Aviation is among the social sectors most impacted by the COVID-19 pandemic, and at the same time has contributed to the rapid global spread of the SARS-CoV-2 virus. SARS-CoV-2 is one of the coronaviruses that have led to outbreaks such as MERS-CoV in the past. This group of pathogens, as well as others that may be unknown at this time, will continue to challenge our society in the future. In order to be able to react better, a research training group was established at DLR in cooperation with 6 institutes, which will develop interdisciplinary approaches to researching and combating current and future pandemics. Engineers, physicists, software developers, biologists and physicians are working closely together on new concepts and the development of interdisciplinary knowledge in order to better control and contain future pandemics and to be able to react in a more targeted manner. One focus is the reduction of germ contamination in airplanes but also in other means of public transport such as buses and trains. In this review, we provide an overview of the baseline situation and possible approaches to address future pandemic challenges.

A semi-empirical model to predict the mass transfer rate of water from humid air in mixed convection together with the global heat transfer in a novel experimental set-up is presented. The cuboidal sample consists of isothermally cooled and heated plates with ventilation channels driving a mixed convective flow with inlet channel Reynolds numbers between 210 and 1270, Grashof numbers up to [[EQUATION]], and with relative humidities from 29% to 83% (at 25°C). The volumetric velocity field was measured by means of tomographic particle image velocimetry together with the fluid temperature and humidity. The measurement results are used to develop a one-dimensional model to predict the global heat and mass transfer by quantifying the dependency of the Nusselt and Sherwood number on the experimental boundary conditions. A relative deviation between the measurement results and the model prediction below 1% for the sensible heat transfer is reported, while the prediction of the vapor-mass transfer rate exhibits an average relative deviation below 6%.

A method for the measurement of position and size of sessile water droplets is presented. Droplets originate from condensation on a plane vertical surface in a vented cuboidal cavity with a mixed convective flow with humid air as the working fluid. Condensation is observed through a transparent cooling device coated with polyvinyl chloride with an average contact angle of 80.0(3) ^∘ . The implemented detection algorithm is based on the circle Hough Transform together with sophisticated pre- and post-processing steps, which are detailed in this work. Validation experiments yield a detection of over 97 13.8 m . Additionally, first experimental results of droplet size distributions are presented.

Portability, ease of use, robustness, and system cost are important parameters in designing flexible measurement systems. To this end, we introduce a cost-efficient and open-source measurement system based on consumer hardware for measuring air properties such as temperature, humidity, particle concentration in order to determine indoor air quality, thermal comfort, or air pollution. Cost and energy efficient sensor modules are integrated into an USB-based measurement interface that supports a wide range of communication protocols including Serial Peripheral Interface, Inter Integrated Circuit, Recommended Standard 232 and Recommended Standard 485. Moreover, the system provides a web interface and an application programming-interface that enables real time access to sensor data. In this paper we present the design of the hardware set-up, an overview of the sensors supported so far, and the software architecture as well as application examples.

Mass transfer in moist air flows with droplet condensation is determined by the mutual interaction of convective and latent heat transfer. To characterize the physical mechanisms of such flows, it is necessary to measure the condensation rate precisely. For this purpose, we applied three sophisticated measurement techniques to determine the mass transfer for droplet condensation on a cooled surface. The experimental set-up consists of a rectangular box with mixed convective airflow. Droplet condensation occurs on a subcooled vertical wall, which has a polymer surface with a droplet contact-angle of 80.07(28) degrees. Time series of the total water mass on the surface, the mass transfer-rate, and total heat transfer are measured for an inlet channel Reynolds number of 428 and at relative humidity between 29% and 83% (at 25 degrees C air temperature). The considered measurement techniques are: strain gauges for total water mass, capacitive humidity probes for mass difference between the inlet and outlet of the sample, and microscopy for the droplet distribution. In the work we present the evaluation and comparison of these measurement techniques, and discuss their advantages and disadvantages based on sample results.

ZUSAMMENFASSUNG Die Luftfahrt gehört zu den am stärksten durch die COVID-19-Pandemie beeinträchtigten gesellschaftlichen Bereiche und hat gleichzeitig zu einer raschen globalen Ausbreitung des SARS-CoV-2-Virus beigetragen. SARS-CoV-2 gehört zu den Coronaviren, die schon in der Vergangenheit zu Ausbrüchen wie MERS-CoV geführt haben. Diese Erregergruppe sowie weitere zum aktuellen Zeitpunkt möglicherweise noch unbekannte Erreger werden auch in Zukunft unsere Gesellschaft herausfordern. Um hier besser reagieren zu können, wurde am DLR unter Kooperation von 6 Instituten ein Graduiertenkolleg ins Leben gerufen, das interdisziplinäre Lösungsansätze zur Erforschung und Bekämpfung von aktuellen und zukünftigen Pandemien entwickeln wird. Dabei arbeiten Ingenieure, Physiker, Softwareentwickler, Biologen und Mediziner in enger Zusammenarbeit an neuen Konzepten und dem Aufbau fachgebietsübergreifenden Wissens, um zukünftige Pandemien besser kontrollieren und eindämmen zu können sowie gezielter reagieren zu können. Ein Schwerpunkt ist hierbei die Reduzierung der Keimbelastung in Flugzeugen aber auch anderen öffentlichen Verkehrsmitteln wie Bussen und Bahnen. In dieser Übersichtsarbeit geben wir einen Überblick über die Ausgangslage und mögliche Ansätze, um künftigen pandemischen Herausforderungen begegnen zu können.

We present an experimental study on the aerosol-dynamics within a test setup representing a class or conference room situation. To ensure realistic flow patterns, the blockage and heat release of the persons are simulated using 18 thermal manikins. The aerosol source is realized by a generator, attached to a thermal manikin, providing a realistic exhalation of artificial saliva. Two different ventilation scenarios are studied regarding aerosol concentration distribution and removal-efficiency. Additionally, the influence of a mask attached to the source and the effect of a moving person on the resulting aerosol concentrations are investigated. Time and spatially resolved concentrations are measured using 61 particulate matter sensors, installed on three height levels. The ventilation scenarios comprise window opening and a low-momentum ventilation concept, where the air is extracted underneath the ceiling and reenters purified (HEPA14) on floor level. Each of the examined counter measures (open-window, low-momentum ventilation and mask) resulted in a significant lower particle concentration compared to the reference scenario. The low-momentum ventilation with an air purifier unit provided the best aerosol removal-efficiency with a decrease in concentration of up to 96%, followed by the window opening with 60%. The buoyancy flow induced by the heat loads and the resulting flow field caused by the lowmomentum ventilation concept lead to well-directed particle transport towards the ceiling. Consequently, a large amount of aerosol was extracted and filtered by the ventilation system resulting in lower particle concentrations. However, local concentrations were strongly depended on the position of the aerosol source.

Temperature and humidity measurements are conducted in mixed convective humid-air duct flow with condensation. The latent and total heat transfer during the experiment are determined through the thermal balance for inlet temperatures from 27.5 ^∘ C to 35.5 ^∘ C, relative humidities from 30

We carried out an experimental study on the moisture transfer and the heat transport in warm and humid air flows between the cabin lining and the fuselage skin. The measurements were performed in a rectangular gap channel, representing the space between fuselage and cabin wall. Long-term measurements were performed for three configurations: without insulation, with fibreglass blanket and with melamine resin foam blanket. To simulate realistic flight conditions in a laboratory setup, we applied a concept of scaling. This concept is intended to guarantee similitude between the real flight conditions and the laboratory experiment. The results reveal that without insulation, the moisture transfer rate is much higher compared to the configurations with insulation blankets. With insulation, most of the water evaporates during ground conditions and just a small amount is entrapped in the insulation. Without insulation, just a small part of the frozen water evaporates on the ground. When comparing the two insulation blankets, it is found that they both have a similar heat transmittance coefficient. However, the condensation rate of the water and the resulting accumulation of water are significant, higher for the fibreglass blanket.

The heat transfer in mixed convective air flows with phase transition is a phenomenon which occurs in nature and a plethora of technical applications. When condensing materials form droplets, condensation leads to an increased heat transfer rate and therefore is advantageous in heat exchangers [1], whereas in other technical applications condensation is oftentimes undesirable. For instance, fogging on the windshield or headlights of motor vehicles leads to restrictions when driving and a reduction of optical transparency influences road safety. In addition, a considerable amount of thermal energy is required for defogging, which can have a negative effect on the range of electric cars [2]. The design and modification of these components with regard to optimizing dehumidification or preventing misting is often based on experience and intuition. Despite the enormous progress of numerical methods in recent years, there is still a lack of reliable and applicable models for the numerical simulation of condensation in general, and in particular of droplet condensation on surfaces. Due to the complexity of the physical processes that determine the heat transport and thus the fogging on the panes, reliable simulations are expensive and time-consuming, and therefore not suitable for industrial applications. Thus, the objective of the present study is to develop a model, using dimensionless numbers, which allows the prediction of the condensation behavior on panes based on a reduced parameter space. In such a configuration the mass transport of the vapor by phase transition, the resulting latent and the sensible heat transfer are determined by the physical processes of convection and diffusion, the boundary conditions and the material properties of the surfaces. In addition, the mass transfer of water vapor changes even with the smallest changes in the boundary conditions. A major challenge of this study is therefore to design and construct an experimental setup with the appropriate measurement technology, which meets the requirements of ensuring defined boundary conditions, reproducibility of the experiments and measurement accuracy. The setup corresponds to a generic replica of a vehicle headlamp. The air flow inside automotive headlights is the result of the superposition of forced and natural convection. The former is characterized by the Reynolds number Re = UL/ν and origins from ventilation holes at the rear wall of the cavity. The latter is a result of the heat emission from the internal light sources on the headlight’s back. This can be expressed using the Grashof number Gr = Lg∆T β/ν. β, g, ν are thermal expansion coefficient, gravitational acceleration and the kinematic viscosity of the working fluid air with respect to the current laboratory condition. The characteristic velocity U is equal to the mean inlet velocity and L is a characteristic system length, i.e. the ratio between the system volume and the inlet’s cross section. ∆T is the temperature difference between the mean temperature of the heating and the cooling plate. If the temperature of the windscreen Tc falls below the dew point Tdp, a vapor mass flow Ṁv occurs due to phase transition. Fogging of the pane thus depends on the flow velocity U , the air temperature Ta, the pane temperature Tc, the heat emission of the lamps Q̇l as well as on their temperature Th and the dew point temperature Tdp. The challenge is to provide an experimental setup that does not only exactly determine all these variables, but also controls them with high precision. For this purpose we have designed, developed and constructed an experimental setup that meets these requirements. The structure consists of a rectangular cavity that is heated at the rear and cooled at the front. To compensate pressure changes caused by temperature shifts, automotive headlights are designed as open systems to allow air exchange with the engine compartment. Hence, the configuration is equipped with an air inlet and an air outlet. This configuration maps all physical processes that determine the fogging of headlamp windshields. The dimensions of the sample are: length L = 0.5m, width W = 0.5m and height H = 0.25m. The air inlet and outlet extend over the entire cell height and have an aspect ratio of 0.1. Both are aligned parallel to the sample’s side walls. A sketch of the configuration is depicted in Fig. 1. The control setup shown in Fig. 2 consists of three control loops. The first loop is connected to the air inlet and splits up into a humidity and a temperature control cycle. The second closed loop cycle sets the temperature of the cooling plate. The transparency of the cooling plate is achieved by using paraffin oil which flows between two parallel glass walls. The third loop controls the air temperature of the housing around the condensation cell. The temperature is kept at the mean cavity temperature of

A state-of-the-art dashboard ventilation system was compared to novel ventilation concepts regarding the heating dynamics in a scale-up genetic car cabin (GCC). The concepts are based on the principle of displacement ventilation with air inlets at floor and ceiling level, well known from studies in aircraft cabins. In the present study, three vertical ventilation concepts were investigated experimentally in the GCC. With the aim to study different climate conditions, a jacket heating/ cooling was used to simulate winter and summer conditions. To simulate the heat release and the obstruction of passengers as well as to measure the thermal comfort four thermal manikins were placed in the GCC. To determine the relevant heat fluxes a plethora of temperature sensors was located at significant positions in the GCC. Furthermore, the surface temperatures were measured by means of an infrared camera. The studies clearly reveal the advantages of the vertical ventilation concept in comparison with the dashboard ventilation with reference to heat efficiency and thermal comfort at comparable boundary conditions.

A simplified state-of-the-art dashboard ventilation system was compared to novel ventilation concepts regarding the cooling dynamics in a full-scale generic car cabin (GCC). The concepts are based on the principle of displacement ventilation with air inlets at floor and ceiling level, well known from studies in aircraft cabins. In the present study, three vertical ventilation concepts were investigated experimentally in the GCC. With the aim to study different climate conditions, a jacket heating system was used to simulate summer conditions. Four thermal manikins were placed in the GCC to simulate the heat release and the obstruction of passengers as well as to measure the thermal comfort. To determine the relevant heat fluxes, a plethora of temperature sensors was installed at significant positions in the GCC. Furthermore, the surface temperatures were measured by means of an infrared camera. The study reveals significant differences in terms of cooling efficiency and thermal comfort for the different ventilation concepts.

Passenger comfort and ventilation efficiency in cars have attracted the attention of scientists and car manufacturers over the last years. The reason for this increase in interest is theconsiderable potential in terms of improving thermal passenger comfort, increasing efficiency and reducing energy consumption. To ensure a realistic measurement environment, a 1:1 scale generic mid range car was developed, constructed and used to simulate different season conditions. Four thermal manikins simulated the metabolism and obstruction of real passengers. To investigate both thermal comfort and ventilation efficiency, velocity and temperature measurements were performed for horizontal and low momentum vertical ventilation concepts. In particular vertical ventilation concepts turned out to be highly suitable in case of the new car models designed for autonomous driving. To assess thermal comfort with regard to temperature, velocity and radiation, the equivalent temperature of the thermal manikins was determined for steady state and dynamic conditions. Clear differences were found between the vertical and horizontal ventilation concepts. Especially for the heating scenario - representing winter conditions vertical ventilation reveals significant benefits in terms of thermal comfort and heating efficiency. However, in case of cooling for the summer scenario, the horizontal high momentum ventilation offers several advantages regarding thermal comfort. At the conference we would like to present a survey of our work on comfortable and efficient climatization of car cabins. To be more specific, the the results of an experimental study of thermal comfort, heating/cooling efficiency and ventilation efficiency for four different ventilation concepts will be presented.

Temperature and humidity measurements are performed in mixed convective moist-air duct flows for the Reynolds numbers \(Re = \) 2000, 4000 and 6000 with condensation at a cooled wall in a vertical rectangular duct. The width-to-height ratio is 10.66:1. A comparison of experimental results obtained with passive insulation on the wall opposite to the cooled wall for \(Re = 2000\) with results of direct numerical simulations performed under adiabatic boundary conditions reveals large differences. The latter are significantly reduced by realising an active insulation with isothermal boundary conditions. Using this set-up, it is shown that the heat and mass transfer in terms of the Nusselt and Sherwood number increase with the Reynolds number.

Abstract A low-momentum ceiling-based ventilation concept is compared to dashboard ventilation in a full-scale generic car cabin (GCC).The dimensions of the cabin correspond to the interior of a typical mid-size car. To provide different boundary conditions, representing winter and summer, the GCC is equipped with a jacket cooling/heating. Thermal manikins simulate the heat release and the obstruction of passengers. With the objective to verify the thermal comfort and the global heat transport characteristics in the GCC, the velocities as well as the air and surface temperatures are recorded. In the present study, the cooling and heating dynamics of the low-momentum ceiling ventilation are examined and compared to a simplified dashboard ventilation with regard to thermal comfort and heating/cooling efficiency. It is found that the cooling and heating dynamics of the low-momentum ventilation differ significantly in comparison with the dashboard ventilation. Overall the low-momentum ceiling offers several benefits regarding the thermal comfort and efficiency.

The flow structure formation and the dynamics in mixed convective air flow are studied experimentally in a miniaturised aircraft cabin equipped with thermal manikins. With the objective to obtain full-scale characteristic numbers for the down-scaled set-up, the measurements are conducted under high-pressure conditions \(P=19.6\) bar. Particle Image Velocimetry (PIV) is performed in order to determine the large-scale flow structures. The flow structure formation is analysed for a Grashof number range of \(8.06 \times 10^9 \le \mathcal {G}r \le 17.72 \times 10^9\) and a constant Reynolds number \(\mathcal {R}e = 1.5 \times 10^5\) to identify the impact of buoyancy flow on the supplied forced convective cold inflow. It is found that the flow structure formation and the velocity distribution strongly depend on the ratio of buoyancy to inertia forces. In conclusion, the structure formation of the flow and its dynamics are discussed in terms of their dependence on the Richardson number \(\mathcal {R}i \) considering the consequences for the thermal comfort of the passengers.

The thermal environment in interior spaces (e.g. cars, trains, aircrafts and office buildings) is often very inhomogeneous. Under such conditions, the human thermal sensation is influenced by a variety of thermal parameters, which renders the determination of the thermal comfort into a complex task. Especially the acquisition of single, pointwise quantities, such as air temperature, air velocity or surface temperatures, is insufficient for robust evaluation of the thermal comfort. The equivalent temperature, which combines several comfort-relevant quantities into a single integral quantity, is considered a mature quantity for the evaluation of passenger thermal comfort. Nowadays, only a few solitary systems exist to assess the thermal comfort based on equivalent temperatures experimentally. These are either very expensive or suitable for pointwise measurements only. However, simultaneous data acquisition at many different locations in the interior space is highly desired, generating the need for cost-effective yet precise systems. These systems are supposed to provide access to local equivalent temperatures and further, especially if convection-driven ventilation systems are considered, to simulate the heat impact of real passengers as well. To accomplish this task, thermal passenger manikins of the German Aerospace Center (DLR) have been turned into thermal comfort manikins. In order to enable the measurement of equivalent temperatures for several body parts, the thermal manikin is calibrated in a thermally isolated, temperature-controlled test chamber. Herein, the surface temperature of the manikin is measured using high-definition infrared thermography. This offers the possibility to calculate local equivalent temperatures at a spatial resolution of 10 cm and with a precision better than ±0.5 K. At the conference we are going to present the thermal manikin and the whole technical procedure regarding the calibration in detail. The performance of the manikin is going to be demonstrated for dedicated ventilation cases in aircraft, car and train cabin models.

A low-cost and practicable measurement instrument which allows the simulation of the heat loads and the obstruction of a human passenger, while simultaneously determining the thermal comfort, is highly desirable. At the DLR, a TM was developed which meets these requirements. The TM reveals a simplified, however, realistic shape and heat load of a human body. Furthermore, we defined a process chain to calibrate the TM in order to use it as an instrument for evaluating the thermal passenger comfort. However, the TM is continuously being developed further. Current projects address the topics of dimensionless characterization of the TM with the objective to identify the physical quantities which determine thermal comfort.

Konvektive Stromungen mit Phasenubergang treten in vielen technischen Anwendungen und alltaglichen Situationen auf. Oft stellt die Kondensation dabei einen ungewunschten Effekt dar. So fuhren beispielsweise Leckagestromungen in der Flugzeugkabine zu Kondensatbildung zwischen Innen- und Ausenwand. Uber mehrere Flugzyklen sammelt sich Wasser in der Isolierung und fuhrt so zu einer Gewichtserhohung, einer geringeren Isolationswirkung und fordert Korrosion. Zur Beschreibung des Skalenverhaltens des Stoff- und Warmetransports durch Kondensation in Abhangigkeit der Temperatur wurde eine experimentelle Studie in einem rechteckigen Stromungskanal mit isothermer Kuhlplatte durchgefuhrt. Im Rahmen des Workshops sollen die weiteren Ergebnisse zu der hier diskutierten Parametervariation vorgestellt werden.

An experimental study of heat and mass transfer in convective flows of humid air has been performed in a vertical, one-sided cooled duct. The analysis of the results focusses on the heat transfer due to phase changes as a function of different wall, system and dew point temperatures. We introduce a set of characteristic numbers, which are deduced from the basic equations for mass, momentum, energy and diffusion to identify possible scaling relations. Experiments are performed within the parameter range of Re ~ 6.1 × 104, 0.025 ≤ Reδ ≤ 0.107, Pr ~ 0.71, Ja ~ 1.7 × 10−2 and Fr ~ 0.116. A linear relation between condensation and convective heat transfer is detected in this parameter range. The experimental results show good agreement with Nusselt's theory of laminar film condensation and Shah's correlation for condensation in vapour ?ows.