scholarly journals FLOW FIELD NEAR AN OCEAN THERMAL ENERGY CONVERSION PLANT

1976 ◽  
Vol 1 (15) ◽  
pp. 174 ◽  
Author(s):  
D.M. Sheppard ◽  
G.M. Powell ◽  
I.B. Chou
Keyword(s):  
Low Temperature ◽  
Shear Flow ◽  
Flow Field ◽  
Energy Conversion ◽  
Thermal Energy ◽  
Temperature Difference ◽  
Cold Water ◽  
Water Pipe ◽  
Thermal Energy Conversion ◽  
Ocean Thermal Energy

The flow field in the vicinity of an Ocean Thermal Energy Conversion (OTEC) Plant is extremely complex. The plants will normally be located in an area of relatively high surface currents and the location must also be such that a large temperature difference exists between the lower layers and the surface. Locations that demonstrate this characteristic can in many cases be modeled as a two layer fluid as shown in Figure 1. A number of different designs for the OTEC plants are being considered, but they all have one thing in common, a large vertical cold water pipe. This pipe extends from near the surface to some point in the cold water layer (see Figure 1). In some designs this pipe is as large as 40 m in diameter and 460 m in length. Having such a large object penetrating the interface between the two temperature layers in the presence of a shear flow can significantly alter the character of the interface. The highly turbulent wake downstream from the pipe can drastically effect the mixing across this density interface. A conventional heat engine cycle is used in the plant with the high temperature source being the water in the upper layers and the low temperature reservoir being the water from the lower depths. \ Since the temperature difference is small for this type of plant (20° max.), vast quantities of both high and low temperature water must be used. The intake and discharge for the warm water as well as the cold water discharge will be in the upper layer; the intake for the cold water will be in the lower layer at or near the end of the cold water pipe. The flow problem is thus one of a vertical cylinder in a two layer stratified shear flow with sources and sinks located along the cylinder.

Current Developments in the Validation of Numerical Methods for Predicting the Responses of an Ocean Thermal Energy Conversion (OTEC) System Cold Water Pipe

2014 ◽  
Author(s):  
John Halkyard ◽  
Rizwan Sheikh ◽  
Thiago Marinho ◽  
Shan Shi ◽  
Matthew Ascari
Keyword(s):  
Numerical Methods ◽  
Energy Conversion ◽  
Thermal Energy ◽  
Cold Water ◽  
Oil Prices ◽  
Model Tests ◽  
Water Pipe ◽  
Ocean Thermal Energy Conversion ◽  
Thermal Energy Conversion ◽  
Ocean Thermal Energy

Ocean Thermal Energy Conversion (OTEC) was a subject of intense research in the late 1970s and early 1980s in response to a historical jump in oil prices from the 1973 oil embargo. The principal author for this paper first met Prof. Paulling as a participant in a National Research Council (NRC) Panel to review OTEC Technology around 1982. Prof. Pauling had authored a frequency domain program to analyze the coupled response of a platform and OTEC pipe. The author was involved in model tests to validate the program. The United States (U.S.) Department of Energy (DoE) and National Oceanic and Atmospheric Administration (NOAA) had sponsored this work, along with the development of other numerical methods. Shortly after the NRC completed its review, oil prices fell and interest in renewable energy, including OTEC, evaporated. Fast forward to the 2000s, the price of oil skyrocketed again, and OTEC research saw a rebirth. Lockheed Martin and others have been working on new OTEC designs over the course of the last several years. As was the case thirty-five years ago, the cold water pipe remains a key technical challenge. A commercial scale OTEC plant requires a pipe diameter of about 10-meter (m) and a length of 1,000m to pump about half the average discharge of the Colorado River from the deep ocean to the surface and through heat exchangers. Because of the large effective mass of the CWP and entrained water, the dynamic response of the OTEC CWP and the platform can only be considered as a coupled system. This conclusion is not new, but is worth repeating and doubly important to consider when the supporting platform is a semi-submersible as opposed to a large water plane ship shaped vessel. A new generation of software is available to analyze the cold water pipe-platform responses, including the important effect of the fluid flow inside the pipe and the local effects at the connection of the pipe to the platform. The DoE and Lockheed Martin recently sponsored a 1:50 scale wave basin model test of a commercial OTEC platform with an elastically scaled model of a 10m pipe. The purpose of the test was to validate the use of current software for the large CWP diameters in the designs of a pilot or commercial systems in the near future. This paper will briefly review past work on the OTEC cold-water pipe and present the current state of the art in numerical modeling and the results of the model tests recently completed. It will include recommendations for further experimental and numerical work to be prepared for the future design of OTEC systems.

scholarly journals Dynamic Simulation of System Performance Change by PID Automatic Control of Ocean Thermal Energy Conversion

2020 ◽  
Vol 8 (1) ◽  
pp. 59 ◽  
Author(s):  
Lim Seungtaek ◽  
Lee Hoseang ◽  
Kim Hyeonju
Keyword(s):  
Control System ◽  
Energy Conversion ◽  
Thermal Energy ◽  
Temperature Difference ◽  
Pid Control ◽  
Seawater Temperature ◽  
Ocean Thermal Energy Conversion ◽  
Control Value ◽  
Thermal Energy Conversion ◽  
Ocean Thermal Energy

Near infinite seawater thermal energy, which is considered as an alternative to energy shortage, is expected to be available to 98 countries around the world. Currently, a demonstration plant is being built using closed MW class ocean thermal energy conversion (OTEC). In order to stabilize the operation of the OTEC, automation through a PID control is required. To construct the control system, the control logic is constructed, the algorithm is selected, and each control value is derived. In this paper, we established an optimal control system of a closed OTEC, which is to be demonstrated in Kiribati through simulation, to compare the operating characteristics and to build a system that maintains a superheat of 1 °C or more according to seawater temperature changes. The conditions applied to the simulation were the surface seawater temperature of 31 °C and the deep seawater temperature of 5.5 °C, and the changes of turbine output, flow rate, required power, and evaporation pressure of the refrigerant pump were compared as the temperature difference gradually decreased. As a result of comparing the RPM control according to the selected PID control value, it was confirmed that an error rate of 0.01% was shown in the temperature difference condition of 21.5 °C. In addition, the average superheat degree decreased as the temperature difference decreased, and after about 6000 s and a temperature decrease to 24 °C or less, the average superheat degree was maintained while maintaining the superheat degree of 1.7 °C on average.

scholarly journals The extraction of power and fresh water from the ocean off the coast of KZN utilising ocean thermal energy conversion (OTEC) techniques

2021 ◽  
Author(s):  
◽  
Makhosonke Gumede
Keyword(s):  
Energy Conversion ◽  
Fresh Water ◽  
Thermal Energy ◽  
Temperature Difference ◽  
Power Output ◽  
Warm Water ◽  
Ocean Thermal Energy Conversion ◽  
Thermal Energy Conversion ◽  
Kwazulu Natal ◽  
Ocean Thermal Energy

Ocean thermal energy conversion (OTEC) is an electric power generation system which uses the temperature difference between warm water at the surface (26 oC) and cold water from the depths (5 oC) of the ocean. Generating electricity is not the only function of OTEC as it can also produce significant amounts of fresh water. This can be very important, for example on islands and in some regions, such as Port Edward, where fresh water is limited. This thesis sets out to harness this fluidic energy, thus generating significant amounts of useful electric power for insertion into the national grid, as well as fresh water in Port Edward on the KwaZulu-Natal (KZN), South Coast. The site of Port Edward is naturally suited to the establishment of alternate energy collection sources such as OTEC; the geographical location of this region is additionally suited to the development of Open Cycle - Ocean Thermal Energy Conversion (OC- OTEC). Port Edward lies just beneath the tropic of cancer and on the shore of the Indian Ocean thus two important elements needed for OTEC namely constant sunlight and large coastal areas can easily be found in this region. More importantly, the steep drop in water depth down to 3000 meters makes this an ideal research site for ocean thermal energy conversion in KwaZulu-Natal (KZN). If the proposed theories are correct, this can possibly be used for base generated energy capacity and fresh water. The results are presented with reference to the temperature difference between the sea surface and the sea bottom because it is an important parameter in choosing an actual plant site and system design of OC-OTEC. This research is mainly laboratory based concentrating on design, calculations, modelling and simulation of OC-OTEC. The thermodynamic fluid calculations were undertaken with a view to design the main mechanical components of an OC-OTEC system, i.e. flash evaporator, condenser and steam turbine. SOLID EDGE software was utilized to design OC-OTEC plant and ASPEN PLUS V8.6 software was used to simulate and model the experiment. An OC-OTEC demonstration plant was designed and constructed in an Electrical Power Laboratory at Durban University of Technology (DUT). The experimental study was carried out on the demonstration plant with consideration given to water temperature, mass flow rate of fluid, and pressure. The measurements were taken before and after each component. The selection of a good process modelling and simulation tool was of extreme importance for the success of this work. Throughout the measurements, we found that the thermal efficiency (%) and the power output increased with increasing temperature difference Δt = tw - tc. The power output was produced when the total temperature difference was sufficient to allow heat transfer within the evaporator and provide a pressure drop across the turbine. There was more heat transfer (steam produced) in the flash evaporator at a constant flow rate because the warm water continuously supplied heat energy to the evaporator without losing much energy through the process, therefore continuous feed to the turbine improved constant power output. The thermal efficiencies were increased with increasing pressure across the turbine. The increase of pressure drops across the steam turbine caused the output power to increase. The larger flow rates of the warm water lead to higher amounts fresh water produced from the condenser. The final step in this process was the design of the main components of a practical plant to be used as a pilot plant at a selected location on the KwaZulu-Natal South coast. This will address the problem of lack of water in the region.

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