Technical experience sharing: Three steps to improve the efficiency of plate heat exchangers

(1) Improving the heat transfer coefficient of the heat exchanger: The heat transfer coefficient of a heat exchanger can be effectively improved only by simultaneously increasing the surface heat coefficients on the cold and hot sides of the plates, reducing the thermal resistance caused by scale buildup, using plates with high thermal conductivity, and decreasing the thickness of the plates. ①Increase the surface heat transfer coefficient of the plates; ② Reduce the thermal resistance of the fouling layer; ③ Use plates with high thermal conductivity; ④ Decrease the thickness of the plates. (2) The flow patterns in plate heat exchangers include counterflow, co-flow, and mixed flow. Under the same operating conditions, the logarithmic mean temperature difference is highest in counterflow, lowest in co-flow, and the mixed flow pattern lies between the two. Methods to increase the logarithmic mean temperature difference of a heat exchanger include using a counterflow or a mixed flow pattern that is close to counterflow as much as possible, raising the temperature of the fluid on the hot side, and lowering the temperature of the fluid on the cold side.

(3) Determination of the inlet and outlet pipe positions: For plate heat exchangers with a single-flow arrangement, to facilitate maintenance, the fluid inlet and outlet pipes should be located as close as possible on the side of the fixed end of the heat exchanger. The greater the temperature difference of the medium, the stronger the natural convection of the fluid, and the more pronounced the effect of the resulting stagnant zone. Therefore, the inlet and outlet positions of the medium should be arranged such that hot fluids enter from above and exit from below, while cold fluids enter from below and exit from above, in order to reduce the impact of the stagnant zone and improve heat transfer efficiency. In fact, aside from the heat exchange efficiency, plate heat exchangers also have some issues that cannot be ignored: 1. The thickness of the plates in a heat exchanger is generally between 0.3–0.4 mm, and if these plates contain impurities, electrochemical corrosion is likely to occur ； 2. The distance between the plates is generally around 2 mm, which makes scaling more likely to occur. 2. Since the plates are directly brazed together, any scale that forms cannot be removed. 3. The direct brazing of the plates results in a low capacity to withstand pressure, and leaks are likely to occur

The shortcomings of plate heat exchangers were identified in the market, leading to the development of direct-heating shell-and-tube heat exchangers, which have the following features: 1. All pipe connections are left exposed to prevent potential corrosion caused by residual welding slag； 2. The pipeline has undergone a pressure test of 200 kilograms, making leaks less likely to occur ； 3. It features a new type of casing structure, resulting in minimal pressure loss, generally less than 0.15 kilograms ；

4. The heat exchange tube has a high-temperature zone for water only in 1/3 of its length; the water flow velocity exceeds 1.5 m/s, and it features external threading； This prevents the heat exchange tubes from scaling easily ； 5. Provide circulation cleaning ports at the inlet and outlet of the heat exchanger to facilitate the removal of local scale buildup ； 6. It requires no circulation water pump or circulation water tank, offering advantages such as small floor space, easy installation, simple control, low pump power, and reduced failures. Heat exchangers are essential devices for enabling heat exchange and transfer in industrial production processes, accounting for approximately 20% to 30% of the total cost of process equipment. As an important energy-saving device in industrial production facilities, heat exchangers are widely used in the industrial sector, especially in energy-intensive industries such as petroleum, chemicals, and power metallurgy. Therefore, the high efficiency and energy savings of direct-heating shell-and-tube heat exchangers are of great significance for achieving water and energy conservation in industry.

It seems to have no flaws. It can be repaired; damaged parts can be replaced. It has a high flow rate, and it’s better than plate-type designs in every aspect. How does it compare to shell-and-tube designs? Its appearance is similar to that of shell-and-tube designs