It is well known to provide mechanical components in machinery, such as gas turbine engines, with cooling systems in order to permit operation of the machinery at higher temperatures than would be possible without such cooling systems. The higher operating temperatures permitted by such cooling systems result in increased performance and efficiency of the machinery.
To design an optimum cooling system for components which will operate in a high temperature environment, it is necessary to determine the heat flux distribution on a surface of the component which is exposed to high temperature. One known method of determining the heat flux distribution is to take actual measurements in an operating system using commercially available heat flux gauges placed on the surface of the component. Examples of such gauges are those obtainable from RdF Corporation of Hudson, N.H. However, these gauges cannot be used in applications where the temperature to which the gauges are exposed exceeds their maximum permissible operating temperature, typically about 500 degrees Fahrenheit. This maximum permissible temperature is too low to take meaningful measurements on a component used in a high temperature environment such as a gas turbine engine in which temperatures may exceed 2000 degrees Fahrenheit. Also, the commercially available film heat flux gauges have dimensions on the order of 0.25 to 0.50 inches making them too large for many applications. In addition, these gauges have considerable thermal resistance which influences heat flux magnitude and distribution and thus may produce serious measurement errors. The heat flux gauges typically have thermal resistances of about 0.003 to 0.010 degrees Fahrenheit/BTU/hr.ft..sup.2 which can cause considerable error when measuring equipment exposed to large amounts of heat flux.
There are commercially available heat flux gauges which can withstand high temperature, for example, circular foil heat flux gauges sold by Thermogage, Inc. of Frostburg, Md. They are about 0.5 to 1.0 inches in diameter, too large to be used on small components.
A second known method of determining heat flux distribution involves predicting heat flux distribution on the surface of a component based solely on analysis. The heat transfer coefficient ("h") is calculated analytically and the heat flux ("q/A") distribution as a function of "x" and "y" coordinate is computed using the following equation: EQU (q/A).sub.x,y =h.sub.x,y (T.sub.mainstream -T.sub.surface,x,y), (1)
where T.sub.mainstream is the temperature of the environment in which the component is being operated, for example, the temperature of a hot fluid flowing over the surface of the component. T.sub.surface is the temperature of the surface for which the heat flux distribution is being determined. However, since it is not possible to accurately predict the heat transfer coefficient "h" except for very simple geometries, this method of determining heat flux distribution is not accurate or reliable for many components having complicated geometries such as those found in modern aircraft engines.
A third known method of determining heat flux distribution involves predicting the heat flux distribution based on an extrapolation of laboratory test measurements taken on a model of the component or taken on the component itself. When using a model, the model is commonly situated in a cool environment with electrical heaters attached to the surface of the model, for example, a series of wire resistance heaters, such as Calrod heaters, situated in grooves machined into the surface of the model. The power supplied to the heaters, T.sub.mainstream, and T.sub.surface are measured. Heat flux is calculated in light of measured heater power and local values of heat transfer coefficient "h" obtained from equation 1. The local values of heat transfer coefficient "h" obtained from the model are extrapolated to equipment design conditions to obtain "h" values for the actual component. Heat flux distribution for the actual component is then calculated from the relationship of equation 1.
However, the accuracy of the heat transfer coefficient distribution obtained using this method is compromised due to the fact that the surface of the model is hotter than the environment. The temperature difference across the boundary layer between the component and the environment is therefore in a direction opposite that for a cooled component in a hotter environment. Since the measured heat transfer coefficient depends on the direction of the temperature difference across the boundary layer, the accuracy of the heat flux distribution calculated with these measured heat transfer coefficients is adversely affected and may not be accurate for actual components operating in an actual apparatus. This method also suffers from the fact that the heaters must be isolated from each other and operated at the same temperature to minimize cross conduction of heat. Specifically, each heater zone must have dimensions of at least 0.25 inches which is too large for testing small components.
Laboratory test measurements taken from an actual component may also be extrapolated to real life operating conditions. In this situation, the component is operated in a high temperature environment with heat flux gauges mounted on its surface. Heat flux values are read from the gauges and T.sub.surface and T.sub.mainstream are measured. Heat transfer coefficient values "h" are calculated using equation 1. The "h" values determined under laboratory conditions are then extrapolated to real life conditions. However, since heat flux gauges are used, the problems inherent with the use of such gauges are present in this method, as they have been in the method described above which also uses such gauges.
In light of the difficulties present in known methods of determining heat flux distribution and heat transfer coefficient distribution on surfaces of cooled components, a long standing and unfulfilled need has existed for a different method of measuring these parameters which avoids those difficulties.