Jamil Ghojel

Waste heat recovery from the exhaust of low-power diesel engine using thermoelectric generators

To meet the increasing world demand for energy, the rate of depletion of non-renewable energy sources must be reduced while developing alternative renewable sources. This can be achieved by increasing the overall thermal efficiency of conventional power plants. One way to do this is by waste heat recovery. Most of the techniques currently available recover waste heat in the form of thermal energy which is then converted to electricity in a conventional steam power plant. Another approach which has received little attention so far is direct conversion of thermal waste energy into electricity. Thermoelectrics is the science dealing with both low-temperature and high-temperature thermal to electrical energy conversion systems. The paper describes a pilot program to investigate the applicability of thermoelectric generators to the recovery of medium-temperature waste heat from a low-power stationary diesel engine. Commercial thermoelectric modules using bismuth telluride based alloys and consisting of 98 couples were used. The modules require a heat source capable of supplying a heat flux of about 8 W/cm/sup 2/. With a temperature difference of 200/spl deg/C, each module converts 5% of the thermal energy that passes through it into electricity generating 14 W of electrical power. Heat transfer modelling was used to locate the optimum mounting position of the waste heat recovery system (WHRS) on the exhaust pipe. A compact device was then designed incorporating six modules with the exhaust pipe acting as the heat source. The required minimum temperature on the cold side of the modules was provided by using water-cooled heat sinks. Tests have shown that the performance specified by the manufacturer can be reproduced. One promising application for the tested WHRD is as a source of electrical power in motor vehicles in lieu of or in addition to the alternator. A detailed analysis of this application is also presented.

Experimental and analytical technique for estimating interface thermal conductance in composite structural elements under simulated fire conditions

Abstract Composite structural elements in the form of steel tubes filled with concrete are being increasingly used in buildings for their dual advantage of increased load bearing capacity and fire resistance. Models to predict the response of composite structures under fire conditions have been developed with varying degrees of accuracy. One of the major drawbacks for these models is ignoring the effect of thermal contact resistance at the steel–concrete interfacial. The reason for this oversight is due mainly to the absence of data in the literature quantifying this parameter. This paper summarizes an experimental and analytical investigation of the interfacial thermal contact conductance of an unloaded circular steel tube filled with non-reinforced normal concrete and exposed to high heat fluxes. Inverse heat conduction analysis and experimental measurements are used to estimate the thermal contact conductance as a function of steel temperature. Sensitivity analysis of the effect of the magnitude of the contact conductance on the temperature response of the composite element using direct heat conduction modelling is also presented.

Application of Inverse Analysis to Thermal Contact Resistance between very Rough Nonconforming Surfaces

A method to determine the contact conductance at the interface between steel and concrete under high temperature conditions, typical of enclosure fires, using experimental measurements and inverse heat conduction analysis is presented. This method is adopted because the interface under investigation is formed by very rough non-conforming surfaces and there are no data or mathematical models capable of describing such an interface. A specimen representing a square steel tube filled with concrete is heated in a modified electrical furnace to temperatures comparable to those observed in structural elements exposed to fire, and temperature-time histories in two-second increments are recorded at ten locations. The results are used to obtain a correlation representing averaged contact conductance for the steel-concrete interface of square steel tube filled with non-reinforced concrete as a function of temperature.

Optimization of the thermal regime of thermoelectric generators in waste heat recovery applications

A thermoelectric generator is a device which directly converts heat to electricity. These generators have been receiving renewed interest in a wide range of applications such as domestic wood heating, remote area power generation, automotive applications and power supply in interplanetary space flights. Applied as waste-heat recovery systems (WHRS), these generators can reduce fuel consumption and greenhouse gases such as carbon dioxide in stationary and mobile power plants. A pilot study of the applicability of thermoelectricity to waste-heat recovery from the exhaust gases of a small-scale steam boiler is presented. The steam boiler is used as the heat source for the low temperature WHRS of a single thermoelectric module (TEM). Two main types of heat sinks are used operating under various conditions, providing the necessary cold side temperature and hence the temperature gradient through the TEM. Both the energy input to the WHRS and the cooling flow rates of air and water are controlled to determine the effect on the electrical power output. The paper experimentally investigate the thermal regime of assorted heat sinks functioning under various circumstances to establish the optimum operating conditions to achieve maximum power outputs from the WHRS. Further work is planned to estimate the thermal contact resistance at various interfaces in the system with different electrical insulators.

The Role of Porous Media in Homogenization of High Pressure Diesel Fuel Spray Combustion

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper, we investigate a novel approach to the development of a homogenous charge-like environment through the use of porous media. The primary purpose of the media is to enhance the spread as well as the evaporation process of the high pressure fuel spray to achieve charge homogenization. In this paper, we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure and temperature plays in further enhancing this process.

Homogenisation of High Pressure Diesel Fuel Spray Combustion Using Porous Ceramic Media

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper we investigate a novel approach to the development of a homogenous charge like environment through the use of porous media. The primary purpose of the media is to enhance the spread of the high pressure fuel spray. In this paper we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure plays in further enhancing this process.Copyright

Modelling of electromagnetically excited turbulent flow of molten metal in a twin-channel induction furnace

Modelling the complex phenomena in channel induction furnaces is quite challenging. These phenomena include electromagnetics, Joule heating, turbulence and heat transfer. The paper describes the methodology and some results of modelling electromagnetically excited turbulent flow of molten metal in a channel induction furnace. The modelling covers both the inductor and the main pot holding the melt. The modelling is carried out for an arbitrary furnace geometry operating under steady state. The objective of the study is to assess the applicability of some of the existing turbulent models to this type of problems and examine the resulting temperature profile of the system.