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boom in renewable power systems and electric vehicles . These are however only certain segments of growth – much is happening in the micro-technology arena as well as developments with electronics that aim to either manage or harvest even the smallest amounts of energy to control heat load and even create micro-energygeneration systems .
This all has led to the fact that technological advancements coupled with constant efforts and investments into product innovation , and research & development , are expected to increase competitiveness over the coming years for manufacturers . The largescale adoption of some of the novel techniques in the production of heat exchangers is likely to further complement the expected growth .
UNDERSTANDING BASIC PRINCIPLES The basic rule in heat transfer theory is that heat will always be transferred from a hot medium to a cold medium , until equilibrium is reached . There needs to be a temperature difference between the two mediums for heat transfer to take place and the heat “ lost ” by the hot medium is equal to the amount of heat gained by the cold medium , except in cases of losses to the surroundings . To continually use this transferred energy between two mediums , heat exchangers are used . The two main types of devices are direct and indirect HEX . In a direct HEX , both mediums are in direct contact with each other and with the indirect HEX both mediums are separated by a barrier through which heat is then transferred .
Outside of a HEX , the predominant heat transfer means is air while internally it ranges from water , with or without additives , to natural and synthetic refrigerants , steam and even oils , to name the most common .
All air-conditioning and refrigeration applications make use of HEX . When determining the right HEX per application , there are a number of factors to consider . Some of the most common factors include :
• flow rates
• maximum pressure inside of the HEX
• pressure drop
• temperature parameters
• system pressures
• liquid viscosity and concentration
• system upset conditions ( start-up / shut-down )
• space availability
• future expansion plans
• life cycle costs
• maintenance requirements
RACA Journal I January 2023