STUDY OF THE EFFECT OF OPERATING AND DESIGN PARAMETERS OF OUTBOARD COOLER ON HEAT TRANSFER IN THE TUBE SPACE
The article considers necessity of increasing heat transfer between outboard coolers and outboard water in conditions of free convection between pipes. Author proposes integrated approach that assumes improvement of design and operating parameters of the heat exchanger which is based on experimental research of heat transfer using method of experiment planning for three operating parameters: temperature and speed of hot freshwater stream, temperature of outboard water and three relative pitches of outboard cooler pipe system construction. Experimental data processing with method of correlation-regression analysis resulted in determination of average coefficient of heat transfer from external heat transfer surfaces of the cooler tubes assembled in bundle with relative pitch 1,5; 2,0 and 3,0 to the outboard water in conditions of free convection. It is revealed that temperature difference and relative pitch of cooler tubes have significant influence on the processes of heat transfer. The greatest heat transfer is provided by cooler tubes assembled in bundle with relative pitch 1,5 and 2,0. Herewith the process of heat exchange consists of two modes. The moment when one mode changes another depends on the temperature difference and cooler tubes layout in bundle. The closer cooler tubes located to each other, the lower value of temperature difference needed to change the mode. The article also considers graphical dependence of average heat transfer coefficient from temperature difference. Average heat transfer coefficient defined as difference of temperature between hot coolant at the inlet to a pipe system of outboard cooler and the outboard water at high and low temperature circuit of the closed cooling system of a diesel engine. It is determined that average coefficient of heat transfer from high temperature circuit cooler to outboard water with a temperature of 305K in 1,8 times higher than average coefficient of heat transfer from low temperature circuit cooler for the same temperature of outboard water.