A Review on Heat Transfer Enhancement of Solar Air Heater Using Various Artificial Roughed Geometries

Solar air heater acts as one of the important components in utilization of solar energy. The air heater absorbs the irradiance and converts it into heat energy at the absorbing surface. The thermal energy is further use in heating flowing air through the duct. Solar air heaters are cost effective as well as simple in design. Solar air heater can be used in space heating, timber seasoning and agricultural drying. In spite of all these advantages the solar air heater has certain challenges such as the air has low heat transfer coefficient. The heat transfer rate from the heated absorber surface to the air is low. Hence in order to enhance the heat transfer coefficient the surface area either increases or the flow made to be turbulent. In order to do so the artificial roughened element must be incorporated on the heated surface. The use of artificial roughness is considered as an effective technique to enhance the heat transfer rate of fluid flowing through the duct of solar air heater. The heat transfer and friction characteristics of number of roughness geometries incorporated solar air heater have been investigated. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heater in order to improve thermal and thermo hydraulic performance of solar air heater ducts.</jats:p

Prevalence of Obesity and Overweight and Its Correlates among 20-40 Year Old Population in an Urban Area in Southern India

Introduction: Obesity has reached epidemic proportions globally, with at least 2.8 million people dying each year as a result of consequences of overweight or obesity. The study was conducted to estimate the prevalence of Overweight and obesity among 20-40 years old residing in an urban area in North Karnataka and to study the risk factors affecting overweight and obesity.&#x0D; Methods: A Cross Sectional Study was done among adults aged 20-40 years in urban field practice area in North Karnataka in 2017-18. The sample size was calculated to be 207. Selection of study subjects was done using systematic random sampling. Data regarding socio-demographic profile and anthropometric measurements were collected and BMI calculated.&#x0D; Results: The prevalence of overweight was 45.9% and obesity was 11.1%. Females had more prevalence of overweight (46.8%) and obesity (13.8%) as compared to males. overweight was more in sedentary workers (50%).There was a high prevalence of obesity among participants with mixed diet(82.6%) and 63.1% of participants eating junk food were overweight and 69.5% were obese. The prevalence of overweight was more among participants with class IV socioeconomic status (45.3%) followed by class III (31.6%).&#x0D; Conclusion: There is a growing prevalence of overweight and obesity in urban areas that calls for an urgent need to prevent the further consequences and decrease the burden.</jats:p