【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20191015

There are two basic types of nozzles: converging nozzles and diverging nozzles

1. Nozzles can be roughly classified into: 1) constant-section nozzles, 2) converging nozzles, 3) diverging nozzles, 4) scaled nozzles. In actual use in steam turbines, converging nozzles and scaled nozzles are employed, with converging nozzles being the most commonly used. 2. How to choose a nozzle? What are their respective uses? Factors considered when selecting nozzles include flow rate, pressure, spray angle, coverage area, impact force, temperature, material, and application, and these factors are often interrelated and mutually restrictive. Flow rate and pressure, as well as spray angle and coverage area, are all directly proportional to each other. The purpose of spraying from any nozzle is to maintain continuous contact between the tank fluid and the workpiece; the flow rate is a more important factor than pressure. The temperature of the liquid does not affect the spraying performance of the nozzle, but it affects viscosity and specific gravity, as well as the choice of material. The material of the nozzle should also be determined based on the chemical properties of the bath fluid; for non-corrosive bath fluids, bronze casting or plastic die-casting can be used depending on the difficulty of processing. To prevent corrosion, non-metallic materials can be used ； For highly corrosive bath solutions such as sulfuric acid and hydrochloric acid, nylon plastic can be used ； The nozzle materials used in phosphating tanks are generally acid-resistant stainless steel; nozzles designed to prevent rust can also be made directly from stainless steel or nylon. For nozzles that require a certain level of impact force, small-angle nozzles should be used, with a liquid column flow (i.e., jet) being the best option ； Fan-shaped nozzles are suitable for cleaning, degreasing, cooling, etc., while cone-shaped nozzles are suitable for rinsing, surface treatment, phosphating, humidification, dust removal, etc ； Venturi mixing nozzles should be installed in the paint storage tanks and basins. Taking the “H”-shaped mixing nozzle (also known as a Venturi nozzle) as an example, the liquid in the basin is drawn in together with the liquid introduced through the inlet at a certain pressure; these liquids are then mixed in a 1:4 flow ratio before being sprayed out, thereby achieving homogeneous mixing of the solute without any air present. This prevents precipitation, as the stirring ensures a uniform mixture of the chemical solutions.

Types of nozzles: straight-through nozzles, lock-type nozzles, and nozzles for special purposes. The nozzle type is primarily determined by the properties of the material being processed, as well as the characteristics and applications of the resulting product. For materials with high viscosity and poor thermal stability, straight-through nozzles with low flow channel resistance, minimal shear effect, and a larger diameter are suitable ； For low-viscosity crystalline materials, a sealed nozzle equipped with a heating device is suitable ；  For thin-walled products with complex shapes, small-diameter nozzles with long range should be used ； For thick-walled products, it is best to use nozzles with a larger diameter and good feeding capabilities.

There are two basic types of nozzles, namely converging nozzles and diverging nozzles

Types of nozzles: straight-through nozzles, lock-type nozzles, and nozzles for special purposes. The nozzle type is primarily determined by the properties of the material being processed, as well as the characteristics and applications of the resulting product. For materials with high viscosity and poor thermal stability, straight-through nozzles with low flow channel resistance, minimal shear effect, and a larger diameter are suitable ； For low-viscosity crystalline materials, a sealed nozzle equipped with a heating device is suitable ；  For thin-walled products with complex shapes, small-diameter nozzles with long range should be used ； For thick-walled products, it is best to use nozzles with a larger diameter and good feeding capabilities.

In a turbine with nozzle regulation, when the external load changes, each control valve is opened or closed sequentially one by one. Since at part load only one or two of the several control valves are not fully open, at the same part load the throttling loss of steam entering the turbine is smaller, and the change in its internal efficiency is also smaller. From an economic perspective, this control method is more reasonable when the unit load changes frequently.