# counter flow heat exchanger example

This chapter offers an approach to temperature calculations having no such limitation. Closure plates seal the full length of both edges of the spiral strip. The change of exergy for the hot stream is denoted by the area 1h-2h-3h-4h-1h, while the unavailable energy is given by 3h-5h-6h-4h-3h. Once the temperature profile of the coolant is determined, the air outlet temperature can be described as a function of x2. The result is a light-weight, economical construction with favorable heat transfer capacity per unit volume envelope. The exergy change of the hot stream is then given by. (104), Similarly, the heat transfer coefficient for the boundary condition is found as. Figure 5.17(a) shows the entropic diagram of the cycle followed by the gas load for these engines. The method proceeds by calculating the heat capacity rates (i.e. If the variation of the mass flow rate with time and the relationship between the mass flow rate and the heat transfer coefficient are known, the heat transfer coefficient is a known function of time. The value of ΔBuniv<0 because the entropy change of the cold steam is greater than that of the hot stream. Second, the temperature of the cold fluid exiting the heat exchanger never exceeds the lowest temperature of the hot fluid. It is worth noting that, in practice, heat recovery in the Ericsson engine is conducted in a balanced counterflow heat exchanger (recuperative heat exchanger), while in the Stirling engine, thermal regeneration passes through storing, then through destoring of heat in a regenerating heat exchanger (with heat capacity). This results in thermal interaction between already warmed up air and the cold windshield. The Spirex appears to offer attractions when compactness and low installation cost are paramount. For this purpose a differential element of the size dA=dx1dx2 is energetically balanced. This means that the ideal dimensions of the heat exchanger can be calculated easily by modelling the heat exchanger with the presented approach. Of Cooling Water Are 15°C And 75°C Respectively. This is because the log mean temperature difference is greater for a counterflow heat exchanger. Consider a parallel-flow heat exchanger, which is used to cool oil from 70°C to 40°C using water available at 30°C. Figure 5. What other equations or assumptions do I need to calculate L? You are going down the right path. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. with a wall thickness of 0.1 in. Temperature recovery ratio is somewhat less than that of a conventional counter flow exchanger of comparable flow passage geometry. A counter-flow heat exchanger is one in which the direction of the flow of one of the working fluids is opposite to the direction to the flow of the other fluid. From Table 137, it can be seen that the and boundary conditions are the special cases of the boundary condition. For this task the well-known Nusselt correlations  were chosen by case differentiation analysis of laminar, turbulent and transitionally flow conditions within the air ducts considering hydraulic diameter based on non-circular cross section. The primary advantage of a regenerative heat exchanger application is conservation of system energy (that is, less loss of system energy due to the cooling of the fluid). Earlier in this module we looked at a method for calculating Uo for both rectangular and cylindrical coordinates. The passenger compartment model equations are presented in the following. Under comparable conditions, more heat is transferred in a counter-flow arrangement than in a parallel flow heat exchanger. The results are shown in figure 3. Simulation results of the temperature profile within the windshield at different times are shown exemplarily in figure 7. This method is not general because (1) the relationship between the heat transfer coefficient and the mass flow rate cannot be universally expressed with Eq. The Inlet And Outlet Temp. If the PTC auxiliary air heater is activated, the air is heated up once more before it flows through several air ducts. It means that the flow direction of fluid 2 can have a sudden change. At the ends of the heat exchanger, the tube-side fluid is separated from the shell-side fluid by a tube sheet. These two cycles involve two isothermal processes: an isothermal expansion 2–3 and an isothermal compression 4–1. The same steam generator can also be analyzed by an energy balance on the primary flow stream with the equation $$\dot{Q} = \dot{m} ~c_p ~\Delta T$$, where $$\dot{m}$$, cp, and ΔT are the mass flow rate, specific heat capacity, and temperature change of the primary coolant. The water flows in the downward direction. They generally consists of large chambers loosely filled with trays or similar wooden elements of construction. The heat exchanger is used to heat a cold fluid from 120°F to 310°F.   Some heat exchanger advertises the availability of finned tubes in a hairpin or double pipe heat exchanger. Privacy Hence, the temperature profile has to be determined in order to calculate the particular convective heat flows as well as the rate of internal energy of the windshield. Common applications of heat exchangers in the nuclear field include boilers, fan coolers, cooling water heat exchangers, and condensers. In order to solve certain heat exchanger problems, a log mean temperature difference (LMTD or ΔTlm) must be evaluated before the heat removal from the heat exchanger is determined. h 7.4. Unlike a regenerator, Spirex avoids direct contact between the warm, contaminated stream and the incoming supply. This result has a further significance, which is that, to obtain the maximum transference of exergy, it is important to reduce the value of T0 (S1 − S2). These relationships are differentiated from one another depending (in shell and tube exchangers) on the type of the overall flow scheme (counter-current, concurrent, or cross flow, and the number of passes) and (for the crossflow type) whether any or both flow streams are mixed or unmixed perpendicular to their flow directions. m The inner heat transfer coefficient is a function of air mass flow into the cabin whereas the outer heat transfer coefficient is primarily dominated by the car's velocity . In order to rate the effect of different heating strategies, the heat-up behaviour of the passenger compartment is modelled. For a heat exchanger with highly conductive materials, e.g., copper or aluminum, the boundary condition may be a good approximation when q′ is constant. It is a fundamentally unsteady process. The effectiveness ( For the hot stream. Combined radiation with conductive and convective heat transfer. The Overall Heat Transfer Coefficient Is 1450W/m2°C. Note that the These are permanent gas engines. i Want to improve this question? 4.11(a) that the unavailable energy of the cold stream is greater than that for the hot stream because T0(S2c − S1c) > T0(S1h − S2h). Example: Calculation of Heat Exchanger. A regenerative heat exchanger typically uses the fluid from a different area of the same system for both the hot and cold fluids. One common example of a heat exchanger is the radiator in a car. is the maximum heat that could be transferred between the fluids per unit time. The temperature gradient within the windshield can not be neglected due to high Biot numbers on both sides of the windshield.