Seawater Heat Research Articles

해수온도차발전-히트펌프 복합 사이클의 국내 적용성 검토

Due to industrialization and urbanization, the energy used by humankind is rapidly increasing, and side effects such as global warming and climate change are appearing. In order to respond to these international problems, research on new and renewable energy is continuously being carried out. In this study, OTEC-Heat pump combined cycle for domestic application was studied.BR Electricity was produced by OTEC through the increased surface water temperature and direct cooling using deep water discharge water in the summer were constructed. A heat pump using seawater is at higher temperature than outside air in the winter. In this study, energy cost and carbon dioxide emissions were compared with existing diesel power generation, EHP cooling, and kerosene heating systems. By applying OTEC, it was possible to produce 757.7 MWh of electricity per year, and through direct cooling, it was possible to save 98% of energy compared to EHP and 82% of energy compared to kerosene heating through a seawater heat pump.

Heat transfer performance analysis of seawater heat exchange pipelines in deep seawater closed cooling air conditioning system

The efficiency improvement of traditional seawater source heat pump system is limited and pipelines of the open seawater cooling air conditioning system experience scaling and corrosion. To overcome these problems, this paper proposes a deep seawater closed cooling air conditioning system. The system directly uses the closed heat exchange pipeline to exchange heat with the deep seawater and extracts the seawater cooling capacity for cooling. Numerical simulation is used to study the effects of different pipe diameters, flow rates, and inlet water temperatures on the heat transfer performance of vertical inlet sections, submarine heat exchange coils and vertical outlet sections. Since seawater has temperature and flow rate gradients in the vertical direction, the use of a hydraulic calculation table of the vertical pipe section and the calculation diagram of design and selection line of submarine heat exchange coil is proposed. Insulating subsections of the outlet section by dividing the section into 3 °C based on the seawater temperature is proposed. And the subsection insulation layer thickness corresponding to different pipe diameters are given. This study proposes a calculation method for the selection of key design parameters of deep seawater closed cooling air conditioning systems, providing a new method for making full use of seawater resources.

Seawater Opportunities to Increase Heating, Ventilation, and Air Conditioning System Efficiency in Buildings and Urban Resilience

In coastal cities, seawater heat pumps (SWHPs) can combine heat pump technology with the availability of seawater to produce the heat and the cold necessary for heating, ventilation, and air conditioning (HVAC) systems installed in buildings. In heating mode, the seawater is used as a cold source and provides the low-temperature heat needed for the operation of the machine. In cooling mode, the seawater removes the heat dissipated by the condenser of the heat pump working for air conditioning. This seawater application seems to be very promising since the temperature trend of the seawater appears to be more favorable than the alternative use of outdoor air, both in winter and in summer. In a case study in Trieste, the performance of a district heating/cooling network supplied with seawater and based on decentralized heat pumps is investigated. For this purpose, annual dynamic simulations were performed, modeling an urban area, the heat pumps, and the network. The energy efficiency evaluation shows a clear superiority of the SWHP solution compared to boilers and airsource heat pumps and thus the possibility to provide a significant contribution to the decarbonization of buildings. Moreover, the results highlight the ability of this GWHP network to reduce the urban heat island (UHI) phenomenon since the heat dissipated by the heat pumps during summer air conditioning is removed from the urban area. Therefore, SWHPs in coastal cities can be among the mitigation measures for UHI to increase outdoor comfort and heat wave resilience in urban areas.

Optimal design of a 5th generation district heating and cooling network based on seawater heat pumps

This work presents the design and the thermo-economic optimization of a novel layout of a 5th generation district heating and cooling network, for a residential district located in the Pantelleria island (South of Italy). The research focuses on a novel arrangement based on two bidirectional low-temperature neutral rings. For both rings, the fluid temperature is controlled by means of two groups of heat pumps cooled by seawater. The investigated layout also includes wind turbines and photovoltaic panels for power production. This layout will be used as a driver to promote the transition from the present centralized energy paradigm to a novel one, based on small-scale distributed generation integrated with renewables. The paper aims at evaluating the energy, economic and environmental savings achieved by this novel layout. A thermo-economic optimization is also implemented in order to determine the set of design/operating variables, maximizing system economic profitability. To this scope, a detailed approach is implemented, developing a dynamic simulation model of the system in TRNSYS 17. The developed simulation tool is able to mimic the real time operation of the system, for whatever weather condition, boundary and/or design variable. The results of the simulations show that the proposed layout achieves significantly positive results, with a primary energy saving and avoided greenhouse gases emissions equal to 133% and 134%, respectively. The economic profitability of the system is limited with the payback period close to 15 years, due to the high capital cost of the plant. The renewable electric production of the plant meets 57% of the district demand, although only 37% of this amount is self-consumed by the district. The study also includes a sensitivity analysis suggesting to limit the capacities of solar and wind fields to reduce the electricity in excess sold to the grid.

Immense variability in the sea surface temperature near macro tidal flat revealed by high-resolution satellite data (Landsat 8)

Sea surface temperature (SST) is crucial for understanding the physical characteristics and ecosystems of coastal seas. SST varies near the tidal flat, where exposure and flood recur according to the tidal cycle. However, the variability of SST near the tidal flat is poorly understood owing to difficulties in making in-situ observations. The high resolution of Landsat 8 enabled us to determine the variability of SST near the macro tidal flat. The spatial distribution of the SST extracted from Landsat 8 changed drastically. The seasonal SST range was higher near the tidal flat than in the open sea. The maximum seasonal range of coastal SST exceeded 23 °C, whereas the range in the open ocean was approximately 18 °C. The minimum and maximum horizontal SST gradients near the tidal flat were approximately − 0.76 °C/10 km in December and 1.31 °C/10 km in June, respectively. The heating of sea water by tidal flats in spring and summer, and cooling in the fall and winter might result in a large horizontal SST gradient. The estimated heat flux from the tidal flat to the seawater based on the SST distribution shows seasonal change ranging from − 4.85 to 6.72 W/m2.

Analysis of an uncovered photovoltaic/thermal solar system powering a seawater reverse osmosis desalination plant

This study aims to quantify how much the uncovered photovoltaic/thermal (PV/T) system is able to assist a small reverse osmosis (RO) desalination unit with a capacity of 1 m3/h of purified water and high salinity seawater (45,000 ppm). For that purpose, a computational tool has been developed, validated, and executed with real meteorological data of Borj-Cedria (Tunisia) site. The validation of both uncovered PV/T and RO separate models has been performed with previous published experiments and different feed flows and locations. When coupling between PV/T and a small-scale seawater RO unit, we found that the use of PV/T not only provides more electricity which reached 21% of the total need for the high pressure pumps of the RO unit (which meet the daily demand for 252 people), but also reduced the electrical energy demand of the desalination unit thanks to the heating of the feed seawater. Economic study showed that the cost of meter cube of purified water produced reached 0.354 US$ including the investment and maintenance cost of the PV/T system. Simulation results also demonstrate that the use of a PV/T can reduce harmful CO2 emissions up to 0.17, 0.70, 1.40, 2.79, and 4.36 ton/year using a caption surface equal to 1.62, 6.48, 12.96, 25.92, and 40.5 m2, respectively. Investigations also showed that the role of the PV/T is still promising for countries like Egypt and Emirates in which the PV/T system can produce about 24.52% and 22.49%, respectively of the energy requirement of the desalination plant.

Heating performance and spatial analysis of seawater-source heat pump with staggered tube-bundle heat exchanger

Seawater-source heat pump (SWHP) system exhibits merits of building energy conservation and reducing carbon emissions, while enhancing the heat transfer of seawater heat exchangers is the key to improve the system performance. Here, a model of SWHP system with staggered tube-bundle heat exchanger is established and its performance in winter is numerically studied and verified by experiments. The wave theory is introduced into the mathematical model to describe the flow field of actual ocean and improve the accuracy. The heat transfer performance of staggered tube-bundle exchanger is investigated under icing conditions, and the results indicate that the ice layer thermal resistance outside the tube accounts for more than 28% of the total thermal resistance. The impacts of seawater temperature on the SWHP system performance are discussed and the average increment of heating capacity and COP is 0.12 kW and 0.046 respectively with the increase of seawater temperature by 1 °C. Furthermore, a spatial analysis of SWHP system in 29 coastal cities of China are analyzed and compared with air-source heat pump (ASHP) system. The results show that SWHP system has greater advantages than ASHP system, especially in the southern cities. This research comprehensively analyzes the technology, economy and geography of SWHP system from a more macro perspective, and it can promote the application of ocean thermal energy.

OPTIMASI LP (LOW PRESSURE) AUXILIARY STEAM PADA DESALINATION PLANT UNTUK MENINGKATKAN PRODUKSI STEAM TURBINE PLTGU GRATI

Desalination Plant, which is an equipment that functions to distill sea water into fresh water by a heating process. The operation of the desalination plant in the generating system affects the production results produced by the steam turbine. The steam used is HP (High Pressure) Auxiliary steam on the ejector which functions to make the chamber a vacuum, and LP (Low Pressure) Auxiliary steam on the brine heater which functions to heat sea water. The use of HP (High Pressure) Auxiliary steam at the ejector causes a greater reduction in electricity production in the steam turbine when compared to the use of LP (Low Pressure) Auxiliary steam. This causes the cost to produce distillate to be more expensive and the production of electricity generated in the steam turbine is not optimal. Currently, the operation of the desalination plant of the Grati PLTGU is still using HP (High Pressure) Auxiliary steam to make the desalination plant chamber into a vacuum condition. The innovation is to replace the use of HP (High Pressure) Auxiliary steam with LP (Low Pressure) Auxiliary steam at the ejector desalination plant, with the aim of reducing distillate costs and increasing the optimization of electricity production generated by the steam turbine. The use of LP (Low Pressure) Auxiliary steam on the ejector is proven that the distillate value, condensate value and load setter are in normal conditions and the performance of the desalination plant is maintained. steam turbine of 26,761 kWh

Seawater as Renewable Energy in Air Conditioning and Plumbing Systems for Coastal Development

Seawater is deemed as renewable energy and supplemental water source in coastal development. Utilizing seawater resources in air conditioning and plumbing system involves implementation of innovative technology such as seawater air conditioning (SWAC), seawater heat pump (SWHP), landscape irrigation system, potable water and greywater recycling. The research aims to demonstrate seawater usage as water efficiency option to reduce energy consumption, save freshwater and environment. The research had adopted systematic literature review (SLR) method to analyze the application of seawater building air conditioning and plumbing system on current publications and papers, and conclude with summary of benefits and challenges.

Simulation Data of Regional Economic Analysis of OTEC for Applicable Area

To mitigate the power shortage problem in the South Pacific island nations and the equatorial area, we studied the development characteristics of ocean thermal energy conversion (OTEC) using abundant clean ocean energy. Through the simulation of open- and closed-cycle OTEC, the generation amount and its economic efficiency were compared, and the application characteristics of the power generation cycle according to the seawater temperature distribution were compared by applying various seawater temperature conditions. According to the characteristics of seawater heat sources in the region, the power generation output was about 883.2 kW in Samoa, and the average power generation by region was about 650.5 kW for the open-cycle OTEC model. Regional revenue up to approximately $8,487,000 was generated in Kiribati, driven by the higher electricity tariff of $0.327/kWh and high water costs of $5.86/ton. With the spread of 50 MW commercial plants, Kiribati had a high net present value of $1,930,402,000, and its internal rate of return was more than 37.0%. This paper is presents a method of securing economic feasibility of OTEC according to various heat source conditions and economic conditions in the region, while it also analyzes the capacity and type of the power plant.

Novel solar membrane distillation enabled by a PDMS/CNT/PVDF membrane with localized heating

Membrane distillation as a means of seawater desalination using solar energy has the potential to help address the challenges associated with the water-energy nexus and reduce energy consumption. However, the development of an efficient, scalable, stable, and sustainable novel solar membrane distillation (SMD) process remains challenging due to the limited number of membrane preparation procedures and system designs. This work, inspired by solar-driven interfacial evaporation, describes an SMD process employing a hydrophobic trilayer membrane and a two-level SMD structure for effective seawater desalination. A polydimethylsiloxane/carbon nanotube/poly(vinylidene fluoride) (PDMS/CNT/PVDF) membrane, prepared by electrospinning and spraying, exhibited broad light absorption, good photothermal conversion, and localized heating of seawater. The novel two-level SMD structure effectively reused the condensed heat and ensured a greater temperature difference for interfacial evaporation and steam transport, thereby improving fresh water productivity. The greatest productivity (1.43 kg m−2 h−1) and salt rejection (99.9%) were achieved under 1 kW m−2 of solar illumination. This low-energy SMD system using solar energy is suitable for emergency water production and offshore seawater desalination.

폐쇄형 해수온도차발전의 실증 적용을 위한 지역 경제성 분석 시뮬레이션

As a means to solve the power shortage problem in the South Pacific island nations and the equator, we studied the development characteristics of ocean thermal energy conversion (OTEC) using near-infinity clean ocean energy. Through the simulation of the closed OTEC plant under development, the generation amount and its economic efficiency were compared and the application characteristics of the power generation cycle according to the seawater temperature distribution were compared by applying various seawater temperature conditions. According to the characteristics of seawater heat sources in the region, the power generation output was about 759.9 kW in Kiribati, and the average power generation by region was about 590.9 kW. Regional electricity sales generated about 8,487 thousand dollars in Kiribati, which had a high power cost of 0.327 $/kWh, and 1,278 thousand dollars in Australia, generating 0.29 $/kWh. With the spread of 50 MW commercial plants, Australia and Kiribati have high net present values (NPV) of 108,000 and 580,000 thousand dollars, respectively, and their internal rate of return (IRR) are more than 8.5% and 19.6%, respectively. In the future, various benefits will be applied to secure economic feasibility and accelerate the spread of closed OTEC plant.

Experimental study on thermal and flow performance of staggered tube-bundle heat exchanger for seawater source heat pump

With the environmental deterioration and economic development, more attention has been paid to seawater heat pump system, which is as a favor technology to utilize natural low-grade energy stored in the seawater. In the present study, two staggered tube-bundle seawater heat exchangers are proposed, and the longitudinal and transversal pitch-to-diameter ratios of heat exchanger 1 are 1.5, while those are 3.5 for heat exchanger 2 (hereafter refer to as HEX-1 and HEX-2, respectively). The tube wall thermal resistance of the seawater heat exchanger is effectively reduced by adopting metal tube material instead of high-density polyethylene material. The thermal and flow performance of heat exchanger immersed in the oscillating flow are experimentally investigated. The results indicate that the wave height affects the heat transfer characteristics significantly. Furthermore, the overall heat transfer coefficient, heat transfer efficiency and pressure drop of HEX-1 are approximately 12 %–17 %, 16 %–19 % and 10 % higher than those of HEX-2, respectively. In addition, the j/f1/3 factor of HEX-2 is higher than that of HEX-1, which indicates that the comprehensive performance of HEX-2 is superior to that of HEX-1. This study is beneficial for further optimization on staggered tube-bundle seawater heat exchanger.

A comparative experimental study on the performance of staggered tube-bundle heat exchanger with unequally-pitch and equally-pitch arrangement in oscillating flow

A novel staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement, which the transversal and longitudinal tube pitches are inhomogeneous, is firstly proposed and applied in the closed-loop seawater source heat pump system. An experimental system that can induce the regular wave to simulate the seawater flow is established to investigate the thermal resistance ratio, overall heat transfer coefficient, thermal efficiency of heat exchanger under various wave parameters. The thermal performance, hydraulic performance, and comprehensive thermal-hydraulic performance of heat exchangers with unequally-pitch arrangement and equally-pitch arrangement are compared. The results indicate that the unequally-pitch arrangement of tube-bundle heat exchanger can significantly enhance the overall heat transfer coefficient and thermal efficiency, meanwhile decrease the pressure drop, and consequently improve the comprehensive performance. The present study is conducive to improve the performance potential of staggered tube-bundle seawater heat exchanger and promote the exploitation of ocean thermal energy.

Detection of salinity in the process of heating seawater by using a directional coupler of the multimode plastic optical fiber with a plane mirror as a reflector

Plastic optical fiber (POF) FD 620 10 has been widely used in various sensors with the basic principle of utilizing the intensity received because of reflection, one of which is used as a displacement sensor. In this study, POF was used as a directional coupler and was applied for the detection of the refractive index of sodium chloride (NaCl) solutions due to changes in concentration and detection of salinity in the process seawater heating. The results of this study indicate that the sensor system has succeeded in detecting the refractive index of the NaCl solution at a concentration of 0–20% and changes in the salinity of seawater due to the heating process. This sensor system is simple and easy to use, and the manufacturing cost is relatively cheap. The results of this study indicate that the sensor system has succeeded in detecting the refractive index of the NaCl solution at a concentration of 0–20% and changes in the salinity of seawater due to the heating process at the temperature range from 13 to 58 °C. This sensor system is simple and easy to use and the manufacturing cost is relatively cheap.

Model development and performance investigation of staggered tube-bundle heat exchanger for seawater source heat pump

Seawater heat pump system exhibits merits of reducing building energy consumption, while enhancing the heat transfer of seawater heat exchangers is the key to improve the system performance. The effect of seawater flow behavior on the thermal performance of seawater heat exchanger immersed in oscillating flow is significant but often neglected. An unsteady mathematical model was firstly developed to describe heat transfer of oscillating flow around the staggered tube-bundle heat exchanger and verified by experimental results. Effects of the structural and operational parameters, such as the tube length, heat transfer fluid velocity, wave parameters and sinking depth on the thermal performance were analyzed. It was shown that the thermal efficiency of seawater heat exchanger ascended with the increase of wave amplitude and decrease of the heat exchanger sinking depth. Additionally, the tube length and heat transfer fluid velocity could be reasonably designed to achieve the optimum value between cost and performance. The heat transfer mechanism in seawater side was predominated by forced convection to natural convection with the increasing sinking depth under various wave parameters. The proposed model is favorable to delicately characterize the heat transfer of seawater heat exchanger with the consideration of seawater flow. The results in this paper is helpful to guide the optimization on designing the staggered tube-bundle heat exchanger in oscillating flow and to promote the application of ocean thermal energy.

Utilization of res using seawater source heat pump with and without energy storage: Comparison of Thermal and Battery Energy Storage

Heat and cooling stands out with the great potential in decarbonisation since they have a large share in the final energy consumption. Power-to-heat technologies may contribute to the heat sector decarbonisation as well as the integration of renewables if they are sufficiently flexible. They are also shown to have a good effect on the system costs. This work will analyse the potential of seawater heat pump system for the utilization of high share of electricity production from the renewables. The Old City of Dubrovnik is selected as a case study because of its specific situation. A large number of the outdoor units are not well approved by UNESCO since the Old City is under the protection of the UNESCO World Heritage Centre. The results of the study showed that the combination of wind and solar electricity production can cover 67% of load for stand-alone seawater heat pump system based on hourly time step. Utilization of renewable electricity generation, for this case, resulted in 433.71 tCO2/y emission reduction. System based on 10 minutes time step gave poorer results by 6%. System with the additional energy storage gained best results in the case of combined wind and solar electricity generation, as well. It resulted in storage capacity reduction by 78% ac-cording to the case of solar electricity generation and by 60% according to the wind electricity generation. Battery energy storage resulted in 40 times lower volume and 13 times higher investment costs and levelised cost of heat in comparison to the thermal energy storage.

Monitoring the temperature of a direct contact membrane distillation

This paper deals with the heat transfer monitoring occurring within an inaccessible membrane distillation system. The membrane separates heated sea water and filtered cooled drinkable water. By adjusting the temperature of the incoming heated sea water and knowing its temperature distribution, engineers can keep its temperature within its best operating parameters and avoid hot spots to form. This would help prolong its life cycle and minimize the cost of the distillation process. In particular, we show that an external observation is enough to reconstruct the temperature of the membrane, which is considered as an unknown source term in a parabolic system.

Experimental investigation on heat transfer characteristics of staggered tube bundle heat exchanger immersed in oscillating flow

Owing to the growing demands to develop sustainable energy, ocean energy is attracting increasing attention for the large amount of renewable, available, and potential energy resources stored in the ocean. An experimental system was constructed to study the heat transfer characteristics of staggered tube bundle heat exchanger immersed in oscillating flow. The results revealed that the instantaneous horizontal and vertical velocities of the oscillating flow exhibited a periodic fluctuation trend. Moreover, the cycle-averaged velocity and the external heat transfer coefficients were clearly affected by the wave height, whereas the wave period had little effect. To quantitatively describe the heat convection of staggered tube bundle heat exchanger in oscillating flow, a correlation of the Nusselt number that accounted for the combined effects of the wave parameters (including the wave height and wave period), water depth, and location depth of the submersed tube bundles was proposed. Comparisons with various correlations revealed that previous correlations could not describe the external heat convection in oscillating flow accurately. The newly proposed correlation was proven to predict the external Nusselt number with an acceptable accuracy under various testing conditions, which benefitted the design of the seawater heat exchanger.

Seawater heat pumps in China, a spatial analysis

Fossil fuel based building space heating and cooling contribute to more than 10% total final energy consumption in China. Consequent carbon dioxide and air pollutants emissions bring about atmospheric pressure and associated respiratory diseases. Seawater heat pumps as a candidate sustainable building space heating and cooling solution can alleviate such environmental pressure since China has a long coastline and many coastal cities have the possibility for seawater heat pump implementation. However, stakeholders are still suffering from insufficient understanding of seawater heat pumps feasibility in different coastal cities of China from techno-economic, environmental and geographical perspectives. This paper proposes a systematic method to evaluate seawater heat pump potential in different locations of China considering various local spatial parameters in the source and sink side of the energy system. A key performance indicator system is introduced to quantitatively analyze the relative advantages and disadvantages of applying seawater heat pumps compared with status-quo systems. Quantitative evaluation results show that seawater heat pumps have a higher potential in north Chinese coastal cities from techno-economic point of view when compared with existing heating and cooling systems. Environmentally, seawater heat pumps have to reach a critical seasonal coefficient of performance value to guarantee its potential in carbon emissions saving. In south Chinese coastal cities, seawater heat pumps have to reach a more satisfactory system efficiency and a more competitive system cost in order to exploit its full advantages over status-quo systems from techno-economic perspectives. Environmentally, seawater heat pumps are more attractive than competing technologies in south cities. Also, north Chinese cities are geographically more feasible for seawater heat pumps applications compared with south cities.