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Sorption-based atmospheric water harvesting (SAWH) holds huge potential due to its freshwater capabilities for alleviating water scarcity stress. The two essential parts, sorbent material and system structure, dominate the water sorption-desorption performance and the total water productivity for SAWH system together. Attributed to the superiorities in aspects of sorption-desorption performance, scalability, and compatibility in practical SAWH devices, hygroscopic porous polymers (HPPs) as next-generation sorbents are recently going through a vast surge. However, as HPPs' sorption mechanism, performance, and applied potential lack comprehensive and accurate guidelines, SAWH's subsequent development is restricted. To address the aforementioned problems, this review introduces HPPs' recent development related to mechanism, performance, and application. Furthermore, corresponding optimized strategies for both HPP-based sorbent bed and coupling structural design are proposed. Finally, original research routes are directed to develop next-generation HPP-based SAWH systems. The presented guidelines and insights can influence and inspire the future development of SAWH technology, further achieving SAWH's practical applications.

This perspective provides possible development paths for future advancement of continuously operated sorption and radiative sky cooling atmospheric water harvesting on material and system levels.

Dual-use devices offer a different path for more-sustainable living

Summary Condensation of humid air is an important process in thermal and process engineering and a subject of many currently research-intensive scientific domains, such as atmospheric water harvesting and seawater desalination. The nature of (water) vapor condensation in the presence of non-condensable gas (NCG) such as air differs significantly from the case with the pure, quiescent vapor condensation. In the literature, simple models that describe the forced flow condensation of water vapor in the presence of air on a series of vertical flat plates are hard to find. Here we present a simple and computationally efficient semi-empirical correlation describing forced flow condensation from humid air inside vertical channels formed by flat plates. The correlation accounts air as a non-condensing gas, different heights of vertical plates, and different thermal-hydraulic parameters. The correlation has been experimentally validated and shows excellent agreement, as 90% of theoretically predicted values are within ±12% of experimental data., Graphical abstract, Highlights • Experimental and theoretical study of humid air condensation on vertical plates • Unique condenser geometry was proposed, allowing re-use of condensation latent heat • A new correlation for humid air condensation on a series of plates was proposed • Potential application of correlation for fresh water generation was demonstrated, Physics; Interdisciplinary physics; Applied sciences

This paper presents the results of a thermo-economic and primary-energy-factor assessment based on the field-test results for a residential air-to-water heat pump (AWHP). The AWHP experimental setup consisted of a supervisory control and data-acquisition system, which was connected to a heat meter, an electricity meter, humidity and temperature sensors, a HP control system and a computer. Based on the experimental data, the 4-year-average seasonal performance factor was determined. This information was then applied in a thermo-economic and primary-energy-factor (PEF) analysis. The results served for a comparison of the AWHP with eight different heating systems (HSs). The results reveal that the considered AWHP represents the most thermo-economically efficient system in terms of the average final costs for heat production. The results of the PEF analysis reveal that the HS with the AWHP under investigation can be characterized as the most efficient system.

This paper presents a study of the thermal characteristics of a concentric-tube heat exchanger that is a key element in local ventilation device. The inner tube of the concentric-tube heat exchanger has a sinusoidal, wavy surface in the longitudinal direction, which enables heat-transfer enhancement. The tube can be stretched to a certain extent and thus change the corrugation of the heat-transfer surface area. We designed an experiment in which we used the Wilson-plot method to separately determine the convective heat-transfer coefficient on the inside and outside of the inner tube of the concentric-tube heat exchanger with different corrugation ratios. Based on the measurements correlation equations were developed to calculate the convective heat-transfer coefficient for any corrugation ratio, which allows us to simplify the design of local ventilation devices. Performed studies showed that, compared to a smooth tube, the convective heat-transfer coefficient increased only in the case of corrugated tubes with a corrugation ratio of less than 1.648, but the heat transfer was more intense for all considered corrugated tubes by 65–90% due to the increased heat-transfer surface area. The highest heat-transfer rate was observed for the case of the maximum-stretched tube with a corrugation ratio of 1.401, which is advantageous also in terms of material consumption.

This paper presents the results of a thermo-economic (TE), primary-energy-factor and CO2-equivalent (CO2 (eq)), emissions-sensitivity analysis for the preparation of sanitary hot water (SHW) in fourth-generation district-heating systems. The annual required additional heat for the SHW provided by a local heating unit, based on an air-to-water heat pump (AWHP), a natural-gas boiler (NG boiler), and an electrical resistance heater (ERH), was determined using a trnsys simulation. Additionally, the seasonal performance factor (SPF) of the HP under consideration was determined. The study considered three possible supply temperatures, i.e., 35, 40, and 45 °C. The results show that a local heating unit based on an AWHP is most efficient in terms of the used primary energy (PE) and CO2 (eq) emissions. This unit is also the second best in terms of TE performance. The unit based on a NG boiler is much more appropriate than an ERH unit in terms of both the primary energy factor (PEF) and the CO2 (eq) emission factors for an electricity generation mix (EGM) that has values higher than the average for the EU-28. The heat generated by this NG unit is also cheaper than the heat produced by an ERH based on the average price for electricity in the EU-28.

The condensation of humid air is a crucial step in air conditioning and process engineering. However, the models that describe the condensation of vapour in the presence of a non-condensable gas require time-consuming numerical calculations that go beyond the Nusselt film theory. Only a small number of publications exist, where simple and computationally effective correlations for the condensation of water vapour in the presence of air are presented for specially designed condenser heat exchangers. Therefore, the objective of this paper is to extend the existing semi-empirical correlations for different geometries and process parameters. For the purpose of the study, an experimental setup with two different condenser heat exchangers based on vertical plates (height 74 mm) and horizontal tubes (3 tubes, diameter 40 mm and 7 tubes, diameter 15 mm) was built. Additionally, based on existing correlations, we developed two semi-empirical models that predict the condensation mass flux for the proposed geometries. Here, we report that the agreement between the experimental and theoretical values predicted by the new, semi-empirical correlations is excellent, with an average uncertainty of less than ±6%. Their usability was demonstrated by a possibly significant performance improvement of the condenser inside a condensation-type tumble dryer.

This paper presents numerical and experimental energy and exergy performance assessments of solar thermal (ST), photovoltaic (PV) and photovoltaic/thermal (PV/T) modules based on roll-bond heat exchangers having three different channel geometries: serial, parallel and bionic. The validation of a coupled numerical simulation encompassing the thermo-hydraulic and electrical properties shows that 78% of all the data lies within a ± 10% uncertainty. The thermo-hydraulic simulation shows that the lowest outlet-water temperature inside the absorber is for the case of the bionic absorber (average 44.1 °C vs. 46.5 °C for the serial). This geometry is also beneficial when considering pressure losses, since compared to the parallel configuration (average 778 Pa) the bionic has significantly lower pressure losses (average 385 Pa). The simulation of the electrical properties of PV/T with all three absorber types showed the highest average solar-to-electrical efficiency (14.5%) in the case of the bionic absorber compared to the PV/T with parallel and serial absorbers (14.4% and 14.3%, respectively). Finally, a set of experiments using the ST, PV and PV/T2 (the index 2 denotes a PV/T collector variant with a foil thickness of 0.3 mm, compared to the thickness of 0.4 mm for PV/T1, positioned between the absorber and the PV cells) modules showed that the PV module, coupled with a bionic absorber plate, achieves the highest average electrical (PV – 8.5% vs. PV/T2 – 9.9%) and exergy (ST – 4.4% vs. PV – 9.2% vs. PV/T2 – 12.7%) efficiencies. Only in terms of the thermal efficiency, the PV/T is at a disadvantage to the ST (PV/T2 – 33.5% vs. ST – 61.4%) due to the air gap between the front glass and the absorber of the latter module.

This paper presents a one-dimensional, steady-state, analytical and a two-dimensional, steady-state, numerical approach to describe heat transfer in the complex solid structure of a skin evaporator used in household refrigerators. Both models are based on a specific form of the energy equation (the heat diffusion equation), which is solved to obtain the temperature distributions and heat flows within the different parts of the structure. Heat transfer is limited by a number of thermal resistances, such as the inner plastic wall of the refrigerator, the aluminum plate, the foil, the tube of the evaporator, and the air gaps. The insulation that prevents heat flowing into the evaporator from the surroundings is also taken into consideration. A comparison of the models showed that the root-mean-square deviation of the calculated temperatures ranged from 0.34 K to 0.60 K and that the area-weighted discrepancy of the calculated heat flows was 4.6%. Experimental validation of the model showed that the calculated and measured evaporator capacities were within ±12%. This demonstrates that several simplifications to the analytical model can be made, so drastically reducing the complexity of modeling a skin evaporator's structure, while retaining sufficient accuracy. These simplifications include reducing the heat transfer to one-dimensional heat conduction in the individual parts of the structure, neglecting the heat flux through the aluminum–air-gap contact, and linearizing the aluminum foil.

This paper presents an experimental and numerical heat transfer analysis of heat-pipe-based CPU coolers and a performance optimization methodology. The first part of the study focuses on the performance of two commercial HP-based CPU coolers under inclination angles of 0°, 90° and 180°. The results show that the 90° orientation provides the best thermal performance. The influence of heat pipe orientation on the performance of the entire system is obscured due to the much higher thermal resistance on the air-side of the cooler. A fourfold increase in air volumetric flow rate has only a minor effect on the cooling performance enhancement with a reduction of the thermal resistance from 0.11 K W [sup minus] 1 to 0.074 K W [sup minus] 1 at the highest heating power. In the second part of the study, heat transfer numerical simulations of the finned part of a cooler were performed and validated using experimental results. The output of the simulation is a 2-D temperature field, which is used as an input for the optimization methodology based on fin effectiveness and fin efficiency. Optimizing the fin geometry by removing unnecessary material yielded a 23% increase of the fin efficiency and decreased the weight of a fin by approx. 30%, proving the usefulness of the proposed methodology, which helps reduce costs, weight and development time of finned HP-based coolers.

Background The main purpose of this research was to develop a new method for differentiating between scoliotic and healthy subjects by analysing the curvatures of their spines in the cranio-caudal view. Methods The study included 247 subjects with physiological curvatures of the spine and 28 subjects with clinically confirmed scoliosis. The curvature of the spine was determined by a computer analysis of the surface of the back, measured with a non-invasive, 3D, laser-triangulation system. The determined spinal curve was represented in the transversal plane, which is perpendicular to the line segment that was defined by the initial point and the end point of the spinal curve. This was achieved using a rotation matrix. The distances between the extreme points in the antero-posterior (AP) and left-right (LR) views were calculated in relation to the length of the spine as well as the quotient of these two values LR/AP. All the measured parameters were compared between the scoliotic and control groups using the Student’s t-Test in case of normal data and Kruskal-Wallis test in case of non-normal data. Besides, a comprehensive diagram representing the distances between the extreme points in the AP and LR views was introduced, which clearly demonstrated the direction and the size of the thoracic and lumbar spinal curvatures for each individual subject. Results While the distances between the extreme points of the spine in the AP view were found to differ only slightly between the groups (p = 0.1), the distances between the LR extreme points were found to be significantly greater in the scoliosis group, compared to the control group (p

Background The main objective of the present method was to automatically obtain a spatial curve of the thoracic and lumbar spine based on a 3D shape measurement of a human torso with developed scoliosis. Manual determination of the spine curve, which was based on palpation of the thoracic and lumbar spinous processes, was found to be an appropriate way to validate the method. Therefore a new, noninvasive, optical 3D method for human torso evaluation in medical practice is introduced. Methods Twenty-four patients with confirmed clinical diagnosis of scoliosis were scanned using a specially developed 3D laser profilometer. The measuring principle of the system is based on laser triangulation with one-laser-plane illumination. The measurement took approximately 10 seconds at 700 mm of the longitudinal translation along the back. The single point measurement accuracy was 0.1 mm. Computer analysis of the measured surface returned two 3D curves. The first curve was determined by manual marking (manual curve), and the second was determined by detecting surface curvature extremes (automatic curve). The manual and automatic curve comparison was given as the root mean square deviation (RMSD) for each patient. The intra-operator study involved assessing 20 successive measurements of the same person, and the inter-operator study involved assessing measurements from 8 operators. Results The results obtained for the 24 patients showed that the typical RMSD between the manual and automatic curve was 5.0 mm in the frontal plane and 1.0 mm in the sagittal plane, which is a good result compared with palpatory accuracy (9.8 mm). The intra-operator repeatability of the presented method in the frontal and sagittal planes was 0.45 mm and 0.06 mm, respectively. The inter-operator repeatability assessment shows that that the presented method is invariant to the operator of the computer program with the presented method. Conclusions The main novelty of the presented paper is the development of a new, non-contact method that provides a quick, precise and non-invasive way to determine the spatial spine curve for patients with developed scoliosis and the validation of the presented method using the palpation of the spinous processes, where no harmful ionizing radiation is present.