mean difference 0.2°C, 95% confidence interval -0.5 to 0.0, p=0.095) was better than in previous studies. Finally, all participants were able to tolerate the cold and complete the study despite thermal discomfort and shivering in the recovery phase. This protocol was successful in showing small changes in body temperature during exercise and recovery in the cold, though some modifications to the current protocol are recommended to elicit a larger effect size.

Incorporation of Hydroxyethylcellulose-Functionalized Halloysite as a Means of Decreasing the Thermal Conductivity of Oilwell Cement

The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. In order to obtain better energy efficiency and mechanical robustness, there is considerable interest in the development of low-thermal-conductivity cement that can provide a combination of enhanced thermal insulation and mechanical resilience upon thermal cycling. However, the current palette of thermal cements is exceedingly sparse. In this article, we illustrate a method for decreasing the thermal conductivity of cement by inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes. Halloysite/hydroxyethylcellulose inclusions offer an abundance of disparate interfaces and void space that can effectively scatter phonons, thereby bringing about a pronounced reduction of thermal conductivity. The microstructure of the nanocomposite cementitious matrix is strongly modified even as the compositional profile remains essentially unaltered. Modified cement nanocomposites incorporating halloysite nanotubes along with hydroxyethylcellulose in a 8:1 ratio with an overall loading of 2 wt.% exhibit the lowest measured thermal conductivity of 0.212 ± 0.003 W/m.K, which is substantially reduced from the thermal conductivity of unmodified cement (1.252 W/m.K). The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites.

The ignition characteristics of the close dual-point laser ignition in a cavity based scramjet combustor

The ignition processes of single-point laser ignition (LI) and dual-point LI were experimentally investigated in a cavity-based Mach 2.52 scramjet combustor fueled with ethylene. The stagnation temperature and total pressure of the supersonic inflow were 1486 K and 1.6 MPa, respectively. The results indicate that the ignition performance of dual-point LI with a plasma distance of 3 mm is the same as the single-point LI. However, further increasing the plasma distance to 7 mm degrades the ignition performance of dual-point LI. Therefore, dual-point LI is not superior to single-point LI in the scramjet combustor, which is contradictory to the investigations performed in quiescent premixed combustible mixtures. The reason is that the high turbulence intensity and strain rate in the cavity recirculation flow (∼100 m/s) lead to serious plasma and flame quenching instead of enhancing the flame propagation. Therefore, expanding the spatial distribution of the plasma by dual-point LI method, which might result in significant radical loss and heat loss, is not recommended for igniting a scramjet combustor.

Analysis and flamelet modelling for laminar pulverised coal combustion considering the wall effect

In this work, the wall effect on the characteristics of pulverised coal combustion is examined. To this end, laminar pulverised coal flames stabilised near a planar non-slip wall with isothermal and adiabatic boundary conditions are simulated with detailed chemistry. The phenomenon of side-wall quenching is observed in the non-adiabatic case due to significant wall heat losses. The temperature difference between the adiabatic flame and non-adiabatic flame at the planar non-slip wall can be as high as 1200 K. It is found that the distributions of different species show various sensitivities to the wall effect. Particularly, the species involved in the volatile matter and char off-gases are significantly influenced by the wall heat losses. In addition, the conventional flamelet model for pulverised coal combustion is extended to consider the heat transfers between the flame and wall. The performance of the extended flamelet model on prediction of the thermo-chemical quantities in both adiabatic and non-adiabatic flames is evaluated through a priori tests. The results show that the thermo-chemical quantities in both adiabatic and non-adiabatic flames can be overall reproduced by the extended flamelet model at both upstream and downstream locations. Interestingly, it is found that the gaseous temperature and CH mass fraction in the non-adiabatic flame can be better predicted by the extended flamelet model than those in the adiabatic flame at the downstream location.

An experimental and numerical study of granular flows through a perforated square lattice for central solar receiver applications

A proposed design for a concentrating solar power (CSP) receiver uses a granular material - such as sand - as the heat transfer and energy storage medium. Early designs of particle heating receivers (PHR) utilize a falling curtain of particles which directly absorbs the concentrated solar radiation. However, falling curtain receivers have several disadvantages, including significant heat and particle losses, and a short residence time within the irradiation zone. One design proposal which overcomes these challenges is the so called “impeded flow PHR design”, in which the particles flow over, around, or through a series of obstacles in the flow path. This reduces the average velocity of the particles, thereby increasing residence time in the irradiation zone of the receiver. It also reduces heat and particle losses from the receiver. However, granular flows through complex structures are not well understood, rendering a priori design of impeded flow PHR geometries difficult. To better understand these flows, lab scale models of a PHR design variant using a perforated square lattice at an oblique angle have been constructed, allowing granular flows through the receiver geometry to be experimentally analyzed. In addition, two different numerical modeling approaches - the discrete element method (DEM) model, and a two-fluid computational fluid dynamics (CFD) model - have been developed to model the flow of particles through the specified receiver geometry. The results of the DEM model are in reasonable agreement with the experimental data with respect to mass flux, and better matches the experimental data than the CFD model.

Modified Harrick reaction cell for in situ/operando fiber optics diffuse reflectance UV–visible spectroscopic characterization of catalysts

UV–visible (UV–vis) spectroscopy is a common, powerful, and affordable technique for the characterization of heterogeneous catalysts. Here, we present an improved design of the commercial ubiquitous Harrick Scientific high temperature reaction cell for use in diffuse reflectance (DR) UV–vis spectroscopy with fiber optics at very close proximity of a catalyst sample and with high time resolution. The cell possesses significant dead volume which was reduced by a homemade compact dome and by volume reduction of cell void space with simple addition of glass beads, thereby, enabling faster transfer of gases. The cell was also improved by adding a second thermocouple to directly monitor the temperature of the catalyst bed via the outlet port without requiring any additional machining. This modified design and the use of an optical fiber DR probe in conjunction with a miniature concave-CCD combination based spectrometer allowed fast acquisition of in situ UV–vis spectra in the order of seconds and at temperatures up to about 500 °C. It is also shown that, unlike probes used in tubular reactors, expensive high temperature DR probes are not required in this design. The flow dynamics of the reaction setup were followed by an analysis of residence time distributions (RTD) via pulse experiments of Ar, O2, H2, CO, and CO2 as analyzed online by mass spectrometry (MS). These tests enabled a rigorous analysis of the fluid dynamics of the modified cell showing average gas residence times (after correcting for transfer lines and MS contributions) of ∼13 s at gas flow rates of 45 cm3/min (or ∼4 s at gas flow rates of 120 cm3/min) and a fluid behavior that could be approximately described by a CSTR reactor model. The RTD method is of general application and can be easily implemented to other reaction cells to rigorously determine gas mean residence times and distribution, regardless of setup and transfer lines design, provided that a reaction cell bypass line is added to the system. A thermal analysis indicated that significant heat losses due to radiation, conduction, and convection contribute to the observed sample bed vs heater temperature differences. Additionally, an example is presented to show the utility of the modified cell to monitor quickly (every 2 s) and continuously UV–vis spectra over an extended period of time during the in situ dynamic response of gold surface plasmon resonance (Au-SPR) peak shifts on a Au(1 wt%)/ZrO2 catalyst as it is exposed to controlled and cycling oxidizing and reducing environments. The results showed that the Au-SPR peak responded rapidly and shifted reversibly at the studied cyclic oxidizing and reducing conditions. The reported modifications of the reaction cell setup were shown to enable in situ spectroscopic characterization of heterogeneous catalysts. It proved useful for monitoring adsorption and desorption of gas species near gold nanoparticles via Au-SPR and for potentially tracking rapid changes (within seconds) on catalysts with characteristic finger prints in the UV–vis region.

Graphene embedded form stable phase change materials for drawing the thermo-electric energy harvesting

We introduce a reusable energy harvesting system that can recover discarded thermal energy by utilizing temperature variation of the environment. The system consists of two different phase change materials (PCMs); poly ethylene glycol (PEG) and 1-tetradecanol (1-TD), and a cell of N and P type semiconductor. Since a large amount of heat energy is absorbed during phase transition, PCMS are generally utilized to maintain isothermal temperature on the opposite sides of the N and P type semiconductor as long as possible. The resulting temperature difference between two sides of semiconductor induces an electric current during the heating and cooling process. It is important for the phase change material (PCM) to possess a good shape stability without significant loss of latent heat. A 3D porous graphene aerogel is selected for the pure phase change material to infiltrate into the aerogel and to increase the shape stability and thermal conductivity of the PCM composite. The thermal conductivity of PEG and 1-TD composites is significantly increased to 0.4268 W/m∙K, and 0.3408 W/m∙K, respectively. Thermal and electrical analyses are performed to predict the energy harvested by the device. The electrical energy is generated in the harvesting system due to the Seebeck effect. The maximum value of the electric current reaches 10 mA in both heating and cooling processes and an LED lamp was turned on successfully. Additionally, the energy harvesting system is modelled by using the finite element method (FEM) and the numerical prediction is in good agreement with the experimental results.

Study of infiltration through sliding windows with respect to closing mechanisms and their locations in a building during winter season

ABSTRACTInfiltration through windows accounts for a significant heat loss in buildings during winter, leading to the need to minimize uncontrolled air flow. Improvement of window air tightness is important for reducing heat loss by infiltration through windows. In this study, infiltration is measured for general sliding (GS), parallel sliding tilt (PST) and lift sliding (LS) windows according to ASTM E283, a standard for window infiltration measurement. Measured window infiltration data, pressure coefficients calculated with STAR-CCM+ and outdoor weather data of Seoul are used in CONTAM, a network based ventilation simulation program to estimate infiltration during winter season for three sliding window types and their locations in a building. The results show that infiltration is highest for east located general sliding type window, and lowest for west located parallel sliding tilt window. Monthly analysis shows that for an east located window, infiltration is highest during January and lowest during December.

A study of granular flow through horizontal wire mesh screens for concentrated solar power particle heating receiver applications – Part I: Experimental studies and numerical model development

A proposed design for a concentrating solar power (CSP) receiver uses granular material – such as sand – as the heat transfer and energy storage medium. Early designs of particle heating receivers (PHR) utilize a falling curtain of particles which directly absorbs the concentrated solar radiation. However, falling curtain receivers have several disadvantages including significant heat and particle losses and short residence time within the irradiation zone. One design proposal which overcomes these challenges is the so called “impeded flow PHR design”, in which the particles flow over, around, or through a series of obstacles in the flow path. This reduces the average velocity of the particles, thereby increasing their residence time in the irradiation zone of the receiver. It also reduces heat and particle losses from the receiver. However, granular flows through complex structures are not well understood, rendering a priori design of impeded flow PHR geometries difficult. To better understand these flows, lab scale models of a PHR design variant using horizontal wire mesh screens have been constructed, allowing granular flows through the receiver geometry to be experimentally analyzed. In addition, two different numerical modeling approaches – the discrete element method (DEM) model, and a two-fluid computational fluid dynamics (CFD) model – have been developed to model the flow of particles through the specified receiver geometry. The results of the DEM model are in reasonable agreement with the experimental data with respect to mass flux, and better matches the experimental data than the CFD model. A companion paper presents parametric studies to assess the sensitivity of model predictions to various design and modeling parameters (Sandlin and Abdel-Khalik, 2017).

Optimisation of Heat Loss through Ventilation for Residential Buildings

This study presents the results of research on heat loss from various types of residential buildings through ventilation systems. Experimental research was done to analyse the effectiveness of ventilation systems of different types and determine the parameters of air discharged via the ventilation ducts. A model of heat loss from the discharge of exhaust air outside through air ducts has since been developed. Experiments were conducted on three experimental systems of building ventilation: gravitational, mechanical, and supply-exhaust ventilation systems with heat recovery. The proposed model dependencies were used to chart the daily fluctuations of the optimum multiplicity of air exchange for precise control of the parameters of mechanical ventilation systems in residential buildings. This study proves that natural ventilation in residential buildings fulfils its function only by increasing the air flow into the building, and that this incurs significant heat loss from buildings during the heating season.

Energetical, exergetical and economical optimization analysis of combined power generation system of gas turbine and Stirling engine

One of the promising methods to increase exergoeconomic performance and decrease effects of environmental adverse of energy systems is integration of energy systems. Gas turbine power plant is one of the favorable power generation systems because of its acceleration in start-up and low investment cost. However, the thermal efficiency of gas turbine cycle is low because of the significant heat loss due to high-temperature effluent gas exhausted from the stack. Therefore, if this huge heat loss is recovered by another heat engine coupled with gas turbine cycle the total efficiency will increase, considerably. Stirling engine owing to its high efficiency is one of the promising candidates which can be used as a part of the combined system. Hence, an optimization analysis on standalone gas turbine cycle, as well as combined cycle of gas turbine and Stirling engine are considered in this paper to find out the optimal operational point, thermodynamically and economically. Both single-objective and multi-objective genetic algorithm is performed to optimize the overall plant parameters, subjecting three optimization scenarios of maximizing exegetic efficiency, minimizing levelized cost of electricity and exergo-economic optimization. A comprehensive comparison of gas turbine and Stirling engine combined cycle and standalone gas turbine cycle was performed for these optimization scenarios. Results show a significant improvement in power output and reduction of levelized cost of electricity in combined cycle of gas turbine and Stirling engine. In the optimal point of this hybrid system, levelized cost of electricity reduces by 10.3% and exergetic efficiency improves by 16.1% compared with the optimal point of standalone gas turbine cycle.

Energy-Saving Analysis of Solar Heating System with PCM Storage Tank

A solar heating system (SHS) with a phase change material (PCM) thermal storage tank is proposed with the view that traditional heat water storage tanks present several problems including large space requirements, significant heat loss and unstable system performance. An entire heating season (November–March) is selected as the research period on the basis of numerical models of the SHS-PCM. In addition, taking a public building in Lhasa as the object, the heating conditions, contribution rate of solar energy, and overall energy-saving capability provided by the heating system are analyzed under different PCM storage tanks and different terminal forms. The results show that an SHS with a PCM tank provides a 34% increase in energy saving capability compared to an ordinary water tank heating system. It is suggested that the design selection parameters of the PCM storage tank should specify a daily heat storage capacity that satisfies 70~80% of the entire heating season. A floor radiant system with supply/return water temperatures of 40/35 °C provides the optimal operation and the largest energy saving capability.

The heat loss calculating methods of external walls in the buildings reconstruction

Heat loss analysis in cladding of brick buildings under reconstruction is presented. Thermograms obtained under thermovision inspection and window systems operating experience in conditions of the Republic of Bashkortostan are thoroughly studied. Live issue of increasing buildings energy performance in public utilities sector may largely be solved by replacement of existing window units made of wood to new PVC profile windows equipped with multi-glazed glass units both in brick and frame-panel old buildings. Significant heat loss occurs in junctions between the window frames and the wall in jamb areas. Therefore for the heat conduction matrix for the finite element is used the heat balance equation. Use of the software application to choose certain measures to eliminate the thermal bridges enables to get the thermotechnical calculations in the junction between the window and the exterior wall in the form of temperature fields. Practical recommendations for arrangement of heat insulation in junctions between the window frames and the wall to eliminate actual defects and for normal room conditions are made under examinations. To get the heat conduction matrix for the finite element we will use the heat balance equation.

Flow Characteristics of Steam and Gas Push in the Presence of Heat Thief Zones Overlying Oil Sands Deposits

This paper presents the effects of the top water-bearing zone on the performance of the steam and gas push, i.e., nitrogen as a non-condensable gas injected with steam into an oil sands deposit. The flow characteristics of fluid mixtures are examined in the presence of different-sized water-bearing formations overlying oil sands deposits, i.e., a finite aquifer with no-flow boundaries and an infinite aquifer with continuous mass flux. The performance efficiency is investigated by respectively implementing the cumulative steam to oil ratio, a simple thermal efficiency parameter, and the oil production on the surface. The top water-bearing area serves as a heat thief zone and negatively impacts bitumen recovery; furthermore, it increases the cumulative steam to oil ratio while decreasing the simple thermal efficiency parameter, as well as the oil production rate. When the steam chamber encounters the top aquifer, a severe heat loss occurs. As increasing mol % of nitrogen, the producing time with energy efficiency increases but the chamber growth is limited. The specific operational conditions would be possible for the finite-sized aquifer, while the continuous water influx and the significant heat loss obstructs the thermal processes for the infinite aquifer.

Vortex dynamics-driven heat transfer and flow regime assessment in a turbulent impinging synthetic jet

Synthetic jets gained attention in the last decade as a thermal management solution, especially in the electronic cooling community. Under certain conditions, they can remove heat more efficiently than conventional steady jets. In this work we aim to further the knowledge on the fundamental behavior of such flows and their role in heat transfer enhancement. A numerical canonical geometry was developed to de-couple the impinging flow from possible artifacts, such as actuator and geometry resonance. The unsteady flow was assumed in turbulent regime, which was approximated via the Finite Volume Method through the software ANSYS Fluent™. The turbulence was modeled using the SST k–ω model, which accurately agreed with experimental data. Synthetic jets generate a train of counter-rotating vortices that, when impinged onto a stationary wall, give rise to secondary vortices that cause a colder fluid downwash into the heated zone. We proposed an alternative definition of the Reynolds number (ReΓ) that characterizes the strength of the generated vortices, consequently representing the strength of the jet. We found that to increase the jet thermal efficiency: (1) Having close consecutive vortices is as important as producing strong vortices, and (2) the jet-to-surface distance should be modified such that the vortex finds its peak intensity nearest to the heated wall. Compared to the classic definition of Re, the Stroke Length based Reynolds number (ReL0) appears as a more suitable definition to establish flow regimes, with the data suggesting ReL0≈10,000 as a threshold where the flow fully transitioned to turbulence. Silva-Llanca et al. (2015) proposed three hypotheses to explain some disagreement found in their data: Turbulent flow at large ReL0, significant heat losses in the experiments at low ReL0 and unaccounted three-dimensional effects. We proved that the first two explained their entire data disagreement, thus rendering the third hypothesis unnecessary.

Mathematical model to investigate the influence of circulation systems on the firing of ceramics

Relatively large amounts of exhaust gas at low temperature level, especially from the cooling of the ware, leave the tunnel kiln and cause significant heat losses. This gas is normally used for drying purposes, but some studies recommend the decoupling of the firing process and drying process in order to optimize them separately. To reduce the heat losses and to improve the efficiency of the firing process, the heat transfer between the gas and the ware, especially in the cooling zone, has to be increased.Therefore, a mathematical model is used to simulate the kiln process. Roof tiles are used as a reference product. Process parameters such as throughput, energy consumption, material properties for tiles and cassettes, geometrical data of the furnace and the setting are oriented on a real production line. Within the model the modes of heat transfer, consisting of forced convection, and gas radiation are considered to investigate the influencing parameters such as gas velocity.Especially in the cooling zone, there is high potential to improve the convective heat transfer with circulation systems. In order to reduce the amount of cooling gas radically and to think about a decoupling of firing process and drying process, the required mean flow velocity through the setting should be in the range of 20 m/s for roof tiles.

Suspended timber ground floors: Heat loss reduction potential of insulation interventions

There are approximately 10 million suspended timber ground floor constructions in the UK and millions more globally. However, it is unknown how many of these floors are insulated and their performance has not been widely investigated. This study investigates the impact of retrofitting insulation on the thermal performance of suspended timber ground floors through the detailed investigation of a UK case study dwelling. Practical and buildable interventions were undertaken: fully-filling the floor void with EPS beads, and 100mm woodfibre insulation between the joists. The performance of both interventions was monitored by high-resolution in-situ heat-flow monitoring in 27 floor locations, allowing for comparison with the uninsulated floor and with modelled results. While floors often remain uninsulated due to the disruption of retrospective works, this study highlighted potentially significant heat loss reductions: the mean whole floor U-value dropped by 65% for woodfibre insulation and 92% for bead-insulation which also benefited from sealed airbricks. A disparity between the in-situ measured and modelled performance was observed; this gap reduced the better insulated the floor was. The findings have implications for policy, retrofit decision-making and carbon emission reduction stock models, especially given the modelled underestimation of floor heat loss, impact of interventions and assumed financial payback for this study.

공공청사 리트로핏 설계 시 외부 수평 차양 장치에 따른 에너지 소비량 절감 방안

Purpose: Recently, significant heat loss through the window takes place in buildings. Nevertheless, there exists little literature concerning the exterior horizontal shading devices and the design criteria are not clearly settled yet. Applying the exterior horizontal shading devices is more efficient as compared to the interior shading devices in that solar radiation can be directly blocked before passing through the window or the envelope. The purpose of this study is to reduce the internal load by designing the exterior horizontal shading devices and verify the degree of reduction in energy consumption. Method: This study aims to reduce energy consumption in cooling and heating through proposing proper length and shape of the exterior horizontal shading devices in public buildings. In the process, actual energy data and the Design Builder simulation program are utilized. In addition, economic aspect is considered to figure out the optimal length of the exterior horizontal shading devices that maximizes efficiency. Result: As a result, the proper length and shape of the exterior horizontal shading devices are provided as follows: 1) Energy consumption in cooling and heating is minimized when the exterior horizontal shading devices are designed as 0.5m*2. 2) Electricity bill is the lowest when the exterior horizontal shading devices are designed as 3.3m*2. The gap between maximum and minimum electricity bill is about 7.8~14%.

An Analysis of the Temperature Change in Warmed Intravenous Fluids During Administration in Cold Environments

This nonhuman simulation study was conducted to determine the decrease in temperature that occurred to 1-L bags of normal saline in a cold environment. The bags were warmed to 39°C and administered through intravenous (IV) tubing at a set flow rate while in a cold environment. The goal was to determine if there was a significant decrease in fluid temperature from the bag to the catheter site. Three trials were completed at temperatures of 0°C, −7°C, −12°C, and 22°C (control). Each bag of normal saline was warmed to 39°C using the SoftSack IV Fluid Warmer (Smithworks Med Inc, Lindale, TX). Fluid was collected and temperatures recorded at 5-minute intervals. The results showed a statistically significant (P = .003) change in temperature between the IV bag and the administration site. The most rapid change occurred within the first 5 minutes. The temperature change was more significant with colder ambient temperatures, with an average of a 28.7°C difference at −7°C and −12°C after 30 minutes. It appears that the most significant heat loss occurs through the IV tubing itself. Therefore, it may be beneficial to insulate the tubing on a trauma patient receiving warmed IV fluids in a cold environment to help prevent hypothermia.

Propagation of combustion waves in the shell-core energetic materials with external heat losses.

In this paper, the properties and stability of combustion waves propagating in the composite solid energetic material of the shell-core type are numerically investigated within the one-dimensional diffusive-thermal model with heat losses to the surroundings. The flame speed is calculated as a function of the parameters of the model. The boundaries of stability are determined in the space of parameters by solving the linear stability problem and direct integration of the governing non-stationary equations. The results are compared with the characteristics of the combustion waves in pure solid fuel. It is demonstrated that a stable travelling combustion wave solution can exist for the parameters of the model for which the flame front propagation is unstable in pure solid fuel and it can propagate several times faster even in the presence of significant heat losses.