Measurement of the interfacial temperature jump during steady-state evaporation of a droplet

Evaporation is an important phenomena that occurs in a wide range of natural and industrial processes. Although this phenomena has been a subject of research for many years, it is still not fully understood.\u3cbr/\u3eExperimental results of the last few decades seem to contradict with each other, and with the theory which describes this process, e.g. the kinetic theory of gasses (KTG) and non-equilibrium thermodynamics (NET). Temperature jumps of about 3.2-8.1oC at the interface of a steady state evaporating water droplet\u3cbr/\u3eat a pressure of about 245 Pa were measured . In order to determine whether this temperature jump exists and what influences this temperature jump, an experimental setup has been developed and the results are compared to theory

Local clothing thermal properties of typical office ensembles under realistic static and dynamic conditions

\u3cp\u3eAn accurate local thermal sensation model is indispensable for the effective development of personalized conditioning systems in office environments. The output of such a model relies on the accurate prediction of local skin temperatures, which in turn depend on reliable input data of the local clothing thermal resistance and clothing area factor. However, for typical office clothing ensembles, only few local datasets are available in the literature. In this study, the dry thermal resistance was measured for 23 typical office clothing ensembles according to EN-ISO 15831 on a sweating agile manikin. For 6 ensembles, the effects of different air speeds and body movement were also included. Local clothing area factors were estimated based on 3D scans. Local differences can be found between the measured local insulation values and local area factors of this study and the data of other studies. These differences are likely due to the garment fit on the manikin and reveal the necessity of reporting clothing fit parameters (e.g., ease allowance) in the publications. The increased air speed and added body movement mostly decreased the local clothing insulation. However, the reduction is different for all body parts, and therefore cannot be generalized. This study also provides a correlation between the local clothing insulation and the ease allowance for body parts covered with a single layer of clothing. In conclusion, the need for well-documented measurements is emphasized to get reproducible results and to choose accurate clothing parameters for thermo-physiological and thermal sensation modeling.\u3c/p\u3

Local thermal sensation modeling: a review on the necessity and availability of local clothing properties and local metabolic heat production

Local thermal sensation modelling gained importance due to developments in personalized and locally applied heating and cooling systems in office environments. The accuracy of these models depends on skin temperature prediction by thermophysiological models, which in turn rely on accurate environmental and personal input data. Environmental parameters are measured or prescribed, but personal factors such as clothing properties and metabolic rates have to be estimated. Data for estimating the overall values of clothing properties and metabolic rates are available in several papers and standards. However, local values are more difficult to retrieve. For local clothing, this paper revealed that full and consistent data sets are not available in the published literature for typical office clothing sets. Furthermore, the values for local heat production were not verified for characteristic office activities, but were adapted empirically. Further analyses showed that variations in input parameters can lead to local skin temperature differences (∆Tskin,loc=0.4 – 4.4ºC). These differences can affect the local sensation output, where ∆Tskin,loc=1ºC is approximately one step on a 9-point thermal sensation scale. In conclusion, future research should include a systematic study of local clothing properties and the development of feasible methods for measuring and validating local heat production. Local thermal sensation modelling gained importance due to developments in personalized and locally applied heating and cooling systems in office environments. The accuracy of these models depends on skin temperature prediction by thermophysiological models, which in turn rely on accurate environmental and personal input data. Environmental parameters are measured or prescribed, but personal factors such as clothing properties and metabolic rates have to be estimated. Data for estimating the overall values of clothing properties and metabolic rates are available in several papers and standards. However, local values are more difficult to retrieve. For local clothing, this paper revealed that full and consistent data sets are not available in the published literature for typical office clothing sets. Furthermore, the values for local heat production were not verified for characteristic office activities, but were adapted empirically. Further analyses showed that variations in input parameters can lead to local skin temperature differences (∆Tskin,loc=0.4 – 4.4ºC). These differences can affect the local sensation output, where ∆Tskin,loc=1ºC is approximately one step on a 9-point thermal sensation scale. In conclusion, future research should include a systematic study of local clothing properties and the development of feasible methods for measuring and validating local heat production

Challenges in modelling local thermal sensation

Recent research on local heating and cooling design show improvements in thermal comfort and energy consumption of office buildings. The impact of these measures on the occupants’ local thermal sensation (LTS) may be investigated using thermophysiological and coupled thermal sensation models. To evaluate their ability to model local skin temperatures and LTS accurately, this paper analyses the most important factors in the thermal modelling concept: 1) the accuracy of the input data for local clothing properties and local muscular metabolic heat distribution, 2) the deviations between computed and measured local skin temperatures, and 3) neurophysiological and dynamic aspects that are missing in LTS models. To fill these gaps, further research might emphasis on 1) performing detailed measurements on local clothing and metabolic input data, 2) a re-evaluation of local heat balances in the thermophysiological models and including blood pressure effects and 3) including more neurophysiology in LTS models. Recent research on local heating and cooling design show improvements in thermal comfort and energy consumption of office buildings. The impact of these measures on the occupants’ local thermal sensation (LTS) may be investigated using thermophysiological and coupled thermal sensation models. To evaluate their ability to model local skin temperatures and LTS accurately, this paper analyses the most important factors in the thermal modelling concept: 1) the accuracy of the input data for local clothing properties and local muscular metabolic heat distribution, 2) the deviations between computed and measured local skin temperatures, and 3) neurophysiological and dynamic aspects that are missing in LTS models. To fill these gaps, further research might emphasis on 1) performing detailed measurements on local clothing and metabolic input data, 2) a re-evaluation of local heat balances in the thermophysiological models and including blood pressure effects and 3) including more neurophysiology in LTS models

The influence of gas-wall interactions on the accommodation coefficients for rarefied gases:a molecular dynamics study

The energy accommodation coefficient (EAC) and the momentum accommodation coefficient (MAC) are two significant parameters determining the gas-solid energy and momentum exchange efficiencies. In this work,\u3cbr/\u3emolecular dynamics (MD) simulations were employed to study the impact of gas-wall interaction potential on energy and momentum accommodation coefficients between Gold and monoatomic gases (Argon and\u3cbr/\u3eHelium). The MD simulation setup consists of two infinite parallel plates of unequal temperature positioned at certain distance (12 nm and 102 nm for Argon and Helium gases, respectively) apart from each other, and\u3cbr/\u3eof gas molecules confined between them. A pairwise Lennard-Jones 12-6 potential was considered at the solid-gas interface. The interaction potential parameters were obtained using the Lorentz-Berthelot (LB) and Fender-\u3cbr/\u3eHalsey (FH) mixing rules, as well as based on existing ab-initio computations. Comparing the obtained results for the accommodation coefficients with empirical values revealed that the interaction potential based on abinitio\u3cbr/\u3ecalculations is the most reliable one for computing ACs. Besides, in the case of Au-Ar, the LB mixing rule substantially overpredicts the potential well depth which leads to sticking gas atoms on the solid surface. As a result, computing accommodation coefficients in this case from numerical point of view was not possible