Performance of a twin power piston low temperature differential Stirling engine powered by a solar simulator

This paper provides an experimental investigation on the performance of a low-temperature differential Stirling engine. In this study, a twin power piston, gamma-configuration, low-temperature differential Stirling engine is tested with non-pressurized air by using a solar simulator as a heat source. The engine testing is performed with four different simulated solar intensities. Variations of engine torque, shaft power and brake thermal efficiency with engine speed and engine performance at various heat inputs are presented. The Beale number, obtained from the testing of the engine, is also investigated. The results indicate that at the maximum simulated solar intensity of 7145 W/m², or heat input of 261.9 J/s, with a heater temperature of 436 K, the engine produces a maximum torque of 0.352 N m at 23.8 rpm, a maximum shaft power of 1.69 W at 52.1 rpm, and a maximum brake thermal efficiency of 0.645% at 52.1 rpm, approximately.     

A four power-piston low-temperature differential Stirling engine using simulated solar energy as a heat source

In this paper, the performances of a four power-piston, gamma-configuration, low-temperature differential Stirling engine are presented. The engine is tested with air at atmospheric pressure by using a solar simulator with four different solar intensities as a heat source. Variations in engine torque, shaft power and brake thermal efficiency with engine speed and engine performance at various heat inputs are presented. The Beale number obtained from the testing of the engine is also investigated. The results indicate that at the maximum actual energy input of 1378 W and a heater temperature of 439 K, the engine approximately produces a maximum torque of 2.91 N m, a maximum shaft power of 6.1 W, and a maximum brake thermal efficiency of 0.44% at 20 rpm.     

The effects of turbocharger on the performance and exhaust emissions of a diesel engine fuelled with biodiesel

This paper investigates the effects of turbocharger on the performance of a diesel engine using diesel fuel and biodiesel in terms of brake power, torque, brake specific consumption and thermal efficiency, as well as CO and NO_x emissions. For this aim, a naturally aspirated four-stroke direct injection diesel engine was tested with diesel fuel and neat biodiesel, which is rapeseed oil methyl ester, at full load conditions at the speeds between 1200 and 2400 rpm with intervals of 200 rpm. Then, a turbocharger system was installed on the engine and the tests were repeated for both fuel cases. The evaluation of experimental data showed that the brake thermal efficiency of biodiesel was slightly higher than that of diesel fuel in both naturally aspirated and turbocharged conditions, while biodiesel yielded slightly lower brake power and torque along with higher fuel consumption values. It was also observed that emissions of CO in the operations with biodiesel were lower than those in the operations with diesel fuel, whereas NO_x emission in biodiesel operation was higher. This study reveals that the use of biodiesel improves the performance parameters and decreases CO emissions of the turbocharged engine compared to diesel fuel.     

Design and performance of a moderate temperature difference Stirling engine

The present work developed a prototype Stirling engine working at the moderate temperature range. This study attempts to demonstrate the potential of the moderate temperature Stirling engine as an option for the prime movers for Concentrating Solar Power (CSP) technology. The heat source temperature is set to 350–500 °C to resemble the temperature available from the parabolic trough solar collector. This moderate temperature difference allows the use of low cost materials and simplified mechanical designs. With the consideration of local technological know how and manufacturing infrastructure, this development works with a low charged pressure of 7 bar and uses air as a working fluid. The Beta-type Stirling engine is designed and manufactured for the swept volume of 165 cc and the power output of 100 W. The performance of engine is evaluated at different values of charge pressures and wall temperatures at the heater section. At 500 °C and 7 bar, the engine produces the maximum power of 95.4 W at 360 rpm. The thermal efficiency is 9.35% at this maximum power condition. Results show that the moderate temperature operation offers a clear advantage in terms of the specific power over the low temperature operation. In terms of the West number, the present work demonstrated that the moderate temperature difference operations could offer the performance on par with the high temperature operations with more simple and less costly development.     

Experimental investigation on performance of a rotating closed loop pulsating heat pipe

Pulsating heat pipes (PHPs) are interesting heat transfer devices. Their simple, high maintaining, and cheap arrangement has made PHPs very efficient compared to conventional heat pipes. Rotating closed loop PHP (RCLPHP) is a novel kind of them, in which the thermodynamic principles of PHP are combined with rotation. In this paper, effect of rotational speed on thermal performance of a RCLPHP is investigated experimentally. The research was carried out by changing input power (from 25 W to 100 W, with 15 W steps) and filling ratio (25%, 50%, and 75%) for different rotational speeds (from 50 rpm to 800 rpm with an increment of 125 rpm). The results presented that at a fixed filling ratio, thermal resistance of RCLPHP decreased with increasing heat input applied to evaporator. Above a certain range of heat input, probability of partial dry-out of evaporator existed, which led into thermal performance deterioration of RCLPHP. Moreover, thermal resistance of RCLPHP decreased with increasing rotational speed and probability of partial dry-out in the evaporating section reached to its least amount.     

Optimization of finned-tube heat exchangers for diesel exhaust waste heat recovery using CFD and CCD techniques

In this paper, response surface methodology (RSM) based on central composite design (CCD) is applied to obtain an optimization design of finned type heat exchangers (HEX) to recover waste heat from the exhaust of a diesel engine. The design is performed for a single point operation (1600 rpm and 60 N m) of an OM314 diesel engine obtained from experimental measurements. Based on the CCD principle, fifteen HEX cases with different fins height, thickness and number are modeled numerically and the optimization is done to have the maximum heat recovery amount and minimum of pressure drop along the heat exchanger.     

Measuring of heat capacity

A simply device was developed and tested. It is designed to measure the heat capacity of square plates with size ～30 × 30 mm, at room temperature. This device consumes permanent electric power. The heat losses to the surroundings are taken into account. A mathematical model, of this heat capacity meter, is described in the paper. The heat capacity of a sample is calculated as a difference between measured heat capacity (of heater and sample) and heat capacity of the heater only. The optimal size of a test body, and reference one, is so as the contact surface of the heater.     

Effect of non-uniform heating on the performance of the microchannel heat sinks

The present study experimentally investigates the performance of a 2-pass microchannel heat sink subject to non-uniform heating. The size of the microchannel heat sink is 132 mm × 82 mm × 6 mm with a rectangular channel of 1 mm × 1 mm. Three independent heaters having identical size (96 mm × 38.5 mm × 1 mm) is placed consecutively below the microchannel heat sink. Two kinds of manifolds are used for testing of the microchannel, one with a side entrance (type A) and the other with a front entrance (type B). Test results show that both maximum temperature and average temperature rise with the total input power, and this is applicable for both manifolds. For uniform heating condition, the maximum temperature for type B manifold is much lower than that for type A manifold due to a better flow distribution and heat transfer performance. The pressure drop is slightly reduced with the rise of supplied power. For non-uniform heating, the maximum temperature and the average temperature depend on the location of heaters. For the same supplied power with non-uniform heating, it is found that heater being placed at the inlet of the microchannel will give rise to a higher maximum temperature than that being placed at the rear of the heat sink. This phenomenon is especially pronounced when the inlet flowrate is comparatively small and becomes less noted as the inlet flowrate is increased to 0.7 L/min.     

Optimization of a dual free piston Stirling engine

This work relates the theoretical study of the dynamic behavior of a dual free-piston Stirling engine (DFPSE) coupled with an asynchronous linear alternator. This machine integrates one piston and two displacers placed in a symmetrical way compared to the piston to improve the stability of the machine. The paper presents an analytical study of the dynamic balance equations of a DFPSE. This model takes into account the non-linear dissipative effects of the fluid and the electromagnetic forces. The dynamic balance equations of the machine are solved by means of linearized pressure in the time domain especially. The objective is to evaluate the thermo-mechanical conditions for stable operation of the engine. The developed model may be used to simulate the dynamic behaviour of a built engine. The DFPSE produces a mechanical power of 1 kW and it has a design operating point of 1.4 MPa corresponding to the frequency about 22 Hz. Helium is the working fluid. This machine is designed to be used as a micro combined heat and power (μCHP) system for combined generation of electricity and heat.     

Conversion of a commercial spark ignition engine to run on hydrogen: Performance comparison using hydrogen and gasoline

The modifications performed to convert the spark ignition gasoline-fueled internal combustion engine of a Volkswagen Polo 1.4 to run with hydrogen are described. The car is representative of small vehicles widely used for both city and interurban traffic. Main changes included the inlet manifold, gas injectors, oil radiator and the electronic management unit. Injection and ignition advance timing maps were developed for lean mixtures with values of the air to hydrogen equivalence ratio (λ) between 1.6 and 3. The established engine control parameters allowed the safe operation of the hydrogen-fueled engine (H₂ICE) free of knock, backfire and pre-ignition as well with reasonably low NO_x emissions. The H₂ICE reached best brake torque of 63 Nm at 3800 rpm and maximum brake power of 32 kW at 5000 rpm. In general, the brake thermal efficiency of the H₂ICE is greater than that of gasoline-fueled engine except for the H₂ICE working at very lean conditions (λ = 2.5) and high speeds (above 4000 rpm). A significant effect of the spark advance on the NO_x emissions has been found, specially for relatively rich mixtures (λ < 2). Small changes of spark advance with respect to the optimum value for maximum brake torque give rise to an increase of pollutant emissions. It has been estimated that the hydrogen-fueled Volkswagen Polo could reach a maximum speed of 140 km/h with the adapted engine. Moreover, there is enough reserve of power for the vehicle moving on typical urban routes and routes with slopes up to 10%.     

Sintered porous heat sink for cooling of high-powered microprocessors for server applications

This paper experimentally investigates the sintered porous heat sink for the cooling of the high-powered compact microprocessors for server applications. Heat sink cold plate consisted of rectangular channel with sintered porous copper insert of 40% porosity and 1.44 × 10^?11 m² permeability. Forced convection heat transfer and pressure drop through the porous structure were studied at Re ? 408 with water as the coolant medium. In the study, heat fluxes of up to 2.9 MW/m² were successfully removed at the source with the coolant pressure drop of 34 kPa across the porous sample while maintaining the heater junction temperature below the permissible limit of 100 ± 5 °C for chipsets. The minimum value of 0.48 °C/W for cold plate thermal resistance (R_cp) was achieved at maximum flow rate of 4.2 cm³/s in the experiment. For the designed heat sink, different components of the cold plate thermal resistance (R_cp) from the thermal footprint of source to the coolant were identified and it was found that contact resistance at the interface of source and cold plate makes up 44% of R_cp and proved to be the main component. Convection resistance from heated channel wall with porous insert to coolant accounts for 37% of the R_cp. With forced convection of water at Re = 408 through porous copper media, maximum values of 20 kW/m² K for heat transfer coefficient and 126 for Nusselt number were recorded. The measured effective thermal conductivity of the water saturated porous copper was as high as 32 W/m K that supported the superior heat augmentation characteristics of the copper–water based sintered porous heat sink. The present investigation helps to classify the sintered porous heat sink as a potential thermal management device for high-end microprocessors.     

Diesterol: An environment-friendly IC engine fuel

Diesterol is a new specific term which denotes a mixture of fossil diesel fuel (D), vegetable oil methyl ester called biodiesel (B) and plant derived ethanol (E). In the context of the present paper, this term refers specifically to the combination of diesel fuel, bioethanol produced from potato waste, dehydrated in a vapor phase using 3A Zeolite, and sunflower methyl ester produced through transesterification. The mixture of DBE, i.e. diesterol, was patented under the Iranian patent No. 39407, dated 12-3-2007. The main purpose of this research work was to reduce engine exhaust NO_x, CO, HC and smoke emissions due to application of biofuel and the increase of fuel oxygen content. It was needed to prepare suitable low cost and renewable additives. The diesterol properties such as pour point, viscosity, flash point, copper strip corrosion, ash content, sulfur content and cetane number were determined experimentally. The optimum ratio of bioethanol and biodiesel was found to be 40/60 considering fuel oxygen content, fuel price and mixture properties. Bioethanol was added to enhance the oxygenated component in the fuel, while the sunflower methyl ester was added to maintain the fuel stability at low temperatures. The parameters considered for investigation are the engine power, torque, specific fuel consumption and exhaust emissions for various mixture proportions. The experimental results showed that bioethanol plays an important role in determining the flash point of the blends. By adding 3% bioethanol to diesel and sunflower methyl ester, the flash point was reduced by 16 °C. The viscosity of the blend was also reduced by increasing the amount of bioethanol. The sulfur content of bioethanol and sunflower methyl ester is very low compared to diesel fuel. The sulfur content of diesel is 500 ppm whereas that of bioethanol and sunflower methyl ester is 0 and 15 ppm, respectively. This lower sulfur content is another factor enhancing the use of fuel blends in diesel engines. The bioethanol and sunflower methyl ester combination has sulfur content less than 20 ppm. The maximum power and torque using diesel fuel were 17.75 kW and 64.2 Nm at 3600 and 2400 rpm, respectively. Adding oxygenated compounds to the new blend seems to slightly reduce the engine power and torque and increased the average sfc for various speeds. The experimental measurement and observation of smoke concentration, NO_x, CO and HC concentration indicated that both of these pollutants reduced by increasing the biofuel composition of diesterol throughout the engine operating range.     

Experimental analysis of flow and heat transfer in a miniature porous heat sink for high heat flux application

A novel miniature porous heat sink system was presented for dissipating high heat fluxes of electronic device, and its operational principle and characteristics were analyzed. The flow and heat transfer of miniature porous heat sink was experimentally investigated at high heat fluxes. It was observed that the heat load of up to 280 W (heat flux of 140 W/cm²) was removed by the heat sink with the coolant pressure drop of about 34 kPa across the heat sink system and the heater junction temperature of 62.9 °C at the coolant flow rate of 6.2 cm³/s. Nu number of heat sink increased with the increase of Re number, and maximum value of 323 for Nu was achieved at highest Re of 518. The overall heat transfer coefficient of heat sink increased with the increase of coolant flow rate and heat load, and the maximal heat transfer coefficient was 36.8 kW(m² °C)^?1 in the experiment. The minimum value of 0.16 °C/W for the whole thermal resistance of heat sink was achieved at flow rate of 6.2 cm³/s, and increasing coolant flow rate and heat fluxes could lead to the decrease in thermal resistance. The micro heat sink has good performance for electronics cooling at high heat fluxes, and it can improve the reliability and lifetime of electronic device.     

Simulation, construction and testing of a two-cylinder solar Stirling engine powered by a flat-plate solar collector without regenerator

In this research, a gamma-type, low-temperature differential (LTD) solar Stirling engine with two cylinders was modeled, constructed and primarily tested. A flat-plate solar collector was employed as an in-built heat source, thus the system design was based on a temperature difference of 80 °C. The principles of thermodynamics as well as Schmidt theory were adapted to use for modeling the engine. To simulate the system some computer programs were written to analyze the models and the optimized parameters of the engine design were determined. The optimized compression ratio was computed to be 12.5 for solar application according to the mean collector temperature of 100 °C and sink temperature of 20 °C. The corresponding theoretical efficiency of the engine for the mentioned designed parameters was calculated to be 0.012 for zero regenerator efficiency. Proposed engine dimensions are as follows: power piston stroke 0.044 m, power piston diameter 0.13 m, displacer stroke 0.055 m and the displacer diameter 0.41 m. Finally, the engine was tested. The results indicated that at mean collector temperature of 110 °C and sink temperature of 25 °C, the engine produced a maximum brake power of 0.27 W at 14 rpm. The mean engine speed was about 30 rpm at solar radiation intensity of 900 W/m² and without load. The indicated power was computed to be 1.2 W at 30 rpm.     

An investigation into feasibility of impingement heat transfer and acoustic abatement of meso scale synthetic jets

While synthetic jets have found more applications in controlling fluid flow especially in aerospace applications, more recently they captured a lot of attention for the thermal management of electronics. While the jet sizes vary and may be large for microfluidic applications, it is preferred that they should be in the meso scale range for removing heat from electronics components. Current study focuses on the heat transfer and acoustic aspects of the small-scale synthetic jets. Synthetic jets designed and developed at the General Electric Global Research Center can provide peak air velocities in excess of 90 m/s from a 1 mm hydraulic diameter rectangular orifice. The jets are driven by a sine wave with an operating frequency of between 3 and 4.5 kHz, providing the highest thermal performance for the current jets. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. Two heater sizes have been studied in the current study to understand the effect of the characteristic length. Several parameters are varied to find the change in the heat transfer rates with the jet location, driving voltage, driving frequency, and heater power. Heat transfer enhancements over the specific heater sizes are presented for the same jet. It is found that the enhancement can be between 4 and 10 times depends on the heater size showing that smaller sizes provide the best jet effectiveness. It is also noted that jet noise can be as large at 73 dB, but possible abatement techniques can decrease this noise level as low as to 30 dB.     

A compact,high efficiency contra-rotating generator suitable for wind turbines in the urban environment

This paper is concerned with the design, development and performance testing of a permanent magnet (PM) generator for wind turbine applications in urban areas. The radially interacting armature windings and magnet array are carried on direct drive, contra-rotating rotors, resulting in a high torque density and efficiency. This topology also provides improved physical and mechanical characteristics such as compactness, low starting torque, elimination of gearboxes, low maintenance, low noise and vibration, and the potential for modular construction. The design brief required a 50 kW continuous rated prototype generator, with a relative speed at the air-gap of 500 rpm. A test rig has been instrumented to give measurements of the mechanical input (torque and speed) and electrical output (voltage, current and power) of the generator, as well as temperature readings from inside the generator using a wireless telemetry device. Peak power output was found to be 48 kW at a contra-rotating speed of 500 rpm, close to the design target, with an efficiency of 94%. It is anticipated that the generator will find application in a wide range of wind turbine designs suited to the urban environment, e.g. types sited on the top of buildings, as there is growing interest in providing quiet, low cost, clean electricity at point of use.     

Experimental investigations on thermal performance enhancement and effect of orientation on porous matrix filled PCM based heat sink

Thermal performance in terms of enhancement ratios and the effect of orientation of a copper porous matrix filled phase change material (PCM) based heat sink are experimentally studied in this paper. N-eicosane is used as the phase change material. A copper open cell metal foam, press fitted into an aluminium casing is the thermal conductivity enhancer. In PCM based heat sinks, low thermal conductivity associated with PCMs makes the use of enhancement techniques inevitable for better thermal performance. A plate heater with an overall dimension of 60 × 42 mm² with 2 mm thickness is used to mimic the heat generation in electronic chips. The effect of orientation of the heat sink on thermal performance is studied by developing a tracking system, capable of placing the heat sink at any specified orientation.     

Experimental investigations on phase change material based finned heat sinks for electronic equipment cooling

This paper reports the results of an experimental investigation of the performance of finned heat sinks filled with phase change materials for thermal management of portable electronic devices. The phase change material (PCM) used in this study is n-eicosane and is placed inside a heat sink made of aluminium. Aluminium acts as thermal conductivity enhancer (TCE), as the thermal conductivity of the PCM is very low. The heat sink acts as an energy storage and a heat-spreading module. Studies are conducted for heat sinks on which a uniform heat load is applied for the unfinned and finned cases. The test section considered in all cases in the present work is a 80 × 62 mm² base with TCE height of 25 mm. A 60 × 42 mm² plate heater with 2 mm thickness is used to mimic the heat generation in electronic chips. Heat sinks with pin fin and plate fin geometries having the same volume fraction of the TCE are used. The effect of different types of fins for different power level (ranging from 2 to 7 W) in enhancing the operating time for different set point temperatures and on the duration of latent heating phase were explored in this study. The results indicate that the operational performance of portable electronic device can be significantly improved by the use of fins in heat sinks filled with PCM.     

Power and thermal characterization of a lithium-ion battery pack for hybrid-electric vehicles

A 1D electrochemical, lumped thermal model is used to explore pulse power limitations and thermal behavior of a 6 Ah, 72 cell, 276 V nominal Li-ion hybrid-electric vehicle (HEV) battery pack. Depleted/saturated active material Li surface concentrations in the negative/positive electrodes consistently cause end of high-rate (∼25 C) pulse discharge at the 2.7 V cell⁻¹ minimum limit, indicating solid-state diffusion is the limiting mechanism. The 3.9 V cell⁻¹ maximum limit, meant to protect the negative electrode from lithium deposition side reaction during charge, is overly conservative for high-rate (∼15 C) pulse charges initiated from states-of-charge (SOCs) less than 100%. Two-second maximum pulse charge rate from the 50% SOC initial condition can be increased by as much as 50% without risk of lithium deposition. Controlled to minimum/maximum voltage limits, the pack meets partnership for next generation vehicles (PNGV) power assist mode pulse power goals (at operating temperatures >16 °C), but falls short of the available energy goal.In a vehicle simulation, the pack generates heat at a 320 W rate on a US06 driving cycle at 25 °C, with more heat generated at lower temperatures. Less aggressive FUDS and HWFET cycles generate 6–12 times less heat. Contact resistance ohmic heating dominates all other mechanisms, followed by electrolyte phase ohmic heating. Reaction and electronic phase ohmic heats are negligible. A convective heat transfer coefficient of h = 10.1 W m⁻² K⁻¹ maintains cell temperature at or below the 52 °C PNGV operating limit under aggressive US06 driving.     

Thermoelectric air-cooling module for electronic devices

This article investigates the thermoelectric air-cooling module for electronic devices. The effects of heat load of heater and input current to thermoelectric cooler are experimentally determined. A theoretical model of thermal analogy network is developed to predict the thermal performance of the thermoelectric air-cooling module. The result shows that the prediction by the model agrees with the experimental data. At a specific heat load, the thermoelectric air-cooling module reaches the best cooling performance at an optimum input current. In this study, the optimum input currents are from 6 A to 7 A at the heat loads from 20 W to 100 W. The result also demonstrates that the thermoelectric air-cooling module performs better performance at a lower heat load. The lowest total temperature difference-heat load ratio is experimentally estimated as ?0.54 W K^?1 at the low heat load of 20 W, while it is 0.664 W K^?1 at the high heat load of 100 W. In some conditions, the thermoelectric air-cooling module performs worse than the air-cooling heat sink only. This article shows the effective operating range in which the cooling performance of the thermoelectric air-cooling module excels that of the air-cooling heat sink only.