The truth about marine plate heat exchangers that affects the heat transfer effect
Marine plate heat exchanger as the main heat exchange equipment on board plays a key role in the safe operation of the whole ship. Its structure is relatively simple compared to other equipment, mainly composed of screw, pressure plate, base, plate and so on. It is widely used as a large ship main engine cylinder liner water, sliding oil cooler and central cooler. It has been greatly developed over the decades. All the major manufacturers are focusing on how to improve the heat transfer effect of marine plate heat exchanger.
Since the plate structure of marine plate heat exchanger directly affects the performance of the heat exchanger. In this paper, we will discuss the influence of a series of plate parameters on the performance of the existing marine plate heat exchanger, in order to provide some reference for further research.
Marine plate heat exchanger in order to its serviceability, between the plates are U-type connection, for the countercurrent way, both sides of the fluid for cold water and hot water or slippery oil. The form of heat transfer between the plates can be abstracted as flat wall heat transfer. As the flow of the fluid in the flow channel of the marine plate heat exchanger is determined by the host diesel engine oil or cylinder liner water heat transfer, so the focus of the study can be placed on the form of the plate.
What are the main factors affecting the effectiveness of plate heat transfer
Plate thickness
Plate angle
Flow rate between plates
Plate thickness
By the expression of the heat transfer coefficient can be seen, the smaller the thickness of the plate δ, the better the heat transfer effect of the heat exchanger, marine plate heat exchanger standards, the proposed heat exchanger plate thickness of 0.6 ~ 0.8mm, the industry's thinnest titanium plate plate has reached 0.4mm. plate and then make thin to improve the heat transfer effect will not be too obvious, but the main purpose is to reduce the cost of reducing the consumption of materials, but the thin plate will relatively reduce the strength of the plate in the press. But the strength of the thin sheet will be relatively reduced after pressing.
Clip angle of plate
Marine plate heat exchanger to improve the k value of one of the main methods is to improve the plate on both sides of the surface of the heat transfer medium fluid disturbance. Marine plate heat exchanger plate is usually processed herringbone corrugated plate. For herringbone corrugated plate, the size of the herringbone angle has a great impact on heat transfer and fluid resistance. The plate with large herringbone angle has high heat transfer coefficient and high fluid resistance; on the contrary, the plate with small herringbone angle has low heat transfer coefficient and resistance. 120° herringbone angle corrugated plate has the best heat transfer effect, and the smaller or larger the angle is, the heat transfer efficiency will be lower, and the usual central cooler and the water cooler of the cylinder liner adopts the plate with 120° herringbone angle, in order to achieve the maximum heat transfer effect.
Flow rate between plates
Fluid flow between the plates, the flow rate is not uniform, the flow rate in the main flow line, about 4 to 5 times the average flow rate, in a process of each flow channel flow rate is not uniform. In order to make the fluid flow between the plate, out of the full turbulence state, it is appropriate to take the average flow rate between the plate 0.3 ~ 0.8 m / s. In the case of resistance drop allowable to take a large value, in order to improve the convection heat transfer film coefficient, thereby reducing the heat transfer area, improve the efficiency of heat transfer. Usually in accordance with the given flow rate to select the appropriate single piece of the plate area and aspect ratio, so that the selection method is the key factor in controlling the flow rate between the plate.
(1) The heat transfer model of the heat exchanger is analysed to find out the key factors affecting the heat transfer coefficient k of the heat exchanger: the heat transfer film coefficient α, the thickness of the plate δ. The characteristic length of the plate and the Reynolds number between the plates, Re, determine the size of the heat transfer film coefficient α.
(2) Specifically analysed the current research direction of the plate heat exchanger plate (plate thickness, plate clamp angle and inter-plate flow rate) for marine use.
(3) After the analysis, it is necessary to improve and optimise the marine plate heat exchanger according to the relevant principles of heat transfer and fluid mechanics in the subsequent work.
