Ravi Koirala

Membrane distillation crystallization (MDC) is an emerging hybrid thermal membrane technology that synergizes membrane distillation (MD) and crystallization, which can achieve both freshwater and minerals recovery from high concentrated solutions. Due to the outstanding hydrophobic nature of the membranes, MDC has been widely used in numerous field...

This study is focused on enhancing secondary vapor entrainment and direct-contact condensation in a water jet eductor for the purpose of developing a compact, medium-scale desalination system. It encompasses an extended investigation of an eductor as a condenser, or heat exchanger, for the entrained phase. Exergy study, experimental measurement, an...

Hydropower has been one of the mature renewable energy systems encompassing a major fraction of renewable energy. Archimedean screw turbines are gaining new interest in hydropower generation that are suitable for low head applications. This paper empirically and experimentally studies the flow inside Archimedean screw turbines along with the influe...

Fluorine doped Tin Oxide (FTO) was used as the substrate for the synthesis of Multi-Walled Carbon Nanotubes/ Zinc Oxide nanorods composites. The first composite was a layer-by-layer sample of Multi-Walled Carbon Nanotubes/ Zinc Oxide nanorods and the second was a mixed sample of Multi-Walled Carbon Nanotubes/ Zinc Oxide nanorods. Characterisation t...

Eductor is a static mechanical device converting primary flow pressure energy to velocity energy, creating low-pressure zone for suction of secondary fluid. The primary fluid is water at low temperature and secondary fluid is saturated water vapor, the vapor gets entrained in the primary fluid and is condensed. This study is focused on developing e...

This is an experimental work performed to identify the influence of direct contact condensation inside an eductor. The fluid used in the experiments is water in two different phases: liquid and vapor, for primary and secondary flows, respectively. This study was conducted in an attempt to establish the suitability of an eductor as a combined vacuum...

Thermal desalination technologies involve two primary processes: vapor generation from saline water, and effective recovery of the resulting condensate. Membrane distillation (MD) systems are among the emerging thermal desalination technologies which use a hydrophobic membrane to recover condensate through either direct or indirect contact (with th...

In the direct contact membrane distillation (DCMD) system, the temperature polarization due to boundary layer formation limits the system performance. This study presents the experimental results and heat transfer analysis of a DCMD module coupled with a salinity gradient solar pond (SGSP) under three different flow channel configurations. In the f...

As one of the state-of-art desalination technologies, membrane distillation (MD) has been widely studied in recent years. In order to better control the performance of the MD, a new model that can predict the membrane surface temperatures, permeate flux as well as salinity variation with the operating time has been proposed in this study. Using the...

Eductors are multi-functional devices that can be used for pumping, mixing, and heat transfer, and hence for commercially available eductors, optimum operational point for one function is not clearly defined. This paper computationally studies two-phase flow and mass transfer in a water jet eductor, involving liquid water as primary fluid and water...

This work reviews the current operational condition and activities on design modification for different applications of ejectors. Ejectors being a simple mechanical system capable of performing multiple fluid related functions (vacuum generation, pumping, mixing, condensing and heat exchanging), have been an essential part of several industrial pro...

This paper explores the potential of water jet eductor to replace large condensers and vacuum pump in the thermal desalination systems, with heat source temperatures below 95°C. The operational limit of eductor has been investigated for active vapor transport and condensation to produce permeate. Combined system and its operational principle have b...

This research aimed to examine the effect of the thermal conductivity model of hydrophobic membranes on performance modelling of direct contact membrane distillation systems. The parallel, series, and two types of Maxwell models were studied. Simultaneously, an iterative numerical model was developed to choose the most appropriate model by analysin...

This study examines the effect of spacers and operating conditions (feed inlet temperature, velocity, and feed concentration) on mass transfer characteristics in direct contact membrane distillation (DCMD) systems. The experimental results showed that velocity of the feed and permeate influenced the mass transfer properties more significantly than...

Guide vanes are stationary component in Francis turbine that performs periodic movement though a pivoted support, in response to the change in flow or load. To allow this movement, small gaps are provided at top and bottom of vanes, called clearance gap. They are internally lined with replaceable or metal claded linings called facing plates. Operat...

Francis turbine operating in sediment laden river projects, excessive wear and damage often occurs on the guide vanes, facing plates, runner and labyrinth rings due to sand erosion. The requirement of dismantling the head cover to repair the facing plates and wearing ring is one of the major influencing parameter of turbine assembly design to incre...

In guide vane cascade of Francis turbine, highest acceleration occurs, which generates equivalent amount of force for work done and erosion due to instantaneous change in flow dynamics. Hence in addition to runner vane, suitable selection of guide vane profile has equal importance. Usually, NACA defined hydrofoils are used for guide vanes. Numerous...

This thesis has been prepared based on two years research work of Masters by research at Turbine Testing Lab, Kathmandu University and State Key Laboratory of Hydroscience and Engineering, Tsinghua University. Sediment erosion has been a crucial issue for hydropower development in Himalayas and Andes valley. Large sediment concentration with highe...

Bifurcation refers to wye division of penstock to divide the flow symmetrically or unsymmetrically into two units of turbine for maintaining economical, technical and geological substrates. Particularly, water shows irrelevant behavior when there is a sudden change in flow direction, which results into the transition of the static and dynamic behav...

Guide vanes in Francis turbine faces frequent erosion due to its operation in sand laden water, which demands focus on design, manufacturing, operation and maintenance of turbines. These vanes are designed on high precision with standard hydrofoils for efficient conversion of pressure to kinetic energy. The erosion on surfaces, upper and lower ends...

Most people in the rural areas of Nepal rely on Micro-hydro Power Plants (MHPs) for their energy sources. With around four decade experiences in design and development of MHPs, Nepalese techno-entrepreneurs have gained wider reputation in the South Asian region and the beyond. However with the lack of competences in developing Francis turbines, maj...

Most people in the rural areas of Nepal rely on Micro-hydro Power Plants (MHPs) for their energy sources. With around four-decade experiences in design and development of MHPs, Nepalese techno-entrepreneurs have gained a wider reputation in the South Asian region and the beyond. However with the lack of competencies in developing Francis turbines,...

Sediment erosion is a crucial issue that affects the reliability of hydraulic turbines operating in sediment laden water. Guide vanes are the prime components for allocating water to produce the useful work, and shape changes due to wear affect the water flow properties. Profile changes can induce wakes, create boundary layer friction, and generate...

Francis turbine guide vanes have pivoted support with external control mechanism, for conversion of pressure to kinetic energy and to direct them to runner vanes. This movement along the support is dependent on variation of load and flow (operating conditions). Small clearance gaps between facing plates and the upper and lower guide vane tips are a...

The present study is conducted to identify a better design and optimal number of Francis runner blades for sediment laden high head micro hydropower site, Tara Khola in the Baglung district of Nepal. The runner is designed with in-house code and Computational Fluid Dynamics (CFD) analysis is performed to evaluate the performance with three configur...

The need of verification for reliability and higher performance of the design felt the practice of turbine testing in order to accelerate research and development in practical path. Development of the designed turbine in suitable scale and installation with measurement system are for performance test, has been considered as major priority. Experien...

The expansion of the existing industries involved in the production of components of hydropower to the Francis turbine manufacturer up to 5 MW unit size has been recognized as one of the most promising business models in Nepal. Given the current fact that the development of Francis turbines with the manufacturers of Nepal has not been done yet, due...

The worldwide demand for production of clean energy through hydro power has been a major issue of concern. Most of the hydropower resources from the developing countries of Asia like Nepal are yet to be harnessed. The technology regarding design of hydromechanical components in Nepal is still in the prenatal phase where the traditional design attem...

Hydropower can be an effective green solution for meeting the current energy demand in Nepal. However, despite having tremendous water resources, only 2% of Nepal's hydroelectricity potential has been tapped. Of the challenges that Nepali hydro faces, sediment erosion is a major one. Sediment erosion refers to an erosive tendency of sediment partic...

The current trend of hydropower development in Nepal infers a lack of collaboration between industries and institutions. Often referred to as a country blessed with a massive geographical diversity and water resources, not even 2% of the total feasible hydropower has been harnessed so far. The run-off river hydropower Projects across these regions...

There are a lot of low head sites in isolated areas, especially in third world countries, where pico and micro hydropower are realistic energy option as national grid extension to those places are unlikely because of sparse population and high transmission cost. While implementing pico hydro system in developing countries turbine manufacturing cost...

Turbine testing for the performance analysis of the design has been one of the mostly accepted and widely used methods in the current trend of Research and Development. Reversible Pump Turbine [RPT] is a new concept in turbine design for Nepalese scenario, which addresses the need of the pump storage and its role for compensating the current demand...

This paper presents 3-D geometry modification techniques in turbo-machinery blades, implementation using a MATLAB code, and its applications in a Francis turbine runner. The modification can be carried out by aligning the sections of the blade from Leading Edge (LE) to Trailing Edge (TE) or from Suction Side (SS) to Pressure Side (PS) without chang...

Most hydropower plants in Nepal are runoff type, which cannot supply the designed amount of energy during dry season and peak demand period resulting in energy crisis. Therefore, pumped storage plants can be an ideal solution to meet the current energy needs of the country. Most of these storage plants make use of a single unit acting both as turbi...

Due to fluctuation in energy production from hydropower plants, the existing plants in Nepal cannot meet the current demand of energy resulting in the power cut during peak hours. Therefore, there is a dire need for an energy storage unit that can meet the surplus demand of energy during peak hours. A pumped storage plants can be used to store elec...