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.     

Investigating the performance and emission characteristics of an SI engine using Peltier element cooling effect

An internal combustion engine can convert only 30–35% of the heat energy supplied to it into useful work, and the remaining heat is lost through exhaust gases. The temperature of gases will be around 600°C. Reduction of heat carried away by the exhaust gases can be done by providing proper engine cooling system. This study deals about improving a two-stroke spark ignition engine’s efficiency by cooling its head using Peltier element. The Peltier element is placed in the engine head by cutting the fins to improve the efficiency of the two-stroke engine by maintaining the working temperature of the engine at 70°C. As per the experimental results, a decrease of 14% in brake-specific fuel consumption and an efficiency improvement of 19% were achieved. The % reduction in carbon monoxide, nitrogen oxides and hydrocarbons recorded are 5%, 20% and 40%, respectively.     

Experimental study and analysis of air heating system using a parabolic trough solar collector

An experimental study of air heating system was carried out using a parabolic trough collector with a U-tube aluminium heat exchanger. An evacuated tube placed at the focal length of the parabolic trough collected the solar radiations reflected from the surface of parabolic trough. The air was used as a working fluid, which was heated by passing it through a U-shaped aluminium heat exchanger placed inside the evacuated tube. It was found that efficiency of the parabolic trough collector depends on the mass flow rate, solar intensity and use of fins. It was observed that by using fins at a high mass flow rate of 4.557?kg/h, the maximum temperature of 126°C was achieved which is 13.27% more than the maximum temperature obtained without fins. Furthermore, for a low-mass-flow rate of 1.69?kg/h, the maximum temperature obtained was 149°C.     

Experimental investigation of the solar cooker during sunshine and off-sunshine hours using the thermal energy storage unit based on a parabolic trough collector

A solar cooker based on a parabolic trough collector with thermal energy storage (TES) was investigated. In this experimental set-up, solar radiations were focused on the absorber tube and the collected heat was transferred to the solar cooker by natural circulation (thermosiphon) of the working fluid. The water and thermal oil (engine oil) were used separately as working fluids. Acetanilide was used as the TES material in the solar cooker. In day time, the phase change material (PCM) stored heat as well as transferred it to the cooking pot. In evening time, the stored energy by PCM was used to cook the food. The cooking process was carried out with different foods and with variation in the quantity of food. It was found that the temperature of thermal oil was 10–24°C higher than water as the working fluid. The system was able to cook the food twice a day and the rate of evening cooking was higher as compared with noon cooking. Using thermal oil as the working fluid, the quantity of heat stored by PCM was increased by an amount of 19.45–30.38% as compared with water.     

Experimental investigation of free convection in roof solar collector

A test set-up was developed for determining the internal convective heat transfer coefficient and the induced air flowrate of a roof solar collector. The set-up was composed of an open-ended inclined rectangular channel. The tilt angle and air gap of channel were fixed at 30° and $\text{140}\text{mm}$, respectively. The inner channel width and length were 680 and $\text{1360}\text{mm}$, respectively. The upper plate was maintained at a uniform temperature and tests were carried out for a wide range of temperature varying between 40°C and 75°C. Data analysis were made to develop Nusselt and Reynolds number correlations as a function of Rayleigh number and aspect ratio (gap/length). The equations could be used for determining the mean convection heat transfer coefficient and the induced air flowrate of the roof solar collectors and a wide range of convective heat exchangers of similar geometry as well.     

A comparative performance analysis of solar heat exchangers for solar hot water application under controlled laboratory conditions

The paper presents the experimental performance evaluation of a novel retrofit heat exchanger (‘SolaPlug’) developed for solar hot water storage applications. The performance of this system was compared with a traditional dual-coil (‘Coil’) solar cylinder under controlled operating conditions. The tests were conducted under different solar-simulated conditions with a 30 and 20 evacuated tube collector. The results showed that after a 6-h test period, the average water temperatures within the store for the ‘SolaPlug’ system were 58.8°C and 40.5°C at 860 and 459?W?m^?2, respectively, and for the ‘Coil’ system were 60.5°C and 40.6°C when a 30 tube collector was used. The performance of the ‘SolaPlug’ system was marginally better than the ‘Coil’ system under the low solar input condition. Under high insolation condition, the overall ‘SolaPlug’ system efficiency was found to be 4.3% lower than that of the ‘Coil’ system. The ‘SolaPlug’ heat exchanger rating was 222?W?K^?1.     

Numerical investigations on the Dish–Stirling engine system

The Stirling engine is an environmentally friendly external combustion heat engine and reduces the complexities of the combustion process, and indirectly helps in reduction of CO₂ emission. Modelling based on cyclic analysis is performed for a Beta configuration Stirling engine of 1.5?kW_e capacity using a rhombic drive for the solar-dish-supported Stirling engine. The analysis helps in estimating the overall efficiency of the system using the experimental correlation of the solar concentrator ARUN160 at the engine operating temperature. The analysis shows that the system will have overall efficiency around 25% in the range of 750–1050?K at the expansion space. The degradation of performance compared to that at an operating temperature of 1025?K is only marginal and makes 750?K a more preferred temperature. The present study evaluates a range of possible design goals and provides suitable alternatives and thus provides a clear understanding of the system design considerations.     

Study on phase change material and its appropriate thickness for controlling solar cell module temperature

ABSTRACT

Appropriate thickness of phase change material (PCM) to control the solar cell module temperature for increasing power generation was carried out. A PCM, RUBITHERM RT42, with the melting point at 42°C and a thickness of 50?mm was used to absorb heat at the back of a 250?W_p polycrystalline solar cell. A numerical enthalpy method to predict the melting phenomenon of the PCM, RT35, 42, 47, and 55, and the solar cell module temperature was developed. The results agreed well with those of the experimental data. It was found that the maximum generated power was around 167?W in comparison with 147?W of the normal unit at a solar radiation of 867?W/m². The daily power outputs were 0.707 and 0.642?kWh, respectively. From the simulation under Chiang Mai climate, for RT42 PCM, it was found that the appropriate thickness was around 40?mm.     

Combustion characteristics of the direct injection diesel engine fuelled with corn oil methyl ester

Petroleum-based fuels is a finite resource that is rapidly depleting. Consequently, petroleum reserves are not sufficient enough to last many years. In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for direct injection (DI) diesel engines. The experimental work has been carried out to estimate the combustion characteristics of a single-cylinder, four-stroke, DI diesel engine fuelled with corn oil methyl ester (COME) and diesel blends. The COME was preheated to temperatures namely 50°C, 70°C and 90°C before it was supplied to the engine. The optimised preheated temperature of 70°C was chosen based on the higher brake thermal efficiency and lower specific fuel consumption. The performance, emission and combustion characteristics are evaluated by running the engine with COME and diesel blends at this preheated temperature. In this paper, the combustion characteristics are only discussed. The combustion characteristics such as ignition delay, maximum rate of pressure, heat release rate, cumulative heat release rate, mass fraction burned and combustion duration of COME methyl ester and diesel were evaluated and compared with neat diesel. The rate of pressure rise and maximum combustion pressure inside the cylinder were high for COME blends compared with neat diesel. The heat release rate of diesel is higher compared with COME blends. The ignition delay and combustion duration are decreased for COME blends compared with neat diesel. The cumulative heat release rate and mass fraction burnt of COME blends are higher than neat diesel.     

Collector characterisation and heat loss tests on a novel batch solar water heater with CPC reflector for households

ABSTRACT

This solar water-heating unit is an integration of the older concept of batch water heating with the modern trends in solar water-heating technologies i.e. incorporating a concentrator in the design. The concentrator used is the compound parabolic type (CPC) which is a non-imaging device having wider acceptance angle (64°) and supported on a wooden cradle, which comprises the two arms of the parabola. To suppress the heat loss, an air gap has been introduced in the arms of the CPC. The collector is a single larger diameter drum which serves both as an absorber and storage unit positioned at the focus of CPC. The parametric study of the model showed the thermal efficiency of the collector as high as 38% and maximum water temperature attained was 53°C. Heat loss tests performed on the collector on a 24-hr cycle period showed good long time performance estimates. The response time of collector computed and performance characteristic curve plotted to predict system response under any given conditions of solar insolation and ambient temperature.     

Numerical simulation on the temperature field in an equipment cabin of a high-speed railway train

With train speed increasing, the heat generation from its key equipment is growing as well and the cooling and ventilation of the equipment cabin become more and more important. In this paper, computational fluid dynamics (CFD) method is adopted to simulate the airflow and the temperature field in indoor and outdoor space of the equipment cabin when the train moves at 250 km/h in open space. The simulation results indicate that the surface temperature of the main heat generation equipment is not beyond the limit. When the train moves forward and backward, the maximum average surface temperature of the heat generation equipment is 56.5 °C and 71.7 °C, respectively, and the airflow rates of the fans in the equipment cabin are decreased by 9.1% and 5.2%, if compared to the rated value, respectively. Both forward and backward running conditions should be considered when designing the layout of the equipment and grilles. It is suggested that, the major heat generation equipment should be located in the middle of the cabin; the flow rate decrement of the cooling fan when the train moves at 250 km/h should be taken into account.     

Performance optimisation for an irreversible variable-temperature heat reservoir air refrigerator

The performance analysis and optimisation of an irreversible air refrigerator with variable-temperature heat reservoirs is carried out by taking the cooling load density, i.e., the ratio of cooling load to the maximum specific volume in the cycle, as the optimisation objective using finite-time thermodynamics (FTT) or entropy generation minimisation (EGM) in this paper. The analytical formulae for the relationships between cooling load density and pressure ratio, as well as between coefficient of performance (COP) and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers, and the irreversible compression and expansion losses in the compressor and expander. The influences of the effectiveness of the heat exchangers, the inlet temperature ratio of the reservoirs, and the efficiencies of the compressor and expander on the cooling load density versus and pressure ratio are provided by numerical examples. The cooling load density optimisation is performed by finding the optimum pressure ratio of the compressor, the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for a fixed total heat exchanger inventory, and the optimum heat capacity rate matching between the working fluid and the heat reservoirs. The influences of some design parameters, including the effectiveness of the heat exchangers between the working fluid and heat reservoirs, the efficiencies of compressor and expander, the inlet temperature ratio of heat reservoirs, the heat conductance distribution and the heat capacity rate matching between the working fluid and the heat reservoirs on the maximum cooling load density are provided by numerical examples. Optimisation of refrigeration plant design leads to a reduction in size of the compressor, expander, and the hot- and cold-side heat exchangers.     

Exploitation thermique du proche sous-sol par pompe a chaleur

In the heating systems using the near underground as cold source for the heat pump, ground calories are taken out by shallow buried exchangers (less than 3 meters deep). Presently, the design of this kind of plantings is quite empirical. In order to forecast more exactly the thermal behaviour of the plant and of the surrounding ground, we built a bi-dimensionnal model of the heat transfers in a ground section perpendicular to the pipes being used as buried exchanger. The first results achieved with this model are presented here. They show the influence on the temperature field in the ground and on the heat exchanges around the pipes, of essential parameters as deepness of the tubes planting, ground thermal properties and eventual injection of calories provided by solar collectors.     

Thermal performance analysis of evacuated tubes solar air collector in Indian climate conditions

The thermal performance of one-ended evacuated tubes solar air collector is experimentally investigated during the winter season at NIT Kurukshetra, India [29 ° 58^′(latitude) North and 76 ° 53 ^′ (longitude) East]. The collector consists of 15 one-ended evacuated tubes with different lengths of directional inner aluminium tubes (inserted tubes) and a manifold channel, with air used as a working fluid. The inlet air flows through the directional inner aluminium tubes as a result of forced convection. In this experiment, evacuated tubes are used for producing hot air corresponding to different lengths of directional aluminium tubes without using any intermediate fluid. The temperature of the outlet air depends on the air flow rate, length of the directional aluminium tube and solar intensity. The maximum temperature difference between outlet air and inlet air at solar intensity 904 W/m² was found to be 72.7 °C with a flow rate of 5.06 kg/h and length of 0.83 m.     

Transient three-dimensional window thermal effects

A model is developed, and checked experimentally, to allow reasonably accurate computer calculations for three-dimensional temperature distributions in sunlit, partly shaded windows. The time evolution of surface temperature profiles, the sideways heat flow to and from adjacent walls, and the heating due to solar absorption in the glazing can be calculated. To reduce computation time, only two layers of cells were taken for each glazing pane, and uniform heat transfer was assumed between the panes. Nevertheless, the calculations matched well with experimental temperatures obtained for nine different full-scale windows at different orientations in a rotatable test hut on 27 clear or nearly clear winter days. In some winter experiments, an average of 15% of the 24-hour heat loss through a south window went sideways to the adjacent walls, with a minimum of 10% near noon, and a maximum of 20% near midnight. Near noon, with an ambient temperature of — 7°C (20°F), the centre of the inside of a south-facing triple-glazed window was above room temperature, due to solar absorption in the glass. At the same time, the inside of the shaded edge of the glazing was below room temperature.     

Efficiency characteristic of building integrated photovoltaics as a shading device

A building-integrated photovoltaic system (BIPV) has been operated over 1 year in the Samsung Institute of Engineering & Construction Technology (SIECT) in Korea. The PV cells are mounted on the south facade and on the roof of the SIECT in the Giheung area. Special care was taken in the building design to have the PV modules shade the building in the summer, so as to reduce cooling loads, while at the same time allowing solar energy to enter the building during the heating season, and providing daylight. This paper gives a 1 year analysis of the system performance, evaluation of the system efficiency and the power output, taking into account the weather conditions. As a part of certain design compromises, that took into account, aesthetic, safety, and cost considerations, non-optimal tilt angles and occasional shading of the PV modules made the efficiency of PV system lower than the peak rating of the cells. The yearly average efficiency of the sunshade solar panel is 9.2% (average over 28.6°C surface temperature), with a minimum of 3.6% (average over 27.9°C surface temperature) in June and a maximum of 20.2% (average over 19.5°C surface temperature) in December.     

热管技术在近室温工况条件下节能应用

本文分析了热管换热技术在近室温工况条件下节能应用的技术适用性及其与工业应用的条件差异；对热管换热器结构形式、材料选择、最佳充液率等参数的确定以及通风空调节能、太阳能利用、地热能利用、低品位废热利用、热管供热系统等工程应用途径和形式、设计方法和原则等一般性工程问题作了系统分析，为实际工程应用和设计提供参考。     

Organismes members du CIB La Nouvelle‐Zélande

Introducing a feature on the controlled storage and release of energy; especially captured solar energy; this article describes a design for a curtain wall which will provide seasonal heating and cooling in a passive solar building. It is being tested at the EEC Commission's Joint Research Centre at Ispra, Northern Italy: The principles and techniques employed in this phase-change concept produce a module which can collect, store and release solar heat at around 20 °C with forced air circulation. It is dimensioned to meet the daily energy demand for air conditioning during the summer and most of the heating demand in the winter.     

Characteristic parameters of a hypocaust construction

Hypocaust, an ancient Roman concept for keeping the inside of buildings warm, has been explained with a survey of a few modern buildings based on these concepts and using solar heat employing a number of design variations. Results expressed in terms of energy requirements per m² of floor area per degree day comes out to be minimum (15.4 kJ m⁻² per DD per annum) for a solar chimney and maximum for solar air collectors (128.4 kJ m⁻² per DD per annum). The basic parameters that determine the performance of a hypocaust construction are size of the cavity determining the heat transfer between the flowing fluid and the building component and the storage capacity of the hypocaust element. The optimum width of the cavity comes out to be between 50 mm and 100 mm. Heat storage capacity of the building element used as hypocaust corresponds to 0.125°K temperature rise per hour in relation to the building heat load.     

Simulation of a domestic ground source heat pump system using a three-dimensional numerical borehole heat exchanger model

Common approaches to the simulation of borehole heat exchangers (BHEs) assume heat transfer in circulating fluid and grout to be in a quasi-steady state and ignore fluctuations in fluid temperature due to transport of the fluid around the loop. However, in domestic ground source heat pump (GSHP) systems, the heat pump and circulating pumps switch on and off during a given hour; therefore, the effect of the thermal mass of the circulating fluid and the dynamics of fluid transport through the loop has important implications for system design. This may also be important in commercial systems that are used intermittently. This article presents transient simulation of a domestic GSHP system with a single BHE using a dynamic three-dimensional (3D) numerical BHE model. The results show that delayed response associated with the transit of fluid along the pipe loop is of some significance in moderating swings in temperature during heat pump operation. In addition, when 3D effects are considered, a lower heat transfer rate is predicted during steady operations. These effects could be important when considering heat exchanger design and system control. The results will be used to develop refined two-dimensional models.