When is the use of the effectiveness-NTU method preferable to the LMTD method for heat exchanger analysis?
Explanation
This question contrasts the two main methods of heat exchanger analysis, LMTD and NTU, and asks for the specific scenario where the NTU method is more convenient, as explained at the beginning of Section 11.4.
Other questions
In which type of concentric tube heat exchanger do the hot and cold fluids enter at opposite ends, flow in opposite directions, and leave at opposite ends?
What is the primary purpose of installing baffles in a shell-and-tube heat exchanger?
What term is used for the additional thermal resistance introduced by the deposition of a film or scale on a heat exchanger surface during operation?
For an unfinned, tubular heat exchanger with an inner surface area Ai and outer surface area Ao, how is the overall heat transfer coefficient (U) related to the individual coefficients (hi, ho) and fouling factors (Rf,i, Rf,o)?
In a parallel-flow heat exchanger, the hot fluid enters at 150 C and exits at 90 C. The cold fluid enters at 40 C and exits at 80 C. What is the Log Mean Temperature Difference (Tlm)?
In a counterflow heat exchanger, a cold fluid is heated from 20 C to 80 C while a hot fluid is cooled from 100 C to 90 C. What is the Log Mean Temperature Difference (Tlm)?
What is a key thermodynamic advantage of a counterflow heat exchanger compared to a parallel-flow heat exchanger for the same inlet and outlet temperatures?
The effectiveness of a heat exchanger is defined as the ratio of the actual heat transfer rate to what other quantity?
How is the maximum possible heat transfer rate (q_max) for a heat exchanger calculated, given the heat capacity rates (Ch, Cc) and inlet temperatures (Th,i, Tc,i)?
A hot fluid with a heat capacity rate of 2000 W/K enters a heat exchanger at 100 C. A cold fluid with a heat capacity rate of 3000 W/K enters at 20 C. What is the maximum possible heat transfer rate?
A heat exchanger has an effectiveness of 0.75. The minimum heat capacity rate is 1500 W/K, and the inlet temperatures of the hot and cold fluids are 250 C and 35 C, respectively. What is the actual heat transfer rate?
What is the dimensionless parameter 'Number of Transfer Units' (NTU) a measure of?
For a heat exchanger where one of the fluids is boiling or condensing, what is the value of the heat capacity ratio, Cr = C_min / C_max?
In a shell-and-tube heat exchanger with one shell pass and two tube passes, what is the LMTD correction factor F if the shell-side fluid temperature changes from 160 C to 100 C and the tube-side fluid temperature changes from 15 C to 85 C?
What is the key feature that distinguishes a compact heat exchanger from a conventional one?
In a cross-flow heat exchanger where the fins inhibit fluid motion in the direction transverse to the main flow, the flow is described as what?
A heat exchanger cools oil with a specific heat of 2131 J/kg-K at a flow rate of 0.1 kg/s from 100 C to 60 C. What is the heat transfer rate?
The overall surface efficiency or temperature effectiveness of a finned surface (η_o) is defined by the relation η_o = 1 - (Af/A)*(1 - η_f). What does the term A represent?
For a parallel-flow heat exchanger with C_min/C_max = 0.5 and NTU = 2.0, what is the effectiveness (ε)?
For a counterflow heat exchanger with C_min/C_max = 0.75 and an effectiveness (ε) of 0.80, what is the Number of Transfer Units (NTU)?
What does a fouling factor of R_f = 0.0002 m2-K/W represent?
For a counterflow heat exchanger where the heat capacity rates of the hot and cold fluids are equal (Ch = Cc), what is the relationship between the temperature difference (ΔT) and the log mean temperature difference (Tlm)?
What is the effectiveness of any heat exchanger when the Number of Transfer Units (NTU) is very small (approaching zero)?
A cross-flow heat exchanger with both fluids unmixed is used to heat water from 35 C to 125 C using hot exhaust gas that cools from 300 C to 100 C. The water flow rate is 1 kg/s and its specific heat is 4197 J/kg-K. What is the effectiveness of this exchanger?
Which type of heat exchanger consistently provides the highest effectiveness for a given NTU and heat capacity ratio (Cr > 0)?
A concentric tube heat exchanger has an overall heat transfer coefficient of 100 W/m2-K and a surface area of 40 m2. The minimum heat capacity rate is 1500 W/K. What is the Number of Transfer Units (NTU) for this exchanger?
What is the primary heat exchanger analysis problem where the fluid flow rates and inlet temperatures are known, and the goal is to determine the heat transfer rate and outlet temperatures for an existing exchanger?
In a steam condenser, the heat capacity rate of the condensing steam (Ch) is considered to be infinite. If the cooling water has a heat capacity rate (Cc) of 1.25e8 W/K, what is the value of Cmin?
For a shell-and-tube exchanger with one shell pass and any multiple of two tube passes, the LMTD correction factor F depends on two dimensionless parameters, P and R. How is the parameter P defined?
According to the provided data for a specific circular tube-circular fin heat exchanger (surface CF-7.0-5/8J), what is the ratio of the fin area to the total area (Af/A)?
In the analysis of a counterflow, concentric tube heat exchanger, a water flow rate of 0.2 kg/s through a 25 mm inner diameter tube results in a Reynolds number of 14,050. The flow is therefore turbulent. Which equation is suggested for computing the Nusselt number?
A shell-and-tube heat exchanger with two shell passes and four tube passes has an effectiveness of 0.9 for the case of C_min/C_max = 0.5. What is the approximate NTU for this exchanger?
For a heat exchanger where C_h = 400 W/K and C_c = 100 W/K, what is the value of the heat capacity ratio Cr?
In the pressure drop calculation for flow across a compact heat exchanger core (Equation 11.37), what does the term G represent?
In a heat exchanger with a large temperature effectiveness (η_o) for its finned surfaces, what does this imply about the fin efficiency (η_f)?
For a shell-and-tube heat exchanger with one shell pass and M = 8 tube passes, each of length L_pass, what is the total length of a single tube?
If a heat exchanger analysis results in a Reynolds number of 56 for oil flow in an annulus, what flow regime should be assumed for that fluid?
For which value of the heat capacity ratio (Cr) does the effectiveness of a heat exchanger become independent of the specific flow arrangement?
What does a negative value for the log mean temperature difference (Tlm) imply in a heat exchanger analysis?
The outlet temperature of water from a condenser is 36 C. The water entered at 20 C, and the total heat transferred was 2e9 W. If the specific heat of water is 4179 J/kg-K, what is the mass flow rate of the cooling water?
In a compact plate-type heat exchanger with N gaps of width 'a' and a cubical exterior dimension L, what is the total heat transfer area A?
When analyzing a finned-tube heat exchanger, if the heat capacity rate of the gas on the finned side (Ch) is 1344 W/K and the rate for the water on the unfinned side (Cc) is 4184 W/K, which is the minimum heat capacity rate, Cmin?
What is the primary reason fins are typically used on the gas-side of a gas-to-liquid heat exchanger?
In a cross-flow heat exchanger with one fluid mixed and the other unmixed, the effectiveness is given by the relation ε = (1/Cr) * [1 - exp(-Cr * (1 - exp(-NTU)))]. Which fluid corresponds to C_min for this specific relation?
If a heat exchanger's performance calculation yields ε = 0.845, and a graphical estimation from a chart gives ε = 0.82, what can be said about the chart-based estimate?
A concentric tube heat exchanger operates in counterflow to cool oil from 100 C to 60 C using water that heats from 30 C to 40.2 C. What is the log mean temperature difference?
What is the area-to-volume ratio (in m2/m3) for a compact plate-type heat exchanger with 60 gaps, an exterior dimension L = 0.131 m, and a total heat transfer area of L^2 * (N-1)?
If the total volume of a concentric tube heat exchanger is 0.10 m3 and the volume of a compact plate-type exchanger that performs the same duty is 0.0022 m3, what is the percentage reduction in volume?
Which heat transfer coefficient typically controls the overall rate of heat transfer in a liquid-to-gas heat exchanger with a low value of ho (oil side) and a high value of hi (water side)?
If you need to design a heat exchanger to heat 2.5 kg/s of water from 15 C to 85 C using hot oil available at 160 C, and the oil outlet temperature is specified as 100 C, which analysis method is most direct for determining the required heat transfer area?