Investigation of Thermal Performance of Nanoparticle Enhanced Ionic Liquids (NEILs) for Solar Collector Applications

Concentrated Solar Power (CSP) is a prominent alternative energy technology, where mirrors or lenses are used to concentrate sunlight from a large area and stored in a collector filled with heat transfer fluid (HTF). The energy from this HTF is used to produce steam for power generation. CSP system requires high heat storage capacity and thermally stable HTF to reduce its operating cost. Having suitable thermophysical properties, ionic liquids (ILs) is considered as a potential HTF for the CSP applications; however thermophysical properties of ILs can be further enhanced by dispersing small volume percentages of nanoparticles. This liquid is called Nanoparticle Enhanced Ionic Liquids (NEILs). The present research focuses on the experimental and numerical evaluation of the NEILs as a potential working fluid for the CSP applications. The experimental assessment includes thermophysical property measurements, and convective heat transfer (forced and natural convection) performance evaluation. For this research, four representative ILs ([C4mpyrr][NTf2], [C4mim][NTf2]. [C4mmim][NTf2], [N4111][NTf2]) are selected. The thermophysical properties of Al2O3 NEILs demonstrate enhanced density, thermal conductivity, viscosity, and heat capacity compared to the base ILs. Plausible reasons of enhanced properties are discussed and compared with the existing model. To evaluate the forced convection performance of ILs and NEILs experiments are conducted in a circular tube with constant heat flux condition. The experimental results obtained for ILs correlate well with the Shah’s equation in laminar flow condition and Gnielinski’s equation for turbulent flow condition. Whereas, results obtained for NEILs show higher forced convection heat transfer coefficient than the base ILs. This is due to enhanced thermal conductivity and particle migration behavior in the boundary layer. The numerical simulation by FLUENT also shows the enhancement of heat transfer coefficient of NEILs compared to base ILs. Natural convection experiments were performed in rectangular cavity with different aspect ratios (1 and 1.5) heated from below. New correlations for Nusselt Number as a function of Rayleigh number is proposed for ILs. It is noted that the natural convection behavior of NEILs demonstrates much lower heat transfer coefficient compared to the base ILs. The relative change of effective thermophysical properties are not fully responsible for the degradation of the natural convection of NEILs which also confirms the numerical simulation of natural convection of ILs and NEILs. In addition to thermophysical properties, particle-fluid interaction and clustering of nanoparticles also plays a role in degrading the natural convection heat transfer

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely