Faculty Publications

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    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. © 2014 30th International PLEA Conference: Sustainable Habitat for Developing Societies: Choosing the Way Forward - Proceedings. All rights reserved.
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    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. © 2018 Elsevier Ltd.
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    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 (34°C, 38°C and 42°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. © 2018 International Heat Transfer Conference. All rights reserved.
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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. © 2018 Taylor & Francis Group, London.
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    Variation of Time Lag, Decrement Factor and Inside Surface Temperature with Solar Optical Properties of Building Envelope in Different Climatic Zones of India
    (Springer, 2020) Mahapatra, D.; Ashok Babu, T.P.
    Maintenance of thermal comfort inside buildings requires a significant amount of energy. According to the Centre for Science and Environment, the energy spent on achieving thermal comfort in commercial buildings and in residential buildings are 31% and 7%, respectively. Considering the energy crisis that world has been suffering; every individual should try to save energy by some means. The increase in urbanization over the last few years gave rise to boom in constructions. Choosing the materials used for the construction of buildings wisely can contribute towards energy saving. The solar optical properties of building envelope affect the surface temperature up to a great extent which in turn affects the energy used for thermal comfort. In this paper, the effect of solar optical properties on time lag decrement factor and inside surface temperature is studied in different Indian climatic zones. © 2020, Springer Nature Singapore Pte Ltd.
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    Theoretical Evaluation of Energy Performance of a Vapour Compression Refrigeration System Using Sustainable Refrigerants
    (Springer, 2020) Vali, S.V.; Ashok Babu, T.P.
    The chief goal of this present investigation is to evaluate performance parameters of various sustainable refrigerants as R22 alternatives. In this investigation apart from R290, R134a and R22, twelve mixture refrigerants were developed at various composition. Results showed that energy efficiency ratio (EER) of mixture refrigerant MR40 (R290/R134a 95/5 in mass%) (4.546) stood greatest among twelve investigated alternatives and it was closer to the EER of R22 (4.602). Compressor discharge temperature of MR40 was lower than R22 by 16.020C. Volumetric refrigeration capacity of MR40 (3424 kJ/m3) was relatively lesser than R22 (3801 kJ/m3). Power spent per ton of refrigeration (PPTR) of MR40 (0.773 kW/TR) stood lowest among twelve investigated alternatives and it was fairly greater than R22 (0.764 kW/TR). Global warming potential (GWP100) of MR40 (68) was very low compared to R22 (1760). Overall, performance of MR40 was closer to R22, when compared with all the twelve investigated alternatives, and hence, it might be treated as a suitable replacement to refrigerant R22. © 2020, Springer Nature Singapore Pte Ltd.
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    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 Te = 7.2 °C, Tk = 54.4 °C, ΔTsup = 11.1 °C and ΔTsub = 8.3 °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 11.79 °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. © Springer Nature Singapore Pte Ltd 2021.
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    Technical aspects of biodiesel and its oxidation stability
    (2009) Kapilan, N.; Ashok Babu, T.P.; Reddy, R.P.
    Biodiesel is a clean burning alternative renewable fuel made from natural renewable sources. It is defined as mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, which conform to ASTM specifications for use in diesel engines. Biodiesel present a very promising alternative fuel to diesel oil and properties of this oil offer the advantage of immediate substitution in existing diesel engines with little or no modifications at all. But one of the major technical problems associated with the biodiesel is its susceptibility to oxidation, which can cause the fuel to become acidic and to form insoluble gums and sediments that can plug fuel filters. This is due to the unsaturated fatty acid chains and the presence of the double bond in the molecule, which produce a high level of reactivity with the oxygen, especially when it placed in contact with air. The oxidation of fatty acid chains is a complex process that proceeds by a variety of mechanisms. The various other factors influence the oxidation process of biodiesel includes light, temperature, extraneous materials, peroxides, size of the surface area between biodiesel and air. One of the methods of improving biodiesel oxidative stability includes the deliberate addition of antioxidants or modification of the fatty ester profile. This article discusses the technical aspects of biodiesel and its oxidation stability.
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    Thermodynamic simulation of ammonia-water absorption refrigeration system
    (Serbian Society of Heat Transfer Engineers, 2008) Sathyabhama, A.; Ashok Babu, T.P.
    The ammonia-water absorption refrigeration system is attracting increasing research interests, since the system can be powered by waste thermal energy, thus reducing demand on electricity supply. The development of this technology demands reliable and effective system simulations. In this work, a thermodynamic simulation of the cycle is carried out to investigate the effects of different operating variables on the performance of the cycle. A computer program in C language is written for the performance analysis of the cycle.
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    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.