Reduce Heat Loss Research Articles

The impact of well spacing on three-dimensional in situ extraction of oil shale using high-temperature air injection

To explore the impact of well spacing on the in situ high-temperature air injection for three-dimensional shale oil recovery, this study constructed six different well-spacing physical models of shale oil for investigation. By comparing factors such as temperature distribution, cumulative oil production volume, heating rate factor, and specific energy consumption per unit volume of shale oil among the six different well-spacing models, the influence of well spacing on the in situ high-temperature air injection for three-dimensional shale oil recovery was analyzed. The results showed that all six shale oil models exhibited a ripple pattern, advancing along the fractured fissures from the heating well to the production well. Model I, Model II, Model III, Model IV, Model V, and Model VI completed the full decomposition of the shale region at 2610, 1530, 1800, 3510, 4050, and 6660 days, respectively. The heating rate factor reached its peak at 1800, 900, 1440, 2340, 3240, and 3960 days. Model III had the lowest specific energy consumption per unit volume of shale oil, which was 905.41 kW/m3. Using Model III for three-dimensional shale oil injection with high-temperature air in situ recovery will shorten the heating time and reduce heat loss.

Two-Phase Crude Oil-Water Flow Through Different Pipes: An Experimental Investigation Coupled with Computational Fluid Dynamics Approach.

The present study deals with two-phase non-Newtonian pseudoplastic crude oil and water flow inside horizontal pipes simulated by ANSYS. The study helps predict velocity and velocity profiles, as well as pressure drop during two-phase crude-oil-water flow, without complex calculations. Computational fluid dynamics (CFD) analysis will be very important in reducing the experimental cost and the effort of data acquisition. Three independent horizontal stainless steel pipes (SS-304) with inner diameters of 1 in., 1.5 in., and 2 in. were used to circulate crude oil with 5, 10, and 15% v/v water for simulation purposes. The entire length of the pipes, along with their surfaces, were insulated to reduce heat loss. A grid size of 221,365 was selected as the optimal grid. Two-phase flow phenomena, pressure drop calculations, shear stress on the walls, along with the rate of shear strain, and phase analysis were studied. Moreover, velocity changes from the wall to the center, causing a velocity gradient and shear strain rate, but at the center, no velocity variation (velocity gradient) was observed between the layers of the fluid. The precision of the simulation was investigated using three error parameters, such as mean square error, Nash-Sutcliffe efficiency, and RMSE-standard deviation of observation ratio. From the simulation, it was found that CFD analysis holds good agreement with experimental results. The uncertainty analysis demonstrated that our CFD model is helpful in predicting the rheological parameters very accurately. The study aids in identifying and predicting fluid flow phenomena inside horizontal straight pipes in a very effective way.

Решение обратной задачи теплопередачи в конденсаторе турбоустановки со встроенным теплофикационным пучком

For power plants reduction of heat losses is one of the main ways to save energy. Energy saving issue is one of the priority areas of the development of science, engineering, and technology in the Russian Federation. Efficiency upgrading of the equipment operation are associated with the condensers of turbine units, since more than 50 percent of the fuel energy is released into the environment with cooling water. The operating efficiency of a condenser with built-in heating beams significantly affects the vacuum in the condenser and, thus, the operating efficiency of the entire unit. Diagnostics of the condition and improvement of operating modes of the condenser of a turbine unit with a built-in heating unit is an urgent scientific and practical issue. To develop a model of a condenser with a built-in heating beam, the methodology of matrix formalization of the description of heat and mass transfer processes has been used. To solve the problem of diagnosing the condition of equipment, methods of least squares and mathematical programming have been used. Within the framework of the matrix formalization methodology, the authors have developed an approach to solve inverse problems of diagnosing and designing multi-flow heat exchange equipment considering the phase transition in coolants. The authors have obtained and analyzed solutions of the inverse problem from the point of view of diagnosing the state of heat exchange equipment using the example of a turbine unit condenser with a built-in heating beam. Analysis of the calculated results has shown an adequate description by the model of the standard data for the analyzed condenser. Analysis results have shown the possibility to use the model for runtime diagnosis of the condition of power equipment and the efficient use of energy resources due to preventing ineffective modes. The proposed approach allows us to formulate and solve inverse problems of diagnosing the state of equipment of condensing units for various purposes.

Heat Transfer Through a Three-chamber Glass Unit

A well-known way to increase the thermal insulation properties of windows in buildings is to increase the number of glasses in a window or, what is the same, to increase the number of glass chambers in a glass unit. This method, in combination with low-emissivity coatings on the inner surfaces of glass, can provide a significant increase in the heat transfer resistance of window structures. The use of such windows in construction can significantly reduce heat loss from the premises in the winter, which leads to a reduction in energy costs for heating and increases the energy efficiency of the building. In this work, the characteristics of heat transfer through a three-chamber glass unit are studied using numerical modeling and experimental study. Options for the absence and presence of low-emissivity coatings on glass are considered. Changes in air velocity and temperature in the chambers are studied. Heat transfer resistance for three-chamber windows are calculated depending on the number of low-emissivity coatings on the glass.

Controlling reaction transfer between Al/Ni reactive multilayer elements on substrates

Reactive multilayers produce exothermic reaction with definite velocity and maximum temperature after ignition, which are the fundamental properties of the reactive multilayer systems. The generated heat with certain velocity makes it widely used in joining, bonding in the packaging, thermal batteries and many more applications. In this work, a distinct approach for achieving a reaction transfer between the reactive multilayers and different materials is demonstrated which can affect the generated temperature and velocity from the self-propagating properties of the reaction. For these intensions, we fabricated the Al/Ni reactive elements with certain separations between elements which allow to observe the reaction front transfer and emitted temperature in the reaction chain. The created separation between reactive elements are periodical and ordered systems with different thermal conductive properties. The temperature and definite velocity were measured by time-resolved pyrometer and high-speed camera measurements. SEM analysis showed the characteristics of the reaction transfer between reactive multilayer elements. It is predicted that: (I) The reaction front stops at a space with critical length; (II) Reducing heat loss through the substrate supports reaction front propagation through spaces; (III) Thermal property design of the spaces between the reactive elements enables property modification of the self-propagating reaction.Graphical abstract

Heat Transfer through Double-Chamber Glass Unit with Low-Emission Coating

The numerical modeling of radiation and convective heat transfer through a double-chamber glass unit was carried out to substantiate the increase in the heat transfer resistance of this unit via the application of low-emission coatings to glass surfaces. In the space between the panes of a window without low-emission coatings, the amount of heat transferred via radiation exceeds the amount of heat transferred via thermal conductivity and convection. The question of the effect of low-emissivity coatings on reducing heat loss through a window has not yet been sufficiently studied. This problem is also not sufficiently reflected in the literature. In this regard, this paper presents the results of numerical simulation aimed at studying the effect of low-emissivity coatings on heat transfer through a double-chamber glass unit. Simulation is carried out by numerically solving a system of equations of fluid dynamics and energy for the air gap and glass. Boundary conditions of the fourth kind are set on the internal surfaces of the chambers, taking into account the radiation and conduction components of the total heat flux emanating from the glass. The results of modeling heat transfer through a glass unit with ordinary glass show that about 60% of the heat is transferred by radiation. Therefore, an effective measure to reduce heat loss through windows is to reduce the radiation component of the total heat flux by applying a low-emissivity coating to the internal surfaces of the glass unit. This allows for the reduction of the overall heat flux (and, accordingly, heat loss to the environment) by 20–34%, depending on the number of glass surfaces with such a coating.

Energy lost study for the steam and solvent assisted gravity drainage process, using reservoirs with Brazilian northeast characteristics

In Brazil, especially in the Northeast, there are still reservoirs containing heavy oils that are being operated by smaller companies that need to produce the fields, reducing production costs. There are different processes to recover heavy oil, one of which is steam and solvent assisted gravity drainage process, which uses two parallel horizontal wells, where the injector is placed above the producer. In this process, a solvent can be used with the steam, to try to reduce the steam rate injected. Process is carried out by injecting a hydrocarbon additive in low concentration together with steam. Steam contributes with the heat to reduce oil viscosity and solvent helps with miscibility, reducing the interfacial tension. The main force acting in this process is gravitational. The mobility of the displaced fluid is then improved, which may imply at an increase of oil recovery. In this study, a semi-synthetic model was analyzed, with average characteristics of the Brazilian northeast, where there is heavy oil in onshore reservoirs. Several simulations were carried out using a commercial oil reservoir thermal simulation software, where the influence of some operational parameters on oil recovery and energy in the reservoir were verified. The main objective of this study was to find a distance between producer and injector wells that allows reducing heat losses to the overburden and underburden when solvent and steam are injected into the process. It was found an optimal vertical distance to improve oil recovery.

Methanol compared to other fuels for on-board hydrogen production in thermally balanced membrane reactors with internal recycle

New processes for hydrogen production from various sources are required, which will enable decentralized hydrogen utilization. Hydrogen is a challenging energy carrier due to its low volumetric energy density, requiring compression or liquefaction, which are costly steps, reducing the overall energy transformation cycle efficiency. Thus, a hydrogen supply route based on distributed on-demand production is more attractive compared to the traditional centralized production route. In this work we analyze the use of methanol as a hydrogen carrier to be converted to hydrogen in a conceptual autothermal scaled-down system for on-board pure hydrogen production. This system integrates two concentric reactors, membrane separation and heat exchange. The required heat is supplied by catalytic combustion of the reforming effluents which are recycled internally. The temperature profile is controlled by distribution of the combustion feed. A validated mathematical model shows that the thermal efficiency of the hydrogen production process from methanol will be much higher (e.g. 45 % vs 15 % in one case, 60 % vs 30 % in another case) compared to the efficiency obtained when feeding other fuels (methane, ethanol or glycerol). In all cases full conversion of the fuel is obtained. The reason for such a significant intensification is the lack of methane formation in the reforming reactor. This leads to higher driving force for hydrogen transport through the membranes and enables lower operating temperatures, reducing heat losses to the surroundings (which are the main source for efficiency loss). The lack of methane formation is due to the Cu-based catalyst used for methanol reforming, as opposed to the Ni-based catalyst used for reforming of other fuels.

Numerical analysis of convective heat loss from a cylindrical–hemispherical receiver using a glass cover and an air curtain

AbstractIt is imperative to mitigate the convective heat loss from the receiver to improve the overall efficiency of the parabolic dish concentrator. In this study, the reductions of convective heat loss from the cylindrical‐hemispherical receiver are numerically analyzed and the model was validated by the experimental data from literature. In the first case, the impact of the glass cover on convective heat loss is examined under conditions of both natural and forced convections at various receiver orientations (γ = 0°, 30°, 60°, and 90°). Numerical results clearly demonstrate that the use of a glass cover significantly reduces the intrusion of surrounding air into the receiver cavity which leads to an enhancement of the stagnation zone inside the cavity and, as a consequence, a noticeable reduction in convective heat loss is observed. To perform analysis of the receiver with glass cover under forced convective condition, the wind velocities over the receiver are considered in the range of 1–6 m/s. The maximum reduction of convective heat loss using the glass cover is achieved to be 58.44% with wind velocity of 5 m/s at γ = 60°. In the second case, the influence of air curtain at the receiver aperture under natural convective heat loss conditions is analyzed. The analysis incorporates three variables: receiver orientation (γ = 0°–60°), nozzle width ( = 0.002–0.004 m), and nozzle outlet velocity ( = 0.5–3.5 m/s). The results show that the air curtain minimizes the outflow of receiver inside air and results in an improvement in the stagnation zone inside the cavity. The maximum effectiveness of the air curtain is found to be 43.2% at nozzle width of = 0.004 m and nozzle velocity of = 1.5 m/s at receiver orientation of 60°. It is also noteworthy that the optimal nozzle velocity decreases with the increase of nozzle widths.

Performance of Automatic Temperature Control System in Pyrolysis Reactor of LDPE Plastic Waste

Pyrolysis is a process of decomposing material at high temperatures without or with limited air and is an alternative waste treatment which is considered quite prospective to be developed. Plastic waste treatment as pyrolysis fuel, is strongly influenced by operating conditions, which consist of the thermal properties of plastics such as the LDPE type, which are still massively used in society. This research processes LDPE type plastic waste using technology fixed bed pyrolysis type batch reactor with a capacity of 0.01 m³ with initial heating from external heat of LPG energy source. The pyrolysis process takes in a closed reactor and the mass flow rate of the condensate flows naturally to the condenser for the condensation process to become pyro-oil product. Optimization of the reactor pyrolysis was carried out by adding insulated heat cover to reduce heat losses during the heating process. The addition of automatic temperature control to regulate the heating rate, makes operation control easier and reducing fluctuations in temperature distribution during pyrolysis process. The research was carried out with three operating temperature variations of 250, 275, and 300 °C using 0.8 kg LDPE plastic waste for batch test. The performance of automatic temperature control was observed using a digital thermometer and a comparison of the results before and after installation was carried out at a temperature of 300 °C. The results showed that heating temperature control which was previously done manually gives fluctuating results with a temperature difference of up to 50 °C. With the addition of an automatic temperature control system, the operating temperature during the pyrolysis process shows relatively lower fluctuations with a maximum difference of 20 °C. The initial heating energy consumption from LPG and the fuel consumption rate (FCR) show an increase along with the increase in the pyrolysis operating temperature setting.

Critical review on thermal performance enhancement techniques for flat plate solar collectors

Supply of energy against continuous increase in energy demand is a great challenge for the present time. This has compelled the researchers to develop energy-efficient and performance-enhanced devices. Solar energy, being the capable source to supply the clean energy can be harvested with the help of flat plate solar collectors (FPSCs). In order to enhance the thermal performance of FPSC researchers have considered various aspects, for example, design modification, heat transfer fluid having enhanced thermophysical properties, use of nanofluids, reduction in heat loss, use of enhancement devices, use of phase change materials and porous materials. The present article describes in detail these methods and compares the results obtained by the respective researches. Experimental as well as numerical works have also been presented. A comprehensive review for the thermal performance enhancement techniques used in FPSC has been presented. The objective of this review is to provide a valuable framework for evaluating and comparing different techniques for enhancing FPSC performance. The review aims to help identify the most appropriate approach and gaps in current research and proposes potential areas for future enhancements, which is expected to assist researchers.

Multi-Span Greenhouse Energy Saving by External Insulation: System Design and Implementation

To address the issues of excessive heat loss from the roofs of multi-span greenhouses and high energy consumption for heating during winter production, we propose an approach for the external insulation of the roof of multi-span glass greenhouses and have developed an external insulation system (EIS) to practice this approach. The system achieved full coverage of the greenhouse roof through mechanized unfurling and furling of external thermal blankets, thereby achieving energy-saving insulation. This paper describes the overall design and working method of the EIS, providing detailed design and structural parameters for critical components such as the traction rope transmission mechanism and the rail-type sealing structure. Through a system verification experiment, the specifications of the traction rope were determined and the rationality of the EIS’s thermal blanket unfurling and furling time was confirmed. An insulation performance experiment indicated that the average heat flux of the greenhouse roof covered with the external thermal blanket over 14 continuous nights was 54.2 W/m2, compared with 198.6 W/m2 for a single-layer glass roof. Covering the roof with the external thermal blanket reduced heat loss from the glass roof by 72.7%. The average heat flux of the roof of the Venlo-type multi-span greenhouse with double-layer internal insulation was 99.9 W/m2 during the same period, indicating that the heat loss from the roof using external insulation was only 50.3%. This study provides a novel thermal insulation approach and an energy-saving system for multi-span greenhouses.

Southern Ocean High‐Resolution (SOhi) Modeling Along the Antarctic Ice Sheet Periphery

AbstractThe Southern Ocean plays a major role in controlling the evolution of Antarctic glaciers and in turn their impact on sea level rise. We present the Southern Ocean high‐resolution (SOhi) simulation of the MITgcm ocean model to reproduce ice‐ocean interaction at 1/24° around Antarctica, including all ice shelf cavities and oceanic tides. We evaluate the model accuracy on the continental shelf using Marine Mammals Exploring the Oceans Pole to Pole data and compare the results with three other MITgcm ocean models (ECCO4, SOSE, and LLC4320) and the ISMIP6 temperature reconstruction. Below 400 m, all the models exhibit a warm bias on the continental shelf, but the bias is reduced in the high‐resolution simulations. We hypothesize some of the bias is due to an overestimation of sea ice cover, which reduces heat loss to the atmosphere. Both high‐resolution and accurate bathymetry are required to improve model accuracy around Antarctica.

The Effects of Syngas Composition on Engine Thermal Balance in a Biomass Powered CHP Unit: A 3D CFD Study

Syngas from biomass gasification represents an interesting alternative to traditional fuels in spark-ignition (SI) internal combustion engines (ICEs). The presence of inert species in the syngas (H2O, CO2, N2) reduces the amount of primary energy that can be exploited through combustion, but it can also have an insulating effect on the cylinder walls, increasing the average combustion temperature and reducing heat losses. A predictive numerical approach is here proposed to derive hints related to the possible optimization of the syngas-engine coupling and to balance at the best the opposite effects taking place during the energy conversion process. A three-dimensional (3D) computational fluid dynamics (CFD) model is developed, based on a detailed kinetic mechanism of combustion, to reproduce the combustion cycle of a cogenerative engine fueled by syngas deriving from the gasification of different feedstocks. Numerical results are validated with respect to experimental measurements made under real operation. Main findings reveal how heat transfer mainly occurs through the chamber and piston walls up to 50° after top dead center (ATDC), with the presence of inert gases (mostly N2) which decrease the syngas lower calorific value but have a beneficial insulating effect along the liner walls. However, the overall conversion efficiency of the biomass-to-ICE chain is mostly favored by high-quality syngas from biomasses with low-ashes content.

Optimizing the Thickness of Multilayer Thermal Insulation on Different Pipelines for Minimizing Overall Cost-Associated Heat Loss

Optimizing the multilayer thermal insulation of pipelines transporting liquids and gases at higher than ambient temperatures is crucial for heat energy conservation and cost optimization. This study utilizes a multi-objective genetic algorithm to optimize the multilayer thermal insulation thickness around a pipe carrying fluid to minimize heat loss and associated costs. The model adopted mathematical associations between design variables and the overall installation cost of layers over a pipe from the available literature. The proposed model considered one or more insulation layers of rock wool and calcium silicate to oil pipelines containing steam, furfural, reduced crude or 300-distillate oil. All calculations considered fixed-charge rates as a fraction of 1 or 0.15. The results were compared with standard values and those predicted by other researchers in the literature. For the steam line, the standard insulation thickness was 50 mm, jumping to 327 mm for rock wool and 232 mm for calcium silicate. However, it decreased to 38 mm for double-layer calcium silicate and 138 mm for double-layer rock wool. For furfural, the insulation thickness was 40 mm, which rose to 159 mm for rock wool and 112 mm for calcium silicate. In general, for all four cases, the results show that using normal insulation thickness is inadequate and not economical. For example, for 300-distillate oil, the present practice puts the cost function at 54 USD/m, which drops to 20 USD/m for rock wool and 24 USD/m each for single-layer silicate and double-layer insulation. This amounts to almost 60% cost savings. Similar trends are observed for the other three cases. This model can provide up to 60% savings in cost and a 92% reduction in heat loss at optimum insulation thickness compared to other models.

Exceptionally Low Thermal Conduction of Basaltic Glasses and Implications for the Thermo‐Chemical Evolution of the Earth's Primitive Magma Ocean

AbstractThe thermal properties of the Earth's primordial magma are the key factors that constrained crystallization and other thermo‐chemical processes in Earth's primitive magma ocean and therefore controlled the Earth's long‐term evolution. Thermal conductivity of the primordial magma is conventionally assumed to be a constant of about 4 W m−1 K−1 under the high pressure‐temperature conditions of the primitive magma ocean. Here we measured the lattice thermal conductivity of a variety of basaltic and silicate glasses at high pressures and a wide range of temperatures. Our results suggest that the primordial magma, if it is indeed represented by basaltic melts, had a thermal conductivity of ∼1.0–1.9 W m−1 K−1, much lower than previously thought. Such low thermal conduction reduced heat loss and thus prolonged the cooling time of the early magma ocean, promoting convection in the solidifying mantle and preventing a global overturn. Moreover, if the seismic ultralow velocity zones presently observed in the lowermost mantle are made of basaltic melts, originating either from remnants of the primitive magma ocean or pieces of subducted crust, the material in these zones must have an ultralow thermal conductivity, which would reduce cooling and thus influence the thermo‐chemical evolution of the present day core‐mantle boundary.

УПРАВЛЕНИЕ ЖИЗНЕННЫМ ЦИКЛОМ ЗДАНИЯ НА ЭТАПЕ ЭКСПЛУАТАЦИИ С ИСПОЛЬЗОВАНИЕМ МОДЕЛЕЙ ИСКУССТВЕННЫХ НЕЙРОННЫХ СЕТЕЙ И МАШИННОГО ОБУЧЕНИЯ

The use of artificial neural networks and machine learning methods for the analysis of heat loss in buildings is of significant relevance in modern construction. These technologies are highly accurate and efficient in data processing. Artificial neural networks have the ability to analyze vast amounts of information and identify complex patterns, which significantly increases the accuracy of determining heat loss in buildings. In turn, machine learning methods make it possible to take into account various influencing factors, such as geographic location and meteorological conditions, thereby making a significant contribution to improving the quality of analytical results. Such approaches provide more reliable and accurate conclusions, which is critical for effective energy management and reducing heat loss in buildings. In this article, the authors conducted a study of heat losses of buildings and their prediction at the operational stage using artificial neural networks and machine learning methods. The technique is based on the analysis of data on heat loss and their relationship with various building parameters. Forecasting was carried out using artificial neural networks in the Statistica software package and the machine learning method based on the scikit-learn library. The proposed approach allows you to effectively manage the energy consumption of a building, optimizing its energy efficiency and improving the life cycle management of a capital construction project. The results demonstrate the high accuracy and convergence of the model with actual values, as well as its ability to predict performance.

Calculation of a heat exchanger using heat pipes in the exhaust air heat recovery system

Objective. The purpose of the work is to develop practical recommendations for the design and manufacture of a heat exchanger using heat pipes, which could find widespread use in heating, ventilation and air conditioning systems at facilities for various purposes. Method. The research is based on methods of thermodynamic analysis, full-scale and computational modeling of processes and objects of refrigeration and cryogenic technology, air conditioning and life support systems. Result. The implementation of the practical recommendations studied in the work on the use and design of heat exchangers using heat pipes in ventilation, heating and air conditioning systems will provide significant savings in energy spent on heating and/or cooling the air supplied to the room served by the HVAC system. To reduce heat loss in a building, it is rational to maintain air balance and compensate for the exhaust air with an organized influx of outside air, to heat which the heat of the removed exhaust air is utilized. Conclusion. Compared to a heat exchanger based on a glycol recuperator, a regenerator using heat pipes is less energy-intensive, requires virtually no maintenance, and is also more energy efficient due to the absence of a pumping device that requires electricity in the design. At the same time, the ability to completely separate the supply and exhaust ventilation flows of the regenerator on heat pipes is preserved, which is extremely in demand in medical institutions, due to the need to comply with strict sanitary standards.

Study of Steam Generation and Distribution in a Hospital to Improve Energy Efficiency Using Thermography, Ultrasound, and Gas Analyzer

This investigation analyzed the energy efficiency of a steam system in a hospital, considering the procedure in ASME EA-3-2009 standard. The obtained boiler energy efficiency was 80.29 %, by applying an energy balance, reaching 15.33 kW for heat losses in the distribution pipes. Two consistent improvement alternatives were proposed, starting by unifying the pipe diameter of the kitchen area of 5 m, generating a reduction of heat loss from 828 to 600 W, which represented a total annual energy saving of around 2.4 GJ/year. The investment cost is USD 47.40, considering the achievement of the break-even point after 9 months, where the insulation of the pipes with glass wool was considered second and it generated a reduction in losses of 5.98 kW, representing a total annual energy saving of about 62.91 GJ/year, which corresponds to approximately USD 1,672. The investment for pipe insulation with a length of 49 m was USD 462, considering the NPV calculation and the possible savings, and the break-even point was reached after approximately 4 months, indicating the economic benefit of applying the two improvement options proposed.

Subjective sleep onset latency is influenced by sleep structure and body heat loss in human subjects.

The present study examined the relationship between subjective sleep onset latency (SOL), sleep structure, changes in skin and body temperature, and subjective evaluation of sleep in healthy young adults to elucidate the pathophysiological mechanisms of insomnia. A total of 28 participants (age 21.54 [0.50] years) with no sleep problems participated in a 1-h polysomnographic recording that obtained objective sleep parameters during the daytime while skin and body temperatures were recorded. The distal-proximal skin temperature gradient (DPG) was calculated. Subjective parameters, such as subjective SOL, sleep time, and restorative sleepiness, were evaluated before and after sleep. Most participants estimated their sleep latency as being longer than their actual SOL (13.7 versus 7.6 min). Objective SOL was significantly correlated with each sleep stage parameter whereas subjective SOL was negatively correlated with Stage N2 sleep duration (Rho = -0.454, p = 0.020), slow-wave activity and delta power (Rho = -0.500, p = 0.011 and Rho = -0.432, p = 0.031, respectively), and ΔDPG (the degree of reduction of heat loss before and after lights-off). Stepwise regression analysis showed that ΔDPG was the strongest predictive factor in explaining the length of subjective SOL. The degree of heat dissipation before and after lights-off contributed most to the sensation of falling asleep in healthy young adults. This finding may be helpful for elucidating the physiological mechanisms of insomnia and its treatment.