The objective of this work is to simulate a single effect (SE) ammonia-water heat pump for domestic water heating, with innovative aspects for cycle simulation and eventual practical implementation. The following practical difficulties are addressed in the simulation: 1. seasonal temperature variations change the operating conditions of the distillation column, calling for insightful design to maintain a suitable refrigerant concentration in all seasons, and particularly in winter; 2. The evaporator activated by outdoor air suffers from immoderate heat transfer requirements, and these demands are considerably reduced if the activation is done by products of combustion; 3. Pumps have head requirements that can be assuaged by judicious selection and inlet solution subcooling. The variables that need to be controlled if the same column is to be used all year round are specified. As configured with the innovations mentioned, the cycle simulation yields a coefficient of performance within the expected range for a single effect, but it harbors the promise of a much smaller evaporator, of small overall height, and of a distillation column capable of operating effectively all year round with the same feed point.

This work considers the possibilities of an air-based Brayton cycle to provide the power, heating and cooling needs of fast-food restaurants. A model of the cycle based on conventional turbomachinery loss coefficients is formulated. The heating, cooling and power capabilities of the cycle are extracted from simulation results. Power and thermal loads for restaurants in Knoxville, TN and in International Falls, MN, are considered. It is found that the cycle can meet the loads by setting speed and mass flow-rate apportionment between the power and cooling functional sections. The associated energy costs appear elevated when compared to the cost of operating individual components or a more conventional, absorption-based CHP system. A first-order estimate of capital investments is provided. Suggestions for future work whereby the operational costs could be reduced are given in the conclusions. (C) 2016 Elsevier Ltd. All rights reserved.

A thermodynamic analysis of cogeneration of power and refrigeration activated by low-grade sensible energy is presented in this work. An organic Rankine cycle (ORC) for power production and a vapor compression cycle (VCC) for refrigeration using the same working fluid are linked in the analysis, including the limiting case of cold production without net electricity production. We investigate the effects of key parameters on system performance such as net power production, refrigeration, and thermal and exergy efficiencies. Characteristic indexes proportional to the cost of heat exchangers or of turbines, such as total number of transfer units (NTUtot), size parameter (SP) and isentropic volumetric flow ratio (VFR) are also examined. Three important system parameters are selected, namely turbine inlet temperature, turbine inlet pressure, and the flow division ratio. The analysis is conducted for several different working fluids. For a few special cases, isobutane is used for a sensitivity analysis due to its relatively high efficiencies. Our results show that the system has the potential to effectively use low grade thermal sources. System performance depends both on the adopted parameters and working fluid.

Pumped hydro storage (PHS) is a crucial technology for balancing large steam power plants, and may become increasingly important for storing renewable energies. Hence, capacity ranges of PHS, as well as its dynamic response to renewable power variability, will become progressively relevant. In this paper, we focus on determining capacity ranges and efficiencies of PHS plants using conventional constant speed Francis runners, adopting unconventional runner sets, arranged in innovative fashion. In the pumping mode, it is assumed that the impellers run at a single speed, but that they can have, depending on the plant, either the same or different design capacities. In the turbine mode, it is assumed that the runners can access the well-established range from 60% to 100% of design capacity via Wicket gate adjustment. In order to extend the capacity ranges with constant speed runners, bypass loops to balance the plant are considered. Because bypass operation implies losses, the possible efficiencies are studied. The results show that (a) bypass is an effective means of extending capacity ranges, but high by-pass ratios decrease efficiencies. (b) One of the impeller sets postulated in this work offers the possibility of almost continuous capacity at high efficiencies, with relatively small capacity variation within the set. (C) 2014 Elsevier Ltd. All rights reserved.

Renewable power production is both variable and difficult to forecast accurately. These facts can make its integration into an electric grid problematic. If an area's demand for electricity can be met without using renewable generation, the addition of renewable generation would not warrant a further increase in generation capacity. However, to effectively integrate large amounts of additional renewable generation, it is likely that a more flexible generation fleet will be required. One way of increasing a generation fleet's flexibility is through the adoption of pumped hydroelectric storage (PHS, see the glossary for definitions of select terms). Like traditional hydropower generation, PHS is capable of quickly varying its power output but it is also capable of operating in reverse to store excess energy for later use. This paper will address many of the operational aspects of combining pumped hydroelectric storage (PHS), which is currently used to store excess energy from traditional generators, with wind and solar power generation.PJM, a grid operator in the Middle Atlantic States, defines capacity value for renewable generation as the percent of installed generating capacity that the generator can reliably contribute during summer peak hours. Existing wind generators inside PJM have an average capacity value of 13% and existing solar generators have a capacity value of 38%. The chief reason for these capacity values is that the renewable power production does not usually coincide with the hours of peak electricity demand during the summer. If PHS were used to firm renewable power generation, it would translate into increased utilization of the renewable generation that would displace the least efficient/most costly generators.A computer model with one minute granularity is constructed in order to study the operational requirements of PHS facilities. PJM electricity demand, power prices, and wind power production data for 2010 were used in conjunction with NREL simulated solar power production as input to the model. Currently, various PHS operational strategies are being tested to ascertain their effectiveness at firming and time shifting renewable generation. Preliminary results show the profound effects of increased penetration of renewable energy on an electric grid. The results also demonstrate a niche for even greater PHS operational flexibility, i.e. variable speed or unidirectional ternary machine (UTM) PHS.

Renewable power production is both variable and difficult to forecast accurately. These traits can make its integration into an electric grid problematic. But because its "fuel" is free, it makes economic sense to utilize renewable energy whenever it is available. When a power grid is unable to accommodate low marginal cost renewable energy due to a generator fleet that lacks sufficient flexibility, the energy is usually wasted and dispatchable fossil fuel generators are utilized instead. However, if a pumped hydroelectric storage (PHS, see the glossary for definitions of select terms) facility is used to time shift the renewable power production, the energy is transformed into a dispatchable resource. Because of this dispatchability, the power can be sold as "firm" generation which typically gets a higher price on the wholesale electricity market. This paper will address the financial aspects of using PHS to firm and time shift the inherently variable wind and solar power generation in the Mid-Atlantic States.The benefits that a PHS facility can offer to renewable power generators are many, but the biggest drawback to doing so is the high capital cost of PHS. In order to study the revenue streams of both PHS facilities and renewable power generators a computer model with one minute granularity was constructed. Electricity demand, power prices and wind power production were obtained from PJM's website for the year 2010. The NREL program PVWatts v.1 was used to generate the simulated solar power production which was combined with the PJM data and used as input to the model. Currently, various PHS configurations are being tested in order to determine their effects on the profits of the PHS facility and the profits of renewable generators. Preliminary results show that the relationship between PHS owners and renewable power generators could be beneficial for both parties. The extents of the financial benefits are largely determined by the dynamics of the applicable wholesale electricity market, the accuracy of the power production forecast for renewable generators, the power capacity, the energy capacity and the round trip efficiency of the PHS facility.

To investigate possible increases of the capacity factor of wind turbines, six airfoils are chosen for evaluation, three based on high Cl, low Cd/C1, and wide operational range, and three others simply based on low Cd. Aerodynamic performance of the chosen airfoils is projected for a 45 m radius turbine using Blade Element Theory (BET) as translated in an existing computer program. Even though the airfoils do not differ significantly in shape, their performance is projected to differ in turbine performance calculations, with some generating more power than others at the same wind speed and air density. The aerodynamic performance obtained with the numerically tested airfoils is compared to that of an actual wind turbine of equal dimensions. Wind speed and directional changes can be large, and assessing their effect is complicated. Using data from the literature, a simple evaluation of the effect of wind speed can be incorporated into the power curve, and shown to be dependent on the airfoil type. Directional changes could lead to reduced output power, but they are more significant for BEs close to the hub than to the tip. The optimal incidence angle calculated with the program shows little variability with wind speed for all airfoils.

Whereas turbomachinery design has evolved over the last two decades, updating instruction on the topic to reflect the new prevailing methods and techniques remains a challenge. Part of this challenge stems from the diversity of technologies covered in the courses; part of it ensues from the extensive use of software by industry designers. A review of the literature shows that varying degrees of complexity in software have been adopted for teaching, and that numerical experimentation has in some universities replaced laboratory experimentation. This paper describes the experience and outcomes of teaching turbomachinery to senior engineering students using advanced design software. The cases and results analyzed by the students for axial compressors and turbines are discussed, and the results of the effort are evaluated from the somewhat different perspectives of the students and of the instructor. Whereas the use of the program must be viewed in the context of the entire course (two hardware labs are held along with conventional lectures and homework), the use of design software could be seen to multiply the skills of the students, enabling broad 3-D design considerations and visualization seldom possible otherwise. In addition, an understanding of prevailing stresses is initiated with the software.

A significant amount of energy is expected to come from wind in the upcoming years. The variability and uncertainty of this power source needs to be managed by the grid operator. Electricity networks with wind energy need extra reserves to deal with the extra uncertainty associated with the presence of wind. This paper evaluates the possibility to couple a 1000 MW wind farm with gas turbines (GTs) to provide firm capacity to the grid with a reasonable investment. Taking into account two different days of wind production with one minute data, the study analyzes the possibility of integrating the wind power output with two different types of GTs (heavy duty and aeroderivative). GTs operational constrains are included in the model in order to correctly demonstrate how the wind variability stresses turbine performance, as it probably would in extreme cases. Limitations on GTs ramps rates and start–up time are considered for both, heavy duty and aeroderivatives. GTs power output profiles, ramp rates and fuel consumption for the selected days of analysis are shown. The results show that the integration between wind and gas turbines could be a viable solution to compensate wind variability and to accommodate the increasing wind penetration into the electrical grid.

As wind power installed capacities increase, it is necessary to deal with the inevitable variability of renewables. Some of that variability can undoubtedly be predicted, but some will in all probability remain unpredictable. In either case, reserve power must be made available. It is clear that the ramp rates that the reserve power must meet will stress technology and call for part-load operation at reduced efficiencies. In the present work, we use a gas turbine (GT) dynamic models to simulate the provision of firm power in the Pennsylvania, New Jersey and Maryland grid, PJM. Rowen GT models [1, 2], well established in the literature, are modified to take into account GT ramp rates constrains and fuel consumption at full and partial load, as well as during startup and shutdown. The GTs operational requirements for two summer days in the PJM area are determined, by selecting their number and capacities to result on at least a few units operating at full load. The dynamic models [1, 2] are implemented in the VisSim simulation environment. The results of the work show how the chosen GTs must be operated to provide firm power. Although the operational strategy determined in this paper meets the firm power, in two occasions during the day excess power is produced during a few minutes, to avoid ramping the units down too fast.

To increase power output and improve thermal efficiency of gas turbines, recourse is often had to inlet air-cooling during hot periods. In some cases, a cost-effective way to accomplish inlet cooling consists of evaporatively cooling the air stream in the inlet duct. In this method, a fine mist of water is created at the compressor inlet, and as the mist droplets evaporate the mixture temperature decreases. This cooling process is analyzed using four simultaneous heat and mass transfer models: (A) diffusion, (B) natural convection, (C) Stokes convection, and (D) perturbed Stokes. Special attention is paid to the critical water injection ratio dividing the low and high fogging cases. Air and droplet temperatures and droplet diameters as evaporation proceeds are obtained for different values of inlet temperature and relative humidity of air, initial droplet diameter, and water injection mass ratios. The results of the computations show good agreement among the models considered in this work.

The Blade Element Theory (BET) has been used to predict performance of wind turbines, and to optimize energy extraction from the wind. A literature search shows that the number of parameters that can be varied to attempt optimization within BET varies for different authors. However, a repeated assumption is that the BE should be operating at the incidence angle resulting in maximum lift to drag ratio. In the present work, the incidence angle is one of the parameters varied for optimization, along with five others: the two induction factors, the chord, and the flow and setting angles. The optimization satisfies five equality constraints and three inequality constraints. The optimizer uses Levenberg-Marquardt, Conjugate Gradient or Quasi-Newton methods to maximize the power extracted. The equations adopted employ the Prandtl tip loss and require specification of the airfoil for the section, the radius of the turbine, the wind speed and the radial distribution of solidity. Up to twenty five elements can be specified for each turbine. The influence of airfoils on power coefficients is shown, and deviations from the expected maximum lift to drag positions noted. Comparisons to the performance of small wind turbines from the commercial and open literature are attempted. Whereas such comparisons are difficult in that airfoils and solidities are not often specified, they yield a baseline for establishing the validity of the optimization procedure.

Gas-turbine cycles with high fogging compression could offer enhanced efficiency and low complexity. Whereas compression power and heat rates decrease when small amounts of water (up to 2% of air flow by mass) are injected at the machine inlet, increased injection amounts could allow implementation of regeneration, further decreasing the heat rate. In this study, an exergy analysis is carried out for two high-fogging cycles. The theoretical projections show that high-injection improves the efficiency from 47% at a pressure ratio of 6-55.5% at a pressure ratio of 22.

Evaporative gas turbine cycles (EvGT) are of importance to the power generation industry because of the potential of enhanced cycle efficiencies with moderate incremental cost. Humidification of the working fluid to result in evaporative cooling during compression is a key operation in these cycles. Previous simulations of this operation were carried out via numerical integration. The present work is aimed at modeling the wet-compression process with approximate analytical solutions instead. A thermodynamic analysis of the simultaneous heat and mass transfer processes that occur during evaporation is presented. The transient behavior of important variables in wet compression such as droplet diameter, droplet mass, gas and droplet temperature, and evaporation rate is investigated. The effects of system parameters on variables such as droplet evaporation time, compressor outlet temperature and input work are also considered. Results from this work exhibit good agreement with those of previous numerical work.

Local single- and two-phase heat transfer distributions are measured under a confined impinging jet issuing from a cross-shaped orifice. Spatially resolved temperature maps and convection coefficients resulting from the impinging flow are obtained via infrared imaging of a thin-foil heat source. The cooling patterns in single- and two-phase operation are explained by an accompanying numerical investigation of the fluid flow issuing from the orifice; computed velocity magnitudes and turbulence intensities are presented. In single-phase operation, the coolest surface temperatures correspond to areas with high liquid velocities. High velocities and developing turbulence are also shown to increase convective heat transfer along the diagonal outflow directions from the impinging jet. During two-phase transport, boiling preferentially begins in regions of low velocity, providing enhanced heat transfer in the areas least affected by the impingement. The cross-shaped orifice achieves local heat transfer coefficients that exceed the stagnation-point value of a circular jet of equivalent open orifice area by up to 1.5 times, while resulting in an increased pressure drop only 1.1 times higher than that of the circular jet.

Renewable power generation exhibits notorious intermittence. The power load varies daily and also seasonally. The topic of renewable generation, storage and grid interfacing is complex in that it brings into one setting many diverse interests and technologies. Our long-term goal is to help define ways to profitably increase renewable generation. In this paper, we focus on normal day for a grid operator, PJM, (Pennsylvania, New jersey and Maryland). The variability of wind and (and assumed) solar outputs require a certain capability for load following or storage. Using dynamic modelling, we estimate the variability of the wind output and we simulate a projected solar penetration of 3% of new capacity. To save for eventual use every unit of energy thus generated, a storage system must have the capability to levelize the supply of renewable power. The capacity requirements for storage and generation of such a system are mapped out in 1 min intervals, and are used to define the capacities and ramp rates for a hypothetical pumped storage plant. Knowledge of weather patterns may be helpful to plan dispatch and storage of renewable energy. The results of a brief excursion into the difficult topic of weather patterns are recorded here too. (C) 2011 Elsevier Ltd. All rights reserved.

Evaporative cooling of fluids under compression reduces the input work with relatively low equipment costs. Currently, water injection at about 1% of the air mass-flow rate is used; additional cooling can be obtained with higher injection rates. Water is non-toxic and relatively non-corrosive, which makes it the fluid of choice for evaporatively-cooled compressors in gas turbines. Water does have a relatively low vapor-pressure, that tends to limit the amount evaporated, although its large heat of vaporization partially compensates for this deficiency. Residence times in compressors are of the order of hundredths of seconds. Hence, the time available for evaporation is brief. One expectation is that higher-vapor-pressure refrigerants could evaporate at higher rates, and hence overcome some of the limitations of water. We present here a study of such a refrigerant, but the results fall short of expectations: evaporation is projected to occur fast initially, but the reduced work expectation does not fully materialize. A heat-and-mass transfer model that predicts droplet evaporation is used for our projections. Three parameters are varied to determine their effects on the compressor calculated performance: injection ratio, initial droplet radius, and pressure ratio. Low compressor discharge temperatures appear possible, which in some applications in gas turbines could uphold definite promise for recuperative cycles. Yet, the difficulties associated with the combustion process involving a refrigerant may very well override all other considerations. For the general case of evaporatively-cooled compression, high-pressure substances would need much larger heats of vaporization than the ones considered here for their application to be sustainable as compared with water.

Humidified gas turbines have the potential of enhanced cycle efficiencies with moderate initial cost. Evaporatively-cooled air compression is of importance to the power generation industry. The present work is aimed at contributing to a number of unanswered questions concerning the wet-compression process. Current operational margins limit the vapor mass fraction to 1∼2% by mass of the inlet flow. Yet, machines specifically designed to accommodate higher mass fractions are conceivable. Our aim is to explain the theoretical limits of those machines via a heat and mass transfer model. Continuous compression cooling via evaporation is modeled numerically based on droplet evaporation analysis. Parametric studies show the effect of variables such as droplet size, water injection ratio or compression ratio on transient behavior. Wet compression parameters such as evaporation time, compressor outlet temperature and compression work are estimated.