What effect does fouling have on a heat exchanger's performance?

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Multiple Choice

What effect does fouling have on a heat exchanger's performance?

Fouling adds thermal resistance on the heat transfer surfaces, so the overall heat transfer coefficient decreases and the heat transfer rate drops for the same temperature difference. In a heat exchanger, the driving force for heat transfer is the temperature difference times the overall coefficient, U. Fouling introduces an extra resistance, often modeled as a fouling resistance, R_f, added to the existing convective resistances on both sides. This makes the total resistance higher, so U = 1 / (R_conv_hot + R_conv_cold + R_f) decreases. Consequently, the exchanger becomes less effective at moving heat, and maintaining the same duty can require more area or more energy to pump the fluids. Increases in the overall coefficient would imply better, not worse, heat transfer, so that choice isn’t correct. Fouling also tends to raise pressure drop due to hindered flow, opposite to the statement that there’s no effect on pressure drop. And improved energy efficiency would not occur; fouling typically lowers efficiency by reducing heat transfer and increasing pumping power to overcome the added resistance.

Fouling adds thermal resistance on the heat transfer surfaces, so the overall heat transfer coefficient decreases and the heat transfer rate drops for the same temperature difference. In a heat exchanger, the driving force for heat transfer is the temperature difference times the overall coefficient, U. Fouling introduces an extra resistance, often modeled as a fouling resistance, R_f, added to the existing convective resistances on both sides. This makes the total resistance higher, so U = 1 / (R_conv_hot + R_conv_cold + R_f) decreases. Consequently, the exchanger becomes less effective at moving heat, and maintaining the same duty can require more area or more energy to pump the fluids.

Increases in the overall coefficient would imply better, not worse, heat transfer, so that choice isn’t correct. Fouling also tends to raise pressure drop due to hindered flow, opposite to the statement that there’s no effect on pressure drop. And improved energy efficiency would not occur; fouling typically lowers efficiency by reducing heat transfer and increasing pumping power to overcome the added resistance.

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