Plate heat exchangers, with their efficiency, compactness, and flexibility, have been widely applied in industries such as chemical processing, energy, and HVAC. The key factors affecting their performance lie not only in the plate material, but also in the arrangement of plates, adjustment of plate number, and the depth of corrugations. Different design logics directly determine the heat transfer efficiency, pressure loss, and operating cost of a plate heat exchanger. This article analyzes the design and application of plate heat exchangers from three aspects: plate arrangement, calculation of heat transfer and plate number adjustment, and corrugation depth.
The core component of a plate heat exchanger is the plate, and the arrangement of the plates directly determines the flow path of fluids inside the exchanger. Different arrangements lead to entirely different distribution logics of hot and cold fluids, thereby affecting heat transfer efficiency and pressure loss. Currently, the main arrangements are three types: series, parallel, and mixed.
Series arrangement, also called single-pass arrangement, is characterized by all plates forming a single flow channel. Imagine hot and cold fluids flowing in their respective single channels, entering from one end of the exchanger, passing through all plates, and exiting from the other end, without any flow splitting or merging during the process.
Advantages: The benefit of this arrangement lies in a large heat transfer temperature difference. Since the fluid flows unidirectionally within the channel, it is easy to achieve "pure counterflow" or "near-counterflow" heat transfer. In this state, the logarithmic mean temperature difference is high, and heat transfer efficiency naturally surpasses other arrangements. At the same time, the fluid velocity in the channel remains stable, avoiding local dead zones, which is a great advantage when handling high-viscosity fluids. Stable velocity reduces fluid stagnation and fouling, thereby extending the service life of the exchanger.
Disadvantages: However, series arrangement also has drawbacks. Because the flow cross-sectional area is fixed, when the fluid flow rate is high, velocity rises sharply, leading to increased pressure loss. A higher-power pump is then required to maintain flow, increasing operating cost. Thus, series arrangement is more suitable for "small flow, large temperature difference" heat transfer scenarios—for instance, small-scale reaction heat exchange in fine chemical processes, or cooling systems of precision instruments, where rapid heat removal from high-temperature components is needed while flow is not very large.
Parallel arrangement, also called multi-pass arrangement, divides plates into multiple parallel flow channels. By setting diversion plates at inlets and outlets, hot and cold fluids are distributed into several parallel channels. For example, with 20 plates, they may be divided into 2 parallel channels, each with 10 plates, where fluids flow in parallel and merge again before exiting.
Advantages: The core advantage of parallel arrangement is low flow resistance. Multi-channel design increases the total flow cross-sectional area, so at the same flow rate, velocity can decrease by 30%–50%, significantly reducing pressure loss. This makes it highly suitable for "large flow, small temperature difference" applications, such as industrial cooling water systems and district heating stations, where a large volume of fluid must be handled with relatively small temperature differences. Parallel arrangement reduces pump power consumption and saves operating cost.
Disadvantages: Its weakness lies in the ease of "uneven flow distribution" among parallel channels, which lowers local heat transfer coefficients. Meanwhile, since pure counterflow is hard to achieve, the temperature correction factor F is relatively low, requiring more plates to compensate for efficiency. This means finer control and adjustment are necessary to ensure proper flow distribution in each channel for optimal performance.
Mixed arrangement, also called series-parallel combination arrangement, is a hybrid of series and parallel. Fluids flow in series first and then in parallel, or vice versa. For example, hot fluid may pass through 2 series channels and then split into 3 parallel channels, while cold fluid first splits into 3 parallel channels and then flows through 2 series channels. The advantage is high flexibility: proportions of series and parallel can be adjusted according to heat transfer needs to balance efficiency and resistance.
Advantages: For "medium flow, medium temperature difference" conditions, mixed arrangement maintains a certain counterflow temperature difference while controlling velocity within the optimal range. It also adapts well to situations where inlet and outlet fluid temperatures vary greatly. By using multiple series stages to adjust temperature gradients, local overheating and thermal stress damage to plates can be avoided. For example, in large chemical processes where reactant temperature changes are complex, mixed arrangement allows flexible heat exchange paths, ensuring stable operation.
Disadvantages: On the other hand, mixed arrangement has higher complexity. Accurate design of diversion plate position and channel number is required, making manufacturing and maintenance more costly than series or parallel. It also demands higher fluid properties: if the fluid contains particles, deposits and blockages may form at diversion points. Therefore, when choosing mixed arrangement, one must consider both fluid characteristics and equipment capability to ensure long-term stable operation.
The heat transfer capacity of a plate heat exchanger refers to the amount of heat transferred between hot and cold fluids per unit time. The core formula is: Q = K × A × ΔT. Where Q is heat transfer, K is heat transfer coefficient, A is heat transfer area, and ΔT is mean temperature difference. Since plate number directly determines A, adjusting plate number is the most direct and common method of changing heat transfer. But this must follow scientific logic to avoid faults or inefficiency.
Each plate has a fixed effective heat transfer area. Total area A = effective area per plate × plate number. For example, if one plate has 0.8 m² effective area, increasing plate number from 20 to 30 increases area from 16 m² to 24 m². With K and ΔT unchanged, Q rises by 50%. This is the principle of enhancing heat transfer by adding plates.
However, resistance and flow matching must also be considered. Adding plates extends the fluid path and changes cross-sectional area, affecting resistance. Too many plates with unchanged flow rate reduce velocity, shifting from turbulent to laminar flow, thereby lowering K. In that case, even with larger A, Q may not increase. Conversely, too few plates with unchanged flow raise velocity sharply, increasing resistance and risking pump overload or overpressure.
In practice, plate adjustment follows three steps:
Calculate target heat transfer Qtarget. Using Qtarget = K × Atarget × ΔT, deduce required heat transfer area Atarget.
Determine plate number based on effective area per plate, then check if velocity remains within the "optimal range." If velocity is too low, reduce plate number or increase passes; if too high, increase plates or reduce passes.
Consider equipment limits. Plate number must not exceed frame capacity, and sealing gaps must stay uniform to prevent uneven stress and leakage.
Through this scientific approach, plate heat exchangers achieve both required performance and optimal operating condition.
Corrugation depth is one of the core structural parameters of plates. By affecting fluid flow and plate surface utilization, it directly links to heat transfer efficiency. However, the relationship is not simple; it has an "optimal range," requiring selection based on actual demand.
Plate corrugations act as "turbulence promoters." When fluid flows through corrugations, they disrupt the laminar boundary layer, inducing vortices and turbulence. Greater depth means stronger disturbance. For instance, increasing depth from 2 mm to 5 mm makes flow paths more complex, raising turbulence by 30%–50%. Since turbulence has much higher heat transfer coefficients, increasing depth improves efficiency within limits.
But deeper corrugations are not always better. Beyond the optimal range, two problems arise:
Sharp increase in resistance. Larger depth means stronger local resistance, raising pump power consumption.
Decline in surface utilization. Deeper corrugations enlarge convex height, reducing the number of plates accommodated per unit volume. Thus, even with larger spacing, total area may not increase as expected, or may even decrease.
Low-viscosity, large-flow fluids: Already turbulent, they need little disturbance. Shallow corrugations ensure adequate heat transfer while keeping resistance low, e.g., cooling water systems.
High-viscosity, low-flow fluids: Prone to laminar flow, they require strong disturbance. Deep corrugations enhance turbulence and compensate for viscosity, e.g., viscous chemical materials.
Medium-viscosity, medium-flow fluids: Medium corrugations balance efficiency and resistance, suitable for most common heat exchange cases.
From the above analysis of plate arrangement, heat transfer calculation with plate adjustment, and corrugation depth, we conclude: selecting the right plate heat exchanger must be tailored to specific needs. Different applications have different requirements, and only by understanding these in detail and combining them with exchanger characteristics can the most suitable equipment be chosen.
For instance:
In small-flow, large-temperature-difference conditions, series arrangement offers high efficiency.
In large-flow, small-temperature-difference cases, parallel arrangement reduces resistance and saves cost.
In medium-flow, medium-temperature-difference or complex conditions, mixed arrangement provides flexibility.
At the same time, adjusting plate number scientifically and choosing suitable corrugation depth further optimize performance, ensuring efficiency and stability.
In summary, plate heat exchangers, as efficient heat transfer equipment, rely on proper design and selection for full performance. Only by understanding requirements and matching them with design features can efficient, energy-saving heat transfer be realized. We hope this article helps you better understand and select plate heat exchangers, bringing convenience and benefits to your production or daily life.
