I have a few questions regarding heat exchange that I’d like to ask everyone

1. The choice of heat transfer medium depends on the heating requirements of your material, and not on the temperature difference. For example, if there is a mixture that is in liquid state at room temperature, around 20 degrees Celsius, and thin-film evaporation separation is to be used, while the temperature of the low-boiling components is over 300 degrees Celsius, then how can I reach such a temperature? Heat transfer oil is necessary; steam, on the other hand, has a temperature of only around 100 degrees Celsius. So the question arises: with such a large temperature difference and a short residence time, can heat transfer oil be used to reach the required temperature? The answer is no; therefore, prior to this step, a preheater is usually used – several preheaters (the number depending on the process design) are employed to preheat the material first, and then heat it with heat transfer oil. The same principle applies to other heating methods as well; the heating medium is chosen based on the highest temperature required by the material being processed, and preheating can be carried out in stages until the desired temperature is reached. 2. Remember that, in order to prevent the accumulation of condensate water and thus avoid water hammer effects, steam must flow from top to bottom. For other liquid heat transfer media, flow must be from bottom to top – this applies to circulating water, cooling water, hot water, and thermal oil as well. If you want to improve the heat transfer efficiency by changing from parallel flow to counterflow, you can only do so by altering the direction in which the material is fed

We use heat transfer oil to heat the cooking oil. Currently, the temperature difference between edible oil and heat transfer oil is around 60°C. I would like to ask whether this temperature difference is economically viable.

The key also lies in what type of heat exchanger the poster chooses. Generally, for fixed tube sheets, it is best not to let the temperature difference exceed 50℃

You’re asking about two issues here. First, it’s necessary to meet the process requirements; only then can we consider the economic viability of things. This involves choosing appropriate equipment to minimize energy losses and make use of energy again. For example, if two companies produce the same product, with identical process routes and similar workflows, their equipment choices may differ, as does the layout of the pipelines. As a result, there will inevitably be some differences in their energy consumption. Nowadays, companies strive to design their processes in as efficient a manner as possible

Our process conditions can definitely meet the requirements; what’s being considered now is whether the temperature difference between hot oil and edible oil is reasonable. If the temperature difference can be reduced, at least the heat loss can be decreased. In other words, for heat exchange scenarios like ours, what temperature difference is generally considered economical when designing such systems?

1. First, the heat transfer oil is generally arranged to enter from below and exit from above； Then, under conditions that meet the process requirements, the smaller the temperature difference, the larger the heat exchange area; this results in higher equipment costs. To reduce the temperature difference and thus minimize heat losses, it is necessary to compare the equipment costs at different temperature differences along with the amount of heat loss reduced, in order to select the temperature difference that offers the best cost-performance ratio.