An introduction to heat transfer

In remote communities where it is not economical and practically possible to take the grid connection, stand-alone small hydro systems can be used to fulfill the energy requirement Small-scale hydroelectric power systems are emerging as a promising source of renewable energy generation, but they require low cost hydraulic and electric equipments to make them economically feasible In such plants, pumps can be used in turbine mode considering various advantages associated with pump eg ease of availability, proven technology, low initial and maintenance cost, availability for a wide range of heads and flows, etc The efficiency of pump as turbine (PAT) is usually lower than that of conventional hydro turbines However, efficiency is not the primary selection criterion for such machines and it is recommended to operate such machines around maximum efficiency point In the present study, different turbines suitable for micro-hydropower plants are discussed The historical development of PAT is described The review of the state-of-the-art of pump running in turbine mode is presented Different pumps suitable to run in turbine mode for low capacity power generation in micro-hydropower plants as well as in water supply piping systems are discussed Theoretical, experimental and numerical investigations carried out by different researchers on PAT are reviewed The research work on PAT including criteria for selection of pump running as turbine, cavitation analysis, force analysis, loss distribution, various methods of performance enhancement, cost analysis of hydropower plant with conventional hydro turbine and PAT, applications of PAT in water supply pipelines, etc is discussed The worldwide implementation of PAT and different manufacturers of PAT are described The limitations in implementation of PAT as well as the recommendations to improve the performance of PAT are described The current trends and future scope for the further improvement and implementation of PAT are also discussed

Investigations on pump running in turbine mode: A review of the state-of-the-art

Based on the biogas feedstock and its generation cycle, a considerable part of biogas ingradients are noncombustible gases. Low calorific value (LCV) of biogas is one of the most important barriers of biogas development in the combined heat and power (CHP) generation. Biogas purification is usually performed in sensitive utilizations, however modification methods such as cryogenic and membrain are not economic. Therefore, new methods of biogas utilization should be experimented. In this study, characteristics of biogas are investigated under various combustion regimes such as biogas conventional combustion, hydrogen-enriched biogas traditional combustion, biogas flameless mode and hydrogen-enriched biogas flameless combustion. Since biogas conventional combustion is not well-sustained due to LCV of biogas, hydrogen addition to the biogas components could improve combustion stability however NOx formation increases. Although flameless combustion of fosil fuel have been developed, few documents could be found about biogas flameless mode. Flameless combustion of biogas could be one of the best methods of pure biogas utilization in CHP generation. Combustion stability and low pollutant formation are the main advantages of biogas flameless combustion. The initial cost of flameless combustion instalation is high due to the cost of instrumentation and special equipments. In order to maintain the temperature inside the flameless chamber, some especial materials such as ceramic should be utilized. Biogas flameless combustion could be modified by hydrogen-enrichment strategy. The temperature distribution inside the flameless chamber is more uniform when small amounts of hydrogen added to the biogas components and the flameless regime is more sustained. In this circumstance the rate of pollutant formation is a little higher than pure biogas flameless combustion.

Development of biogas combustion in combined heat and power generation

Surge limit definition in a specific test bench for the characterization of automotive turbochargers

Experiments and modelling of surge in small centrifugal compressor for automotive engines

The regenerative flow pump (RFP) and regenerative flow compressor (RFC) are turbomachines capable of developing high pressure ratios in a single stage. They are also known by other names, such as peripheral, side channel, turbine, traction and vortex compressor/pump. Even though the efficiency of RFP/RFC is usually less than 50 per cent based on past design experience, they have found wide applications in automotive and aerospace fuel pumping, booster systems, water supply, agricultural industries, shipping and mining, chemical and food stuffs industries, and regulation of lubrication and filtering. RFCs have been proposed for use in hydrogen gas pipelines and as helium compressors for cryogenic applications in space vehicles. RFTs are used as accessory drives on aircraft and missiles. With the aim of improving the performance and efficiency of an RFP, this paper proposes an improved and modified theoretical model that can explain the change in the circulatory velocity caused by variation in chann...

A modified theory for the flow mechanism in a regenerative flow pump

The performance of centrifugal compressors can be seriously degraded by inlet flow distortions that result from an unsatisfactory inlet configuration. In this present work, the flow is numerically simulated and the flow details are analyzed and discussed in order to understand the performance behavior of the compressor exposed to different inlet configurations. In a previous work, complementary to this present work, experimental tests were carried out for the comparison of a centrifugal compressor stage performance with two different inlet configurations: one of which was a straight pipe with constant cross-sectional area and the other a 90-deg curved pipe with nozzle shape. Steady-state compressor stage simulation including the impeller and diffuser with three different inlets has been carried out to investigate the influence of each inlet type on the compressor performance. The three different inlet systems included a proposed and improved inlet model. The flow from the bend inlet is not axisymmetric in the circumferential and radial distortion, thus the diffuser and the impeller are modeled with fully 360-deg passages

The Inlet Flow Structure of a Centrifugal Compressor Stage and Its Influence on the Compressor Performance

The performance of centrifugal compressors can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow struc...

The influence of inlet flow distortion on the performance of a centrifugal compressor and the development of an improved inlet using numerical simulations

This paper presents the experimental and numerical investigation of an outward volute of rectangular cross section. The investigation is carried out at the level of stage performance, volute performance, and detailed flow field study at selected peripheral positions for various operating points. The objective of the investigation was to gain further knowledge about the flow structure and loss mechanism in the volute. Simultaneously with the experimental investigation, a numerical simulation of the flow in the volute was carried out. A three-dimensional Euler code was used in which a wall friction term and a tuned artificial dissipation term account for viscous effects. A reasonable agreement between the experimental and numerical results is observed. As a result a good and detailed knowledge about the pressure recovery and loss mechanism in the volute is obtained.

Abraham Engeda

Papers

A modified theory for the flow mechanism in a regenerative flow pump

The Inlet Flow Structure of a Centrifugal Compressor Stage and Its Influence on the Compressor Performance

The influence of inlet flow distortion on the performance of a centrifugal compressor and the development of an improved inlet using numerical simulations

Experimental and Numerical Investigation of the Flow in a Centrifugal Compressor Volute

Performance of centrifugal pumps running in reverse as turbine: Part II- systematic specific speed and specific diameter based performance prediction