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.

Short answer

Answer: When comparing heat exchanger options, the factors to consider include initial costs, energy consumption over time, specific facility conditions, and requirements, such as noise level and space limitations.

Step-by-step solution

Evaluate the cost of each heat exchanger option

Determine the total initial cost of both heat exchanger options, including the cost of each heat exchanger and their respective required pumps. Let's denote the total cost of smaller and cheaper heat exchanger (Option A) as C_A and the total cost of the larger and more expensive heat exchanger (Option B) as C_B.

Compare Initial Costs

Analyze whether C_A < C_B or C_A > C_B. If the initial cost of Option A is cheaper than Option B, then you might choose Option A. Conversely, if Option B is cheaper upfront, you might choose Option B.

Consider Energy Costs

Calculate the energy consumption for each heat exchanger option over their life expectancy, factoring in their respective pump sizes and pressure drops. Denote these values as E_A and E_B for Options A and B, respectively.

Compare Energy Costs

Analyze whether E_A < E_B or E_A > E_B. If energy consumption for Option A is lower than Option B, then it might be more beneficial to choose Option A in the long run, regardless of their initial costs. Conversely, if Option B consumes less energy over time, then it might be the better choice despite being more expensive upfront.

Assess Facility Conditions and Requirements

It is essential to consider any specific facility conditions or requirements that may impact the overall efficiency of the chosen heat exchanger. For example, if the facility requires a low operating noise level, you may prioritize the heat exchanger with the smaller pump, which may produce less noise. Similarly, if space is limited within the facility, the smaller heat exchanger may be the better choice to conserve space.

Make the Final Decision

Based on the comparisons and analyses made in the previous steps, choose the heat exchanger that best suits the facility's requirements, economic preferences, and operating conditions.

Key concepts

Cost Analysis

When choosing between two heat exchangers, cost analysis is a crucial step. It involves evaluating the initial and long-term expenses related to each option. Start by calculating the total initial cost for each heat exchanger, including costs for the unit itself and the required pump. For clarity, let’s call the smaller, cheaper one Option A with cost \( C_A \), and the larger, pricier one Option B with cost \( C_B \). If \( C_A \) is substantially lower, it might seem the better initial choice.

However, don't stop there; consider long-term costs like energy expenditure (examined further in the next section). A comprehensive cost analysis helps ensure that you aren't solely swayed by initial costs but are making a prudent decision based on complete economic evaluation.

Energy Consumption

Energy consumption is a significant factor when evaluating heat exchangers. You need to consider how much energy each system will use over its lifespan.

Each exchanger's energy demand is influenced by its pump size and the pressure drop it creates. Calculate the energy consumption of Option A (\( E_A \)) and Option B (\( E_B \)) over the expected life of the equipment.

• An exchanger with a larger pump may use more energy due to increased demand.
• Those with a significant pressure drop typically require more energy to circulate fluids effectively.

If, over time, \( E_A \) is less than \( E_B \), Option A might be less costly to operate even if the initial price is higher.

Facility Requirements

Each facility has unique requirements that can affect which heat exchanger is most suitable. Consider the physical space, noise restrictions, and any specific operational needs.

For example, if your facility is cramped for space, a smaller heat exchanger might fit better, while a larger one might require costly renovations. Additionally, look into noise level regulations; a smaller pump might be desirable if quiet operation is critical, since larger pumps can be noisier.

Aligning the choice of heat exchanger with these facility-specific criteria ensures the selected system integrates smoothly and works efficiently within its environment.

Pressure Drop

Pressure drop occurs as fluid flows through a system and should be minimized to reduce operational costs. It represents the resistance the fluid encounters, requiring more energy to maintain flow.

Generally, a larger heat exchanger (Option B) will have a lower pressure drop, meaning less energy is needed for pumping, translating to lower energy costs over time. This can be vital for long-term economical operation.

• Low pressure drop: reduces pump energy consumption.
• High pressure drop: increases energy expenditure due to higher resistance.

Therefore, while considering pressure drop, see if fewer operational costs offset the higher initial expense.

Pump Size

The size of the pump needed for an exchanger affects both initial setup and ongoing energy costs. A larger pump might necessitate more space and power, thereby increasing both initial setup costs and ongoing energy consumption.

Smaller pumps are often preferred for energy efficiency, providing they deliver the needed capacity. When evaluating pumps:

• Larger pumps may require bigger spaces and lead to increased energy use.
• Smaller pumps could save energy but need a heat exchanger with a low pressure drop to be effective.

In conclusion, balance the pump size with energy efficiency for optimal performance and cost savings over the equipment's life.