WO2003038362A2

WO2003038362A2 - Thermal stratifying contact condenser for use in and relating to vapour cycle devices

Info

Publication number: WO2003038362A2
Application number: PCT/IE2002/000153
Authority: WO
Inventors: Gerard Moran
Original assignee: Gerard Moran
Priority date: 2001-11-02
Filing date: 2002-10-31
Publication date: 2003-05-08
Also published as: WO2003038362A8

Abstract

The subject of the invention is a condenser to obtain thermal stratification contact condensation in and relating to a wettable conduit condensing structure, in conditions approaching constant enthalpy. It is intended for use in vapour cycle devices, typically steam engines or heat pumps. Vapour to be condensed is brought into contact with wettable surfaces having a high surface area per unit volume, ideally in a counter flow arrangement where the vapour is circulated upward through the structure against the downward attraction of gravity. Condensate is drained from the structure by gravity along its length for recover at the highest available temperature. Valve means can be provided to restrict the downward flow of condensate and to allow the upward ingress of vapour through the structure. The invention adapts methods of distillation and fluidisation, but it is not limited to these embodiments. It is intended to use the phenomena of gravity, thermal buoyancy, boundary layer and surface energies as well as the effects of static pressure and centrifugal action for optimum vapour liquid contact and to obtain separation of wet vapour and to enforce condensation. Pressurisation of the condenser and of a condensate storage receiver can be provided to promote further thermal enrichment and stratification of the condensate. Throttle means can also be used to provide isenthalpic cooling in recirculated condensate, in a closed cycle.

Description

THERMAL STRATIFYING CONTACT CONDENSER FOR USE IN AND

RELATING TO VAPOUR CYCLE DEVICES

Technical Field of the Invention: High effectiveness condensers intended for use in and relating to heat pump and vapour power cycles to minimise compression work and recover heat. The phenomena of gravity, thermal buoyancy, boundary layer and surface energies, together with static pressure and centrifugal effects of fluid motion, are used to obtain thermal stratification contact condensation. A new use is intended of contact condensers and of the methods of distillation and fluidisation with the objective of obtaining condensation in conditions approaching constant enthalpy.

Background of the Invention:

The history of heat, engines and condensers are closely connected. The Savery engine circa. 1660 generated a vacuum to pump water by condensing steam. The single greatest improvement in steam engine design was the use of a separate condenser, by Watt in 1765. The development of higher pressure operation and steam expansion in the early 19^th century attracted the attention of theorists with a belief in a need for heat dumping. Although heat recovery in heat engine cycles is theoretically possible, particularly with external combustion vapour expansion cycles, such as the steam engine, it is practically very difficult. For high efficiency, expansion to the lowest possible pressure is required and the possibility for vapour compression is limited by an adverse work ratio and problems associated with cavitation.

As with a heat pump, performance of vapour cycle engines is heavily dependent on hear exchanger effectiveness. Design is concerned with optimising those factors known from Fourier's law of heat transfer. Increasing surface area generally increases cost. Higher heat transfer coefficients are generally associated with higher mass flow rates and momentum transfers. For cycles involving vapour expansion or compression the cost performance trade off is generally determined by the third factor, the temperature difference. Contact condensers provide a simple cost effective solution to condense vapour at low pressure, but jet and barometric condensers are no longer extensively used because condensate becomes contaminated by coolant. With surface type condensers heat transfer rates are lower and heat recovery must be to a temperature lower than the coolant. By recirculating the condensate and by thermal stratification within the cycle, the possibility exists to retain the advantages of a contact condenser, to reduce or eliminate compression work, to recover heat at higher temperatures and to dump heat more effectively in a separate coolant circuit.

A contact condenser capable of condensing at a higher temperature than the vapour is possible because the vapour pressure increases with temperature. Sensible heat capacities are less temperature dependent although they increase with temperature and pressure. This increasing heat capacity is of particular advantage when the objective is to fully condense the vapour in the condensate. Although the heat of vaporisation of water is about 5 times greater than the sensible heat capacity of boiling water, about 420 Kj/kg between 0 and 100 degree centigrade , for refrigerants in general enthalpies of liquid and vapour phases at saturation are in closer agreement with sensible heat capacities. Heat capacities also increase more rapidly with temperature and pressure, as does vapour pressure at higher temperatures. Thermal stratification condensation is possible by contacting separated streams of vapour and condensate in and relating to wettable surfaces, having a high surface area per unit volume. A conduit can contain one or both fluids and it can be arranged to use the effects of boundary layers and gravity to separate wet vapour and to draw of the condensate at the highest available temperature. The effects of gravity together with one way valves in a vertical column structure can restrict downward flow of condensate and allow upward ingress of vapour. By recirculation, by storage of condensate or by pressurisation of the condenser or condensate, greater thermal stratification and enrichment can be obtained. Pressurisation of the condensate also provides a means for isenthalpic cooling to assist recirculation in vapour power cycles. Material coating means as well as capillary action can be used to optimise contact condensation through surface energy effects.

Use of steam engines is limited to fixed units and large scale where condensation is by cooling or heat dumping in an open cycle to the environment. The objective of constant enthalpy condensation in a closed cycle is to facilitate more efficient, smaller scale, more mobile and solar power applications for vapour power cycles. A novel thermal stratifying contact condenser also provides a means for more effective and versatile operation of heat pumps in which applications the technology of vapour compression, refrigerant recirculation and isenthalpic expansion is well developed. Summary of the Invention:

The invention discloses a contact condenser capable of thermally stratifying the condensate in the condensing process and in the peripheral condensate storage receivers. The design objective of the invention is to obtain constant enthalpy condensation in contrast to the conventional practise of isothermal condensation. It is intended for use in and relating to vapour power cycles and heat pumps to recover heat and to reduce or eliminate compression work.

According to the invention vapour to be condensed, is circulated by a forced or induced draught, substantially vertically, through a conduit or column structure. Said structure comprises wettable surfaces having a high surface area per unit volume. Said surfaces may also have a high porosity. Said wettable structures can be provided by the methods of distillation, of packed columns or by a series of staged trays and plates, on which vapour streams and liquid are contacted in a countercurrent flow. Restrictions to downward flow of condensate can be provided by means of bubble cap plates, sieve trays, weirs or by means of any one way flow device. Alternatively constant enthalpy condensation can be approached by suspension or fluidisation of wettable granular material in a vertically rising stream of vapour. In a further alternative the conduit structure may be substantially open axially to vapour flow so that wettable surfaces provided by finning or packing means, by boundary layer effects, pull differentially and separate wet vapour for condensation on said surfaces. In this mode circulation or re-circulation can take place by thermosiphon effects comprising a type of condensation heat pipe. Vortex or cyclone effects can be generated within the conduit to promote separation of wet vapour. In a further embodiment condensate is regulated to flow between the porous wettable sides of a conduit, open to a space containing vapour to be condensed. The static pressure depression together with surface energy effects, particularly the advantages of those effects with downward flow under gravity, can be used to draw in and entrain vapour through the porous sides of the conduit and to condense and transport it in the condensate stream. In this mode the active conduit condensing element can be embodied in motion, for example, in the vanes of a centrifuge or a fan or in the inner walls of a rotating drum, to increase the pressure differential between the vapour and the condensate stream, thereby to enforce condensation. Condensate is removed laterally from the sides of the conduit condensing structure or with the flow of the condensate stream from the lower end of the structure. It is removed at the highest available temperatures from where it can be brought to a storage tank for thermal stratification. Said tank may be pressurised for optimum thermal stratification and enrichment. Said tank may also be combined with a porous plug throttle type restriction to provide constant enthalpy cooling of the condensate recirculated to the condenser.

The objective of the invention is the use the phenomena of gravity, thermal buoyancy, boundary layer and surface energies as well as the effects of static pressure and centrifugal action of moving streams of vapour and condensate, in contact with wettable surfaces. The design objective is to obtain optimum vapour liquid equilibrium contact for thermal stratification contact condensation in conditions approaching constant enthalpy.

Brief Description of Drawings:

Figure 1 : A sectioned side view showing a distillation column embodiment of the invention.

Figure 2: A sectioned side view showing a fhiidized bed embodiment of the invention.

Figure 3 : A sectioned side view showing an axial duct embodiment of the invention. Figure 4: A sectioned side view showing a porous walled conduit embodiment of the invention in a unified structure together with a throttle element and a thermal stratifying storage tank.

Description of Preferred Embodiments:

A distillation column embodiment of the invention is shown in figure 1. Vapour from a vessel 1 is circulated vertically through a series of stages containing trays or plates 2 which retain the condensate. The condensate and vapour pass through the column in opposite directions cascading over weirs 3 through vertical downcomers 4 and through sieve trays 5. Condensate is removed from the liquid tray receivers through tap holes in the side of the column 6 and from a sump 7 at the bottom of the vapour containing vessel 1. Condensate can be removed from the column through tap holes at a differential mass flow rate from the column so as to optimise the temperature stratification. The thermally stratified condensate can be brought to a tank 8 for further thermal stratification. Condensate from the lower end of the tank can be recirculated through the condenser and the tank may be pressurised for thermal enrichment and to facilitate return of condensate through a throttle device 9 for isenthalpic cooling. Heat exchange can take place from the condenser through the sides or by constructing the inner members of the column from heat exchange tubes and plates or by any heat exchange means. The tray structures, for example, by means of porous sides can also comprise condensate removal means. Heat can also be removed from the tank by sensible heat exchange means. The invention is not limited to the specific arrangement of trays and plates as shown or to a countercurrent flow or by the separate arrangement of the column element and the stratifying tank and throttle elements. Any effective arrangement of wettable conventional distillation devices, such as, bubble cap trays, valve trays or packed column structures, is intended and the flow arrangement may be cocurrent or crosscurrent or act through horizontal redistribution decks to collect and redistribute the condensate through the inner structure at successive intervals of height. The invention can be embodied as a distillation column alone, without tank and throttle elements.

Figure 2 shows the invention embodied by the methods of fluidisation. A housing 10 containing wettable granular material 11 over a perforated supporting plate 12 through which vapour to be condensed is blown from a containing vessel 13 below. The supporting plate 12 may be slotted or fitted with nozzles or sized and arranged by any other means, to uniformly distribute upflowing vapour and to contain the granular material in the bed. Selection of bed material should be of a size and specific gravity to ensure the necessary countercurrent behaviour of a turbulent fluid and to enable stable operation at the vapour velocities and rate of condensation activity of a specific design. Said bed material maybe porous. Additional means can be used to restrict the downflow of bed material and liquid condensate, such as, the baffle ball valve one way flow device 14 or any effective one way flow device. Said devices or a plurality of said devices suitably sized and staged can serve to lengthen the effective operating height of the bed and to contain the liquid condensate in the upper section of the bed. They can also serve to entrap and drain condensate from the bed by, for example, having porous sides. They can also be constructed as heat exchange members, having optimum heat transfer contact with the condensate and bed material. As with the distillation column embodiment of the invention, condensate can be removed laterally through tap holes at the sides of the bed 15 or from a sump 16 in the lower containing vessel to a tank for thermal stratification and recirculation, but it can also be embodied as a fluidized bed alone.

In a third embodiment the condenser comprises a duct open axially to the flow of vapour, as shown in Figure 3. Said duct can be arranged vertically or at an angle and by fmning or packing means 17 or by some combination of the two, provides wettable surfaces having a high surface area per unit volume. Axial flow of vapour through the duct can be by forced draught or by thermosiphon and may be recirculated through the duct or through a plurality of said ducts. Boundary layer effects as well as those of gravity are used to separate wet vapour to the wetted surfaces for condensation. The vapour may also be circulated by a cyclone or vortex action to separate wet vapour and promote condensation by centrifugal effects. The geometry of said duct may also be arranged so that by diffusive action the pressure in the vapour can change with length, for more effective use of boundary layer, centrifugal and gravity effects. The geometry and arrangement of the duct is not limited to the proportions and shape, as shown in Figure 3. The packing structure may also be moveable by, for example, vibration so as to minimise filming and to accelerate condensation by raining condensation drops through the vapour. The effect of condensation raining as a means to promote contact condensation is an intention of the duct embodiment in particular when the vapour flow and the duct are horizontal. The effectiveness of boundary layers as a means to separate wet vapour and to improve heat transfer by momentum transfer are dependent on velocity. To great a velocity and the heat and mass transfers will be in the opposite direction to that intended. By additional means of grid like matrices or barriers 18 vapour flow can be restricted and redirected to generate turbulence and greater heat and mass transfers to the wetted sides of the duct. The fining and packing structure 17 should be arranged to entrap the condensate and drain it through the sides of the duct. Inner grid like structures 18 can also be constructed to provide condensate and heat removal means. As in the earlier embodiments condensate should be removed through the sides and sump of the condenser at the highest available temperatures and can be brought to a tank for further stratification and/or recirculation. The invention can also be embodied as an axial flow condenser duct alone. In a further embodiment the invention comprises a porous sided wettable conduit structure through which condensate flows. This embodiment is shown in Figure 4 as a unified structure, comprising the active conduit condensing element 19 vertically arranged, a throttle restriction 20 above the conduit, open to a condensate storage tank 21 thereabove. Condensate in the tank leaks through a porous plug type restriction or any type of isenthalpic throttle device, to enter the conduit below. Condensate flows through the conduit under gravity thereby to use the static pressure depression caused by the flow, together with the surface energy effects and capillary action in the porous walls of the conduit, to draw in vapour to the condensate stream for condensation. The design, regulation and rate of flow in the conduit structure is such as to ensure that the pressure in the condensate stream is lower than that of the vapour. Additional means can be used to entrap and collapse entrained vapour bubbles which rise in the condensate stream to the upper end of the conduit. Said addition mean can comprise capillary ducts 22 through the profiled lower surface of the throttle structure 23 entering to the upper section of the tank, packed column duct type structures entering through the throttle structure to the upper section of the tank or by means of a parallel duct structure to draw off said vapour bubbles, to collapse them by surface energy effects and to transport the resultant condensate by capillary action or by pumping means to the upper section of the tank. The condensate is recirculated from a sump or tail pipe 24, at the bottom of the vapour containing vessel 25, by a pump or compressor 26, to the upper section of the tank. Condensate is removed from the tank by pipe means 27 at the highest available temperature. The tank can include a surface heat exchanger 28 for heat transfer according to requirement. The active conduit condensing element or a plurality of said elements may be spaced and sized in the vessel 23, so as to use the boundary layer effects of vapour flow through said vessel, to separate wet vapour. Said vessel may also contain a wettable packing structure to condense vapour for recover from the sump 22. Said vessel may also be elongated comprising a duct like structure.

The embodiment shown in Figure 4 is not limited to a unified structure arrangement or to a gravity feed arrangement. The tank, throttle and condensing elements may be spaced apart, being connected by pipe or duct means and this embodiment may comprise the active condensing element alone. In this latter mode of embodiment the condensing element is not limited to a gravity feed vertical arrangement. With any angular arrangement and with a forced draught condensate flow this element can be effectively embodied. As an ejector pump type compressor, for example, together with a diverging diffuser conduit section at exit. A porous walled conduit condensing element can also be embodied in the walls and vanes of rotating centrifuge and fan type blowers. The centrifugal effect of a rotating drum, for example, can draw in vapour for enforced condensation on its inner wall which comprises porous sided ducts, embodied according to the invention. The same centrifugal effect can also serve to pump the condensate through said rotating equipment. Fan type blowers comprising condensation elements in the fixed and moving parts can also act to cool and dehumidify/humidify air in heating and ventilating applications.

The invention can be embodied to minimise the work consumed in a number of vapour compression processes. As an element in a conventional or absorption type heat pump, for example. A thermal stratifying contact condenser which can reduce or eliminate compression work and which can incorporate a heat exchanger in its structure is of particular use in heat pumps where heat transfers from a condenser are necessary. In its simplest embodiment in a heat pump the invention can act as a type of forced draught open ended heat pipe. Vapour power cycles which use refrigerants together with an effective thermal stratifying condenser, for use in a closed cycle, are of particular value in solar energy applications where available cooling capacities are limited. This intended use has been a primary objective of the invention. In heating/ventilating applications air is generally removed from a space to be conditioned. The possibility exists of using a porous sided contact condenser element, according to the invention, to cool and humidify or dehumidify a space directly. The cooling fluid in said element should feed to the evaporator of conventional heating and ventilation equipment thereby to increase the evaporation temperature and reduce the compression work consumed. Thermal comfort is dominated by radiant heat transfers and the invention can be further embodied as a radiant cooler in a space to be conditioned. This embodiment can be ideally formed as a gravity feed panel, as an architectural feature. Because of the static pressure depression said panel can be easily constructed from matted fabric type materials.

In all the embodiments the sizing, design and controls are such as to find the right balance between the several phenomena the invention is intended to exploit. For thermal stratification contact condensation in conditions approaching constant enthalpy, pressures in the condensate are in general lower than those in the vapour. The control objectives are to maintain the necessary temperature and pressure differences for optimum vapour liquid equilibrium contact, to recover condensate at the highest possible temperature. By suitable choice of refrigerants the objective is to recover all the heat in vapour power cycles. Closed cycle vapour power cycles are an objective of the invention but the invention is not limited to closed cycle applications. Glazing or other material coating means can be used to promote filmwise or dropwise condensation.

The invention may be ideally embodied in retrofit as condensers of existing power cycles where there is an available cooling capacity. Alternatively smaller scale, more mobile vapour power cycle applications are realistic objectives. The possibility exists by pressurising the vapour in the cycle to obtain condensation at higher temperatures and pressures with minimal compression work and fewer equipment problems than with conventional vapour compression practise. All applications are intended, existing or novel, for an effective thermal stratifying contact condenser.

Claims

CLAIMSI claim, as follows,

1. A thermal stratifying contact condenser intended for application in and relating to vapour power and heat pump cycles, said condenser uses the phenomena of gravity and surface energy in configurations of reported vapour-liquid contactings of separated vapour condensate streams, in and relating to a wettable conduit structure, having a high surface area per unit volume and having a condensate removal means; characterised in that, Thermal stratification contact condensation in said applications takes place in and relating to said wettable conduit structure or a plurality of said structures, which by optimum vapour liquid contact of said separated streams, condenses at temperatures higher than the temperature of the vapour to be condensed.

2. A condenser as claimed in Claim 1 ; characterised in that, It uses the methods of distillation for optimum vapour liquid equilibria contact.

3. A condenser as claimed in Claim 1; characterised in that, it uses the methods of fluidisation to obtain condensation in conditions approaching constant enthalpy.

4. A condenser as claimed in Claim 1 comprising a duct or a plurality of ducts, open to the axial circulation or recirculation of vapour and having extended wettable inner surfaces and having condensate removal means by tap holes to the external sides of said duct; characterised in that, the effects of boundary layer friction and of gravity are used to separate wet vapour for condensation on the inner sides of the duct.

5. A condenser as in Claim 4; characterised in that, vapour is circulated or recirculated in the duct by thermosiphon effects.

6. A condenser as claimed in Claim 1 comprising a porous sided wettable conduit structure through which condensate flows; characterised in that,

The static pressure depression in the condensate draws in vapour through the porous sides of said conduit for condensation and removal in the condensate stream.

7. A condenser as in Claim 6; characterised in that,-

It comprises a gravity feed panel for use in heating and ventilating applications as a latent and radiant heat cooler, humidifier/dehumidifier.

8. A condenser as in Claim 6 comprising a component in centrifugal and rotating drum or any type of periodic fluid moving device; characterised in that, Centrifugal effects generate a pressure difference between the vapour and the conduit contained condensate so as to enforce condensation through the porous sides of the conduit embodied in said rotating devices.

9. A condenser as in any one of the previous claims comprising a condensate storage tank; characterised in that, said tank is designed and arranged to thermally stratify the condensate.

10. A condenser as in any one of Claims 1 to 8 comprising a condensate storage tank; characterised in that,

Said storage tank is pressurised to promote temperature enrichment and stratification.

11. A condenser as in any one of Claims 1 to 8 comprising a porous plug throttle type restriction in the return feed of a recirculated stream of condensate; characterised in that, said throttle device provides isenthalpic cooling of the condensate.

12. A condenser as in any one of Claims 1 to 8 comprising a heat exchanger in the active condensing element.

13. A condenser as in Claim 4; characterised in that,

It acts as an open ended type heat pipe for heat and mass transport.

14. A condenser as in any Claim 1 to 8 or Claim 13 or 14; characterised in that,

Capillary action is used to promote condensation and to transport condensate.

15. A condenser according to the invention; characterised in that, it provides thermal stratification contact condensation in all applications where it is useful.

16. A condenser as in any Claim 1 to 8 or claim 13 or 15; characterised in that, Material or material coating means are used to promote filmwise or dropwise condensation as required.