Relative Heat Loss Research Articles

Heat loss along the pipeline and its control measures

In this study, we present the derivation of the formulas for calculating the temperature drop and heat loss along the heat transporting pipeline and the methods of controlling the heat loss. Our results show that, both the temperature drop and the relative heat loss increase with the pipeline length, and increase close to linearly; the relative heat loss is nearly proportional to the thermal conductivity and is inversely proportional to the insulation thickness; the relative heat loss along or across the pipeline decreases with the increase in pipeline diametre, initial temperature, flow velocity or surrounding temperature. And we can control the relative heat loss within a determined range, even less than 10%. Especially, some thermal problems of the pipeline can be easily handled. Reducing its heat loss by 50%, for example, can be achieved by doubling the insulation thickness or by cutting down the thermal conductivity by half. As well, the causations of all the results are exhibited in detail.

Numerical simulation of flow and heat transfer performance during supercritical water injection in vertical wellbore: A parameter sensitivity analysis

Supercritical water injection is a promising technology for heavy oil thermal recovery. Predicting and regulating the thermophysical parameters of supercritical water at bottomhole are the prerequisite for achieving high recovery efficiency. In this paper, a novel numerical model was proposed to simulate wellbore flow and heat transfer of supercritical water injection. A modified correlation of frictional coefficient was developed to calculate water flow resistance near its critical point, where its properties change abruptly. The unsteady heat loss to the formation was calculated directly by solving two-dimensional unsteady heat conduction equations. They were respectively coupled in momentum and energy balance equations using an iterative scheme. This model was proved to be accurate by two oilfield cases in which the relative errors of wellbore fluid pressure and temperature are less than 1%. Then parameters sensitivity analysis of the injection pressure, temperature, mass flux and the apparent heat conductivity of insulating tube was conducted. The results indicated that the temperature variation of wellbore fluid depended on both enthalpy drop (or heat loss) and Joule-Thomson effect. An abnormal phenomenon that the fluid temperature increased with wellbore depth near the critical and pseudo-critical points was found because of the sudden increase in high heat capacity and Joule-Thomson coefficient of water. Raising the bottomhole fluid temperature was the key to enhanced oil recovery by supercritical water injection. Low apparent heat conductivity of insulating tube contributed richly to raise bottomhole fluid temperature by enlarging thermal resistance and reducing wellbore heat loss. There existed an optimal mass flux for maximizing bottomhole temperature, because when the mass flux increased, the shortened resident time within wellbore and the decreased fluid pressure favored temperature increase and decrease respectively. Selecting an injection pressure near the critical or pseudo-critical point and raising the injection temperature would increase the bottomhole temperature and reduce relative fluid heat loss.

Confined combustion of polymeric solid materials in microgravity

Microgravity experiments are performed to study the effects of confinement on the burning behavior of polymeric solid materials. Flat, 100 × 22 × 1 mm PMMA samples are burned in concurrent air flow in a small flow duct aboard the International Space Station. Three different burning scenarios are examined, double-sided, single-sided, and parallel samples. In the first two scenarios, single samples are burned on both sides and on one side, respectively. Flat baffles are placed parallel to the sample to confine the available space for combustion. The distance between the baffle and the sample (H) is varied in different tests. In each test, imposed flow is reduced in steps and steady flame spread is achieved at each flow speed until the flame quenches. The results show that at the same confined condition, steady state flame length and spread rate are proportional to flow speed over the range tested. When confinement increases (or H decreases), the flame spread rate and flame length increase first and then decrease. In addition, the quenching flow speed decreases and then increases with decreasing H. These results suggest that the confinement can increase or decrease solid fuel flammability depending on conditions. In the third burning scenario, two PMMA samples are placed parallel to each other separated by a distance H. Twin flames are observed and combustion is confined between the two samples. Among the three tested burning scenarios, twin flames have the largest flame length and burning rate at the same confinement level (H). This is because the thermal interaction between the twin flames enhances the heat feedback to the solid fuel and reduces the relative heat loss to the surrounding flow duct. Comparing single- and double-sided flames with the same baffle-sample distance, the spread rate of a single-sided flame is slightly less than half of that of a double-sided flame. This is due to the halved pyrolysis area exposed to the flame and heat loss on the back side of the sample. Optimal transport of oxygen to the flames also plays a role.

Overview of Solutions for the Low-Temperature Operation of Domestic Hot-Water Systems with a Circulation Loop

The operation of typical domestic hot water (DHW) systems with a storage tank and circulation loop, according to the regulations for hygiene and comfort, results in a significant heat demand at high operating temperatures that leads to high return temperatures to the district heating system. This article presents the potential for the low-temperature operation of new DHW solutions based on energy balance calculations and some tests in real buildings. The main results are three recommended solutions depending on combinations of the following three criteria: district heating supply temperature, relative circulation heat loss due to the use of hot water, and the existence of a low-temperature space heating system. The first solution, based on a heating power limitation in DHW tanks, with a safety functionality, may secure the required DHW temperature at all times, resulting in the limited heating power of the tank, extended reheating periods, and a DH return temperature of below 30 °C. The second solution, based on the redirection of the return flow from the DHW system to the low-temperature space heating system, can cool the return temperature to the level of the space heating system return temperature below 35 °C. The third solution, based on the use of a micro-booster heat pump system, can deliver circulation heat loss and result in a low return temperature below 35 °C. These solutions can help in the transition to low-temperature district heating.

Two-fluid model of rf current condensation in magnetic islands

The stabilization of tearing modes with rf waves is subject to a nonlinear effect, termed rf current condensation, that has the potential to greatly enhance and localize current driven within magnetic islands. Here we extend previous investigations of this effect with a two fluid model that captures the balance of diffusive and thermal equilibration processes within the island. We show that the effective power and resulting strength of the condensation effect can be greatly enhanced by avoiding collisional heat loss to the ions. The relative impact of collisions on the overall power balance within the island depends on the ratio of the characteristic diffusion timescale and the electron–ion equilibration time, rather than the latter alone. Although relative heat loss to ions increases with island size, the heating efficiency does as well. In particular, we show that the latter safely dominates for large deposition profiles, as is typically the case for lower hybrid current drive. This supports the possibility of passive stabilization of neoclassical tearing modes without the precise aiming of the rf waves required for electron cyclotron current drive stabilization.

The efficiency of thermosyphon solar water heating system and traditional solar water heating system

Loop thermosyphon (LT) is typically used for solar water heaters (SHW) to solve the freezing and corrosion issues. The LT – SWH system has a less night time heat loss compared to conventional SWH due to its thermal diode property but a greater heat loss due to the secondary heat exchange. However, the above interactions have rarely had an effect on system performance based on long-term operation [6]. In this paper, the annual results of above two processes, including productive supply day numbers and efficient heat gains and night power losses, was evaluated in this analysis in two separate operating modes on the basis of standard meteorological year data from the City of Fuzhou. Variations of the above variables are addressed with the change in the stated temperature. The results show that the effective delivery days of the LT – SWH system are 139 and 153, respectively, in irregular heating method. The number of days is 168 to 173 in ongoing heating method. The SWH system is predictable to have a higher ratio at nighttime with an annual average of 15.07%, which equates to 6.15% for the LT – SWH system. In fact the LT – SWH method results in a lesser decrease in temperature at night and therefore a smaller raise in the temperature on the following day because of multiple relative heat loss factors running at various hours. The results produced are unpredictable, and lead to an approximately successful heat gain for the same month between November and April. The fixed temperature influences substantially the relative quantities of effective annual supply days and effective annual heat gain, slowly reducing the overall dominance of the LT – SWH method and even changing it as the set temperature increases [12]. This shift is triggered by the biggest daily heat loss leading the domination. In combination with a long static reimbursement time, a conventional SWH system must be substituted by an LT - SWHsystem, particularly when water temperatures are high on demand.

Experimental and numerical investigations of the effect of charge density and scale on the heat transfer behavior of Al/CuO nano-thermite

In this paper, to study the propagation behavior and the burning rate enhancement of Al/CuO nano-thermite in confined burn tubes, modification of the component was achieved by introducing energetic binder nitrocellulose (NC). The combustion behavior of Al/CuO and Al/CuO@NC nano-thermites in burn tubes was contrastively investigated by turning the charge density and the tube diameter in the range of 0.8–1.8 g/cm3 and 0.3–2 mm, respectively. Our experiments and theoretical calculation results show that the seepage of the gas flow is an important factor affecting the heat transfer process of Al/CuO nano-thermite in burn tubes, which makes the propagation velocity decrease with the increase of the charge density. Meanwhile, by introducing a certain amount of NC into the component, the reactivity can be improved while the gas production and pressurization capacity can be increased at the same time. This can greatly improve the propagation velocity of Al/CuO nano-thermite under constraint conditions. Moreover, with the decrease of the tube diameter, it can be inferred that the significant increase of the relative heat loss is the main reason for the decrease of the propagation velocity while the dimensionless parameter θ can be used to analyze the heat loss coefficient under different charge diameters.

Performance evaluation and analyses of novel parabolic trough evacuated collector tubes with spectrum-selective glass envelope

Evacuated collector tubes (ECTs), the key components of the parabolic trough collector, suffer considerable heat loss at high operating temperature. Based on the characteristic of uneven distribution of solar irradiance around the absorber tube, novel ECTs covered with infrared (IR)-reflectors on the partial area of glass envelope were proposed to effectively reduce the heat loss and enhance the performance. Two kinds of ideal IR-reflectors, namely, the first one with a fixed cutoff wavelength, the second one with a variable and optimal cutoff wavelength were proposed. A real material of transparent conductive oxide (TCO) film was also used as an IR-reflector in novel ECTs for the analysis. The mathematical models relying on spectral parameter calculation method were established for comprehensively investigating the overall performance of the novel ECTs. Moreover, the influences of TCO film reflectivity and emissivity on the ECTs were investigated. Results demonstrated that the novel ECTs with TCO films, the first ideal films, and the second ideal films achieved obvious superior thermal performance compared with the conventional ECTs. Their relative heat loss reductions at an absorber temperature of 600 °C reached 18.7, 25.3, and 43.8%, the heat-collecting efficiencies were relatively enhanced by 7.2, 10.8, and 16.7%, respectively.

Modeling the metabolic costs of swimming in polar bears (Ursus maritimus)

Climate change is expected to increase the frequency and duration of long-distance swims by polar bears (Ursus maritimus). The energetic costs of such swims are assumed to be large, however, no estimates of metabolic costs of swimming for polar bears are available. Here, I use data on internal body temperature and external ambient temperature for two swimming polar bears, combined with mathematical modeling of heat production and of heat conduction to the surrounding water, to estimate the metabolic rate of swimming. Using this metabolic rate, I then examine the relative heat production and heat loss for bears of a range of sizes and body conditions. I calculated overall mean metabolic rate for a swimming bear to be 2.75 ml O2 g−1 h−1, which is generally higher than metabolic rates previously reported for walking polar bears. When compared at the same movement rate, the cost of transport for swimming was estimated to be approximately 5× that of walking. I further show that for small bears (less than approx. 145 cm body length or 90 kg) and bears in poor body condition, heat loss while swimming in cold Arctic waters should exceed heat production, and long swims should therefore not be thermodynamically sustainable. These results support previous claims that increasing frequency and duration of long-distance swims in polar bears is energetically stressful. Energetic and thermodynamic costs of long swims may be further exacerbated by recent declines in body condition that have been documented due to climate warming.

Mineralogical transformations of spodumene concentrate from Greenbushes, Western Australia. Part 2: Microwave heating

Spodumene in its natural α-spodumene modification is a refractory silicate interlocking lithium species. Therefore, in order to effectively extract the lithium, its alteration to the less densely packed β-spodumene modification is necessary. The current method used for the conversion to β-spodumene is calcination at 950–1100°C using conventional heating. However this is an energy intensive approach. The use of microwave irradiation as an alternative, potentially less energy intensive, method of heating is examined in this work. Spodumene concentrate was obtained from Greenbushes, Western Australia, and subjected to (i) direct and (ii) hybrid microwave heating. The results showed that spodumene concentrate is transparent to direct microwave irradiation. However, using hybrid heating, to preheat the sample, it was found that once heated to above 634°C by conventional heating, the α-spodumene irradiated with microwaves undergoes rapid localised conversion into γ- and β-spodumene, which in a matter of seconds forms a β-spodumene product in either sintered or melted form, depending on the treatment time and relative heat loss from the system. The process appears to involve an exothermic conversion of α-spodumene to γ-spodumene, followed by endothermic formation of β-spodumene. It was found that the critical temperature for microwave absorption by β-spodumene is lower than that for α-spodumene by 190°C. Calculations of energy input suggested that the energy consumed to produce the sintered product could be much less than the energy required to convert α- to γ- and β-spodumene in a muffle furnace. These findings could help commercial plant operators and researchers to develop an industrial calcination process utilising microwave energy.

Evaluation Factor for District Heating Network Heat Loss with Respect to Network Geometry

The district heating (DH) networks are widely in use in northern countries. It is often necessary to compare the efficiency of different DH networks from their size and layout and for this purpose mostly the “relative heat loss” is used. Generally, this parameter gives a first impression of the network. However, relative heat loss does not reflect the actual efficiency of pipe insulation or overall efficiency of the network; moreover, at least heat consumption density should be considered. E.g., the average relative heat loss in Denmark is about 20% and in Sweden only 9%. Does this mean that the Swedish network insulation is 2 times better? The data from different networks is taken in order to make an analysis and figure out a proper comparison methodology. The following main parameters are taken into account: supply, return and ambient temperatures; the network average diameter and length; annual heat consumption or linear heat density.

Small-scale, self-propagating combustion realized with on-chip porous silicon.

For small-scale energy applications, energetic materials represent a high energy density source that, in certain cases, can be accessed with a very small amount of energy input. Recent advances in microprocessing techniques allow for the implementation of a porous silicon energetic material onto a crystalline silicon wafer at the microscale; however, combustion at a small length scale remains to be fully investigated, particularly with regards to the limitations of increased relative heat loss during combustion. The present study explores the critical dimensions of an on-chip porous silicon energetic material (porous silicon + sodium perchlorate (NaClO4)) required to propagate combustion. We etched ∼97 μm wide and ∼45 μm deep porous silicon channels that burned at a steady rate of 4.6 m/s, remaining steady across 90° changes in direction. In an effort to minimize the potential on-chip footprint for energetic porous silicon, we also explored the minimum spacing between porous silicon channels. We demonstrated independent burning of porous silicon channels at a spacing of <40 μm. Using this spacing, it was possible to have a flame path length of >0.5 m on a chip surface area of 1.65 cm(2). Smaller porous silicon channels of ∼28 μm wide and ∼14 μm deep were also utilized. These samples propagated combustion, but at times, did so unsteadily. This result may suggest that we are approaching a critical length scale for self-propagating combustion in a porous silicon energetic material.

Study on high efficient heat recovery cycle for solid-state cooling

Traditional vapor compression cycles (VCCs) use mainly halogenated refrigerants such as hydrochloroflurocarbons and hydrofluorocarbons that are considered as greenhouse gases. Therefore, their regulations are imposed on a global scale. As an alternative cooling technology other than VCCs, solid-state cooling technologies, such as magnetic cooling, thermoelastic cooling and electrocaloric cooling, demonstrate its advantage of not using greenhouse gases as working fluids. However, one of the most challenging issues of these solid-state cooling technologies is the relative high parasitic internal latent heat loss, which could significantly deteriorate the system performance. In order to improve the system performance of solid-state cooling, the authors propose a novel and high-efficient heat recovery (HR) cycle for solid-state materials with high thermal conductivity. The novel heat recovery process was first compared as an analog of spatial scale counter-flow heat transfer process. A simplified ideal model was developed to quantitatively investigate the heat recovery process performance limit and the physics behind the analogy of the spatial scale counter-flow heat transfer process. Experiment was conducted and 60% HR efficiency was achieved. In addition, a detailed dynamic model validated by the experiment results was developed and used to further investigate the limiting factors together with the theoretical analysis.

RELATIVE HEAT LOSS REDUCTION FORMULA FOR WINDOWS WITH MULTIPLE PANES

We derive an expression for the heat flux through a window con- structed with multiple panes of glass separated pairwise by air layers of a given thickness. We compute the relative heat loss reduction achieved in comparison to a window with no air gap and the same amount of glass. We examine how the relative heat loss reduction function behaves when we scale the number of panes up to a large value.

Heat removal using microclimate foot cooling: a thermal foot manikin study.

It has been proposed that microclimate cooling systems exploit the peripheral extremities because of more efficient heat transfer. The purpose of this study was to quantify, using a patented microclimate cooling technique, the heat transfer from the plantar surface of the foot for comparison to other commonly cooled body regions. A military boot was fitted with an insole embedded with a coiled, 1.27 m length of hollow tubing terminating in inlet and outlet valves. A thermal foot manikin with a surface temperature of 34 degrees C was placed in the boot and the valves were connected to a system that circulated water through the insole at a temperature of 20 degrees C and flow rate of 120 ml x min(-1). The manikin foot served as a constant heat source to determine heat transfer provided by the insole. Testing was done with the foot model dry and sweating at a rate of 500 ml x h(- 1) x m(-2). Climatic chamber conditions were 30 degrees C with 30% RH. Heat loss was approximately 4.1 +/- 0.1 and approximately 7.7 +/- 0.3 W from the dry and sweating foot models, respectively. On a relative scale, the heat loss was 3.0 W and 5.5 W per 1% (unit) body surface area, respectively, for the dry and sweating conditions. The relative heat loss afforded by plantar foot cooling was similar compared to other body regions, but the absolute amount of heat removal is unlikely to make an impact on whole body heat balance.

PTU-131 Oesophageal Thermal Sensitivity and Mucosal Integrity in Healthy Subjects. A Study using a Novel Peltier-Based Heating Device and Impedance

IntroductionInvestigation of oesophageal sensitivity might help better improve phenotyping of patients with GERD, functional heartburn and non-obstructive dysphagia. Studies on oesophageal thermal sensitivity have used balloon techniques with circulating water....

972 Esophageal Thermal Sensitivity and Mucosal Integrity in Healthy Subjects. A Study Using a Novel Peltier-Based Heating Device and Impedance

Introduction Investigation of oesophageal sensitivity might help better improve phenotyping of patients with GERD, functional heartburn and non-obstructive dysphagia. Studies on oesophageal thermal sensitivity have used balloon techniques with circulating water. This lacks linear control of heating, has relative heat loss, and provokes mechanical stimulation by the distended balloon. Oesophageal mucosal integrity is important in symptoms perception and can be studied using impedance “in vivo”. We developed a catheter device incorporating a “thermal stimulator” using Peltier heating technology and impedance electrodes to assess mucosal contact and integrity. We aimed to investigate oesophageal heat sensation/pain thresholds and their relationship with mucosal integrity in healthy human subjects. Methods 21 healthy volunteers underwent thermal stimulation using an oesophageal catheter with a 7 mm electronic Peltier heater, to deliver a ramp heating protocol up to 60°C at 5 and 15 cm above LOS. Symptoms were recorded by computerised Visual Analogue Score (VAS). The delivered temperature at Pain Detection Threshold (PDT), time to PDT was measured and the area under the heating curve (AUC) was calculated. Oesophageal impedance was assessed over 10 minutes pre (basal), during and post heating in the distal and proximal oesophagus. The protocol was repeated after 2 weeks to assess reproducibility. Results Temperature at PDT showed a very low SD in the distal and proximal oesophagus and Bland-Altman Tests showed good reproducibility (–0.1905 95% CI –1.4132 to 1.0327). There were no significant differences in thermal sensitivity parameters between distal and proximal oesophagus. Due to the low inter-individual variability in thermal sensitivity between healthy subjects, we could not find a significant correlation between impedance and perception parameters in the proximal or distal oesophagus. Conclusion A novel Peltier-based thermal stimulator device can accurately and reproducibly determine oesophageal thermal sensitivity. In healthy subjects we could not demonstrate a correlation between basal impedance and sensitivity to heating. Current experiments are assessing this correlation in NERD patients with hypersensitivity to acid. Disclosure of Interest None Declared

Dynamic response of constant temperature hot-wire system in turbulence velocity measurements

Analytical solutions have been derived for the first time for temperature fluctuations along a hot wire when it is exposed to turbulent velocity fluctuations of different frequencies and wave numbers. The solutions are used to analyse the dynamic response of the hot wire alone first. The results show that attenuation to the velocity fluctuations exists at high frequencies and depends on the relative end-conduction heat loss from the hot wire to its supports. A simplified circuit for a hot-wire anemometer is then used to analyse the frequency response of the combined hot wire and its anemometer. It is found that even though the frequency response of the anemometer (as that determined from a square wave test) can be very high, the cut-off frequency of the combined system is low, depending on the hot-wire length to diameter ratio, Reynolds numbers, overheat ratio and the hot-wire material used. A preliminary investigation of the spatial resolution of the hot wire to the velocity fluctuations at different wave numbers is also presented.

Heat loss characteristics of the ELCAP residential sample

The fundamental purpose of this study is to analyze heat loss characteristics of the End-Use Load and Consumer Assessment Program (ELCAP) samples of residential buildings and compare these results in a regional context. The two basic objectives of the analysis are to determine the distribution of insulation levels and heat loss potential among the various building components in existing homes as a function of construction vintage and climate zone, and to calculate theoretical residential heat loss potentials for use in subsequent analyses. The vintage and climate zone dimensions explored in this analysis are of particular interest in testing the extent to which the sample supports the general perception that newer houses and houses in colder climates tend to be better insulated than older houses and houses in warmer climates. The distributions of overall heat loss potential and insulation levels, for the houses as a whole and for the houses excluding the foundation, are examined. The effects of house size, shape, and foundation type on these distributions are also examined. Similarly, the distributions of effective insulation levels for each building envelope component are developed. The sample weighted average heat loss potential for each envelope component is also determined by climate zone, to provide information about the relative heat loss through components that are the targets of energy conservation retrofit programs. A principal result of this analysis is the information that home insulation levels are primarily related to vintage rather than climate severity, at both the whole house and component levels. The sole exception to this trend is windows, which exhibit a trend in climate zone but not vitage. The general trend toward vintage as a determinant of thermal integrity of residences may be the consequence of a lack of climatically appropriate energy standards. This illustrates that the lost opportunities for achieving an energy-efficient housing population can be large in the face of a tendency to build to common practices that are not adapted to particular climates. It should also be noted that the historical trend toward larger homes does result in higher thermal conductance, but this is more than compensated by the trend toward increased insulation levels. The homes built to the Model Conservation Standards clearly exceed the historical trends when they are viewed as representative of the next decade of construction.

Activity patterns of Capercaillie, Tetrao urogallus, during winter

Winter activity patterns of 16 radio‐marked capercaillie, Tetrao urogallus, were studied during 1981–83 at Varaldskogen, SE Norway. Activity was confined to the light hours of the day, closely following the photoperiod. Diel distribution showed a major peak near sunset during every month. A second peak was found in the morning. This peak was comparable to the evening peak in early and late winter, but nearly disappeared in midwinter. Ambient temperature rather than photoperiod seemed to be the important proximate factor responsible for the changes in morning activity. By postponing activity to the afternoon, capercaillie avoids energy expenditure during the coldest morning hours.Total daily activity (TDA) during the period November‐April averaged about 3 h for both sexes. TDA of cocks was U‐shaped with the lowest values (2.0 h) in December‐January, whereas TDA of hens was fairly stable during November‐March with mean value of 2.7 h, increasing abruptly to 4 h in April. TDA during December‐January is believed to express the time used for feeding in pine trees. The significantly higher TDA of hens (26%) compared with cocks during this period may be explained by a higher relative heat loss of hens (body weights: hens 2.0 kg, cocks 4.3 kg). The increased level of activity during early and late winter among cocks was probably due to display and related territorial behaviour, whereas increased activity of hens during April probably was caused by a shift from feeding in pines to more time‐consuming, selective feeding on the ground