The plate heat exchanger is composed of a group of corrugated metal plates. There are four corner holes on the plate for the two liquids for heat transfer to alternately exchange heat through their respective channels. What is the temperature difference method for designing plate heat exchangers?
(1) Calculate unknown temperature or flow. The unknown temperature or flow rate is calculated from the heat balance equation, and the heat load Q is also calculated.
(2) Estimate the heat exchange area and calculate the approximate heat exchange area based on the heat exchange amount.
(3) Select the matching heat exchanger plate model. According to the heat exchange capacity and flow size, select the matching plate model. The choice of plate model depends on the specific working conditions. When the flow is large and the pressure drop is low, a plate with a small resistance should be selected; otherwise, a plate with a larger resistance coefficient can be used.
(4) Calculate the average temperature difference.
(5) Select the flow and channel number of the plate heat exchanger. The cold and hot fluid flows and the number of channels are initially selected, and the flow velocity is calculated from them.
(6) Calculate the convective heat transfer coefficient and the total heat transfer coefficient. Calculate the convective heat transfer coefficients of the cold and hot fluids respectively to calculate the total heat transfer coefficient.
(7) Calculate the heat exchange area. Turning back to calculate the heat exchange area, check the pressure drop, and the allowable pressure drop often becomes a limiting factor in the design of the plate heat exchanger.The design always requires sufficient pressure drop to be allowed. If the process layout is changed, the relationship between heat transfer load, flow rate and allowable pressure drop cannot be coordinated. We can only change to make efficient designs.