Numerical investigation on the performance of the helical and conical coil heat exchanger configuration in the dynamic mode of heat extraction

. Owing to the high heat transfer performance, compact design and large surface area per unit volume, the curved and helical circular tubes have many applications such as heating, refrigeration, air conditioning, steam generation, heat extraction etc. One of the ways to improve the performance of water heating systems is to enhance the performance of immersed heat exchanger. In solar heating systems, immersed heat exchangers of curved shape are used to charge and discharge sensible heat water storage tanks. Effect of arrangement and position of the tubes, geometry of coil, configuration, shape, flow rate, type of working fluid, Reynolds number associated with flow, and inlet temperature to coil, on the performance of storage systems have been studied in the literature. Rate of discharge, heat transfer coefficient, effectiveness of heat exchanger, heat transfer rate, discharging efficiency and increment in temperature of outlet fluid are the standard performance parameters to evaluate the heat transfer and fluid flow phenomenon in the curved tubes. Heat transfer characteristics are investigated and analyzed for one helical and two conical coil (conical and inverted conical) configurations using a three-dimensional unsteady numerical model. The numerical model is validated against reported experimental result and a good agreement is found. For the same length of the coil, the inverted conical configuration presents more heat transfer surface area to the incoming hot fluid entering the thermal energy storage tank, as compared to conical coil and helical coil configurations, leading to higher extraction of thermal energy. Based on the performance parameters, inverted conical coil experiences enhanced heat transfer, high overall heat transfer coefficient and better effectiveness of heat exchanger as compared to helical and conical coil configurations

Logotherapy: Learnings from the past and relevance in the COVID-19 pandemic

The experience of COVID-19 pandemic had been severely stressful for many of us. As the pandemic affected the whole world, many intellectuals described these experiences as stressful as during wartime. Human suffering and uncertainty about recovery or falling victim had been quite similar in both situations. Logotherapy developed by Dr. Viktor Frankl during World War II (WW-II) has the underpinning to search for meaning in such experiences that motivate the person to remain socially connected and look for better prospects in future. The therapy has the bases in the cognitive psychology, spirituality, and philosophy which are quite different from the modern-day practice of psychodynamic and cognitive therapies. The authors reviewed Viktor Frankl's book “Man's search of meaning” in the context of COVID-19 pandemic, and found marked similarities between the human suffering of the current situation and what Frankl has described in his book. In this narrative review, the authors have attempted to compare the situation during WW-II and current pandemic and have commented about the usefulness of practice of logotherapy in the current situation

Response Surface Methodology-based Prediction Model for Working Fluid Temperature during Stand-Alone Operation of Vertical Cylindrical Thermal Energy Storage Tank

Domestic hot water applications rely on the stand-alone operation of thermal energy storage (TES), in which natural convection significantly affects the efficiency of a storage system. The present study develops a two-dimensional axisymmetric numerical model for detailed simulation. Subsequently, an effective prediction model for a vertical stand-alone cylindrical storage tank is formed. The results of the detailed model are found to have good agreement with the findings of the in-house experiments. The experimental and numerical results show the formation of temperature gradients with time, known as thermal stratification, which affects the storage efficiency and thermodynamic quality of the stored heat. A seven parameter three-level Box-Behnken Design (BBD) Response Surface Methodology (RSM) is used to develop a prediction model for the working fluid temperature inside the tank. Analysis of variance (ANOVA) is performed to evaluate the effects and interactions of the process parameters for selecting the statistically significant terms. Based on the ANOVA, a reduced prediction equation is generated. Various plots such as normal probability, predicted versus actual response, versus fits, versus order, Pareto charts, main effects and interaction effects are created to analyze the model. Comparing the results of the detailed model and prediction equation, it is concluded that the newly formulated scaling-based prediction equation can predict and characterize the performance of the TES under test with adequate accuracy

Thermal stratification characteristics during simultaneous charging and discharging for different storage tank geometries with immersed discharging coil

The geometrical shapes of the thermal energy storage and the configurations of immersed discharging coils dictate the efficacy of low-to-medium temperature hot water applications. This study uses a three-dimensional numerical model to investigate the thermal characteristics of three storage configurations for simultaneous charging and discharging. The same tank volume and height, as well as the same coil tube dimensions, are considered for three different configurations - cylindrical tank with a helical discharging coil, as well as circular truncated cone-shaped and paraboloidal tanks with conical discharging coils. The discharging flow rate is varied for a deeper understanding of the realistic interplay between energy demand and supply. Results obtained for the cylindrical tank are found to have good agreement with the observations from the in-house experiments. The energy stored, discharging coil outlet temperature, and the extent of thermal stratification decrease with increasing coil flow rate, whilst discharging efficiency and primary thermocline thickness increase. The paraboloidal tank equipped with a conical discharging coil exhibited the highest cumulative energy stored (8821 kJ) just before the commencement of dynamic dual operation, owing to the minimal thermal losses attributable to the lowest surface-area-to-volume ratio. Thermocline thickness is found to expand with time for all the cases, and the highest thermocline thickness expansion rate of 0.208 mm/s is found for the cylindrical tank indicating a higher degree of energy degradation. The peak values for the cumulative energy discharged (9788 kJ), and average discharging efficiency (0.36) occurred for the paraboloidal tank with the conical discharging coil configuration. Based on the detailed analyses, the paraboloidal storage tank configuration is found to exhibit better system reliability and energy management, leading to more efficient heat dispatch controllability due to the enhanced energy harnessing features

Experimental investigation of heat dispatch controllability through simultaneous charging-discharging and stand alone- discharging opeations in vertical cylindrical heat storage tank

Using a vertical cylindrical thermal energy storage (TES) tank with helical discharging coil fitted inside, the present study experimentally investigates the scarcely studied simultaneous charging and discharging (SCAD) mode, as well as the discharging-alone operation following a substantial stand-alone period. The temperature distributions within the tank, coil outlet temperature and primary thermocline thickness serve as the key performance trackers for the storage tank. The primary thermocline thickness increases with increasing coil side flow rate during the SCAD operation. The SCAD operation exhibited the splitting of the primary thermocline, leading to the formation of a secondary thermocline in the lower half of the tank. The sustenance of secondary thermocline, thermal gradients across the tank height, and the discharging efficiency are found to decrease with increasing charging flow rate, whereas the coil outlet temperature and the primary thermocline thickness increase. The highest average discharging efficiency of 80.1 % is observed for the TES charging at 0.5 L/min at 70 °C, accompanied by the 2 L/min discharging flow rate. The average thermal energy stored is the maximum (1758 kJ) for the TES charging at 1.25 L/min at 70 °C, with discharging rate of 0.5 L/min. The stand-alone period prior to the discharging-alone operation exhibits the heat content retention capability of the storage and allows for the thermocline formation. The time required for thermal stratification is more with the higher initial charging temperature. The time required for the complete discharging of the TES storage tank decreases with increasing coil-side flow rate. These modes provide ample operational flexibility and heat content dispatch controllability, resulting in the versatility of the system

Delirious mania in geriatric age: A rare presentation

Delirious mania is a rare psychiatric syndrome characterized by the presence of delirious and manic symptoms at the same time in a patient with history of bipolar disorder. After its first description in 1832, delirious mania in the literature exists only in the form of case reports and case series. Among the elderly, its occurrence is still rarer. However, an unsuspecting clinician may come across this rare entity and may misdiagnose it for delirium, which needs to be managed aggressively. Hence, we preferred to describe a case of an elderly male here, who presented to us with delirious mania and responded well to olanzapine