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Growing demand for air conditioning in recent years has caused a significant increase in demand for primary energy resources. Solar-powered cooling is one of the environmentally-friendly techniques which may help alleviate the problem. A promising solar cooling method is through the use of a liquid desiccant system, where humidity is absorbed directly from the process air by direct contact with the desiccant. The desiccant is then regenerated, again in direct contact with an external air stream, by solar heat at relatively low temperatures. The liquid desiccant system has many potential advantages over other solar air conditioning systems and can provide a promising alternative to absorption or to solid desiccant systems. Earlier work by the authors included theoretical simulations and preliminary experiments on the key components of the liquid desiccant system. The objective of the present study has been to construct a prototype system based on the knowledge gained, to monitor its performance, identify problems and carry out preliminary design optimization. A 16 kWt system was installed at the Energy Engineering Center at the Technion, in the Mediterranean city of Haifa. The system comprises a dehumidifier and a regenerator with their associated components operating together to dehumidify the fresh (ambient) air supply to a group of offices on the top floor of the building. LiCl-water is employed as the working fluid. The system is coupled to a solar collector field and employs two methods of storage--hot water and desiccant solution in the regenerated state. The performance of the system was monitored for five summer months under varying operating conditions. The paper describes the operation of the experimental system and presents the measured data and the calculated performance parameters. Keywords: Solar cooling; Solar air conditioning; Dehumidification; Liquid desiccant; Open absorption

The growing demand for air conditioning, particularly in hot and humid climates has caused a significant increase in demand for energy resources. A promising solar technology with potential to alleviate the problem is an open absorption system, where humidity is absorbed directly from the air to be treated by direct contact with the absorbent. The absorbent is then regenerated, again in direct contact with an external air stream, at relatively low temperatures of the heat source. The paper describes a study of a liquid desiccant cooling system designed to air-condition a group of offices on the top floor of a building in the Mediterranean city of Haifa, Israel. The system is capable of using as its source of power low-grade solar heat, of the type obtainable from low-cost flat plate collectors, and has a potential to provide both cooling and dehumidification in variable ratios, as required by the load. Several cycle variations have been considered, corresponding to different design options. A parametric study shows that entrance conditions of the ambient air significantly affect the heat and mass transfer occurring during the dehumidification process. The temperatures and flow rates of the heating and cooling water and the flow rates of solution through the dehumidifier and regenerator affect the humidity of the supply air delivered to the conditioned space, and show an optimum in certain cases. [DOI: 10.1115/1.1690284] Keywords: Dehumidifier, Evaporator, Regenerator, Absorber, Cooling, Dehumidification, Air Conditioning

In earlier work, a novel open absorption cycle was proposed, capable of producing both cooling and dehumidification for air conditioning, utilizing low-grade heat. The system, referred to as DER (Dehumidifier-Evaporator-Regenerator), uses ambient air in conjunction with an absorbent solution; the air is dehumidified and then employed to produce chilled water in an evaporative cooler Alternatively, a portion of the dehumidified air may be used directly for air conditioning purposes. The system thus has the potential to provide both cooling and dehumidification in variable ratios, as required by the load. Computer simulations and theoretical investigations were carried out to analyze and predict the performance of the system. The objective of the present study has been to construct a laboratory system to test the concept, identify problems and carry out preliminary design optimization. The characteristic performance of individual components, analyzed theoretically in the simulation, was studied experimentally. Measurements have provided much-needed realistic data about heat and mass transfer coefficients. The performance of the system has been studied under varying operating conditions. The paper describes the operation of the experimental system and presents the measured data and the resulting transfer coefficients. [DOI: 10.1115/1.1643075] Keywords: Dehumidifier, Evaporator, Regenerator, Absorber, Cooling, Air Conditioning

This paper describes the results of a search for an optimum profile that will maximize the dynamic stability of gas lubricated ringless pistons. Previous work indicated that the common cylindrical piston design is not the best choice for this purpose. Many noncylindrical profiles were investigated for ringless pistons used in helium gas cryocoolers. An improved design was found that considerably extends the range of stable operation of these systems.

A parametric study is performed for a relatively large size helium cryocooler which utilizes a ringless piston. The results are presented in a dimensionless form and may be useful for other ringless-piston systems as well. Altogether twelve different parameters were studied and their effect on piston stability and sealing performance was analyzed and discussed. Although the cylindrical piston shape is commonly used for ringless piston applications, it seems that this is not the best choice for an optimum design.

A mathematical model is developed for analyzing the dynamics of gas lubricated ringless pistons. It takes into account the effects of piston-cylinder geometry, dynamic properties of piston and connecting rod, and operating conditions. A corresponding computer program is described which enables to obtain the piston trajectory and evaluate its stability. Preliminary results are presented for a reference case of a cryocooler which uses a stirling cycle design where helium gas is compressed by a motor driven piston. It is found that the connecting rod inertia plays an important role in stabilizing the piston motion. It is also found that the stability of piston motion strongly depends on the thermohydrodynamic condition of operation. Under isothermal condition the piston can be stable while under adiabatic condition its dynamic equilibrium may be unstable.

In the absence of gravity, surface tension dominates over the behavior of liquids. While this often poses a challenge in adapting Earth-based technologies to space, it can also provide an opportunity for novel technologies that utilize its advantages. In particular, surface tension drives a liquid body to a constant-mean-curvature shape with extremely smooth surfaces, properties which are highly beneficial for optical components. We here present the design, implementation and analysis of parabolic flight experiments demonstrating the creation and in-situ measurement of optical lenses made entirely by shaping liquids in microgravity. We provide details of the two experimental systems designed to inject the precise amount of liquid within the short microgravity timeframe provided in a parabolic flight, while also measuring the resulting lens' characteristics in real-time using both resolution target-imaging and Shack-Hartmann wavefront sensing. We successfully created more than 20 liquid lenses during the flights. We also present video recordings of the process, from the lenses' creation during microgravity and up until their collapse upon return to gravity. The work thus demonstrates the feasibility of creating and utilizing liquid-based optics in space., (© 2023. Springer Nature Limited.)

We present a new method for accurate detection of sample location in peak mode isotachophoresis (ITP). The technique is based on the design of a microchannel with multiple constrictions and on detecting the passage of the ITP interface through these constrictions. We achieve this by monitoring the electric current across the channel, which exhibits sharp decreases as the ITP interface moves more rapidly through the higher current density constrictions. We show that cross-correlation between the electric current signal and a predefined step function is an effective method for detecting changes in the slope of the electric current curve in real-time and is robust to changes in the composition of the buffers. We demonstrate the use of the technique to deliver sample to a designated location in the channel with an accuracy as low as 50 μm. Importantly, the method does not require the use of any optics and thus can be used to monitor the location of unlabeled species for application in a variety of ITP assays.