FR2547399A1 - Heat pump with high performance coefficient - Google Patents

Abstract

An adiabatic compressor C delivers air - or any other practically perfect gas - through a heat exchanger 2, 3 where it gives up its compression heat, into a reservoir 4, from which it actuates a motor D, recovering its elastic energy by isothermal pressure reduction at ambient temperature T0. The cycle obtained, in the form of a curved triangle, has the property of taking heat from the cold source with a performance coefficient which is greater than the inverse of the Carnot efficiency between the two extreme temperatures T and T0. It then becomes possible to couple this heat pump to a prime mover, of which it constitutes the hot source, and to obtain the conversion into mechanical energy of the internal heat of a natural element taking the place of the cold source.

Description

It is known that the thermal efficiency # 7 OR coefficient of performance of a heat pump 3 is the ratio of the heat obtained Q to the motor energy W expended to drive it, that is, in suitable units,
g = JQ / W
According to conventional theory and technique, this efficiency can not be higher than the Rc Carnot efficiency defined by the extreme heat pump Toet T operating temperatures, ie # # 1 / Rc
It goes without saying that it would be desirable to exceed this limitation, if only because of the increase in the profitability of heat pumps which would result. But such a result would have a much greater significance. Indeed, by putting d> 1 / Rc which can be written # Rc> 1 relation which will be designated by "condition (1)" in what follows, it becomes possible to obtain motive energy at the expense of the thermal energy of natural elements is to say at the expense of terrestrial ambient heat.

 The conversion of ambient heat into motive power has been considered up to this day as utopian although there is no evidence in thermodynamics of its impossibility. The decisive element would be a heat pump fulfilling the condition (1) as will be demonstrated later.

 Now, the conversion in question is the specific property of the isothermal hold of an ideal gas maintained at room temperature. The resultant work is the exclusive product of the internal heat energy U of the heat source. in contact with which this gas keeps satemperature constant.

 Accordingly, the present invention relates to a high efficiency heat pump fulfilling the condition (1). It also aims at the combination of this type of heat pump with a motor thermal machine to obtain the conversion of ambient heat to usable energy.

The heat pump object of the invention is of the "air machine" type, that is to say that it uses as active fluid a virtually perfect gas such as air - or any other gas, it is essentially characterized by the introduction, in its mechanics, of an isothermal expansion motor whose energy comes from the motor energy necessary to operate it so as to obtain the following cycle of transformations:
a) Adiabatic compression.

b) Transfer of the heat of compression to the user medium by a heat exchanger which brings the gas back to its initial temperature
c) Isothermic relaxation, ue =
According to one of its preferred embodiments, the invention also provides means for producing an isothermal engine.
is essentially characterized by the fact that the variable volume chamber
in which is carried out the relaxation of a gas engine consists of a metal bellows whose folds are conditioned to obtain a large surface
this contact favoring heat exchange by convection and whose con
gaseous is maintained at substantially constant temperature, equal to
the outside ambient temperature, by means such as a blower or circula
water acting from the outside.

 In particular, the folded wall of this bellows can be made by stacking a plurality of thin and flexible rings, obtained from disks of a metal very good conductor of heat, pierced with an orifice cen tral and welded to each other alternately by their inner and outer peripheries. The central orifice is of small diameter relative to the large diameter, at most equal to one third of the latter, so as to promote maximum turbulence of the introduced gas, thus ensuring the best thermal contact with the pleated wall .

 The expandable chamber thus formed is provided with two bottoms, one fixed forming a cylinder head and having a valve distribution system, the other movable actuating a linkage. This motor is mechanically coupled with the compressor and its engine torque is deducted from the torque that must be provided by the main drive motor of the heat pump.

 Finally, the invention relates to an ambient heat converter in driving energy essentially characterized by the combination of a heat pump of the type just described and a heat engine with sufficient efficiency and otherwise used as a motor. The first supplies heat to the second, which reciprocally furnishes it with motive energy.

 In particular, these two machines have as a common cold source the internal thermal energy of natural elements at room temperature. The heat pump transmits the heat of compression of its active gas to the working fluid of the prime mover by a heat exchanger.

 According to a preferred embodiment the invention provides, in particular, to use for this combination a steam engine.

 The invention will be understood in any case with reference to the following description of one of its embodiments given by way of non-limiting example and to the drawings which illustrate it.

 Figure 1 schematically shows a heat pump according to the invention.

FIG. 2 schematically represents, in section, the essential details of an isothermal expansion motor which is the subject of the invention
Figure 3 shows schematically a steam machine that can be connected to the outputs A, B of the heat pump.

 Fig. 4 is a diagram for illustrating the theory of the heat pump.

 In the circuit 1, FIG. 1, of the heat pump, there is successively an adiabatic compressor C, the primary tubing 2 of a heat exchanger, associated with a secondary tubing 3 whose outputs are indicated A, B, a tank 4 of compressed air and finally a motor D, isothermal expansion operating with compressed air.

 Since dry air constitutes a virtually perfect gas, the present description refers to this gas as the active fluid of the heat pump, but it goes without saying that any other equivalent gas can be used.

 The heat exchanger operates in a conventional manner by exchanging the temperatures of the fluids circulating in the tubings 2 and 3 in opposite directions, as indicated by the arrows. Hot air enters the temperature T in the tubu lure 2 to come out at the temperature To + close to T ,. The fluid of the use circuit enters the tubing 3 at the temperature TD to come out to that T, - s, close to T ,. The two tubes are concentric and isolated against external losses. If their length is sufficient and the conductivity of the inner tubing 3 optimal, the constant temperature difference called "transfer temperature" is relatively low and can be neglected in the theoretical calculations. The fluids then exchanged their temperatures if their flow has been properly adjusted to their heating capacities.

 The invention is based on the practice of isothermal expansion, the engine D, whose essential details are shown in Figure 3, is the main element, named in the following "isothermal engine". It is clearly stated that the general scope of the invention would not be exceeded by using an isothermal motor of any construction. However, obtaining the isothermal expansion of a gas poses a technical problem which the invention proposes a solution. Indeed, in a piston cylinder, the gas relaxes without turbulence and a large part of its mass does not come into contact with the walls with which it exchanges only little heat. The relaxation curve is closer to the adiabatic so the gas cools.

To avoid this, it is important to increase the heat exchange surface and to make sure, thanks to a certain induced turbulence, that all the molecules have encountered a heat-conducting wall.To suppress the artifice, it would suffice to consider a very slow engine but its slowness would be prohibitive,
Accordingly, the invention provides for replacing the cylinder and the piston with a bellows. This ancient technique is known per se in many applicatic but the proposed inventive layout is based on the use of folds of the wall of the bellows suitably sized to promote both the turbulence and the importance of the exchange surface, provided that it The pressure expansion chamber of the compressed air is constituted by a kind of metallic accordion composed of annular elements such as a metal thin and flexible, alternately welded on their outer and inner peripheries.

In order to promote the required effect, the inside diameter of the annular elements is relatively small compared to their outer diameter, the third or less. This chamber is closed, at one end, by a cylinder head 6 and, at the other, by a movable bottom 7 secured to a rod with a stick 8, guided by a slide 9 and on which is articulated a connecting rod 10 actuating the crankpin 11 of the motor shaft 12. A wind tunnel 13 ensures the constancy of the temperature of the wall of the bellows. It is also possible to use a circulation of water for this purpose.

 The cylinder head 6 comprises a valve distribution system comprising an intake inlet 14 controlled by a valve 15 and an exhaust outlet 16 controlled by a valve 17. The control of the intake valve 15 is such that the air admitted at each time is limited to the volume referenced v ,, Figure 4, so as to relax according to the asc isotherm and occupy the volume vO at its minimum pressure p ,, having been introduced at the initial pressure p ,.

As for the exhaust valve 17, it opens at the right moment, as soon as the accordion chamber begins to retract, which has the effect of emptying the latter of the relaxed air. The minimum pressure can: correspond to the atmospheric pressure although it is not a theoretical obligation. Practically this has the advantage of being able to put a point of the circuit in the open air provided that there is at this point a system of protection of the indoor air against moisture. The heat pump can also be placed in a watertight box in order to surround it with pressurized air so as to increase the calorific mass used and thus compensate for the low specific heat of this gas. the case of the production technique and are not covered by the present invention
This isothermal motor constituting an energy recovery device, it is coupled by a transmission system not shown to the compressor C so that according to the invention of the invention the motive power to provide said compressor is reduced accordingly.

It is specified that the isothermal engine D is a slow and bulky machine and that it is difficult to envisage that its shaft 13 is common with that of the compressor C
The outlets A, B of the secondary pipe of the exchanger can be connected to any use circuit containing a suitable fluid.

 It is also possible, for space heating, to replace the exchanger with one or more convectors introduced into the primary circuit.

 However, the essential objective of the invention consists in associating this heat pump with a driving thermal machine of which it constitutes the hot source, the common cold source being a natural element at ambient temperature.

Indeed, by implementing very well built machines, with very good real yields, it may be possible to keep the condition (1) with these real yields, ie 1 <# 'R'<# Rc (1 ')
As will be demonstrated later, a motor energy gain results at the expense of the internal energy U of the cold source and the device can operate by itself, by coupling the heat pump to the prime mover.

There is no breach of the law of conservation of energy knowing that the first principle or principle of equivalence imposes no limitation to the transformation into mechanical work of a quantity of heat obtained at the expense of internal energy of a heat source. We simply
dU = dQ - dW (2)
The slight variations of temperature and pressure used in the present system allow us to hold to the hypothesis of a perfect gas for the theory of gold, as will be apparent from the calculations which follow if the laws of Perfect gases respect the first principle, they do not respect the sacond in certain cases where the isothermal relaxation intervenes.

The inlet and outlet A, B of the exchanger of Figure 1 are shown in Figure 3 where they are extended by the circuit 19 of a steam engine. This comprises in the conventional manner, an evaporator boiler represented by a balloon 20 in which the active fluid passes from the liquid state to the gaseous state at the temperature T, - E close to, The steam thus formed actuates the engine M then cools in the condenser 21 which brings it back to room temperature Tc. The reformed liquid is reintroduced to the inlet 0 in the exchanger by a pump 22
The theory of this device is as follows
Referring to the diagram of FIG. 4, it can be seen that the work of the compressor C is proportional to the area p, where ba represents an adiabatic sound compression X along the line ab followed by a pressure work at a pressure p, constant, account given the relatively large capacity of the tank 4.

During this flow, the air cools in the heat exchanger, pipe 2 then goes into the tank 4 at the temperature To + @ very close to To. In the following, we consider the quantity E as negligible. The symbols Cp , Cv designate the two specific heats of a perfect gas at constant pressure and volume, their gamma ratio; = Cp / Cv is 1.41 for air. On the other hand, it is convenient to use the ratio k = T @ / To, greater than 1, in the calculations.

The adiabatic compression taking place without heat exchange with the outside, work and heat produced are equivalent; we have Wc = JCp (T, - To), that is, taking into account k
Wc = JCpTo (kl) (3) while the heat produced, having the value Q = CpT (kl), can be considered as integrally transferred to the motor machine M while neglecting E
The work produced by the isothermal motor D and returned to the compressor is proportional to the area p, ba Po, generated by an isothermal expansion according to the ac segment of an equilateral hyperbola. The operation represents a work whose value is expressed by the relation Wi = PoVoLog v / v, that is again Wi = RTo Log vO / v, .Signing that according to Mayer's law, R = J (Cp-Cv ), which can be written as R = JCp (&gamma; -1), and that (vo / v @) ### = k, it finally comes,
Wi = JCpToLog k (4)
As a result, the motor work to be provided to operate the heat pump is proportional to the area in the form of a curvilinear triangle abc and is the difference Wc-Wi is
Wp = JCpTo (kl-Logk) (5)
Since Wc is the mechanical equivalent of abandoned heat? at the heat exchanger, the coefficient of performance thereof is: d kl-Logk 1 - Logk / (kl) (6)
Taking into account the value of the Carnot yield Rc - (kl) / k, the product p Rc takes the form of a function of k following k-1
f (k) = # Rc =
k (1 - logk / (k-1))
This function takes the value 2 for k = 1 and tends to that 1 when k tends to infinity. For small temperature differences, # T = T1-T0, it remains close to 2 and up to AT = 100 degrees, approximately. By setting 1 # Rs.f (k) the quantity Rs is the overall threshold yield above which the system produces energy. For the usual #Ts Rs is therefore close to 50%. Thus for AT = 35, it comes f (k) = 1.93 2 Rs = 52%. By considering the equality of the organic yields of the heat pump and the prime mover, taking into account the transfer temperature, the organic yield of the individual threshold of each of these machines is around the value r = V Rs S 72%.

 Beyond this value, the system becomes energy producer at the expense of the natural source of ambient heat used as a cold source.

 One of the most interesting applications of the device which is the subject of the invention may be the conversion of the thermal energy of the seas into motive power with a view to the propulsion of the ships.

Claims (2)

1.- Heat pump with a high coefficient of performance, superior to the inverse of the Carnot yield corresponding to its two extreme temperatures TOet T, using air or any other almost perfect gas as active fluid, essentially characterized by the combination of an adiabatic compressor, a heat exchanger and a motor recovering the elastic energy of the gas, after passing through the exchanger, provided with means for this recovery to proceed from isothermal expansion so that this gas undergoes the cycle of transformation 2 in the form of a curvilinear triangle (fig.4), following  a) Adiabatic compression and heating from the state poTo to that p, T,, pO and p, designating the extreme pressures.  b) discharge in the state p, T, in the heat exchanger where it gives its compression heat to the user medium to exit in the state p, To.  c) Isothermal relaxation from p, To state to poTo 2.- Heat pump according to claim 1, essentially characterized by the fact that the incorporated isothermal expansion engine has its mechanism comprises a variable volume expansion chamber consisting of a bellows whose folded wall, heat conducting, is arranged to have a maximum surface by its folds, an outer means being provided to maintain the temperature of this wall, and that of the inner gas, to a value very close to that of the tempXrature To of a natural element taken as a cold source.  Heat pump according to Claim 2, essentially characterized in that the external means for maintaining the wall of the bellows at a temperature very close to To consists of a blower using the atmospheric air as a natural element 4. - Heat pump according to the claim 2 essentially characterized in that the outer means for maintaining the wall of the bellows at a temperature very close to To consists of a circulation of water. 5. A heat pump according to claim 1 essentially characterized in that it operates in combination with a driving thermal machine for which it acts as a hot source while it provides the mechanical energy necessary for its operation, a natural element at room temperature To instead of common cold source 6.- Heat pump according to claim 5 essentially characterized in that the associated thermal machine operates according to the steam engine mode.