Design calculations of a plate heat exchanger include flow distribution and pressure drop and heat transfer. The former is an issue of Flow distribution in manifolds.[3] A layout configuration of plate heat exchanger can be usually simplified into a manifold system with two manifold headers for dividing and combining fluids, which can be categorized into U-type and Z-type arrangement according to flow direction in the headers, as shown in manifold arrangement. Bassiouny and Martin developed the previous theory of design.[4][5] In recent years Wang [6][7] unified all the main existing models and developed a most completed theory and design tool.
The total rate of heat transfer between the hot and cold fluids passing through a plate heat exchanger may be expressed as: Q = UA∆Tm where U is the Overall heat transfer coefficient, A is the total plate area, and ∆Tm is the Log mean temperature difference. U is dependent upon the heat transfer coefficients in the hot and cold streams.[2]
Manifold arrangement for flow distribution
Their cleaning helps to avoid fouling and scaling without the heat exchanger needing to be shut down or operations disrupted. In order to avoid heat exchanger performance to decrease and service life of the tube extension, the OnC (Online Cleaning) can be used as a standalone approach or in conjunction with chemical treatment. The re-circulating ball type system and the brush and basket system are some of OnC techniques. OfC (Offline Cleaning) is another effective cleaning method that effectively increases the performance of heat exchangers and decreases operating expenses. This method, also known as pigging, uses a shape like bullet device that is inserted in each tube and using high air pressure to force down the tube. Chemical washing, hydro-blasting and hydro-lancing are other widely used methods other than OfC. Both these techniques, when used frequently, will restore the exchanger into its optimum efficiency until the fouling and scaling begin to slip slowly and adversely affecting the efficiency of the heat exchanger.
Operation and maintenance cost is necessary for a heat exchanger. But there are different ways to minimize the cost. Firstly, cost can be minimized by reducing fouling formation on heat exchanger that decreases the overall heat transfer coefficient. According to analysis estimated, effect of fouling formation will generate a huge cost of operational losses which more than 4 billion dollars. The total fouling cost including capital cost, energy cost, maintenance cost and cost of profit loss. Chemical fouling inhibitors is one of the fouling control method. For example, acrylic acid/hydroxypropyl acrylate (AA/HPA) and acrylic acid/sulfonic acid (AA/SA) copolymers can be used to inhibit the fouling by deposition of calcium phosphate. Next, deposition of fouling can also be reduced by installing the heat exchanger vertically as the gravitational force pulls any of the particles away from the heat transfer surface in the heat exchanger. Second, operation cost can be minimized when saturated steam is used compared to superheated steam as a fluid. Superheated steam acts as an insulator and poor heat conductor, it is not suitable for heat application such as heat exchanger.