A Method for Ocean Thermal Energy Conversion
Summary:An improved condensing system utilizing the magnetocaloric effect is used to enhance the efficiency and expand the climatic operating range of Ocean Thermal Energy Conversion systems. (Patent Pending)
Full Description:
The proposed system improves upon an existing method of renewable power generation
known as Ocean Thermal Energy Conversion (OTEC) by employing the phenomenon known as
the Magnetocaloric Effect (MCE). Background details of both OTEC and MCE are provided
below.
OTEC is a method of power generation that uses temperature differences between ocean layers
of different depths to drive a heat engine. In an OTEC system a working fluid with a low boiling
point, in most cases pressurized Ammonia, is brought into thermal contact with the relatively
warm waters in the upper or surface layers of a liquid body. This vaporizes the working fluid and
its pressure rises. The vaporized working fluid is then used to drive a prime mover, usually a
turbine driving an electrical generator. After leaving the prime mover the working fluid is brought
into thermal contact with relatively low temperature water from deeper ocean layers which
removes heat from the working fluid allowing it to recondense and be returned to the start of the
system. This method of power generation has many advantages, being a way to continuously
generate power from a widely available source with zero carbon emissions. The drawbacks of
the system however prevent it from being employed on a large scale currently. These include: 1.
The necessity of a high temperature differential between the warm and cold water layers, high
enough differentials being almost exclusively found in tropical and subtropical waters, limiting
the range of the system.
2. Related to number one, owing to the need for high temperature differentials, the cold layer
water must be pumped from very deep, usually a kilometer or more, in order to reach sufficiently
cold ocean layers. This presents a number of engineering challenges and confines the system
mostly to large scale installations. Thus the present invention proposes the use of a condensing
system that utilizes the Magnetocaloric Effect (MCE) to amplify temperature differences between
the warm and cold layers and thus expand the systems range and scope. The Magnetocaloric
Effect is a magneto-thermodynamic phenomenon defined as: “A reversible change in the
temperature of a magnetizable substance in a magnetic field of
varying intensity with the temperature rising or falling accordingly as the field intensity is
increased or decreased. MCE is an intrinsic property of magnetic materials. This effect is due to
the coupling of a magnetic field with the magnetic sublattice. The isothermal magnetization of a
paramagnet or a soft ferromagnet reduces the entropy. In the reverse process, demagnetization
restores the zero field magnetic entropy of a system. In this process, the temperature of the
system is lowered. At constant pressure the entropy of a magnetic solid, S(T H), (function of
both the magnetic field strength (H) and the absolute temperature (T)) is the sum of magnetic
contribution SM(T M), the entropy associated with the lattice SL(T) and electronic contribution
SE(T) as put in eqn [1]:
S(T, H) =SvM(T, H) + SvE(T) +SvL(T)
The lattice and electronic contributions are essentially independent of magnetic fields, whereas
the magnetic entropy is lowered due to ordering of the magnetic spins when subjected to an
external magnetic field. The lowering of magnetic entropy results in an increase of the lattice
entropy if the material is kept isolated from its surroundings, that is, under adiabatic
conditions.”[1][2]
A method for cooling using this effect follows four basic steps:
1. Magnetic field is introduced/intensity is increased to Magnetocaloric Material
(MCM) held in thermal isolation, causing the temperature of the MCM to rise.
2. With the magnetic field held constant, a Heat Transfer Fluid (HTF) is brought through
thermal contact with the MCM, removing the heat of magnetization.
3. The MCM is again thermally isolated and the magnetic field is removed/intensity is
decreased, causing the MCM to lower in temperature.
4. A HTF is again brought through thermal contact with the now lower temperature MCM,
sinking heat and lowering in temperature.
By employing a condensing system utilizing this effect the temperature differential between the
Warm and Cold water layers (heat source and heat sink) may be amplified, allowing for
operation across a shorter vertical pumping distance, allowing for smaller and more efficient
systems to be constructed. Additionally, decreasing the minimum temperature range between
Warm and Cold water layers allows the system to operate across a broader climatic range,
permitting operation in temperate waters as well as tropical and subtropical waters.
Attached files:
OTEC (7) (2) (1).pdf
Asking price: [CONTACT SELLER]
Available for consultation? Yes
Invention #12456
Date posted: 2023-01-27
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