Positive Temperature Difference Research Articles

Operability thresholds for thermally damaged EBW detonators

Operability thresholds that differentiate between functional RP-87 exploding bridge wire (EBW) detonators and nonfunctional RP-87 EBW detonators (duds) were determined by measuring the time delay between initiation and early wall movement (function time). The detonators were inserted into an externally heated hollow cylinder of aluminum and fired with current flow from a charged capacitor using an exploding bridge wire (EBW initiated). Functioning detonators responded like unheated pristine detonators when the function time was 4 μs or less. The operability thresholds of the detonators were characterized with a simple decomposition cookoff model calibrated using a modified version of the Sandia Instrumented Thermal Ignition (SITI) experiment. These thresholds are based on the calculated state of the PETN when the detonators fire. The operability threshold is proportional to the positive temperature difference (ΔT) between the maximum temperature within the PETN and the onset of decomposition (∼406 K). The temperature difference alone was not sufficient to define the operability threshold. The operability threshold was also proportional to the time that the PETN had been at elevated temperatures. That is, failure was proportional to both temperature and reaction rate. The reacted gas fraction is used in the current work for the reaction correlation. Melting of PETN also had a significant effect on the operability threshold. Detonator failure occurred when the maximum temperature exceeded the nominal melting point of PETN (414 K) for 45±5 s or more.

Response of salinity gradient power generation to inflow mode and temperature difference by reverse electrodialysis

Sustainable utilization has been becoming the core idea of concentrated seawater disposal, which makes the harvest of salinity gradient power based on reverse electrodialysis (RED) become one of the important ways. As the important factors affecting RED performance, different flow orientations along the membrane and solution temperature have been studied in the previous researches. However, there are still some details that need to be clarified. In this study, the inflow mode was further detailed investigated. The results showed that after eliminating the interference of bubbles in the counter-current, the co-current was still better than the counter-current; when the solution of HCC (high concentration compartment) and LCC (low concentration compartment) was circulated for 3 h, the concentration of concentrated seawater discharge liquid was reduced by 6.93%, which was conducive to reducing the negative impact on the marine ecological environment. Meanwhile, the response of salinity gradient power generation to temperature difference was that high temperature had a positive effect on power density, and the order was both the HCC and LCC (0.44 W m−2) > LCC (0.42 W m−2) > HCC (0.39 W m−2). Although the RED performance was more sensitive to the temperature rise of LCC, the positive temperature difference between HCC and LCC is a more practical advantage because the temperature of concentrated seawater in HCC is usually high. These new observations could provide supports for the industrial development of RED in generating electricity economically and reducing the negative environmental impact of concentrated seawater.

Smoothed Particle Hydrodynamics Modeling of Natural Convection Around a Heated Horizontal Cylinder: A Comparison With Experiments

AbstractAn experimental and numerical smoothed particle hydrodynamics (SPH) analysis was performed for the convective flow arising from a horizontal, thin cylindrical heat source enclosed in a glycerin-filled, slender enclosure at low Rayleigh numbers (1.18≤Ra≤242). Both the experiments and the SPH calculations were performed for positive (0.1≤ΔT≤10 K) and negative (−10≤ΔT≤−0.1 K) temperature differences between the source and the surrounding fluid. In all cases, a pair of steady, counter-rotating vortices is formed, accompanied by a plume of vertically ascending flow just above the source for ΔT>0 and a vertically descending flow just below the source for ΔT<0. The maximum flow velocities always occur within the ascending/descending plumes. The SPH predictions are found to match the experimental observations acceptably well with root-mean-square errors (RMSE) in the velocity profiles of the order of ∼10−5 m s−1. The fact that the SPH method is able to reveal the detailed features of the flow phenomenon demonstrates the correctness of the approach.

Temperature Correction for FWD Deflection in Cement Pavement Void Detection

The use of the falling weight deflectometer (FWD) for detecting pavement voids is based on the principle that, under the same impact load, the deflection of pavements with voids increases significantly. Under the effect of temperature, the cement pavement becomes warped, which affects the deflection detection accuracy. In order to improve the accuracy of FWD detection of cement pavement voids, a three-dimensional numerical model of cement pavement on a multilayered elastic foundation under the coupled action of temperature and load is established in this paper. In addition, under different pavement void, climatic, and load conditions, the influence of temperature difference between top and bottom of the plate on the deflection of the center point of plate angle load is studied. Considering the temperature difference between top and bottom, the temperature correction coefficient is established and experimentally verified the accuracy of the temperature correction coefficient. The results showed that, within the ranges of positive and negative temperature differences, the fitting degree of the temperature correction coefficient for the cement pavement exceeded 0.99, which was consistent with the variation trend of the temperature correction coefficient obtained through field tests. The error was lower than 7%, which verified the applicability of the temperature correction coefficient for the dynamic deflection of cement pavements based on FWD. The accuracy of the FWD method in detecting cement pavement voids was improved, and this study demonstrated theoretical reference value and practical engineering significance.

Temperature-depended ion concentration polarization in electrokinetic energy conversion

Previous studies on the electrokinetic energy conversion (EKEC) are limited to the isothermal condition at the environmental temperature. Here effects of temperature and membrane thermal conductivity are systematically investigated. Under isothermal conditions, elevated temperature can improve the electric power while the energy efficiency stays unchanged. Under non-isothermal conditions, at small membrane thermal conductivities, a negative temperature difference contributes to the electric power for dramatically enhanced streaming current as enhanced ion mobility along the streaming direction induces an internal ion concentration polarization (IICP) that generates a co-flow concentration gradient in the nanopore interior. At large membrane thermal conductivities, the positive temperature difference reverses the external ion concentration polarization (EICP) in the solution reservoirs due to the Soret effect, resulting in more obvious electric power improvement. Furthermore, a criterion to enhance the EKEC performance via employing asymmetric temperatures is proposed, and an alternative way to construct the tunable ionic current source is presented. Present study provides guidance for enhancing the EKEC performance by employing waste heat, and fabricating nanofluidic functional devices.

The impact of vertical resolution in reducing biases in sea surface temperature in a tropical Pacific Ocean model

Motivated by observations of fine scale vertical shear and its contribution to mixing in the tropical ocean, this study explores the impact of vertical resolution in an ocean model on sea surface temperature in the tropical Pacific Ocean. We conduct two model experiments that differ in the vertical discretization only, with the grid spacing in one being significantly smaller than the other in the upper ocean. We examine the temperature difference between the high and low vertical resolution experiments. We find that the difference in the upper-most layer is positive in the equatorial cold tongue and negative along the South American coast, thus reducing the commonly seen cool and warm biases in the two regions, respectively. The change in the structure of the vertical diffusivity, as determined by the K-profile parameterization, is identified as the primary cause in reducing the biases. In the central equatorial Pacific, the change in the vertical diffusivity from low to high vertical resolution in the upper pycnocline results in a positive temperature difference that propagates eastward as an equatorial Kelvin wave, rising to the sea surface in the central and eastern regions to increase the sea surface temperature there. In the far eastern equatorial Pacific, the change in the vertical diffusivity in the lower pycnocline produces a negative temperature difference that propagates poleward as coastal Kelvin waves along the west coast of the American continent, outcropping along the South American coast to reduce the sea surface temperature there. The high vertical resolution experiment captures much of the small-scale vertical velocity shear and resolves the fine details of the stratification in the upper ocean. Our analysis suggests that the shear-generated turbulence is the primary contributor to the change in the vertical diffusivity in the central region whereas stratification is the dominant factor in the far eastern region.

Wildfire and spruce beetle outbreak have mixed effects on below‐canopy temperatures in a Rocky Mountain subalpine forest

AbstractAimFine‐scale topography and canopy cover can play an important role in mediating effects of regional‐scale climate change on the below‐canopy environment in mountain forests. The aim of this study was to determine how below‐canopy temperatures in a high‐elevation Rocky Mountain forest have been affected by canopy change resulting from severe wildfire and spruce beetle outbreak within the last 10–15 years.LocationEastern San Juan Mountains, Colorado, USA.TaxonPicea engelmannii, Abies lasiocarpa, Dendroctonus rufipennis.MethodsWe used a network of sensors to record temperatures for a full year in burned and beetle‐impacted areas. Using a Bayesian model that accounted for spatial structure in temperatures, we derived covariate parameters to determine the relative influence of topographic variables (elevation, aspect, slope, topographic position and solar radiation), live tree basal area and burned/unburned status on average daily maximum and minimum temperatures (Tmax, Tmin) in summer and winter.ResultsModel parameters indicated that burned areas were warmer than unburned forest, with three of four average temperature variables (summer Tmax, winter Tmax, and winter Tmin) having >95% likelihood of a positive temperature difference in burned versus unburned locations. Mean temperature changes for these variables ranged from 0.41 to 0.74°C. Conversely, canopy loss in unburned, beetle‐killed forests did not meaningfully affect Tmax but resulted in slight cooling of Tmin. Modelled temperature changes resulting from 100% overstorey mortality were −1.29°C for summer Tmin (95% credible interval: −0.027 to −2.56°C) and −1.31°C for winter Tmin (95% credible interval: 0.17 to −2.79°C).Main ConclusionsOur results indicate that severe wildfire may exacerbate effects of climate change and increase the probability of ecosystem transitions. However, the effects of bark beetle outbreaks are more complex. Cooling of overnight minimum temperatures may counteract warming trends, but an increase in diurnal temperature ranges may have uncertain ecological consequences.

A Proposed New Approach for the Assessment of Selected Operating Conditions of the High Voltage Cable Line

Calculation models for the selection of cable lines used for expansion and modernization in the energy system and energy transmission planning are recognized tools supporting decision-making in both the energy sector and energy policy. At the same time, the above calculation models contain a large number of correction factors taking into account the temperature of the external environment at various points, the mutual influence of which is not taken into account. This means limitations to today’s common approaches to solutions, especially with regard to the required safety buffer for cable line selection. To meet this challenge, this article presents a parameter that takes into account the change and difference in temperature at various points in the external environment in the analyzed cable line systems. The purpose of this paper was to develop a new approach to the selection of a cable line in order to minimize failure during operation. For this purpose, possible temperature cases that may occur during line operation in different countries and at different rated voltages have been identified. Simulation models for individual cable line layouts were developed and the extreme temperature cases of the line operation for the maximum negative and positive temperature difference between the cable core and the external environment were considered in detail. The development of the curve of the change of the correction factor for the difference in the operating temperature of the cable line will allow for a more precise selection of the cable line parameters and the shortening of the current calculation model in terms of cable selection. In addition, this article presents a comparison of the change in the value of the correction factor from the change in temperature of a selected phase of a cable line system.

INFLUENCE ANALYSIS OF DESIGN SOLUTIONS OF UNDERGROUND PIPELINES CURVED SECTIONS ON THEIR STRESS-STRAIN STATE

Background Underground pipelines of main oil and gas pipelines are being built in all climatic and geographical zones of the country. A significant part of the main oil and gas pipelines are laid in flat-hilly and mountainous terrain. In hilly and mountainous areas, pipelines are laid in a trench with a vertical turn. During the operation of oil and gas main pipelines, longitudinal compressive forces arise under the influence of a positive temperature difference and operating pressure. These forces lead to longitudinal and transverse movements of the underground pipeline in convex sections of the turn in the vertical plane. When the underground pipeline moves in the longitudinal and transverse directions, additional bending stresses arise. At the same time, a decrease in longitudinal compressive forces occurs, which leads to a decrease in the values of longitudinal compressive stresses. In accordance with the requirements of SP 36.13330.2012 «Trunk Pipelines», the maximum total longitudinal stresses acting in the pipe wall should be determined from all (taking into account their combination) standard loads and actions, taking into account the longitudinal and transverse displacements of the pipeline. At the same time, the longitudinal and transverse movements of the pipeline and the resulting stresses due to these movements depend on the design solutions for underground pipeline laying. Aims and Objectives Ensuring the strength of pipes and the safe operation of oil and gas pipelines based on the improvement of calculation methods and design of curved sections of underground pipelines. Results The assessment of the level of the maximal longitudinal stresses in the underground pipeline is carried out for various design solutions of the angle of rotation on convex areas of the terrain. Technical solutions to ensure the strength of pipes for oil and gas trunk pipelines have been proposed.

Vertical Gradient Temperature Difference of the Main Arch with Single Pipe Section in Tibet Based on Statistical Analysis

A 75 m long experimental arch with a 1.6 m diameter was constructed in Tibet for a one‐year test to determine the most unfavourable vertical temperature difference for a single pipe in the main arch of a concrete‐filled steel tube arch bridge. Actual temperature observation data were used to analyse the vertical temperature difference in the single circular pipe arch rib using statistical methods. The standard value for the vertical temperature difference in the single pipe under a return period of 50 years was calculated. The results showed that the influence range of the vertical gradient temperature was 25 cm. The vertical temperature difference followed a lognormal distribution, and the standard values of the positive temperature difference at the upper and lower ends of the single pipe were 16 and 10°C, respectively; the standard values of the negative temperature difference at the upper and lower ends of the single pipe were both ‐8°C under a return period of 50 years. These results are considerably different from the values specified in the current Chinese code. These could serve as references for calculations involving arch bridges in Tibet with single circular pipes in the main arches.

Effects of heat transfer and the membrane thermal conductivity on the thermally nanofluidic salinity gradient energy conversion

Originating from advances in nanofabrication, functional materials have been developed to construct bioinspired or mimic nanochannels for efficient nanofluidic energy conversion. In previous studies regarding nanofluidic energy conversion, the material thermal conductivity has been never taken into consideration, however, which shall be addressed with transmembrane temperature difference applied. Thermal conductivities of widely used bulk materials for fabricating nanopores vary from 0 to 120 W/(m·K). Heat transfer occurs both in the liquid solution and solid membrane, impacting trans-channel solution temperature distribution and ion transportation, and yielding counterintuitive phenomena. Under positive temperature differences, the electric power shifts from inhibition to promotion as the membrane thermal conductivity increases. Larger membrane thermal conductivity evens temperature distribution in the nanochannel, weakening ion aggregations or depletions, which result in degraded electric power improvement under a negative temperature difference and upgraded power enhancement under a positive one. At a temperature difference of 30 K, the electric power is enhanced by 56.22% for a thin PET membrane (length = 50 nm) under the negative temperature difference. If the membrane thermal conductivity can be well tuned to nearly thermal insulation, the electric power can be enhanced by 120.07%. To step further, we proposed a criterion for membrane selection based on thermal conductivities in the thermally nanofluidic energy conversion: For thick membranes, materials of large thermal conductivity with a positive temperature difference are preferred for obvious power and energy efficiency enhancement. For thin membranes, materials of small thermal conductivity with a negative temperature difference are appealing. These findings reveal the importance of a long-overlooked factor, membrane thermal conductivity, in nanofluidic energy harvesting and can serve as a guidance for selecting appropriate membrane materials and developing high-performance nanofluidic power devices.

TECHNOLOGICAL PARAMETERS DETERMINATION FOR MAIN PIPELINES OVERHAUL UNDER CONDITIONS OF LONGITUDINAL COMPRESSIVE FORCE IN THE PIPE WALL

Background One of the important factors in the pipeline transport development is the efficient use of fixed assets. Along with the development of pipeline construction technologies, scientifically based technologies for their operation and overhaul ensure the operability and preservation of pipelines in a normative operational state. Aims and Objectives To obtain analytical dependences of technological parameters of trunk pipelines linear part overhaul on longitudinal compressive forces acting in the pipeline and to estimate the impact of these forces on the repair works safety. Methods Theoretical research of pipeline stress-strain state in the overhaul process with its lifting by pipe-layers under the action of longitudinal compressive force in the pipe wall. Results Analytical dependences of main pipelines overhaul technological parameters on longitudinal compressive forces in the pipe wall are obtained. It is concluded that the presence of longitudinal compressive force in the pipeline from the impact of positive temperature difference leads to an increase in the mechanical stress level. In order to ensure safety of performed repair works it is necessary to determine overhaul technological parameters taking into account longitudinal forces.

Ionic thermal up-diffusion in nanofluidic salinity-gradient energy harvesting.

Advances in nanofabrication and materials science give a boost to the research in nanofluidic energy harvesting. Contrary to previous efforts on isothermal conditions, here a study on asymmetric temperature dependence in nanofluidic power generation is conducted. Results are somewhat counterintuitive. A negative temperature difference can significantly improve the membrane potential due to the impact of ionic thermal up-diffusion that promotes the selectivity and suppresses the ion-concentration polarization, especially at the low-concentration side, which results in dramatically enhanced electric power. A positive temperature difference lowers the membrane potential due to the impact of ionic thermal down-diffusion, although it promotes the diffusion current induced by decreased electrical resistance. Originating from the compromise of the temperature-impacted membrane potential and diffusion current, a positive temperature difference enhances the power at low transmembrane-concentration intensities and hinders the power for high transmembrane-concentration intensities. Based on the system's temperature response, we have proposed a simple and efficient way to fabricate tunable ionic voltage sources and enhance salinity-gradient energy conversion based on small nanoscale biochannels and mimetic nanochannels. These findings reveal the importance of a long-overlooked element—temperature—in nanofluidic energy harvesting and provide insights for the optimization and fabrication of high-performance nanofluidic power devices.

Cool skin signals observed from Advanced Along-Track Scanning Radiometer (AATSR) and in situ SST measurements

Nighttime cool skin sea surface temperature (SST) signals, defined in this study as the differences between the SSTskin from the Advanced Along-Track Scanning Radiometer (AATSR) onboard Envisat satellite and in situ SSTs from drifting buoys and moorings, ΔT = SSTskin − SSTinsitu, are investigated on a global scale from July 2002 to April 2012. Global mean ΔT, averaged over the full study period, is −0.13 K, with most values falling between −0.1 and −0.2 K. The dominant role of wind speed on the ΔT is shown, with weaker winds usually corresponding to a cooler skin. The effect of air-sea temperature difference is also significant: warm skin (ΔT > 0 K) can be observed under large positive air-sea temperature differences. Other geophysical variables, such as the total column water vapor, in situ SST, and net heat flux, also affect ΔT, but to a lesser degree. Significant increase of ΔT size with SSTinsitu is observed when SSTinsitu is >28 °C. Tropical waters, such as the tropical Indian Ocean and the tropical warm pool (western Pacific and eastern Indian Ocean), are more frequently covered with a cool skin, largely due to the calm winds, very warm waters (especially for SSTinsitu >28 °C), and other environmental conditions supporting the development of large cool skin events. The ΔT seasonal pattern in the southern hemisphere is more regular, compared to the northern hemisphere. In both hemispheres, larger cool skin signals are seen during the local summer, mainly due to weaker winds. According to several previous cool skin models, higher winds tend to result in thinner cool skin layer depths, and hence in smaller ΔT amplitudes, regardless of stronger evaporation and heat loss. Given that wind is closely coupled with waves and turbulent mixing with wave breaking, the dependencies of ΔT on a few wave parameters are also investigated. A strong (moderate) dependency of ΔT on wave height (wave steepness) is identified, while the dependency of ΔT on wave breaking probability is less discernible.

A coupled thermo-poroelastic analysis of wellbore stability for formations with anisotropic strengths

The temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole and tend to cause borehole instability problems in oil and gas drilling process. The wellbore stability models used in thinly laminated rock formations integrate the in situ stresses, pore pressure, well trajectory, and rock strength parameters to improve the wellbore stability; however, a limited amount of research has focused on the factor of formation temperature and its difference between drilling mud. Hence, a wellbore stability model is introduced based on the stress transformations and the Mohr-Coulomb failure criteria, which incorporate the rock strength anisotropy and the temperature difference between formation and drilling mud. The wellbore instability problems of anisotropic strength formation are analyzed using this model. The results show that the shear failure of rock matrix mainly occurs at two symmetric locations around the borehole and the size of failure region decreases with the inclination angle, in contrast, the shear slip failure of weak plane occurs at four locations around the borehole. The mud density required for isotropic strength should be selected as the required mud density to keep the wellbore stable if the inclination angle less than a certain value, and it almost keeps a constant with the inclination angle changes. On the contrary, the mud density required for slippage along the plane of weakness should be selected when the inclination angle larger than this value, and it is increasing with the inclination angle. Positive temperature difference will aggravate the wellbore instability, the larger the temperature difference the bigger the mud density is required.

On the theoretical aspects of improved fog detection and prediction in India

The polluted Indo-Gangetic Basin (IGB) in northern India experiences fog (a condition when visibility degrades below 1km) every winter (Dec-Jan) causing a massive loss of economy and even loss of life due to accidents. This can be minimized by improved fog detection (especially at night) and forecasting so that activities can be reorganized accordingly. Satellites detect fog at night by a positive brightness temperature difference (BTD). However, fixing the right BTD threshold holds the key to accuracy. Here I demonstrate the sensitivity of BTD in response to changes in fog and surface emissivity and their temperatures and justify a new BTD threshold. Further I quantify the dependence of critical fog droplet number concentration, NF (i.e. minimum fog concentration required to degrade visibility below 1km) on liquid water content (LWC). NF decreases exponentially with an increase in LWC from 0.01 to 1g/m3, beyond which it stabilizes. A 10 times low bias in simulated LWC below 1g/m3 would require 107 times higher aerosol concentration to form the required number of fog droplets. These results provide the theoretical aspects that will help improving the existing fog detection algorithm and fog forecasting by numerical models in India.

Effect of wind and buoyancy interaction on single-sided ventilation in a building

In this study, we performed numerical simulations of three-dimensional turbulent flows over an isolated building with a door-type opening by using a CFD model in order to investigate the combined effect of wind and buoyancy on windward single-sided ventilation. Positive and negative temperature differences between the inside and outside of the building were considered. The Archimedes number (Ar) was introduced as an index for evaluating the interaction between buoyancy and wind effects. The interaction between the two opposing forces under a positive temperature difference was found to be destructive, resulting in the combined effect reducing the volume flow rate. Furthermore, the wind effect was found to be dominant for Ar0.5<0.45, with the buoyancy effect beginning to increase at Ar0.5=0.2, and tending to be dominant for Ar0.5>0.45. The two effects were found to be fairly comparable at Ar0.5=0.45. The interaction between the two assisted forces under a negative temperature difference was always constructive, resulting in the combined effect reinforcing the ventilation for all the Archimedes numbers.

The impact of eastern equatorial Pacific convection on the diversity of boreal winter El Niño teleconnection patterns

It is widely recognized that no two El Nino episodes are the same; hence the predictable variations of the climate impacts associated with El Nino remain an open problem. Through an analysis of observational data and of large ensembles from six climate models forced by the observed time-varying sea surface temperatures (SSTs), this study raises the argument that the most fundamental predictable variations of boreal wintertime El Nino teleconnection patterns relate to the distinction between convective (EPC) and non-convective eastern Pacific (EPN) events. This distinction is a consequence of the nonlinear relationship between deep convection and eastern Pacific SSTs, and the transition to a convective eastern Pacific has a predictable relationship with local and tropical mean SSTs. Notable differences (EPC minus EPN) between the teleconnection patterns include positive precipitation differences over southern North America and northern Europe, positive temperature differences over northeast North America, and negative temperature differences over the Arctic. These differences are stronger and more statistically significant than the more common partitioning between eastern Pacific and central Pacific El Nino. Most of the seasonal mean composite anomalies associated with EPN El Nino are not statistically significant owing to the weak SST forcing and small sample sizes; however, the EPN teleconnection is more robust on subseasonal timescales following periods when the EPN pattern of tropical convection is active. These findings suggest that the differences between EPC and EPN climate impacts are physically robust and potentially useful for intraseasonal forecasts for lead times of up to a few weeks.

ОЦЕНКА НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ И БЕЗОПАСНОСТИ ПОДЗЕМНЫХ ТРУБОПРОВОДОВ, ЭКСПЛУАТИРУЮЩИХСЯ В УСЛОВИЯХ ДЕЙСТВИЯ ВЫСОКИХ ПРОДОЛЬНЫХ СЖИМАЮЩИХ УСИЛИЙ

Background Safe operation of pipelines is largely ensured by scientifically reasoned technical solutions at the design stage and based on the assessment of pipeline stress-strain state, with account for specific conditions of the pipeline construction and loading. Where intense longitudinal compressive forces act on the pipeline, the curved sections are characterized by the highest mechanical stresses. Provision of acceptable level of reserve strength for these sections ensures pipeline safety at the normal mode of pipeline operation. Aims and Objectives Assess the stress-strain state and reserve strength of the underground pipeline curved sections of various designs under the action of the intense longitudinal compressive forces. Methods Theoretical study of stress-strain state of underground pipelines under the impact of positive temperature difference and internal pressure. Results The relationship of the maximum equivalent stresses and reserve strength to the operating loads and technical solutions adopted in designing the pipeline. The analysis of these relationships has been conducted.

A new pinch based method for simultaneous selection of working fluid and operating conditions in an ORC (Organic Rankine Cycle) recovering waste heat

ORC (Organic Rankine Cycles) are widely used in low temperature waste heat recovery which can lead to considerable energy saving. Huge amounts of waste heat need to be cooled to the ambient temperature in refineries. The target temperature of this type of waste heat can be as low as the ambient temperature. The selection of working fluid and operating conditions exert significant influence on the performance of an ORC system. In this paper, a new method is proposed to simultaneously determine the working fluid and operating conditions in an ORC system, which recovers this type of waste heat in refineries. PPP (Preheating Pinch Point) and VPP (Vaporization Pinch Point) are newly introduced. The method is based on a newly defined parameter (PREDICTOR) that can predict the Pinch position between the waste heat carrier and the working fluid accurately, calculate the mass flow rate of working fluid and the amount of heat recovered easily, and determine the optimum working fluid and corresponding operating conditions simultaneously. Two illustrative examples are used to demonstrate the effectiveness of the proposed method. The waste heat can be recovered completely and the power output reaches the maximum with the following conditions: (1) An appropriate positive temperature difference between the waste heat inlet temperature and the working fluid critical temperature exists. (2) Working fluid evaporates in its near critical region. However, if the working fluid critical temperature is close to the waste heat inlet temperature, the working fluid evaporating in the near critical region cannot provide maximum heat recovery and power output.