WO2004027364A1

WO2004027364A1 - A system and method for measuring one or more properties of a gas

Info

Publication number: WO2004027364A1
Application number: PCT/GB2003/004053
Authority: WO
Inventors: Howard Hodson; Robert Miller
Original assignee: Turbintel Limited
Priority date: 2002-09-20
Filing date: 2003-09-22
Publication date: 2004-04-01
Also published as: AU2003267589A1; GB0221866D0

Abstract

A system for determining in situ one or more properties of a gas, the system including a passage having an inlet at a proximal end thereof, a mass flow measuring device for the measurement of mass flow of gas through the passage; a pressure measuring device for measuring the pressure of gas within the passage; and a gas flow controller for controlling the flow of gas through the passage between at least two states, a first state at which the pressure of gas in the passage as measured by the pressure measuring device corresponds to the gas pressure at the inlet of the passage, and a second state at which the temperature of the gas at the inlet can be derived from the mass flow as measured by the mass flow measuring device and the pressure of the gas at the inlet.

Description

A SYSTEM AND METHOD FOR MEASURING ONE OR MORE PROPERTIES

OF A GAS

The present invention relates to a method and system for measuring one or more properties of a gas. Knowledge of gas properties can be important in, for example, the fields of gas turbines, aircraft engines, furnaces, road vehicles, gas storage systems and gas transport systems. Properties of interest can include temperature, pressure, the ratio of specific heat capacities, specific heat capacity at constant volume, specific heat capacity at constant pressure.

Thermocouples are extensively used in many applications to provide low cost temperature measurements of gases. However, their accuracy at high temperatures is compromised by radiation to the surrounding environment and conduction of heat through the stem of the probe. The durability of thermocouples is limited by the need to make a protective barrier between the sensor and the gas relatively thin to allow the temperature of the sensor to reach that of the gas. Where pressure and temperature measurements are both required in a gas, conventionally two measurement probes have been used, one being connected to or containing a pressure measurement device and one containing a thermocouple. The use of two probes can cause problems when the probes are large with respect to the scale of the gas flow.

It is an aim of the present invention to provide an alternative method and system for measuring one or more properties of a gas. It is a particular aim of this invention to provide a measuring system that is capable of making measurements of temperature and pressure, particularly in high temperature environments at one location in a gas.

It is another particular aim of the present invention to provide a measuring system that is capable of making measurements of the ratio of the specific heat capacities of a gas or mixture of gases and therefore allowing the user to derive the gas concentration of a mixture of gases .

It is another particular aim of the present invention to provide a system that allows the user to determine the temperature, pressure and gas concentration of a mixture of gases.

According to the present invention, there is provided a system according to claim 1. The reference to a gas includes gas mixtures.

According to another aspect of the present invention, there is provided a system according to claim 14.

According to a further aspect of the present invention, there is provided a method of determining the temperature of a gas according to claim 10.

According to a further aspect of the present invention, there is provided a method of determining the ratio of specific heat capacities of a gas according to claim 11. According to a further aspect of the present invention, there is provided a method of determining the temperature of a gas mixture according to claim 12.

According to one embodiment of the present invention, there is provided a device for the measurement of gas temperature and pressure, including an orifice, downstream a means of cooling the gas, downstream a means of measuring the mass flow of the gas, all the gas that passes through the orifice passing through the cooling system and the mass flow measurement system, the flow of gas through the probe is alternately present when the gas flow through the upstream orifice is choked and not present when the pressure is being measured, from said measurements calculating the temperature of the gas wherein T.sub.t=(C*(Rsub.t*P.sub.t)/(M*M))

where T.sub.t is the stagnation temperature of the gas, P.sub.t is the stagnation pressure measured when the no gas flows through the probe, M is the mass flow measured when gas flows through the probe, C is a calibration factor that depends on the ratio of specific heat capacities and the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment.

Preferably, the mass flow measurement is determined from pressure measurements upstream and downstream of an orifice plate.

According to another embodiment of the present invention, there is provided a device for measuring the ratio of specific heat capacities of a gas including a means of measuring temperature, a means of measuring pressure, a choked orifice, downstream of the choked orifice a means of measuring mass flow rate, from said measurements calculating the ratio of specific heat capacities of the gas wherein, g=D*T.sub.t*(M*M)/(P.sub.t*P.sub.t) where T.sub.t is the measured stagnation temperature of the gas, P.sub.t is the measured stagnation pressure, M is the mass flow measured when gas flows through the orifice, g is a function of the ratio of specific heat capacities of the gas and D is a calibration factor that depends on the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment.

According to another embodiment of the present invention, there is provided a device for the measurement of the ratio of specific heat capacities including a means of measuring temperature, downstream an orifice, downstream a means of measuring mass flow rate, the flow of gas through the probe is alternately present when the gas flow through the upstream orifice is choked and not present when the pressure is being measured, from said measurements calculating the ratio of specific heat capacities of the gas wherein g=D*T.sub.t*(M*M)/(P.sub.t*P.sub.t) where T.sub.t is the measured stagnation temperature of the gas, P.sub.t is the measured stagnation pressure, M is the mass flow measured when gas flows through the orifice, g is a function of the ratio of specific heat capacities of the gas and D is a calibration factor that depends on the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment.

According to another embodiment of the present invention, there is provided a device for the measurement of gas temperature, gas pressure and the ratio of specific heat capacities including an orifice, downstream a means of cooling the gas, downstream the gas being divided into two parallel paths, in the first path a means of measuring mass flow, in the second path a means of measuring the ratio of specific heat capacities of the

gas, three measurement phases in time being used, during the first phase the flow being stopped in the second path and the flow passes through the first path while the orifice is choked and the mass flow of the gas is measured, during the second phase the flow is stopped in the first path and the flow passes through the second path and the ratio of specific heat capacities of the gas is measured, during the third of the time periods the flow is both the two paths is stopped and the pressure is measured downstream of the cooler, these three phases may occur in any order, from said measurements calculating the temperature of the gas wherein

T.sub.t=(g*E*(P.sub.t*P.sub.t)/(M*M)) where T.sub.t is the stagnation temperature of the gas, P.sub.t is the stagnation pressure measured when the no gas flows through the probe, M is the mass flow measured when gas flows through the first path, E is a calibration factor that depends on the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment and g is a function of the ratio of specific heat capacities of the gas.

Embodiments of the present invention are described in detail hereunder, by way of example only, with reference to the accompanying drawings, in which:

Figures 1 and 2 show a system according to a first embodiment of the present invention;

Figures 3 and 4 show an embodiment according to a second embodiment of the present invention;

Figure 5 shows an embodiment according to a third embodiment of the present invention; and

Figure 6 is a graph showing the performance of the system of Figure 2.

A first embodiment allows the user to calculate the temperature of a gas. It consists of three main parts, an orifice, downstream of the orifice a method of cooling the gas and downstream of that a method of measuring the mass flow of the gas. The flow is alternately stopped and started through the probe. When the flow is stopped the pressure downstream of the cooling system is the same as at the head of the probe and so a pressure measurement device mounted downstream of the cooler can be used to measure the probe's inlet stagnation pressure. When there is a flow through the probe the first orifice is choked and the mass flow is measured downstream of the cooler. This means that both the mass flow and pressure measurements can be made at low temperatures. The stagnation temperature at the orifice is then given by

T.sub.t=(C*P.sub.t*P.sub.t/(M*M))

where T.sub.t is the stagnation temperature of the gas, P.sub.t is the stagnation pressure measured when no gas flows through the probe, M is the mass flow measured when gas flows through the probe, C is a function of the ratio of specific heat capacities and the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment.

With reference to schematic Figure 1, the gas enters the probe at 1 and passes through an orifice 2, is then cooled 3 and the mass flow is measured 4. The valve 5 is used for stopping and starting the flow.

Figure 2 shows an example of the implementation of the first device. The gas passes through a nozzle 6, and is then cooled by a water jacket 7. The mass flow is measured using an orifice plate 9, a means of measuring the upstream pressure 8a and a means of measuring the upstream temperature 8b and a means of measuring the downstream pressure 10. There is a valve 11 for starting and stopping the gas flow.

Figure 6 shows a plot of the temperature measured by the system of Figure 2 against the temperature measured by a thermocouple mounted next the probe head when the head of the probe is inserted into a large volume of hot gas. The temperature of the gas was set to 43 temperatures between 300K and 900K. Six tests were completed and are plotted on top of each other.

The second embodiment allows the user to calculate the ratio of specific heat capacities of a gas. This may allow the user to calculate the gas concentration in a mixture of gases. It consists of two main parts, an orifice with upstream temperature measurement and a downstream method of measuring the mass flow of the gas. The flow is alternately stopped and started through the probe. When the flow is stopped the pressure is the same as at the head of the probe and so a pressure measurement device mounted in the mass flow measurement device can be used to measure the probe's inlet stagnation pressure. When there is a flow through the probe the first orifice is choked and the inlet temperature of the first orifice and the mass flow through the second orifice is measured. From the said measurements the ratio of specific heat capacities of the gas can be determined g=D*T.sub.t*(M*M)/(P.sub.t*P.sub.t) where T.sub.t is the measured stagnation temperature of the gas, P.sub.t is the measured stagnation pressure, M is the mass flow measured when gas flows through the orifice, g is a function of the ratio of specific heat capacities of the gas and D is a calibration factor that depends on the specific heat capacity at constant pressure of the gas and which may be determined by calculation or experiment.

With reference to schematic Figure 3, the gas enters the probe at 12 and its temperature is measured upstream of the inlet orifice 13. The mass flow of the gas is measured 14. The valve 15 is used for stopping and starting the flow. Figure 4 shows an example of the implementation of the second device. The gas enters the device 16, then its temperature is measured 17 and it passes through an orifice 18. The mass flow is measured using an orifice plate 20, a means of measuring the upstream pressure 19a and a means of measuring the upstream temperature 19b and a means of measuring the downstream pressure 21. The valve 22 is for stopping and starting the flow.

The third embodiment allows the user to calculate the temperature and the ratio of specific heat capacities of the gas and may also allow the concentration of a mixture of gases to be determined. It is made up from a combination of the first and second embodiments. The device consists of four main parts. The first two consist of an orifice and a downstream method of cooling the gas. Downstream of the cooler the gas path is split into two parallel streams, the first, passing the gas through a device to measure mass flow and, the second, passing the gas through a device that allows the user to calculate the gas concentration and ratio of specific heat capacities of the gas mixture.

The device has three operating phases. In the first phase a valve is shut so that the flow only passes through a device for measuring the mass flow through the upstream choked orifice. In the second phase a valve is shut so that the flow only passes through a device that allows the user to determine the ratio of specific heat capacities of the cooled gas and gas concentration. During this phase the upstream orifice is unchoked. In the third phase both valves are shut and no gas flows through the probe. The stagnation pressure throughout the probe is then constant and the probe's inlet stagnation pressure can be measured. If a mixture of two gases is being measured the stagnation temperature at the orifice may then be calculated using the measured stagnation pressure, mass flow rate, the gas concentration and knowledge of the ratio of specific heat capacities and the specific heat capacities at constant pressure of the two gases.

Figure 5 is a schematic view of the third embodiment. The gas enters the probe at 23 and passes through an orifice 24, is then cooled 25. The flow is then split and passes through a mass flow measurement device 26 and a valve 27 on one path and a device to measure the ratio of specific heat capacities and gas concentration 28 and a valve 28 on the second path.

Inlet devices 2, 6, 13, 18 and 24 may be an orifice, a nozzle or a venturi.

In each of these three embodiments, the valves 11, 15, 22 and 27 may be connected to a device for developing a pressure ratio across the passage i.e. between the inlet and the valve, of a sufficient size to cause the gas to flow through the inlet orifice, nozzle or venturi at Mach Speed 1 when the valve is opened, thereby allowing the temperature of the gas at the inlet to be derived from the mass flow and the pressure at the gas inlet.

Claims

1. A system for deteπrmiing in situ one or more properties of a gas, the system mcluding a passage having an inlet at a proximal end thereof; a mass flow measuring device for the measurement of mass flow of gas through the passage; a pressure measuring device for measuring the pressure of gas within the passage; and a gas flow controller for controlling the flow of gas through the passage between at least two states, a first state at which the pressure of gas in the passage as measured by the pressure measuring device corresponds to the gas pressure at the inlet of the passage, and a second state at which the temperature of the gas at the inlet can be derived from the mass flow as measured by the mass flow measuring device and the pressure of the gas at the inlet.

2. A system according to claim 1, wherein the pressure measuring device is a part of the mass flow measuring device.

3. A system according to claim 1 or claim 2, wherein the mass flow measurement device includes a temperature sensor.

4. A system according to any preceding claim, further including a cooler positioned upstream of the mass flow measurement device for cooling the gas passing through the mass flow measurement device.

5. A system according to claim 4, firrther including a temperature sensor positioned upstream from the cooler for directly measuring the temperature of the gas at the inlet of the passage.

6. A system according to any preceding claim, firrther including a choked orifice upstream of the mass flow measurement device to facilitate the flow of a gas through the passage at a speed at which the temperature of the gas at the inlet can be derived from the mass flow and the pressure at the inlet.

7. A system according to claim 6, wherein the device firrther includes a temperature sensor upstream of the choked orifice for directly measuring the temperature at the inlet of the passage.

8. A system according to claim 1, wherein the passage includes a main passage having the inlet at a proximal end thereof, and connected at a distal end to first and second branch passages; the first branch passage provided with the mass flow measuring device; and the second branch passage provided with a gas concentration measuring device for measuring the concentration of the components in the gas; and wherein the gas flow controller is adapted for controlling the flow of gas in the main passage and first and second branch passages between (i) a first state at which the pressure of gas in the main passage and first and second passages corresponds to the gas pressure at the inlet of the passage, (ii) a second state in which gas is caused to flow through the second passage for measurement of the gas concentration of the components of the gas by the gas concentration measuring device, and (iii) a third state in which gas is caused to flow at a speed through the main passage and first passage so as to allow the temperature of the gas at the inlet to be derived from the mass flow as measured by the mass flow measuring device, the pressure of the gas at the inlet and the gas concentration.

9. A system according to claim 8, wherein the gas concentration measuring device measures the gas concentration of the components in the gas by measurement of the ratio of specific heat capacities.

10. A system according to claim 8 or 9, wherein the main passage is provided with a cooler for cooling gas in the main passage.

11. A method of determining the temperature of a gas, including the steps of: providing a system according to claim 1; locating the inlet of the passage in the gas to be measured; controlling the gas flow controller so as to switch between said first and second states, and calculating the temperature of the gas from the mass flow measured by the mass flow measuring device in the first state and the pressure measured by the pressure measuring device in the second state.

12. A method of determining the ratio of specific heat capacities of a gas, mcluding the steps of: providing a system according to claim 5 or claim 7; locating the inlet of the passage in the gas to be measured; controlling the gas flow controller so as to switch between said first and second states, and calculating the ratio of specific heat capacities of the gas from the temperature measured by the temperature sensor, the mass flow measured by the mass flow measuring device in the first state and the pressure measured by the pressure measuring device in the second state.

13. A method of deteπnining the temperature of a gas mixture, the method including the steps of: providing a system according to claim 8; locating the inlet of the passage in the gas mixture to be measured; controlling the gas flow controller so as to switch between said first, second and third states; and calculating the temperature of the gas mixture from the mass flow measured in the first state, the gas concentration measured in the second state and the pressure measured by the pressure measuring device in the third state.

14. A system for determining insitu one or more properties of a gas, the device including a passage having an inlet at a proximal end thereof; first and second measuring devices for measuring first and second parameters of the gas witfiin the passage; and a gas flow controller for confrolling the flow of gas through the passage between at least two different flow states, the values respectively measured for the first and second parameters in said first and second flow states allowing one or more properties of the gas at the inlet to be derived.