Compressed air heater

Abstract

FIELD: heating equipment.SUBSTANCE: heater is designed to equip a universal rig for climatic and thermal strength testing of tropical-based aviation and large-tonnage ground equipment that require high-temperature heat sources. A compressed air heater consisting of a cylindrical housing, inlet and outlet pipes at the ends of the housing, and a heating unit in the form of a tube bundle located in the housing across the flow is proposed. Quartz lamps with contact petals made of heat-resistant alloy are installed in the tubes of the tube bundle. Along the ends of the tube bundle, longitudinal metal walls are placed along the flow of compressed air. The walls are mounted on electrical insulators and serve as current-carrying buses for powering quartz lamps. The walls are perforated with holes along the axes of the quartz lamps to bring out the contact petals to the outer side of the wall and screw fastening on its outer surface. The walls form longitudinal channels for the removal of part of the compressed air entering the heater, which is not heated and cools the screw contacts of the quartz lamps on the outer surface of the wall.EFFECT: it is possible to heat the air up to +250 °C at an air flow rate corresponding to the maximum compressor capacity.1 cl, 3 dwg

Description

[0001] The invention relates to the field of heat exchange equipment for climatic and thermal strength testing of large-tonnage aviation and ground equipment of Arctic and tropical basing.

[0002] Climatic chamber heaters are known in the form of electric heaters equipped with heating elements for heating the air inside the chamber and fans for supplying the heated air to the test object. Heaters are also known for thermal strength testing of aircraft structures on test machines, using similar mobile heaters with heating elements and fans for convective heating of the test objects (see patent for invention RU No. 2796304 C1 by A.S. Dzyuba and V.L. Notkin). These heating devices are widely used for climatic testing of aircraft structures or conventional ground vehicles in climatic chambers or stand-alone rigs, but are not suitable for heating massive, heavy-duty equipment such as diesel locomotives, for example, during the same climatic tests.The fact is that with a relatively low flow rate when the coolant is supplied to the test object by a fan and the low density of warm air at ambient atmospheric pressure, the heat transfer coefficient on the heating surface is low and does not provide the intensive heat exchange necessary to warm up a massive, multi-ton structure. Heat exchange on the heating surface can be increased by increasing the coolant flow rate by using a jet blast of hot compressed air heated in a high-temperature heater.This means that the objective of the invention is to create a high-temperature (+250° in air) compressed air heater that ensures heating of a massive ground object to a temperature above 100 degrees in a given time interval of the test cycle or to a temperature level corresponding to the supersonic flight mode during thermal strength tests of aircraft (180 - 200 degrees), if an aircraft is being tested.

[0003] A compressed air heater is known, comprising a cylindrical housing, inlet and outlet pipes, a tubular core located coaxially with the housing, and a heating unit consisting of thermoelectric heaters (TEHs) installed around the tubular core. (See Patent RU 147 858 U1)

[0004] The disadvantage of this design, in relation to the stated requirements, is the insufficient maximum power and maximum temperature of standard heating elements, which are not structurally designed to heat air to a temperature of +250°C.

[0005] The technical result of the invention is to provide the ability to heat air up to +250°C with an air flow rate corresponding to the maximum compressor capacity (each compressor has its own heater).

[0006] The technical result is achieved in that in a compressed air heater, characterized in that it consists of a horizontal cylindrical body with conical ends, inlet and outlet pipes at the ends, a heating unit in the form of a tube bundle located inside the heater body across the flow, quartz lamps with contact petals made of heat-resistant alloy are installed in the tubes of the tube bundle, longitudinal metal walls made of stainless steel are placed along the ends of the tube bundle along the flow, which:

[0007] - installed on electrical insulators and serve as current-carrying buses for powering quartz lamps;

[0008] - perforated with holes along the axes of the quartz lamps to bring out the contact petals to the outer side of the wall and screw them onto its outer surface;

[0009] - form longitudinal channels for removing part of the compressed air entering the heater, which is not heated and cools the screw contacts of the quartz lamps on the outer surface of the wall.

[0010] Fig. 1 shows the external view of the heater in section.

[0011] Fig. 2 shows the assembled heating unit.

[0012] Fig. 3 shows a photograph of the operating heater included in the test bench circuit.

[0013] As an example, let us consider the design of an experimental heater manufactured and launched into trial operation at the Federal Autonomous Institution "TsAGI".

[0014] The heater consists of a cylindrical housing 1 with conical ends 2, inlet 3 and outlet 4 compressed air pipes, and current leads 5 at the inlet end of the housing. The heating unit, in the form of a cross-flow tube bundle, is shown separately in Fig. 2. It is located inside the housing and consists of 100 stainless steel tubes 6 with a diameter of 25 mm. A quartz lamp 200 mm long and with a power of 1 kW is inserted into each tube. The petal contacts of the lamps 7 are brought out to the outer side of the wall 8 and secured there with screws. Generally, the number and size of the tubes depend on the selected heater power and are determined during the design of the device.

[0015] Limiting parameters of the experimental heater (for reference):

[0016] - air flow rate equal to the compressor capacity 9.5 nm3 / min - maximum air temperature at the outlet 250°C - tube surface temperature 1000°C - heater power 100 kW

[0017] The main problem when using such a heater is overheating and oxidation of the screw contacts of quartz lamps located in a closed space under the direct influence of radiation from the filament bodies of the lamps (1700 0 ). Therefore, special attention was paid to protecting the contacts from overheating during the heater design. Fig. 2 shows the assembled heating unit. Side wall 8 of the unit serves as a busbar for supplying power to the lamps. It also shields the contacts from direct radiation from the lamp end and forms a channel along the side wall of the housing to divert part of the airflow that washes over the wall and cools the contacts. Thus, double protection of the contacts from overheating (shielding and convection) allows for the production of a high-temperature heater with the required service life.

[0018] The heater operates as follows. Compressed air enters the conical end section 2 of the housing and is divided into two streams. The main stream passes straight through, washing the tubes 6 of the tube bundle and heating to a predetermined temperature. A portion of the stream, cut off by the side walls 8 at the cone exit, passes unheated through the side channels between wall 8 and housing 1, washing the contacts of quartz lamps 7 and cooling them. The streams then mix in the outlet cone and enter the test object through outlet pipe 4.

[0019] The heater presented in the application was manufactured, tested, put into trial operation and is currently used as part of a universal test bench designed for climatic testing of aircraft structural elements.

[0020] Summarizing the results of this development, it should be noted that the advantage of the chosen method for reproducing extreme thermal effects is the possibility of high-temperature heating of the coolant by using quartz lamps during climatic tests of large-capacity tropical-based equipment.

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