ES2358488A1 - ACCUMULATOR EQUIPMENT WITH STRATIFICATION THROUGH VERTICAL TUBES. - Google Patents

Abstract

Accumulator equipment with stratification by means of a bundle of vertical tubes. The main objective of the invention is an electric or thermo accumulator designed to avoid the mixture of hot and cold water inside the accumulator itself. The equipment contains the insert inside the accumulation tank or casing (1) of a set of tubes (2) that act as mini accumulators and minimize the mixing between hot and cold water; The equipment also contains an electrical resistance (3), upper (4) and lower (5) discs, upper (6) and lower (7) microperforated plates as well as other elements.The technical solution provided by the invention is the considerable reduction of size and weight of the thermos without reducing its ability to obtain sanitary hot water. The invention is an alternative to the conventional electric hot water tank.

Description

Accumulator equipment with stratification by bundle of vertical tubes.

Technical sector

The accumulator equipment described is from Application in the industrial technical manufacturing sector of electric hot water storage devices intended mostly to the domestic sphere.

State of the art

Most of the individual systems of hot water production using electricity use the thermos electric to heat and store water. There are other teams applicable electric, such as the instant heater (which requires high operating powers).

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Hot water production systems They can be grouped into the following two categories:

to)

Continuous heating.

The warm-up of water is produced in any period of day depending on the demand. Thus, the extraction of hot water from the thermos means the cold water inlet, which then begins to get warm.

This system is used in low capacity thermoses or, to be more precise, thermos whose volume covers only a small part of the total needs of hot water.

For this reason, continuous heating does not take sufficient advantage of the Rate Night, and the percentage of consumption during the night is not usually exceed 20% of total hot water consumption.

b)

Night heating.

The warm-up of water is done primarily at night, in the 8 hours of reduced price.

The limitation of the heating time means increasing the capacity of the thermos in relation to the previous case, whereby the equipment is called hot water accumulators .

Depending on volume of the thermos, the hot water produced overnight will attend most or all of the day's needs next. In any case, the thermos must also be able to connect during the day, at the user's discretion, to deal with a Water demand not covered with the volume stored.

This system of heating provides a great use of the Rate Nocturnal, with percentages of consumption during the night ranging from 60% to 100%, depending on the capacity of the thermos.

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Regarding stratification, two types of stratification can be distinguished according to their nature: natural or artificial :

to)

Natural stratification

The utilization of natural stratification instead of physical separators Maximize download capacity. For a given accumulator the maximum discharge capacity results from minimizing transfer Internal heat and mixing.

To obtain natural stratification is necessary to use diffusers at the outlet and especially at the entrance of the water to the accumulator. The The primary function of these diffusers is to reduce mixing produced by the cold water that arrives.

Two exists mechanisms to consider. One is the mixing that occurs at beginning of discharge during thermocline formation. This Mix largely determines its initial thickness.

It is produced simultaneously with the heat transfer between the water that enters and the solid components of the accumulator with which the water He gets in touch.

The other important mixing mechanism occurs on the side of the thermocline that is at the entrance of the water, once that one has formed. It is associated with circulatory movement and formed vortices by the fluid that enters and depends on the number of Froude and the number of Reynolds for the inflow.

The design of the diffuser has a main effect on mixing and only one Side effect on heat transmission. It is obvious that if the water enters the accumulator with a high vertical speed the mixed will be excessive.

b)

Artificial stratification

Appearance The novelty of the patent is the use of a technique, that of artificial stratification, which although it has been widely used in energy storage situations (both water hot as cold water) is new in the design of accumulators Electrical for homes.

Bliss stratification will allow separation in our case between the cold and hot layers of fluid and therefore the optimization of the energy contained in our accumulator through minimal heat exchange

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Description of the invention Realization

For the realization of this invention, as well as for the evaluation of its effectiveness the following have been followed Steps:

1) Bibliographic review.

2) Construction of prototypes and the necessary installation. To carry out the experiments, they have built three different prototypes that have been tested assuming some typical consumption of the average Spanish family. Of the the same way the infrastructure facilities have been equipped necessary for carrying out the studies.

3) Performing laboratory tests:

quad

Static regime:

i.

Charging Period Temperatures will be determined inside the accumulator while the resistance is supplying heat

ii.

Relaxation period (cooling). Reached every one of the temperatures of our study is allowed the 24/48 hour cooling of the accumulator to check the temperature variations inside the accumulator as well as its losses abroad.

quad

Dynamic regime:

i.

Full download Through this consumption pattern the most favorable conditions for stratification have been tested natural The tests have been carried out at different temperatures of heating and with different flows.

ii.

Downloads according to consumption patterns. In conditions normal operating domestic hot water consumption not it is produced continuously but it is produced continuously discontinuous throughout the day. It is in these conditions that the problem of mixing between the hot and cold water of the inside of the thermos.

4) Analysis of modeling programs Mathematics existing in the market.

5) Computer simulation of prototypes proposed.

6) Comparison between the results of said simulation and those extracted from the experiments performed on laboratory.

7) Conclusions and possible improvements proposed to The prototypes presented.

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For the realization of the experiments it has been It has the following laboratory equipment:

?

KEITHLEY 7000 multimeter with module 7100.

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PC computer + software own programming control.

?

PC-LAB card 512.

?

K probes with range of temperatures from 0 to 100 ° C.

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The TERMO v.2.1 program of its own programming allows you to control the installation at the same time as record the status of the temperature probes on disk system.

With the joint use of this software and of the usual consumption patterns in Spanish families, has been able to automate the performance of experiments while guarantees accuracy in measurements.

For the realization of the invention have been manufactured three different prototypes: a classic one based on natural stratification, another based on the use of horizontal stratification using horizontal separator discs and finally one that manages to perform a stratification artificial by means of a beam of vertical tubes, this last reason of the invention of the present patent.

For the correct simulation of the physical problem what concerns us is important to predict the movement of water which will be defined by a laminar regime that requires the use of same time, the Navier-Stokes equations and the general equation of energy.

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In addition, there are moments in the operation of a domestic hot water tank in which it is also necessary the presence of different computer models:

i)

In the warm up. When electrical resistance the surrounding water becomes hot instantly and, due to density gradients, it tends to Ascend in the warehouse. For the same reason, cold water will tend to descend.

ii)

At the time of hot water extraction it produces a forced convection movement and simultaneously there a column of water that rises to replace the water extracted.

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Are these and others the reasons they do necessary a complex mathematical simulation that, at present, it is possible by using modern programs simulation software such as FEMLAB (engine based mathematician of MATLAB).

For computer simulation have been performed a series of simplifications on the mathematical model in order to reduce the necessary calculation time and the needs of equipment. Thus, and due to the use of a program of simulation using finite elements, the cylindrical surface of the accumulator in a surface mesh triangular Using a sufficiently high number of polygons a good approximation of the results is obtained without being Very high computing power is necessary.

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For the resolution of the original problem it has been used a system of coupled differential equations, to to know:

i) Heat transfer:

one

where

q = Internal heat flow

h = Thermal Transfer Coefficient

T_ {inf} = External Temperature

Const = Time Dependent Constant

T_ {amb} = Ambient Temperature

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ii) Fluid mechanics (Navier-Stokes):

2

where

\ rho = Density

u = Dynamic Viscosity

F_ {i} = Volume Force on axis i

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All values used in the simulations they come from the characteristics of the material that have been provided by different manufacturers.

Once a test sampling has been performed between computer simulations and experiences in laboratory can be considered that such simulations are accurate by 93%, a sufficiently high number considering the number of experimental parameters that escape the field of Current computer simulation.

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Prototypes Conventional prototype

The main physical characteristics of Prototype used are the following:

Capacity Nominal: 87 (l)

Real Capacity: 87 (l)

Maximum power: 2000 (W)

Thickness of insulation: 40 (mm)

Total height: 625 (mm)

Internal height: 600 (mm)

Diameter boiler: 416 (mm)

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The actual capacity being the nominal minus the space occupied by separator discs, tubes and other interior elements to the boiler.

This prototype unlike the object prototype of this invention (with stratification by vertical tubes) It has an empty tank; temperature probe data is made through the holes made along the deposit (as in the prototype with stratification by vertical tubes). In this case the stratification will be natural and will will achieve, as far as possible, thanks to the existence of a small intermediate layer called thermocline that separates the volume of hot water of cold water.

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Prototype with artificial stratification using discs horizontal

The most notable physical characteristics of This prototype are:

Capacity Nominal: 87 (l)

Real Capacity: 82 (l)

Maximum power: 2000 (W)

Thickness of insulation: 40 (mm)

Total height: 625 (mm)

Internal height: 600 (mm)

Diameter boiler: 416 (mm)

No. of baffles: 5

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Unlike the prototype object of this invention (with stratification by vertical tubes) in this case a central structure consisting of a tube and of some discs united in solidarity with this one (Davis and Bartera (1975) they performed various experiments to check the effect of placing various sheets in the thermal stratification achieved). In this case we observed a decrease in the useful volume inside the thermos and the existence of better temperature maintenance inside the compartments by minimizing the ability to mixture between hot water and cold water; polling data from temperatures are made through holes made at tank length (as in the prototype with stratification by vertical tubes).

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Prototype with artificial stratification by tubes vertical

The most notable physical characteristics of This prototype are:

Capacity Nominal: 87 (l)

Real Capacity: 76 (l)

Maximum power: 2000 (W)

Thickness of insulation: 40 (mm)

Total height: 625 (mm)

Internal height: 600 (mm)

Diameter boiler: 416 (mm)

No. of tubes interiors: 32

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The last of the proposed prototypes, and object of this invention, is based on the research conducted by Lavan and Thompson (1977) who developed an empirical model that demonstrates that stratification efficiency increases by doing so height / diameter ratio.

As you can see in the drawing of this prototype with stratification using 1 vertical tubes (Fig. 1) it is the insertion into the main tank or housing (1) of a set of tubes (2) that act as mini accumulators in the that the height / diameter ratio is greater than the original allowing in each of them the thickness of the thermocline is minor and, therefore, also less mixed between water hot and cold; temperature survey data is performed through the holes made along the tank (8).

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Conclusions

According to the data obtained, you can distinguish the following common general conclusions for the artificial stratification prototype using horizontal discs and for the artificial stratification prototype using tubes vertical (object of this patent):

i)

Thermal conductivity

quad

As it expected to decrease {p} X (thermal conductivity of the walls) losses from the hot zone to the cold zone is decreased, which improves the quality of stratification.

ii)

Wall thickness.

quad

The decrease in thickness e_ {p} (thickness of the wall) implies a reduction of conductive thermal flux along of the wall and, therefore, an improvement of the stratification.

iii)

Storage volume

quad

Thermal losses at the level of the hot zone decrease with increasing the volume of the accumulator.

iv)

Influence of Thermal Conductivity of Fluid.

quad

The increase in fluid conductivity causes consequent increase in the heat exchange coefficient at wall length

v)

Influence of Insulation Thickness.

quad

The greater the thickness of the insulation, the smaller are the losses produced in the accumulator.

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From these studies it can be concluded that the ideal manufacturing and operating conditions within a accumulator are as follows:

i)

Decrease the thermal conductivity of the wall.

ii)

Decrease wall thickness.

iii)

Decrease the thermal conductivity of liquid.

iv)

Increase insulation thickness

v)

Use a geometry that minimizes the relationship surface / volume

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Conclusions prototype with artificial stratification by horizontal discs

The different tests carried out in this prototype lead us to obtain the following conclusions: for a side the prototype allows to effectively achieve a artificial stratification improving system performance for discontinuous downloads (in the case of continuous downloads said advantages are minimized by allowing thermocline a separation very good temporary between hot and cold water). But nevertheless Problems have appeared to avoid the existence of tubes of specific characteristics current inside the fluid forming hot water pockets that remain unchanged inside the accumulator while the cold water He goes between them abroad.

In simulations performed by computer shows that by decreasing the height / diameter ratio water needs a greater horizontal component in its speed causing said hot water bags on the sides of the volume. These problems can be solved using different "obstacles" that force the water to make a greater travel and, therefore, allowing said water to have greater contact with the present inside the accumulator, however the use of this solution causes an increase in losses circuit load and therefore hinders natural convection necessary for the correct functioning of the prototype both in the heating phase as in the discharge phase.

In conclusion we discard the use of horizontal discs to improve thermal stratification within of the accumulator because the horizontal distribution of the different elements.

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Conclusions prototype with artificial stratification by vertical tubes

The vertical arrangement of the elements that make up allows to solve the problems involved in the use of horizontal discs. In fact, the use of the plates upper (6) and lower (7) microperforated allows to achieve a uniform and vertical distribution of speeds within the thermos that It is adequate to achieve a better stratification within of the accumulator.

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Description of the drawings

Inside the housing (1) the set of vertical tubes (2). The bottom microperforated plate (7) is fixedly trapped between the casing (1) and the disc bottom (5) and has two through holes that house the electrical resistance (3). The upper microperforated plate (6) remains fixed between the casing (1) and the disk upper (4).

The holes (8) practiced along the housing (1) are intended to serve as a penetration path to conduct temperature surveys.

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Embodiments of the invention

The present invention is further illustrated. by the following example, which is not intended to be limiting of its reach

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Example one

The physical characteristics to use for a correct realization of a thermo accumulator like the one described In this patent they could be:

Capacity Nominal: 87 (l)

Real Capacity: 76 (l)

Maximum power: 2000 (W)

Thickness of insulation: 40 (mm)

Total height: 625 (mm)

Internal height: 600 (mm)

Diameter boiler: 416 (mm)

No. of tubes interiors: 32

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The elements that the realization must contain of a thermo accumulator similar to that described in this patent have to be:

-

storage tank or housing (one)

-

set of inner tubes (2)

-

electrical resistance (3)

-

disk superior (4)

-

disk lower (5)

-

plates upper (6) and lower (7) microperforated

-

holes for introduction of probes temperature that allow obtaining data for modeling and the design of the accumulator (8).

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The materials that could be used for construction of a thermo accumulator with beam stratification of vertical tubes could be:

AIS1-304 steel

Type = 316

AISI designation = 316

Specific weight for 20 ° C = 8.06 (g / cm 3)

Resistance electric for 20ºC = 74 (ohms)

Specific heat = 501.6 (J / Kg. ° C)

Conductivity thermal = 0.16302 (J / cm2).

Tecaform

Denomination Chemistry = Polyoxymethylene (Polyacetal colimero)

DIN abbreviation = POM

Color / Additives = Opaque

Density = 1.41 (g / m 3)

Capacity of specific heat conductivity = 0.31 (W / m.ºC)

Capacity Caloric = 1.5 (J / g.ºC).

Claims (2)

1. Accumulator equipment with stratification by means of a bundle of vertical tubes characterized in that it comprises an accumulator tank or housing, a set of inner tubes, an electrical resistance, an upper disk, a lower disk and upper and lower microperforated plates. 2. Accumulator equipment according to claim 1 characterized in that it comprises inner tubes arranged vertically for the purpose of artificial water stratification.