AN EXPERIMENTAL INVESTIGATION OF THE GOVERNING PROPERTIES IN A VORTEX TUBE

Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes dates back at least nine decades, some mystery surrounding the phenomenon remains to this day. These devices split an incoming stream of fluid into two streams—one with a greater total temperature than the incoming fluid and the other with a lower total temperature. This temperature separation is accomplished with no moving parts and no external sources of energy including heat transfer to or from the device. In attempts to understand the physics of the temperature separation, previous researchers have characterized the effect through various inlet temperatures and pressures as well as various gases with different properties. Unfortunately, the findings documented in the literature are sometimes inconsistent indicating the possibility that previously uncontrolled properties and flow conditions govern temperature separation to an unappreciated degree. In the present research, two new flow characteristics are examined for their role in temperature separation—volumetric heat capacity, ρC_p, and nozzle velocity. In the present experiments with air, it was found that by matching nozzle velocity and ρC_p—even with disparate pressures, temperatures, Reynolds numbers, and Mach numbers—the resulting temperature separation curves are identical. This is the first known documentation of such a finding. The results suggest that nozzle velocity is fundamental to scaling the performance of a vortex tube, while the nozzle volumetric heat capacity is also relevant to its behavior.

Testing a Gypsum Composite Based on Raw Gypsum with a Direct Admixture of Paraffin and Polymer to Improve Thermal Properties

The implemented new legal regulations regarding thermal comfort, the energy performance of residential buildings, and proecological requirements require the design of new building materials, the use of which will improve the thermal efficiency of newly built and renovated buildings. Therefore, many companies producing building materials strive to improve the properties of their products by reducing the weight of the materials, increasing their mechanical properties, and improving their insulating properties. Currently, there are solutions in phase-change materials (PCM) production technology, such as microencapsulation, but its application on a large scale is extremely costly. This paper presents a solution to the abovementioned problem through the creation and testing of a composite, i.e., a new mixture of gypsum, paraffin, and polymer, which can be used in the production of plasterboard. The presented solution uses a material (PCM) which improves the thermal properties of the composite by taking advantage of the phase-change phenomenon. The study analyzes the influence of polymer content in the total mass of a composite in relation to its thermal conductivity, volumetric heat capacity, and diffusivity. Based on the results contained in this article, the best solution appears to be a mixture with 0.1% polymer content. It is definitely visible in the tests which use drying, hardening time, and paraffin absorption. It differs slightly from the best result in the thermal conductivity test, while it is comparable in terms of volumetric heat capacity and differs slightly from the best result in the thermal diffusivity test.

The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

Effects of sonication and freezing on the color, mechanical and thermophysical properties of osmo-microwave-vacuum dried cranberries

The aim of study was to determine the effects of sonication (S), convective freezing (F), convective freezing preceded by sonication (SF) as well as cryogenic freezing (N) on the osmo-microwave-vacuum drying kinetics, energy usage and properties of dried cranberries such as moisture content, moisture diffusion, water activity, density, porosity, thermal conductivity, thermal diffusivity, volumetric heat capacity, lightness, redness, yellowness, total differences in color, saturation and hue, hardness, cohesiveness, springiness, and chewiness. Osmo-microwave-vacuum drying of cranberries took from 13.5 to 16.0 min. All initial treatments increased the moisture diffusivity and thus reduced the drying time. The most energy effective method was osmo-microwave-vacuum drying preceded by sonication (S) of fruits. Osmo-microwave-drying of cranberries subjected to convective freezing preceded by sonication (SF) resulted in the highest lightness (32.5 ± 0.5), redness (33.9 ± 0.7), and yellowness (11.3 ± 0.5) of fruits, as well as the lowest cohesion (the lowest resistant to stress associated with manufacturing, packaging, storage, and delivery). The lowest hardness, i.e. 12.3 ± 0.4 N and the highest cohesiveness and springiness, i.e. 0.38 ± 0.02 and 0.74 ± 0.03 of dried fruits, were noted for berries subjected to initial cryogenic freezing (N). Cryogenic freezing (N) combined with osmo-microwave-vacuum drying resulted in the largest color changes of fruits and the highest thermal conductivity. Sonicated and convectively frozen (SF) fruits were characterized by the highest thermal diffusivity. Sonication (S), convective freezing (F) and their combination (SF) significantly reduced the volumetric heat capacity of cranberry fruits.

Specific Heat and Volumetric Heat Capacity of Some Saudian Soils as affected by Moisture and Density

The ability to monitor soil heat capacity is an important mean in managing the soil temperature regime, which in turn, affects its ability to store heat. The effect of water content and bulk density on the specific heat and volumetric heat capacity of two Saudian soils (sand and loam) was investigated through laboratory studies. These laboratory experiments used the calorimetric method to determine specific heat of soils. For the type of soils studied, specific heat increased with increased moisture content. Also, volumetric heat capacity increased with increased moisture content and soil density. Volumetric heat capacity ranged from 1.55 to 3.50 for loam and from 1.06 to 3.00 MJ/m3 / o C for sand at moisture contents from 0 to 0.20 (kg/kg) and densities from 1200 to 1400 kg/m3 . Specific heat ranged from 1140 to 2090 for loam and from 800 to 1530 J/kg/ oC for sand at moisture contents from 0.01 to 0.20 (kg/kg) and soil density of 1200 kg/m3 . The volumetric heat capacity and specific heat of soils observed in this study under varying moisture content and soil density were compared with independent estimates made using derived theoretical relations. The differences between the observed and predicted results were very small. Loam soil generally had higher specific heat and volumetric heat capacity than sandy soil for the same moisture content and soil density.

Thermal Characterization of Phantoms Used for Quality Assurance of Deep Hyperthermia Systems

Tissue mimicking phantoms are frequently used in hyperthermia applications for device and protocol optimization. Unfortunately, a commonly experienced limitation is that their precise thermal properties are not available. Therefore, in this study, the thermal properties of three currently used QA phantoms for deep hyperthermia are measured with an “off-shelf” commercial thermal property analyzer. We have measured averaged values of thermal conductivity (k = 0.59 ± 0.07 Wm−1K−1), volumetric heat capacity (C = 3.85 ± 0.45 MJm−3K−1) and thermal diffusivity (D = 0.16 ± 0.02 mm2s−1). These values are comparable with reported values of internal organs, such as liver, kidney and muscle. In addition, a sensitivity study of the performance of the commercial sensor is conducted. To ensure correct thermal measurements, the sample under test should entirely cover the length of the sensor, and a minimum of 4 mm of material parallel to the sensor in all directions should be guaranteed.

Sensitivity analysis of the PALM model system 6.0 in the urban environment

Sensitivity of the PALM model 6.0 is tested in a real urban environment in the vicinity of a typical crossroad in a densely built-up residential area in Prague, Czech Republic. Two types of scenarios are employed. First are the synthetic scenarios altering mainly surface and material parameters such as albedo, emissivity or wall conductivity, testing sensitivity of the model simulations to potentially erroneous setting of model inputs. Second, real-life type scenarios are analyzed, in which commonly considered urban heat island mitigation measures are applied, such as greening of the streets or changing surface materials. For the first-type scenarios, surface parameters used in radiation balance equations are found to be the most sensitive overall followed by volumetric heat capacity and thermal conductivity of walls. Other parameters show limited average effect, however, some can still be significant in some parts of the day, such as surface roughness in the morning hours. Second type, the mitigation scenarios, show urban vegetation to be the most effective measure, especially when considering both physical and biophysical temperature indicators. Influence of both type scenarios was also tested for air quality, specifically PM10 dispersion which generally shows behaviour opposite to thermal indicators, ie., improved thermal comfort brings deterioration of PM10 concentrations.