Equivalent Temperature Difference Research Articles

Performance of all-air wall induction unit for displacement ventilation in a four-bed hospital ward during the cooling period

The existing induction air-conditioning system faces ventilation shortcomings and condensation risks. We developed an all-air wall induction air terminal unit (wall IU) that doesn't require reheating and eliminates water pipes to address condensation. Moreover, with modifications to its supply method, it can achieve displacement ventilation (DV) in an adiabatic environment. However, the real-world performance of this system needs to be further confirmed. This study examines wall IU performance during the cooling period. A full-scale experiment was conducted in a room furnished as a four-bed hospital ward with an outdoor climate chamber (OCC) to simulate summer conditions. IU's cooling and ventilation performance was evaluated by examining steady-state temperatures and tracer gas distributions. Moreover, CFD simulations to reproduce the experiment were performed to supplement the results. Patients' thermal comfort and infection risk while cohabiting with an infected individual were estimated using detailed temperature, airflow, and concentration data from an experiment-based CFD analysis. Furthermore, the DV stratification height under various perimeter heat loads and performance comparison between wall and ceiling-mounted induction units were also studied. In conclusion, the wall IU improved ventilation efficiency by achieving DV under cooling supply conditions. Satisfied thermal comfort is ensured based on ADPI and DR evaluation. DV's stratification height can be kept high enough under a 20 °C equivalent temperature difference when using a single glass window or more after thermal insulation enhancement. Compared with ceiling-mounted induction units, wall-mounted units can reduce infection risk by more than double while making cold drafts less noticeable.

Prestress Self-Equilibrium Force-Finding Method for Cable-Supported Grid Structures Considering Zero-Stress State Form-Finding and the Construction Process

The cable-supported grid structure (CSGS) is a hybrid structure combined with rigidity and flexibility. Its formed state is closely related to the zero-stress state, construction process, and prestress distribution. The prestress self-equilibrium force-finding method is proposed in this paper to continuously conduct zero-stress state form-finding, the construction process, and prestress state force-finding analysis. As the first engineering project adapting CSGS with an internal compression ring, Shanghai Pudong Football Stadium was taken as the analysis object. The structural finite element model was established in ANSYS, structural components were divided into prestress and ordinary components to form a prestress self-equilibrium system, and the equivalent temperature difference was applied to the prestress components as prestress. The Newton–Raphson method was used for geometric nonlinear analysis. The analysis results show that the internal forces and displacements of the formed structure are consistent with the design state, which proves the validity of the method and provides significant guidance for the actual construction. The method proposed in this paper can effectively and accurately obtain the zero-stress state configuration, structural response during construction, and the prestress distribution after forming in a single analysis, without analyzing the above three separately, which improves the analysis efficiency.

An Overall Assessment of JPSS-3 VIIRS Radiometric Performance Based on Pre-Launch Testing

Satellite imagery and data are playing an increasingly important role in scientific studies of the Earth and its climate. The scientific community has been demanding ever-increasing capabilities and accuracy from the data provided by these satellites. One key instrument on board a series of satellite platforms is the Visible Infrared Imaging Radiometer Suite (VIIRS), which provides high-quality data of the Earth from low Earth orbit covering the visible to long-wave infrared parts of the spectrum. The fourth build in the series, set to be launched on the Joint Polar-orbiting Satellite System 3 (JPSS-3) platform, has recently completed its main ground calibration program and is set to be integrated into the satellite bus in the near future. This calibration program covered a comprehensive series of performance metrics designed to demonstrate the quality of the science data and ensure the instrument can maintain its calibration successfully once on-orbit. The subject of this work covers the radiometric calibration metrics including dynamic range, signal-to-noise ratio/noise equivalent differential temperature (SNR/NEdT), polarization sensitivity, scattered light response, relative spectral response, response versus scan angle, and uniformity, as well as uncertainties; all key metrics met or exceeded their design requirements with some minor exceptions. Comparisons to previous builds will also be provided.

The in-plane expansion of fractured thermally pre-stressed glass panes: -An equivalent temperature difference model for engineering glass design

The present paper is concerned with deriving simplified design equations and charts for modelling in-plane expansion of fractured thermally pre-stressed soda-lime-silica glass panes using the method of equivalent temperature differences (ETD) together with a thermal expansion analogy for strains. The starting point is a theoretical method based on linear elastic fracture mechanics merged with approaches from stochastic geometry to predict the 2D-macro-scale fragmentation of glass. The approach is based on two influencing parameters of glass: (i) fragment particle size, δ, and (ii) fracture particle intensity, λ, which are related to the pre-stress induced strain energy density, UD, before fracture. Further Finite Element (FE) analysis of single cylindrical glass particles allow for establishing functional relations of the glass fragment particle dimensions, the pre-stress level and the resulting maximum in-plane deformation. Combining the two parts of two-parameter fracture pattern modelling and FE results on fragment expansion, formulas and engineering design charts for quantifying the in-plane expansion of thermally pre-stressed glass panes due to fracturing via an ETD approach is derived and provided within this paper. Two examples from engineering practice serve as demonstrators on how to use our ETD approach to compute the equivalent temperature difference and resulting internal forces as well as deformations. This approach serves furthermore as a basis to estimate secondary effects (such as fracture-expansion-induced deformations or stresses) on support structures or remaining parts of glass laminates in form of handy ETD load cases within analytical as well as FE analysis.

A novel hybrid adsorption heat transformer – multi-effect distillation (AHT-MED) system for improved performance and waste heat upgrade

Multi-effect distillation (MED) systems are considered to be the most energy-efficient thermal desalination methods. This paper introduces the development of a novel thermal desalination system for performance superior to MED systems for the same operating temperature limits. Such an unprecedented achievement was attained by upgrading the heat source using the chemical potential of adsorption phenomena. The proposed Adsorption Heat Transformer (AHT) cycle hybridized with Multi-effect distillation system (AHT-MED) exhibits higher performance ratio and water production rate than a conventional MED system for the same heating source and sink. The heat generated by the heat of adsorption with the temperature higher than the heat source is supplied to the first effect of the MED system, thus, extending the temperature difference between the Top Brine Temperature (TBT) and Bottom Brine Temperature (BBT). The higher temperature difference offers more number of effects, with the equivalent temperature difference between the effects (ΔTe) as the design parameter. Using the low-temperature heat source (as low as 58 °C), the system can employ an increased number of effects (as high as 11) due to the supply of heat at an increased temperature of around 80 °C. The proposed system achieves a higher performance ratio (approximately 5.4) and water production rate (2 kg/s) compared to the standalone MED system (PR: 4.2, WPR: 1 kg/s) with the number of effects of the hybrid system as 10 at constant interstage temperature difference between the standalone and hybrid systems. This novel AHT-MED system opens up new possibilities for low-temperature heat source-driven thermal desalination with significantly improved performance.

Calibration of standard radiation thermometers using two fixed points

Radiation thermometry based on the measurement of two fixed points, the so-called n = 2 scheme, is studied in this work. Verification of the scheme was undertaken for various measurement conditions using seven radiation thermometers with nominal centre wavelengths of 650 nm, 890 nm, 900 nm, and 1600 nm. Comparison between the signals calculated using the n = 2 scheme and the signals measured directly with fixed-point cells was studied. For temperatures between the two reference fixed points, the equivalent temperature difference was less than 0.14 K in the temperature range from the In to Cu fixed points, and less than 0.3 K in the temperature range from the Cu to Re–C fixed points. The maximum normalised error was 0.35, confirming the validity of the n = 2 scheme; the consistency was observed not only in the interpolation temperature range, but also in the extrapolation range. The results also indicate that temperature realisation in the range from 150 °C to 2500 °C can be achieved by maintaining only the Zn, Cu, and Re–C fixed-point facilities. The n = 2 scheme would be of great benefit to developing national metrology institutes in terms of time consumed for scale realisation and cost for maintenance of the measurement system.

Heat transfer and flow behaviors of a wavy corrugated tube

A new design of wavy corrugated tube (WCT) aiming to improve heat transfer by employing multi-longitudinal vortices was put forward. Effects of corrugation number N (N=1, 2, 3 and 4), arrangement (parallel arrangement, counter arrangement, two-parallel and counter arrangement and five-parallel and counter arrangement), corrugation amplitude A (A=1mm, 3mm, 5mm and 7mm), corrugation width W (W=3mm, 5mm, 7mm and 9mm) and corrugation height H (H=0.5mm, 0.8mm, 1.1mm and 1.4mm) on turbulent fluid flow and heat transfer behaviors were investigated numerically as well as overall thermal performance evaluation criterion (PEC) also being discussed. The operating Reynolds number (Re) ranged from 7500 to 20000 and the constant temperature condition was imposed on the tube wall. Local streamlines, velocity contours, turbulent kinetic energy contours, turbulent intensity contours, temperature contours, heat flux contours and variations of absolute vorticity versus axis distance were plotted to illustrate the heat transfer enhancement mechanisms. Equivalent temperature difference (ETD) stemming from the entransy dissipation extremum principle theory was used to evaluate heat transfer enhancement. It is found that the varying geometric parameters of the WCT play an important role in thermal-hydraulic characteristics. The main findings are that the WCTs exhibits superior heat transfer rate and PEC compared with the plain tube, due to improved flow mixing and enhanced heat flux by multi-longitudinal vortices induced by corrugations. The Nusselt number, friction factor and PEC in the WCTs with both parallel arrangement and counter arrangement increase generally with the rise in corrugation number until N=3 and then decrease with the further increase of corrugation number from N=3 to N=4. The obtained results in ETD are matched with the heat transfer performance for WCTs with parallel arrangement which indicates that the heat transfer ability in the WCTs can be well described. Among the investigated different arrangements, it is found that the WCT with parallel arrangement has the maximum PEC. Furthermore, in results of corrugation amplitude variations versus thermal performance, the PEC in the WCT with A=5mm has the largest value. The PEC can be further enhanced by increasing corrugation width with the largest PEC obtained by the WCT with W=9mm. For varying corrugation height, the WCT with H=1.1mm has the best PEC at most of Re. Under operating conditions and geometric parameters considered, the WCT with A=5mm, N=3, W=9mm, H=1.4mm and parallel arrangement at Re=7500 offers the highest PEC value of about 1.56.

Environmental load for design of airport concrete pavements

This paper presents a method for calculating the environmental load that is essential to the mechanistic design of airport concrete pavements, based on the equivalent linear temperature difference (ELTD) between the top and bottom of the slab. To assess its application, the total ELTDs at 17 airports (military and civilian) across the Korean peninsula, representing the full range of regional climates in the country, were calculated according to slab thickness. Based on the results, a multiple regression model was developed. The environmental load can be considered by simply inputting the ambient temperature, relative humidity and slab thickness into the proposed models. The results can be applied worldwide.

Effect of Internal Curing on Moisture Gradient Distribution and Deformation of a Concrete Pavement Slab Containing Pre-Wetted Lightweight Fine Aggregates

Internal curing technology has been proven effective in improving many properties of concrete. The application of this technology to the transportation infrastructure holds promise with increasing resistance to cracking and enhanced durability. On the other hand, an investigation of moisture distribution in concrete slabs is of significance for predicting slab deformation and the associated stress and failure. This study is performed to investigate the characteristics of the pre-wetted sintered fly ash lightweight fine aggregate (LWFA) used as an internal curing agent and the influence of internal curing on concretes exposed to sealed curing, external drying, and surface wetting conditions. The internal curing effects on the moisture distributions in concrete pavement slabs at w/c = 0.3 and 0.4 were evaluated through experimental measurements, and the effects on slab deformations were quantified using an equivalent temperature difference. The findings of this study will benefit the further application of internal curing technology to the transportation infrastructure's construction.

Discussion of Method for Computing Temperature Load during Operation Period on High Arch Dam

According to the existing arch dam design specification, the temperature load is obtained based on analytic solution of infinite long free plate, it only considers the average temperature and the equivalent linear temperature difference of dam section in operation period, the influence of non-linear temperature difference has not been considered. This kind of simplification has some approximation; especially it can not reflect spatial effect of larger temperature gradient changes in the upstream and downstream water level change area. This paper first takes the free plate as an example, has calculated the temperature field corresponding to analytical method, finite element method, standard method, explains the rationality of using written program to carry on finite element analysis. On this basis, take Xiluodu arch dam as an example, the dam temperature load and temperature stress has been analyzed by using finite element method and standard method, the difference between both has been discussed

Evaluation of Dowel Bar Retrofit Alternatives Using Accelerated Pavement Testing

This paper presents the results of accelerated pavement testing using the heavy vehicle simulator (HVS) to evaluate the performance of dowel bar retrofit (DBR) joints and cracks as measured by deflections and load transfer efficiency (LTE). Four HVS sections were constructed and tested: one with four epoxy-coated steel dowels per wheelpath, one with three epoxy-coated steel dowels per wheelpath, one with four fiber-reinforced polymer (FRP) dowels per wheelpath, and one with one joint with four epoxy-coated steel dowels per wheelpath and the other with four hollow stainless steel dowels per wheelpath. HVS and falling weight deflectometer (FWD) testing indicated that DBR significantly improved the LTE and reduced deflections compared with the undoweled pavement. Previous HVS trafficking damaged LTE on undoweled joints, but no significant loss of LTE was found after heavy HVS trafficking on DBR joints or originally doweled joints. Under FWD testing, the LTE from DBR joints (four steel dowels per wheelpath) was typically between 85 to 90% at lower temperatures before trafficking and greater than 95% for joints with originally installed dowels. The configuration using three dowels per wheelpath was found to have significantly lower LTE than that using four dowels per wheelpath. FRP and grout-filled hollow stainless steel dowels had similar performance to epoxy-coated steel dowels. The equivalent built-in temperature difference values of after-DBR sections are lower than those of before-DBR sections, likely as a result of the time of construction when the slabs were expected to be flattest. This finding indicates that tensile stresses in the concrete slabs could also be decreased by DBR.

Evaluation of Dowel Bar Retrofit Alternatives Using Accelerated Pavement Testing

This paper presents the results of accelerated pavement testing using the heavy vehicle simulator (HVS) to evaluate the performance of dowel bar retrofit (DBR) joints and cracks as measured by deflections and load transfer efficiency (LTE). Four HVS sections were constructed and tested: one with four epoxy-coated steel dowels per wheelpath, one with three epoxy-coated steel dowels per wheelpath, one with four fiber-reinforced polymer (FRP) dowels per wheelpath, and one with one joint with four epoxy-coated steel dowels per wheelpath and the other with four hollow stainless steel dowels per wheelpath. HVS and falling weight deflectometer (FWD) testing indicated that DBR significantly improved the LTE and reduced deflections compared with the undoweled pavement. Previous HVS trafficking damaged LTE on undoweled joints, but no significant loss of LTE was found after heavy HVS trafficking on DBR joints or originally doweled joints. Under FWD testing, the LTE from DBR joints (four steel dowels per wheelpath) was typically between 85 to 90% at lower temperatures before trafficking and greater than 95% for joints with originally installed dowels. The configuration using three dowels per wheelpath was found to have significantly lower LTE than that using four dowels per wheelpath. FRP and grout-filled hollow stainless steel dowels had similar performance to epoxy-coated steel dowels. The equivalent built-in temperature difference values of after-DBR sections are lower than those of before-DBR sections, likely as a result of the time of construction when the slabs were expected to be flattest. This finding indicates that tensile stresses in the concrete slabs could also be decreased by DBR.

Equivalent temperature differences with respect to ambient temperature difference as a function of background temperature

The performance evaluation of a thermal imager includes the comparison of a measurement to some specified temperature differential. It is uncommon to find a specification that is a function of absolute temperature. Since detectors respond to differential power, equivalent temperatures are presented with respect to an ambient (25°C background) differential temperature as a function of background temperature. The changes in the equivalent temperature difference are shown to be significant in both the near and far infrared regions ofthe spectrum. A simple curve is obtained to estimate the equivalent temperature difference for the far infrared region. The curve shape of the near infrared region varies too significantly to obtain any simple and accurate curve fit. The current thermal imager test methods should be reevaluated and specified in terms of background temperature.

A new diagram for evaluating the relationship between convective and evaporative heat transfer during the cooling of carcasses

During the cooling of a carcass, both its heat losses by convection and by evaporation are governed by the convective heat transfer coefficient αc. While both phenomena occur at the same temperature difference δ w between the surface of the carcass and the cold air, the quantity of heat flux of the former part becomes α cδ w, and the latter part becomes the product of α c multiplied by an equivalent temperature difference δ D which is a function of the vapour pressure differences between the wet surface and the cold air. The ratio δ D/δ w can be established from the diagram and the heat loss by convection and by evaporation can be calculated for any given value of α c. Consequently, the anticipated theoretical weight loss of the carcass can be calculated.

Steam heat transfer to small drops of water

In cases of drop heat transfer in which a saturated atmosphere condenses into the liquid of the drop, a point is reached when the drop is at the atmospheric temperature. If formal treatment is given to the heat transfer up to that time, the end temperature difference being zero, the conception of logarithmic mean temperature difference cannot be used and an arbitrary choice which may give misleading results must be made. That heat transfer does continue with this apparent zero difference is obvious and therefore a potential difference must exist which is shown to be expressible as an equivalent temperature difference.