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Few studies have used a multidimensional approach to describe lifestyle changes among undergraduate students during the COVID-19 pandemic or have included controls. This study aimed to evaluate lifestyle behaviors and mental health of undergraduate students and compare them with an age and sex-matched control group. A cross-sectional web survey using snowball sampling was conducted several months after the beginning of COVID-19 pandemic in Spain. A sample of 221 students was recruited. The main outcome was the total SMILE-C score. Students showed a better SMILE-C score than controls (79.8 + 8.1 vs. 77.2 + 8.3; p < 0.001), although these differences disappeared after controlling for covariates. While groups did not differ in the screenings of depression and alcohol abuse, students reported lower rates of anxiety (28.5% vs. 37.1%; p = 0.042). A lower number of cohabitants, poorer self-perceived health and positive screening for depression and anxiety, or for depression only were independently associated (p < 0.05) with unhealthier lifestyles in both groups. History of mental illness and financial difficulties were predictors of unhealthier lifestyles for students, whereas totally/moderate changes in substance abuse and stress management (p < 0.05) were predictors for the members of the control group. Several months after the pandemic, undergraduate students and other young adults had similar lifestyles.

The present paper evaluates a jet ejector refrigeration system intended to cool down diesel engine intake below ambient conditions. Performance is assessed by means of 1D thermodynamic model of the cycle fed with ejector maps obtained with CFD code using R134a as working fluid. In the first study, no particular ejector geometry is fixed thus allowing the genetic algorithm to adapt the cycle to different engine conditions. Following this approach engine intake temperatures close to 0 ° can be attained in those engine operating points in which exhaust thermal power is sufficient to drive the jet-ejector refrigeration system. In the second evaluation, ejection cycle configuration which provided best results for the most frequent operating point in a standard driving, designated as 2000 rpm and 50% load, is selected. With this particular configuration the rest of engine operating points are reassessed. In this study performance degradation is found away from the design point showing that ejector size is a limiting factor.

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In the present paper, a numerical investigation of a jet-ejector is carried out using a real gas model of R1234yf. The prototype under investigation works with specific operating conditions of a jet-ejector refrigeration system intended for waste heat recovery in an internal combustion engine (ICE). In the first instance, the geometry optimization involving nozzle exit diameter, mixing chamber diameter, and nozzle exit position (NXP) is performed. Once the optimum geometry has been obtained, the jet-ejector prototype is tested with different operating pressure ratios to determine its off-design performance. The flow structure in relevant cases has been examined with an emphasis on critical and subcritical modes. The flow phenomena occurring during expansion, entrainment, and mixing processes are discussed so performance degradation can be directly related to physical processes. The analysis has been completed fitting simulated points to critical and subcritical planar surfaces. The results in terms of goodness of fit are satisfactory so the jet-ejector performance in off-design operating conditions can be reflected through simple mathematic models. When the overall cycle is assessed by using previous computational fluid dynamics (CFD) maps, it is observed that the achievable cooling drops significantly when an ambient temperature of 31 °C is exceeded.