Constant Base Temperature Research Articles

Comparative temperature and consumption data measurement of model buildings with different thermal time constants

In this study, three identically designed model buildings and their heating energy consumption was compared. Those pilot scale buildings are equal by size and were located on the same location. During the measuring campaign both external and internal temperatures were recorded, beside the energy consumption. The model buildings were labeled as A (constant baseline), B (baseline varying according to a time program), and C (unheated, blank). During the measurements, the thermal mass of the buildings was altered. The same amount of thermal mass was installed in all three model buildings during all measurements. According to our results under real weather conditions, the intermittent heating requires less energy than maintaining a constant temperature, and the energy saving is inversely proportional to the time constant at intermittent heating. Instead of specific heat mass, a thermal time constant was used to compare intermittent and constant heating. It was established that as the thermal constant of the model building increases, the energy savings between maintaining a variable base temperature and maintaining a constant base temperature decrease. The expected savings are between 4% and 7%.

Unraveling the effect of temperature and humidity on the life cycle of Diatraea saccharalis (Lepidoptera: Crambidae) and the impact on pest outbreaks.

Temperature and humidity are considered the main abiotic factors that affect both the development and survival of ectothermic organisms. In this study, we estimated the development time as well as the thermal requirements of the sugarcane borer, Diatraea saccharalis (Fabricius, 1794; Lepidoptera: Crambidae), a key insect pest of sugarcane and discussed the influence of temperature and relative humidity and its infestation intensity in a scenario of climate change. The models Brière-1 and Ikemoto-Takai provided the best fit to the data of development rate versus temperature. The average life cycle (from egg to adult) ranged from 39.21 ± 4.84 at 32 °C to 137.10 ± 7.47 at 18 °C days. The thermal constant and average base temperature were 547.69 degree-days and 13.64 °C, respectively. The number of larval instars varied from 4 to 7 depending on the temperature, being higher at lower temperatures. The thermal range comprised the interval from 16.7 °C to 33.9 °C and the optimum temperature was estimated as 27.4 °C. Locations with elevated temperature (≥25 °C) and high relative humidity (≥70%) presented larger populations of D. saccharalis. Our findings show that the infestation pressure of this species is highly influenced by both temperature and humidity, and the studied models allow to forecast pest outbreaks. In the context of climate change, information about the thermal range and the optimum temperature contributes to predicting the spatial-temporal distribution of D. saccharalis and, consequently, aids decision making in pest management.

Innovative standard degree-day indicator (SDI) concept and application for monthly energy consumption control

In practice, monthly temperature records play a major role calculating the heating and cooling degree-days of the air conditioner management in buildings. Classically, heating and cooling degree calculations are based on the comparison of outdoor temperature measurements with a standard level called the base temperature. Truncating the temperature series at a constant base temperature causes heating (deficits) and cooling (surpluses) degrees. Since outdoor temperature records are of random character, future predictions with probabilistic and statistical methods are convenient means for calculations. All previous methodologies in the literature are based on crisp logic with simple mathematical calculations. This paper proposes a new methodological approach by converting the actual temperature record probability distribution function (PDF) into a probabilistic standardized degree indicator (SDI) in normal (Gaussian) PDF form with zero mean and unit standard deviation. Furthermore, as a new evaluation methodology fuzzy logic inference calculations are provided. SDI is divided into seven classes, three for cooling, heating, and a single class for uncooled-unheated states. Heating and cooling degree changes according to SDI values are presented with crisp and fuzzy sets. The application of the methodology is made for Kadıköy urban area on the Asian side of Istanbul, Turkey. In the case of fuzzy set SDI air conditioned operation, it has been determined that there is cooling energy saving of approximately 25% compared to the crisp set. The same is true for the heating degree-day side.

Definition and Determination of Fin Substitution Factors Accelerating Thermal Simulations

The effort of numerical heat transfer calculations increases with the complexity and size of the domains and surfaces under consideration. When calculating heat transfers on finned arrays, one way to reduce this effort is to substitute the fins. Therefore, this work defines the fin substitution factor by considering that a smooth surface behaves thermally sufficiently similar to a specific finned array. A process for determining the case-specific most accurate analytical computation path for fin substitution factors is also defined. The performance of the process and the resulting solution is demonstrated using the example of vertical rectangular finned arrays under natural convective heat transfer with a constant fin base temperature and air as the surrounding fluid. The heat flows determined in solid-state simulations of flat plates considering fin substitution factors deviated by an average of 6.2% from the heat flows resulting from detailed CFD simulations of the corresponding finned arrays.

Screening for Cold Tolerance during Germination within Sweet and Fiber Sorghums [Sorghum bicolor (L.) Moench] for Energy Biomass

Within the project “BIOSEA” funded by the Italian Ministry of Agriculture and Forestry, a preliminary laboratory test was conducted to assess the variability for cold tolerance during germination in 30 cultivars of biomass sorghum, among fiber and sweet types. Seed germination (%) and mean germination time (MGT) were examined at seven constant temperatures (from 8 °C to 35 °C) and base temperature (Tb) and thermal time (θT) for 50% germination were calculated. A wide genetic diversity in the germination response of sorghum was ascertained at 8 °C (CV 45%) and 10 °C (CV 25.4%). At 8 °C, in cultivars of ‘Padana 4’, ‘PR811F’, ‘PSE24213’, ‘PR849’ and ‘Zerberus’, seed germination exceeded 80%. Seeds of ‘Zerberus’ were also the fastest, requiring less than 13 days for final germination at this low temperature. Great differences were found in Tb and θT among cultivars. Tb varied between 7.44 °C (‘PR811F’) and 13.48 °C (‘Nectar’). Thermal time (θT) was, on average, 24.09 °Cd−1, and ranged between 16.62 (‘Nectar’) and 33.42 °Cd−1 (‘PSE24213’). The best combination of the two germination parameters (i.e., low Tb and θT) corresponded to ‘Zerberus’, ‘Sucrosorgo 506’, ‘Jumbo’ and ‘PR811F’. Accordingly, these cultivars are more tolerant to cold stress during germination and, thus, more adapt to early spring sowings in Mediterranean areas (March-April). Cultivars ‘PR811F’ (fiber type) and ‘Sucrosorgo 506’ (sweet type) also combine high cold tolerance with good productivity in terms of final dry biomass, as assessed in open-field conditions (late spring sowing). The genetic variation in the germination response to a low temperature is useful for the identification of genotypes of sorghum suitable to early sowings in semi-arid areas. Selection within existing cultivars for cold tolerance during germination may also contribute to the expansion of biomass sorghum into cooler cultivation areas, such as those of Northern Europe, which are less suitable to this warm season crop.

Experimental and numerical study of natural convection heat transfer from arrays of zigzag fins

In this study natural convection heat transfer from arrays of zigzag fin is studied numerically and experimentally. The length and width of the fins are L = 75 mm and H = 25 mm. Fin thickness and fin spacing are t = 2 mm and s = 6 mm, and zigzag arrangement is made with different pitches along the rectangular fins length. Finite volume scheme is used to solve three-dimensional equations of laminar flow and heat transfer numerically. For ten different zigzag fin geometries, both constant temperature and constant heat flux boundary conditions at the base plate are examined numerically and results have been compared with solid rectangular fin array. Rectangular and zigzag fin arrays with 4 and 14 triangles are made and tested experimentally at different heat inputs, and air flow field and natural convection heat transfer rate for each case are determined. Experiments are done in a thermally insulated room with specific equipment to control test conditions and measure necessary data. Results of experiments and numerical solutions are compared for various power input. By comparison with solid rectangular fin, 22 triangles zigzag fin array has the same heat transfer but with 50% reduction in mass for constant base temperature. For experiments for different input power, natural convection heat transfer coefficient of 4 triangles zigzag fin array is increased 36%–50% in comparison with solid rectangular fin array with 50% reduction in mass.

The CUORE Cryostat

The Cryogenic Underground Observatory for Rare Events (CUORE) is a bolometric experiment for neutrinoless double-beta decay in $^{130}$Te search, currently taking data at the underground facility of Laboratori Nazionali del Gran Sasso (LNGS). The CUORE cryostat successfully cooled down a mass of about 1 ton at $\sim$7\,mK, delivering an uniform and constant base temperature. This result marks a fundamental milestone in low temperature detectors techniques, opening the path for future ton-scale bolometric experiments searching for rare events. In this paper we present the CUORE cryogenic infrastructure, briefly describing its critical subsystems.

Geometric Size Optimization of Annular Step Fin Using Multi-Objective Genetic Algorithm

Although an annular stepped fin can produce better cooling effect in comparison to an annular disk fin, it is yet to be studied in detail. In the present work, one-dimensional heat transfer in a two-stepped rectangular cross-sectional annular fin with constant base temperature and variable thermal conductivity is modeled as a multi-objective optimization problem. Taking cross-sectional half-thicknesses and outer radii of the two fin steps as design variables, an attempt is made to obtain the efficient fin geometry primarily by simultaneously maximizing the heat transfer rate and minimizing the fin volume. For further assessment of the fin performance, three more objective functions are studied, which are minimization of the fin surface area and maximization of the fin efficiency and effectiveness. Evaluating the heat transfer rate through the hybrid spline difference method, the well-known multi-objective genetic algorithm, namely, nondominated sorting genetic algorithm II (NSGA-II), is employed for approximating the Pareto-optimal front containing a set of tradeoff solutions in terms of different combinations of the considered five objective functions. The Pareto-optimal sensitivity is also analyzed for studying the influences of the design variables on the objective functions. As an outcome, it can be concluded that the proposed procedure would give an open choice to designers to lead to a practical stepped fin configuration.

Hydrothermal time models for conidial germination and mycelial growth of the seed pathogen Pyrenophora semeniperda

Population-based threshold models using hydrothermal time (HTT) have been widely used to model seed germination. We used HTT to model conidial germination and mycelial growth for the seed pathogen Pyrenophora semeniperda in a novel approach to understanding its interactions with host seeds. Germination time courses and mycelial growth rates for P.semeniperda were measured on PDA amended to achieve a series of five water potentials (ca. 0 to −6 MPa) at six constant temperatures (5–30 °C). Conidial germination was described with alternative population-based models using constant or variable base and maximum temperature and water potential parameters. Mycelial growth was modeled as a continuous, linear process with constant base temperature and base water potential. Models based on HTT showed reasonable fit to germination and growth rate data sets. The best-fit conidial germination model (R2 = 0.859) was based on variable base and maximum temperature as a function of water potential. The good fit of the linear mycelial growth model (R2 = 0.916) demonstrated the utility of HTT for modeling continuous as well as population-based processes. HTT modeling may be a useful approach to the quantification of germination and growth processes in a wide range of filamentous fungi.

An ease of analysis for optimum design of an annular step fin

In the present study, exact and approximate analytical techniques are developed to determine the optimum design of a rectangular stepped annular fin with constant base temperature. An algebraic expression based on the mean value theorem is used as the vehicle for an approximation tool. The corresponding temperature distribution and heat transfer characteristics in the fin are determined using exponential functions. The standard modified Bessel function formulation is employed for the exact analysis. Error analysis has been carried out to compare between the exact and approximate results. It is found that the integral approach of calculating the rate of heat transfer is more accurate than the differential approach while applying the approximate analytic technique. The errors associated with the approximate analytic methods falls well within acceptable accuracy levels for engineering analysis and design.

Towards dynamic thermal performance benchmarks for naturally ventilated buildings in a hot-dry climate

This article focuses on evolving dynamic thermal performance benchmarks for naturally ventilated buildings located in hot-dry climates of India. The study presents a framework which translates the steady-state performance metrics prescribed by the national building code to dynamic metrics. By means of collating the adaptive comfort boundaries and the thermal inertia requirements for this climate, a dynamic performance limit has been developed. Similarly, by means of replacing the constant base temperature used in the existing thermal performance index for opaque walls with the variable adaptive-comfort based thermo-neutral temperature, a dynamic index has been presented. A review of these indices using data obtained from real-time field measurements has been provided. Influence of wall density, absorptivity, glazing type, ventilation strategy and orientation on thermal discomfort has been discussed through parametric studies. The steady state wall – U value requirement prescribed by the national code has been reviewed through factorial analysis. The interactive effects of wall – U value, fenestration area, insolation and orientation has been analyzed. Optimal fenestration sizes have been derived for different boundary conditions.

The use of computational fluid dynamics in analysing the performance of an elliptical annular fin

The Elliptical Annular Fin (EAF) circumscribing circular tube could be a good choice where the space is restricted to one direction and enough space is present in perpendicular direction or one side for material saving. This paper presents the performance of the EAF circumscribing circular tube. In this work fins with constant base temperature by free, forced convection and with heat dissipation from the fin to the surroundings have been considered. The performance of the EAF is evaluated from the surface temperature. The Shaped Tube Efficiency (STE) and Fin Effectiveness (FE) with respect to Biot number are calculated using surface temperature. The result shows that STE and FE decrease with increase in Biot number. With the same parameter of the experimental setup, the surface temperature, STE, and FE are analyzed by computational fluid dynamics (CFD). The surface temperature is calculated by experimental method, and CFD analysis is predicted with a maximum deviation of 0.4% and R2 values were 99.6%. For STE and FE, the average deviation between the present computations and the experimental computations was observed to be less than 1.8% and 2%—it is an acceptable range. Based on the above results, the thermodynamic model has been developed.

Effect of accumulated temperature on seed germination—a case study of 12 Compositae species on the eastern Qinghai-Tibet Plateau of China

Aim Temperature is an important environmental factor influencing seed germination. Our objective was to re- search the seed germination response of 12 Compositae species from the eastern Qinghai-Tibet Plateau of China to different temperatures using the accumulated temperature model. Methods All 12 species belong to four genera of Compositae. Seeds of each species were germinated at five constant temperatures (5, 10, 15, 20 and 25 °C), and germination was recorded once per day. We combined the logistic function and the accumulated temperature equation and used non-linear regression to estimate the base temperature and accumulated temperature for seed germination of each species. Important findings The average base temperature and accumulated temperature of the 12 species were 0 °C and 94.5 °C·d, respectively. The base temperature was lower and the accumulated temperature was higher than re- ported by previous researchers. These are the result of long-term adaptation to the temperature environment of the Qinghai-Tibet Plateau. There was a significant negative correlation between base temperature and accumulated temperature (p = 0.04). Therefore, species with lower base temperature would avoid the risk of seeds germinating earlier in an environment with changeable temperature. A significant positive correlation existed between seed mass and accumulated temperature (p = 0.01). Under relatively constant base temperature, small-seeded species germinated faster than large-seeded ones, giving them priority of germination in early succession.

Thermal Performance of a Functionally Graded Radial Fin

This paper investigates the steady-state thermal performance of a radial fin of rectangular profile made of a functionally graded material. The thermal conductivity of the fin varies continuously in the radial direction following a power law. The boundary conditions of a constant base temperature and an insulated tip are assumed. Analytical solutions for the temperature distribution, heat transfer rate, fin efficiency, and fin effectiveness are found in terms of Airy wave functions, modified Bessel functions, hyperbolic functions, or power functions depending on the exponent of the power law. Numerical results illustrating the effect of the radial dependence of the thermal conductivity on the performance of the fin are presented and discussed. It is found that the heat transfer rate, the fin efficiency, and the fin effectiveness are highest when the thermal conductivity of the fin varies inversely with the square of the radius. These quantities, however, decrease as the exponent of the power law increases. The results of the exact solutions are compared with a solution derived by using a spatially averaged thermal conductivity. Because large errors can occur in some cases, the use of a spatially averaged thermal-conductivity model is not recommended.

An experimental investigation on freckles formation during solidification of aqueous ammonium chloride

The formation of freckles during the unidirectional solidification of aqueous ammonium chloride from the bottom is investigated experimentally under a constant base temperature of -27 °C. The test rig could be inclined at15° and 30° and vibrated at several amplitudes of 2.54 mm, 4.45 mm and 6.35 mm under a constant frequency of 20 Hz. The effects of inclination angle and vibration on the freckles formation are investigated from the observations of channels and temperature distribution inside the solid and mushy zone. The application of vibration to the test cell shows that the mushy zone thickness and the number of channels are reduced. Channel suppression is influenced by the vibration amplitude, with the larger-amplitude vibration being more effective. The effect of inclination angle on the suppression on the occurrence of channels is negative.

Variations and Trends in Turkish Seasonal Heating and Cooling Degree-Days

The potential effect of climate change on energy demand is important especially for the developing and non-oil-producing countries. Cooling and heating degree-day (CDD and HDD) concepts are among the most significant meteorological variables related to residential energy consumption. This paper presents the spatial and temporal characteristics of Turkish seasonal CDD and HDD in the context of climate change. CDD and HDD are defined objectively by truncation of the temperature series at any constant base temperature level. This leads to surpluses and deficits as deviations. The surpluses are instances for cooling and the deficits for heating. Depending on temperature fluctuations, the degree-day statistics at any location show local and seasonal variations. In this study, regional variations of seasonal HDD and CDD are mapped for Turkey and their relations to local topography and climatic features are examined with conclusive interpretations. The sequential version of Mann–Kendall rank statisticis applied to demonstrate any existence of possible non-linear trends in accumulated HDD and CDD over the seasons. Spatially coherent and statistically significant trends of HDD and CDD appear in some regions of Turkey. In general, the sign of the trends is inconsistent with General Circulation Models (GCM) predictions.

PERFORMANCE ANALYSIS OF ECCENTRIC ANNULAR FINS WITH A VARIABLE BASE TEMPERATURE

The paper presents a numerical technique for the determination of the performance of eccentric annular fins with a variable base temperature. The differential equation for heat conduction in the fin has been written in a bipolar coordinate, which facilitates proper imposition of the boundary conditions. The control volume based finite difference method has been adopted to obtain the temperature distribution in the fin. Accuracy of the numerical result has been checked against that obtained from a semianalytical technique for the limiting condition of constant base temperature. Efficiencies of eccentric annular fins have been computed for different parametric variations. It has further been shown that for a nonuniform base temperature distribution, eccentric annular fins may dissipate more heat compared to a concentric fin of the same volume and there exists an optimum value of eccentricity that maximizes the rate of heat transfer. Therefore a saving in fin material may be achieved using eccentric annular fins if there exists a variation of base temperature.

Theoretical Risk Formulation for Degree-day Calculations

Energy consumption, agricultural activities and comfort in building design are all related to temporal temperature variations. Truncation of the temperature series at a constant base temperature level leads to surpluses and deficits as deviations. Surpluses are instances for cooling and deficits for heating. In meteorology and heat engineering these are referred to as cooling and heating degree-days, respectively. Since the temperature records are random in character their future predictions are necessary through statistical and probabilistic methods. In this paper, the degree-days are assumed to have a normal probability distribution function and therefore, their averages and standard deviations are considered sufficient for modeling cooling and heating degree-day amounts. Theoretical derivations are presented for degree-day risk calculations in their general forms and a simple implementation is given for two cities in Turkey.

Modeling Sea Ice as a Granular Material, Including the Dilatancy Effect

Abstract A dynamic sea ice model based on granular material rheology is presented. The sea ice model is coupled to both a mixed layer ocean model and a one-layer thermodynamic atmospheric model, which allows for an ice albedo feedback. Land is represented by a 6-m thick layer with a constant base temperature. A 10-year integration including both thermodynamic and dynamic effects and incorporating prescribed climatological wind stress and ocean current data was performed in order for the model to reach a stable periodic seasonal cycle. The commonly observed lead complexes, along which sliding and opening of adjacent ice floes occur in the Arctic sea ice cover, are well reproduced in this simulation. In particular, shear lines extending from the western Canadian Archipelago toward the central Arctic, often observed in winter satellite images, are present. The ice edge is well positioned both in winter and summer using this thermodynamically coupled ocean–ice–atmosphere model. The results also yield a sea ic...

Heat-capacity determination by temperature-modulated DSC and its separation from transition effects

Temperature-modulated calorimetry offers three methods of establishing heat capacity: (1) the traditional method of scanning thermal analysis by finding the heat flow into the sample during a measured temperature increase: (2) the quasi-isothermal method by finding the maximum amplitude of the periodic heat flow in response to a temperature modulation at a constant base temperature; and (3) the pseudo-isothermal analysis of a temperature-modulated scanning experiment by subtracting the effect due to the underlying (usually constant) heating rate and evaluating the effect due to the modulation as in a quasi-isothermal experiment. The background, advantages, and limitations of the three methods are discussed along with the possibility of establishing apparent heat capacities in dynamic systems, and the separation of heat capacities from phase transitions.