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Thermal Engineering Design
Heat is a form of energy potential that can be defined in terms of temperature and mass, and - like mechanical, chemical and electrical potentials - its flow described with respect to length and time. It is transmutable with other energy formats, and pervades all dynamic systems. As an engineering fundamental, it rarely stands alone: Thermal Design is just a convenient term for a very broad church, and draws on most other disciplines. Much the same can be said of thermal failure modes in process plant design – they are generally associated with other contributory mechanisms
Design for Site Utilities
Some projects can require special-purpose waste heat recovery equipment such as economisers and recuperators, feed tanks, hotwells and emissions control plant to meet specific site requirements and improved environmental standards. Others entail start-to-finish thermal engineering design, mechanical layout and prototyping of both proprietary and custom-built factory services plant. Changes in manufacturing economy means that there are now fewer large U.K. manufacturing sites. Companies like Tate & Lyle Sugars, Plessey, Alcan and English Sewing all supported considerable site infrastructures, for whom we have undertaken wide-ranging Consult Design Construct projects, factory services restructuring programmes, and Energy Survey reports. These brought Steam-raising and distribution facilities, cooling water and compressed air services, and site effluent systems together under a common thermal design services umbrella. Along with other projects for T&L, we were engaged as consulting thermal engineers for a major development of Silvertown refining capacity. Sir Oliver Lyle (“The Great Sir O.”) wrote “The Efficient Use of Steam” and an equally seminal textbook on Sugar Technology. Our boiler plants run from a few hundred pounds of steam per hour for a small dyehouse, to over 15 tonne/hour for a factory making expanded polystyrene products. They include coal-, gas-, oil-, wood waste- and biofuel-fired LPHW, HPHW, thermal fluid and steam boiler installations, with associated waste heat recovery equipment. Systems recirculating synthetic heat transfer fluids can operate in liquid phase under atmospheric pressure at temperatures approaching 350°C, while liquid sodium systems can be worked to 600°C without thermodynamic effect. Further information is given in our pages about Liquid Phase and Hot Oil Heating and Process Heating Systems elsewhere on this site.
Heat Transfer - The Definitive Inexact Science?
Messrs. Webster and Collins might agree that an inexact science is not precise, but needs appeal to other definitions if they wish to argue over the degree to which that might imply inaccuracy. Traditionally, the practice of heat transfer is recognized to be as much an Art as a Science, or vice versa. We hark back to the days of pencil, paper and slide rule, while digitized CFD and FEA frequently visualize what we we would claim to have been the preserve of our minds’ eyes. It is vitally important that we retain our long-learned skills should we resort to off-the-self application program suites. Our analogue brains should not be allowed to fade for wont of exercise.
Thermal Design References
Perry & Chilton’s Chemical Engineers’ Handbook provides a comprehensive and concise review of the topic, with a breadth of coverage not found in more specialist literature. Following a straightforward introduction of fundamental concepts, the thermal engineering design of many types of heat & mass transfer equipment is described in accessible terms. Single- and multi-phase solid-, liquid- and gaseous operations are referred to the plant in which they are undertaken, while several types of surface equipment (heat exchangers, condensers, evaporators et al.) - along with direct contact systems towers and columns - are discussed in practical detail. Other much-respected vade mecums in the field are: William H McAdams’ Heat Transmission, Donald Q Kern’s Process Heat Transfer, and Herman J Stoever’s Applied Heat Transmission – all giving a different slant on the subject from a common ground. McAdams and Kern have been our constant companions in over thirty years as practicing thermal design engineers. The Industrial Cooling Tower by K K McKelvey and Maxey Brooke has probably not been bettered by the several titles since published dealing with mechanical and natural draught systems, although Jackson’s Cooling Towers with Special Reference to Mechanical-Draught Systems is a clear and direct primer on gas cooling columns and mass transfer equipment generally. Geoffrey F Hewitt’s loose-leaf Heat Exchanger Design Handbook has passed through many editions, and is the most exhaustive reference in its field, although - as remarked by M A Mehrabian – “much of design data for plate heat exchangers remain proprietary”.
The Thermal Design Environment
Determining the character and parameters of a given application might represent a greater part of the Design Process than other fields of science and engineering. Taken with its nested discipline of fluid mechanics, Thermal equipment design has witnessed profound changes in mathematical, physical and engineering methodologies during the past 50 years. It now has the facility to be more precise and flexible; whether this aids comprehension depends upon how thoroughly contemporary tools and their use is understood. We undertake Consult Design Construct projects in support of energy efficiency and thermal design services similar to those previously available under DTI schemes and provide comprehensive energy audit programmes for any U.K. site.
Dove Thermal Engineering Limited, Uttoxeter, ST14 8QX
Telephone: 01889 569933