Rotary heat and/or mass transfer arrangements

Details Rotary heat and/or mass transfer arrangements Rotary heat and/or mass transfer arrangements

1999-09-24

2001-09-18

Bushey, C. Scott (Department: 1724)

Gas and liquid contact apparatus

Contact devices

Rotating

C261S090000

Reexamination Certificate

active

06290216

ABSTRACT:

This invention relates to rotary heat and/or mass transfer arrangements.
In particular, though not exclusively, the invention is concerned with heat/mass transfer enhancements in apparatus which makes use of process intensification, for example in a rotary absorption heat pumps. Examples of such pumps are disclosed in U.S. Pat. No. 5,009,085 and our co-pending International Patent Application No. PCT/GB96/02486, the entire contents of which are incorporated herein by reference. In such apparatus it is common to make use of rotating surfaces to provide thin films for the transference of heat and mass. For example, in one region of a typical rotary absorption heat pump, a stream of a working mixture which is rich in a volatile component is directed onto a radially inner surface of a rotating generator wall through a single outlet pipe, the other side of the wall receiving heat from a gas burner.
To provide an acceptable cycle efficiency it is extremely important to maximise the heat and mass transfer from the generator wall. Earlier work in this field, (for example Cross, W. T. and Ramshaw, C. Process Intensification: Laminar Flow Heat Transfer. Chem. Eng. Res. Des., Vol. 64, pp 293-301) indicates that, theoretically, heat and mass transfer coefficients in laminar flow situations can be equivalent to or better than their turbulent counterparts and so it would be expected that laminar flow should be maintained. Surprisingly we have found that, by redesign of the system, it is possible to achieve far greater heat and mass transfer rates, by deliberately disturbing the fluid film, e.g. by wave generation or wake interaction.
Accordingly, in one aspect of this invention, there is provided a rotary heat and/or mass transfer arrangement, comprising:
a rotor means for being rotated in use;
means for delivering a supply of liquid to a radially inner region of a surface of said rotor to provide a fluid film which flows over said surface accompanied by heat and/or mass transfer to or from said liquid, and
means for disturbing said flow, thereby to enhance at least one of said heat and mass transfer.
We have found that by disturbing the flow, the heat and mass transfer coefficients may be increased. Generally we have found that the disturbance creates waves or a wake interaction which enhance mass and heat transfer.
This arrangement is particularly appropriate where a liquid/vapour interaction occurs at the exposed surface of said liquid, for example the absorption of vapour into the liquid, the giving off vapour from the liquid, or chemical absorption or chemical reactions at the surface thereof.
Preferably, said delivering means comprises a plurality of nozzle means disposed around the rotary axis of said rotor, to provide in use a film thickness in which the non-uniformities are reduced compared to those generated by rise of a single delivery nozzle means. We believe that the combination of a substantially uniform film thickness applied by the plurality of nozzle means, and suitable disturbance of the flow either by a main nozzle means, or by a recirculating nozzle means, can increase the heat transfer coefficient by up to 2, and the mass transfer coefficient by up to 2. The plurality of nozzle means may in certain embodiments also constitute the means for disturbing said flow. Thus by suitable location and direction of the liquid jets, a wave generation or wave interaction effect may be set up. For a recirculating arrangement, flow leaving the rotor means may be collected and recirculated to be directed back on to the rotor by means of one or more disturbing nozzle means directed towards the surface of said rotor means. Preferably, a plurality of additional nozzle means are directed at different radial positions thereby to provide a re-stirring of the film and consequently mixing of concentration and temperature profiles within the film for each complete revolution of the rotor. In this way, the local heat and mass transfer rates may be increased.
These arrangements may be applied to any of the “rotating disc” processes within a rotary absorption heat pump.
Accordingly, in another aspect, this invention extends to a rotary absorption heat pump incorporating one or more rotary heat and/or mass transfer arrangements as described above.
We have found that the cycle efficiency of the heat pump can be substantially enhanced by using these arrangements.
In another aspect, there is provided a method of enhancing the heat or mass transfer coefficient in a rotary system comprising a rotor over which liquid is required to flow in use accompanied by heat and/or mass transfer to or from said liquid, said method comprising disturbing said flow, thereby to cause at least partial re-stirring and/or re-mixing of liquid within said flow.
In another aspect, the invention extends to a rotary heat and/or mass transfer arrangement comprising:
a rotor for being rotated in use;
means for delivering a supply of liquid to a radially inner region of a surface of said rotor to flow in use over said surface accompanied by heat and/or mass transfer to or from said liquid,
wherein said means for delivering comprises a plurality of nozzle means disposed about the rotary axis of said rotor adapted to provide a non-laminar flow of fluid across said rotor.
Whilst the invention has been described above it extends to any inventive combination of the features set out above or in the following description.


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