SIMULATION OF PLATE HEAT EXCHANGER

Abstract

This thesis deals with a simulation investigation of a plate heat exchanger. Basically, it includes the development of a mathematical model to describe its operation and analysis. The model, after testing against the existing data, has been solved to obtain the effect of various parameters like mass flow rate, number of flow channels, plate configurations and flow patterns. The analysis has also been extended to cover multi-pass arrangements of plate heat exchanger. Model of a plate heat exchanger has been described by a set of continuity, momentum and energy balance equations with a number of simplifying assumptions. Heat transfer rate equation has also been included in the energy balance equation to take care of phenomena occurring therein. This mathematical model has been solved by the use of finite difference technique with interval of At = 0.0025 s and Az = 0.005 ni to obtain the transients and steady state behaviour. The results of the model have been compared with the data of Lakshmanan et al. (12) and Khan et al. (10), and deviations between the computed and experimental values of outlet temperature of fluids have been obtained in the range of -2.279% to 0.987% and -5.649% to 6.103% respectively. This deviation clearly indicates the validity of model and therefore, it has been applied for the simulation of plate heat exchanger. Effect of hot and cold fluid mass flow rates on heat exchanger effectiveness has been evaluated for loop, series and complex flow patterns of plate heat exchanger. It has been found that the effectiveness decreases with increase in mass flow rate of fluid in loop, series and complex flow patterns. The effect of number of flow channels on the effectiveness has also been obtained and the effectiveness has been found to increase with the increase in number of flow channels for all flow patterns studied here. However, in the case of loop flow, the maximum value of effectiveness is only 0.218 as against the value of unity in the case of series and complex flow patterns. Plate configuration, represented in terms of 0, has also been found to affect the effectiveness significantly. Its value increases as the value of 0 increases. The analysis has also been extended to multi-pass plate heat exchanger systems and the value of LMTD correction factor, Ft has been evaluated as a function of parameters R and S. Two cases: 1-2 pass and 1-4 pass systems have been considered in this investigation. It has been found that the value of Ft is a function of both the parameters R and S. The maximum value of Ft of unity is obtained for smaller value of R (ratio of flow capacity of fluids) and S (effectiveness). This analysis is similar to that usually used for shell and tube heat exchanger. Finally, a step input is imposed in hot fluid temperature to obtain its effect on the steady state values of the outlet temperature of the fluids. It has been found that the loop flow has the lowest response time, the series has the highest and the complex lying in between the t