http://hdl.handle.net/20.500.12228/67 Wed, 15 Apr 2026 21:27:44 GMT 2026-04-15T21:27:44Z http://hdl.handle.net/20.500.12228/447 Studies on Long Term Average Optical Efficiency for Principal Solar Collectors and Shading Factors for Windows Rahman, A. N. M. Mizanur Assessment of techno-economic viabiity of solar energy systems is based on long term performance. The popular design methods for active as wel1 as passive solar energy systems require certain proprocessed parameters in addition to meteorological information on appropriate time scale. The present thesis deals with defining monthly average transmittance-absorptance product for flat plate collectors and optical efficiency for concentrating collectors consistent with the definition of monthly average daily utilizability. The procedure involved comparing the monthly average daily useful energy gain for flat plate collectors obtained by hour by hour summation procedure with the monthly average daily useful energy gain obtained as a product of heat removal factor, monthly average daily solar radiation on the collector aperture, monthly average daily utilizability and monthly average. Transmittance-absorptance product. In the second calculation transmission-absorptance product is an all day average value on the mean day of the month. The difference and an examination of the definition of monthly average daily utilizability established that the transmittance-absorptance product needs to be (defined as a weighted average of the instantaneous transmittance- absorptance I)product and solar radiation on the collector aperture above the critical radiation level. An eqaivalemit mean day (EMD) calculation has been proposed and validated to obtain the monthly average transmittance-absorptance product for flat plate collectors and the optical efficiency for concentrating collectors tracked in the five principal modes according to the above definition. A method to estimate the monthly average shading factors for recievers shaded by finite overhangs taking atmospheric transmittance into account has been developed and validated. The procedure involved developing sim pie equations relating finite shading factor values to the infinite values which are easily calculable in terms of the tilt factors for different planes. The present approach is valid for south as well as non-south facing receivers. Finally, expressions for the monthly average shading factors for infinite wingwalls, analogous to the expressions for infinite overhangs, have been developed validated. A feature of these algorithms is that they take into account the monthly average daily diffuse fraction and are valid for south facing as well as for non-south facing receivers. This thesis is submitted to the Department of Mechanical Engineering, Indian Institute of Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy, September 1997.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 242-251). Mon, 01 Sep 1997 00:00:00 GMT http://hdl.handle.net/20.500.12228/447 1997-09-01T00:00:00Z http://hdl.handle.net/20.500.12228/446 The Effects of Car A-Pillar and Windshield Geometry on Local Flow and Noise Alam, Dr. Firoz A desirable requirement in the production of modern vehicles world-wide is the provision of a high level of driving comfort. An important aspect of this is the minimisation of aerodynamic noise. As structure-borne, engine, tyre, and power-train noise sources have been reduced in recent years, the aerodynamic noise is significant, especially at driving speeds exceeding 100 km/h. Prior experimental studies have revealed that the flow around a passenger car's A-pillar region is a primary source of aerodynamic noise, since the highest pressure fluctuation occurs here. Also, this region is closest to the driver's ears. Whilst a small part of the noise can come from aerodynamic noise generated by the mirror as the flow is first incident on the A-pillar, this study will only be addressing flow around the A-pillar. It is known that the area and strength of the A-pillar flow separation depend mainly on the local A-pillar and windshield geometry and yaw angle. However, the effects of scaling, local radii and yaw angle on the potential for noise generation are not well understood. Scaling is important so that model-scale results can be translated to the full-scale. Computational Fluid Dynamics methods (CFD) are not sufficiently developed either to predict the surface pressure fluctuations or the resulting acoustic waves with the required degree of accuracy. The objectives of this work were to investigate the scale effects, the influence of the local A-pillar and windshield radii on the flow characteristics, and the influence of yaw angle. In order to address these objectives, a series of experimental investigations was conducted using five 40% scale generic models with different A-pillar and windshield geometries and using three production vehicles. One model had a sharp-edged vertical windscreen. The other four models had a 60° inclined windscreen, which is a typical slant angle for contemporary production passenger cars, and various degrees of edge rounding including a model with a sharp edge. These models were used to measure the surface mean and fluctuating pressures in the A-pillar region at different speeds and steady yaw angles. Production vehicles were used to evaluate the surface mean and fluctuating pressures close to the A-pillar region, and the 'in-cabin noise' as a function of steady yaw angle and increased rounding of the A-pillar. The production vehicle tests were performed at different speeds and yaw angles in wind-tunnels and on-road. Flow visualisation was used to supplement the pressure data. The surface mean and fluctuating pressures were converted to non-dimensional pressure coefficients and the frequency content of the fluctuating pressure was investigated via the normalised power spectral density. Generally the surface mean and fluctuating pressure coefficients were found to be independent of Reynolds numbers. However, when yawed, a slight dependency was found to occur on the leeward side. This minor dependency was noted in the separated regions, but was not evident in the re-attached areas. The amplitudes and frequencies of the fluctuating pressures scaled well with velocity head and Strouhal number. Therefore, a scale model can be used for the prediction of the surface hydrodynamic pressures in the Apillar region of a future vehicle when suitable scaling laws are used. The magnitudes of fluctuating pressures and the area of flow separation close to the A-pillar region depended largely on the local radii. Most energy from the fluctuating pressures in the A-pillar region was between Strouhal numbers 5 to 12. The maximum hydrodynamic pressure fluctuation was found to be between the separated and reattached areas rather than at the re-attachment points as has been proposed by other researchers. Yaw could increase the area and magnitude of the flow separation on the leeward side by an order of magnitude compared to the windward side for the slanted sharp-edged model. However, the model shape with no slant angle (i.e., a vertical windshield) produced an intense but relatively small flow separation on the windward side when yawed. Negligible flow separation was found on the models with corner rounding and increase of yaw angle did not increase the separation substantially, even on the leeward side. However, future work is recommended on an additional model incorporating a smaller corner radius. For the production vehicles an increased rounding of the A-pillar significantly reduced the magnitude of the external fluctuating pressures, although the 'in-cabin noise' typically reduced by 2-3 dB. The amplitudes and frequencies of the fluctuating pressures scaled well with velocity head and Strouhal number. Atmospheric turbulence, correlation between the external pressure fluctuations and in-cabin noise, and boundary layer characteristics in the A-pillar region were not included in this work but are thought to be worthy of further investigation. This thesis is submitted to the Department of Mechanical and Manufacturing Engineering, RMIT University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, September 2000.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 146-157). Fri, 01 Sep 2000 00:00:00 GMT http://hdl.handle.net/20.500.12228/446 2000-09-01T00:00:00Z http://hdl.handle.net/20.500.12228/298 Studies on Some Aspects of Electrochemical Grinding Bhowmick, Tarapada Electrochemical grinding (ECG) has become more and more important for its industrial use, in machining problems associated with grinding hard and wear resisting and even very soft electrically conductive materials. In a survey on ECG process, little attempts on theoretical analysis of the process rather more experimental investigations have been made. The main objective of the present work was to develop theoretical models to explain joint phenomena, mechanism and electrochemistry i.e. (i) to determine metal removal rate due to mechanical and that of electrochemical action individually, (ii) to find out the feed force required in ECG process, and (iii) to corroborate the models with experimental results. For this, an industrial model for the electrochemical grinding machine with hydraulic feed control system has been developed retrofitting an existing obsolete manual feed surface grinder. Different stages of grinding action are thoroughly analyzed and corresponding force components are established in terms of chip thickness, stress and loading coefficients. An octagonal extended ring type grinding dynamometer of stainless steel has been designed, constructed and calibrated. A high gain operational amplifier has been built to record force components. Electrochemical grinding geometry and kinematics are analyzed, and electrochemical and mechanical aspects of the process have been extensively studied. Investigation on the different process parameters and their inter-relations are also made. Experiments have been conducted on stainless steel and tungsten carbide (GT20) to examine the validity of the theoretical works and other experimental investigations. Theoretical analyses have been carried out on the determination of MRR and feed force. Different stages of grinding actions viz, sliding, ploughing, cutting, rubbing, viscous drag due to electrolyte pool are considered in feed force analysis. The depth of cut is used for combined mechanical and electrochemical actions. They are experimentally verified and found within the closure range of acceptance for industrial exploitation. The results indicate that material removal rate due to electrochemical action can be achieved up to 90% of the total material removed, and as a result, the feed force in ECO is found very less compared to conventional grinding. This thesis is submitted to the Department of Mechanical Engineering, Indian Institute of Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering, August, 1999.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 164-173). Sun, 01 Aug 1999 00:00:00 GMT http://hdl.handle.net/20.500.12228/298 1999-08-01T00:00:00Z http://hdl.handle.net/20.500.12228/297 Some Studies on Heat Transfer in Circulating Fluidized Beds Moral, Md. Nawsher Ali Experimental investigations were made to study the effect of fin and vertical probe height on hydrodynamics and heat transfer in circulating fluidized beds (CFB). The experiments were conducted in a 100 mm I.D., 5.15 m tall CFB unit. Air was supplied by a high pressure centrifugal blower. The distributor plate used was straight hole onfice type having 12.4% open area. The test section was located at 2.75 in above the distributor and electric tape heater was used as the source of heat. The temperatures of the inside wall and the bed at about the midpoint in the test section were measured with copper constantan thermocouples. Five plain and five finned test sections have been examined, three of which had rectangular fins and two had pin fins. Local sand of mean diameter 310 μm was used as the bed material. Measurements covered a range of superficial air velocity from 5.6 to 12.5 m/s, suspension density from 18 to 76 kg/m3 and bed temperature from 330 to 365 K. Three bed inventories of 20, 26 and 32 kg and five heat fluxes in the range of 3580 to 7876 W/m2 were used. One empirical model was developed with the help of dimensional analysis to predict heat transfer in a hot CFB to bare tube surfaces. One analytical model has been developed for the prediction of heat transfer to finned surfaces in a CFB both for long and short fins. An empirical equation has been developed correlating the parameters Nup, Rep and Lh/D to estimate heat transfer from the probes of different vertical heights. In addition one expression for calculating particle residence time has also been derived. The results predicted from the models and correlations have been compared with the present experimental results as well as those of other investigators and good agreement is observed. With the use of fins, the heat transfer coefficient was found to decrease by a maximum of 32% but the total heat transfer got enhanced by about 103% due to the additional surface area provided by the fins. Heat transfer coefficient was found to decrease and particle residence time was found to increase with the increase of vertical height of the probe. This thesis is submitted to the Department of Mechanical Engineering, Indian Institute of Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering, December 1990.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 381-398). Sat, 01 Dec 1990 00:00:00 GMT http://hdl.handle.net/20.500.12228/297 1990-12-01T00:00:00Z