Ascending or descending spacecraft passing through the earth's atmosphere, or spacecraft orbiting in an orbit around the earth, are exposed to extreme thermal stress conditions. Therefore, it is necessary to provide a safe and reliable heat discharge.
German Patent Publication (DE-PS) 3,718,873 describes an evaporating heat exchanger suitable for the above stated purpose of cooling a spacecraft. In the known heat exchanger the medium to be cooled circulates in an active liquid circulating circuit for heat exchanges. For this purpose, the medium to be cooled is brought into a heat transfer contact with a medium to be evaporated. The medium to be evaporated is carried in a supply container in the spacecraft. The generated vapor is blown off from the spacecraft into its environment.
It is desirable to evaporate the cooling medium as much as possible to use it with an optimal efficiency. For this purpose it is further desirable to achieve a sufficiently high heat transfer between the cooling medium to be evaporated and the flow channels which carry the liquid to be cooled. To perform these two functions efficiently, it is necessary that the generated vapor is separated from the medium portion which is still liquid to make sure that liquid portions of the evaporating medium are not discharged from the spacecraft in the form of large liquid drops which have not participated in the evaporation, and thus in the cooling process.
In the above mentioned German Patent Publication (DE-PS) 3,718,873 it is the aim to deposit non-evaporated liquid remainders with the aid of mass inertia forces on the walls of the cooling liquid channels. For this purpose, the cooling liquid channels are arranged in a folded pattern as viewed in the flow direction. The so deposited liquid remainders are then transferred into the gas phase on the surface of these channels. However, tests performed with the known heat exchanger have shown that the utilization of the cooling medium to be evaporated is not at all optimal and hence not efficient for the intended purpose.
U.S. Pat. No. 5,101,884 (Leidinger), issued Apr. 7, 1992, describes an evaporation heat exchanger having at least one active circulating circuit for a coolant liquid to be cooled, and is constructed for removing heat in a spacecraft under a gravity-free operating condition and under different acceleration conditions. For this purpose, a housing encloses an evaporating space provided with at least one inlet valve for controlling the admission of a medium to be evaporated. The produced vapor or steam is discharged through a respective port. A plurality of cooling tubes interconnected in a meandering shape form a number of tube panels in which the individual tubes are arranged in a zig-zagging pattern to form respective flow passages for the medium to be evaporated. The individual tubes extend in parallel to each other and perpendicularly to the flow direction of the medium to be evaporated, while the meandering configuration is forming the zig-zag pattern. This arrangement of the cooling tubes assures a high efficiency in the heat transfer and also in the complete conversion of the liquid to be evaporated into vapor or steam. Due to the zig-zag pattern, the medium to be evaporated, or droplets thereof, are repeatedly intercepted and deposited by the exchanger surfaces of the tubes so that the exchanger functions as a drip-catcher evaporator. This earlier evaporation heat exchanger still leaves room for improvement.