Browsing by Author "Ashok Babu, T.P."

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Analytical computation of gwp, odp, rf number and tewi analysis of various r134a/r1270/r290 blends as r22 alternatives
(CRC Press/Balkema, 2018) Vali, S.S.; Ashok Babu, T.P.
The principal objective of the present work is to compute the GWP, ODP, RF number and TEWI analysis of various ternary R134a/R1270/R290 blends as alternatives to R22. In this study thirteen refrigerant blends consists of R134a, R1270 and R290 at different compositions are taken. GWP and ODP of refrigerant blends are computed by using various simple correlations. The estimation of emission of greenhouse gases and flammability study of refrigerants are done by using TEWI and RF analysis respectively. Analytical results revealed that all the thirteen studied fluids are ozone friendly in nature. The GWP of refrigerant M6 (651) is lower than that of GWP of R22 (1760). RF analysis exhibited that all the thirteen refrigerant blends are categorized as ASHRAE A2 flammability category. Thermodynamic analysis revealed that COP of M6 (3.608) is higher that of COP of R22 (3.534). TEWI of M6 is lower among the R22 and thirteen studied fluids. Hence refrigerant M6 (R134a/R1270/R290 50/5/45 by mass%) is an alternative to R22. Â© 2018 Taylor & Francis Group, London.
Analytical computation of thermal response characteristics of homogeneous and composite walls of building and insulating materials used in India
(CEPT University Press, 2014) Saboor, S.; Ashok Babu, T.P.
Climate responsive building design involves the study of the thermal response of building and insulating materials exposed to periodic changes of environmental conditions. For calculation of such unsteady thermal characteristics, one dimensional heat flow diffusion equation under periodic boundary conditions was solved using matrix algebra and thermal characteristics like admittance, transmittance, decrement factor, time lag, surface factor and surface factor time lags were calculated for homogeneous and composite walls. In this study, ten building and ten insulating materials were studied. Optimum wall thicknesses of building and insulating materials were calculated. From the results, it was concluded that mud phuska and coconut pitch are the most recommended homogeneous building and insulation materials respectively, among studied building and insulating materials, from lower decrement factor and higher time lag point of view. It is found that the insulation materials are highly responsive to short wave radiation than that of building materials. From the study, ultimately it is concluded that Burnt brick composite walls with Coconut pitch insulation is the best composite wall among all studied walls for reduced cooling loads and the most energy efficient building construction. Â© 2014 30th International PLEA Conference: Sustainable Habitat for Developing Societies: Choosing the Way Forward - Proceedings. All rights reserved.
Analytical computation of thermodynamic performance of various new eco-friendly alternative refrigerants applicable for air conditioners
(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2021) Vali, S.V.; Ashok Babu, T.P.; Mahapatra, D.; Saboor, S.; Gorantla, K.K.; Sai Siva Subramanyam, V.
The objective of the present investigation is to do the theoretical thermodynamic analysis of various new eco-friendly R22 substitutes used in vapour compression refrigeration (VCR) cycle. In this work, nine mixture refrigerants were considered at different compositions. Thermodynamic properties of all the considered refrigerants were developed and the same properties were used in the performance analysis of alternative refrigerants. Standard VCR cycle was considered for the thermodynamic assessment of alternative refrigerants. The working conditions considered are expressed as TeÂ =Â 7.2Â Â°C, TkÂ =Â 54.4Â Â°C, Î”TsupÂ =Â 11.1Â Â°C and Î”TsubÂ =Â 8.3Â Â°C, respectively. Results revealed that the COP of mixture refrigerant MR20 (R600a/R134a/R1270 5/47.5/47.5 in mass%) was 2.02% higher than the COP of R22 and other nine investigated refrigerants. Discharge temperature of compressor obtained for MR20 was 11.79Â Â°C lower compared to that of R22. Compressor power obtained for MR20 was 1.96% lower than that of R22. Volumetric refrigeration capacity obtained for MR20 was relatively closer to that of R22. GWP100 of MR20 (619) was lower compared to the GWP100 of R22 (1760). Overall, the performance of mixture refrigerant MR20 was better compared to all the considered R22 alternatives, and therefore it might be an appropriate candidate to replace R22 used in air conditioners. Â© Springer Nature Singapore Pte Ltd 2021.
Assessment of mixture boiling heat transfer correlations for ammonia/water mixture
(2009) Sathyabhama, A.; Ashok Babu, T.P.
The aim of this work is to present a critical examination of both the available experimental data and the performance of the available mixture boiling heat transfer correlations for ammonia/water mixture. First, a selection and comparison of the experimental database found in the open literature at the mentioned working conditions is presented. Subsequently, after a short description of the most relevant heat transfer correlations, and in accordance with the selected data, a detailed analysis of the performance of each correlation is carried out. Results show a small divergence between the experimental data sets and conclude that the presently available correlations show considerable discrepancies in heat transfer coefficients within the selected conditions. © 2009 Wiley Periodicals, Inc.
Characterization and effect of using Mahua oil biodiesel as fuel in compression ignition engine
(2009) Kapilan, N.; Ashok Babu, T.P.; Reddy, R.P.
There is an increasing interest in India, to search for suitable alternative fuels that are environment friendly. This led to the choice of Mahua Oil (MO) as one of the main alternative fuels to diesel. In this investigation, Mahua Oil Biodiesel (MOB) and its blend with diesel were used as fuel in a single cylinder, direct injection and compression ignition engine. The MOB was prepared from MO by transesterification using methanol and potassium hydroxide. The fuel properties of MOB are close to the diesel and confirm to the ASTM standards. From the engine test analysis, it was observed that the MOB, B5 and B20 blend results in lower CO, HC and smoke emissions as compared to diesel. But the B5 and B20 blends results in higher efficiency as compared to MOB. Hence MOB or blends of MOB and diesel (B5 or B20) can be used as a substitute for diesel in diesel engines used in transportation as well as in the agriculture sector. © 2009 Science Press, Institute of Engineering Thermophysics, CAS and Springer Berlin Heidelberg.
Condensation heat transfer and pressure drop of R-134a saturated vapour inside a brazed compact plate fin heat exchanger with serrated fin
(Springer Verlag service@springer.de, 2017) Ramana Murthy, K.V.; Chennu, C.; Ashok Babu, T.P.
This paper presents the experimental heat transfer coefficient and pressure drop measured during R-134a saturated vapour condensation inside a small brazed compact plate fin heat exchanger with serrated fin surface. The effects of saturation temperature (pressure), refrigerant mass flux, refrigerant heat flux, effect of fin surface characteristics and fluid properties are investigated. The average condensation heat transfer coefficients and frictional pressure drops were determined experimentally for refrigerant R-134a at five different saturated temperatures (34, 38, 40, 42 and 44 °C). A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 22 kg/m2s. In the forced convection condensation region, the heat transfer coefficients show a three times increase and 1.5 times increase in frictional pressure drop for a doubling of the refrigerant mass flux. The heat transfer coefficients show weak sensitivity to saturation temperature (Pressure) and great sensitivity to refrigerant mass flux and fluid properties. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. Correlations are provided for the measured heat transfer coefficients and frictional pressure drops. © 2016, Springer-Verlag Berlin Heidelberg.
Evaluation of heat transfer surfaces for compact recuperator using a CFD code
(2009) Ashok Babu, T.P.; Talekala, M.S.
Exhaust recovery recuperator is mandatory in order to realize a thermal efficiency of 30% or higher for micro turbines. In this work an attempt is made to select the cross corrugated heat transfer surface with minimum core volume of a recuperator matrix using a CFD code. Analysis is carried out for selected cross corrugated heat transfer surface configurations. The relation between the minimum core volume from design calculation and average skin friction coefficient from CFD analysis has been established. © 2008 Springer-Verlag.
Evaluation of properties and storage stability of Madhuca indica biodiesel
(Japan Oil Chemists Society yukagaku@jocs-office.or.jp, 2009) Kapilan, N.; Ashok Babu, T.P.; Reddy, R.P.
Mahua Oil (MO) is an underutilized non-edible vegetable oil, which is available in large quantities in India. In the present work, biodiesel was derived from the MO by the transesterification process. The fuel properties of the MO biodiesel were found to be within the limits of biodiesel specifications of many countries. The chemical nature of biodiesel makes it more susceptible to oxidation during long-term storage which leads to degradation of fuel properties that can compromise fuel quality. The effect of long storage condition on the stability of the MO biodiesel was studied in the present work. The biodiesel samples were stored in plastic containers at room temperature. The study was conducted for a period of 12 months and the test sample was kept in the darkness. From the experimental results, it was observed that the acid value and viscosity increases with the storage time, but the iodine value decreased with increasing storage time. This is due to the presence of the double bond in the molecule of the biodiesel which produce a high level of reactivity. This high level reactivity produces formation of hydroperoxides, soluble polymers and other secondary products. From the experimental results, a slight difference in the acid value, iodine value and viscosity of the MO biodiesel stored for a period of 30 days was observed. But after this period, the differences were significant. © 2009 by Japan Oil Chemists' Society.
Experimental analysis of SI engine performance and emission characteristics with gasoline-denatured spirit blends as alternative fuels
(2010) Hubballi, P.A.; Ashok Babu, T.P.
The experimental study focused on investigating benefits of unleaded gasoline (P100) - denatured spirit [DNS (ethanol 93.3% v/v + water 6.7% v/v)] blends as fuel in a four cylinder four stroke SI engine. Performance tests were conducted to study volumetric efficiency (VolE), brake thermal efficiency (BThE), brake power (BP), engine torque (torque), brake specific fuel consumption (BSFC). Engine exhaust emissions were investigated for carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and carbon dioxide (CO2). Experiments were conducted at different engine speeds between 2500 - 4500 rpm maintaining throttle position of 50% throughout the experiments. The fuel blends used include DNS30P70 (ethanol 28 % + water 2% + gasoline 70 %), DNS50P50 (ethanol 46.65 % + water 3.35 % + gasoline 50 %) and DNS85P15 (ethanol 79.3 % + water 5.7 % + gasoline 15 %) which were compared with base fuel P100. The investigations revealed that blending DNS with P100 increases BThE, VolE, BP, torque and BSFC. The CO, HC, NOx and CO2 emissions in the exhaust decrease when compared to P100 operation. The DNS85P15 blend produced encouraging results in improved engine performance and decreased engine exhaust emission.
Experimental and theoretical investigations on the cyclic operation of TSA cycle for air dehumidification using packed beds of silica gel particles
(Elsevier Ltd, 2013) Ramzy K, A.K.; Kadoli, R.; Ashok Babu, T.P.
Dehumidification using desiccant beds provide a good alternative for the conventional vapor compression cooling system. Desiccant material in the desiccant dehumidification system should undergo both adsorption and desorption processes. In the present work, experimental tests have been carried out for thermal swing adsorption (TSA) cycle utilizing two packed beds of silica gel spherical particles. The pseudo gas side controlled (PGC) mathematical model has been presented for predicting the cycle performance. The mathematical model has been validated using the experimental results. The root mean square of errors ranges from 1.15% to 9.03% for the exit air humidity ratio and from 1.08% to 9.68% for exit air temperature. The dynamics of desiccant bed during the cyclic operation has been investigated numerically. In addition, it has been found from the parametric study that the cycle efficiency is maximum for a regeneration temperature of 90-95°C when the bed length varies from 50 to 300mm and for desiccant particle diameter ranging from 2 to 5mm. A sensible cooling for the process air before undergoing the dehumidification period is recommended for increasing the cycle efficiency and the dehumidification time which is an added advantage. © 2013 Elsevier Ltd.
Experimental investigation of pool boiling heat transfer in ammonia-water-lithium nitrate solution
(2012) Sathyabhama, A.; Ashok Babu, T.P.
The nucleate pool boiling heat transfer coefficient of an NH 3-H 2O-LiNO 3 mixture was investigated on a cylindrical heated surface at low pressure of 4 to 8 bar, low ammonia mass fraction of 0 < xNH 3 < 0.3, and different heat fluxes. The lithium nitrate concentration of the solution was chosen in the range of 10-50% of mass ratio of lithium nitrate in pure water. The effects of concentrations, heat flux, and pressure on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in the mixture decreases with increase in ammonia mass fraction, increases with the addition of lithium nitrate, and increases with an increase in heat flux and pressure in the investigated range. © 2012 Copyright Taylor and Francis Group, LLC.
Experimental investigation on heat transfer coefficients and frictional pressure drop during R134a condensation inside a plate-fin heat exchanger with wavy fin
(Begell House Inc., 2018) Ramana Murthy, K.V.; Chennu, C.; Ashok Babu, T.P.; Luo, X.
This paper presents the heat transfer coefficients and frictional pressure drops measured during the saturated vapor condensation of R134a inside a small plate-fin heat exchanger with wavy fin surface for air-conditioning systems in aircraft. The experiments were carried out at three different saturated temperatures (34Â°C, 38Â°C and 42Â°C). The effects of the saturation temperature, heat flux and mass flux on the mean condensation heat transfer coefficient and core frictional pressure drop were investigated experimentally and discussed in detail. The condensation heat transfer coefficients and frictional pressure drops are compared with serrated fin surfaces obtained in previous experiments. The correlations for heat transfer coefficient and frictional pressure drop during downward flow condensation of R134a inside the plate-fin heat exchanger with wavy fin are developed based on the experimental data. Compared with the serrated fins for saturated conditions of R134a at same mass flux and saturated temperature/pressure conditions, it is found that although the wavy fins have low condensation heat transfer coefficients, its two-phase frictional pressure drop is even lower than that of the serrated fins. Therefore, if the pressure drop limitation is critical, the wavy fins can be a good selection. Â© 2018 International Heat Transfer Conference. All rights reserved.
Experimental study of nucleate pool boiling heat transfer to ammonia-water-lithium bromide solution
(2011) Sathyabhama, A.; Ashok Babu, T.P.
Visualization of bubble nucleation during nucleate pool boiling outside a vertical cylindrical heated surface was done for ammonia-water binary and ammonia-water-lithium bromide ternary mixture in order to obtain a descriptive behavior of the boiling which was directly compared with the measured heat transfer coefficient at low pressure of 4-8. bar and at low ammonia mass fraction of 0
Flow boiling heat transfer and pressure drop analysis of R134a in a brazed heat exchanger with offset strip fins
(Springer Verlag service@springer.de, 2017) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.
The saturated flow boiling heat transfer and friction analysis of R 134a were experimentally analyzed in a brazed plate fin heat exchanger with offset strip fins. Experiments were performed at mass flux range of 50–82 kg/m2 s, heat flux range of 14–22 kW/m2 and quality of 0.32–0.75. The test section consists of three fins, one refrigerant side fin in which the boiling heat transfer was estimated and two water side fins. These three fins are stacked, held together and vacuum brazed to form a plate fin heat exchanger. The refrigerant R134a flowing in middle of the test section was heated using hot water from upper and bottom sides of the test section. The temperature and mass flow rates of water circuit is controlled to get the outlet conditions of refrigerant R134a. Two-phase flow boiling heat transfer and frictional coefficient was estimated based on experimental data for offset strip fin geometry and presented in this paper. The effects of mass flux, heat flux and vapour quality on heat transfer coefficient and pressure drop were investigated. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier ?f, and Martinelli parameter X. © 2017, Springer-Verlag Berlin Heidelberg.
Improved utilization of desiccant material in packed bed dehumidifier using composite particles
(2011) Ramzy K, A.; Kadoli, R.; Ashok Babu, T.P.
Solid desiccant dehumidifiers are widely used in drying processes. In most of these dehumidifiers, the desiccant material is used as packed bed of granule or spherical particles. Investigations of intra-particle heat and mass transfer processes has shown that the entire portion of the particle is not participating effectively during adsorption as well as desorption processes [Pesaran AA, Mills F. Moisture transport in silica gel packed beds-I. Theoretical study. International Journal of Heat and Mass Transfer 1987; 30: 1037-49]. This is because the diffusion rate is very small compared to that of convection. In the present work, a new desiccant composite particle, in which the unutilized portion of the spherical desiccant particle is replaced with an inert particle, is proposed. By replacing the conventional particles with composite particles for the same mass of desiccant material, the available area for heat and mass transfer increases and more amount of desiccant material is effectively utilized. Further, in order to ascertain the improvement in the performance of the desiccant bed using the composite particles, various factors like thermo-physical properties of the inert material, composite particle thickness ratio, bed configuration, bed volume, the pressure drop and the increase in total adsorbed or desorbed mass have to be considered. In view of this, a theoretical investigation of the operation of vertical solid desiccant packed bed dehumidifier, using both conventional silica gel particles as well as the new proposed composite silica gel particles has been reported. A modified solid side resistance (MSSR) model is developed for the prediction of intra-particle temperature and water content profiles. Results of the present theoretical models, when applied to packed bed of conventional silica gel particles, agree well with the experimental results from the literature for both desorption and adsorption processes. From the theoretical results, more utilization for the desiccant material is obtained when ordinary silica gel particles are replaced by composite silica gel particles. For the same amount of desiccant material and same mass flow rate of air, using particles of 0.2 thickness ratio the pressure drop decreases by about 60% for the case investigated. In addition, an increase of about 11.07% and 20.46% in total mass adsorbed and desorbed respectively are obtained. At the time when adsorption process ends, an increase of 15.5% in the bed effectiveness has been obtained. In addition, the expected improvement in total mass adsorbed and desorbed is observed to be dependent on the inert material thermo-physical properties for thickness ratio less than 0.5. An optimization technique relating the composite particle design, resulting savings in pressure drop and bed volume increase is proposed. © 2010 Elsevier Ltd.
Improvement of performance of dual fuel engine operated at part load
(Universiti Malaysia Pahang editor.ijame@gmail.com, 2010) Kapilan, N.; Ashok Babu, T.P.; Reddy, R.P.
Rising petroleum prices, an increasing threat to the environment from exhaust emissions, global warming and the threat of supply instabilities has led to the choice of inedible Mahua oil (MO) as one of the main alternative fuels to diesel oil in India. In the present work, MO was converted into biodiesel by transesterification using methanol and sodium hydroxide. The cost of Mahua oil biodiesel (MOB) is higher than diesel. Hence liquefied petroleum gas (LPG), which is one of the cheapest gaseous fuels available in India, was fumigated along with the air to reduce the operating cost and to reduce emissions. The dual fuel engine resulted in lower efficiency and higher emissions at part load. Hence in the present work, the injection time was varied and the performance of the dual fuel engine was studied. From the engine tests, it is observed that an advanced injection time results in higher efficiency and lower emissions. Hence, advancing the injection timing is one of the ways of increasing the efficiency of LPG+MOB dual fuel engine operated at part load. © Universiti Malaysia Pahang.
Investigation of flow boiling heat transfer and pressure drop of R134a in a rectangular channel with wavy fin
(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2020) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.
The saturated flow boiling heat transfer and pressure drop studies of R134a were experimentally investigated in a rectangular channel with wavy fin. Experiments were performed at mass flux range 30–50 kg m?2 s?1, heat flux range 11–18 kW m?2 and quality 0.26–0.8. The experimental data were obtained in a brazed test section. In preliminary step, single phase experiments were conducted to find out the j and f data of the wavy fin. In second step, two-phase flow boiling experiments were conducted to estimate the heat transfer and frictional coefficient based on experimental data. The trends of heat transfer and pressure drop with respect to mass flux, heat flux and quality were studied. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier, ?f and Martinelli parameter, X. © 2019 Elsevier Masson SAS
Investigation of various wall and window glass material buildings in different climatic zones of India for energy efficient building construction
(Elsevier Ltd, 2018) Gorantla, G.; Saboor, S.; Ashok Babu, T.P.
The commercial and residential buildings consume about 33% of energy for cooling and day lighting in India. This paper presents the thermal performance of buildings constructed with various building and window glass materials in five different climatic zones of India such as hot and dry (Ahmedabad), moderate (Bangalore), cold (Guwahati), warm and humid (Madras) and composite (New Delhi) climatic zones. In this study, four building materials such as laterite stone, dense concrete, burnt brick and mud brick were selected and four window glass materials such as clear, bronze, green and bronze-reflective glasses were selected. The spectral optical properties of four glass materials were measured experimentally using Perkin-Elmer lambda 950 spectrophotometer from wavelengths ranging from 300 nm- 2500 nm. Total eighty building models were designed using Design builder 4.3.0.039 and thermal analysis was carried out in Energy plus 8.1 simulation tool. From the results, it is observed that mud brick with bronze-reflective glass window buildings were found to be energy efficient from the least heat gain point of view among eighty building models studied in five climatic zones of India. The results of the study help in selecting the best combination of building and window glass materials for reducing cooling loads in buildings of five different climatic zones of India. Â© 2018 Elsevier Ltd.
Nucleate pool boiling heat transfer measurement and flow visualization for ammonia-water mixture
(2011) Sathyabhama, A.; Ashok Babu, T.P.
Visualization of bubble nucleation during nucleate pool boiling outside a vertical cylindrical heated surface was done for ammonia-water binary mixture in order to obtain a descriptive behavior of the boiling, which was directly compared with the measured heat transfer coefficient data at low pressure of 4-8 bar and at low mass fraction of 0 < x < 0.3 and at different heat flux. Still images taken with high speed camera are used to demonstrate the decrease in boiling heat transfer coefficient with increase in ammonia mass fraction. Jensen and Memmel model has better agreement with experimental bubble diameter. Further work is required to obtain quantitative information about bubble nucleation parameters. It is found that both Calus and Rice and Stephan-Koorner correlation can predict the experimental heat transfer coefficient values with a maximum deviation of ±20%. © 2011 American Society of Mechanical Engineers.
Performance characteristics of a dual fuel engine operated with Mahua biodiesel and liquefied petroleum gas
(ASTM International, 2011) Kapilan, N.; Ashok Babu, T.P.; Reddy, R.P.
Fuel crisis because of dramatic increase in vehicular population and environmental concerns have renewed the interest of the scientific community to look for alternative fuels of bio-origin such as vegetable oils and ethanol. India is looking at biodiesel derived from Mahua oil (MO), as one of the renewable alternative fuels for compression ignition (CI) engine. Although MO biodiesel (MOB) has several advantages over fossil diesel, in the present scenario, the use of biodiesel is restricted due to its high cost. In India, liquefied petroleum gas (LPG) is easily available and is one of the cheapest gaseous fuels. Hence, use of LPG to fuel a CI engine along with MOB seems to be an option for substitution of fossil diesel. In the present work, LPG, which was fumigated along with the air and biodiesel was admitted into the engine cylinder through conventional fueling device as an igniter. A single cylinder CI engine was modified to work in dual fuel mode and engine tests were carried out at rated speed under variable load conditions. The performance of the engine in dual fuel mode was compared with the diesel. The dual fuel operation results in thermal efficiency close to the diesel and also reduces the NOx and smoke emissions significantly. From the experimental results, we concluded that biodiesel in dual fuel mode with cheaper gaseous fuel induction is an option for reducing the operating cost of the biodiesel fuelled CI engine. Copyright ©2011 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.