TEJENDRA PATEL | Gujarat Technological University (original) (raw)

Papers by TEJENDRA PATEL

Capacity and efficiency of any refrigerating system diminish rapidly as the difference between th... more Capacity and efficiency of any refrigerating system diminish rapidly as the difference between the evaporating and condensing temperature is increased by a reduction in the evaporator temperature. The single stage vapour compression refrigeration system using various refrigerants are limited to an evaporator temperature of -40 0C. Below temperature of -40 0C the either cascade refrigeration system or multi stage vapour compression system is employed. Present work describes thermal design of condenser (HTS), cascade condenser and evaporator (LTS) of R404A-R508B and R410A-R23 cascade refrigeration system. Heat transfer area of condenser, cascade condenser and evaporator for both systems are compared and the effect of condenser and evaporator temperature on heat-transfer area for both systems is studied under same operating condition. The results shows that the required heat-transfer area of condenser and cascade condenser for R410A-R23 cascade system is lower than the R404A-R508B casc...

International Journal for Scientific Research and Development, 2015

The sun which is source of all energy the solar energy which is available from sun can be used fo... more The sun which is source of all energy the solar energy which is available from sun can be used for many application water heating, air heating and power generation like solar water heater are the system those collect solar energy and transfer the heat to passing water. The present work includes to carry out comparative study for thermal performance of the straight tube solar water heater with the proposed spiral tube solar heater experimental set up; it consists copper tube in shape of spiral shape, flat plate collector, K type thermocouple the change in water temperature for 100 litter per day water capacity. The thermal performance was evaluated extensively throughout the month of May; a maximum temperature difference of 16 ֯C between inlet and outlet of the solar water heater. The efficiency of spiral tube solar water heater was calculated. The maximum value during the experimental period was found to be 47.63% which was more than the straight tube solar water heater.

International Journal for Scientific Research and Development, 2016

The heat transfer characteristic of R32, R22 and R152a during condensation were experimentally in... more The heat transfer characteristic of R32, R22 and R152a during condensation were experimentally investigated in a horizontal mini channels. The experiments used different parameters like saturation temperature, mass flux, vapour quality, channel diameter, channel geometry and thermos physical properties on the heat transfer coefficients. Several literatures are used to find a assessment correlations. Condensation heat transfer correlations and theoretical solutions are used to predict the experimental data in this research.

MATEC Web of Conferences, 2018

Heat exchanger developments are driven by increase in energetic efficiency and emission reduction... more Heat exchanger developments are driven by increase in energetic efficiency and emission reduction. To reach the required standards, new systems are required based on mini-channels along with macro channels also. Mini-channels can be described as tubes with one or more ports extruded in aluminium or any other material like copper, steel etc. with hydraulic diameter in the range of 0.2 to 3 mm. Its use in refrigeration systems became a reality; thanks to the human ability to make micro-scale systems. Some heat exchanger enterprises have some models developed specially for their use in automotive sector, cooling sector and industrial refrigeration without having knowledge of how these reduced geometries affect the most important parameters such as pressure drop and the heat transfer coefficient. To overcome this, an exhaustive literature review of the last two decades has been performed to determinate the state of the research. Among all the publications, several models have been reviewed to check the predicting capacities of them as most of them were developed for macro channels along with single port mini-channel tubes. This work presents a comparative study of existing heat transfer correlations for horizontal flow through mini-channels. Present work total 317 experimental results of condensation heat transfer coefficient obtained from several published literatures and also various condensation heat transfer correlations are reviewed for horizontal flow through mini-channels. Results of condensation heat transfer coefficient obtained for various correlations are compared with the experimental results. Among all correlations used the Bohdalet's correlation gives value of condensation heat transfer coefficient closer to experimental results and has a mean relative deviation (MRD) of 5.4 % whereas mean absolute relative deviation (MARD) of 20.72%.Hence in present work the effort has been made to find better model to predict the condensation heat transfer coefficient which can fit the experimental data with least MRD and MARD.

The method of wave energy conversion utilizes an oscillating water column (OWC). The OWC converts... more The method of wave energy conversion utilizes an oscillating water column (OWC). The OWC converts wave energy into low-pressure pneumatic energy in the form of bi-directional airflow. Wells has been used to convert this pneumatic power into uni-directional mechanical shaft power. But a Wells turbine has inherent disadvantages like lower efficiency and poorer starting characteristics. This paper provides current status of wells turbine and reviews various researches done to improve starting and running characteristics of wells turbine.

Heat and Mass Transfer, 2019

The present study aims to investigate the effect of working fluid, mass flux, vapour quality and ... more The present study aims to investigate the effect of working fluid, mass flux, vapour quality and saturation temperature on local condensation Heat Transfer Coefficient (HTC) and local Frictional Pressure Drop (FPD) in a horizontal circular mini-channel. The refrigerants HFO-1234yf and HFC-R134a have been used as a working fluids. The mass flux was varied from 200 to 800 kg/ m 2 s whereas two distinct saturation temperatures were used: 35°C and 40°C. The experimental analysis was carried out using horizontal circular single port mini-channel of hydraulic diameter 1 mm. During experiment, inlet condition of refrigerant was maintained to be saturated vapour. The results show that HTC and FPD increases with increase in vapour quality and mass flux whereas decreases with increase in saturation temperature. The experiment results of present study and previously published results are compared with various predictive models. Models which show minimum deviation from experimental results were used to develop new modified model to predict HTC with MARD of ± 15 % and FPD with MARD of ± 10 %. Nomenclature A s Heat transfer area, m 2 A o Cross sectional area or free flow area, m 2 A1, A2 Moser's constant Bo Bond number C Lockhart-Martinelli coefficient Ca Capillary number Co Confinement number Cou Courant number C1, C2 Cavallini's constant C p Specific heat at constant pressure, kJ/kg K C v Specific heat at constant volume, kJ/kg K D, d hydraulic channel diameter, mm E entrainment ratio F Frictional Fr Froude number g Gravitational acceleration, m/s 2 G Mass flux, kg/m 2 s Ga Galileo number h Heat transfer coefficient, W/m 2 K h lv Heat of vaporization, kJ/kg k Thermal conductivity, W/m K

Heating, Ventilation and Air Conditioning (HVAC) sector is responsible for consumption of most of... more Heating, Ventilation and Air Conditioning (HVAC) sector is responsible for consumption of most of the energy of the world. Main reason for the energy consumption in the cooling sector is reliability on conventional mechanical air conditioning system which consist of compressor, a high energy consuming device. Also, conventional mechanical air conditioning system uses refrigerant as working media, which if leaks will be harmful for the surrounding environment and humans. To overcome theselacking, evaporative cooling system is the suitable substitute. Direct evaporative cooling system cause fair drop in the temperature of air but at the same time it rises the humidity of the air, which is not desirable for human health. Whereas indirect evaporative cooling control the humidity rises but fails to drop temperature of air sufficiently. To utilize the advantages of both direct and indirect evaporative cooling Prof. ValeriyMaisotsenko introduced Maisotsenko Cycle (also called as M-Cycle). ...

Iranian Journal of Science and Technology, Transactions of Mechanical Engineering

Capacity and efficiency of any refrigerating system diminish rapidly as the difference between th... more Capacity and efficiency of any refrigerating system diminish rapidly as the difference between the evaporating and condensing temperature is increased by a reduction in the evaporator temperature. The single stage vapour compression refrigeration system using various refrigerants are limited to an evaporator temperature of -40 0C. Below temperature of -40 0C the either cascade refrigeration system or multi stage vapour compression system is employed. Present work describes thermal design of condenser (HTS), cascade condenser and evaporator (LTS) of R404A-R508B and R410A-R23 cascade refrigeration system. Heat transfer area of condenser, cascade condenser and evaporator for both systems are compared and the effect of condenser and evaporator temperature on heat-transfer area for both systems is studied under same operating condition. The results shows that the required heat-transfer area of condenser and cascade condenser for R410A-R23 cascade system is lower than the R404A-R508B casc...

International Journal for Scientific Research and Development, 2015

The sun which is source of all energy the solar energy which is available from sun can be used fo... more The sun which is source of all energy the solar energy which is available from sun can be used for many application water heating, air heating and power generation like solar water heater are the system those collect solar energy and transfer the heat to passing water. The present work includes to carry out comparative study for thermal performance of the straight tube solar water heater with the proposed spiral tube solar heater experimental set up; it consists copper tube in shape of spiral shape, flat plate collector, K type thermocouple the change in water temperature for 100 litter per day water capacity. The thermal performance was evaluated extensively throughout the month of May; a maximum temperature difference of 16 ֯C between inlet and outlet of the solar water heater. The efficiency of spiral tube solar water heater was calculated. The maximum value during the experimental period was found to be 47.63% which was more than the straight tube solar water heater.

International Journal for Scientific Research and Development, 2016

The heat transfer characteristic of R32, R22 and R152a during condensation were experimentally in... more The heat transfer characteristic of R32, R22 and R152a during condensation were experimentally investigated in a horizontal mini channels. The experiments used different parameters like saturation temperature, mass flux, vapour quality, channel diameter, channel geometry and thermos physical properties on the heat transfer coefficients. Several literatures are used to find a assessment correlations. Condensation heat transfer correlations and theoretical solutions are used to predict the experimental data in this research.

MATEC Web of Conferences, 2018

Heat exchanger developments are driven by increase in energetic efficiency and emission reduction... more Heat exchanger developments are driven by increase in energetic efficiency and emission reduction. To reach the required standards, new systems are required based on mini-channels along with macro channels also. Mini-channels can be described as tubes with one or more ports extruded in aluminium or any other material like copper, steel etc. with hydraulic diameter in the range of 0.2 to 3 mm. Its use in refrigeration systems became a reality; thanks to the human ability to make micro-scale systems. Some heat exchanger enterprises have some models developed specially for their use in automotive sector, cooling sector and industrial refrigeration without having knowledge of how these reduced geometries affect the most important parameters such as pressure drop and the heat transfer coefficient. To overcome this, an exhaustive literature review of the last two decades has been performed to determinate the state of the research. Among all the publications, several models have been reviewed to check the predicting capacities of them as most of them were developed for macro channels along with single port mini-channel tubes. This work presents a comparative study of existing heat transfer correlations for horizontal flow through mini-channels. Present work total 317 experimental results of condensation heat transfer coefficient obtained from several published literatures and also various condensation heat transfer correlations are reviewed for horizontal flow through mini-channels. Results of condensation heat transfer coefficient obtained for various correlations are compared with the experimental results. Among all correlations used the Bohdalet's correlation gives value of condensation heat transfer coefficient closer to experimental results and has a mean relative deviation (MRD) of 5.4 % whereas mean absolute relative deviation (MARD) of 20.72%.Hence in present work the effort has been made to find better model to predict the condensation heat transfer coefficient which can fit the experimental data with least MRD and MARD.

The method of wave energy conversion utilizes an oscillating water column (OWC). The OWC converts... more The method of wave energy conversion utilizes an oscillating water column (OWC). The OWC converts wave energy into low-pressure pneumatic energy in the form of bi-directional airflow. Wells has been used to convert this pneumatic power into uni-directional mechanical shaft power. But a Wells turbine has inherent disadvantages like lower efficiency and poorer starting characteristics. This paper provides current status of wells turbine and reviews various researches done to improve starting and running characteristics of wells turbine.

Heat and Mass Transfer, 2019

The present study aims to investigate the effect of working fluid, mass flux, vapour quality and ... more The present study aims to investigate the effect of working fluid, mass flux, vapour quality and saturation temperature on local condensation Heat Transfer Coefficient (HTC) and local Frictional Pressure Drop (FPD) in a horizontal circular mini-channel. The refrigerants HFO-1234yf and HFC-R134a have been used as a working fluids. The mass flux was varied from 200 to 800 kg/ m 2 s whereas two distinct saturation temperatures were used: 35°C and 40°C. The experimental analysis was carried out using horizontal circular single port mini-channel of hydraulic diameter 1 mm. During experiment, inlet condition of refrigerant was maintained to be saturated vapour. The results show that HTC and FPD increases with increase in vapour quality and mass flux whereas decreases with increase in saturation temperature. The experiment results of present study and previously published results are compared with various predictive models. Models which show minimum deviation from experimental results were used to develop new modified model to predict HTC with MARD of ± 15 % and FPD with MARD of ± 10 %. Nomenclature A s Heat transfer area, m 2 A o Cross sectional area or free flow area, m 2 A1, A2 Moser's constant Bo Bond number C Lockhart-Martinelli coefficient Ca Capillary number Co Confinement number Cou Courant number C1, C2 Cavallini's constant C p Specific heat at constant pressure, kJ/kg K C v Specific heat at constant volume, kJ/kg K D, d hydraulic channel diameter, mm E entrainment ratio F Frictional Fr Froude number g Gravitational acceleration, m/s 2 G Mass flux, kg/m 2 s Ga Galileo number h Heat transfer coefficient, W/m 2 K h lv Heat of vaporization, kJ/kg k Thermal conductivity, W/m K

Heating, Ventilation and Air Conditioning (HVAC) sector is responsible for consumption of most of... more Heating, Ventilation and Air Conditioning (HVAC) sector is responsible for consumption of most of the energy of the world. Main reason for the energy consumption in the cooling sector is reliability on conventional mechanical air conditioning system which consist of compressor, a high energy consuming device. Also, conventional mechanical air conditioning system uses refrigerant as working media, which if leaks will be harmful for the surrounding environment and humans. To overcome theselacking, evaporative cooling system is the suitable substitute. Direct evaporative cooling system cause fair drop in the temperature of air but at the same time it rises the humidity of the air, which is not desirable for human health. Whereas indirect evaporative cooling control the humidity rises but fails to drop temperature of air sufficiently. To utilize the advantages of both direct and indirect evaporative cooling Prof. ValeriyMaisotsenko introduced Maisotsenko Cycle (also called as M-Cycle). ...

Iranian Journal of Science and Technology, Transactions of Mechanical Engineering