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Research Problem -1

Title: Natural convection in water/nanofluid filled closed and open cavity

Statement of problem

The theoretical investigations evidenced an enhancement in heat transfer capabilities of nanofluids in natural convection, whereas, a deterioration was reported in the experimental findings. The above conflict on the natural convection is the inspiration of the current study.

A square enclosure, heated from the bottom and cooled from the top (open for open cavity experiments), identical to Rayleigh-Bénard cavity is filled by working fluid. First, the water is used as the working fluid to validate the test section, followed by the nanofluids of different particle concentrations and sizes. The Nusselt number, thermal boundary layer thickness and r.m.s. temperature distributions are evaluated.

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Contribution

The heat transfer in the presence of nanoparticles in the base fluid is enhanced at a particle concentration of 0.01 vol.%, while there is deterioration in the heat transfer at the particle concentration of 0.1 vol.%. The heat transfer is also increased with the Rayleigh number, function of height (aspect ratio) and temperature gradient (heat flux). At a constant temperature gradient, the Nusselt number is increased with the aspect ratio. A generalized correlation is also developed to demonstrate the essence of aspect ratio, particle size and concentration and Rayleigh number on the Nusselt number. The dependency of Nusselt number on the Rayleigh number and Prandtl number for the nanofluids is also formulated, which is a major contribution of the present study, as it is not reported in literature. Above results are furthermore experienced by estimating the thermal boundary layer thickness and statistical analysis. On the basis of Rayleigh number, the difference between the transition regime and intensive turbulence is also explained using the probability density function of temperature fluctuation data. The power spectrum of temperature fluctuations reported the transformation of energy from larger to smaller scale and reached a maximum value near the thermal boundary layer thickness in the mixing zone of thermal convection.

Publications on this problem

  1. Aditya Kumar and Sudhakar Subudhi, “Thermal fluctuations and boundary layer properties of turbulent natural convection inside open cavities of different dimensions heated from below”, Physics of Fluids, Vol. 32, 067114, 2020.

  2. Rajesh Choudhury, Adarsh Saini & Sudhakar Subudhi, “Oberbeck-Boussinesq approximations and geometrical confinement effects of free convection in open cavity”. Heat and Mass Transfer, Vol. 55, page. 2095-2102, 2019.

  3. Rajesh Choudhury, Deepak Khurana, Aditya Kumar & Sudhakar Subudhi, “Stability analysis of Al2O3/Water nanofluids”. Journal of Experimental Nanoscience Vol.12, page.140-151, 2017.

  4. Rajesh Choudhury & Sudhakar Subudhi, “Aspect ratio dependence of turbulent natural convection in Al2O3/water nanofluids”. Applied Thermal Engineering, Vol.108, page.1095-1104, 2016.

  5. L Gangadhara Kiran Kumar, Shailesh Ranjan Kumar & Sudhakar Subudhi, “Experimental study of the turbulent free convection over horizontal smooth or grooved surfaces in an open cavity”. Heat and Mass Transfer, Vol.52, page.245-253,2016.

 

 

 

Research Problem -2

Title: Effects of spiral tape inserts, pH and surfactant on the forced convection of Al2O3/water and TiO2/water

Statement of problem

The present problem investigates the effects of spiral tape inserts, pH and surfactants on heat transfer and pressure drop characteristics during the forced convection of the distilled water, Al2O3/water and TiO2/water nanofluids in a Cu horizontal pipe heated by a nichrome heater under uniform heat flux boundary condition. So that the heat transfer performance of nanofluids can be analyzed and compared with that of distilled water. For this an experimental setup was designed and fabricated. It consists of a flow loop including a pump, a flow measuring device, a test section with heating element, a cooling unit and a reservoir.

 

Contribution

Simple spiral tape and modified spiral tape inserts are efficient to enhance the heat transfer but with the increase in penalty of pressure drop. For distilled water, the enhancement in Nusselt number for simple spiral tape (STT) compared to plain tube is observed to be 18, 26 and 39 % for the twist ratio of 5.65, 4.35 and 3.04 respectively. There is further enhancement in heat transfer with modified twisted tape (MTT) for distilled water. The enhancement for MTT compared to plain tube is observed to be 44, 60 and 77 % at a twist ratio of 5.65, 4.35 and 3.04 respectively.

For Al2O3/water nanofluids and 0.025 vol % concentration, the enhancement in heat transfer was 14.9 % at a pH of 3.7 and for TiO2/water it was 18 % at a pH of 3.6. For 12.5±0.5 the enhancement in heat transfer was 10.35 and 14.12 % for Al2O3 and TiO2 nanofluids respectively. The heat transfer of nanofluids using SDS surfactant increases with increasing particle concentration. The maximum enhancement for Al2O3/water was observed to be 16.03 % at a particle concentration of 0.1 vol % and the maximum enhancement for TiO2 nanofluid was 21.32 % at the same concentration of 0.1 vol %.

 

Publications on this problem

  1. Deepak Khurana & Sudhakar Subudhi, “Forced convection of Al2O3/water nanofluids with simple and modified spiral tape inserts”. Heat and Mass Transfer, Vol. 55(6), Page. 1-13, 2019.

  2. Deepak Khurana, Rajesh Choudhury & Sudhakar Subudhi, “A critical review of forced convection heat transfer and pressure drop of Al2O3, TiO2 and CuO Nanofluids”. Heat and Mass Transfer Vol.53, page.343-361,2017.

  3. Rajesh Choudhury, Deepak Khurana, Aditya Kumar & Sudhakar Subudhi, “Stability analysis of Al2O3/Water nanofluids”. Journal of Experimental Nanoscience Vol.12, page.140-151, 2017.

  4. Deepak Khurana, Rajesh Choudhury & Sudhakar Subudhi, “Investigation of Thermal Conductivity and Viscosity of Al2O3/Water Nanofluids using Full Factorial Design and Utility Concept”. Nano, Vol.11, No. 8, page.1650093-1-10, 2016.

  5. Deepak Khurana & Sudhakar Subudhi, “Effects of pH and surfactant on the forced convection of Al2O3/water and TiO2/water”. ASME-J. Therm. Sc. Eng. Appl., (Under review).

 

 

Research Problem -3

Title: Novel solar assisted liquid desiccant air conditioning system using single storage system

Statement of problem

The main problem in the use of liquid desiccant air conditioning is the utilization energy for regeneration, corrosiveness to metals and carryover of the solution to the air. To overcome this problem, there is the development of a dehumidifier using corrosion-resistant materials and regeneration using solar energy rather than fossil fuel. The main components to use liquid desiccant as air conditioning are dehumidifier, evaporative cooler and the regenerator. The dehumidifier is made of 316L SS and these tubes are stacked in aluminium fins to maintain the desiccant solution temperature using the evaporative cooler. In this experiment, calcium chloride solution (CaCl2-H2O) is used as a liquid desiccant solution.

Contribution

The inlet air is humidified and controlled by a constant temperature bath to maintain the inlet conditions. The inlet parameters considered are solution volume flow rate, inlet temperature, inlet relative humidity, regeneration temperature, and desiccant solution temperature. The performance parameters are the absolute humidity reduction, outlet temperature and dehumidifier and enthalpy effectiveness of the dehumidifier. The solution volume flow rates of 14 L/min, 16 L/min, 18 L/min and 20 L/min are used for the experiments. The experiments show that for a fixed Ta, inlet and RH% as solution volume flow rate increases, there is increase in absolute humidity reduction. The temperature of the dehumidified air is reduced compared to that of inlet air if this air is passed over the pad used for the evaporating cooler. It is seen that the increase in relative humidity from 68.88% to 92.8% for the flow rate of 20 L/min and fixed inlet air temperature, increases absolute humidity reduction from 5.56 to 13.3 g/kg. The increase in solution temperature reduces the absolute humidity reduction and dehumidifier effectiveness. When the solution temperature changes from 31.5 to 34 0C, there are reductions in the absolute humidity reduction and dehumidifier effectiveness by 34.4% and 13.04% respectively.

 

Publications on this problem

  1. Geleta Fekadu and Sudhakar Subudhi, “Liquid Desiccant Dehumidification Using Solar Regenerated System”, Springer Proceedings in Energy, Suneet Singh and Venkatasailanathan Ramadesigan (Eds): Advances in Energy Research, Vol 2, pp.229-238, 2020.

  2. Geleta Fekadu, Sudhakar Subudhi, Experimental Study of Internally−Cooled Dehumidification of Liquid Desiccant for A Single Storage Tank, IHMTC-2019, Pages 1137-1142, IIT Roorkee, Dec.28-31, 2019. Doi: 10.1615/Ihmtc-2019.1910.

  3. Geleta Fekadu Sudhakar Subudhi, ‘Experimental Study of Internally Cooled Desiccant Dehumidification System, 7th International and 45th National Fluid Mechanics and Fluid Power Conference (FMFP2018), IIT Bombay, Mumbai, India, December 10-12, 2018.

  4. Geleta Fekadu & Sudhakar Subudhi, “Renewable energy for liquid desiccant air conditioning systems: A review”. Renewable and Sustainable Energy Reviews, Vol. 93, page.364-379, 2018.

  5. Sajesh M, Geleta Fekadu, Kalpana Singh & Sudhakar Subudhi, “Liquid desiccant air conditioning using single storage solution tank, evaporative cooling and marquise shaped solar collector”. ASME-J. of Energy Res. Tech. (Under review).

 

 

 

Research Problem -4

Title: Study of marquise shaped channel solar flat plate collector

Statement of problem

This problem investigates the performance of a Marquise shaped channel Flat-plate solar collector using Al2O3–water nanofluid and pure water as the base fluid. The experimental setup comprises of developing a marquise shaped channel flat plate collector of the aluminum absorber plate, a closed-loop working fluid system and measurement devices (thermocouples, temperature meter, flow meter and solar Pyranometer). The absorber plate is made of two aluminum plate sandwiched together with Marquise-shaped flow channels. The effect of various parameters like mass flow rate of fluid, collector inlet and outlet fluid temperature, solar radiation, and ambient temperature on the collector efficiency is investigated.

Contribution

The observed results illustrate that their collecting efficiencies are all superior to that of water. The experiment findings show that enhancement in the efficiency of solar flat plate collector is the highest at 83.17% and 59.72% for nanofluid and water respectively at the mass flow rate of 3 lpm. The percentage enhancement in efficiency of nanofluids, when compared to that of water, is as follows: 8.61%, 23.67%, 23.45%, 30.7% and 27.62% for 1, 2, 3, 4 and 5 lpm flow rates respectively. The efficiency is found to be increasing with the increase in solar intensity. Also, the addition of nanoparticles to distilled water increases the thermal conductivity of water and the heat transfer capacity. The competence of solar collector is found to increase with an increase in mass flow rate initially and goes on decreasing on further increasing of mass flow rate. The exergy efficiency of the Al2O3/water nanofluid is also higher compared to that of water. The exergy efficiency for 0.1 % nanofluids is increased by 18.73% at the mass flow rate of 1 lpm when compared with that of water. The innovative design of the absorber plate (Marquise shaped channel) and use of nanofluids enhances the efficiency of solar flat collector.

 

Publications on this problem

  1. Pankaj Raj, Geleta Fekadu and Sudhakar Subudhi, “Study of Performance of Solar Flat Plate Collector Using Al2O3/Water Nanofluids”, Springer Proceedings in Energy, Suneet Singh and Venkatasailanathan Ramadesigan (Eds): Advances in Energy Research, Vol 2, pp.149-158, 2020.

  2. Sahil Arora, Geleta Fekadu & Sudhakar Subudhi, “Energy and Exergy Analysis of Marquise Shaped Channel Flat Plate Solar Collector Using Al2O3–Water Nanofluid and Water”. ASME-Journal of Solar Energy Engineering, Vol.141, page.041008-1-9, 2019.

  3. Pankaj Tiwary & Sudhakar Subudhi, “A review of studies using nanofluids in flat-plate and direct absorption solar collectors”. Renewable and Sustainable Energy Reviews, Vol. 84, page.54-74, 2018.

  4. Pankaj Tiwary, Geleta Fekadu Sudhakar Subudhi, ‘Study of performance of solar flat plate collector using Al2O3/water nanofluids’ 6th International Conference on Advances in Energy Research 2017 (ICAER 2017), IIT Bombay, Mumbai, India, December 12-14, 2017.

  5. Sajesh M and Sudhakar Subudhi, “Performance effect of Marquise Shaped Channel Flat Plate Solar Collector on series and parallel connection of collectors” (under preparation).

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Research Problem -5

Title: Thermoregulatory mechanism of human body during different activities

Statement of problem

The present topic deals with the experimental and analytical study of physiological thermoregulation of the human body at hot and cold thermal conditions.  Experimentally, the hot environments and cold environments with different humidities are simulated in a climate chamber, MIED, IIT Roorkee. The study is performed for the different activities like seating, walking, running and cycling. The skin temperatures at ten different body parts are measured. The study is performed for various combinations of temperature and relative humidity. In addition, the analytical model of thermal balance is presented. The skin temperature sensitivity for both hot and cold environment conditions are analyzed.

Contribution

From the study, it is observed that the temperature of the back is maximum among all body parts for both hot and cold conditions. For the hot condition, the temperature of the thigh is lowest, and for the cold condition, the hand and foot have the lowest temperatures. By observing the skin temperature in a boxplot for different temperatures, it is concluded that for higher temperature, there is a lesser deviation in skin temperature for both before and after running on the treadmill. Further, both the experimental and analytical results show that, for a particular ambient temperature (at 34⁰C, 38⁰C and 42⁰C), the mean skin temperature increases with the increase in relative humidity and at a lower temperature (30°C), the effect of relative humidity is negligible. Furthermore, by performing the subjective analysis, the neutral temperature for the hot environment before running and after running has been calculated. It is found that at 40% RH, the neutral temperature is 29.93°C before running and 27.46°C after running whereas for 80% RH, it is 27°C and 26.16°C before and after running respectively. From this result, it is concluded; higher the humidity required neutral temperature that will provide comfort to the thermal environment would be lower than that of low humidity.

Publications on this problem

  1. Myat Sithu Lwin, Shashikant Das and Sudhakar Subudhi, “Human thermoregulatory behavior during fixed-intensity and self-paced cycling”. Experimental Physiology (Under review).

  2. Shashikant Das and Sudhakar Subudhi, “A review on different approaches to study thermal comfort”. J. Housing and Built Environment (Under review).

  3. Shashikant Das, Sudhakar Subudhi and E Rajasekar, “Evaluation of thermoregulation and thermal sensation in hot and cold thermal environments”. Indoor & Built Environment (Under review).

  4. Shashikant Das and Sudhakar Subudhi, Study of thermoregulation of the human body using the steady-state energy balance model, FMFP-2020, IIT Guwahati, Dec.09-11, 2020. (Submitted).

  5. Shashikant Das, Krishan Upadhyay, Sudhakar Subudhi, Rajasekar Elangovan, Study of Physiological Thermoregulation of Human Body at Extreme Thermal Condition. IHMTC-2019, Pages 931-936, IIT Roorkee, Dec.28-31, 2019. Doi: 10.1615/Ihmtc-2019.1560.

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