Question

There are two heat exchangers that can meet the heat transfer requirements of a facility. One is smaller and cheaper but requires a larger pump, while the other is larger and more expensive but has a smaller pressure drop and thus requires a smaller pump. Both heat exchangers have the same life expectancy and meet all other requirements. Explain which heat exchanger you would choose and under what conditions. 11-138C A heat exchanger is to be selected to cool a hot liquid chemical at a specified rate to a specified temperature. Explain the steps involved in the selection process.

Short answer

Answer: The choice between the smaller, cheaper heat exchanger and the larger, more expensive one depends on factors such as initial cost, space availability, energy efficiency, and system requirements. The smaller, cheaper heat exchanger may be preferred if initial cost is a major concern, space is limited, and the operating cost difference between the pumps is not significant. The larger, more expensive heat exchanger may be chosen if long-term operation costs outbalance the initial investment, space is not a constraint, and better efficiency is prioritized. The steps in selecting a heat exchanger involve defining application requirements, determining the type and material of construction, calculating the heat transfer area, selecting a heat exchanger model, performing an economic analysis, and finally purchasing and installing the chosen heat exchanger.

Step-by-step solution

Heat exchanger comparison

In this scenario, we have two heat exchangers to choose from. The first heat exchanger is smaller, cheaper, but requires a larger pump, while the second one is larger, more expensive, but needs a smaller pump due to its smaller pressure drop. To decide which heat exchanger to choose, various factors need to be considered. These factors include: - Total cost of ownership (initial cost, operation cost, maintenance cost) - Space availability at the facility - Energy efficiency - Any specific requirements of the facility or system

Conditions for selection

Depending on the case, one may prefer the smaller and cheaper heat exchanger if: - Initial cost is a major concern - Space available at the facility is limited - The operating cost difference between the larger and smaller pump is not significant On the other hand, the larger and more expensive heat exchanger may be chosen if: - Long term operation costs (such as energy consumption) outbalance the initial investment - Space is not a constraint - Better efficiency is prioritized due to environmental or system requirements

Steps in heat exchanger selection

When selecting a heat exchanger for cooling a hot liquid chemical, the following steps should be followed: 1. Define the application requirements: Determine the specific cooling duty, required temperature change, flow rates, operating pressures, and any chemical compatibility or safety concerns. 2. Determine the type and material of construction: Based on the application requirements, select the most suitable type of heat exchanger (plate, shell and tube, spiral, etc.) and the material of construction (copper, aluminum, stainless steel, etc.) 3. Calculate the heat transfer area: Based on the selected heat exchanger type and material, calculate the required heat transfer surface area using the heat transfer rate, temperature difference, and an estimated heat transfer coefficient. 4. Select a heat exchanger model: Based on the calculated heat transfer area and the specific requirements of the system, select the most appropriate heat exchanger model that satisfies all the requirements. 5. Perform economic analysis: Assess and compare the total costs of ownership (including initial cost, operation cost, and maintenance cost) of the available options and select the heat exchanger with the most favorable balance between performance and cost. 6. Procure and install the selected heat exchanger: Finally, purchase the chosen heat exchanger and install it in the facility according to the proper integration and safety guidelines.