Designing an appropriate process heat system requires knowledge and experience. Unfortunately, this fact does not always receive the appreciation it deserves, which can lead to systems that are not well thought-out (often falling into one of the several most common pitfalls). At STANMECH, we’ve seen the consequences of poorly designed systems that have proceeded forward to implementation. The shortcomings of the system are not discovered until it has been built and is in the testing and validation phase. At this stage potential solutions are limited by both design and financial constraints, as the solution must fit into a box that has already been built and the budget has already been allotted and spent.
While STANMECH is happy to consult and recommend equipment to help solve these cases, we would much prefer to be involved in the project during the design phase to help avoid these headaches altogether! When is it Appropriate to Use a Compressed Air Supply?
STANMECH typically recommends that Leister’s LHS air heaters be supplied with air by a blower. This is because a blower-based process heat system, when correctly sized and installed, will be far more energy efficient than an equivalent compressed air system. The associated cost-savings increase with the power rating of the heater—larger heaters require larger volumetric air flows resulting in more savings.
However, when broken down to its basics, LHS air heaters simply require a consistent supply of air flow regardless of its source. As long as the system is capable of providing an uninterrupted supply of air that meets the minimum flow requirements for the heater, the LHS air heaters can be operated safely using compressed air. 1. Mixing up heat and temperature
The most commonly made mistake when designing a hot air system is the confusion of heat and temperature. While the terms are often used interchangeably, by definition they are very different. Heat relates to the amount of energy that is required in order to raise the temperature of a material or change its state (i.e. water changing from a liquid to a gas). Temperature is usually a specific design criteria or limitation, such as the melting point of a material or a temperature above which the material will degrade. When designing a process heat system both are important, however temperature is a design variable and heat is a calculated output. Read our article about the difference between temperature and heat for more information.
2. Making equipment choices without sufficient investigation
Choosing the right equipment for a hot air system is a complex task that requires a thorough application analysis. Simplistic choices are often made without enough examination of the key design elements. For example, a system may be designed considering only the required target temperature while ignoring the amount of heat or type of air supply required. This results in the wrong equipment being specified and a system that does not work. Read our article about using hot air to create an oven as an example of the complexity of designing a hot air system.
Computational Modelling of Thermal Dynamics and Fluid Mechanics – what is it and how can it help me?9/15/2015
Computational modelling is powerful tool that can be used to simulate many types of systems and their behaviour. In this article we will focus on computational modelling of thermal dynamics and fluid mechanics. Many engineers are introduced to thermal dynamics and fluid mechanics in school and later work with them while designing processes for manufacturing applications. Unfortunately, the knowledge provided in an undergraduate degree alone is not always adequate to ensure a successful project years later. An incomplete understanding of the fundamentals of thermal dynamics and fluid mechanics is often the root cause of system inefficiencies, poor performance, or the outright failure of a project.
What is computational modelling?
The physics behind thermal dynamics and fluid mechanics are governed by a series of partial differential equations. On a very basic level computational modelling involves breaking down a proposed system design into small parts (this is called meshing) and applying the governing equations to each individual part. The program simultaneously solves the equations for each element, ensures continuity throughout the system, and checks for adherence to any prescribed boundary conditions inputted by the designer. This allows complex problems to be solved much faster and more reliably than through manual calculations.
This video shows how to set up the LHS SYSTEM series of air heaters and how the different modes work, both with and without an external controller, and in open and closed loop control modes. You will see how to connect a LHS SYSTEM air heater proper with the signal wire, the main power wire, and the alarm contact. Need help setting up a system? Contact our Application Engineering department for support at 1-888-438-6324.
This video shows how a thermocouple, controller, PWM-signal, SSR (Solid State Relay), and a LHS CLASSIC air heater work together and how hook it all up to get an external closed loop control system. Also covered is how the alarm-port on the LHS CLASSIC air heater works and how you can use it to protect the tool in an overheat situation. Need help setting up a system? Contact our Application Engineering department for support at 1-888-438-6324.
Air heaters come in many shapes and sizes but the fundamentals of how they work is consistent across most tools. A resistance wire element heats up when a current flows through it and an air source provides air flow across the heated wires. Passing air across the hot element heats the air which can then be used to perform any desired task.
Heaters are specified according to power rating (related to the current flowing through the element and the source voltage), this article will use the SI unit for power: kilowatts or kW. Power is a quantification of how much energy per unit time the heater is able to transfer. It’s this energy transfer that causes heating or a rise in temperature of the object subjected to the flow of hot air.
Hot air is widely used in all kinds of manufacturing processes but when it comes to specifying an air heater they are not all interchangeable. There are several types of air heaters available and the best type for a particular application depends on a number of factors. This article outlines the differences between high and low flow heaters and gives tips on when and how to use each type correctly.
How are High Flow and Low Flow Heaters alike?
Both types of heaters are categorized as in-line heaters. This means that air is heated by passing over a heating element as it passes through the heater travelling from the inlet to the outlet. In most cases the air is supplied by an industrial blower but it can also be supplied by an air compressor.
The Leister HOTWIND SYSTEM is a versatile tool with several distinct operational modes. This application note will outline the functionality of these modes, as well as explain how they are selected through the setup menu. As the heat and airflow are set independently of each other, their modes of control will be described in separate sections.
The HOTWIND PREMIUM, is a simpler version of the HOTWIND SYSTEM with no digital display, integrated thermocouple, or connections for external control. The HOTWIND PREMIUM operates the same as Mode 1 for both airflow and heat control (See below). The other modes described here are not applicable to the HOTWIND PREMIUM. Air heaters are used for many applications and the nozzle that should be attached to the outlet of your heater depends on the requirements of your application. In designing a hot air process, careful thought is usually given to the type of heater, size of heater, etc. but nozzle selection is often done as an afterthought without much consideration. Many people underestimate the importance of good nozzle design to the success of their process heat application. 1. What is the purpose of the nozzle?
The first question to ask when selecting or designing a nozzle is ‘what do you want to accomplish?’ Do you want to focus the air into a fast moving stream? |