GB2242940A

GB2242940A - Wind-powered heating device

Info

Publication number: GB2242940A
Application number: GB9008472A
Authority: GB
Inventors: Charles Madden
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-04-12
Filing date: 1990-04-12
Publication date: 1991-10-16
Anticipated expiration: 2010-04-12
Also published as: GB9008472D0; GB2242940B

Abstract

A wind-powered heating device comprises a rotor 1 having a horizontal section formed of aerofoil blades 4 with foils 5 mounted on their ends. The rotor drives a hydraulic friction heater 2 through a shaft 3. The rotary element 6 in the heater 2 is constructed such that the power required to drive it increases with speed to such an extent that it has a sufficient braking effect on the rotor to prevent excessive speeds which might lead to failure of the device. The rotary element 6 has arms 9 which spread out under the action of centrifugal force during rotation, the arms 9 being resilient or being hinged at their upper ends. <IMAGE>

Description

WIND-POWERED HEATING DEVICE The invention relates to a device using power obtained from a wind-driven rotor to drive a liquid heater and more particularly relates to a wind-powered heating device comprising a rotor adapted to be driven in rotation by wind; a heater comprising a liquid reservoir and rotary means at least partially immersed, in use, in liquid within the reservoir and adapted to be driven in rotation so as to heat the liquid through joule heating; and drive means connecting the rotary means to the rotor to be driven thereby.

A major problem with wind-powered devices is the need to control maximum operating speeds to avoid physical failure of the devices. This problem arises since the power generated by the rotor rises with the cube of wind-speed whereas the load power (i.e. the power required to drive the load) may rise only linearly with rotor speed. Thus the load itself does not prevent excessive speeds being reached. Past solutions have been to construct the rotor such that it will alter its configuration at high speeds so that its efficiency is greatly reduced. such solutions are not satisfactory since they require the rotor to have moving parts which are liable to failure. Also these arrangements are such that the efficiency of the device is greatly reduced to control speed and available power is therefore wasted.

The present invention overcomes the problem by provising a liquid heater which is constructed such that the power required to drive it varies as a function of its speed of rotation in such a manner that it has a braking effect on the device which tends to limit the operating speed of the device to a desired maximum speed. The power/speed profile of a liquid heater is normally similar to that of the power/wind-speed profile of a rotor. Thus a rotor is able to drive a liquid heater at ever increasing speed as wind-speed increases. The present solution to this is to provide a liquid heater whose profile rises more steeply at speeds approaching the desired maximum operating speed.The result of this is that the liquid heater will provide a sufficiently great load on the rotor at speeds approaching the desired maximum that it will have a braking effect on the device which tends to limit the operating speed of the device to the desired maximum speed.

Accordingly the present invention provides a wind-powered heating device comprising a rotor adapted to be driven in rotation by wind; a heater comprising a liquid reservoir and rotary means at least partially immersed, in use, in liquid within the reservoir and adapted to be driven in rotation so as to heat the liquid through joule heating; and drive means connecting the rotary means to the rotor to be driven thereby; wherein the rotary means is constructed such that the power required to drive it is a function of its speed of rotation such that it has a braking effect on the device which tends to limit the operating speed of the device to a desired maximum speed.

In a preferred embodiment the required power/speed profile of the liquid heater is provided by constructing the rotary means such that its configuration changes with speed of rotation as a result of centrifugal forces. In this manner the extra power taken by the heater is converted into extra heat energy in the heater.

An embodiment of the invention is described below with reference to the accompanying drawings in which: FIGURE 1 is a side elevation of a wind-powered heating device; FIGURE 2 is a plan view of the rotor of the device; FIGURE 3 is a section on the line A-A of Figure 2; and FIGURE 4 is an enlarged part-section through the liquid heater of the device.

As shown in the Figures, the device consists of a rotor 1, a liquid heater 2, and a connecting drive shaft 3. The device is supported with the shaft 3 vertical by support and bearing means not shown. The rotor comprises a horizontal section of arms 4 in the form of cut-off aerofoil blades (Savonius blades). Figure 3 shows a cross-section through one of the arms. Vertically extending foils 5 (Darrieus foils) are mounted on the ends of the arms 4. The lower end of the shaft 3 is housed within the heater 2 as shown in more detail in Figure 4.

At the lower end of the shaft 3 a U-shaped rotary element 6 is mounted. The rotary element 6 is immersed in a liquid whose correct level is indicated at 7. Stationary baffles 8 are mounted in the heater and cooperate with the rotary element 6 such that rotation of the shaft 3 leads to joule heating of the liquid in known manner. In order to provide the required power/speed profile of the heater, the limbs 9 of the rotary element 6 are constructed so that they can spread out under the action of centrifugal force as indicated at 10 in phantom. The lower ends of the limbs 9 may be weighted. The upper ends of the limbs 9 may be hingedly attached to allow them to spread out.

Alternatively they may be of resilient construction to allow this.

A floating weight 11 surrounds the shaft 3 above the rotary element 6 and is prevented from rotating by the engagement of a stop 12 cooperating with a corresponding formation 13 formed in the weight. If the liquid level in the heater falls substantially, the weight will come to rest on the rotary element 6 and act as a brake on it.

The operation of the heating device will now be described. In the case of the Darrieus foils 5, the apparent wind at the foils is the vector sum of the wind speed and the foil speed impinging at an apparent angle alpha. At slow foil speed this angle is large and the foil is stalled, as foil speed is increased (for a given wind speed) the angle alpha becomes smaller and at a certain point the foil unstalls and generates forward thrust which accelerates the foils to a maximum speed.

Typically the foils will be at their most efficient and develop maximum torque when the ratio of their speed to wind speed is about 10:1. The efficiency of the foils is reduced when this ratio is substantially lower or greater. Typically such foils will stall when this ratio is lower than about 4:1. Thus it will be seen that a rotor 1 having Darrieus foils 5 will need to be started by other means and got up to a sufficient speed for the foils to unstall. In the embodiment this is achieved by the horizontal section of the rotor formed by the blades 4 which provide an eccentric resistance to the wind to start the rotor turning and build up the speed to the condition where the drive vector of the foils 5 becomes forward and.

they accelerate the rotor to the maximum speed for the prevailing wind-speed.

The power/speed characterstic of the heater is designed such that it will absorb relatively little power as the rotor is accelerating to operating speed but will take a greater and greater proportion of available power as its speed approaches the desired maximum operating speed. Thus at speeds approaching the desired maximum operating speed the heater will act as a brake on the device to restrain any further increase in speed.

In high winds, the rotors maximum operating speeds (as maintained by the braking effect of the heater) will lead to a reduction in the foil speed/wind-speed ratio thus reducing the efficiency of the foils and the torque produced and aiding in the prevention of excess speeds.

If wind-speeds become sufficiently high this ratio may fall sufficiently for the foils to stall and for the rotor to continue to rotate solely under the action of the blades 4 forming the horizontal section of the rotor and at a substantially reduced speed.

The device may be used, for example, as a heater or pre-heater for a domestic water supply, heating the water directly or through a heat exchanger.

Claims

Claims:

1. A wind-powered heating device comprising a rotor adapted to be driven in rotation by wind; a heater comprising a liquid reservoir and rotary means at least partially immersed, in use, in liquid within the reservoir and adapted to be driven in rotation so as to heat the liquid through joule heating; and drive means connecting the rotary means to the rotor to be driven thereby; wherein the rotary means is constructed such that the power required to drive it is a function of its speed of rotation such that it has a braking effect on the device which tends to limit the operating speed of the device to a desired maximum speed.

2. A heating device as claimed in claim 1 wherein the rotary means is constructed such that its configuration changes with its speed of rotation as a result of centrifugal forces whereby at higher speeds it presents a greater resistance to rotation than would otherwise have been the case.

3. A heating device as claimed in claim 2 wherein the rotary means comprises a U-shaped element the limbs of which spread out under the action of centrifugal force.

4. A heating device as claimed in any preceding claim wherein the reservoir contains one or more stationary baffle plates which cooperate with the rotary means.

5. A heating device as claimed in any preceding claim wherein the drive means comprises a shaft, the rotor being mounted at one end of the shaft and the rotary means being mounted at the other end of the shaft.

7. A heating device as claimed in any preceding claim wherein the rotor rotates about a vertical axis and comprises a horizontal section formed of aerofoil blades and has foils mounted generally vertically on the ends of the horizontal section.

7. A heating device as claimed in claim 5 wherein a floating weight is located in the reservoir to float above the rotary element such that it will rest on the rotary element and act as a brake on it if the liquid is leaked from the reservoir.

8. A heating device substantially as described herein with reference to the accompanying drawings.