Virendra Bhojwani

Design and manufacturing of travelling wave thermo-acoustic engine with varying regenerator length

ABSTRACT Thermo-acoustic engines are devices suitable to convert heat energy into acoustic energy and vice versa. In this paper, travelling wave thermo-acoustic engine was designed and fabricated for the operating conditions of 30 bar mean pressure of working fluid (Air, Helium, Hydrogen, Nitrogen) and 500°C hot side temperature. The regenerator was made up of the can(s) of stainless steel SA-347and can be adjusted to achieve the required length. The access to change wire mesh size and its length enables to reduce the test set-up time and to enhance flexibility during experimentation. The modified secondary cold heat exchanger was developed for effective heat extraction from the working fluid and the effect of modified regenerator on the intensity of the thermo-acoustic power was also addressed. The present study shares the suitable alternatives for material selection, design considerations and preliminary estimation of heat exchangers at the operating temperature and pressure. It provides initial dimensions and enables to make a prototype.

An experimental study to investigate the dynamic behaviour of thermal conductivity for different concentrations of Al2O3 nanofluid

ABSTRACT Thermal conductivity (k) is an important property of the fluid which contributes to the heat transfer. Presence of nanomaterial enhances the k of the base fluid and can be used as potential heat transfer medium in many industrial, domestic applications. Experimentation to study the effect on k due to nanomaterial addition to the base fluid is carried out. Alumina Oxide (Al2O3) of different concentrations was selected as nanomaterial with water as the base fluid. Results showed that nanofluid with 7.5% Al2O3 gives 22% increase in k as compared to base fluid. Also, it was observed that as nanomaterial % concentration increases, the % decrease in k increases. For test period, water shows a negligible reduction in k; compared to 5.5% decrease in k for 7.5% Al2O3 nanofluid. This study leads to the conclusion that nanofluids are having good k for certain time period; after that replacement of fluid is necessary.

Resonance analysis of opposed piston linear compressor for refrigerator application

ABSTRACT The opposed piston linear compressor is considered to be the future of silent, reliable and efficient compression technologies. For long valves, less linear compressors have been widely used in cryocoolers for space applications. Recently research has established its high-performance characteristics which are useful in household refrigeration application. Unlike reciprocating compressors which are driven by rotary motors and need a crank connecting rod mechanism to convert rotary into linear motion, a linear compressor is driven by a linear motor which reduces the number of moving parts. This feature makes the compressor more reliable, more efficient and has a silent operation. The piston (suspended on spring stiffness) in the linear compressor is a free piston, i.e. motion of the piston is not constrained hence the performance of the linear compressor is highly dependent on system resonance. Free piston motion offers the unique advantage of ease of modulation, i.e. the stroke of the compressor and hence the delivery mass flow rate coming out of the compressor can be easily controlled by changing the supply voltage. Resonance in the linear compressor is a function of moving mass, spring stiffness and operating or electrical frequency. Achieving resonance in the linear compressor results in maximising the cooling performance of the refrigerator and minimising the input power requirement and hence an increase in the COP of the refrigeration system. The present paper discusses the results from resonance testing of the opposed piston linear compressor for household refrigerator using the fast Fourier transformation analysis. There are different parameters that are considered to optimise the natural frequency of the opposed piston linear compressor, consisting of frequency, moving mass, and spring stiffness. The piston performs compression and suction in a similar manner as in the conventional reciprocating compressor. An opposed piston linear compressor exhibits high energy efficiency due to its simple construction and less moving parts, its mechanical losses are much less than the reciprocating compressor.

Reduction in the exhaust emissions of four-stroke multi-cylinder SI Engine on application of multiple pairs of magnets

ABSTRACT Static magnetic field produced by permanent magnets applied to the fuel lines of internal combustion engines reduces viscosity of fuel, leading to better atomisation and improved carburetion, which enhances the combustion of the fuel and performance of the engine. Increased combustion reduces HC (hydrocarbon) and CO (carbon monoxide) % emitted from exhaust. Experiments in present work emphasise the effect of use of multiple pairs of permanent magnets of 3000 gauss intensity each, installed to the fuel line of four-stroke SI engine. It is evident from experiments that with increasing number of pairs of magnet lead to decrease in emissions. Results validate the impact of magnetic field strength on emissions from exhaust. Experimental results show that with application of magnetic flux to the fuel at constant load of 2 kg, there is 17.46% reduction in CO emissions, 18.048% reduction in HC and 1.118% increase in CO2 from the exhaust on the use of 5 pairs of magnets.

Investigation on a diesel engine’s performance with integration of magnetic flux on the fuel line

ABSTRACT Application of magnetic flux (MF) on the fuel line of diesel engines is a promising technique to enhance the performance of the engine. In this work, MF was applied by placing neodymium magnet pairs (MP) on the fuel line of a diesel engine test setup. Tests were carried out for different loads in the range of 0–8 kg. In the first stage, performance of the test setup was evaluated without MF for fixed load condition; in the second stage, performance evaluation was done by increasing number of MP on the fuel line – that is, the number of magnetic pairs was increased from 1 to 4. The experimental results confirmed that fuel consumption rate decreases with an increase in magnetic pair from 1 to 3; after employing the fourth magnetic pair, an increase in fuel consumption rate was observed. This clearly gives an idea for the presence of critical magnetic field for fuel savings.

Performance predictions and parametric analysis of a valved linear compressor using a mathematical model

ABSTRACT A mathematical model for a linear compressor with valves is developed. A linear compressor consists of an oscillating motor and a piston rigidly coupled to it. The mathematical model deals with the dynamic equation of a linear compressor consisting of inertia, motor force, and damping. It also solves the electrical circuit equation to estimate the current flowing through the motor circuit. The model considers the dynamic operation of suction and discharge valves. The refrigerant properties are estimated by interfacing the programme with REFPROP to predict the cylinder instantaneous pressure and temperature. Finally, the model predicts the net cooling capacity, compressor input power, and COP for the given compressor geometry. The mathematical model is validated with the experimental results reported by Lee et al. (2004. ‘Linear Compressor for Air-Conditioner.’ L. G. Electronics, international compressor engineering conference, Purdue University, C047, 1–7). Parametric analysis of the compressor is done by varying parameters like input voltage, refrigerant, and superheating temperature of the refrigerant. Results generated by the mathematical model are presented and discussed.